Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Submarine channel formation and acoustic remote sensing of suspended sediments and turbidity currents… Hay, Alexander Edward 1981

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1981_A1 H39.pdf [ 35.99MB ]
Metadata
JSON: 831-1.0053188.json
JSON-LD: 831-1.0053188-ld.json
RDF/XML (Pretty): 831-1.0053188-rdf.xml
RDF/JSON: 831-1.0053188-rdf.json
Turtle: 831-1.0053188-turtle.txt
N-Triples: 831-1.0053188-rdf-ntriples.txt
Original Record: 831-1.0053188-source.json
Full Text
831-1.0053188-fulltext.txt
Citation
831-1.0053188.ris

Full Text

SUBMARINE CHANNEL FORMATION AND ACOUSTIC REMOTE SENSING OF SUSPENDED SEDIMENTS AND TURBIDITY CURRENTS IN RUPERT INLET, B.C. by ALEXANDER EDWARD HAY B. Sc., U n i v e r s i t y of Western O n t a r i o , 1971 M. Sc., U n i v e r s i t y of Western O n t a r i o , 1972 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE DEPARTMENT OF OCEANOGRAPHY We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA September 1981 ©Alexander Edward Hay, 1981 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t . f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f fJr eewt0$ /z? The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e V ancouver, Canada V6T 1W5 Date n r . 0. I 0 /"7Q ^ ABSTRACT T u r b i d i t y c u r r e n t s , both c o n t i n u o u s f l o w and s u r g e - t y p e , have been d e t e c t e d w i t h a c o u s t i c sounders o p e r a t i n g a t 42.5, 107 and 200, kHz. The t u r b i d i t y c u r r e n t s a r e a s s o c i a t e d w i t h the d i s c h a r g e of mine t a i l i n g i n t o Rupert I n l e t . A l i n e a r r e l a t i o n i s o b t a i n e d between the b a c k s c a t t e r e d a c o u s t i c s i g n a l a t 200 kHz and the o n e - h a l f power of suspended p a r t i c u l a t e c o n c e n t r a t i o n from 10 to 1000 mg 1~ 1. T h i s r e l a t i o n i s c o n s i s t e n t w i t h R a y l e i g h s c a t t e r i n g t h e o r y i n form and ( r e l a t i v e t o a s t a n d a r d t a r g e t ) a m p l i t u d e , and i s used t o g e n e r a t e a c r o s s - s e c t i o n a l p r o f i l e of sediment c o n c e n t r a t i o n i n the d i s c h a r g e plume. E s t i m a t e s of surge speeds from the a c o u s t i c r e c o r d s based on a u n i v e r s a l shape f o r d e n s i t y c u r r e n t heads range from 30 t o 120 cm s " 1 . The e x c e s s d e n s i t y of one surge was e s t i m a t e d from the r e v e r b e r a t i o n a m p l i t u d e t o be 0.12 g cm" 3. The a d d i t i o n a l a t t e n u a t i o n of sound waves by suspended p a r t i c l e s i s i m p o r t a n t i n t u r b i d i t y c u r r e n t s and may be used t o e s t i m a t e suspended p a r t i c u l a t e c o n c e n t r a t i o n . Thermal p r o c e s s e s c o n t r i b u t e v e r y l i t t l e t o the a d d i t i o n a l a t t e n u a t i o n by p a r t i c l e s w i t h the g r a i n d e n s i t i e s of common m i n e r a l s . A l e v e e d submarine c h a n n e l extended from the p o i n t of the t a i l i n g d i s c h a r g e ( o u t f a l l ) over the s u r f a c e of the t a i l i n g d e p o s i t as e a r l y as 1974. The upper r e a c h of t h i s system was b u r i e d i n 1978, and by l a t e 1979 a new c h a n n e l had d e v e l o p e d . In 1976-77, the o r i g i n a l c h a n n e l c o n s i s t e d o f : (1) a l e f t - h o o k i n g upper re a c h w i t h an average s l o p e of 2.2°, (2) a m i d d l e r e a c h (l° s l o p e ) w i t h pronounced meanders (700-1100 m wavelengths) " i n c r e a s i n g i n c u r v a t u r e w i t h d i s t a n c e downstream and (3) a s t r a i g h t lower r e a c h ( 0 . 5 ° s l o p e ) . The c r o s s - s e c t i o n a l a r e a of the c h a n n e l d e c r e a s e d w i t h d i s t a n c e downstream, e x c e p t i n g an i n c r e a s e i n the f i r s t 1 0 0 - 2 0 0 m, u n t i l the c h a n n e l d i s a p p e a r e d about 5 . 5 km from the o u t f a l l . A c o u s t i c r e c o r d s of the d i s c h a r g e plume i n bends i n d i c a t e o v e r s p i l l from the o u t e r bank and an upward t i l t of the upper i n t e r f a c e away from th e c e n t r e of bend c u r v a t u r e . The i n t e r f a c i a l s l o p e i s s t e e p e r than i n d i c a t e d by t h e c r o s s - c h a n n e l d i f f e r e n c e i n l e v e e h e i g h t s . These r e c o r d s t o g e t h e r w i t h o b s e r v e d t i d a l c u r r e n t s suggest t h a t the l e f t hook i n the upper r e a c h i s caused by a mechanism s i m i l a r t o t h a t which has been suggested f o r deep-sea c h a n n e l s . T u r b i d i t e s i n g r a v i t y c o r e s from the l e v e e s a r e p r e s e n t as l a y e r s of v e r t i c a l l y - g r a d e d , C u - r i c h and Fe-poor sand and s i l t , some of which have l o a d - c a s t e d f l a m e - s t r u c t u r e s or l o a d - p o c k e t s a t t h e i r b a s a i c o n t a c t s . These l a y e r s c o mprise more of the sediment column w i t h d i s t a n c e down-channel, s u g g e s t i n g t h a t l e v e e -b u i l d i n g by overbank s p i l l a g e from c o n t i n u o u s f l o w becomes l e s s i m p o r t a n t , and t h a t most of the m a t e r i a l t r a n s p o r t e d through the lower r e a c h i s c a r r i e d by t u r b i d i t y s u r g e s . Surge r e c u r r e n c e i n t e r v a l s of 2 - 5 d a r e o b t a i n e d from the number t u r b i d i t e s per c o r e and t h e l o c a l d e p o s i t i o n r a t e . The l a t t e r ranged from 0 . 3 -4 m y r ~ 1 , as g i v e n by changes i n water d e p t h , i n t a i l i n g t h i c k n e s s from s e i s m i c r e f l e c t i o n s u r v e y s , and i n d i a t o m f r u s t u l e abundance i n the c o r e s . A model of c o n t i n u o u s t u r b i d i t y f l o w i n submarine c h a n n e l s i n c l u d i n g e n t r a i n m e n t i s a p p l i e d t o the Rupert I n l e t c h a n n e l . R e s u l t s a r e c o n s i s t e n t w i t h a sediment budget based on changes i n the t a i l i n g d e p o s i t volume, and w i t h t u r b i d i t y surge r e c u r r e n c e i n t e r v a l s . i v (a ) (b) Turbidity Channel Current h—H T H-H 1 3 1 2 1 3 2 0 1 3 2 2 1 3 2 7 1 3 3 2 P D T F r o n t i s p i e c e - Echograms a t 200 kHz of a t u r b i d i t y c u r r e n t f l o w i n g w i t h i n a submarine c h a n n e l i n Rupert I n l e t on Auaust 26, 1976. (a) f i r s t c r o s s i n g , c h a n n e l empty;' (b) second c r o s s i n g ' t u r b i d i t y c u r r e n t f i l l i n g c h a n n e l and waning i n t h i r d and f o u r t h c r o s s i n g s (c and d ) . V TABLE OF CONTENTS ABSTRACT LIST OF TABLES LIST OF FIGURES ACKNOWLEDGEMENTS Chapter 1 INTRODUCTION 1.1 The M i n i n g O p e r a t i o n 1.2 P r e v i o u s Work i n Rupert I n l e t 1.2.1 P h y s i c a l Oceanography - 1.2.2 Sediments 1.2.3 E n v i r o n m e n t a l Impact S t u d i e s 10 2 SOUND SCATTERING AND ATTENUATION IN SUSPENSIONS 11 2.1 The I n v i s c i d , N o n - c o n d u c t i n g Case 14 2.1.1 S o l i d Sphere 1 4 2.1.2 F l u i d Sphere 16 2.1.3 S o l i d S p h e r i c a l S h e l l 17 2.2 V i s c o t h e r m a l E f f e c t s . 18 2.2.1 G o v e r n i n g E q u a t i o n s 19 2.2.2 G e n e r a l S o l u t i o n 23 2.2.3 The Boundary-Value Problem 26 2.3 The I n v i s c i d Non-Conducting L i m i t 29 2.4 The Long-Wavelength L i m i t 30 2.4.1 The I s o t r o p i c • (n=0) Term 30 2.4.2 The D i p o l e (n=l) Term 31 2.4.3 The A t t e n u a t i o n of the I n c i d e n t Wave 31 2.4.4 Comparison w i t h Experiment ' 33 i i x x i i x x i i i 1 7 8 8 9 v i 2.5 Summary 37 3 DETECTING SUSPENDED SEDIMENT WITH SONAR:THEORY AND EXPERIMENT 40 3.1 Theory 43 3.1.1 B a c k s c a t t e r i n g from a S i n g l e S c a t t e r e r 43 3.1.2 B a c k s c a t t e r i n g from a Cloud of P a r t i c l e s 44 3.1.3 The Sonar E q u a t i o n 48 3.1.4 S t a n d a r d T a r g e t s 52 3.2 E x p e r i m e n t a l A p p a r a t u s and P r o c e d u r e s 53 3.3 A n a l y s i s and R e s u l t s 58 3.3.1 Suspended Sediment A n a l y s i s 60 3.3.2 A n a l y s i s of A c o u s t i c S i g n a l s 64 3.4 D i s c u s s i o n 75 3.4.1 S i g n a l S t a t i s t i c s 75 3.4.2 Comparison w i t h P r e v i o u s S t u d i e s 78 3.4.3 Other R e v e r b e r a t i o n Mechanisms 78 4 THE MORPHOLOGY OF THE TAILING DEPOSIT 83 4.1 The R e s u l t s of E a r l i e r S u r v e y s 83 4.2 B a t h y m e t r i c and S e i s m i c Surveys 88 4.3 Meandering Channel Regime 95 4.3.1 Upper Reach 96 4.3.2 Middle- Reach: The Meanders 99 4.3.3 Lower Reach 106 4.4 The Apron Regime 109 4.5 R e c h a n n e l i z e d Regime 114 4.6 Comparison w i t h Deep-Sea F a n - V a l l e y s 121 5 SEDIMENTS 128 5.1 Sampling and L a b o r a t o r y Techniques 128 5.1.1 S i z e A n a l y s i s 130 v i i 5.1.2 G r a i n D e n s i t y 132 5.1.3 M e t a l A n a l y s i s 133 5.2 S u r f i c i a l Sediments 134 5.2.1 C h a n n e l i z e d Regime 134 5.2.2 S u r f i c i a l Sediments: Apron Regime 137 5.2.3 S u r f i c i a l Sediments: R e c h a n n e l i z e d Regime 140 5.2.4 S u r f i c i a l Sediments: Summary 142 5.3 The Sediment Column 144 5.3.1 The C h a n n e l i z e d Regime 148 Upper Reach 150 M i d d l e Reach 153 Lower Reach 159 H o l b e r g I n l e t 161 5.3.2 The Apron Regime: Cores 164 5.3.3 D e p o s i t i o n Rates.: T u r b i d i t y C u r r e n t F r e q u e n c i e s 167 5.3.4 L a m i n a t i o n Time S c a l e 169 5.3.5 T r a n s i t i o n t o the Apron Regime 169 6 CURRENT MEASUREMENTS 171 6.1 Taut-Wire M o o r i n g s : Meandering Channel Regime 171 6.1.1 August 1976 . 171 6.1.2 November 1976 " 173 6.2 O v e r - t h e - S i d e C u r r e n t Measurements: Apron Regime 177 6.3 I n t e r p r e t a t i o n 182 7 THE ACOUSTICAL CHARACTER OF THE DISCHARGE PLUME AND TURBIDITY SURGES 189 7.1 The D i s c h a r g e Plume 192 7.1.1 Meandering Channel Regime 192 7.1.2 Apron Regime 199 v i i i 7.1.3 R e c h a n n e l i z e d Regime 199 7.2 T u r b i d i t y Surges 203 7.2.1 Meandering Channel Regime 203 7.2.2 Apron Regime 206 7.3 Other E v e n t s 216 8 THE SEDIMENT BUDGET AND CHANNELIZED TURBIDITY FLOW 222 8.1 Sediment Budget " " 223 8.2 Two-Dimensional T u r b i d i t y Flow: Theory 226 8.2.1 Surge Flow 226 8.2.2 C o n t i n u o u s Flow 231 8.3 T u r b i d i t y Flow and the Meandering Channel 235 8.3.1 Upper Reach: Mean Flow 235 Flow a t C o n s t a n t R i c h a r d s o n Number 237 8.3.2 E n t r a i n m e n t and Sediment T r a n s p o r t i n the Upper Reach 239 8.3.3 Lower Reach 241 8.3.4 The Frequency of T u r b i d i t y Surges 242 9 SUMMARY AND CONCLUSIONS 244 BIBLIOGRAPHY 250 APPENDIX 1: THE SCATTERED WAVE 267 A1.1 The i s o t r o p i c (n=0) term 267 A1.2 Long-wavelength l i m i t (n=0) 268 A1.3'The d i p o l e (n=l) term 271 A1.4 Long-wavelength l i m i t (n=1) 272 A1.5 G l o s s a r y of symbols 273 APPENDIX 2: SPECIAL-PURPOSE INSTRUMENTATION AND EQUIPMENT 275 A2.1 A c o m b i n a t i o n sampler f o r h i g h suspended l o a d e nvironments 275 A2.2 A m o d i f i e d boomerang c o r e r 276 A2.3 The UBC l a u n c h and the t r a n s d u c e r mount . . 277 i x APPENDIX 3: SHIP POSITIONS 279 APPENDIX 4: A SEDIGRAPH MIXING CELL FOR FINE SAND AND MUD 283 APPENDIX 5: RESULTS OF SEDIMENT ANALYSES 288 APPENDIX 6: A DIATOM CHRONOLOGY FOR RUPERT INLET SEDIMENTS 293 A6.1 P r i m a r y p r o d u c t i v i t y i n Rupert I n l e t 295 A6.2 Sampling and e x p e r i m e n t a l methods 298 A6.2.1 Diatom p r e p a r a t i o n and c o u n t i n g 299 A6.2.2 Dry b u l k d e n s i t y 300 A6.2.3 Water samples 300 A6.3 R e s u l t s . ~. 300 . A6.3.1 The 1978 dia t o m bloom 300 A6.3.2 1979 c o r e s 304 A6.3.3 The 1979 dia t o m r e c o r d 305 A6.3.4 Diatom f l u x e s and s e t t l i n g r a t e s : 1979 307 A6.3.5 Sediment a c c u m u l a t i o n r a t e s : 1979 309 A6.3.6 1976 C o r e s : The d i a t o m r e c o r d and d e p o s i t i o n r a t e s 312 APPENDIX 7: OVER-THE-SIDE CURRENT MEASUREMENTS 315 X L i s t of T a b l e s I I -I I I IV V VI V i l a V I I b V I I I IXa IXb X XI X l l a X I I b X I I I Developments i n the t h e o r y of s c a t t e r i n g and a t t e n u a t i o n of sound i n d i l u t e s u s p e n s i o n s and e m u l s i o n s . P h y s i c a l p r o p e r t i e s a t 20°. A c o u s t i c Sounder C h a r a c t e r i s t i c s . R e s u l t s of g r a v i m e t r i c and s i z e a n a l y s e s , of f i l t e r e d samples. X' i s d e f i n e d i n Eq. 3.26. d i s the median d i a m e t e r . R e s u l t s of d i g i t a l p r o c e s s i n g of t a p e - r e c o r d e d a c o u s t i c s i g n a l s . The columns l a b e l l e d ' b e f o r e ' and ' a f t e r ' i n d i c a t e the s i g n a l l e v e l s b e f o r e and a f t e r each c a s t . Mean s i g n a l l e v e l s p r i o r t o a p p l y i n g r e j e c t i o n c r i t e r i o n ( 3 ) . Summary of the number of c h a n n e l s observed i n CSP s u r v e y s . The l e t t e r s N and S i n d i c a t e t h a t the main c h a n n e l was c l o s e t o the n o r t h or s o u t h w a l l of the i n l e t . Summary of the number of c h a n n e l s o b s e r v e d i n the f i r s t 20 ICM s u r v e y s . N=north s i d e ; S=south s i d e ; C=centre. Meander di m e n s i o n s i n m. The meander a m p l i t u d e i s a. The mean v a l u e of L / r i s 3.8 ± 0.4. A x i a l s l o p e s ( i n degrees) of submarine c h a n n e l s w i t h a meander r e a c h . A x i a l s l o p e s of submarine c h a n n e l s w i t h e i t h e r no meander r e a c h or low a m p l i t u d e meanders. T a i l i n g m i n e r a l o g y from Evans and P o l i n g (1975) and C a r g i l l (1975). D e p o s i t i o n r a t e s and p r o b a b l e t u r b i d i t y c u r r e n t r e c u r r e n c e i n t e r v a l s from the 1976 c o r e s . Volume of t a i l i n g d e p o s i t from CSP s u r v e y s . Average d i s c h a r g e r a t e s d u r i n g the i n t e r v a l s between CSP s u r v e y s . Observed mass a c c u m u l a t i o n r a t e s i n the p r o x i m a l zone d u r i n g the i n t e r v a l between CSP s u r v e y s . 13 33 54 61 67 68 87 87 106 1 23 123 •136. 167 225 225 225 x i X l V a XI Vb XV XVI XVII X V I I I XI Xa XI Xb XX XXI XXII X X I I I XXIV C o n t i n u o u s - f l o w parameters i n the upper r e a c h a t l i n e 5 ( l o c a t i o n g i v e n i n F i g . 2 7 ) . Bottom slope=2.2°, c r o s s - s e c t i o n a l area=450 m2. T r a n s p o r t s by .continuous f l o w i n the between l i n e s 2 and 5 ( l o c a t i o n s C r o s s - s e c t i o n a l a r e a s a t l i n e s 2 and 5 450 m2 r e s p e c t i v e l y . Q and Q' a r e upper r e a c h i n F i g . 2 7 ) . a r e 7 00 and i n u n i t s of nr s " 1 and kg s " 1 r e s p e c t i v e l y . December 1977 s u r f i c i a l s e d i m e n t s . F e b r u a r y 1979 grab samples. August 1979 grab samples. 1976 c o r e s . 1979 c o r e d e s c r i p t i o n s . Cu c o n c e n t r a t i o n s i n c o r e 79-1B. Summary of major c h l o r o p h y l l peaks (>2.5 mg n r 3 ) from 5 m at s t a t i o n A from 1971-1978. The number of peaks (blooms) and the mean and s t a n d a r d d e v i a t i o n of c h l o r o p h y l l a a r e shown. T o t a l c e l l c o u n t s of C o s c i n o d i s c u s spp. and c h l o r o p h y l l a v a l u e s (from 5 m) a t s t a t i o n A d u r i n g 1974-1976 ( d a t a from S u l l i v a n , 1979). Numbers of d i a t o m s p e c i e s on t h r e e f i l t e r s from September 1978. Diatoms found i n t r a c e q u a n t i t i e s . The t o t a l s i n column a t l e f t a r e f o r a l l c o r e s , b o t h 1976 and 1979. Sediment a c c u m u l a t i o n rates, f o r the 1979 c o r e s based on the d i a t o m c h r o n o l o g y . The average v a l u e s do not i n c l u d e the T3 -T, e s t i m a t e a t z e r o d e l a y . 239 239 288 289 290 291 292 292 297 298 303 307 310 x i i L i s t of F i g u r e s L o c a t i o n map showing Rupert I n l e t and the mine s i t e . (a) The r a t i o of the a d d i t i o n a l a t t e n u a t i o n c o e f f i c i e n t due t o suspended p a r t i c l e s w i t h d e n s i t y 2.65 g cm" 3 t o t h a t i n sea water at 10° C w i t h 30 ppt s a l i n i t y , p l o t t e d a g a i n s t f r e q u e n c y as a f u n c t i o n of p a r t i c l e s i z e , per f r a c t i o n a l volume c o n c e n t r a t i o n . Both v i s c o u s and s c a t t e r i n g l o s s e s i n c l u d e d . (b) R a t i o of a t t e n u a t i o n c o e f f i c i e n t s due t o s c a t t e r i n g l o s s ( x l O 3 ) and v i s c o u s a b s o r p t i o n . Optimum f r e q u e n c y f o r d e t e c t i o n of R a y l e i g h s c a t t e r i n g v e r s u s maximum o p e r a t i n g range i n sea water at 10 °C w i t h 30 ppt s a l i n i t y assuming t h e r m a l background n o i s e . 47 51 (a) Scanning e l e c t r o n m i c r o g r a p h of l a r g e r p a r t i c l e s a f t e r r e d i s p e r s i o n . (b) S c a n n i n g e l e c t r o n m i c r o g r a p h of t y p i c a l a g g r e g a t e . 59 Bathymetry i n August, 1979 showing s t a t i o n l o c a t i o n s and sounding t r a n s e c t o c c u p i e d i n September, 1979, and I s l a n d Copper Mine (ICM) s t a t i o n A. 60 7 8 (a) (b) (a) (b) of s i z e s p e c t r a l d e n s i t y n ( d p ) d 6 P ( + ).. Note t h a t p o i n t s beyond assuming t h a t l o g n ( d f H i s t o g r a m 6e x t r a p o l a t e d by remains l i n e a r . H i s t o g r a m of n(d i s p r o p o r t i o n a l t o n(dp) and 80 yum a r e ) v e r s u s d p The i n t e g r a l of t h i s c u r v e the t o t a l volume per u n i t mass. P l o t s of n ( d p ) d ^ f o r a l l f i l t e r s . See T a b l e IV. Each t r a c e i s the average of the b a c k s c a t t e r e d s i g n a l from n o n - o v e r l a p p i n g s e t s of 20 c o n s e c u t i v e t r a n s m i s s i o n s ( p i n g s ) , or 10 seconds of d a t a a t a the bottom and from a l a r g e g i v e n d e l a y ( d e p t h ) . The echoes from the plume a r e i n d i c a t e d , as i s t h a t a m p l i t u d e m o b i l e s c a t t e r e r or ' f i s h ' . T y p i c a l . t a p e - r e c o r d e d echoes from c a r b i d e spheres ( l o w e r two p a n e l s ) , t e n n i s b a l l s (upper p a n e l ) . Note t r a n s i e n t response ( T ) . two- t u n g s t e n and 5 t a b l e t a p e - r e c o r d e r 62 63 65 Echograms c o r r e s p o n d i n g t o F i g s . 8a and 10. A=pre-c a s t r e c o r d i n g , sounder gain=5.5; B=post~cast r e c o r d i n g , g a i n = 5.5; C = b o t t l e s i_n s i t u , g a i n = 6.0; D = d i e l - m i g r a t i n g s c a t t e r i n g l a y e r ; E=top s a m p l i n g b o t t l e ; F = ' f i s h ' i n F i g . 8a. 66 10 2 8 - p o i n t - a v e r a g e t i m e - s e r i e s c e n t r e d a t each b o t t l e d e p t h a t s t a t i o n 2 b e f o r e c a s t I . No a v e r a g i n g over x i i i s u c c e s s i v e p i n g s . 66 11 (a) N o r m a l i z e d s i g n a l l e v e l s' v e r s u s the square r o o t of the p a r t i c l e c o n c e n t r a t i o n . S o l i d l i n e i s v i s u a l b e s t - f i t t o the d a t a . Broken l i n e i s the v a l u e of s' e x p e c t e d on the b a s i s of the echo from the s t a n d a r d t a r g e t , (b) P l o t of s'(rms) v e r s u s square r o o t of c o n c e n t r a t i o n . See s e c t i o n 3.4 f o r e x p l a n a t i o n of the broken l i n e . 69 12 A m p l i t u d e s t a t i s t i c s p l o t t e d as c u m u l a t i v e f r e q u e n c y c u r v e s (+) a g a i n s t a R a y l e i g h - d i s t r i b u t e d p r o b a b i l i t y s c a l e and as f r e q u e n c y h i s t o g r a m s . F i g s . 12a-c a r e the d i s t r i b u t i o n s of the a m p l i t u d e s i n a 2 8 - p o i n t window c e n t r e d a t the d e l a y s i n d i c a t e d (28x399 p o i n t s ) . F i g s . 12d-f a r e the d i s t r i b u t i o n s of the 2 8 - p o i n t a v e r a g e s (399 po i n t s ) . 72 13 (a) C o n t o u r s of s i g n a l l e v e l ( i n 0.5 v o l t i n t e r v a l s ) , u n c o r r e c t e d f o r s p r e a d i n g or a t t e n u a t i o n . G r i d p o i n t s a r e a t t h e i n t e r s e c t i o n s of h o r i z o n t a l and v e r t i c a l hash marks, and r e p r e s e n t a v e r a g e s over 28 p o i n t s (1m) i n the v e r t i c a l and 5 p o i n t s (2.5s) i n the h o r i z o n t a l . (b) Same as ( a ) , but c o n v e r t e d t o c o n c e n t r a t i o n u s i n g F i g . 11a a f t e r a p p l y i n g s p r e a d i n g and a t t e n u a t i o n c o r r e c t i o n . Contour i n t e r v a l i s 500 mg l " 1 . 73 14 Echogram c o r r e s p o n d i n g t o F i g . 13. A=tape r e c o r d e d p a s s , sounder gain=5.5; B = t h i r d p a s s , sounder gain=6.0; C=second p a s s , o p p o s i t e d i r e c t i o n , sounder gain=5.5; D = d i e l - m i g r a t i n g s c a t t e r i n g l a y e r ; p = discharge plume ( c h a n n e l i z e d ) ; X=buoyant c l o u d (see Chapter 7 ) . 74 15 T y p i c a l T, S and M (TSP) p r o f i l e s t h r o u g h the d i s c h a r g e plume (see a l s o Chapter 7 ) . 81 16 Time s e r i e s of b a t h y m e t r i c s u r v e y s showing ( a ) , the meandering c h a n n e l regime i n November 1976, ( b ) , the apron regime i n September 1978 and ( c ) , the r e c h a n n e l i z e d regime i n August 1979. C o n t o u r s i n m. 84 17 T a i l i n g t h i c k n e s s i n meters, 29 November, 1974. Heavy l i n e i s the c h a n n e l a x i s . 85 18 T a i l i n g t h i c k n e s s i n meters, 21 O c t o b e r , 1975. 85 19 Pre-mine bathymetry i n Rupert I n l e t . L o c a t i o n s of s e i s m i c r e f l e c t i o n l i n e s (CSP) and the mine's echo-sounding l i n e s (ICM) are a l s o shown. 86 20 Bathymetry i n November, 1976. To o b t a i n ' t r u e ' depths ( z ' ) from depths i n d i c a t e d ( z ) , z'=[(z-x i v 3 . 7 ) /I .031 ] c V / C y , where =1483.4 m s" 1 i s the sounding speed t o 100 m d e p t h . The heavy l i n e i n d i c a t e s the c h a n n e l a x i s . 91 21 T a i l i n g t h i c k n e s s i n meter s , 12 J a n u a r y , 1977. 91 22 S i d e - s c a n sonar r e c o r d , June 1977. The numbers 1-6 i d e n t i f y t h e axes of the s i x c o n s e c u t i v e bends; the v e r t i c a l l i n e s i n d i c a t e r a d a r f i x e s ; S and B the s u r f a c e and bottom echoes and 0 z e r o range on each c h a n n e l . The upper h a l f of each p a n e l i s the r e c o r d from the s t a r b o a r d t r a n s d u c e r ; the lower h a l f t h a t from t h e p o r t t r a n s d u c e r . (See a l s o F i g . 29). 92 23 (a) V e s s e l p o s i t i o n s f o r December, 1977 s u r v e y . S o l i d t r i a n g l e s a r e r a d a r f i x e s ; s o l i d c i r c l e s a r e a d j u s t e d p o s i t i o n s , (b) Bathymetry i n December, 1977. A x i s of November, 1976 c h a n n e l i s a l s o shown (dashed l i n e ) . 93 24 December 1977 c r o s s - c h a n n e l p r o f i l e s , l o o k i n g down-c h a n n e l , a t l o c a t i o n s i n F i g . 23. 94 25 Depth of November, 1976 c h a n n e l a x i s as a f u n c t i o n of l o n g - c h a n n e l d i s t a n c e . 95 26 C r o s s - c h a n n e l p r o f i l e s , l o o k i n g down-channel, i n November 1976. (a) upper r e a c h (b) m i d d l e r e a c h (c) lower r e a c h (d) meander r e a c h a t c h a n n e l c r o s s -o v e r s . See F i g . 27 f o r l o c a t i o n s . 97 27 S o u n d i n g . t r a n s e c t s f o r p r o f i l e s i n F i g . 26. 98 28 S e i s m i c r e f l e c t i o n p r o f i l e s a c r o s s upper r e a c h : (a) A x i a l L i n e 2, 1977; (b) A x i a l L i n e 2, 1975. See F i g . 18, 19 and 21 f o r l i n e l o c a t i o n s . 99 29 (a) Channel axes i n J a n u a r y , 1977 ( s o l i d l i n e ) and November, 1976 (dashed l i n e ) , (b) Channel axes i n June, 1977 ( s o l i d l i n e s ) and November, 1976. (dashed l i n e ) . Note o f f s e t of s i d e -scan p r o f i l e due t o s h i p t o t o w - f i s h s e p a r a t i o n . (See a l s o F i g . 2 2 ) . 101 30 D e f i n i t i o n s k e t c h of meanders. Based i n p a r t on F i g . 1 i n L e o p o l d and Wolman (1960). 102 31 S e i s m i c p r o f i l e s a c r o s s the meander r e a c h , January 1977, l o o k i n g down-channel. 104 32 S e i s m i c p r o f i l e s a c r o s s the a r e a of the 1976-77 lower r e a c h i n 1975, l o o k i n g d o w n - i n l e t . 108 33 Bathymetry, September 1978. z'=zc s'/c 5, c j =1492.8 m s" 1 . where 1 1 1 X V 34 Bathymetry, F e b r u a r y 1979. z'=zc 3'/c 5, where cs' =1 473.2 m s" 1 . 111 35 Depth d i f f e r e n c e map, November 1976-September 1978. P o s i t i v e v a l u e s i n d i c a t e net d e p o s i t i o n . N e g a t i v e v a l u e s are shaded. 112 36 Bathymetry, August 1979. 115 37 C r o s s - c h a n n e l p r o f i l e s , August 1979, l o o k i n g down-c h a n n e l , (a) and (b) Upper c h a n n e l ; (c) Lower c h a n n e l . See F i g . 37 f o r l o c a t i o n s . 116 38 Sounding l i n e s c o r r e s p o n d i n g t o p r o f i l e s i n F i g . 31. Channels a r e i n d i c a t e d by s o l i d l i n e s . 117 39 Depth of c h a n n e l a x i s , August 1979. 118 40 (a) Bathymetry o f f Hankin P o i n t i n January 1977 and (b) August 1979; (c) Depth d i f f e r e n c e map, Hankin P o i n t a r e a : J a n u a r y , 1977-August, 1979. (Note change i n s c a l e ) . N e g a t i v e v a l u e s a r e shaded and i n d i c a t e e r o s i o n . 120 41 Redondo canyon and f a n - v a l l e y (adapted from Haner, 1971). 125 42 H y p o t h e t i c a l submarine c h a n n e l t r a j e c t o r i e s i n s l o p e - d i s c h a r g e space. The broken l i n e i s t h a t s e p a r a t i n g b r a i d e d from meandering and s t r a i g h t r i v e r s ( L e o p o l d and Wolman, 1960). Meander c u r v a t u r e i n c r e a s e s w i t h d e c r e a s i n g s l o p e . 126 43 Comparative s i z e a n a l y s i s : S e d i g r a p h a l o n e v e r s u s S e d i g r a p h p l u s s i e v i n g . 132 44 S u r f i c i a l s e d i m e n t s , December 1977. (a) Median d i a m e t e r ( / i m ) . (b) Cu c o n c e n t r a t i o n (ppm). (c) S p e c i f i c g r a v i t y . The 1977 c h a n n e l a x i s i s i n d i c a t e d by the dashed l i n e . 135 45 Core and grab sample l o c a t i o n s , F e b r u a r y 1979. 138 46 Sand c o n t e n t (%) of s u r f i c i a l sediments i n F e b r u a r y , 1979. 138 47 C l a y c o n t e n t (%) of s u r f i c i a l sediments i n F e b r u a r y , 1979. 139 48 Cu c o n c e n t r a t i o n (ppm) i n s u r f i c i a l sediments i n F e b r u a r y , 1979. 139 49 Grab sample l o c a t i o n s , August 1979. 140 50 Sand c o n t e n t (%) i n s u r f i c i a l s e d iments, August 1979.' 141 x v i 51 Cu c o n c e n t r a t i o n (ppm) i n s u r f i c i a l s e d i m e n t s , August 1979. 141 52 P e r c e n t sand v e r s u s Cu c o n c e n t r a t i o n i n the 1979 s u r f i c i a l s e d i m e n t s . 142 53 (a) P e r c e n t c l a y and (b) p e r c e n t s i l t v e r s u s Fe c o n c e n t r a t i o n i n the 1979 s u r f i c i a l s e d i m e n t s . . 144 54 Core l o c a t i o n s and bathymetry, November 1976. 148 55 M o s a i c s of some of the h a l f - c o r e s from November, 1976. The s o l i d c i r c l e s on o p p o s i t e s i d e s of a c o r e i d e n t i f y the l o c a t i o n of a s p l i c e between two p h o t o g r a p h i c p r i n t s . 76-6 i s a q u a r t e r - c o r e . D i s t u r b a n c e s due t o s p l i t t i n g a r e p r e s e n t a t 5 cm i n 76-3, 33-35 cm and 60-78 cm i n 76-4, and 42 cm i n 76-8. S l i g h t b r e a k s i n sand l a y e r s o c c u r a t 22, 36 and 61 cm i n 6; 19 and 31 cm i n 7; and 2 cm i n 8. E was gouged by m a t e r i a l a d h e r i n g t o the s p l i t t i n g w i r e . Other l a b e l s a r e d i s c u s s e d i n the t e x t . 149 56 Core 76-1, showing mosaic of the h a l f - c o r e and s i z e and Cu a n a l y s i s r e s u l t s . Note the l i g h t and dark bands : l i g h t bands a r e a t 12-15, 28-38, 48-52 and 58-60 cm depth. F i n e r l a m i n a e are i n each band. The down-turning of the laminae a t the edges i s due t o f r i c t i o n a t the l i n e r w a l l d u r i n g p e n e t r a t i o n . 151 57 Core 76-2. The dark v e r t i c a l s t r e a k i n t h e upper 20 cm i s i r o n - o x i d e formed d u r i n g d e w a t e r i n g . The l i g h t s t r e a k s i n the lower 30 cm were formed by m a t e r i a l a d h e r i n g t o the s p l i t t i n g w i r e . Note i n c l i n e d l a m i n a e , and d i s t u r b a n c e i n upper 10 cm. 152 58 Core 76-5, upper h a l f . Note d i s t u r b a n c e i n top 8 cm. 154 59 Core 76-5, lower h a l f . Note p o s s i b l e l o a d - c a s t e d flame s t r u c t u r e s a t 100 cm and m u d - b a l l a t 112-115 cm. 155 60 Upper p a r t of c o r e 76-6. Note the change i n the s l o p e of the laminae a t 54 cm. 157 61 Lower s e c t i o n of c o r e 76-6. Note the w e l l - r e s o l v e d c o a r s e l a y e r s a t 76 cm. 158 62 Lower s e c t i o n of c o r e 76-7. V e r t i c a l s c a l e of the b a r g r a p h i s t w i c e t h a t of the photograph. The h o r i z o n t a l s c a l e s f o r Cu and Fe are d i f f e r e n t f o r t h i s c o r e . Note d i s t u r b e d b a s a l s e c t i o n , and u n c l a s s i f i e d s t r u c t u r e at 27-28 cm. 159 63 Core 76-9. Note Ta (massive,graded) i n t e r v a l a t 16-x v i i 34 cm, and p o s s i b l e Tb and Td ( p a r a l l e l l a m i n a t e d ) i n t e r v a l s a t 8-16 cm. 160 64 Core 76-10. Note m o t t l e s and h o l e s , p a r t i c u l a r l y i n lower h a l f , and dark pre-mine sediment a t base. 162 65 Core 76-11. Note c o p p e r - and i r o n - p o o r dark p r e -mine sediment e x t e n d i n g t o the base of the c o r e ( a t 42 cm, not shown). 163 66 Cores from F e b r u a r y 1979. Note t h a t d a r k e r c o l o r a t i o n i m p l i e s c o a r s e r m a t e r i a l e x cept f o r t h e pre-mine sediments i n d i c a t e d by the c r o s s - h a t c h i n g i n c o r e s 1A-1C. 165 67 T a i l i n g t h i c k n e s s , as d e r i v e d from CSP s u r v e y s , v e r s u s time a t 1976 c o r e s i t e s . 168 68 Photograph ( l e f t ) and X - r a d i o g r a p h ( r i g h t ) of 1 cm t h i c k s l a b from c o r e 79-6. Note congruence i n shades of g r e y between the two p r i n t s , and the v e r y f i n e laminae i n the X - r a d i o g r a p h . 170 69 1976 mooring l o c a t i o n s , p l u s s t a t i o n J ( l o c a t i o n of Run 2 from Johnson, 1974). 171 70 C u r r e n t meter r e c o r d s a t 76/1, 24-26 August 1976. (a) Temperature, s a l i n i t y , p r e s s u r e and p r e d i c t e d t i d e s ( d o t s ) , d i r e c t i o n (-1 80°=down-inlet) and speed. (b) A x i a l (u) and c r o s s - i n l e t (v) v e l o c i t y components r e l a t i v e t o an u p - i n l e t d i r e c t i o n of 70° t r u e . Time 0 i s 0 h PDT, 24 August 1976. 172 71 Records from lower meter a t 76/2, w i t h t h e p r e d i c t e d t i d e . Up-inlet=0°. Time 0 i s 0 h PST, 20 November 1976. The u and v components a r e p a r a l l e l t o and t r a n s v e r s e t o the i n l e t a x i s , r e s p e c t i v e l y . Recorded speed i s z e r o f o r most of the r e c o r d due t o r o t o r f o u l i n g (see t e x t ) . 174 72 Record from upper meter a t 76/2. A x i a l (u) and t r a n s v e r s e (v) v e l o c i t y components are p l o t t e d . 175 73 V e s s e l mooring s t a t i o n s , September 1978. 176 74 C u r r e n t meter r e c o r d s a t f o r e - a n d - a f t mooring s t a t i o n 78/2 and p r e d i c t e d t i d e on 14-15 September 1978. Arrows- i n d i c a t e 0330 h and 0525 h PST. Note the absence of major h i g h - f r e q u e n c y f l u c t u a t i o n s i n the d i r e c t i o n r e c o r d s . U p - i n l e t i s 72° t r u e . The p r e s s u r e s e n s o r on t h e BOTTOM meter m a l f u n c t i o n e d d u r i n g the f i r s t p a r t of the second c a s t . 179 •75 T r a n s v e r s e (v) and a x i a l . ( u ) components of v e l o c i t y a t 78/2 w i t h s h i p m o t i o n , ( b ) , removed. X and Y a r e e a s t - w e s t and n o r t h - s o u t h d i s p l a c e m e n t s of the x v i i i s h i p . 180 76 77 78 79 80 81 82 83 84 85 Contour p l o t s of a t 78/2. s a l i n i t y and suspended p a r t i c u l a t e A x i a l component of v e l o c i t y a t s t a t i o n J ( F i g . 69) a t 1.0-1.5 m from the bottom i n J u l y 1973. T i d a l extrema a r e t h o s e p r e d i c t e d f o r C o a l Harbour (adapted from Johnson, 1974). Schematic r e p r e s e n t a t i o n of component i n the deep water as a phase and range of the t i d e . a x i a l v e l o c i t y f u n c t i o n of the C u r r e n t d i r e c t i o n and smoothed speed from a l l t h r e e meters and the p r e d i c t e d t i d e a t s t a t i o n 78/2, September i n l e t . 14-15 1978. A d i r e c t i o n of 72' 1 s up-A x i a l (u) and t r a n s v e r s e (v) components of v e l o c i t y , c o r r e c t e d f o r s h i p m o t i o n , a t each of the t h r e e meters a t 78/2, on 14-15 September 1978. Sonograph of the c h a n n e l and d i s c h a r g e plume, l o o k i n g upstream, d u r i n g f l o o d t i d e 3.5 h a f t e r low w a t e r , 22 November 1976, 1050 h PST. S=side-echo, P=plume. V e r t i c a l l i n e s i n d i c a t e t imes of p o s i t i o n f i x e s t a ken a t 1 min i n t e r v a l s . See F i g . 83 f o r l i n e l o c a t i o n . F a c s i m i l e r e c o r d s showing the plume r e a c h a t d i f f e r e n t t i m e s , November t o bottom, the runs were made a t 1 water, 2 h a f t e r LW, 3.5 h a f t e r HW and a t LW. F i n e L i n e a m p l i f i e r was s w i t c h e d o f f and i n the upper 1976. From top h b e f o r e low The the T r i s p o n d e r bottom r u n . beacons were not i n p l a c e d u r i n g the L o c a t i o n s of t r a n s e c t s sonographs shown i n F i g , ( l i n e s 24, 48 and 5 4 ) . c o r r e s p o n d i n g t o the 81 ( l i n e 78) and F i g . 82 (a) F a c s i m i l e r e c o r d s showing the plume w i t h i n and s p i l l i n g from t h e c h a n n e l a t i n c r e a s i n g d i s t a n c e s from the o u t f a l l , 22 November 1976. The t i m e s of the p r o f i l e s from top t o bottom are 1050, 1100 and 1110 h PST (b) P r o f i l e l o c a t i o n s . The p r o f i l e s i n F i g . 85 and i n the f r o n t i s p i e c e were o b t a i n e d a l o n g l i n e s 67 and TT'. P r o f i l e l o o k i n g down-channel a t l i n e 67 ( F i g . 84b) a t 2124 PST on 21 November 1976, showing suspended m a t e r i a l a g a i n s t the r i g h t bank. 181 183 1 84 187 188 1 93 194 1 95 1 96 197 86 (a) P r o f i l e s p a r a l l e l i n g the upper r e a c h a x i s at 1935 ( l i n e 58) and 1944 ( l i n e 59) PST on November x i x 1976. (b) P r o f i l e l o c a t i o n s . 198 87 Temperature, s a l i n i t y and t o t a l suspended p a r t i c u l a t e (TSP) p r o f i l e s from the plume d u r i n g the apron regime a t 78/2, September 1978. 200 88 Sonographs c o r r e s p o n d i n g t o p r o f i l e s i n F i g . 87, showing the near-bottom t u r b i d zone and the s a m p l i n g b o t t l e s d e s c e n d i n g i n t o and r e m a i n i n g suspended w i t h i n i t . The bottom echo (B) and a f a l s e echo (F) a r i s i n g from i n t e r f e r e n c e w i t h a n o t h e r sounder a r e i n d i c a t e d . 201 89 ( a ) , (b) and (c) P r o f i l e s t a k e n i n September 1979 d u r i n g the r e c h a n n e l i z e d regime. Note the ' c l o u d ' r i s i n g out of the c h a n n e l . Depths i n m. (d) P r o f i l e l o c a t i o n s . 202 90 Sonographs of the 25 August, 1976 t u r b i d i t y c u r r e n t a t (a) 200 kHz (b) 107 kHz and (c) 42.5 kHz. A l l sounders s e t a t 0.1 ms p u l s e l e n g t h and 5°xl0° beamwidth. Note paper take-up problem w i t h the 200 kHz r e c o r d e r ( A ) , and i n t e r f e r e n c e (F) among the sounders. Compare w i t h f r o n t i s p i e c e and see F i g . 84b f o r t r a n s e c t l o c a t i o n . 205 91 Surge a t 2344 h PST on 12 September 1978. (a) 200 kHz (b) 107 kHz. P u l s e lengths=0.5 ms. B a c k s c a t t e r from the d i s c h a r g e plume and l a r g e - a m p l i t u d e m o b i l e s c a t t e r e r s a r e a l s o e v i d e n t . S l a n t i n g l i n e s a t 200 kHz (S) a r e 60 Hz i n t e r f e r e n c e . 207 92 Surge a t 0225 h PST on 13 September 1978. (a) 200 kHz (b) 107 kHz. 208 93 Surge a t 0525 h PST on 15 September 1979. (a) 200 kHz (b) 107 kHz. 209 94 Two t y p e s of t u r b i d i t y s u r g e : s l u g ( s o l i d l i n e ) and c o n t i n u o u s source (dashed l i n e , adapted from Komar, 1977). 210 95 Record from the 11 kHz p i n g e r , 15 September, 1978. A= d i r e c t p u l s e , B= b o t t o m - r e f l e c t e d p u l s e , C= p u l s e s r e f l e c t e d by c u r r e n t meters and weight (W). 211 96 Contour p l o t of d i g i t a l l y p r o c e s s e d 200 kHz r e v e r b e r a t i o n from the surge a t 0225 h PST on 13 September 1978. ( A l s o see F i g . 92). Each p o i n t i n the c o n t o u r g r i d i s the average of 10 samples v e r t i c a l l y (0.2 ms) and of 10 c o n s e c u t i v e t r a n s m i s s i o n s (5 s) h o r i z o n t a l l y . Note t h a t the 1.0-2.0 v o l t i n t e r v a l i s c r o s s - h a t c h e d n o r m a l l y t o the c r o s s - h a t c h i n g i n the 0.5-1.0 v o l t i n t e r v a l . 213 XX 97 V e r t i c a l p r o f i l e s of the s i g n a l b a c k s c a t t e r e d from the surge i n F i g s . 92 and 96. P u l s e length=0.5 ms. No a v e r a g i n g of the s i g n a l . A z e r o v o l t r e f e r e n c e i s p l o t t e d a t the b e g i n n i n g and end of each p r o f i l e . 214 98 T i d a l l y i n d u ced change i n the a c o u s t i c b a c k s c a t t e r a t 200 kHz a t 78/2 a t 0330 h PST, September 15, 1978. Depths i n fm; 0=50, 20=60 fm. 217 99 T i d a l l y i n d u ced change i n a c o u s t i c b a c k s c a t t e r a t 78/1. 219 100 C u r r e n t meter r e c o r d s a t 78/1 on 15-16 September 1978. . 220 101 S h i p motion a t 78/1 on 15-16 September 1978. X and Y a r e e a s t - w e s t and n o r t h - s o u t h d i s p l a c e m e n t s of the s h i p . 221 102 Area c o v e r e d by t a i l i n g of a g i v e n t h i c k n e s s f o r d i f f e r e n t CSP s u r v e y s . 224 103 Schematic diagram of a d e n s i t y s u r g e , (a) on a h o r i z o n t a l bottom, (b) on a s l o p i n g bottom. Except f o r the v e l o c i t y p r o f i l e a t x , f o r which v e l o c i t i e s a r e r e l a t i v e t o the bed, v e l o c i t i e s and c o o r d i n a t e s a r e r e l a t i v e t o the nose. 227 104 P l o t s of 2 1 / 2 C „ v e r s u s bottom s l o p e u s i n g M i d d l e t o n ' s (1966b) r e s u l t s . Those of Shwartz et a l (1973) a r e shown by s o l i d l i n e s , ( a : s a l i n e s l u g s ; b: t u r b i d i t y s l u g s ) . 229 105 C o m b i n a t i o n 250 ml suspended s o l i d s sampler and NIO b o t t l e . 275 106 UBC 5 m l a u n c h : f i b r e g l a s c o n s t r u c t i o n , i n b o a r d -o u t b o a r d e n g i n e . 277 107 (a) Transducer f a i r i n g and 19.6 cm d i a m e t e r 192 kHz t r a n s d u c e r ( s o l i d dark c i r c l e ) . (b) Transducer f a i r i n g w h i l e under way. Winch exhaust p i p e a l s o e v i d e n t . 278 108 November, 1976 s h i p p o s i t i o n s . 279 109 (a) and (b) September, 1978 s h i p p o s i t i o n s . 280 110 (a) and (b) F e b r u a r y , 1979 s h i p p o s i t i o n s . 281 111 August, 1979 s h i p p o s i t i o n s . 282 •112 (a) 50 ml m i x i n g c e l l used w i t h c o r e samples showing s t a i n l e s s s t e e l o u t l e t a t the base (b) 50 ml c e l l used i n m i x i n g t e s t showing rubber x x i s t o p p e r (A) and s t a i n l e s s s t e e l o u t l e t tube ( B ) . 284 113 M i x i n g c e l l t e s t r e s u l t s , showing s e d i m e n t a t i o n d i a m e t e r d i s t r i b u t i o n s t a ken a t the h e i g h t s i n d i c a t e d ( i n cm) above the bottom of the c e l l . Note t h a t 2 runs were, made a t each h e i g h t . 286 114 T y p i c a l grab sample d i s t r i b u t i o n s showing b i m o d a l i t y a t the s p l i t p o i n t (0.0625 mm). Frequency h i s t o g r a m s and c u m u l a t i v e p e r c e n t c o a r s e r c u r v e s , one a g a i n s t a l i n e a r s c a l e (+), a n o t h e r a g a i n s t a n o r m a l l y d i s t r i b u t e d p r o b a b i l i t y s c a l e ( A ) , a r e p l o t t e d . 287 115 Bathymetry i n September 1978 showing s t a t i o n l o c a t i o n s . 296 116 Monthly c h l o r o p h y l l a l e v e l s (1971-1978) from 5 m depth a t s t a t i o n A. 296 117 Average c o u n t s of d i s c - s h a p e d diatoms on f i l t e r s from samples a t s t a t i o n s 1-4. The e r r o r b a r s r e p r e s e n t the s t a n d a r d d e v i a t i o n from the mean: (a) 13 b o t t l e c a s t s (b) 5 c a s t s (c) 8 and (d) 2. 302 118 F e b r u a r y 1979 c o r e l o c a t i o n s and bathymetry. 304 119 Diatom r e c o r d s from c o r e s 79-6 and 79-11. 306 120 (a) Water depth a t c o r e s i t e 79-6 and t h i c k n e s s of the t a i l i n g d e p o s i t a t s i t e 79-6 and 79-11, (b) and ( c ) , v e r s u s t i m e . 311 121 1976 c o r e s i t e s and bathymetry. 312 122 Diatom p r o f i l e s of c o r e 76-4. 313 123 T h i c k n e s s of the t a i l i n g d e p o s i t a t c o r e s i t e 76-4 v e r s u s t i m e . 314 124 A x i a l (u) and c r o s s - i n l e t (v) v e l o c i t y components w i t h s h i p motion ( F i g . 101) removed, as r e g i s t e r e d by the t o p ( a ) , m i d d l e (b) and bottom (c) meters a t 78/1 on 15-16 September, 1978. 316 125 Records from the t o p meter a t s t a t i o n 78/3 on 17-18 September, 1978. 318 126 Records from the m i d d l e meter at s t a t i o n 78/3 on 17-18 September, 1978. 319 127 Records from the bottom meter a t s t a t i o n 78/3 on 17-18 September, 1978. 320 128 A x i a l (u) and c r o s s - i n l e t (v) v e l o c i t y components, w i t h s h i p motion ( F i g . 129) removed, from the top x x i i ( a ) , m i d d l e (b) and bottom (c) meters a t 78/3 on 17-19 September, 1978. 321 129 S h i p motion a t 78/3. X and Y are the n o r t h - s o u t h and e a s t - w e s t components of d i s p l a c e m e n t ; u and v are the c o r r e s p o n d i n g a x i a l and t r a n s v e r s e v e l o c i t y components. 322 130 Records from the t o p ( a ) , m i d d l e (b) and bottom (c) meters at 78/4 on 19-20 September, 1978. 324 131 A x i a l (u) and c r o s s - i n l e t (v) v e l o c i t y components a t 78/4 c o r r e c t e d f o r s h i p motion ( F i g . 132). 325 132 S h i p motion a t 78/4. X and Y a r e the n o r t h - s o u t h and e a s t - w e s t components of d i s p l a c e m e n t ; u and v are the c o r r e s p o n d i n g a x i a l and t r a n s v e r s e v e l o c i t y components. 326 x x i i i ACKNOWLEDGMENTS I w i s h t o e x p r e s s my g r a t i t u d e t o the many i n d i v i d u a l s who c o n t r i b u t e d t o the c o m p l e t i o n of t h i s t h e s i s , and e s p e c i a l l y t o my s u p e r v i s o r s , Dr. R. W. B u r l i n g and Dr. J . W. Murray, for, t h e i r d i r e c t i o n and s u p p o r t ; t o Dr. S. E. C a l v e r t , Dr. P. H. L e B l o n d , Dr. A. G. Lewis and Dr. S. Pond f o r t h e i r d i s c u s s i o n s and c r i t i c i s m of t h i s m a n u s c r i p t . I a l s o w i s h t o thank Capt. J . M a r s t e n and Capt. K. Sjoholm (CSS V e c t o r ) , Capt. M. Wheeler (CSS R i c h a r d s o n ) , Mr. H. Hole ( W a l t e r M.) and the crews of these v e s s e l s ; P. D. Reimer and the t e c h n i c a l s t a f f of the Department of G e o l o g i c a l S c i e n c e s who r e b u i l t the l a u n c h ; H. H e c k l , R. D. Macdonald, Dr. S. J . de Mora, A. Ramnarine, P. D. Reimer, P. S t o d d a r t , M. P. Storm, and M. And A. Von Breymann f o r t e c h n i c a l a s s i s t a n c e . Dr. E. V. G r i l l p r o v i d e d l a b o r a t o r y f a c i l i t i e s and guidance f o r the t r a c e m e t a l a n a l y s e s and f i l t r a t i o n p r o c e d u r e s . A. S t i c k l a n d s u p e r v i s e d the c u r r e n t meter deployment and r e c o v e r y . M. S u l l i v a n and P. D. Reimer a s s i s t e d w i t h the s i z e a n a l y s e s . Rosemary Waters i d e n t i f i e d and counted the d i a t o m s . D. L a p l a n t e and G. Kamitakahara wrote or m o d i f i e d s o f t w a r e f o r d i g i t i z i n g the a n a l o g a c o u s t i c r e c o r d i n g s and t r a n s l a t i n g Aanderaa r e c o r d s , r e s p e c t i v e l y . G. Hodge d r a f t e d most of the f i g u r e s . J . H e l l o u typed the m a n u s c r i p t . Thanks are a l s o due t o the i n d i v i d u a l s and o r g a n i z a t i o n s who g e n e r o u s l y l o a n e d equipment: Dr. D. M. Farmer ( p o s i t i o n i n g equipment, c u r r e n t meters and mooring components); Canadian H y d r o g r a p h i c S e r v i c e ( s i d e - s c a n sonar and p o s i t i o n i n g e quipment); Dr. C. H. Pharo ( S e d i g r a p h and g r a v i t y - c o r i n g g e a r ) ; Department of C i v i l E n g i n e e r i n g , U. B. C. ( s u r v e y i n g equipment), x x i v Dr. P. J . H a r r i s o n ( C o u l t e r C o u n t e r ) ; Dr. T. R. Osborn and Dr. S. Pond ( e l e c t r o n i c equipment). I am g r a t e f u l t o I s l a n d Copper Mine and i t s s t a f f . , R. H i l l i s and C. P e l l e t i e r i n p a r t i c u l a r , f o r t h e i r generous c o o p e r a t i o n i n making both d a t a and f a c i l i t i e s , i n c l u d i n g the Mac I , a v a i l a b l e t o me. I was s u p p o r t e d by a M a c M i l l a n F a m i l y S c h o l a r s h i p from 1977-1979 and NRC Grant A5374 t o Dr. R.W. B u r l i n g and NRC Grant A3542 t o Dr. J.W. Murray. The p r o j e c t was funded by NSERC S t r a t e g i c Grant (Group) G0208 t o Dr. R.W. B u r l i n g and Dr. J.W. Murray i n November 1978. 1 CHAPTER _1_ INTRODUCTION T h i s t h e s i s c o n c e r n s the f o r m a t i o n and e v o l u t i o n of submarine c h a n n e l systems as a r e s u l t of t u r b i d i t y c u r r e n t s g e n e r a t e d by the d i s c h a r g e of mine t a i l i n g i n t o Rupert I n l e t by I s l a n d Copper Mine. The h y p o t h e s i s i n u n d e r t a k i n g t h e p r o j e c t was t h a t the q u a s i - s t e a d y r e l e a s e of l a r g e q u a n t i t i e s of sediment from a submerged p o i n t s o u r c e a f f o r d e d an o p p o r t u n i t y t o study t h e s e p r o c e s s e s i n r e a l time - p r o c e s s e s which have l e f t t h e i r mark i n the g e o l o g i c r e c o r d but f o r which almost no d i r e c t o b s e r v a t i o n s e x i s t . T u r b i d i t y c u r r e n t s have r e p r e s e n t e d a problem of l o n g s t a n d i n g i n t e r e s t i n oceanography ever s i n c e D a l y (1936) proposed t h a t they were the e r o s i v e agent r e s p o n s i b l e f o r the f o r m a t i o n of submarine canyons i n the c o n t i n e n t a l s h e l f and s l o p e . T h i s h y p o t h e s i s i s now g e n e r a l l y a c c e p t e d , and the submarine fans and f a n - c h a n n e l s emanating from the mouths of the canyons a r e a l s o a s c r i b e d t o t h e s e f l o w s , which appear t o have been the p r i m a r y mechanism by which sand has been t r a n s p o r t e d from the c o n t i n e n t s t o the deep sea (Horn et a l , 1971). The e x i s t i n g e v i d e n c e i s l a r g e l y i n f e r e n t i a l , and i s based i n l a r g e measure on the assumption t h a t t u r b i d i t e s - d e p o s i t s w i t h more or l e s s w e l l d e f i n e d c h a r a c t e r i s t i c s (Bouma, 1962) - r e p r e s e n t m a t e r i a l l a i d down by i n d i v i d u a l t u r b i d i t y c u r r e n t s (Kuenen and M i g l i o r i n i , 1950). The r e l a t i v e ease w i t h which t u r b i d i t e s can be i d e n t i f i e d has l e d t o t h e i r p l a y i n g a fundamental r o l e i n p a l e o b a s i n a n a l y s i s . In s p i t e of the g e n e r a l s u c c e s s which the t u r b i d i t y 2 c u r r e n t - t u r b i d i t e model has had i n the i n t e r p r e t a t i o n of the g e o l o g i c r e c o r d , t h e r e have been v e r y few, i f any, i n s t a n c e s i n w hich the model has been v e r i f i e d by a c t u a l o b s e r v a t i o n , o t h e r than i n r a t h e r s m a l l s c a l e l a b o r a t o r y e x p e r i m e n t s (e.g. K e u l e g a n , 1957 and 1958; M i d d l e t o n , 1966b, 1966c and 1967). The o n l y s u c c e s s i v e r e a l - t i m e o b s e r v a t i o n s of s u r g e - t y p e t u r b i d i t y c u r r e n t s has been t h r o u g h submarine c a b l e b r e a k s such as the s e r i e s f o l l o w i n g the 1929 Grand Banks earthquake ( e . g . Heezen, 1963), and even i n t h e s e c a s e s the assumed c u r r e n t was not o b s e r v e d d i r e c t l y . To quote Normark (1978a), "...our u n d e r s t a n d i n g of the a c t u a l mechanism of the p r o c e s s i s based l a r g e l y on t h e o r e t i c a l c o n s i d e r a t i o n s tempered by few e m p i r i c a l c o n s t r a i n t s - so f a r , t h e r e has been no w i t n e s s t o d e s c r i b e an a c t u a l f u l l s c a l e t u r b i d i t y c u r r e n t . " In the e a r l y s t a g e s of the p r e s e n t s t u d y , a t u r b i d i t y c u r r e n t was ' w i t n e s s e d ' u s i n g h i g h f r e q u e n c y s o n a r . The sonographs of t h i s event a r e reproduced i n the f r o n t i s p i e c e , and a r e d i s c u s s e d a t l e n g t h i n Chapter 7. The l e n g t h s c a l e s , of the surge are s e v e r a l o r d e r s of magnitude above those i n l a b o r a t o r y t e s t s , a l t h o u g h p r o b a b l y one or two o r d e r s below tho s e which are e x p e c t e d t o have produced the l a r g e r submarine canyons and fan v a l l e y s i n the deep ocean. Perhaps t h e n , the event i n q u e s t i o n i s most a p p r o p r i a t e l y r e g a r d e d as b e i n g of medium s c a l e . Channel o v e r s p i l l , w hich has g e n e r a l l y been c o n s i d e r e d r e s p o n s i b l e f o r the f o r m a t i o n of l e v e e s , i s q u i t e o b v i o u s i n the a c o u s t i c r e c o r d . Cores from the l e v e e s c o n t a i n d e p o s i t s which have some of the f e a t u r e s c h a r a c t e r i s t i c of t u r b i d i t e s . To my 3 knowledge, t h i s c o m b i n a t i o n of r e s u l t s - the o b s e r v a t i o n of a c h a n n e l i z e d t u r b i d i t y surge and the presence of t u r b i d i t e s i n the l e v e e s - i s unprecedented. A c o u s t i c remote s e n s i n g , systems can be used t o o b t a i n d i r e c t e s t i m a t e s of the parameters g o v e r n i n g the dynamics of the fl o w i t s e l f , i n c l u d i n g the f l o w t h i c k n e s s and p o t e n t i a l l y the c o n c e n t r a t i o n of s o l i d s . Such systems a r e i d e a l l y s u i t e d t o the study of t u r b i d i t y s u r g e s , which s u b j e c t i_n s i t u i n s t r u m e n t a t i o n t o s e v e r e r i s k of damage and b u r i a l . In a more or l e s s c o n t r o l l e d environment l i k e Rupert I n l e t , the i m p l i c a t i o n i s t h a t o b s e r v a t i o n s c o u l d be o b t a i n e d not o n l y t o t e s t the t h e o r y of t u r b i d i t y surge f l o w s , but a l s o t o r e l a t e the c h a r a c t e r i s t i c s of the r e s u l t i n g d e p o s i t t o the s c a l e s of the motion and of i t s c o n f i n i n g c h a n n e l . The t h e s i s r e p r e s e n t s a f i r s t s t e p i n t h i s d i r e c t i o n . The use of a c o u s t i c b a c k s c a t t e r i n g t e c h n i q u e s f o r the purpose of d e t e c t i n g t u r b i d i t y c u r r e n t s and suspended sediment i s c e n t r a l t o t h i s s t u d y . The r e s u l t s i n d i c a t e t h a t under a p p r o p r i a t e c i r c u m s t a n c e s i t i s p o s s i b l e t o o b t a i n the c o n c e n t r a t i o n of suspended m a t t e r from the a m p l i t u d e of the b a c k s c a t t e r e d s i g n a l . T h i s appears t o be the f i r s t s u c c e s s f u l a p p l i c a t i o n of the method w i t h r e s p e c t t o the q u a n t i t a t i v e d e t e c t i o n of suspended sediment i n a marine environment. The remainder of t h i s c h a p t e r i s concerned w i t h a review of p r e v i o u s work i n Rupert I n l e t . D e t a i l e d r e v i e w s of p r e v i o u s r e s e a r c h i n f i e l d s of s p e c i a l i n t e r e s t , such as a c o u s t i c remote s e n s i n g , a r e p r e s e n t e d i n the a p p r o p r i a t e c h a p t e r s . The second c h a p t e r r e v i e w s the t h e o r y of s c a t t e r i n g and 4 a t t e n u a t i o n of a p l a n e sound wave by a s o l i d s p h e r i c a l p a r t i c l e , the c i r c u m f e r e n c e of which i s much l e s s than the l e n g t h of the i n c i d e n t wave. A new r e s u l t i s o b t a i n e d which a l l o w s the d e t e r m i n a t i o n of the r e l a t i v e magnitude of t h e r m a l and v i s c o u s a b s o r p t i o n i n the boundary l a y e r s a t the s o l i d - f l u i d i n t e r f a c e , and i n many c a s e s of p r a c t i c a l i n t e r e s t p e r m i t s a c o n s i d e r a b l y s i m p l i f i e d c a l c u l a t i o n of the a t t e n u a t i o n . In Chapter 3, the r e s u l t s of Chapter 2 a r e used t o o b t a i n e x p r e s s i o n s a p p r o p r i a t e t o the d e t e c t i o n of c l o u d s of suspended sediment u s i n g a c o u s t i c s o u n d i n g . O b s e r v a t i o n s of the b a c k s c a t t e r e d s i g n a l and suspended matter i n the t a i l i n g d i s c h a r g e a r e p r e s e n t e d , and the o b s e r v e d b a c k s c a t t e r i s shown t o be c o n s i s t e n t w i t h t h e o r y . Chapter 4 d e s c r i b e s the e v o l u t i o n of t h e t a i l i n g d e p o s i t morphology from i t s i n i t i a l c h a n n e l i z e d s t a t e , t h r o u g h 'the d i s a p p e a r a n c e of the c h a n n e l t o the f i n a l r e c h a n n e l i z e d phase. Emphasis i s p l a c e d upon the i n i t i a l c h a n n e l , which e x h i b i t e d pronounced meanders, and i t s m o r p h o l o g i c a l c h a r a c t e r i s t i c s a r e compared w i t h those of o t h e r submarine c h a n n e l s and of s u b a e r i a l r i v e r beds. E n t r a i n m e n t of o v e r l y i n g f l u i d , and m a t e r i a l l o s s e s t h r o u g h c h a n n e l o v e r s p i l l and d e p o s i t i o n - p r o c e s s e s which e i t h e r do not occur or a r e of l i m i t e d importance i n r i v e r s not i n f l o o d - appear t o e x e r c i s e c o n s i d e r a b l e i n f l u e n c e on the morphology of submarine c h a n n e l s . In Chapter 5, the p r o p e r t i e s of the sediments - both s u r f i c i a l and w i t h i n the sediment column - a r e p r e s e n t e d . T h i s work was conducted i n o r d e r t o c h a r a c t e r i z e the p r o p e r t i e s of the sediments w i t h i n and beyond the l e v e e d c h a n n e l , and to 5 i d e n t i f y t u r b i d i t e s w i t h i n the sediment column. The use of copper and i r o n as t r a c e r s f o r d e p o s i t s l a i d down by l a r g e - s c a l e mass movements i s e x p l o r e d . The t u r b i d i t y c u r r e n t r e c u r r e n c e i n t e r v a l i s e s t i m a t e d from the number of t u r b i d i t e s and the d e p o s i t i o n r a t e . The l a t t e r was o b t a i n e d from changes i n depth and/or accumulated t a i l i n g t h i c k n e s s as i n f e r r e d from s e i s m i c r e f l e c t i o n p r o f i l e s , and from the s e a s o n a l changes i n the c o n c e n t r a t i o n of l a r g e d i a t o m f r u s t u l e s i n " the c o r e s . In Chapter 6, the r e s u l t s of c u r r e n t measurements a r e p r e s e n t e d and a n a l y s e d i n terms of the deep-water response t o t i d a l f o r c i n g . These d a t a a r e c o n s i s t e n t w i t h measurements by Johnson (1974) and w i t h a d e s c r i p t i v e model p r e s e n t e d by D r i n k w a t e r (1973). Some r e f i n e m e n t s t o t h i s model a r e sugg e s t e d . P e r t u r b a t i o n s due t o t u r b i d i t y surge f l o w s a r e p r e s e n t i n some of the r e c o r d s . In C h a p t e r 7, sonographs of the d i s c h a r g e plume and t u r b i d i t y c u r r e n t surges a r e presented,- and used t o i n f e r some of the p r o p e r t i e s of t h e s e f l o w s , and t h e i r i n f l u e n c e on the f o r m a t i o n of submarine c h a n n e l s . In Chapter 8, a s i m p l i f i e d a n a l y t i c a l model of c o n t i n u o u s t u r b i d i t y f l o w i n the submarine c h a n n e l i s d e v e l o p e d , based on an e a r l i e r model by Komar (1969) but i n c l u d i n g e n t r a i n m e n t of ambient water a t the upper boundary. T h i s model y i e l d s r e l a t i v e sediment t r a n s p o r t r a t e s b y c o n t i n u o u s and surge f l o w which a r e c o n s i s t e n t w i t h those o b t a i n e d from a sediment budget based on s e i s m i c r e f l e c t i o n s u r v e y s and from g r a v i t y c o r e s . 6 1.1 The M i n i n g O p e r a t i o n I s l a n d Copper Mine (ICM) began t a i l i n g d i s p o s a l i n October 1971. The t a i l i n g i s d i s c h a r g e d a t a r a t e of 380 .kg s~ 1 from a p i p e 1.07 m i n diameter as a s l u r r y of s o l i d s , f r e s h w a t e r and sea water i n the r a t i o 1:4:5 p a r t s by volume. The volume d i s c h a r g e r a t e i s 1.4 m3 s " 1 . The sea water i s drawn from a depth of 15m, and the d i s c h a r g e p o i n t i s 49 m below the s u r f a c e and 1 m above bottom ( o u t f a l l , F i g . 1). In October 1975 a new d i s c h a r g e p i p e was l a i d , but the o u t f a l l p o i n t was the same. The o l d d i s c h a r g e l i n e i s s t i l l used d u r i n g maintenance on i t s rep l a c e m e n t . The t a i l i n g i s t h a t p a r t of the h o s t rock which remains a f t e r m i l l i n g and removal of the o r e - b e a r i n g p a r t i c l e s by f r o t h - f l o t a t i o n . The p a r t i c l e s c o n s t i t u t i n g the t a i l i n g have a median d i a m e t e r of 0.030 mm and 65-75% a r e s m a l l e r than 0.074 mm. The grade of the o r e body i s 0.52% Cu, the c u t o f f grade i s 0.3%, and e x t r a c t i o n e f f i c i e n c y i s i n the 80-90% range. Rock of grades below the c u t o f f i s dumped i n t o the i n l e t a t the waste dump ( F i g . 1) a t a r a t e a p p r o x i m a t e l y t h r e e t o f o u r t i m e s t h a t of the t a i l i n g . F u r t h e r d e t a i l s may be found i n Evans and P o l i n g (1975) and P o l i n g (1979) . As p a r t of the r e q u i r e m e n t s f o r i t s p e r m i t , ICM m a i n t a i n s an e x t e n s i v e e n v i r o n m e n t a l m o n i t o r i n g program. The p r e s e n t study and o t h e r s have been a b l e t o make c o n s i d e r a b l e use of these d a t a . In p a r t i c u l a r , t h e t i m e - s e r i e s of monthly h y d r o g r a p h i c s t a t i o n s has been v e r y u s e f u l i n s t u d i e s of the deep-water exchange p r o c e s s o u t l i n e d i n the next s e c t i o n . 8 1.2 P r e v i o u s Work i n Rupert I n l e t 1.2.1 P h y s i c a l Oceanography Rupert I n l e t and H o l b e r g I n l e t t o g e t h e r form a s i n g l e b a s i n ( F i g . 1 ) , which i s con n e c t e d t o Q u a t s i n o Sound and thence t o the P a c i f i c Ocean v i a Q u a t s i n o Narrows. C u r r e n t s i n t h i s t i d a l passage r e a c h 3 m s" 1 ( S a i l i n g D i r e c t i o n s , B r i t i s h Columbia C o a s t , 1976). The s i l l i s a t a depth of 18 m a t the n o r t h e r n end of the Narrows. The maximum depth i n the Hankin P o i n t a r e a was 172 m b e f o r e m i n i n g o p e r a t i o n s began. The major f r e s h w a t e r d i s c h a r g e i s from the M a r b l e R i v e r (140 m3 s " 1 on a v e r a g e ) , compared t o an average t i d a l i n f l o w of 7.8 x 10 3 m3 s~ 1 ( D r i n k w a t e r , 1973) and the s l u r r y d i s c h a r g e r a t e of 1.4 m3 s " 1 . Rupert I n l e t i t s e l f i s 10 km l o n g and 1.8 km wide. P i c k a r d (1963) noted t h e near homogeneity of the d e n s i t y f i e l d i n the v e r t i c a l and the h i g h c o n c e n t r a t i o n of d i s s o l v e d oxygen a t depth (>3 ml l " 1 ) . T h i s c o m b i n a t i o n of f e a t u r e s i s unus u a l among B r i t i s h Columbia i n l e t s , and l e d t o the c o n c l u s i o n t h a t i n t e n s e v e r t i c a l m i x i n g had taken p l a c e . Subsequent s t u d i e s of t he t i d a l m i x i n g and deep-water exchange p r o c e s s e s have been co n d u c t e d by D r i n k w a t e r and Osborn (1975), S t u c c h i and Farmer (1976) and S t u c c h i (1980, 1981). Deep-water exchange o c c u r s s e a s o n a l l y . Temperature and s a l i n i t y i n the deepest p a r t of the b a s i n change by 4-5 °C and 3-4 ppt a n n u a l l y , each r e a c h i n g a minimum i n January-March and a maximum i n August-September. The exchange p r o c e s s appears t o be c o n t r o l l e d p r i m a r i l y by f r e s h w a t e r r u n o f f from the Marble R i v e r which peaks i n the l a t e autumn f o l l o w i n g heavy r a i n f a l l . S e a s o n a l changes i n the o c e a n i c w a t e r s a t s i l l d epth may a l s o p l a y a r o l e . D u r i n g p e r i o d s of 9 h i g h r u n o f f , v e r t i c a l t u r b u l e n t d i f f u s i o n of f r e s h w a t e r i s i n d u c e d by the j e t s t r e a m i n g i n t o the b a s i n from Q u a t s i n o Narrows d u r i n g f l o o d t i d e , r e s u l t i n g i n d i l u t i o n of the water a t d e p t h . T h i s i s the s a l t e x t r a c t i o n phase of the exchange c y c l e , d u r i n g which the t i d a l j e t i s p o s i t i v e l y buoyant w i t h r e s p e c t t o the deep water.- As the r u n o f f d i m i n i s h e s , the water e n t e r i n g the b a s i n d u r i n g f l o o d t i d e e v e n t u a l l y becomes more dense than the water a t d e p t h , g e n e r a t i n g a n e g a t i v e l y buoyant j e t and i n i t i a t i n g the s a l t replacement phase. I t p e r s i s t s throughout the s p r i n g and summer months, d u r i n g which p e r i o d the s a l i n i t y and temperature of the deep water i n c r e a s e on a v e r a g e , w h i l e d i s s o l v e d oxygen d e c r e a s e s because of the low c o n c e n t r a t i o n i n the dense water o u t s i d e the s i l l ( D r i n k w a t e r , 1973). S t u c c h i (1980, 1981) e s t i m a t e s t h a t 63% of the water i n the b a s i n i s exchanged i n 2-3 weeks d u r i n g t h i s phase. T h i s i s s i m i l a r t o the e s t i m a t e of 1-4 weeks made by D r i n k w a t e r and Osborn (1975) f o r the deep water t o respond t o i n c r e a s e d r u n o f f d u r i n g the s a l t e x t r a c t i o n phase. 1.2.2 Sediments Johnson (1974) conducted a study of the s e d i m e n t a t i o n regime i n the i n l e t d u r i n g the p e r i o d i m m e d i a t e l y b e f o r e and a f t e r commencement of m i n i n g o p e r a t i o n s . Based on the g r a i n - s i z e d i s t r i b u t i o n s i n s u r f i c i a l s e d i m e n t s , s e i s m i c r e f l e c t i o n p r o f i l e s and near-bottom c u r r e n t measurements, Johnson c o n c l u d e d t h a t m a t e r i a l eroded from the bottom i n the Hankin P o i n t area d u r i n g p e r i o d s of deep-water replacement was c a r r i e d headward i n Rupert I n l e t and d e p o s i t e d on the s l o p e on the n o r t h s i d e of the b a s i n , as p a r t i a l l y i n d i c a t e d by the d e c r e a s e i n g r a i n s i z e w i t h 10 d i s t a n c e from Hankin P o i n t . Of p a r t i c u l a r importance t o t h i s argument and t o the p r e s e n t study i s h i s o b s e r v a t i o n t h a t on 4 of the 7 s u c c e s s f u l meter deployments i n Rupert I n l e t , maximum u p - i n l e t v e l o c i t i e s exceeded maximum d o w n - i n l e t v e l o c i t i e s a t depths from 79-157 m. In 1979 and p o s s i b l y as e a r l y as 1973, a l e v e e d submarine c h a n n e l was found i n the t a i l i n g d e p o s i t d u r i n g s e i s m i c r e f l e c t i o n s u r v e y s conducted a n n u a l l y by the Department of G e o l o g i c a l S c i e n c e s a t UBC. A st u d y of the s t a b i l i t y of the l e v e e s l o p e s by D a v i s (1978) found the l e v e e s t o be m a r g i n a l l y s t a b l e , and p r o b a b l y not s u b j e c t t o l i q u e f a c t i o n under shock l o a d i n g such as t h a t from the d a i l y p i t b l a s t . 1.2.3 E n v i r o n m e n t a l Impact S t u d i e s A v a r i e t y of impact s t u d i e s have been made s i n c e the m i n i n g o p e r a t i o n began. Many of t h e s e a r e o u t l i n e d and r e v i e w e d by Waldichuk and Buchanan (1980). Somewhat c o n f l i c t i n g v iews of the s i t u a t i o n a r e p r e s e n t e d by G o y e t t e and Nels o n (1977) and Evans (1978). A m o n i t o r i n g group was s e t up a t the U n i v e r s i t y of B r i t i s h Columbia under the d i r e c t i o n of P r o f . J.B. Evans, then head of the Dept. of M i n e r a l E n g i n e e r i n g , t o review the d a t a c o l l e c t e d by the mine's E n v i r o n m e n t a l C o n t r o l Program. The a u t h o r was i n v o l v e d i n s e v e r a l r e p o r t s s u b m i t t e d t o the group, which were co n c e r n e d w i t h the e x t e n t and morphology of the t a i l i n g d e p o s i t (Hay, MacDonald and Murray, 1976 and .1978), the e f f e c t s of deep-water exchange on t u r b i d i t y (Hay, 1978a) and the changes i n sediment t r a c e m e t a l c o n c e n t r a t i o n s w i t h d i s t a n c e from the o u t f a l l (Hay, 1978b). 11 CHAPTER 2 SOUND SCATTERING AND ATTENUATION IN SUSPENSIONS . F u n d a m e n t a l l y , the problem of d e t e c t i n g d i l u t e c l o u d s of suspended m a t t e r i n the ocean t h r o u g h the use of a c o u s t i c b a c k s c a t t e r i n g reduces t o o b t a i n i n g an e x p r e s s i o n f o r the a m p l i t u d e and phase of the wave s c a t t e r e d by a s i n g l e p a r t i c l e . These par a m e t e r s are a f f e c t e d by energy l o s s mechanisms which o p e r a t e near the s u r f a c e of the s c a t t e r e r and which r e s u l t i n both the a b s o r p t i o n of energy from the i n c i d e n t wave and a r e d u c t i o n i n t o t a l s c a t t e r e d energy. The l o s s mechanisms c o n s i d e r e d here a r e t h e r e s u l t of t h e r m a l d i f f u s i o n and v i s c o s i t y . The purpose of t h i s p r e s e n t a t i o n i s both t o r e v i e w the r e l e v a n t e a r l i e r work and t o p r e s e n t some new r e s u l t s . A summary of p r e v i o u s t h e o r e t i c a l t r e a t m e n t s of the problem i s g i v e n i n T a b l e I . For a c o u s t i c b a c k s c a t t e r i n g s t u d i e s , i t i s u s e f u l t o have e x p r e s s i o n s f o r the wave s c a t t e r e d from a s i n g l e p a r t i c l e which i n c l u d e the e f f e c t s of the v i s c o u s and t h e r m a l l o s s mechanisms. A l t h o u g h Morse and I n g a r d (1968, p.435) have d e r i v e d such e x p r e s s i o n s f o r a f l u i d sphere suspended i n a gas, e q u i v a l e n t r e s u l t s s u i t a b l e f o r s o l i d s c a t t e r e r s i n f l u i d media have not appeared i n the l i t e r a t u r e and a r e d e v e l o p e d h e r e . The g e n e r a l s o l u t i o n p r e s e n t e d by A l l e g r a and Hawley (1972) i s r e f o r m u l a t e d by e x p r e s s i n g the a m p l i t u d e s of the p a r t i a l s c a t t e r e d waves i n terms of the phase a n g l e s used by Faran (1951). S p e c i a l i z i n g t o the l o n g - w a v e l e n g t h l i m i t , e x p r e s s i o n s e q u i v a l e n t i n form t o those of Morse and I n g a r d (1968, p.435) a r e o b t a i n e d , and- the r a t i o of t h e r m a l t o v i s c o u s a b s o r p t i o n emerges i n a r e l a t i v e l y 12 s i m p l e form. T h i s r a t i o i s the p r i n c i p a l r e s u l t of the p r e s e n t approach. I t i s found t o agree f a v o u r a b l y w i t h t h e e x p e r i m e n t a l r e s u l t s of A l l e g r a and Hawley (1972) f o r aqueous s u s p e n s i o n s of p o l y s t y r e n e s p h e r e s , and of U r i c k (1948) f o r aqueous s u s p e n s i o n s of q u a r t z and k a o l i n i t e . Because t h i s r a t i o a l l o w s the r e l a t i v e i mportance of the two a b s o r p t i o n mechanisms t o be e v a l u a t e d , i t has c o n s i d e r a b l e p r a c t i c a l v a l u e . In p a r t i c u l a r , the c a l c u l a t i o n of the a t t e n u a t i o n i s g r e a t l y s i m p l i f i e d i f i t can be shown t h a t t h e r m a l a b s o r p t i o n i s n e g l i g i b l e . In p r i n c i p l e , t h e s e r e s u l t s c o u l d have been o b t a i n e d d i r e c t l y from the e x p r e s s i o n s f o r the c o e f f i c i e n t s of the p a r t i a l s c a t t e r e d waves d e r i v e d by A l l e g r a and Hawley (1972). The p r e s e n t approach, however, does o f f e r s e v e r a l d i s t i n c t a d v a n t a g e s . The use of the phase a n g l e f o r m a l i s m r e s u l t s i n a t l e a s t a f o r m a l s i m p l i f i c a t i o n of the r a t h e r t e d i o u s a l g e b r a . T h i s , and the f a c t t h a t the p a t h t o the i n v i s c i d n o n - c o n d u c t i n g l i m i t i s c l e a r t hroughout the m a n i p u l a t i o n of the e q u a t i o n s , made the f i n a l a p p r o x i m a t i o n i n the r e d u c t i o n t o the l o s s r a t i o q u i t e o b v i o u s . S e c t i o n 2.1 i s a d i s c u s s i o n of s c a t t e r i n g i n the i n v i s c i d n o n - c o n d u c t i n g c a s e , i n c l u d i n g a summary of Faran's (1951) s o l u t i o n . S c a t t e r i n g by f l u i d s p h e r e s , and by s p h e r i c a l s h e l l s and t h e i r p o s s i b l e marine a n a l o g u e s i s a l s o d i s c u s s e d . The waves s c a t t e r e d from these p a r t i c l e s a r e compared t o t h a t from a s o l i d sphere i n the l o n g - w a v e l e n g t h l i m i t . In s e c t i o n 2.2 the e f f e c t s of heat c o n d u c t i o n and v i s c o s i t y on the wave s c a t t e r e d by a s o l i d sphere are examined. S e c t i o n s 2.2.1 and 2.2.2 are l a r g e l y a r e v i e w of the A l l e g r a - H a w l e y t h e o r y . For the r e a d e r ' s 13 c o n v e n i e n c e , a l i s t of symbols i s i n c l u d e d i n Appendix 1. T a b l e I . Developments i n the t h e o r y of s c a t t e r i n g and a t t e n u a t i o n of sound i n d i l u t e s u s p e n s i o n s and e m u l s i o n s . Wave S c a t t e r e d by a S i n g l e P a r t i c l e R a y l e i g h ( 1 896): f l u i d sphere i n an i n v i s c i d , n o n - c o n d u c t i n g f l u i d a t l o n g w a v e l e n g t h s . Faran (1951): s o l i d or f l u i d sphere i n a v i s c o u s , non-c o n d u c t i n g f l u i d a t a l l w a v e l e n g t h s . Morse and I n g a r d (1968, p.435): f l u i d sphere i n a v i s c o u s , h e a t - c o n d u c t i n g gas a t l o n g w a v e l e n g t h s . A t t e n u a t i o n * E p s t e i n (1941): s o l i d or f l u i d s p heres i n a v i s c o u s , non-c o n d u c t i n g f l u i d . • E p s t e i n and C a r h a r t (1953): f l u i d spheres i n a v i s c o u s , h e a t - c o n d u c t i n g f l u i d Morse and I n g a r d (1968, p.435): f l u i d spheres i n a v i s c o u s , h e a t - c o n d u c t i n g gas at l o n g wavelengths * A l l e g r a and Hawley (1972): e x t e n s i o n of E p s t e i n and C a r h a r t (1953) t o i n c l u d e s o l i d s c a t t e r e r s * These a u t h o r s e x p r e s s e d the a t t e n u a t i o n i n terms of the c o e f f i c i e n t s of the p a r t i a l s c a t t e r e d waves, but d i d not d e r i v e e x p l i c i t e x p r e s s i o n s f o r the s c a t t e r e d wave. 1 4 2.1 The I n v i s c i d , N o n -conducting Case 2.1.1 S o l i d Sphere C o n s i d e r the p a r t i c l e t o be a moveable sphere of r a d i u s a, c o n s i s t i n g of an e l a s t i c , i s o t r o p i c m a t e r i a l of d e n s i t y ^ . Such m a t e r i a l admits the p r o p a g a t i o n of both c o m p r e s s i o n and shear waves which have phase v e l o c i t i e s and wavenumbers g i v e n by c ' 2 = (*'+2y )/f>: , k c ' = u , / C (2.1) and ' c s ' 2 = X / A ' • k;=^/c s' (2.2) r e s p e c t i v e l y , where A ' and ^  a r e Lame's e l a s t i c c o n s t a n t s ( S o k o l n i k o f f 1956, p.66) and primes denote the s c a t t e r e r . The ambient f l u i d i s i n v i s c i d , of d e n s i t y p0 , i n which the v e l o c i t y of sound i s C 2 = l/Tffo (2.3) where )\ i s the a d i a b a t i c c o m p r e s s i b i l i t y and k t = u j / c i s the wavenumber. In s p h e r i c a l p o l a r c o o r d i n a t e s ( r , e , <f>) a pl a n e wave t r a v e l l i n g a l o n g the p o l a r a x i s i s g i v e n by the r e a l p a r t of p^ = p o exp[ i ( k c r c o s e - to t ) ] (2.4) where p i s the sound p r e s s u r e . D r o p p i n g the time dependence and f o l l o w i n g Faran (1951), the s o l u t i o n f o r the s c a t t e r e d wave a t l a r g e d i s t a n c e s from a sphere c e n t r e d a t the o r i g i n t a k e s the form p r = p D e x p ( i k c r ) £^ (2n+1 ) i s i n ^ e - " ? " P„ (cos 0 )/kcr (2.5) where the P n ( c o s e ) a r e Legendre p o l y n o m i a l s . The phase a n g l e ( >]n) of the n t h p a r t i a l wave i s g i v e n by 15 tan;?,, = t a n o ^ (x) {t a n < ( x ) + t a n ^ ( x * , s')} {tan ^  (x) +tan J n (x ' , s ' )} ( 2 . 6 ) where t a n ^ ( x ) = - j n ( x ) / n n ( x ) (2.7a) t a n ^ ( x ) = - x j ; (x)/j„ (x) (2.7b) t a n ^ ( x ) = -xn; ( x ) / n n (x) (2.7c) i n w h i c h x = k c a , x ^ k ^ a , s'=k s'a, a n d j n ( x ) and n n ( x ) a r e t h e s p h e r i c a l B e s s e l f u n c t i o n s o f t h e f i r s t and s e c o n d k i n d . P r i m e s on t h e B e s s e l f u n c t i o n s d e n o t e d i f f e r e n t i a t i o n w i t h r e s p e c t t o t h e a r g u m e n t . The p r o p e r t i e s o f t h e m a t e r i a l c o n s t i t u t i n g t h e s p h e r e a f f e c t t h e r e s u l t s o l e l y t h r o u g h t h e v a l u e s o f t a n § n . T h e s e v a l u e s a r e s u c h t h a t t h e c o n d i t i o n s a t t h e b o u n d a r y r=a; e q u a l d i s p l a c e m e n t o f f l u i d and. s o l i d , c o n t i n u o u s n o r m a l s t r e s s , and z e r o s h e a r s t r e s s , a r e s a t i s f i e d . N o t i n g an e r r o r o b s e r v e d by H i c k l i n g ( 1 9 6 2 ) , F a r a n ' s r e s u l t f o r t h e t a n $ n may be w r i t t e n as tanecjx' ) ( n 2 + n j tancf„ = A S ' 2P: t a n W x ' ) + 1 (n 2+n-1 ) - s ' 2 + t a n * ( s ' ) n 2 + n - s j _ 2 + 2 t a n ^ ( x ' ) 2 t a n ^ ( x ' ) + 1 ( n 2+n) (1+tan<(s' ) ) ( n 2 + n - i ) - s ' 2+tan<<(s' ) (2.8) In t h e l o n g - w a v e l e n g t h l i m i t ( x , x ' , s'<<1), (2.8) becomes (2.9) fts' 2 {(n+1 ) (2n + 3)-n(2n+1 ) ( 2n + 3 ) s j _ 2 + ( 2n+1 )s_L2 } pi 2x' 2 2 ta n f i =• " {s' 2 [ y - ( 2 n + 1 ) (2n + 3)s_l_ 2]+2(n-1 ) (2n+3) [c[s^ 2-(n+1 ) (n + 2) ]} 2 x ' 2 2 x ' 2 where y = 2 ( n 2 + 3 n + l ) and q=(2n 2+4n+3). F o r n=0 and n=1, t a n §0 = -x2^/3K t a n §, = pjpj - 7( f'x 2/5 ?f (2.10a) (2.10b) 1 6 w h e r e 7^ = 1 / ( A ' + 2 / * - ' / 3 ) i s t h e b u l k c o m p r e s s i b i l i t y o f t h e s o l i d ( S o k o l n i k o f f 1 9 5 6 , p . 6 9 ) . B e c a u s e | 7 „ | « 1 , t a n r\n = s i n ^ n e x p ( - i 7„ ) ( 2 . 1 1 ) t o f i r s t o r d e r i n " \ n , w h i c h i s s u f f i c i e n t s i n c e rjn i s o f o r d e r ( k c a ) 3 . E q u a t i o n ( 2 . 5 ) b e c o m e s P r - P o k c 2 a 3 3 r •V -ft + 3( A'-/°.)cose e x p ( i k t r ) ( 2 . 1 2 ) i f t h e s e c o n d o r d e r t e r m i n ( 2 . 1 0 b ) i s d r o p p e d . G o o d m a n a n d S t e r n ( 1 9 6 2 ) d e r i v e d ( 2 . 1 2 ) a s a s p e c i a l c a s e o f t h e i r r e s u l t f o r a s p h e r i c a l s h e l l . T h e s a m e e x p r e s s i o n c a n b e o b t a i n e d f r o m e q u a t i o n s ( 4 9 ) a n d ( 5 1 ) i n E p s t e i n ( 1 9 4 1 ) . 2 . 1 . 2 F l u i d S p h e r e Now c o n s i d e r t h e c a s e o f a f l u i d s p h e r e , i n w h i c h t h e s p e e d o f s o u n d i s c ' 2 = l / 7 ( ' / ? ; ( 2 . 1 3 ) N o t e i n p a s s i n g t h a t ( 2 . 1 ) a n d ( 2 . 2 ) r e d u c e t o ( 2 . 1 3 ) i f t h e c o e f f i c i e n t o f r i g i d i t y (yu! ) v a n i s h e s . T h e s o l u t i o n o f M o r s e a n d I n g a r d ( 1 9 6 8 , p . 4 2 5 ) m a y b e r e c a s t i n t h e f o r m o f ( 2 . 5 ) , i n w h i c h c a s e t h e t a n ^ i n ( 2 . 6 ) a r e t a n c j n ( x ' ) = - t a n * n (x ' ) . pJp? ( 2 . 1 4 ) I t may b e s h o w n t h a t ( 2 . 8 ) r e d u c e s t o ( 2 . 1 4 ) i d e n t i c a l l y f o r yw'= 0 . I n t h e l o n g - w a v e l e r i g t h l i m i t ( x ' < < 1 ) , ( 2 . 1 4 ) b e c o m e s t a n $ n = [ n - x ' 2 / ( 2 n + 3 ) ] pjp2 ( 2 . 1 5 ) a n d f o r n=0 a n d n = 1 , t a n $a = - 7 ^ ' x 2 / 3 ( 2 . 1 6 a ) t a n $ = p0/p: - 7 < ' x 2 / 5 ^ ( 2 . 1 6 b ) T h e f i r s t o r d e r s o l u t i o n f o r t h e s c a t t e r e d w a v e i s 17 P r = Po k c 2 a 3 3r »\' -"K + 3( Po" - p. ) c o s e T 2pJ +f>. exp( i k c r ) (2.17) Comparing (2.16) and (2.17) t o the p r e v i o u s r e s u l t s (2.10) and ( 2 . 1 2 ) , i t w i l l be o b s e r v e d t h a t the s c a t t e r e d waves a r e i d e n t i c a l i n form f o r b o t h s o l i d and f l u i d s c a t t e r e r s even t o o r d e r ( x ) 5 , f o r n<1. For n>1, however, the tan $ n a r e v e r y s m a l l ( 0 ( s ' ) 2 ) f o r a s o l i d , whereas they are of o r d e r p°n/po f o r a f l u i d s p h e re. When the terms of h i g h e r o r d e r i n k c a may be n e g l e c t e d , the waves s c a t t e r e d by s o l i d and f l u i d s pheres of the same d e n s i t y , c o m p r e s s i b i l i t y , and r a d i u s a r e i d e n t i c a l t o o r d e r ( k c a ) 5 . 2.1.3 S o l i d S p h e r i c a l S h e l l For t he sake of completeness and because of i t s r e l e v a n c e t o the s c a t t e r i n g of sound by p h y t o p l a n k t o n w i t h t h i n o u t e r s h e l l s ( e . g . d i a t o m f r u s t u l e s ) , we i n c l u d e the r e s u l t Pr =Po ( k c 2 a 3 ) 3 A 3r a "( <Y>' ~ X ) ( 1 + 4 A' ^ /3) 3( ^ ' y j c o s e l e ' ^ (2.18) H (1+4 /* ,7f;/3) + p. J which i s based on e q u a t i o n (20) of Goodman and S t e r n (1962). E q u a t i o n (2.18) a p p l i e s t o a t h i n s p h e r i c a l s h e l l of t h i c k n e s s ( A ) , such t h a t A/a<<1, and i n which the c e n t r a l f l u i d i s the same as the ambient f l u i d . The primed q u a n t i t i e s r e f e r t o the m a t e r i a l c o n s t i t u t i n g the s h e l l . The a m p l i t u d e of the s c a t t e r e d wave i s p r o p o r t i o n a l t o the volume of the s h e l l r a t h e r than t h a t of the sphere. Suppose t h a t the t h i n s i l i c a f r u s t u l e of a di a t o m can be m o d e l l e d by such a s h e l l . I t would then be e x p e c t e d t h a t the a m p l i t u d e of the 18 s c a t t e r e d wave s h o u l d be c o n s i d e r a b l y l e s s than t h a t s c a t t e r e d by a s o l i d s i l i c a body of the same shape and s i z e as a di a t o m . T h i s s u p p o s i t i o n assumes, of c o u r s e , t h a t the por e s i n . the f r u s t u l e a r e unimportant i n the f r e q u e n c y range of i n t e r e s t . 2.2 V i s c o t h e r m a l E f f e c t s The a t t e n u a t i o n of a sound wave p r o p a g a t i n g i n an inhomogeneous medium i s d e f i n e d as the sum of s c a t t e r i n g and a b s o r p t i o n l o s s e s . E p s t e i n and C a r h a r t (1953) d e v e l o p e d a t h e o r y f o r t h e a t t e n u a t i o n of sound by f l u i d s pheres suspended i n a f l u i d medium. The a t t e n u a t i o n was o b t a i n e d s o l e l y i n terms of the a m p l i t u d e s of the p a r t i a l waves s c a t t e r e d from a s i n g l e s p h ere, which a r e m o d i f i e d by v i s c o u s drag and t h e r m a l c o n d u c t i o n . A l l e g r a and Hawley (1972) extended t h i s t r e a t m e n t t o i n c l u d e the case of s o l i d s p h e r e s . In the i n v i s c i d , n o n - c o n d u c t i n g c a s e , t h r e e waves - a s c a t t e r e d compression wave i n the f l u i d , and co m p r e s s i o n and shear waves i n the s o l i d - are n e c e s s a r y t o a d e q u a t e l y d e s c r i b e the response of the f l u i d - s o l i d system t o an i n c i d e n t c o mpression wave. When v i s c o u s and t h e r m a l e f f e c t s a r e i n c l u d e d , t h r e e new waves a r i s e - a v i s c o u s shear wave i n the f l u i d and a t h e r m a l compression wave i n both the f l u i d and the s c a t t e r e r . M a t h e m a t i c a l l y , the i n c r e a s e d a b s o r p t i o n of the i n c i d e n t wave i n the p r e s e n c e of the s c a t t e r e r i s due to the damping of these a d d i t i o n a l waves. P h y s i c a l l y , energy l o s s a r i s i n g from t h e r m a l c o n d u c t i o n i s due t o the d i f f e r e n c e s i n a m p l i t u d e and phase of the a c o u s t i c a l l y d r i v e n t emperature f l u c t u a t i o n s i n the f l u i d and the p a r t i c l e . V i s c o u s l o s s e s a r e the r e s u l t of the r e l a t i v e 19 motion of the f l u i d and the p a r t i c l e . Both e f f e c t s depend on a f l u x - of heat i n one c a s e , momentum i n the o t h e r - between the f l u i d and the p a r t i c l e . T h i s f l u x i s a p p r e c i a b l e where the g r a d i e n t s of t e m p e r a t u r e and v e l o c i t y a r e s u f f i c i e n t l y h i g h , which i s the case o n l y i n t h i n boundary l a y e r s a t the s u r f a c e of the s c a t t e r e r . -The t h i c k n e s s e s of the boundary l a y e r s a r e p r o p o r t i o n a l t o the wavelengths of the v i s c o u s and t h e r m a l waves. From m a t e r i a l t o be p r e s e n t e d , i t can be shown t h a t f o r most s o l i d s and f l u i d s i n water ( e . g . t h o s e w i t h c o m p r e s s i b i l i t i e s l e s s than 10" 6 g"~1 c m - 1 s 2 and t h e r m a l c o n d u c t i v i t y t o s p e c i f i c heat r a t i o s of about 10" 2 or l e s s ) , the w a v e l e n g t h of the t h e r m a l wave i s much s m a l l e r than t h a t of e i t h e r the i n c i d e n t wave or the c o m p r e s s i o n wave i n the s c a t t e r e r a t f r e q u e n c i e s l e s s than about 10 MHz. T h i s p e r m i t s an assumption fundamental t o the t h e o r y , namely t h a t | k £ / k T | , | k c'/k;| « 1 (2.19a) where k T i s the t h e r m a l wavenumber. In t h e f l u i d , the a d d i t i o n a l a s s u m p t i o n | k c / k s | « 1 (2.19b) can be made, where k s i s the v i s c o u s wavenumber. The E p s t e i n -C a r h a r t t h e o r y , as m o d i f i e d by A l l e g r a and Hawley, i s r e v i e w e d i n s e c t i o n s (2.2.1) and ( 2 . 2 . 2 ) . The c e n t r a l r e s u l t s of the p r e s e n t work a r e p r e s e n t e d i n s e c t i o n s (2.3) and ( 2 . 4 ) . 2.2.1 G o v e r n i n g E q u a t i o n s The s t r e s s t e n s o r f o r a f l u i d ( B a t c h e l o r 1967, p.147) i s Sij = - P V 2/-. [e, - ( 2 . 2 0 ) where i s the Kroneker d e l t a t e n s o r and the r a t e of s t r a i n t e n s o r i s 20 J 2 by,; + d Vj (2.21 ) The are the vel o c i t y components, juB i s the shear v i s c o s i t y and p, the pressure, i s the mean normal stress. The stress tensor for an iso t r o p i c s o l i d i s (Sokolnikoff 1956, p.71) S£j = A'du^- + 2/t,'€ij (2.22) where the s t r a i n tensor i s e t j = 1 f + <t"i) (2.23) 2 V <>xj dxi The u£ are the components of the displacement vector, A' and /<.' are Lame's e l a s t i c constants. In i t s mean state the medium i s stationary and is o t r o p i c . The amplitude of the sound wave i s taken to be s u f f i c i e n t l y small that non-linear effects can be ignored. In t h i s case the deviation of a variable from i t s mean value i s also small, and products of such deviations are n e g l i g i b l e . Dropping these terms and time and space derivatives of mean quantities, the equations of continuity and conservation of momentum (using (2 .20) become, P + pJv^dx; = 0 (2.24) dx- 3 "5x-\ dxkj dxk\ 6xkl (2.25) where the dot indicates p a r t i a l d i f f e r e n t i a t i o n with respect to time. In a s o l i d , f> ' + P^uL / a x . = 0 (2.26) dx7 3 dx\dxkJ dxk\dxkJ (2.27) where the acoustic pressure in the s o l i d i s 21 p'= - ( V + 2 / u ' / 3 ) . <3u t/t!x^ ( 2 . 2 8 ) which i s the mean normal s t r e s s . A s i m i l a r r e s u l t c o u l d be d e r i v e d f o r the p r e s s u r e i n the f l u i d , but i t i s c o n v e n i e n t t o use a d i f f e r e n t form. Primes a r e used t o denote the s c a t t e r e r and t h e s u b s c r i p t o t o denote mean q u a n t i t i e s . The e q u a t i o n f o r c o n s e r v a t i o n of i n t e r n a l energy (E) f o r a f l u i d i s d i s c u s s e d i n d e t a i l by B a t c h e l o r ( 1 9 6 7 , p . 1 5 1 ) . In the a p p r o x i m a t i o n used h e r e , i t becomes T i s the t e m p e r a t u r e ; K the t h e r m a l c o n d u c t i v i t y . In an analogous f a s h i o n , t he c o n s e r v a t i o n of i n t e r n a l energy i n the s o l i d i s w r i t t e n I t i s i m p o r t a n t t o note t h a t the v i s c o u s d i s s i p a t i o n term has been dropped from ( 2 . 2 9 ) because i t i n v o l v e s p r o d u c t s of the s m a l l q u a n t i t i e s c W ; /<3XJ . T h i s means t h a t v i s c o u s damping of the f l u i d motion (the sound wave) a r i s e s from the c o u p l i n g of ( 2 . 2 5 ) and ( 2 . 2 9 ) t h r o u g h the d i v e r g e n c e of the v e l o c i t y f i e l d , which i s g r e a t e s t i n the neighbourhood of the s c a t t e r e r . V i s c o u s damping of the energy i n the sound wave r e s u l t s p r i m a r i l y from the momentum f l u x (drag) n e c e s s a r y t o overcome the i n e r t i a of the p a r t i c l e . S i m i l a r l y , the term i n B a t c h e l o r ' s e x p r e s s i o n f o r the me c h a n i c a l p r e s s u r e ( B a t c h e l o r 1 9 6 7 , p . 1 5 4 ) , i n v o l v i n g the second c o e f f i c i e n t of v i s c o s i t y has been dropped t o o b t a i n ( 2 . 2 9 ) . The m e c h a n i c a l p r e s s u r e can t h e r e f o r e be i d e n t i f i e d w i t h ( 2 . 2 9 ) ( 2 . 3 0 ) 22 the thermodynamic e q u i l i b r i u m p r e s s u r e , which can be d e t e r m i n e d from the e q u a t i o n of s t a t e . I t a l s o means t h a t i n the absence of heat c o n d u c t i o n p r e s s u r e changes w i t h i n the f l u i d i t s e l f a r e r e v e r s i b l e , e x c e p t i n the neighbourhood of the p a r t i c l e . Because t h e r m a l c o n d u c t i o n i s i n c l u d e d i n (2.29) the s c a t t e r e r a c t s as a heat s i n k d u r i n g a c o m p r e s s i o n c y c l e , and as a s o u r c e d u r i n g the subsequent e x p a n s i o n c y c l e . In b o t h c a s e s , the a m p l i t u d e of the p r e s s u r e , b e i n g p r o p o r t i o n a l t o the t e m p e r a t u r e , i s reduced. In each medium the t h r e e c o n s e r v a t i o n e q u a t i o n s , i n c o n j u n c t i o n w i t h two i m p l i c i t r e l a t i o n s between p and E and the s t a t e v a r i a b l e s p and T a r e reduced t o two c o u p l e d e q u a t i o n s . The d e t a i l s may be found i n E p s t e i n and C a r h a r t (1953). W i t h 6/dt = - i c j , t h e s e e q u a t i o n s a r e , f o r a f l u i d co 2 v + / c J - i um.\ V(^- v) + i t j c 2 / a ^ T - i t o A t 0 V 2 v = 0 (2.31a) and (r- 1 ) 7-v-icjT- yg- V2T =0 (2.31b) where Y = Cp/C¥ i s the r a t i o of s p e c i f i c h e a t s , c i s the speed of sound, i s the c o e f f i c i e n t of t h e r m a l e x p a n s i o n and cr i s the t h e r m a l d i f f u s i v i t y . In a s o l i d , the e q u i v a l e n t e q u a t i o n s a r e oo2u+(c,'2 + m'Xv(V-u)- c,'2fi,VT+ /X'^72U=0 (2.32a) and (-ih)) (y' -1 ) V-u - iojT' - r'<r' V2T' =0 . (2.32b) where c/ 2 = ( \'+2y/3)/p: = 1 / ( / * . ' ) (2.33) 23 The e q u a t i o n s ( 2 . 3 1 ) a n d ( 2 . 3 2 ) r e p r e s e n t t h e a c o u s t i c f i e l d i n t h e f l u i d medium a n d t h e s o l i d s c a t t e r e r , r e s p e c t i v e l y . The p r o b l e m i s t o f i n d g e n e r a l s o l u t i o n s t o t h e s e e q u a t i o n s i n s p h e r i c a l c o o r d i n a t e s , w h i c h must t h e n be s p e c i a l i z e d by t h e u s e o f a p p r o p r i a t e b o u n d a r y c o n d i t i o n s a t t h e s u r f a c e o f t h e s p h e r e a n d a t i n f i n i t y . 2.2.2 G e n e r a l S o l u t i o n The v e l o c i t y f i e l d i n t h e f l u i d a n d d i s p l a c e m e n t f i e l d i n t h e s o l i d a r e r e p r e s e n t e d by s c a l a r p o t e n t i a l s <f> a n d v e c t o r p o t e n t i a l s A s u c h t h a t v = - ? f + V x A ( 2 . 3 4 ) u = -fif'+ V x A' ( 2 . 3 5 ) where r/-/t-0 a n d f = <fl + (j>r ( 2 . 3 6 ) i n w h i c h (f)c a n d <^ T a r e t h e s c a l a r p o t e n t i a l s f o r t h e c o m p r e s s i o n a n d t h e r m a l w a v e s . I n t h e f l u i d fc= <t>o + 4>r ( 2 . 3 7 ) (j)0 a n d (fsr b e i n g t h e s c a l a r p o t e n t i a l s f o r t h e i n c i d e n t a n d s c a t t e r e d w a v es. B e c a u s e o f s y m m e t r y , A=(0,0,A^) a n d A ' = ( 0 , 0 , A ^ ) . A s s u m i n g w a v e l i k e s o l u t i o n s , t h e f i e l d e q u a t i o n s ( 2 . 3 1 ) a nd ( 2 . 3 2 ) e a c h r e d u c e t o t h r e e e q u a t i o n s o f t h e f o r m V2<t>c + k c 2£ = 0 V2(p7 + k2<^T = 0 (2 . 3 8 ) V2f\^\l 4 = 0 w h e r e , f o r t h e s c a t t e r e r , t h e p r i m e s a r e u n d e r s t o o d . I n t h i s way 24 t h e wavenumbers o f t h e c o m p r e s s i o n , t h e r m a l a n d s h e a r waves a r e de f i n e d . I n t h e f l u i d medium, K2 = u>2[ 1 - iu> { ) o - (2.39a) c 2 c 2 3 ^ k 2 * i w /c (2.39b) k 2 = i w ^ / / . (2.39c) p r o v i d e d t h e t e m p e r a t u r e i s g i v e n by T = [bc<£c +br<j>r ]/(-i«J ) ( 2 . 4 0 ) where b c = --r [ - / c l - 4icjAt.\ k 2 ] ( 2 . 4 1 a ) b T = - y [ C J 2 - / c 2 - 4 W.\ k 2 ] ( 2 . 4 1 b ) c 2 , 6 Vy 3?° ' N o t e ( 2 . 3 9 a ) a n d ( 2 . 3 9 b ) h o l d o n l y i f | k t / k T | « 1 , | k e|~u>/c a n d w«3 /o 0c 2/(4 yu.y ) o r | k c / k s | « 1 ( 2 . 4 2 ) F o r w a t e r , t h e l a s t c o n d i t i o n r e q u i r e s t h a t t h e f r e q u e n c y be much l e s s t h a n 1 0 1 1 Hz, w h i c h w i l l n o t be a l i m i t a t i o n i n most c a s e s . I t s h o u l d a l s o be n o t e d t h a t 0 2.39a) d o e s n o t i n c l u d e a t e r m i n v o l v i n g t h e s e c o n d c o e f f i c i e n t o f v i s c o s i t y a s d o e s e q u a t i o n ( 7 . 4 ) i n E p s t e i n a n d C a r h a r t (1953) b e c a u s e o f t h e f o r m c h o s e n f o r t h e s t r e s s i n ( 2 . 2 0 ) I n a s o l i d , t h e e q u i v a l e n t r e l a t i o n s a r e k/ 2 = w 2 c' 2 1 - i c j o-' ( y'-1 ) ( /3) c ' 2 (A' +2^') ( 2 . 4 3 a ) k; 2 = i c j /cr' ( 2 . 4 3 b ) k5' 2 = } : ^ 2 / ^ ( 2 . 4 3 c ) 25 p r o v i d e d T'= be'# +bT' ft (2.44) where bc' = -y' [ w 2 - /c,'2+ 4/,'U/2 ] (2.45a) bT' = -y' [ w 2 - /c,'2+ 4 V U ; 2 ] (2.45b) A g a i n the e q u a t i o n s f o r kc' and kT' h o l d o n l y i f | kc' | ~ w/c' and | ke'/kT-|«l. Rather than a r e s t r i c t i o n on the f r e q u e n c y , as was the case i n the ambient f l u i d , i n the s c a t t e r e r y' must be v e r y c l o s e t o 1. U n t i l t h i s p o i n t the development has been concerned o n l y w i t h s o l i d s c a t t e r e r s . I t i s of i n t e r e s t t o c o n s i d e r the case where the s c a t t e r e r i s f l u i d . E q u a t i o n s (2.34) and (2.35) are i d e n t i c a l i f c)u/<3t=v, <£=-icj$' and A=-icu A' , and (2.39) and (2.43) become e q u i v a l e n t i f c i 2 _ p r o v i d e d w « fie2//*,' which i s e q u i v a l e n t t o ( 2 . 4 2 ) . E q u a t i o n s (2.41) and (2.45) a r e e q u i v a l e n t i f c,' i s r e p l a c e d by c' and by - i u>yuay . E q u a t i o n s (2.40) and (2.44) a r e e q u i v a l e n t i f f -*- #'/(-io> ). F i n a l l y , t he f i e l d e q u a t i o n s f o r a s o l i d (2.32) reduce t o t h o s e f o r a f l u i d (2.31) p r o v i d e d -icju=v and /t'-*-iww,. The s o l u t i o n s w i l l t h e r e f o r e a p p l y t o both f l u i d and s o l i d 26 s c a t t e r e r s , and the r e s u l t s o b t a i n e d f o r s o l i d p a r t i c l e s can be s p e c i a l i z e d t o the case of f l u i d ones by s i m p l y r e p l a c i n g kc', , , b^ , and b^ by t h e i r f l u i d e q u i v a l e n t s u n l e s s noted o t h e r w i s e . N o t i c e t h a t s i n c e | k c / k T | « 1 and | k,!/k_;|«1, t h a t | b c / b T | and | bc' /b^. | a r e a l s o <<1. F u r t h e r m o r e , i n c a s e s where k c a kc' , which i s t r u e f o r most l i q u i d and s o l i d p a r t i c l e s i n water, | b c/b||«1 and | bJ/b T|<<1 as w e l l . These r e l a t i o n s w i l l prove v e r y u s e f u l i n d e r i v i n g e x p l i c i t e x p r e s s i o n s . 2.2.3 The Boundary-Value Problem The s o l u t i o n s of e q u a t i o n s (2.38) i n s p h e r i c a l p o l a r c o o r d i n a t e s w i t h symmetry about t h e p o l a r a x i s , and which remain f i n i t e a t the o r i g i n and a t i n f i n i t y , a r e , i n the f l u i d medium, £ i " (2n+1 ) j„ ( k c r ) P„ (cos e ) £ i n ( 2 n + 1 ) A„h„(k tr) P n (cos 6 ) (2 .46 ) 2 i"(2n+1) B n h n ( k T r ) P„ ( c o s e ) j£ i"(2n+1) C.h n ( k ^ r ) d P n (cos 6 ) and i n the s o l i d s c a t t e r e r , £'= £1 i"(2n+1) A ^ U ^ r ) P j c o s Q ) oo (2 .47 ) CO (\1= C i"<2n+1.) j n ( k ^ r ) d P ^ (cos© ) The v a l u e s of the unknown c o e f f i c i e n t s A„ ,B„ ,Cn ,A^ ,B^ , and are d e t e r m i n e d by the boundary c o n d i t i o n s a t the s u r f a c e of the 27 sphere. These c o n d i t i o n s a r e t h a t the r a d i a l v e l o c i t y , t a n g e n t i a l v e l o c i t y , t e m p e r a t u r e , heat f l u x , r a d i a l s t r e s s and t a n g e n t i a l s t r e s s be c o n t i n u o u s . They may be found i n A l l e g r a and Hawley (1972) and i n E p s t e i n and C a r h a r t (1953). We note o n l y a m i s p r i n t i n A l l e g r a and Hawley's e q u a t i o n ( 6 e ) , i n which a f a c t o r of 2 i s absent from the f i r s t term. In the i n v i s c i d n o n - c o n d u c t i n g l i m i t , t he n o - s l i p c o n d i t i o n ( c o n t i n u o u s t a n g e n t i a l v e l o c i t i e s ) and the c o n d i t i o n s on tem p e r a t u r e and heat f l u x must be dropped - the o t h e r boundary c o n d i t i o n s can be shown t o be e q u i v a l e n t to those" used by Faran (1951). E x p r e s s i o n s f o r the (2.23) i n s p h e r i c a l p o l a r c o o r d i n a t e s may be found i n S o k o l n i k o f f (1956, p.184). By r e p l a c i n g the s t r a i n (u) by the r a t e of s t r a i n (v) i n the s e r e l a t i o n s , the e- (2.21) may be o b t a i n e d . The r e s u l t i n g e q u a t i o n s a r e : (a) R a d i a l v e l o c i t y x j ; ( x ) + x A n h ; ( x ) + t B n h ; ( t ) + C n n ( n + 1 ) h n ( s ) (2.48a) = (-iuu J f x ' A j j ^ x ' l + t ' B ^ j ^ t M + q n i n + D j J s ' ) ] (b) N o - s l i p c o n d i t i o n j„(x)+A nh„(x)+B^h n(t)+C n[h n(s)+sh;(s)] (2.48b) = ( - i c j ){A^jn (x' )+B; j„(t' )+C^[ j"„(s' )+s" ] \ ( s ' ) ] } (c) Temperature b c[j n(x)+A„h n(x)]+b TB nh n(t) (2.48c) = (-ico H b ' A ^ U ' K b ^ j ^ f ) ] (d) Heat f l u x b c [xj;(x)+A„xh;(x)]+B nb Tth^(t) (2.48d) = (-ico ) j T f A ^ ' x ' j ; (x' )+B;b^f j j t f )] K 28 (e) R a d i a l s t r e s s (-icjp. a 2+2/, 0x 2 ) j„ (x)+2 /u ax 2 j„"(x)+An[ (-ico^a 2 + 2 / W < >x 2 ) h n (x) + 2 A x 2 h ; ' ( x ) ] + B j (-ioj /o ea 2 + 2 / , 0 t 2 ) h n ( t ) + 2 y a 0 t 2 h ; , ( t ) ] -C„ 2 A n ( n + 1 ) [ h n ( s ) - s h ^ (s) ] (2.48e) = [ (- u J 2 / J o , a 2 + 2 X x ' 2 ) j n ( x ' ) * 2/x' 2 j n " ( x ' ) ]+B,| [ ( V ^ a ' +2/*'t' 2 ) j n ( f )+2 /u'f 2 j n " ( f ) ]-C«2y n(n+1 ) [ j„ ( s ' )-s' j n ' ( s ' ) ] ( f ) T a n g e n t i a l s t r e s s ^ { x j ; (x)-jn(x)+A„[xh;(x)-h„(x) ]+B„[th,; ( t ) - h n ( t ) ] +Cjs 2h„"(s) + (n 2+n-2)h„(s) ]/2} (2.48f) =/t'{A;[x'j:(x' (x' ) ] + B A [ t ' j ^ ( f ) - j „ ( f ) ] + C ; [ s ' 2 j ; ' ( s ' ) + ( n 2 + n - 2 ) j r i ( s ' ) ] / 2 } where x=k ca, t = k r a , s=k 5a and the primes denote the s c a t t e r e r e x cept i n the case of the s p h e r i c a l Hankel and B e s s e l f u n c t i o n s , i n w hich case they denote d i f f e r e n t i a t i o n . The e q u a t i o n s (2.48) a r e i d e n t i c a l t o A l l e g r a and Hawley's e q u a t i o n s ( 8 ) , w i t h two e x c e p t i o n s . The f i r s t i s the s i g n of the (n 2+n-2) terms i n ( f ) , as D a v i s (1979) a l s o o b s e r v e d . The second i s t h a t the C„ and C,| terms a r e a l l the n e g a t i v e of t h o s e o b t a i n e d by A l l e g r a and Hawley because t h e i r v e c t o r p o t e n t i a l i s d e f i n e d as the n e g a t i v e of t h a t g i v e n h e r e . The a t t e n u a t i o n of the i n c i d e n t wave, as E p s t e i n and C a r h a r t (1953) have shown, depends e x p l i c i t l y on the kn o n l y . T h i s c o n s i d e r a b l y s i m p l i f i e s the problem. F u r t h e r m o r e , we are i n t e r e s t e d p r i m a r i l y i n the l o n g - w a v e l e n g t h l i m i t and s h a l l be c o n t e n t w i t h o b t a i n i n g r e s u l t s f o r n=0 and n=1. For n=0, the boundary c o n d i t i o n s on the t a n g e n t i a l v e l o c i t y and s t r e s s a r e such t h a t e v e r y term c o n t a i n s dP„/de =0 as a 29 m u l t i p l i c a t i v e f a c t o r . Of the f o u r r e m a i n i n g e q u a t i o n s , the c o n d i t i o n (2.48c) on the t e m p e r a t u r e may be f u r t h e r s i m p l i f i e d a f t e r d i v i d i n g by b T by. d r o p p i n g a l l but the B 0 and B„ terms (see the f i n a l p a r a g r a p h i n S e c t i o n 2.2.2, and E p s t e i n and C a r h a r t , 1953). For n=1 a s i m i l a r argument ( E p s t e i n and C a r h a r t , 1953), can be used t o show t h a t the B, and B,' terms a r e n e g l i g i b l e i n a l l but (2.48c) and (2.48d), which may t h e r e f o r e be dropped. In o t h e r words, t h e r m a l e f f e c t s a r e u n i m p o r t a n t f o r n=1 and the s i x e q u a t i o n s a r e reduced t o - f o u r i n w h i c h B, and B/ a r e s e t t o z e r o . 2.3 The I n v i s c i d Non-Conducting L i m i t In t h i s l i m i t , the t h e r m a l boundary c o n d i t i o n s and the no-s l i p c o n d i t i o n may be dropped. In the r e m a i n i n g e q u a t i o n s , jja ,B„ ,B^ and Cn a r e s e t t o z e r o . E q u a t i o n (2.48f) then becomes C„'= -2A„ [x' j ; (x' )-j„ (x* ) ] (2.49) s' 2 j„"(s' )+(n 2+n-2) j n ( s ' ) D e f i n i n g F R ( x , A n ) = j„(x) + A„h„(x) (2.50) and t a k i n g the r a t i o of (2.48a) and (2.48e) xF n'/F n = tan <|o(x' ,s' ) where t a n § n i s g i v e n by ( 2 . 8 ) , and xFn' =x j \ (x) +A nxh^ (x) . I t i s e a s i l y shown t h a t i f A„ = - i s i n - | n e x p ( - i > ] r t ) (2.50a) and t a n c£„=xF^ /Fn , then tan/| n i s as g i v e n i n ( 2 . 6 ) . The e q u a t i o n s (2.48) reduce to Faran's r e s u l t i n the l i m i t . 3 0 T h i s l e a d s t o t h e d e p a r t u r e f r o m t h e a p p r o a c h t a k e n b y E p s t e i n a n d C a r h a r t ( 1 9 5 3 ) a n d A l l e g r a a n d H a w l e y ( 1 9 7 2 ) . W h e n v i s c o t h e r m a l e f f e c t s a r e i n c l u d e d , t h e e q u a t i o n s a r e s o l v e d f o r xF„' / F „ r a t h e r t h a n A„ . T h e t a n § n i n ( 2 . 6 ) a r e r e p l a c e d b y t a n $ n = x F ; / F „ ( 2 . 5 1 ) T h e d e t a i l s a r e i n A p p e n d i x 1 . 2 . 4 T h e L o n g - W a v e l e n g t h L i m i t T h e e q u a t i o n s ( 2 . 4 8 ) w i l l n o w b e r e d u c e d t o a p p r o x i m a t e f o r m s f o r n=0 a n d 1 . A l l e g r a a n d H a w l e y ( 1 9 7 2 ) f o u n d t h a t i n a q u e o u s s u s p e n s i o n s o f p o l y s t y r e n e s p h e r e s , t h e a t t e n u a t i o n f r o m t h e n=2 t e r m e x c e e d e d t h a t f r o m t h e n=1 t e r m f o r k c a > 0 . 0 5 , a n d a p p r o a c h e d t h a t f r o m t h e n=1 t e r m f o r k , . a > 0 . 2 . O n t h a t b a s i s , t h e f o l l o w i n g t h e o r y a p p l i e s o n l y t o t h e r e g i o n k c a < 0 . 1 . 2 . 4 . 1 T h e I s o t r o p i c ( n = 0 ) T e r m U s i n g ( 2 . 1 9 ) , t h e e q u a t i o n s ( 2 . 4 8 ) r e a d i l y r e d u c e t o t h e t h r e e e q u a t i o n s ( A 2 ) f o r n = 0 . W i t h t h e a d d e d r e s t r i c t i o n s I k c ' / k s | « 1 ( 2 . 5 2 ) | k s ' / k s | « 1 ( 2 . 5 3 ) a n d t h a t 0 . 1 ; $ P°/f>° £ 1 0 ( s e e A p p e n d i x 1 ) , t h e n i n t h e l o n g -w a v e l e n g t h l i m i t e q u a t i o n s ( A 2 ) r e d u c e t o - t a n r j . =xl~ n + 4 b ; t a r w . ( t ' ) x 3 / 3 b T ' s ' 2 3 s ' 2 H - K ' b ; V b . - p.\ - 1 + K ' b T ' b c x ' 2 4 x ~ * ~ l v K b T / \ b e ' pi) K b T b c ' x 2 A , + 2 y a ' / 3 ) f l - K ' t a n ^ f )\ ( 2 . 5 4 ) x ' + 2 y ) \ K t a n y ( t ) p r o v i d e d ( r ' - ! ) | t a n oco ( t ' ) / t ' 2 | « s ' 2 / 4 x ' 2 ~ 0 . 1 ( 2 . 5 5 ) 31 I t i s the c o n d i t i o n (2.53) which r e s t r i c t s the r e s u l t t o s o l i d p a r t i c l e s . The f u r t h e r r e s t r i c t i o n (2.55) was not assumed by A l l e g r a and Hawley (1972) and i s examined i n Appendix 1. E q u a t i o n (2.54) i s independent of the v i s c o s i t y of the f l u i d and i n the no n - c o n d u c t i n g l i m i t (K'=0), the second term v a n i s h e s . 2.4.2 The D i p o l e (n=1) Term In the l o n g - w a v e l e n g t h l i m i t , and a g a i n i n v o k i n g (2.53) and so r e s t r i c t i n g the r e s u l t t o s o l i d s c a t t e r e r s , the e q u a t i o n s (A10) become tann, = ( p,-pJ ) ( t a n y, (s)+1) (2.56) x 3 / 3 - (f, +2f>: ) ( t a n y, (s) + 1 )+6(p. -/>; ) which i s e q u i v a l e n t t o (15) i n A l l e g r a and Hawley (1973) and g i v e s the a p p r o p r i a t e r e s u l t i n the i n v i s c i d l i m i t (s = °° ). 2.4.3 The A t t e n u a t i o n of the I n c i d e n t Wave E p s t e i n and C a r h a r t (1953) have shown t h a t i n the l o n g -w a v e l e n g t h l i m i t , the c o e f f i c i e n t f o r the a d d i t i o n a l a t t e n u a t i o n of the i n c i d e n t p r e s s u r e wave due t o the s c a t t e r e r s i s g i v e n by * = -3£ Re[A 0+3A, ] / 2 k 2 a 3 = *.+ 5f, (2.57) where € i s the volume c o n c e n t r a t i o n of suspended m a t e r i a l . On the b a s i s of e x p e r i m e n t s by U r i c k (1948) and Hampton (1967), the l i n e a r dependence of «r on c o n c e n t r a t i o n appears t o be v a l i d t o c o n c e n t r a t i o n s of about 8-9%. T h i s r e g i o n of l i n e a r dependence i s taken as the range of c o n c e n t r a t i o n s over which the su s p e n s i o n may be c o n s i d e r e d d i l u t e , meaning t h a t the e f f e c t s of p a r t i c l e i n t e r a c t i o n , such as m u l t i p l e s c a t t e r i n g , may be i g n o r e d . In our case A n i s g i v e n by (2.5 0 a ) , and i t can be shown 32 t h a t Re (A, ) = Im[tan( 7 „ ) ] (2.58) f o r | 7„|<<1. Re and Im r e p r e s e n t the r e a l and i m a g i n a r y p a r t s of t h e i r arguments. Because t h e r m a l and v i s c o u s e f f e c t s a r e c o m p l e t e l y d e c o u p l e d i n the approximate r e s u l t , the r a t i o of the im a g i n a r y p a r t s of (2.54) and (2.56) s h o u l d g i v e t he r a t i o of th e r m a l t o v i s c o u s a b s o r p t i o n p r o v i d i n g the h i g h e r o r d e r terms a r e n e g l i g i b l e , as d i s c u s s e d a t the b e g i n n i n g of t h i s s e c t i o n . P r o c e e d i n g f o r t h e case | t'|»1 f o r which (2.55) d e f i n i t e l y h o l d s , and a l s o t a k i n g |s1»1, (2.54) and (2.56) become •tan/?. & f: - Y, x 3 / 3 3( 1+i) ( y ' - l )dl2al 2Q a 3c,' 2 -tanc], = pi ~ pa -x 3 / 3 p + 2f>: ( H i ) 3 ^ . ' - / t ) *d/ \f>*2p: J a_ where Q= | k T a | , | k T'a|»1 (2.59a) | k sa|»1 (2.59b) 3c.2 p - K ' b ^ V bt-A." 4c.' 2 V K b T A b ' pl, 1+K'cr K <r' - 1 (2.59c) 1 +K' bT' b c c 2 S \ " ~ T / \ ~ c Po The parameters dT' and d„ a r e the t h i c k n e s s e s of the t h e r m a l and v i s c o u s boundary l a y e r s i n the s c a t t e r e r and the medium r e s p e c t i v e l y , and a r e g i v e n by (Morse and I n g a r d , 1968) dT' = V2/| k; | = ( 2 o ' A > ) 1 / 2 =(2K ' /co /o 0 'c; ) " 2 (2.60a) d v = ^ 2/l M = (2/i,/p.u>)r/z The r a t i o of t h e r m a l t o v i s c o u s a b s o r p t i o n i s (2.60b) R0, =Im(tan /y. ) = _2_( y'-1 )c^ I 2 Im(3tan7,) 9 I 2 k: /a.' " p. (2.61 ) I t w i l l be noted t h a t t h i s r a t i o does not i n c l u d e s c a t t e r i n g . l o s s e s . 33 2.4.4 Comparison w i t h Experiment The v a l u e s i n T a b l e I I may be used t o e v a l u a t e the r a t i o (2.61) f o r aqueous s u s p e n s i o n s of p o l y s t y r e n e and q u a r t z s p h e r e s , w i t h the h e l p of the r e l a t i o n ( P i p p a r d 1966, p.61) y ' - l " T ^ ' V ^ ' C p (2.62) where T a i s the a b s o l u t e t e m p e r a t u r e . T a b l e I I . P h y s i c a l p r o p e r t i e s at 20 °C Water 1; " d e n s i t y t h e r m a l c o n d u c t i v i t y s p e c i f i c heat t h e r m a l exp. c o e f f . v i s c o s i t y speed of sound A K C P V -C 0.998 1.41 x 10" 3 1 .000 2.1 x 10"" 5.77 x l O ' 3 1.002 x 10" 2 1 483 g cm" 3 cal°C" 1cm-'s" 1 cal°C- 1g- 1 o c- 1 g cm - 1 s" 1 m s _ 1 P o l y s t y r e n e " d e n s i t y t h e r m a l c o n d u c t i v i t y s p e c i f i c heat t h e r m a l exp. c o e f f . comp. wave speed shear wave speed P" K c P c C s 1 .055 0.27 x 10~3 0.287 2.64 x 10-" 0.069 2380 1 1 00 g cm" 3 cal°C-'cm''s" 1 cal°C-'g- 1 °C" 1 m s~ 1 m s" 1 Q u a r t z and G r a n i t e 2 ; 3 d e n s i t y t h e r m a l c o n d u c t i v i t y s p e c i f i c heat t h e r m a l exp. c o e f f . comp. wave speed shear wave speed P' K CP fi y - i c C s 2.65 8.4 x 10" 3 0. 1 92 3.4 x 10" 5 5.2 x 10- 3 51 00 3200 g cm - 3 c a l 0 C " ' c m - ' s " 1 cal°C-'g-' °C" ' m s" ' m s - 1 ' B a t c h e l o r (1967, pp.595-597) 2 C l a r k (1966, p.92, 167, 197-201) 3 Weast (1978/1979, p. E-16) " A l l e g r a and Hawley (1972) The t h e r m a l d i f f u s i v i t y ( cr ) i s g i v e n by cr = K/( PoCp ) (2.63) w i t h the r e s u l t t h a t f o r p o l y s t y r e n e , the r a t i o R 0 1 (2.61) i s 34 R 0 | = 12.5 x \0-*{{2p: + pa )/(p.'- p.)]2 = 3.6 (2.64a) and f o r q u a r t z , R01 = 3.72 x ] 0 - u [ ( 2 f o ' + / o a ) / ( P : - p . ) ] 2 = 5.4 x 10' 3 (2.64b) Note t h a t the v a l u e of Q i s of o r d e r -1 (-1.274 and -0.658) i n each c a s e . The f o l l o w i n g a p p r o x i m a t e forms were used i n e v a l u a t i n g Q: b c = -( y -1 )g>2 b T= _ k l /3 c 2 P b'= -( y'-1 )u2 • bT' = c' 2 k ; 2 p' c ' 2 c,' 2^' These r e s u l t s d e s e r v e some d i s c u s s i o n . In the f i r s t p l a c e t h e y a p p l y o n l y t o t h e case where the s k i n depths of the t h e r m a l and v i s c o u s waves i n the f l u i d and the t h e r m a l wave i n the s o l i d p a r t i c l e a r e much l e s s than the p a r t i c l e r a d i u s . S e c o n d l y , the r a t i o of t h e r m a l t o v i s c o u s e f f e c t s as embodied by (2.61) i s independent of e i t h e r the r a d i u s of the p a r t i c l e or the f r e q u e n c y of the i n c i d e n t wave. T h i s i s i n agreement w i t h F i g u r e 7 (a = 0.653 /*m) and F i g u r e 8 (a=0.504 ^ m) i n A l l e g r a and Hawley ( 1972), i n which the v a l u e s of o(0 and ~°(, , d e t e r m i n e d from a n u m e r i c a l s o l u t i o n of the e q u a t i o n s ( 2 . 4 8 ) , a r e p l o t t e d and shown t o agree w i t h d a t a f o r aqueous s u s p e n s i o n s of p o l y s t y r e n e s p h e r e s . Over the f r e q u e n c y range 3-20 MHz, f o r which k ca<0.1 and s c a t t e r i n g l o s s e s a r e u n i m p o r t a n t , not o n l y i s t h e i r r a t i o c^/o? , r e l a t i v e l y c o n s t a n t , but i t v a r i e s between 4.2 and 6.7 w i t h a mean of 5.4, i n q u i t e r e a s o n a b l e agreement w i t h ( 2 . 6 4 a ) . U r i c k (1948) was a b l e t o account f o r a t t e n u a t i o n i n aqueous s u s p e n s i o n s of q u a r t z and k a o l i n i t e (0.5^a<10/*m) by c o n s i d e r i n g o n l y v i s c o u s and s c a t t e r i n g l o s s e s over the f r e q u e n c y range 1-15 35 MHz, i n agreement w i t h ( 2.64b). I t i s c o n c l u d e d t h a t i f the bu l k d e n s i t y of the p a r t i c l e i s c l o s e t o t h a t of water, the r e l a t i v e v e l o c i t y of the s u r r o u n d i n g f l u i d i s s m a l l . V i s c o u s a b s o r p t i o n i s reduced a c c o r d i n g l y , t o t h e p o i n t where t h e r m a l l o s s e s may be i m p o r t a n t , as i s the case f o r p o l y s t y r e n e . I t would appear t h a t (2.61) may be used t o e v a l u a t e the r e l a t i v e importance of v i s c o u s and t h e r m a l a b s o r p t i o n i n s u s p e n s i o n s of s o l i d p a r t i c l e s i n wa t e r , f o r f r e q u e n c i e s or p a r t i c l e s i z e s t o which t h e l o n g - w a v e l e n g t h l i m i t and the s k i n d epth c r i t e r i a a p p l y . These c o n d i t i o n s impose an upper and lower bound on t h e p a r t i c l e s i z e f o r which (2.61) may be used. For a fre q u e n c y of 200 kHz, q u a r t z p a r t i c l e d i a m e t e r s must be < 250/tm and >2 /am, a t which k t a and kc'a=1. The approach can be extended t o s m a l l e r d i a m e t e r s , however, by t a k i n g the r a t i o of (A7) and (2.56) and e v a l u a t i n g the B e s s e l f u n c t i o n s n u m e r i c a l l y . R e t u r n i n g t o (2.61) and ( 2 . 6 4 ) , i t i s c l e a r t h a t a l t h o u g h the magnitude of the r a t i o i s d e t e r m i n e d t o a l a r g e e x t e n t by ( y ' - 1 ) and the d e n s i t y d i f f e r e n c e ( pDy'-pe ) , the o t h e r f a c t o r s , w i t h the p o s s i b l e e x c e p t i o n of Q, a r e a l s o i m p o r t a n t . G i v e n the ve r y d i f f e r e n t t h e r m a l and a c o u s t i c p r o p e r t i e s of p o l y s t y r e n e and q u a r t z , i t would appear t h a t Rol - 10-M (2 /> 0 ,+ /o 0 )/{f>:- pa) ]2 (2.65) may be a u s e f u l a p p r o x i m a t i o n . T h i s a l l o w s an e s t i m a t e t o be made of t h e d e n s i t y below which t h e r m a l l o s s e s must be i n c l u d e d . For the sake of d i s c u s s i o n , suppose t h a t an e r r o r of 5% i n the a b s o r p t i o n c o e f f i c i e n t i s a c c e p t a b l e . S e t t i n g R0, = 0.05 i n (2 . 6 5 ) , t h e r m a l l o s s e s would be n e g l i g i b l e under t h e s e c o n d i t i o n s f o r p a r t i c l e s w i t h d e n s i t i e s g r e a t e r than about 1.6 36 g cm" 3. The d e n s i t i e s of most p h y t o p l a n k t o n a r e w e l l below t h i s v a l u e , w i t h the r e s u l t t h a t v i s c o u s a b s o r p t i o n s h o u l d be s m a l l , and t h e r m a l c o n d u c t i o n l o s s e s may have t o be c o n s i d e r e d . Watson and M e i s t e r (1963), however, found t h a t a t t e n u a t i o n ( i n c l u d i n g s c a t t e r i n g l o s s e s ) was not measurable i n s u s p e n s i o n s of the d i a t o m N i t s c h i a c l o s t e r i u m f . m i n u t i s s i m a over the f r e q u e n c y range 125-750 kHz, even a t v e r y h i g h c o n c e n t r a t i o n s (3.25 g 1 ~ 1 ) . T h e i r o b s e r v a t i o n s i n d i c a t e b o t h t h a t t h e r m a l a b s o r p t i o n i n the p r e s e n c e of t h e s e diatoms must be v e r y s m a l l , and t h a t they s c a t t e r v e r y l i t t l e energy over t h i s f r e q u e n c y range. The l a t t e r i s c o n s i s t e n t w i t h the d i s c u s s i o n of s c a t t e r i n g by s p h e r i c a l s h e l l s i n S e c t i o n 2.3. I t i s worth n o t i n g t h a t Duykers (1967) used a p a r t i c l e d e n s i t y of 2.65 g cm" 3 t o e s t i m a t e the v i s c o u s a b s o r p t i o n of sound by suspended matter i n the open ocean. S i n c e much of t h i s m a t e r i a l i s l i k e l y t o be b i o l o g i c a l i n o r i g i n , such a h i g h b u l k d e n s i t y does not seem a p p r o p r i a t e and as a r e s u l t h i s e s t i m a t e s of a t t e n u a t i o n may be h i g h . F i n a l l y , the r e s u l t s (2.59)-(2.60) s h o u l d be compared w i t h the f l u i d sphere formulae (8.2.22) i n Morse and I n g a r d (1968, p.435). The two s e t s of e q u a t i o n s a r e q u i t e s i m i l a r i n form, but f o r the f o l l o w i n g d i f f e r e n c e s : (a) n=0 - t h e presence of the f a c t o r Q2cs' 2/3c'2 - t h e r a t i o of s p e c i f i c h e a t s ( y ) and the t h e r m a l b o u n d a r y - l a y e r t h i c k n e s s p e r t a i n t o the s c a t t e r e r r a t h e r than the ambient medium. 37 (b) n=1 -t h e term ( p^ -p„ ) 2 r e p l a c e s p<? ( p„ ' - pe ) i n t h e i r r e s u l t . T h e i r e x p r e s s i o n f o r the v i s c o u s p a r t of t h e a b s o r p t i o n c r o s s - s e c t i o n does, however, depend on ( p. '"/><,)2 • The E p s t e i n - C a r h a r t and M o r s e - I n g a r d t h e o r i e s a r e not e q u i v a l e n t , however, p r i m a r i l y because d i f f e r e n t boundary c o n d i t i o n s a re used. Morse and I n g a r d do not i n c l u d e the v i s c o u s and t h e r m a l waves i n s i d e the s c a t t e r e r i n t h e i r f o r m u l a t i o n , i n s t e a d f o r c i n g the tem p e r a t u r e f l u c t u a t i o n s t o z e r o f o r r<a. T h i s approach i s u s e f u l f o r a f l u i d sphere i n a gaseous medium, t h e i r c a s e i n p o i n t . 2.5 Summary Some a s p e c t s of the t h e o r y of the s c a t t e r i n g and a t t e n u a t i o n of sound by s p h e r i c a l p a r t i c l e s have been p r e s e n t e d , w i t h the emphasis on s o l i d s c a t t e r e r s . Much of the m a t e r i a l i s a s y n t h e s i s of somewhat s c a t t e r e d l i t e r a t u r e i n a form s u i t a b l e t o the problem of a c o u s t i c b a c k s c a t t e r i n g and r o u g h l y p a r a l l e l t o the t r e a t m e n t of f l u i d spheres i n Morse and I n g a r d (1968). The a d d i t i o n a l a t t e n u a t i o n of a sound wave p r o p a g a t i n g i n a s u s p e n s i o n i s assumed t o r e s u l t from heat c o n d u c t i o n and v i s c o u s d r a g a t the s u r f a c e of the p a r t i c l e as w e l l as s c a t t e r i n g . Any e f f e c t the p a r t i c l e might have on m o l e c u l a r r e l a x a t i o n l o s s e s i n sea water i s i g n o r e d . In the i n v i s c i d , n o n - c o n d u c t i n g c a s e , the form of the s c a t t e r e d wave i s compared f o r d i f f e r e n t t y p e s of s c a t t e r e r . The s o l u t i o n a p p r o p r i a t e t o a f l u i d sphere emerges as a s p e c i a l case of t h a t f o r a s o l i d s p h e re. In the l o n g - w a v e l e n g t h l i m i t , the 38 two s o l u t i o n s a re i d e n t i c a l i n form t o terms of o r d e r ( k c a ) 5 . The wave s c a t t e r e d by a t h i n s p h e r i c a l s h e l l , however, i s q u i t e d i f f e r e n t . The m o d i f i c a t i o n of the s c a t t e r e d wave by v i s c o - t h e r m a l e f f e c t s i s examined. The t r e a t m e n t of t h i s problem by E p s t e i n and C a r h a r t (1953), as extended by A l l e g r a and Hawley (1972) t o i n c l u d e the case of s o l i d s c a t t e r e r s , i s r e f o r m u l a t e d i n terms of the phase a n g l e s used by Faran (1951). T h i s approach was tak e n because i t p r o v i d e s a u n i f o r m t r e a t m e n t of the o v e r a l l problem, i n c l u d i n g the i n v i s c i d n o n - c o n d u c t i n g c a s e . The f i n a l r e s u l t s a r e a l s o f o r m a l l y more c o n c i s e . An e x p l i c i t e x p r e s s i o n f o r the wave s c a t t e r e d by a s o l i d p a r t i c l e , i n c l u d i n g the e f f e c t s of t h e s e l o s s mechanisms, i s d e r i v e d . A c c o r d i n g l y , the r a t i o of t h e r m a l t o v i s c o u s a b s o r p t i o n i s o b t a i n e d i n a r e l a t i v e l y s i m p l e form. T h i s r a t i o i s shown t o be c o n s i s t e n t w i t h the e x p e r i m e n t a l r e s u l t s of U r i c k (1948) and A l l e g r a and Hawley (1 9 7 2 ) , and i s of p a r t i c u l a r i n t e r e s t t o t h i s t h e s i s . I t i s argued t h a t the r e l a t i v e importance of t h e r m a l and v i s c o u s e f f e c t s depends p r i m a r i l y on the d i f f e r e n c e i n the b u l k d e n s i t i e s of the s c a t t e r e r and the ambient f l u i d . In p a r t i c u l a r , f o r p a r t i c l e s w i t h the t h e r m a l and e l a s t i c p r o p e r t i e s of q u a r t z and p o l y s t y r e n e and d e n s i t i e s g r e a t e r than 1.3 and 1.7 g cm " 3, r e s p e c t i v e l y , t h e r m a l l o s s e s can be i g n o r e d f o r f r e q u e n c i e s a t which the s k i n depths of the t h e r m a l and v i s c o u s waves a r e much l e s s than the p a r t i c l e r a d i u s . Most p a r t i c l e s composed of s o l i d m i n e r a l s s h o u l d s a t i s f y t h e s e c o n d i t i o n s . T h i s i s not l i k e l y f o r p h y t o p l a n k t o n , which i n g e n e r a l have b u l k d e n s i t i e s c l o s e t o t h a t of sea water. In the case of 39 d i a t o m s , the t h i n - w a l l e d s i l i c a f r u s t u l e might be u s e f u l l y a p p r o x i m a t e d by a s o l i d s p h e r i c a l s h e l l . Under such c i r c u m s t a n c e s , both the energy s c a t t e r e d and absorbed by a d i a t o m s h o u l d be s u b s t a n t i a l l y lower than t h a t by a s o l i d s i l i c a body of the same shape and s i z e . A t h e o r y of the a t t e n u a t i o n of sound i n s u s p e n s i o n s of s p h e r i c a l s h e l l s has not appeared i n the l i t e r a t u r e . 40 CHAPTER 3 DETECTING SUSPENDED SEDIMENT WITH SONAR: THEORY AND EXPERIMENT H i s t o r i c a l l y , the use of a c o u s t i c b a c k s c a t t e r i n g t o o b t a i n q u a n t i t a t i v e e s t i m a t e s of d i s c r e t e s c a t t e r e r p o p u l a t i o n s i n the ocean has been devoted p r i m a r i l y t o f i s h e r i e s a p p l i c a t i o n s . There a r e s u g g e s t i o n s i n the e a r l y l i t e r a t u r e t h a t t h i s approach might be u s e f u l f o r the d e t e c t i o n of suspended sediment. D i e t z (1948) r e p o r t e d d e t e c t i n g 0.5 mm d i a m e t e r sand a t a f r e q u e n c y of 18 kHz and a t depths of up t o 120 m a f t e r r e l e a s i n g t h e sand a t the s u r f a c e . Hersey and Backus (1962) p r e s e n t e d echograms showing i n t e r n a l wave s i g n a t u r e s and suggested t h a t p a r t i c u l a t e m a t t e r c o l l e c t i n g i n the p y c n o c l i n e might be a s i g n i f i c a n t c o n t r i b u t o r t o the echo. P r e v i o u s l y , r e p o r t s had been made of sonar d e t e c t i o n of i n t e r n a l waves (Trout e t a l , 1952), a p o s s i b l e f r o n t (Cushing et a l , 1956) and i n t e r n a l t i d e s and t h e r m o c l i n e deepening i n response t o the wind (Weston, 1958). I n c r e a s e d r e v e r b e r a t i o n was r e p o r t e d from l a y e r s w i t h h i g h t e m p e r a t u r e g r a d i e n t s ( T r o u t et a l , 1952; Herdman, 1953; Cushing et a l , 1956; Weston, 1958) and w i t h i n c r e a s e d c o n c e n t r a t i o n s of d i a t o m s and d e t r i t u s (Cushing e t a l , 1956). Shepard and D i l l (1963) r e p o r t e d i n c r e a s e d r e v e r b e r a t i o n from a p p r o x i m a t e l y the same depth as the submerged o u t f l o w from the Rhone R i v e r i n Lake Geneva as measured w i t h drogues. Schroeder and Schroeder (1964) d e t e c t e d i n c r e a s e d r e v e r b e r a t i o n •from a l a y e r c o n t a i n i n g f i n e suspended sand and d e t r i t u s i n an i n t e r f l o w from the R i v e r Toce i n Lake Maggiore. Renewed a t t e m p t s have been made r e c e n t l y t o use a c o u s t i c sounding f o r f l o w v i s u a l i s a t i o n and f o r d e t e c t i o n of suspended 41 matter i n the oceans. T h i s work has been concerned w i t h d e t e c t i n g f l o a t i n g mud l a y e r s ( T s u c h i y a e t a l , 1973; G a l l e n n e , 1974), dredge s p o i l s ( P r o n i e t a l , 1975,1976a and B o k u n i e w i c z e t a l , 1978), sewage s l u d g e ( P r o n i e t a l , 1976b), i n t e r n a l waves and m i c r o s t r u c u r e ( P r o n i and A p e l , 1975), p r e c i p i t a t e - f o r m i n g c h e m i c a l waste (Orr and Hess, 1978a), sediment r e s u s p e n s i o n and water mass i n t r u s i o n s (Orr and Hess, 1978b) and i n t e r n a l h y d r a u l i c jumps, bores and l e e waves (Farmer and S m i t h , 1980). No q u a n t i t a t i v e r e l a t i o n s h i p s between the s i g n a l and s c a t t e r e r d e n s i t y were e s t a b l i s h e d . The v e r y v a r i e t y of o b s e r v e d phenomena u n d e r l i n e s a problem fundamental t o the p r a c t i c a l a p p l i c a t i o n of the method f o r q u a n t i t a t i v e p u r p o s e s : more than one s c a t t e r i n g mechanism t u r b u l e n c e v e l o c i t y and d e n s i t y f l u c t u a t i o n s , p a r t i c l e s , b u b b l e s , b i o t a or r e f l e c t i o n from l a y e r s of d i f f e r e n t mean - d e n s i t y - may c o n t r i b u t e t o the r e c e i v e d s i g n a l . In an attempt t o d e f i n e t h e cause of the i n c r e a s e d r e v e r b e r a t i o n from the t h e r m o c l i n e i n the N o r t h Sea, Weston (1958) c o n c l u d e d i t might be p a r t l y due t o the i n c r e a s e d t u r b i d i t y and c o n c e n t r a t i o n of d e t r i t u s known t o be a s s o c i a t e d w i t h the t h e r m o c l i n e , but t h a t p l a n k t o n were a more l i k e l y c a u s e . On the b a s i s of the r e l a t i v e a m p l i t u d e s of the echoes from.the t h e r m o c l i n e and the sea bed, he c o n c l u d e d t h a t the a c o u s t i c impedance d i f f e r e n c e due t o the change i n t e m p e r a t u r e a c r o s s the l a y e r c o u l d not account f o r the e f f e c t . A l t h o u g h some of the s c a t t e r i n g mechanisms may be d i s t i n g u i s h a b l e on the b a s i s of t h e i r f r e q u e n c y dependence ( P r o n i and A p e l , 1975), no work has y e t been done i n which the s e p a r a t e c o n t r i b u t i o n s of both the p h y s i c a l and b i o l o g i c a l 42 s c a t t e r i n g mechanisms have been d e t e r m i n e d i n c i r c u m s t a n c e s where b o t h a r e i m p o r t a n t . There has, of c o u r s e , been e x t e n s i v e work i n which b i o t a a r e the s o l e s c a t t e r e r s of i m p o r t a n c e . T h i s i n c l u d e s most of the s t u d i e s of b a c k s c a t t e r i n g from f i s h , from d i e l - m i g r a t i n g s c a t t e r i n g l a y e r s and from i n d i v i d u a l t a r g e t s i n  s i t u , such as t h a t by Beamish (1969 and 1971) w i t h z o o p l a n k t o n . The work r e p o r t e d here was done i n an a r e a where i t was f e l t t h a t s c a t t e r i n g from i n o r g a n i c p a r t i c l e s would dominate the s i g n a l . Measurements were made a t 192 kHz i n the n e g a t i v e l y buoyant plume g e n e r a t e d by the submarine m i n e - t a i l i n g d i s c h a r g e i n Rupert I n l e t . The t a i l i n g i s d i s c h a r g e d a t a depth of 49 m and a r a t e of 390 kg s " 1 as a s l u r r y of 10% s o l i d s , 40% f r e s h water and 50% s a l t water by volume. The t a i l i n g i t s e l f c o n s i s t s p r i m a r i l y of q u a r t z and s i l i c a t e m i n e r a l s ( 9 0 % ) , ground t o a powder of which 65-75% i s l e s s than 0.074 mm i n d i a m e t e r (Evans and P o l i n g , 1976). An e m p i r i c a l r e l a t i o n s h i p between s i g n a l a m p l i t u d e and c o n c e n t r a t i o n i s o b t a i n e d , and i s used t o g e n e r a t e a c r o s s -s e c t i o n a l p r o f i l e of c o n c e n t r a t i o n i n the plume from the t a p e -r e c o r d e d r e v e r b e r a t i o n . T h i s r e l a t i o n s h i p i s shown t o be c o n s i s t e n t w i t h t h e o r y , and w i t h the a m p l i t u d e of the echo from a s t a n d a r d t a r g e t . Other than the work by B r a i t h w a i t e (1974) i n r i v e r s , i n which measurements were a l s o o b t a i n e d a t a s i n g l e f r e q u e n c y r e l a t i v e t o a s t a n d a r d t a r g e t , t h e r e seems t o be no o t h e r study i n which an e m p i r i c a l r e l a t i o n s h i p between echo a m p l i t u d e and suspended sediment c o n c e n t r a t i o n has been r e p o r t e d f o r a n a t u r a l aqueous environment. S e c t i o n 3.1 i s a s y n o p s i s of the t h e o r y of the d e t e c t i o n of 43 suspended sediment u s i n g c o n v e n t i o n a l sonar i n the l o n g -wavelength r e g i o n . In s e c t i o n 3.2 the d e t a i l s of the e x p e r i m e n t a l work are p r e s e n t e d , and the r e s u l t s a r e d i s c u s s e d i n s e c t i o n 3.3. 3.1 Theory 3.1.1 B a c k s c a t t e r i n g from a S i n g l e S c a t t e r e r When the wavenumber ( k t ) of the i n c i d e n t c o m p r e s s i o n wave i s much s m a l l e r than the r a d i u s (a) of a c o m p r e s s i b l e sphere which i s f r e e t o move, the a m p l i t u d e ( p r ) of the s c a t t e r e d p r e s s u r e wave i s g i v e n by p r= p, k 2 a 3 ( x + r cos 8 ) e x p [ i ( k c r - w t ) ] (3.1a) 3r ... where 7X= K (3.1b) K X, = 3 ( Pa — Po) (3.1c) 2 P : + p a In t h e s e r e l a t i o n s , r i s the r a d i a l d i s t a n c e from the c e n t r e of the s p h e r e , 9 i s the s c a t t e r i n g a n g l e , oL the a m p l i t u d e of the i n c i d e n t p r e s s u r e wave, ?( the b u l k c o m p r e s s i b i l i t y , pa the d e n s i t y and w the a n g u l a r f r e q u e n c y . Primed q u a n t i t i e s r e f e r t o the s c a t t e r e r . In the remainder of t h i s d i s c u s s i o n , the f a c t o r exp[ i ( k e r - u t ) ] w i l l be u n d e r s t o o d . The e x p r e s s i o n (3.1a) was f i r s t p u b l i s h e d i n 1878 by R a y l e i g h (1945, p. 283) f o r f l u i d s p h e r e s . U s i n g the e x p r e s s i o n s f o r the p a r t i a l s c a t t e r e d waves o b t a i n e d by Faran (1951) f o r e l a s t i c s o l i d s p h e r e s , i t was shown i n Chapter 2 t h a t the s c a t t e r e d wave has the same form f o r both t y p e s of s c a t t e r e r t o o r d e r ( k c a ) 5 . T h i s h i g h e r o r d e r term has been dropped from 44 ( 3 . 1 a ) . The b u l k c o m p r e s s i b i l i t y of a s o l i d i s g i v e n by V = [ A*+2 /x'/3]- 1 (3.2) where A' and yu.' a r e Lame's e l a s t i c c o n s t a n t s . For a f l u i d s c a t t e r e r , ^'=0. 3.1.2 B a c k s c a t t e r i n g from a C l o u d of P a r t i c l e s F o r p a r t i c l e s c o n s i s t i n g of q u a r t z - l i k e m a t e r i a l (Y^=-0.93, "^=0.77; see Table I I ) , which i s b oth s i g n i f i c a n t l y denser and l e s s c o m p r e s s i b l e than water, c o n s i d e r a b l y more energy i s s c a t t e r e d backward (0=180°) than f o r w a r d . Both t h i s and the f a c t t h a t k c a « 1 imply t h a t c o h e r e n t f o r w a r d - s c a t t e r i n g can be i g n o r e d . Under i d e a l c o n d i t i o n s and the assumption t h a t m u l t i p l e s c a t t e r i n g i s u n i m p o r t a n t , the i n c i d e n t sound p r e s s u r e p i n a d i l u t e c l o u d of s c a t t e r e r s i s p-= pp r 0 Dexp(-«r- A ) (3.3a) r where r A = j * dr (3.3b) f o r r>>r 0 . The a t t e n u a t i o n , c o e f f i c i e n t i n the ambient f l u i d i s ocj t h a t due t o the suspended p a r t i c u l a t e i s ~x . The d i s t a n c e from th e t r a n s d u c e r t o the near edge of the c l o u d i s r, ; r i s the d i s t a n c e t o the p a r t i c l e , r„ the d i s t a n c e a l o n g the a c o u s t i c a x i s t o the p o i n t a t which the sound p r e s s u r e l e v e l i s p„, and D i s the t r a n s d u c e r d i r e c t i v i t y . I t i s assumed t h a t the b u l k a c o u s t i c p r o p e r t i e s of the medium a r e not s u f f i c i e n t l y changed by the p r e s ence of the s c a t t e r e r s t o a f f e c t D. The a t t e n u a t i o n of sound i n d i l u t e s u s p e n s i o n s of s o l i d s p h eres has been d i s c u s s e d i n the p r e v i o u s c h a p t e r . I t was shown t h a t t h e r m a l a t t e n u a t i o n i s n e g l i g i b l e ( l e s s than 5% of v i s c o u s 45 a b s o r p t i o n ) f o r p a r t i c l e s w i t h s u f f i c i e n t l y h i g h d e n s i t i e s -g r e a t e r than 1.3 g c m - 3 f o r p a r t i c l e s w i t h the p r o p e r t i e s of q u a r t z . A l t h o u g h the a n a l y s i s was v a l i d o n l y f o r p a r t i c l e r a d i i much g r e a t e r than the w a velengths of the damped v i s c o u s and t h e r m a l waves ( a p p r o x i m a t e l y 2^m a t 200 k H z ) , i t w i l l be assumed here t h a t v i s c o u s a b s o r p t i o n dominates t h e r m a l c o n d u c t i o n l o s s e s f o r a l l p a r t i c l e s i z e s . In t h i s c a s e , the a t t e n u a t i o n c o e f f i c i e n t f o r e x c e s s v i s c o u s a b s o r p t i o n i s ( U r i c k , 1948), 6k. (s-1 ) 2 l 8 b 2 ( b + 1 ) (3.4) 8 1(b+1) 2 + b 2 [ ( 4 s + 2 ) b + 9 ] 2 where s=p0'/po and £ i s the. volume f r a c t i o n o c c u p i e d by s c a t t e r e r s . The parameter b i s the r a t i o of p a r t i c l e r a d i u s t o the v i s c o u s boundary l a y e r t h i c k n e s s ( e q u a t i o n 2.60b) b = a ( w/2>/) , / 2 where v i s the k i n e m a t i c shear v i s c o s i t y of the f l u i d . The a t t e n u a t i o n c o e f f i c i e n t f o r s c a t t e r i n g l o s s i s (Morse and I n g a r d , 1968, p. 435) . « s = e k t assuming t h a t the m o d i f i c a t i o n of the a m p l i t u d e of the s c a t t e r e d wave by t h e r m a l c o n d u c t i o n and d rag (see the p r e v i o u s c h a p t e r ) i s n e g l i g i b l e . Because t h e s e e f f e c t s r e s u l t i n reduced s c a t t e r i n g a m p l i t u d e s , (3.5) s l i g h t l y o v e r e s t i m a t e s the s c a t t e r i n g l o s s . The l i n e a r dependence of the a t t e n u a t i o n c o e f f i c i e n t on c o n c e n t r a t i o n has been e s t a b l i s h e d e x p e r i m e n t a l l y i n aqueous s u s p e n s i o n s up t o volume c o n c e n t r a t i o n s of 9-10% by U r i c k (1948) w i t h q u a r t z and k a o l i n i t e , by Hampton (1967) w i t h k a o l i n i t e and by B l u e and McLeroy (1968) w i t h a l u m i n o s i 1 i c a t e ( c l a y ) pigments. k c 3 a 3 (*2 + 3 (3.5) 46 T h i s i m p l i e s t h a t i n t e r a c t i o n between p a r t i c l e s v i a m u l t i p l e s c a t t e r i n g or any o t h e r p r o c e s s i s u n i m p o r t a n t , and i s taken here as an o p e r a t i o n a l d e f i n i t i o n of the term ' d i l u t e ' . Busby and R i c h a r d s o n (1956) found t h a t a t t e n u a t i o n was l i n e a r up t o volume c o n c e n t r a t i o n s of g r e a t e r than 13% f o r s u s p e n s i o n s of g l a s s s pheres (diameter 95 /xm). S i n c e the o t h e r e x p e r i m e n t s i n v o l v e d mean p a r t i c l e d i a m e t e r s of 1-5 /<-m, the e x t e n t of the d i l u t e range may be a f u n c t i o n of p a r t i c l e s i z e . The e x p e r i m e n t s of U r i c k (1948) and B l u e and McLeroy (1968) b o t h c o n f i r m e d the v a l i d i t y of ( 3 . 4 ) , "even f o r i r r e g u l a r q u a r t z and p l a t y c l a y p a r t i c l e s . B l u e and McLeroy (1968) d i d f i n d , however, t h a t (3.4) p r e d i c t e d the a t t e n u a t i o n l e s s a c c u r a t e l y i n s u s p e n s i o n s of needle-shaped s c a t t e r e r s . The a t t e n u a t i o n c o e f f i c i e n t i n sea water ( i n rrr 1 ) a t 1.0 °C i s g i v e n by ( C l a y and Medwin 1977, p.98) <X = 3.595 x 1 0" 8 f 2 + 2.337 x 1 Q-6 S * f f 2 (3.6) f2 + * f 2 where f i s the f r e q u e n c y i n kHz, S the s a l i n i t y i n ppt and * f t h e m o l e c u l a r r e l a x a t i o n f r e q u e n c y of MgSO^ . The p r e s s u r e dependence has been dropped from the second term because i t i s s m a l l a t the water depths b e i n g c o n s i d e r e d . The r a t i o ( < + •*T)A€ i s p l o t t e d i n F i g . 2a as a f u n c t i o n of f r e q u e n c y f o r v a r i o u s d i a m e t e r s of q u a r t z d e n s i t y p a r t i c l e s . The r a t i o of v i s c o u s and s c a t t e r i n g a t t e n u a t i o n c o e f f i c i e n t s i s p l o t t e d i n F i g . 2b. S c a t t e r i n g l o s s i s n e g l i g i b l e over most of the range c o n s i d e r e d . F i g . 2a shows t h a t the e x t r a a t t e n u a t i o n due t o suspended m a t t e r i s i m p o r t a n t ( 3 > 0.1 << ) o n l y i f the c o n c e n t r a t i o n i s g r e a t e r than 18-260 mg l " 1 , depending upon the s i z e d i s t r i b u t i o n . 47 F i g . 2 (a) The r a t i o of t h e a d d i t i o n a l a t t e n u a t i o n c o e f f i c i e n t due t o suspended p a r t i c l e s w i t h d e n s i t y 2.65 g c m - 3 t o t h a t i n sea water a t 10°C w i t h 30 ppt s a l i n i t y , p l o t t e d a g a i n s t f r e q u e n c y as a f u n c t i o n of p a r t i c l e s i z e , per f r a c t i o n a l volume . c o n c e n t r a t i o n . Both v i s c o u s and s c a t t e r i n g l o s s e s i n c l u d e d , (b) R a t i o of a t t e n u a t i o n c o e f f i c i e n t s due t o s c a t t e r i n g l o s s ( x l O 3 ) and v i s c o u s a b s o r p t i o n . 48 3.1.3 The Sonar E q u a t i o n Now c o n s i d e r a t y p i c a l sonar system i n w h i c h the same t r a n s d u c e r i s used both t o t r a n s m i t and r e c e i v e . Suppose t h a t the c l o u d of s c a t t e r e r s i s u n i f o r m l y d i s t r i b u t e d (on average) a c r o s s t h e w i d t h of the main l o b e of the t r a n s d u c e r antenna p a t t e r n . Assuming a . l a r g e number of s c a t t e r e r s randomly d i s t r i b u t e d i n space, the s c a t t e r e d waves a r e i n c o h e r e n t . As o u t l i n e d below, E q u a t i o n s (3.1a) and (3.3a) can be combined, squared ( t h e i n t e n s i t y I = p 2 / p c ) and i n t e g r a t e d over the d e t e c t e d volume t o g i v e the e f f e c t i v e " b a c k - s c a t t e r e d i n t e n s i t y a t t h e t r a n s d u c e r . From (3.1) and ( 3 . 3 ) , the e f f e c t i v e p r e s s u r e a t the t r a n s d u c e r of the wave b a c k - s c a t t e r e d from a s i n g l e p a r t i c l e i s P k = ^ _ r o D 2 k c 2 a 3 (i^-v,)exp[-2.(«r + A ) ] (3.7) 3 r 2 L e t be an a n g l e c h a r a c t e r i z i n g the h a l f - w i d t h of the main l o b e of the beam. The d e t e c t e d volume i s then c r ( 2 7r ) fr 2sin(ftdc/ (3.8) where 7 i s the d u r a t i o n of the t r a n s m i t t e d p u l s e , or the ' p u l s e l e n g t h ' . Assuming a c i r c u l a r t r a n s d u c e r of r a d i u s a u n i f o r m l y s e n s i t i v e over i t s s u r f a c e , the d i r e c t i v i t y i s ( C l a y and Medwin, 1977, p. 144) D = 2J,(k, a„ sin<£ ) (3.9) k t a 0 s i n ^ where (f> i s the a n g l e w i t h r e s p e c t t o the a c o u s t i c a x i s and J, i s the B e s s e l f u n c t i o n of the f i r s t k i n d . The rms p r e s s u r e l e v e l of the r e t u r n s i g n a l becomes 49 Pb = P° r° r 16ffcTk 3 I'/z ( rK- Xf )exp[-2(o<r+ A ) ]BAM 1 / 2 (3.10) 9a where M i s t h e mass c o n c e n t r a t i o n of suspended m a t t e r and B 2= J," ( k r an sin<f>) a<t> (3.11a) J (k c a^ s i n ^ ) 3 For narrow-beam t r a n s d u c e r s , t h i s i n t e g r a l becomes B 2 = _ J [ J," (x) dx = B' 2 (3.11b) kc ao J x k c a 0 s i n c e the i n t e g r a t i o n i s - o n l y over the main l o b e (x = 3.832) f o r which sinc^ = <f> and x=k 0a oc& . The f a c t o r A depends on the s i z e d i s t r i b u t i o n of the p a r t i c l e s and i s g i v e n by OO OO A 2= 2- 6 | d 6 n ( d p ) d d = [ n ( a ) a 6 d a (3.12) 0 0 where dp=2a i s the p a r t i c l e d i a m e t e r and n ( d p ) i s the s i z e s p e c t r a l d e n s i t y d e f i n e d such t h a t the t o t a l number of p a r t i c l e s per u n i t mass of sediment i s g i v e n by 00 N = I n ( d p ) d d p (3.13) 0 Note t h a t e = a-M ^ n ( d p ) d 3 d d r I t i s wort h n o t i n g from (3.10) t h a t w i t h A = 0 , d i f f e r e n t o p e r a t i n g f r e q u e n c i e s y i e l d no a d d i t i o n a l i n f o r m a t i o n r e g a r d i n g t h e p a r t i c l e c o n c e n t r a t i o n and s i z e d i s t r i b u t i o n i n the l o n g -wavelength r e g i o n . Such i n f o r m a t i o n can be o b t a i n e d o n l y t h r o u g h the f r e q u e n c y dependence of A , or from f r e q u e n c i e s f o r which terms of h i g h e r o r d e r i n k c a i n (3.1a) a r e i m p o r t a n t . Because the a t t e n u a t i o n c o e f f i c i e n t (<*) i n c r e a s e s w i t h f r e q u e n c y , i t i s c l e a r from (3.10) and (3.11b) t h a t f o r a g i v e n range ( r ) t h e r e w i l l be an optimum o p e r a t i n g f r e q u e n c y . T h i s f r e q u e n c y w i l l depend i n ^  g e n e r a l upon the spectrum of the ambient n o i s e and the maximum power which can be d e l i v e r e d t o 50 the w a t e r . The l a t t e r depends upon the c a v i t a t i o n t h r e s h o l d p r e s s u r e but does not have a w e l l - d e f i n e d f r e q u e n c y dependence. Ambient n o i s e l e v e l s i n t h e ocean have been reviewed by Wenz (1962) and a t the h i g h f r e q u e n c i e s c o n t e m p l a t e d here ( >30 kHz) w i l l be dominated by background t h e r m a l n o i s e . Kendig (1965) has shown t h a t the e q u i v a l e n t rms t h e r m a l n o i s e p r e s s u r e f o r a d i r e c t i o n a l t r a n s d u c e r i s independent of f r e q u e n c y ( w h i t e ) and i s g i v e n by p = (kTaPoc'A f j 1 / 2 (3.14) a t f r e q u e n c i e s such t h a t t h e w a v e l e n g t h . i s much l e s s than the t r a n s d u c e r d i a m e t e r . T a i s the a b s o l u t e t e m p e r a t u r e , k i s Boltzman's c o n s t a n t and f i s the bandwidth of the t r a n s d u c e r -r e c e i v e r i n Hz. From (3.10) and (3.11b) the optimum freq u e n c y w i l l be t h a t f o r which the f a c t o r $= f e x p ( - 2 * r ) (3.15) i s a maximum s i n c e B' i s independent of f r e q u e n c y . The e x t r a a t t e n u a t i o n due t o suspended m a t t e r has been dropped, so t h e s e arguments a p p l y o n l y t o the near edge of the c l o u d . D i f f e r e n t i a t i n g (3.15) w i t h r e s p e c t t o f , the optimum fr e q u e n c y f o r a t h e r m a l n o i s e - l i m i t e d system i s such t h a t f d a = _ J _ (3.16) df 2 r , where r A i s the maximum e x p e c t e d o p e r a t i n g range. The optimum fr e q u e n c y o b t a i n e d from an i t e r a t i v e s o l u t i o n of (3.16) and (3.6) i s p l o t t e d as a f u n c t i o n of r^ i n F i g u r e 3, a t 30ppt and 10 °C. The same dependence a p p l i e s i f the s i g n a l i s e i t h e r not n o i s e - l i m i t e d at a l l or i s l i m i t e d by any w h i t e n o i s e source-. 51 1400-1 1200H 1000^ N 800 H X *" 600 400 200 50 100 r x ( m e t r e s ) — i — 150 200 F i g . 3. Optimum f r e q u e n c y f o r d e t e c t i o n of R a y l e i g h s c a t t e r i n g v e r s u s maximum o p e r a t i n g range i n sea water a t 10°C w i t h 30 ppt s a l i n i t y assuming t h e r m a l background n o i s e . An e s t i m a t e of t h e minimum d e t e c t a b l e s i g n a l can be o b t a i n e d from the e q u i v a l e n t p r e s s u r e l e v e l of the background n o i s e . For t h e r m a l n o i s e - l i m i t e d systems, e q u a t i o n s ( 3 . 1 0 ) , (3.11b) and (3.14) can be combined t o g i v e an e s t i m a t e of the minimum d e t e c t a b l e c o n c e n t r a t i o n of suspended m a t t e r f o r a g i v e n s i z e o r range. Assuming a s u s p e n s i o n of u n i f o r m l y s i z e d p a r t i c l e s , f o r which n(dp') = o~(d p-d) the minimum d e t e c t a b l e c o n c e n t r a t i o n ( € m ) i s g i v e n by P02 ^ - r 2 e * ^ r 2 ( rK- J T ) 2 B ' 2 3 <o.kT a,Af\ 1 4TTX k 2 / d 3 (3.17) at a s i g n a l - t o - n o i s e r a t i o of 1. W i t h B'=0.239 t h i s reduces t o D 2 f- = 3.69 x 10 - 1 6 r 2 e " c < r ( A f ) 1 (3.18) r 0 2 V k ta 0:rk 2 / d 3 52 f o r q u a r t z p a r t i c l e s a t 10 °C. From (3.18) a t 30 p p t , f = 200 kHz, T= 0.5 ms and a 0 = 0.095 m, the v a l u e of the minimum d e t e c t a b l e mass c o n c e n t r a t i o n (M = 2.65 x 10 6 mg l " 1 ) of 10 /tin d i a m e t e r p a r t i c l e s a t a range of 100 m i s 41.7 mg 1~ 1 per kHz of bandwidth per P a 2 of s o u r c e p r e s s u r e ( p 2 ) . U s i n g (3 . 1 8 ) , e s t i m a t e s of M a t o t h e r ranges and p a r t i c l e d i a m e t e r s may be s c a l e d from t h i s v a l u e , and a r e found t o be comparable t o t h o s e p r e s e n t e d i n F i g . 1 of Orr and Hess (1978b) f o r a s p e c i f i c system c o n f i g u r a t i o n . I t s h o u l d be noted t h a t £=0.09 i s the maximum c o n c e n t r a t i o n t o which the t h e o r y a p p l i e s . 3.1.4 S t a n d a r d T a r g e t s I t can be seen from (3.10) t h a t f o r a g i v e n p r e s s u r e l e v e l p a t f=200 kHz and T=100 m, an e r r o r of 10% i n the a t t e n u a t i o n c o e f f i c i e n t e( r e s u l t s i n a 30% e r r o r i n the e s t i m a t e of c o n c e n t r a t i o n . The s c a t t e r i n the d a t a r e v i e w e d by Thorpe (1965) i s g r e a t e r than 10% of the v a l u e of o( p r e d i c t e d by the e q u i v a l e n t ,of ( 3 . 6 ) . I t i s not c l e a r whether t h i s s c a t t e r r e f l e c t s r e a l v a r i a b i l i t y i n the a t t e n u a t i o n c o e f f i c i e n t a t a g i v e n s a l i n i t y and t e m p e r a t u r e or u n c e r t a i n t i e s i n the measurements. F u r t h e r m o r e , i t i s d i f f i c u l t t o show t h a t the a d d i t i o n a l a t t e n u a t i o n due t o o t h e r s c a t t e r e r s - f i s h , z o o p l a n k t o n , bubbles - can be n e g l e c t e d . One way t o a v o i d t h i s s e n s i t i v i t y t o the v a l u e of the a t t e n u a t i o n c o e f f i c i e n t i s t o use a s t a n d a r d t a r g e t a t or near the depth of i n t e r e s t . The e f f e c t i v e p r e s s u r e of the wave b a c k s c a t t e r e d from a s p h e r i c a l t a r g e t i s 53 P*= p. r„ D* 2a*exp ( - 2 c<r*)F* 2 r * 2 (3.19) where a* i s the r a d i u s of the t a r g e t sphere, D* i s the t r a n s d u c e r d i r e c t i v i t y a t the p o s i t i o n of the t a r g e t and F* i s the t a r g e t form f a c t o r (e.g. Neubauer, Vogt and D r a g o n e t t e , 1974). D i v i d i n g (3.10) by (3.19) g i v e s S i n c e the r e c e i v e r output i s p r o p o r t i o n a l , t o the sound p r e s s u r e l e v e l , the r e c o r d e d v o l t a g e s s h o u l d a l s o be i n the r a t i o pb/p*. As a r e s u l t , (3.20) y i e l d s an e s t i m a t e of c o n c e n t r a t i o n which i s both independent of the t r a n s d u c e r e f f i c i e n c y and r e c e i v e r s e n s i t i v i t y and i s much l e s s s e n s i t i v e t o the v a l u e of °( i f r * i s c l o s e t o r . T h i s s i m p l i f i c a t i o n i s a c h i e v e d a t the not i n c o n s i d e r a b l e c o s t of i n t r o d u c i n g a D*~* dependence i n the e s t i m a t e of M. B r a i t h w a i t e (1974) used ping-pong b a l l s as s t a n d a r d t a r g e t s i n r i v e r s . I n the p r e s e n t s t u d y they were found t o implode a t depths of 50-80 m, and were abandoned i n f a v o u r of t u n g s t e n -c a r b i d e s p h e r e s . The a c o u s t i c impedance of t u n g s t e n - c a r b i d e i s h i g h enough t h a t the b a c k s c a t t e r e d echo i s e s s e n t i a l l y t h a t of a r i g i d sphere a t wavenumbers or d i a m e t e r s g r e a t e r than u n i t y and below the f i r s ^ resonance a t k ca=7 (Neubauer e t a l , 1974). 3.2 E x p e r i m e n t a l A p p a r a t u s and P r o c e d u r e s The a c o u s t i c d a t a a c q u i s i t i o n system was o p e r a t e d from a 5 m l a u n c h b e l o n g i n g t o the UBC Department of G e o l o g i c a l S c i e n c e s and m o d i f i e d p a r t l y f o r t h i s p r o j e c t (Appendix 2 ) . The echo-54 sounder was a commercial p r o t o t y p e b u i l t by Ross L a b o r a t o r i e s , I n c . and m o d i f i e d f o r t h i s s t u d y . I t s c h a r a c t e r i s t i c s a r e summarised i n T a b l e I I I . T a b l e I I I . A c o u s t i c Sounder C h a r a c t e r i s t i c s T r a n s m i t t e r p u l s e l e n g t h 0.5 ms output p u l s e 400 V peak-peak 800 w rms R e c e i v e r s e n s i t i v i t y * 0.65 x 10" 6 V bandwidth 5 kHz Tran s d u c e r impedance 100 ohms resonant f r e q u e n c y 192 kHz bandwidth 18 kHz * i n p u t which s a t u r a t e s d e t e c t o r a t maximum g a i n The r e c e i v e r s e n s i t i v i t y , g a i n and bandwidth and the t r a n s d u c e r resonant f r e q u e n c y were de t e r m i n e d w i t h a G e n e r a l R adio Type 1001-A S t a n d a r d S i g n a l G e n e r a t o r . The t r a n s d u c e r c o n s i s t s of 32 barium t i t a n a t e elements and has a res o n a n t f r e q u e n c y of 192 kHz. The beam w i d t h - the a n g l e between the h a l f - p o w e r p o i n t s of the main l o b e - was e s t i m a t e d t o be 2.3° u s i n g E q u a t i o n ( 3 . 8 ) . T h i s was checked i n a flume u s i n g a s t a n d a r d t a r g e t . The r e t u r n s i g n a l and t r i g g e r p u l s e were r e c o r d e d on s e p a r a t e c h a n n e l s of a H e w l e t t - P a c k a r d Model 3960 f o u r - c h a n n e l FM analogue tape r e c o r d e r . The r e c o r d e d s i g n a l i s the envelope (0-12V) of the f u l l - w a v e r e c t i f i e d echo. The sounder's t i m e -v a r i a b l e g a i n ramp was not used. S i g n a l l e v e l s were m o n i t o r e d on a T e k t r o n i x Model 422 p o r t a b l e o s c i l l o s c o p e . R e c o r d i n g s were made a t a tape speed oi 38.1 cm s " 1 , f o r which the r e c o r d e r 55 f r e q u e n c y response was f l a t from 0-4 kHz, -3 dB at 6.5 kHz and -19 dB a t 10 kHz. The rms tape n o i s e l e v e l was -40 t o -43 dB f o r a 2 kHz 2V peak-peak s i n e wave. Each analogue tape was c a l i b r a t e d by r e c o r d i n g the output of 5 DC l e v e l s from the r e c o r d e r ' s c a l i b r a t o r o u t p u t . The t a p e s were d i g i t i s e d a t an e f f e c t i v e r a t e of 20 kHz by u s i n g a p l a y b a c k tape speed of 9.5 cm s " 1 and a r e a l - t i m e s a m p l i n g r a t e of 5 kHz. The r e c o r d e d t r i g g e r p u l s e was used t o a c t i v a t e a p r e s e t s o f t w a r e d e l a y t o p o s i t i o n the d i g i t i s i n g time window which was up t o 2046 d a t a words i n l e n g t h . D i g i t i s i n g was done on the UBC Department of Oceanography PDP-12 mini-computer and 9 - t r a c k tape d r i v e system w i t h a 12 b i t A-D c o n v e r t e r . The e f f e c t i v e v o l t a g e r e s o l u t i o n was 12 mV per l e a s t s i g n i f i c a n t b i t . D i g i t a l d a ta tapes were p r o c e s s e d on the UBC Computing C e n t r e Amdahl 470 V/S Model I I . The s t a n d a r d t a r g e t s were 0.794 cm d i a m e t e r t u n g s t e n -c a r b i d e gauging s p h e r e s . They were suspended from a w e i g h t e d n y l o n monofilament l i n e w i t h a 1m l e n g t h of 0.013 cm d i a m e t e r nichrome w i r e . The w i r e was cemented w i t h epoxy i n t o a h o l e about 0.025 cm i n d i a m e t e r and about 0.1 cm deep which had been s p a r k - e r o d e d i n t o the sphere. T h i s method was based on t h a t used by Neubauer e t a l (1974), who made l a b o r a t o r y d e t e r m i n a t i o n s of the b a c k s c a t t e r e d a m p l i t u d e from s i m i l a r spheres as a f u n c t i o n of f r e q u e n c y . The w e i g h t e d monofilament l i n e was i n t u r n suspended beneath the t r a n s d u c e r such t h a t the t a r g e t was a t a depth of 70-75 m. The l a t e r a l p o s i t i o n of the p o i n t of s u s p e n s i o n c o u l d be changed w i t h l i n e s r u n n i n g to the t i p s , of f o u r 3m booms e x t e n d i n g beam-wise and f o r e - a n d - a f t . T h i s 56 p o s i t i o n was a d j u s t e d u n t i l the echo from the t a r g e t reached a maximum v a l u e . Water samples were c o l l e c t e d u s i n g a c o m b i n a t i o n sampler c o n s i s t i n g of a small-volume (250 ml) sampler mounted on a s t a n d a r d 1.2 l i t r e NIO b o t t l e . The water from the s m a l l sampler was drawn t h r o u g h a f u n n e l i n t o g l a s s b o t t l e s which had been p r e r i n s e d w i t h d e i o n i s e d - d i s t i l l e d water. These samples were f i l t e r e d i n the l a b o r a t o r y u s i n g 0.4 /cm pore s i z e , 47 mm d i a m e t e r p r e - r i n s e d , pre-weighed N u c l e p o r e f i l t e r s and s u c t i o n f i l t r a t i o n . The d e t a i l s of the c o m b i n a t i o n sampler and a s s o c i a t e d f i l t r a t i o n system are d i s c u s s e d i n Appendix 2. Each f i l t e r was weighed a t l e a s t t w i c e b e f o r e and a f t e r f i l t r a t i o n a f t e r b e i n g o v e n - d r i e d a t 60 °C f o r .2-3 hours and a l l o w e d t o e q u i l i b r a t e w i t h room temperature and h u m i d i t y o v e r n i g h t . Weights were determined t o 0.01 mg w i t h a s t a n d a r d e r r o r of 0.03 mg i n a s i n g l e d e t e r m i n a t i o n on a M e t t l e r H20 m e c h a n i c a l b a l a n c e . T h i s y i e l d s an e r r o r of 0.04 mg i n the d i f f e r e n c e of the means, and a t h e o r e t i c a l d e t e c t i o n l i m i t of 0.2 mg l " 1 . In p r a c t i c e t h i s l i m i t i s p r o b a b l y c l o s e r t o 0.5-1.0 mg l " 1 . Together w i t h the 2% e r r o r i n volume (measured w i t h a graduate c y l i n d e r ) , the combined e r r o r i n the mass c o n c e n t r a t i o n was l e s s than 5% a t 10 mg l " 1 . The water samples were c o l l e c t e d w h i l e the l a u n c h was moored f o r e - a n d - a f t . The a c o u s t i c s i g n a l s were r e c o r d e d f o r s e v e r a l m i n u t e s b e f o r e and a f t e r each b o t t l e c a s t . A 5-10 min i n t e r v a l s e p a r a t e d each p a i r of r e c o r d i n g s . Because space was l i m i t e d on the l a u n c h , o n l y 3 s a m p l i n g b o t t l e s were used. These were p o s i t i o n e d w i t h r e s p e c t t o the bottom by u s i n g the echoes from the b o t t l e s and from the s a m p l i n g w e i g h t . 57 P a r t i c l e s i z e a n a l y s e s were made on a Model TAII C o u l t e r Counter w i t h a 200 / t m a p e r t u r e . A known weight ( a p p r o x i m a t e l y 1 mg) of sediment from each f i l t e r was d i s p e r s e d f o r 60 s i n 1 ml of a f i l t e r e d d i s p e r s a n t (5 g 1~ 1 aqueous s o l u t i o n of sodium hexametaphosphate) i n an u l t r a s o n i c b a t h ( B r a n s o n i c 220). T h i s s u s p e n s i o n was made up t o 200 ml u s i n g a s o l u t i o n of g l y c e r o l and I s o t o n I I i n a r a t i o of 1:9 by volume. G l y c e r o l a t t h i s c o n c e n t r a t i o n s h o u l d reduce the S t o k e s ' s e t t l i n g v e l o c i t i e s of q u a r t z d e n s i t y p a r t i c l e s by 25-30% of t h e i r v a l u e s i n pure water (see weast, 1975-1976, p. D-230 f o r v i s c o s i t i e s of aqueous s o l u t i o n s of g l y c e r o l ) . An e x t e r n a l s t i r r e r was used t o ensure t h a t p a r t i c l e s were not s e t t l i n g o u t . A t o t a l of 1.5 x 10" t o 3.0 x 10 4 p a r t i c l e s were c o u n t e d per d i s p e r s e d sample, c o r r e s p o n d i n g t o about 15-30% of the i n i t i a l 200 ml. Q u a d r u p l i c a t e samples from each of two f i l t e r s y i e l d e d a p r e c i s i o n of ±4-10% and ±33-40% i n the mas s - n o r m a l i s e d number d e n s i t i e s a t d i a m e t e r s of 4.5 and 57.4 /<m r e s p e c t i v e l y . A l l s p e c t r a were c o r r e c t e d f o r background, which amounted t o about 10% of the t o t a l c o u n t s i n each c h a n n e l . P r o b a b l e c o i n c i d e n c e e r r o r s were l e s s than 5%. Samples were p r e p a r e d f o r s c a n n i n g e l e c t r o n m i c r o s c o p y (SEM) t o v e r i f y b o th the complete d i s p e r s i o n of the sample i n the u l t r a s o n i c b a th and t h a t t h e l a r g e s t p a r t i c l e s were i n f a c t b e i n g d e t e c t e d by the C o u l t e r C o u n t e r . A f t e r d i s p e r s i o n , the s u s p e n s i o n was washed onto a 47 mm d i a m e t e r 0.4/^m p o r e - s i z e N u c l e p o r e f i l t e r and o v e n - d r i e d a t 60 °C f o r 2 h. The e n t i r e f i l t e r was then p l a c e d on t h r e e aluminum SEM s t u b s c o a t e d w i t h g r a p h i t e cement. A f t e r a l l o w i n g the cement t o d r y , the f i l t e r 58 was c u t and trimmed around each s t u b . The s t u b s were g o l d - c o a t e d i n a vacuum e v a p o r a t o r . The s u r f a c e of the f i l t e r was examined under a m i c r o s c o p e a t each s t a g e of t h i s p r o c e d u r e t o check t h a t the l a r g e s t p a r t i c l e s were not b e i n g l o s t . F i n e m a t e r i a l (<20 /xm) was removed from samples t o be examined f o r maximum p a r t i c l e s i z e .by r e p e a t e d s e t t l i n g and a s p i r a t i o n of the s u p e r n a t a n t b e f o r e f i l t r a t i o n . Thus more m a t e r i a l (4 mg i n s t e a d of 1 mg) c o u l d be examined a t s u i t a b l e i n t e r p a r t i c l e s p a c i n g s . R e l a t i v e l y u n i f o r m d i s p e r s i o n of the p a r t i c l e s on the f i l t e r s u r f a c e was a c h i e v e d with- a c e l l u l o s e " a c e t a t e b a c k i n g f i l t e r . S i z e s t a n d a r d s were p r e p a r e d i n the same f a s h i o n from s u s p e n s i o n s of the same p o l y s t y r e n e beads used f o r the C o u l t e r Counter c a l i b r a t i o n . The d i s t r i b u t i o n of l a r g e p a r t i c l e s ( F i g . 4a) c o n f i r m e d the c o a r s e end of the C o u l t e r Counter s p e c t r a . Note the a n g u l a r shapes of t h e s e p a r t i c l e s . A g g r e g a t e s of c l a y - s i z e p a r t i c l e s were p r e s e n t ( F i g . 4b) but i n s m a l l numbers ( l e s s than 5%) and were c o n f i n e d f o r the most p a r t t o the s m a l l diameter end of the spectrum. The degree t o which the measured d i s t r i b u t i o n s r e f l e c t t h o s e _in s i t u i s not known, and w i l l d i f f e r a t l e a s t t o the e x t e n t t h a t f l o c c u l a t i o n o c c u r s i n the d i s c h a r g e . 3.3 A n a l y s i s and R e s u l t s Data were c o l l e c t e d a t two s t a t i o n s ( F i g . 5) i n September, 1979. The bathymetry i s from a s u r v e y conducted d u r i n g August 1979. A l e v e e d submarine c h a n n e l extended from t h e t a i l i n g o u t f a l l t o the southwest. The l a u n c h was moored f o r e - a n d - a f t a c r o s s the c h a n n e l a x i s a t s t a t i o n s 1 and 2. F i g . 4b. S c a n n i n g e l e c t r o n m i c r o g r a p h o f t y p i c a l a g g r e g a t e . 60 1 F i g . 5. Bathymetry i n August, 1979 showing s t a t i o n l o c a t i o n s and sounding t r a n s e c t o c c u p i e d i n September, 1979, and I s l a n d Copper Mine (ICM) s t a t i o n A. 3.3.1 Suspended Sediment A n a l y s i s The r e s u l t s of b oth the g r a v i m e t r i c d e t e r m i n a t i o n s of i n  s i t u c o n c e n t r a t i o n and the s i z e a n a l y s i s are summarized i n T a b l e IV. The v a l u e s of A (Eq. 3.12) and the v i s c o u s a b s o r p t i o n c o e f f i c i e n t per u n i t mass ar e a l s o shown. These were o b t a i n e d i n the f o l l o w i n g manner. The C o u l t e r Counter a s s i g n s a p a r t i c l e t o one of 16 c h a n n e l s on the b a s i s of a v o l u m e - p r o p o r t i o n a l r e d u c t i o n i n a p e r t u r e c u r r e n t . L e t t i n g d; be the e q u i v a l e n t s p h e r i c a l d i a m e t e r a t the t h r e s h o l d of the i t h c h a n n e l , the mean dia m e t e r i n the c h a n n e l i s d, = d„, + d.-2 The m a s s - n o r m a l i z e d s i z e s p e c t r a l d e n s i t y at d t i s 61 n(d~ £) = (3.21) - d i where N d i s the number of p a r t i c l e s per u n i t sediment mass i n the c h a n n e l . N o t i n g t h a t d£„, =2 </3 dL , i t can be shown t h a t the volume c o n c e n t r a t i o n i s a p p r o x i m a t e l y £ i 7TM £ NL d 3 (3.22) 6 * and A 2 = 2"6M £ N-d* (3.23) where M i s the i n s i t u mass c o n c e n t r a t i o n . S i m i l a r l y , t he v i s c o u s a t t e n u a t i o n c o e f f i c i e n t due t o suspended matter i s M £ * . ( d £ ) (3.24) where o?t i s the a b s o r p t i o n c o e f f i c i e n t per u n i t mass from ( 3 . 4 ) . T a b l e IV. R e s u l t s of g r a v i m e t r i c and s i z e a n a l y s e s of f i l t e r e d samples. X' i s d e f i n e d i n Eq. 3.26. d i s the median d i a m e t e r . Stn Cast F i l t e r (m) M* d (^ m) A** — *** K 1 I 21 70.9 79 12.0 3.66 1 .07 22 73.6 390 11.3 3.61 1.14 1 .022 I I 23 70.6 280 14.3 4.88 1 .03 24 73. 1 480 13.4 4.69 1 .27 1 .023 25 74.7 870 17.4 5.99 0.99 1 .048 2 I 26 86.6 220 14.3 4.60 1.12 27 89.6 640 14.9 4.84 0.94 1 .026 28 91.2 1080 13.3 4.04 1.01 1 .031 I I 29 86.6 380 14.3 4.65 1.01 30 89.6 640 14.2 4.94 1 .09 1 .034 31 91 .2 800 13.3 4.39 1.18 1 .060 I I I • 32 87.6 22 33 90.7 190 13.7 4.50 1.17 1 .008 34 92.2 550 14.1 4.64 1.21 1 .022 * ** * * * (mg 1 d o - 1 d o - 5 - 1) 3 mg' 1/ 2 nr 'mg-"1 1) 1) 62 2.5 42.5 82.5 122.5 162.5 D I H M E T E R ( M I C R O N S ) F i g . 6. (a) His t o g r a m of s i z e s p e c t r a l d e n s i t y n ( d P ) and n ( d p ) d * (+). Note t h a t p o i n t s beyond 80>.m a r e e x t r a p o l a t e d by assuming t h a t l o g 1 0 n ( d p ) v e r s u s dp remains l i n e a r . (b) H i s t o g r a m of n(dP)c\p. The i n t e g r a l of t h i s c u r v e i s p r o p o r t i o n a l t o the t o t a l volume per u n i t mass. 63 T y p i c a l m ass-normalized d i s t r i b u t i o n s of n ( d 0 ) , n ( d p ) d 3 and n(dp)dp a r e p l o t t e d i n F i g u r e s 6a and 6b. Because A i s s e n s i t i v e m a i n l y t o the l a r g e r d i ameter p a r t i c l e s , t he d i s t r i b u t i o n s have been e x t r a p o l a t e d t o d i a m e t e r s beyond the upper l i m i t (80 //m) of the l i n e a r response range of the 200 /*m a p e r t u r e by e x p l o i t i n g the l i n e a r dependence between l o g ) 0 n ( d p ) and dp . The l a r g e s t i n c r e a s e i n the e s t i m a t e of A t h r o u g h t h i s p r o c e d u r e was 8%. F i g . 7 i l l u s t r a t e s the v a r i a b i l i t y i n the d i s t r i b u t i o n of n ( d p ) d p among the samples. The p r e c i s i o n i n the v a l u e of A, based upon q u a d r u p l i c a t e samples from f i l t e r s 25 and 31, was ±7% and ±4%, r e s p e c t i v e l y . CM 79/19 A z CD Z s ; -CD CD X X ! a -21 a | CD -22 X i A -23 a K + -24 ' — ' 1 X -25 O -26 V f -27 CD X -28 O z -29 1 00 = Y -30 X -31 K -33 S -34 2.5 42.5 82.5 122.5 DIAMETER(MICRONS) 162.5 Fig.- 7. P l o t s of n(dp)d p 6 f o r a l l f i l t e r s . See T a b l e IV. 64 3.3.2 A n a l y s i s of A c o u s t i c S i g n a l s . A s e c t i o n of a t y p i c a l d i g i t i z e d r e c o r d i s shown i n F i g . 8a. I t c o r r e s p o n d s t o the p o s i t i o n i n d i c a t e d by F on the echogram reproduced i n F i g . 9. F i g . 8b i s a t y p i c a l echo from the s t a n d a r d t a r g e t . For comparison w i t h in s i t u c o n c e n t r a t i o n s , 28 p o i n t s c e n t r e d a t d e l a y s c o r r e s p o n d i n g t o the m i d p o i n t s of each of the sa m p l i n g b o t t l e s were averaged over the u s e a b l e s e c t i o n s of each r e c o r d i n g . F i g . 10 shows an example of these 2 8 - p o i n t - a v e r a g e t i m e - s e r i e s . T h i s i s the be s t d a t a s e t , and was r e c o r d e d b e f o r e the f i r s t c a s t a t s t a t i o n 2. B e f o r e computing the o v e r a l l average of each t i m e s e r i e s , p o i n t s were r e j e c t e d a t t h r e e l e v e l s . (1) P o i n t s b e l o n g i n g t o echoes which s a t u r a t e d the d e t e c t o r ( a m p l i t u d e > 12V). (2) P o i n t s b e l o n g i n g t o echoes which c o u l d be i d e n t i f i e d w i t h f i s h - l i k e t r a c k s on the echogram ( F i g . 8 ) . Such echoes were i d e n t i f i e d on a g r a p h i c d i s p l a y of the average of f i v e c o n s e c u t i v e r e c o r d s . (3) 2 8 - p o i n t averages w i t h v a l u e s g r e a t e r than two s t a n d a r d d e v i a t i o n s from the mean a f t e r the f i r s t two of t h r e e passes through the t i m e - s e r i e s . The r e s u l t s f o r both the mean and rms v o l t a g e s a r e summarized i n T a b l e V. T a b l e VI shows the average s i g n a l b e f o r e and a f t e r a p p l y i n g the t h i r d r e j e c t i o n c r i t e r i o n . The mean s i g n a l l e v e l s i n these t a b l e s a r e a l l n o r m a l i z e d t o the same r e c e i v e r g a i n . B O T T O M 0 ~1 ; 1 1 1 r r i 110 120 130 EQUIVALENT DEPTH (ms) F i g . 8. ( a ) E a c h t r a c e i s t h e a v e r a g e o f t h e b a c k s c a t t e r e d s i g n a l f r o m n o n - o v e r l a p p i n g s e t s o f 20 c o n s e c u t i v e t r a n s m i s s i o n s ( p i n g s ) , o r 10 s e c o n d s o f d a t a a t a g i v e n d e l a y ( d e p t h ) . T h e e c h o e s f r o m t h e b o t t o m a n d t h e p l u m e a r e i n d i c a t e d , a s i s t h a t f r o m a l a r g e - a m p l i t u d e m o b i l e s c a t t e r e r o r ' f i s h ' , ( b ) T y p i c a l t a p e - r e c o r d e d e c h o e s f r o m t w o t u n g s t e n c a r b i d e s p h e r e s , ( l o w e r t w o p a n e l s ) a n d 5 p i n g - p o n g b a l l s ( u p p e r p a n e l ) . N o t e t a p e r e c o r d e r t r a n s i e n t r e s p o n s e ( T ) . 66 F i g . 9. Echograms c o r r e s p o n d i n g t o F i g s . 8a and 10. A=pre-cast r e c o r d i n g , sounder gain=5.5; B=post-cast r e c o r d i n g , gain=5.5; C = b o t t l e s ijn s i t u , g a i n = 6; D = d i e l - m i g r a t i n g s c a t t e r i n g l a y e r ; E=top samp l i n g b o t t l e ; F = ' f i s h ' i n F i g . 8a. o _ STN 2 PRECAST I NBRV-28 CO CD > a ZD CL. ^Z c r b o t t o m + 7 m "1 i r + 3 i i + 2 I I I I ! 1 1 i i i — r 0 . 1 4 0 . 1 1 1 1 1 8 0 . 1 2 0 . T I M E ( S E C ) i i i 1 6 0 . 2 0 0 . F i g . 10. 2 8 - p o i n t - a v e r a g e t i m e - s e r i e s c e n t r e d a t each b o t t l e depth a t s t a t i o n 2 b e f o r e c a s t I . No a v e r a g i n g over s u c c e s s i v e p i n g s . 67 Letting v b be the average backscattered voltage in a 28-point-average time-series, define a depth-normalized signal l e v e l s" = Xvb where X = a*r exp[2c<(r-r*) ] (3.25) 2 r * 2 F i n a l l y , a second normalized signal (s') i s defined such that s' = X'.s where X' = exp[2( A A + A | 3 ) ] and X^ and X^ are the extra attenuation due to suspended matter between the top ( f i r s t ) sampling bottle and each of the two lower bottles (second and t h i r d ) . X^ - was determined from the average concentration between .the f i r s t and second and second and t h i r d samplers. The values of X are given in Table V. Results of d i g i t a l processing of tape-recorded acoustic signals. The columns l a b e l l e d 'before' and 'after' indicate the signal l e v e l s before and after each cast. Stn Cast F i l t e r vfc (vc >lts) X )lts) before after d o - 5 ) before after 1 I 21 2.14 * 2.74 2.68 22 2.55 * 2.95 3.06 II 23 0.95 3.18 2.72 1 .34 3.79 24 2.08 2.38 2 . 9 1 2.55 2.92 25 1 .82 2.12 3.04 2.26 2.61 2 I 26 1.15 1 .55 4.13 1 .46 • 1 .91 27 1 .49 1 .70 4.45 1 .85 2.09 28 1.81 1 .95 4.62 2.22 2.37 II 29 1 .92 * 4.13 2.33 30 1 .73 * 4.45 2.09 31 1.81 * 4.62 2.24 I I I 32 1.10 0.56 4.23 1 .45 0.81 33 1 .07 1 .5 4.56 1 .49 1 .97 34 1 .68 1 .43 4.74 2.16 1 .89 *No recording due" to instrumental f a i l u r e . 68 T a b l e V, f o r r * = 71.4 m and *= 6.67 x 10 " 3 nr 1. The l a t t e r was d e t e r m i n e d from temperature and s a l i n i t y p r o f i l e s a t s t a t i o n A ( F i g u r e 5) taken by ICM on September 17, 1980, from which the mean te m p e r a t u r e and s a l i n i t y were 11.54 °C and 31.87 ppt from 75-105 m. The v a l u e s of X/£ a r e g i v e n i n T a b l e IV. Ta b l e V I . Mean s i g n a l l e v e l s p r i o r t o a p p l y i n g r e j e c t i o n c r i t e r i o n (3) Stn Cast F i l t e r v ( v o l t :s) b e f o r e a f t e r 1 I 21 2.14 22 2.35 I I 23 1 .04 3.45 24 2.19 2.48 25 1 .92 2.18 2 I 26 1 .20 1 .73 27 1 .57 1 .94 28 1 .89 2.07 I I 29 2.03 30 1 .80 31 1 .85 I I I 32 1.17 0.62 33 1 .08 1 .60 0 34 1 .76 1 .59 F i g . 11a i s a p l o t of s' v e r s u s M 1 / 2 ; F i g . 11b a p l o t of s'(rms) v e r s u s M 1 / 2 . The da t a from s t a t i o n 1 —11 a r e not i n c l u d e d , because the s i g n a l was h i g h l y n o n - s t a t i o n a r y between r e c o r d i n g s . A s t r a i g h t l i n e ( v i s u a l f i t ) appears t o be a r e a s o n a b l e r e p r e s e n t a t i o n of these d a t a . The dashed l i n e i n F i g . 11a i s the s i g n a l l e v e l ( s " ) e x p e c t e d on the b a s i s of the echo from the s t a n d a r d t a r g e t . The a m p l i t u d e of t h i s echo, n o r m a l i z e d t o the same g a i n and depth as s', was v*= 19.0 ± 1.2 V. The v a l u e of s c o r r e s p o n d i n g t o t h i s v o l t a g e i s , from (3.25) and 69 10 20 — i — 30 M 1 / 2 ( r n g f V / 2 F i g . 11. (a) Normalized s igna l l e v e l s ' versus the" square root of the p a r t i c l e concent ra t ion . S o l i d l i n e i s v i s u a l b e s t - f i t to the da ta . Broken l i n e i s the value of s ' expected on the bas is of the echo from the standard ta rge t . (b) P lo t of s 1 ( rms) versus square root of concent ra t ion . See sect ion 3.4 for explanat ion of the broken l i n e . 70 (3.20) w i t h D* and F* s e t t o u n i t y s " / v * = UcT) 1 / 2 4 k c (\~ K ) B ' A M 1 / 2 (3.27) I S " . ' The dashed l i n e i n F i g . 11a i s a p l o t of s" u s i n g a mean v a l u e of A = 4.63 x 10" 1 0 kg - 1 / 2 m3 ( T a b l e I V ) . The broken l i n e i n F i g . 11b i s a p l o t of 2S"//T7' , and i s d i s c u s s e d i n S e c t i o n 5. There i s r e a s o n a b l e agreement between t h e o r e t i c a l and measured s i g n a l l e v e l s a t h i g h c o n c e n t r a t i o n s , and apparent agreement between the s l o p e s of the e m p i r i c a l and t h e o r e t i c a l c u r v e s . The o f f s e t between them c o u l d be due t o a background r e v e r b e r a t i o n independent of p a r t i c l e c o n c e n t r a t i o n . I t i s c l e a r - from e q u a t i o n (3.10) t h a t a l i n e a r r e l a t i o n s h i p between the rms b a c k s c a t t e r e d p r e s s u r e l e v e l and the square r o o t of the c o n c e n t r a t i o n can be ex p e c t e d o n l y i f the s i z e d i s t r i b u t i o n , or more p r e c i s e l y the shape of the l a r g e d i a m e t e r end of the d i s t r i b u t i o n , i s independent of c o n c e n t r a t i o n . The r e l a t i v e l y c o n s t a n t v a l u e s of A i n T a b l e IV ( w i t h the e x c e p t i o n of S t a t i o n 1 —11) i n d i c a t e t h a t such was the c a s e . To the e x t e n t t h a t the measured s i z e d i s t r i b u t i o n s , p a r t i c u l a r l y the l a r g e d i a m e t e r t a i l , r e f l e c t the _in s i t u d i s t r i b u t i o n , t h i s l i n e a r i t y can be taken as c o n f i r m a t i o n of the t h e o r y . A s i z e d i s t r i b u t i o n independent of d i s t a n c e above the bottom i s somewhat c o u n t e r -i n t u i t i v e . I t was not p o s s i b l e , however, t o sample c l o s e r than 1.5-2 m from the bottom, which i s the zone where the s t r o n g e s t g r a d i e n t s i n s i z e d i s t r i b u t i o n a r e e x p e c t e d , as d i f f e r e n t t r a n s p o r t mechanisms come i n t o p l a y . Because t h e b a c k s c a t t e r e d echo i s the s u p e r p o s i t i o n of a p p r o x i m a t e l y monochromatic s i n u s o i d a l waves of random a m p l i t u d e s and phase, the magnitude of the i n s t a n t a n e o u s 71 r e s u l t a n t a m p l i t u d e s h o u l d be R a y l e i g h - d i s t r i b u t e d ( e . g . G e r j u o y and Yaspan, 1968, p. 325). That i s , the i n s t a n t a n e o u s b a c k s c a t t e r e d p r e s s u r e s h o u l d have a p r o b a b i l i t y d e n s i t y P(p) such t h a t P (p)dp = 1 exp[-pV<P b 2 >]p dp (3.28) 2<Pb2> where <p^  > i s the mean-square a m p l i t u d e . The fr e q u e n c y d i s t r i b u t i o n of the i n s t a n t a n e o u s and average a m p l i t u d e s of the re c o r d e d s i g n a l were d e t e r m i n e d f o r s t a t i o n 2-1. F i g u r e s 12a-c are the a m p l i t u d e d i s t r i b u t i o n s of 1 p o i n t i n 399 c o n s e c u t i v e r e c o r d s c e n t r e d on each of the sampli n g b o t t l e s . These d i s t r i b u t i o n s do not change s i g n i f i c a n t l y when a l l 28 p o i n t s i n the a v e r a g i n g i n t e r v a l ( e . g . 399x28 p o i n t s ) a r e used. Both the p r o b a b i l i t y d e n s i t y h i s t o g r a m s and c u m u l a t i v e p r o b a b i l i t y c u r v e s a r e shown, the l a t t e r b e i n g p l o t t e d a g a i n s t a R a y l e i g h -d i s t r i b u t e d p r o b a b i l i t y s c a l e . I f the a m p l i t u d e s were R a y l e i g h -d i s t r i b u t e d , t he c u m u l a t i v e a m p l i t u d e d i s t r i b u t i o n would p l o t as a s t r a i g h t l i n e . I t can be seen t h a t t h i s i s the case o n l y f o r l a r g e a m p l i t u d e s i g n a l s , and t h a t the tendency toward the R a y l e i g h d i s t r i b u t i o n appears t o i n c r e a s e w i t h d e p t h i n the plume. The f a i l u r e of these d a t a t o f o l l o w the R a y l e i g h d i s t r i b u t i o n i s not unexpected, p a r t i c u l a r l y a t s m a l l a m p l i t u d e s , because of the use of echo-envelope d e t e c t i o n . I t can be seen from F i g u r e s I 2 d - f , however, t h a t the 2 8 - p o i n t means do f o l l o w a R a y l e i g h d i s t r i b u t i o n which i s t r u n c a t e d . a t s m a l l a m p l i t u d e s . 72 121.10 MSEC MEAN 121.10 MSEC MEAN F i g . 12. Am p l i t u d e s t a t i s t i c s p l o t t e d as c u m u l a t i v e f r e q u e n c y c u r v e s (+) a g a i n s t a R a y l e i g h - d i s t r i b u t e d p r o b a b i l i t y s c a l e and as f r e q u e n c y h i s t o g r a m s . F i g s . 12a-c are the d i s t r i b u t i o n s of the a m p l i t u d e s i n a 28 - p o i n t window c e n t r e d a t the d e l a y s i n d i c a t e d (28x399 p o i n t s ) . F i g s . 12d— f a r e the d i s t r i b u t i o n s of the 2 8 - p o i n t averages (399 p o i n t s ) . 73 7 9 / 1 9 2 3 S E P T . 7 9 j—:—:—! i—i—i—i—I—I—|—i—i—i—i—i—i—i—i—i—j—i—i—i—i—i—i—i—i—l—|—i—i 1.32 27.82 54 .32 80.82 T I M E ( S E C ) F i g . 13. (a) Contours of s i g n a l l e v e l ( i n v o l t s ) , uncorrected f o r spreading or a t t e n u a t i o n . G r i d p o i n t s are at the i n t e r s e c t i o n s of h o r i z o n t a l and v e r t i c a l hash marks, and represent averages over 28 p o i n t s (1 m) i n the v e r t i c a l and 5 po i n t s (2.5 s) i n the h o r i z o n t a l . (b) Same as ( a ) , but converted t o co n c e n t r a t i o n using F i g . 11a a f t e r a p p l y i n g spreading and a t t e n u a t i o n c o r r e c t i o n . Contour interval=500 mg 1" 74 The e m p i r i c a l c u r v e i n F i g . 11a was used t o e s t i m a t e c o n c e n t r a t i o n s from s i g n a l l e v e l s r e c o r d e d on an echo-sounding run a c r o s s the c h a n n e l and p a s t s t a t i o n 2 ( F i g u r e 5 ) . The r e s u l t s a r e shown i n F i g u r e s 13a and 13b, and the c o r r e s p o n d i n g echogram i n F i g . 14. Data were r e j e c t e d a t the f i r s t and second l e v e l s p r e v i o u s l y mentioned. The c o n t o u r s were computer drawn thr o u g h a g r i d c o n s i s t i n g of c o n s e c u t i v e n o n - o v e r l a p p i n g 28-p o i n t v e r t i c a l and 5-ping h o r i z o n t a l a v e r a g e s . The g r i d p o i n t s a r e a t the i n t e r s e c t i o n s of l i n e s j o i n i n g the hashmarks a l o n g each a x i s . The p o s i t i o n of the bottom echo, chosen a u t o m a t i c a l l y on the b a s i s of a s i m p l e a l g o r i t h m , i s a l s o shown. The l a s t 28-p o i n t i n t e r v a l used i n c o n s t r u c t i n g each v e r t i c a l column i n the g r i d was t h a t i m m e d i a t e l y p r e c e d i n g but not i n c l u d i n g the bottom echo. F i g . 14. Echogram c o r r e s p o n d i n g to F i g . 13. A=tape r e c o r d e d p a s s , sounder gain= 5.5; B = t h i r d p a s s , sounder gain=€.0; C=second p a s s , o p p o s i t e d i r e c t i o n , gain=5.5; D = d i e l - m i g r a t i n g s c a t t e r i n g l a y e r . P=discharge plume ( c h a n n e l i z e d ) X=buoyant c l o u d . See Chapter 7. 75 The c o n c e n t r a t i o n s i n F i g . 13b are h i g h e r than" any d e t e r m i n a t i o n s by d i r e c t s a m p l i n g , p o s s i b l y because the s t a t i o n was l o c a t e d c l o s e t o the c h a n n e l a x i s and t h e r e f o r e t o the r i g h t of t h e h i g h c o n c e n t r a t i o n zone over the l e f t bank. I t i s a l s o p o s s i b l e t h a t ' the h i g h c o n c e n t r a t i o n s a r e due i n p a r t t o in c o m p l e t e d i s c r i m i n a t i o n a g a i n s t echoes from l a r g e - a m p l i t u d e s c a t t e r e r s , s p a t i a l changes i n p a r t i c l e s i z e d i s t r i b u t i o n or the f a c t t h a t p o i n t s e x c e e d i n g two s t a n d a r d d e v i a t i o n s from the mean were not r e j e c t e d from t h e s e d a t a . The s i g n a l s t a t i s t i c s a r e d i s c u s s e d i n 'the next s e c t i o n . The apparent i n c r e a s e i n c o n c e n t r a t i o n a t the g r i d p o i n t c l o s e s t t o the l e f t bank (arrow i n F i g . 13b) i s undoubtedly due t o s i d e - e c h o . The c o n c e n t r a t i o n i s o p l e t h s t i l t upward t o the l e f t w i t h i n the c h a n n e l , which would r e s u l t i n a c r o s s - c h a n n e l p r e s s u r e g r a d i e n t . Such a p r e s s u r e g r a d i e n t would oppose the c e n t r i f u g a l f o r c e a s s o c i a t e d w i t h down-slope f l o w i n a c h a n n e l w i t h r i g h t w a r d c u r v a t u r e ( F i g . 5 ) . I f thes e f o r c e s were i n b a l a n c e , e s t i m a t e s of downslope v e l o c i t y and mass t r a n s p o r t c o u l d be o b t a i n e d from such r e l a t i v e l y i n s t a n t a n e o u s t w o - d i m e n s i o n a l p r o f i l e s of the c o n c e n t r a t i o n f i e l d , p r o v i d e d the d e n s i t y i s c o n t r o l l e d by c o n c e n t r a t i o n . 3.4 D i s c u s s i o n 3.4.1 S i g n a l S t a t i s t i c s The a p p a r e n t l y l i n e a r r e l a t i o n s h i p between the mean of the envelope of the f u l l - w a v e r e c t i f i e d s i g n a l and the s q u a r e - r o o t of t h e mean c o n c e n t r a t i o n r e q u i r e s f u r t h e r d i s c u s s i o n . The e l e c t r i c a l c u r r e n t g e n e r a t e d by the t r a n s d u c e r i s p r o p o r t i o n a l 76 t o t h e v e l o c i t y o f t h e t r a n s d u c e r f a c e a n d t h e r e f o r e t o t h e p r e s s u r e o f t h e i n c i d e n t wave. The i n s t a n t a n e o u s p r e s s u r e o f t h e b a c k s c a t t e r e d wave a t t h e t r a n s d u c e r i s t h e r e a l p a r t o f p n = e x p ( - i w t ) £ p n e x p ( i 0 j n ) ( 3 . 2 9 ) j where p. a n d d n a r e t h e . a m p l i t u d e a n d p h a s e o f t h e wave f r o m t h e j t h s c a t t e r e r . The s u b s c r i p t n d e n o t e s a g i v e n s p a t i a l c o n f i g u r a t i o n o f s c a t t e r e r s . F o r a p u l s e d b a c k - s c a t t e r i n g d e t e c t i o n s y s t e m , t h e c h a n g e i n p o s i t i o n o f t h e p a r t i c l e s i n t h e d e t e c t e d v o l u m e ( t h i c k n e s s c7/2) w i l l n o r m a l l y be a v e r y s m a l l f r a c t i o n o f a w a v e l e n g t h d u r i n g t h e p a s s a g e o f t h e i n c i d e n t p u l s e . The <^-„ may t h e r e f o r e be c o n s i d e r e d e s s e n t i a l l y c o n s t a n t o v e r t h e d e t e c t e d v o l u m e , a n d i n t h i s s e n s e t h e b a c k s c a t t e r e d wave i s c o h e r e n t . The i n s t a n t a n e o u s p r e s s u r e a t a g i v e n d e l a y a f t e r e a c h p i n g i s t o be r e g a r d e d a s t h e outcome o f a r e a l i z a b l e c o n f i g u r a t i o n o f p a r t i c l e s . I f t h e p o s i t i o n s a ssumed by t h e s c a t t e r e r s a r e random f u n c t i o n s o f t i m e , t h e mean s q u a r e p r e s s u r e l e v e l a t a g i v e n d e l a y i s <p 2> = <p 2> = £ <p.2> (3. 3 0 ) j J n i n w h i c h <> d e n o t e s t h e a v e r a g e o v e r a l l p o s s i b l e c o n f i g u r a t i o n s . The b a c k s c a t t e r e d waves i n t h e c o n f i g u r a t i o n e n s e m b l e a r e i n c o h e r e n t . The a v e r a g e o v e r a s u f f i c i e n t l y l a r g e number o f p i n g s w i l l a p p r o x i m a t e t h e c o n f i g u r a t i o n a v e r a g e p r o v i d e d t h e mean c o n c e n t r a t i o n i s c o n s t a n t . T h i s a r g u m e n t was t a c i t l y a s s u m e d i n w r i t i n g ( 3 . 1 0 ) , f r o m w h i c h i t was c o n c l u d e d t h a t t h e mean s q u a r e v o l t a g e s h o u l d be p r o p o r t i o n a l t o t h e c o n c e n t r a t i o n . The p r o b l e m i s , h o w e v e r , t h a t w i t h an e n v e l o p e d e t e c t i o n s y s t e m , t h e i n f o r m a t i o n n e c e s s a r y - t o c a l c u l a t e t h e c o n f i g u r a t i o n a v e r a g e o f t h e s q u a r e d s i g n a l i s n o t 77 a v a i l a b l e . The s i g n a l has been f u l l - w a v e r e c t i f i e d and low-pass f i l t e r e d t o get the e n v e l o p e . A low-pass f i l t e r w i t h a c u t - o f f a t 5 kHz i s e q u i v a l e n t t o a we i g h t e d average over a g r e a t many c y c l e s of the 192 kHz c a r r i e r . I f , however, the p r e s s u r e i s R a y l e i g h - d i s t r i b u t e d , then the average p r e s s u r e i s g i v e n by <p> 2 =JL<P2> (3.31) 4 Because low-pass f i l t e r i n g s h o u l d not change the mean v a l u e of a s i g n a l , t h i s means t h a t the average v o l t a g e s h o u l d a l s o be p r o p o r t i o n a l t o the rms p r e s s u r e and e x p l a i n s the l i n e a r r e l a t i o n s h i p i n F i g . 11a. I t s h o u l d be emphasized t h a t the rms v o l t a g e i n . F i g . 11b i s not e q u i v a l e n t t o the c o n f i g u r a t i o n rms v o l t a g e . The broken l i n e i n t h i s f i g u r e was o b t a i n e d by a p p l y i n g (3.31) t o the e m p i r i c a l c u r v e f o r s 1 , and r e p r e s e n t s the l i n e about which the t r u e rms average p o i n t s s h o u l d l i e . The c h o i c e of a 2 8 - p o i n t a v e r a g i n g i n t e r v a l was governed by the f o l l o w i n g c o n s i d e r a t i o n s . A v e r a g i n g over s e v e r a l p u l s e l e n g t h s was n e c e s s a r y t o reduce the v a r i a n c e of the e s t i m a t e , and 1m was the minimum v e r t i c a l r e s o l u t i o n which c o u l d be t o l e r a t e d . I n t e r e s t i n g l y , t h e s e 2 8 - p o i n t averages a r e R a y l e i g h -d i s t r i b u t e d . I t i s worth n o t i n g t h a t the s i g n a l s t a t i s t i c s impose a b a s i c l i m i t a t i o n on the use of a c o u s t i c b a c k s c a t t e r i n g systems t o d e t e r m i n e average s c a t t e r e r p o p u l a t i o n s i n the R a y l e i g h r e g i o n . T h i s i s an a d d i t i o n a l f a c t o r t o be c o n s i d e r e d i n the c h o i c e of o p e r a t i n g f r e q u e n c y and range, which d e t e r m i n e the p u l s e r e p e t i t i o n r a t e and t h e r e f o r e the r e s o l v a b l e time and l a t e r a l space s c a l e s of the the f i e l d of s c a t t e r e r s . 78 3.4.2 C o m p a r i s o n W i t h P r e v i o u s S t u d i e s T h e s e r e s u l t s s h o u l d be compared w i t h t h o s e o f B r a i t h w a i t e ( 1 9 7 4 ) , w h i c h were p r e s e n t e d i n t e r m s o f s c a t t e r i n g s t r e n g t h . I n t h i s n o t a t i o n , t h e l o g a r i t h m o f t h e r a t i o o f (3.10) and (3.19) f o r r = r * , A =0 and D*=F*=1 u l t i m a t e l y r e d u c e s t o S „ - TS* = l01og„Y p K 2 \ (3.32a) V p * 2 5 V l where <5V = 1 6-ncTr 2 B 2 (3.32b) TS* = 201og, o ( a * / 2 ) " (3.32c) and S v= I01og, 0 f ( r - r,,) 2A 2Mk«1 (3.32d) i 9 TS* i s t h e t a r g e t s t r e n g t h o f t h e s t a n d a r d t a r g e t , bV i s t h e d e t e c t e d volume and Sv i s t h e s c a t t e r i n g s t r e n g t h o f t h e s u s p e n d e d m a t t e r p e r u n i t volume. B r a i t h w a i t e ' s (1974) measurements were made a t 1 MHz, b u t u n f o r t u n a t e l y n e i t h e r t h e v a l u e s of r nor IT were g i v e n , so d i r e c t c o m p a r i s o n w i t h o u r r e s u l t s c a n n o t be made. 3.4.3 O t h e r R e v e r b e r a t i o n Mechanisms F i n a l l y , a d i s c u s s i o n of o t h e r p o t e n t i a l c o n t r i b u t o r s t o th e r e v e r b e r a t i o n i s p e r t i n e n t , even t h o u g h o n l y l i m i t e d s t a t e m e n t s c a n be made, (a) T u r b u l e n c e v e l o c i t y f l u c t u a t i o n s S c h r o e d e r and S c h r o e d e r (1964) r e p o r t e d d e t e c t i n g r e v e r b e r a t i o n a t 50 kHz from ' t u r b u l e n t ' z o n e s i n e s s e n t i a l l y i s o t h e r m a l l a k e w a t e r . T h e s e z o n e s were g e n e r a t e d a t a d e p t h o f 10 m t h r o u g h a g i t a t i o n w i t h an e l e c t r i c a l l y d r i v e n 3 cm d i a m e t e r 79 i m p e l l e r . The zones p e r s i s t e d f o r about 140 s a f t e r s w i t c h i n g the motor o f f , and rose a t r a t e s of 0.03-0.2 m s _ 1 . I t was suggested t h a t s m a l l bubbles of gas r e l e a s e d from s o l u t i o n were b e i n g g e n e r a t e d by the t u r b u l e n c e . S i n c e s i m i l a r r i s i n g zones were a l s o o b s e r v e d d u r i n g the s t e p - w i s e r a i s i n g and l o w e r i n g of a thermometer and a f t e r the passage of s c h o o l s of f i s h , such bubbles a r e not n e c e s s a r i l y the r e s u l t of c a v i t a t i o n . A l t h o u g h not a t t e m p t e d by the s e a u t h o r s , the d i a m e t e r s of the 'bubbles' can be e s t i m a t e d from the r a t e s of a s c e n t , and the d i f f u s i o n l i f e t i m e s can be compared w i t h the obser v e d echo d u r a t i o n . At 7 °C, the v i s c o s i t y of water i s 1.4X10~ 2 g cm" 1 s - 1 , g i v i n g a bubble d i a m e t e r range of 2.8-7.2 /xm u s i n g S t o k e s ' law. These d i a m e t e r s a r e such t h a t the bubbles s h o u l d s h r i n k as they r i s e ( L e B l o n d , 1969). A lower l i m i t on the l i f e t i m e s ( TL ) of bubb l e s w i t h c l e a n s u r f a c e s can be o b t a i n e d by assuming t h a t they remain a t the same depth. U s i n g e q u a t i o n (5) i n L e b l o n d (1969), the e x p r e s s i o n f o r the l i f e t i m e i s Dc i s the m o l e c u l a r d i f f u s i v i t y of the gas and i t s mass c o n c e n t r a t i o n i s C i n the bubble and C i n the water. F o l l o w i n g L e b l o n d (1969), C'= K/2 and C=KP where P i s the bub b l e ' s i n t e r n a l p r e s s u r e , c l e a n b u b b l e s of oxygen w i t h t h e s e d i a m e t e r s c o u l d not l a s t f o r more than 80-130 s a t 10 m. T h i s i s c o n s i s t e n t w i t h the i n t e r p r e t a t i o n t h a t the i n c r e a s e d r e v e r b e r a t i o n i n the wake of the i m p e l l e r or a moving o b j e c t was due t o the f o r m a t i o n of b u b b l e s . (3.33a) (3.33b) 80 Schroeder and Schroeder (1964) a l s o seem t o suggest t h a t some of the b a c k s c a t t e r i n g c o u l d be from v e l o c i t y f l u c t u a t i o n s . Sound s c a t t e r i n g from the t u r b u l e n c e v e l o c i t y f i e l d i n a homogeneous f l u i d has been t r e a t e d t h e o r e t i c a l l y by K r a i c h n a n (1953), however, and i t was found t h a t the s c a t t e r i n g a m p l i t u d e v a n i s h e d a t s c a t t e r i n g a n g l e s of 180°. (b) T u r b u l e n c e d e n s i t y f l u c t u a t i o n s T u r b u l e n c e f l u c t u a t i o n s i n the d e n s i t y f i e l d , however, can cause b a c k s c a t t e r i n g . Without d i r e c t measurements of the a m p l i t u d e s of the f l u c t u a t i o n s i n s a l i n i t y , t e m p e r a t u r e and p a r t i c l e c o n c e n t r a t i o n , i t does not seem p o s s i b l e t o e s t i m a t e the magnitudes of the wave b a c k s c a t t e r e d from such i n h o m o g e n e i t i e s . T h i s mechanism may c o n t r i b u t e t o the background r e v e r b e r a t i o n suggested by F i g . 11. (c) R e f l e c t i o n from d e n s i t y d i s c o n t i n u i t i e s A l t h o u g h t e m p e r a t u r e s were not measured r o u t i n e l y as p a r t of the s a m p l i n g program d e s c r i b e d h e r e , t y p i c a l p r o f i l e s of T,S and M from a p r e v i o u s c r u i s e a r e shown i n F i g . 15 t o g e t h e r w i t h the echogram. Sharp g r a d i e n t s of s c a l a r p r o p e r t i e s cannot be d e t e r m i n e d from d i s c r e t e samples, but the echograms have c o n s i s t e n t l y g i v e n the i m p r e s s i o n of a d i f f u s e upper i n t e r f a c e , and the p r o f i l e s of suspended sediment tend t o c o n f i r m t h i s i m p r e s s i o n . These p r o f i l e s i n d i c a t e t h a t the plume i s g r a v i t a t i o n a l l y u n s t a b l e w i t h r e s p e c t t o t e m p e r a t u r e and s a l i n i t y a l o n e , and t h a t the suspended . s o l i d s a r e r e q u i r e d t o p r e v e n t v e r t i c a l c o n v e c t i o n . There i s o f t e n e v i d e n c e of an a b r u p t break i n s l o p e i n the T and S p r o f i l e s w i t h i n the plume, but i t i s never r e f l e c t e d i n any o b v i o u s way on the echograms. 81 F u r t h e r m o r e , u s i n g the same arguments as Weston (1958), but w i t h the s t a n d a r d t a r g e t as an a m p l i t u d e r e f e r e n c e , r e f l e c t i o n s from such an i n t e r f a c e s h o u l d not be a s i g n i f i c a n t c o n t r i b u t o r t o the b a c k s c a t t e r e d energy. I t s h o u l d be noted t h a t b o t h C u s h i n g e t a l (1956) and Schroeder and Schroeder (1964) have r e p o r t e d l a y e r s w i t h pronounced t e m p e r a t u r e g r a d i e n t s (as h i g h as 9.5°C n r 1 ) from which no echo was r e c e i v e d . 11.0 11.2 11.4 I 11.6 n.a TEMP (°C) 50-B I r-0. I l l a ii<H 31.8 I 32.0 32.1 S (%o) •s. **y RUP 26* 13 Sept. 1978 A \ > 10 20 SO — I — 100 TSP (mg/l) F i g . 15. T y p i c a l T, S and M (TSP) p r o f i l e s t h r o u g h the d i s c h a r g e plume (see a l s o Chapter 7 ) . (d) Gas bub b l e s In 1975 the mine changed t h e i r d i s c h a r g e c o n f i g u r a t i o n t o t r a p a i r b u b b l e s which were e n t r a i n e d i n the s l u r r y and which had p r e v i o u s l y r e s u l t e d i n some of the t a i l i n g b e i n g c a r r i e d t o the s u r f a c e w i t h the r i s i n g b u b b l e s . I t i s u n l i k e l y t h a t a l l of thes e b u b b l e s a re removed b e f o r e d i s c h a r g e w i t h the new system, a l t h o u g h t h e r e i s no l o n g e r any s u r f a c e m a n i f e s t a t i o n of t h e i r 82 e x i s t e n c e . B u b b l e s , t h e n , must be of some c o n c e r n , and t h i s i s e s p e c i a l l y t h e case because \ i n e q u a t i o n (3.1) i s so h i g h ( 10 4 a t the s u r f a c e ) compared t o t h a t f o r m i n e r a l p a r t i c l e s t h a t even non-resonant bubbles a r e e x t r e m e l y i m p o r t a n t . In the l i g h t of the d i s c u s s i o n c o n c e r n i n g e q u a t i o n ( 3 . 3 3 ) , however, any bubb l e s which do not r i s e f a s t enough t o escape the plume a r e u n l i k e l y t o s u r v i v e t o depths of 90 m a t a d i s t a n c e of 0.75 km from the p o i n t of d i s c h a r g e ( F i g . 5 ) . (e) B i o t a I t i s o b v i o u s from the a c o u s t i c r e c o r d s , p a r t i c u l a r l y t hose t a k e n w h i l e a t anchor (e.g. F i g . 9, t h a t t h e r e a r e s i g n i f i c a n t numbers of m o b i l e l a r g e - a m p l i t u d e s c a t t e r e r s w i t h i n the plume. I t i s q u i t e l i k e l y t h a t t h e s e s c a t t e r e r s are f i s h . They a r e easy enough t o d i s t i n g u i s h and t o e l i m i n a t e , however, p r o v i d e d they do i n f a c t pass t h r o u g h a s u f f i c i e n t l y s e n s i t i v e p a r t of the beam p a t t e r n ( e . g . F i g . 8 ) . Those on the p e r i p h e r y of the p a t t e r n cannot be i d e n t i f i e d and a r e a source of e r r o r . T h i s e r r o r i s not f e l t t o be s i g n i f i c a n t on average, i n view of the low c o n c e n t r a t i o n of such s c a t t e r e r s as d e t e r m i n e d from the echo-sounding runs (e.g. F i g . 14). ( f ) F l o c c u l e s I t i s l i k e l y t h a t f l o c c u l e s form i n the d i s c h a r g e plume. Assuming the c o n c e n t r a t i o n of p a r t i c l e s i n a f l o c c u l e i s l e s s than 9% by volume, the p a r t i c l e s s h o u l d behave as independent s c a t t e r e r s , and would c o n t r i b u t e no more to the r e t u r n echo than i f they were u n i f o r m l y d i s p e r s e d t h r o u g h the d e t e c t e d volume. 83 CHAPTER 4 THE MORPHOLOGY OF TOE TAILING DEPOSIT The bathymetry of the t a i l i n g d e p o s i t o f f the mine s i t e a t t h r e e s u c c e e d i n g t i m e s i s shown i n F i g . 16. These s u r v e y s show the e v o l u t i o n of the d e p o s i t over a t h r e e - y e a r p e r i o d from a s t a t e i n which a l e v e e d and meandering c h a n n e l was the dominant m o r p h o l o g i c a l f e a t u r e , t h r o u g h a regime i n which the upper r e a c h of t he c h a n n e l was r e p l a c e d by "a submarine d e l t a or 'apron', t o the redevelopment of a c h a n n e l on the west f l a n k of the apron i n the l a s t s u r v e y . In t h i s c h a p t e r t h e r e s u l t s of t h e s e and o t h e r b a t h y m e t r i c and s e i s m i c r e f l e c t i o n s u r v e y s a r e p r e s e n t e d . The m o r p h o l o g i c a l c h a r a c t e r i s t i c s of the c h a n n e l s a r e compared t o tho s e of r i v e r s and deep-sea f a n - v a l l e y s . 4.1 The R e s u l t s of E a r 1 i e r Surveys The submarine c h a n n e l was f i r s t o b s e r v e d i n 1974 i n a Co n t i n u o u s S e i s m i c r e f l e c t i o n P r o f i l i n g (CSP) su r v e y ( F i g . 17). T h i s was the f o u r t h i n a s e r i e s c o n d u c t e d a n n u a l l y from 1971 t h r o u g h 1975 and a g a i n i n 1977 by the Dept. of G e o l o g i c a l S c i e n c e s and the then I n s t i t u t e of Oceanography a t UBC as p a r t of t h e mine's e n v i r o n m e n t a l m o n i t o r i n g program. A c h a n n e l was a l s o p r e s e n t i n 1975 ( F i g . 18). Johnson (1974) has d i s c u s s e d the f i r s t t h r e e s u r v e y s and does not mention a c h a n n e l . The 1971 sur v e y was conducted b e f o r e d i s c h a r g e had begun, but a r e -e x a m i n a t i o n of the 1972 and 1973 p r o f i l e s r e v e a l s p o s i t i v e but i n c o n c l u s i v e e v i d e n c e of a c h a n n e l , p r i n c i p a l l y because of the absence of a t r a n s e c t a l o n g the n o r t h s l o p e a t a s u i t a b l e d i s t a n c e from the o u t f a l l . 84 F i g . 16. Time s e r i e s of b a t h y m e t r i c s u r v e y s showing ( a ) , t h e meandering c h a n n e l regime i n . November 1976, ( b ) , the apron regime i n September 1978 and ( c ) , t h e r e c h a n n e l i z e d regime i n August 1979. C o n t o u r s i n m. F i g . 18. T a i l i n g t h i c k n e s s i n meters, 21 O c t o b e r , 1975. 86 F i g . 1 9 . P r e - m i n e b a t h y m e t r y s e i s m i c r e f l e c t i o n l i n e s ( C S P ) l i n e s ( I C M ) a r e a l s o s h o w n . i n R u p e r t I n l e t . L o c a t i o n s o f a n d t h e m i n e ' s e c h o - s o u n d i n g I n 1 9 7 5 t h e m i n e b e g a n r u n n i n g e c h o - s o u n d i n g l i n e s m o n t h l y . T h e a p p r o x i m a t e l o c a t i o n s o f t h e s e l i n e s a r e s h o w n i n F i g . 1 9 , t o g e t h e r w i t h t h o s e o f t h e s e i s m i c r e f l e c t i o n s u r v e y s , s u p e r i m p o s e d o n t h e p r e - m i n e b a t h y m e t r y . T h e n u m b e r a n d a p p r o x i m a t e l o c a t i o n s o f c h a n n e l s o b s e r v e d i n e a c h p r o f i l e a r e s u m m a r i z e d i n T a b l e V I I . T h e m a i n c h a n n e l w a s s e l e c t e d o n t h e b a s i s o f r e l a t i v e r e l i e f a n d c r o s s - s e c t i o n a l a r e a . 87 T a b l e V I I a . Summary of the number of c h a n n e l s o b s e r v e d i n CSP s u r v e y s . The l e t t e r s N and S i n d i c a t e t h a t the main c h a n n e l was c l o s e t o the n o r t h or s o u t h w a l l of the i n l e t . Date 8A 8 9 10 1 1 1 1 A 1 2 13 14 Sept 73 * 1 2 1 3 * 0 0 0 Nov 74 * 1 1 1 1 * 1N IN • 1N Oct 75 1 1 1 1 2 2 2 1N 0 Jan 77 1 1 1 1 1 1N 1N 1N 0 * l i n e not run T a b l e V I l b . Summary of the number of c h a n n e l s o b s e r v e d i n the f i r s t 20 ICM s u r v e y s . N=north s i d e ; S=south s i d e ; C=centre. Date 8 10 1 1 12 1 3 14 15 1 6 8 Mar 75 1 2 2N 1N 18 Mar 75 1 2 2N 1N 2 May 75 1 1N 3N 1S I S is 23 Jun 75 3N 1N 1S 1S 16 J u l 75 1 2S 3 1 I S 1 1 3 Aug 75 1 2 3 0 0 22 Sept 75 1 2 3 0 0 28 Oct 75 1 2 1N 0 1 1 1 0 17 Nov 75 1 2S 1N 0 0 1 1 0 1 5 Dec 75 1 2 1N 0 1 1 5. Jan 76 1 2N 0 1N 2 1 1 1 12 Feb 76 2 1N 1 1 12 Mar 76 1 2 0 1N 1 1 9 Apr 76 2N 1N 1N 1 1 18 May 76 1 1N IN 2C 1 > 1S 22 Jun 76 1 0 1N 2C 1 0 27 J u l 76 1 1N 0 27 Aug 76 1C 0 28 Sept 76 1 I S 4 Nov 76 0 0 In g e n e r a l , both the c h a n n e l r e l i e f and c r o s s - s e c t i o n a l a r e a d e c r e a s e w i t h d i s t a n c e downstream. The f o l l o w i n g p o i n t s a r e a l s o n oteworthy. ( 1 ) A c h a n n e l was never o b s e r v e d a t or beyond CSP-18 or ICM-17. Bottom s c o u r i n g by t i d a l c u r r e n t s i s p r o b a b l y at l e a s t p a r t l y r e s p o n s i b l e f o r the f a i l u r e of the c h a n n e l t o b u i l d beyond t h i s a r e a , and w i l l be d i s c u s s e d i n d e t a i l e l s e w h e r e . 88 (2) A l o n g the c r o s s - i n l e t s e c t i o n of the c h a n n e l , a t CSP p r o f i l e s 8A, 8, 9 and 10, and a t ICM-8, more than one c h a n n e l was o b s e r v e d o n l y once (CSP 9, Sept. 1973). (3) Two or more c h a n n e l s were o b s e r v e d a t and d o w n - i n l e t of CSP-10 i n 1975, and on many o c c a s i o n s a t and beyond ICM-10. The number and l o c a t i o n of the c h a n n e l s i n t h i s a r e a a r e v a r i a b l e . 4.2 B a t h y m e t r i c and S e i s m i c Surveys The c h a n n e l was a c c u r a t e l y s u r v e y e d f o r the f i r s t time i n November, 1976 ( F i g . 20) u s i n g a D e l N o r t e Model 202A T r i s p o n d e r range-range p o s i t i o n i n g system w i t h a r a t e d a c c u r a c y of ±1 m on each range and ±3 m i n the p o s i t i o n . The t r a n s p o n d e r s i t e s were su r v e y e d by t r i a n g u l a t i o n w i t h a W i l d T2 t h e o d o l i t e , r e a d a b l e t o 1 s of a r c , from benchmarks i n the ICM s u r v e y i n g g r i d . The ICM s t a f f e s t a b l i s h e d two new benchmarks f o r t h i s s t u d y . The c o o r d i n a t e s of the t r a n s p o n d e r s i t e s a r e known t o w i t h i n +0.5 m. The T r i s p o n d e r system was c a l i b r a t e d by s e t t i n g the base u n i t up a t s i t e C ( F i g . 20) and a d j u s t i n g the range r e a d i n g s from the t r a n s p o n d e r s a t s i t e s A and B ( F i g . 20) t o t h e i r t r i a n g u l a t e d v a l u e s . The p o s i t i o n f i x e s f o r t h i s and subsequent s u r v e y s a r e documented i n Appendix 3. Soundings were made from the CSS V e c t o r a t speeds of 4-6 knots w i t h a Ross L a b o r a t o r i e s Model 200 F i n e L i n e echo-sounder ( f r e q u e n c y 200 kHz, beam-width 5° x 10°). Depths were c o r r e c t e d t o t i d a l datum u s i n g a c o s i n e - i n t e r p o l a t i o n scheme between c o n s e c u t i v e t i d a l extrema as p r e d i c t e d by the Canadian H y d r o g r a p h i c S e r v i c e (1976). A r e f l e c t o r was low e r e d t o d i f f e r e n t depths t o • o b t a i n a c o r r e c t i o n f o r v a r i a t i o n s in- the speed of sound. T h i s p r o c e d u r e was abandoned i n l a t e r s u r v e y s i n 89 which t h e maps were c o n s t r u c t e d i n the f i e l d w i t h o u t a p p l y i n g a c o r r e c t i o n . The c o r r e c t i o n f a c t o r was d e t e r m i n e d subsequent t o each c r u i s e as the r a t i o c s'/c s , where c s i s the sounding speed f o r which the echo-sounders were c a l i b r a t e d (1463 m s* 1) and c j i s the s o u n d i n g speed t o a depth of 100m. The l a t t e r i s 100/T, where T i s the time ( i n seconds) f o r sound t o t r a v e l t o a depth of 100 m, and was d e t e r m i n e d from the temperature and s a l i n i t y p r o f i l e s u s i n g the e q u a t i o n f o r the speed of sound i n C l a y and Medwin (1977, p. 8 8 ) . The a p p r o p r i a t e n o r m a l i z a t i o n e q u a t i o n i s g i v e n w i t h each b a t h y m e t r i c map. The depths a t l i n e i n t e r s e c t i o n s u s u a l l y d i f f e r e d by l e s s than 0.2 m. A s e i s m i c r e f l e c t i o n s u r v e y was conducted i n January 1977 ( F i g . 2 1 ) from the p u r s e - s e i n e r W a l t e r M., u s i n g the same p o s i t i o n i n g system. I n t e r p r e t a t i o n i n terms of t a i l i n g t h i c k n e s s made use of p r e v i o u s s u r v e y s ( e . g . F i g s . 17 and 18), as d i s c u s s e d i n d e t a i l i n Hay, Macdonald and Murray (1978). The s e i s m i c equipment i n c l u d e d an EG&G Model 236 boomer and a s i n g l e l i n e a r a r r a y of 25 hydrophones spaced a t 0.30 m i n t e r v a l s . The r e c e i v e r had a nominal band-width of 0.4 - 2 kHz. The a n g u l a r s e n s i t i v i t y of the system was c a l c u l a t e d from the a p p r o p r i a t e t h e o r e t i c a l formulae i n Tucker and Gazey (1966, p.172 and 181). At 1 kHz, the o u t g o i n g p u l s e from the boomer ( d i a m e t e r 0.41 m) i s a h e m i s p h e r i c a l wave of n e a r l y u n i f o r m a m p l i t u d e ( o n l y -0.7 dB a t 73° from the v e r t i c a l ) . A l i n e a r hydrophone a r r a y i s u n i f o r m l y s e n s i t i v e i n any d i r e c t i o n i n a p l a n e p e r p e n d i c u l a r t o i t s a x i s . The main l o b e of the a r r a y has a p r e d i c t e d w i d t h p a r a l l e l t o i t s a x i s of 10° between the -3 dB p o i n t s . Because of the v i r t u a l l y u n i f o r m a n g u l a r d i s t r i b u t i o n of energy i n the 90 o u t g o i n g p u l s e , t h i s system i s p a r t i c u l a r l y s e n s i t i v e t o s i d e -echo from bottom and sub-bottom f e a t u r e s which a r e l a t e r a l l y d i s p l a c e d from the p a t h of the s h i p . A s i d e - s c a n survey was co n d u c t e d i n June, 1977 from the CSS ; R i c h a r d s o n u s i n g a K l e i n Model 401 s i d e - s c a n sonar (100 kHz, 0.1 ms p u l s e l e n g t h ) . The t r a n s d u c e r s on the t o w - f i s h (Model 402) have h o r i z o n t a l beam-widths of 1° and a 40° v e r t i c a l beam-w i d t h . The a x i s of the main l o b e of the beam i s t i l t e d a t 30° below the h o r i z o n t a l . P o s i t i o n s were f i x e d u s i n g r a d a r - r a n g i n g t o shore l o c a t i o n s . The s i d e - s c a n r e c o r d i s shown i n F i g . 22. A su r v e y was conducted on December 23, 1977 ( F i g . 23) from the Mac I (ICM) u s i n g a Furuno echo-sounder w i t h a 30° beam-w i d t h and r a d a r r a n g e - a n d - b e a r i n g p o s i t i o n i n g . The r e s u l t s a r e p r e s e n t e d i n F i g . 23. The p o s i t i o n s were c o r r e c t e d as shown by assuming c o n s t a n t v e s s e l v e l o c i t y , w i t h the r e s u l t t h a t F i g . 23 i s j u s t a q u a l i t a t i v e i l l u s t r a t i o n of the bathymetry a t the t i m e . The c h a n n e l p r o f i l e s a r e shown i n F i g . 24. A pronounced l e v e e d submarine c h a n n e l was p r e s e n t i n each of t h e s e s u r v e y s . F u r t h e r m o r e , a s e r i e s of w e l l - d e f i n e d meanders was obser v e d i n t h a t s e c t i o n of the c h a n n e l i m m e d i a t e l y below the c r o s s - i n l e t r e a c h , e x c e p t i n g the 1974 and 1975 CSP s u r v e y s f o r which the p o s i t i o n f i x e s were not s u f f i c i e n t l y a c c u r a t e , and the December,' 1977 survey which d i d not c o v e r t h i s a r e a . The l a t t e r was the l a s t s u r v ey i n which the upper r e a c h of the ch a n n e l system was o b s e r v e d . 91 F i g . 20. Bathymetry i n November, 1976. To o b t a i n ' t r u e ' depths (z') from depths i n d i c a t e d ( z ) , z' = [ (z-3.7 ) / l . 031 ]c s' / c where cs' = 1483.4 m s~ 1 i s the sounding speed t o 100 m d e p t h . The heavy l i n e i n d i c a t e s the c h a n n e l a x i s . F i g . 21. T a i l i n g t h i c k n e s s i n mete r s , 12 J a n u a r y , 1977. 92 CO CO F i g . 22. S i d e - s c a n sonar r e c o r d , June 1977. The numbers 1-6 i d e n t i f y the axes of the s i x c o n s e c u t i v e bends; the v e r t i c a l l i n e s i n d i c a t e r a d a r f i x e s ; S and B the s u r f a c e and bottom echoes and 0 z e r o range on each c h a n n e l . The upper h a l f of each p a n e l i s the r e c o r d from the s t a r b o a r d t r a n s d u c e r ; the lower h a l f t h a t from the p o r t . (See a l s o F i g . 2 9 ) . F i g . 2 3 . (a) Ves se l p o s i t i o n s f o r December, 1977 s u r v e y . S o l i d t r i a n g l e s a r e r a d a r f i x e s ; s o l i d c i r c l e s a r e a d j u s t e d p o s i t i o n s , (b) Ba thymet r y i n December, 1977. A x i s o f November , 1976 channe l i s a l s o shown (dashed l i n e ) . vo oo 94 F i g . 24. December 1977 c r o s s - c h a n n e l p r o f i l e s , l o o k i n g down-c h a n n e l , a t l o c a t i o n s g i v e n i n F i g . 23. 95 4.3 Meandering Channel Regime The d e p t h of the c h a n n e l a x i s i n November, 1976 as a f u n c t i o n of d i s t a n c e ( a l o n g the a x i s ) from the o u t f a l l i s shown i n F i g u r e 25. Note t h a t t h i s a x i s i s the l o c u s of the maximum depth of the cha n n e l on each sounding t r a v e r s e , and does not n e c e s s a r i l y c o i n c i d e w i t h the c h a n n e l thalweg - the l o c u s of maximum c h a n n e l depths - because t h e p r o f i l e s a r e not a l l p e r p e n d i c u l a r t o the t h a l w e g . The c h a n n e l may be d i v i d e d i n t o t h r e e p r i n c i p a l s e c t i o n s , h e n c e f o r t h c a l l e d r e a c h e s , each of" s u c c e s s i v e l y d e c r e a s i n g s l o p e : t h e c r o s s - i n l e t s e c t i o n (upper r e a c h ) , the meander s e c t i o n ( m i d d l e r e a c h ) , and the r e l a t i v e l y s t r a i g h t lower r e a c h . Each r e a c h e x h i b i t e d d i s t i n c t m o r p h o l o g i c a l f e a t u r e s . 40 - i Axes of Bends ,§ 6 0 " AXIAL DISTANCE (km) F i g . 25. Depth of November, 1976 c h a n n e l a x i s as a f u n c t i o n of l o n g - c h a n n e l d i s t a n c e . 96 4.3.1 Upper Reach The bottom s l o p e i n t h i s s e c t i o n ranged from an e s t i m a t e d 9.5°-12° at the o u t f a l l t o 1.9° a t the end of the r e a c h ( i n s e t , F i g . 2 5 ) . C r o s s - c h a n n e l p r o f i l e s , l o o k i n g down-channel, a r e shown i n F i g . 26a. These p r o f i l e s were chosen because they a r e n e a r l y p e r p e n d i c u l a r t o the c h a n n e l a x i s ( F i g . 2 7 ) . Those i n the lower t h r e e f o u r t h s of the r e a c h e x h i b i t a marked l e f t - r i g h t asymmetry, the r i g h t l e v e e b e i n g g e n e r a l l y h i g h e r than the l e f t i n the c e n t r a l s e c t i o n of the r e a c h b e f o r e the c h a n n e l b e g i n s t o t u r n d o w n - i n l e t . The c h a n n e l a x i s ( F i g . 20 and 27) has a s l i g h t tendency t o hook t o the l e f t i n t h i s r e a c h . These f e a t u r e s - the l e f t hook and the h i g h e r r i g h t l e v e e - a r e c h a r a c t e r i s t i c of submarine c h a n n e l s on deep-sea f a n s i n the n o r t h e r n hemisphere, and have been a t t r i b u t e d t o p r e f e r e n t i a l d e p o s i t i o n on the r i g h t l e v e e due t o the t i l t i n g of the upper s u r f a c e of t u r b i d i t y c u r r e n t s i n response t o the C o r i o l i s f o r c e (Menard, 1955). The d i s c u s s i o n w i l l r e t u r n t o t h i s p o i n t l a t e r . The bank of the r i g h t l e v e e a l s o tends t o be s t e e p e r than the l e f t , w i t h s l o p e s r a n g i n g from 25°-30°. A s l o p e - s t a b i l i t y s tudy by D a v i s (1978) found t h a t the l e v e e s were m a r g i n a l l y s t a b l e . The i n c r e a s e i n c h a n n e l r e l i e f and w i d t h between the f i r s t and second p r o f i l e s i n F i g . 26a i s p r o b a b l y due t o e n t r a i n m e n t of ambient sea w a t e r , p o s s i b l y i n a h y d r a u l i c jump. Note t h a t the c h a n n e l c r o s s -s e c t i o n d e c r e a s e s s u b s e q u e n t l y . T h i s f e a t u r e was a l s o e x h i b i t e d by the 1977 survey ( F i g . 2 4 ) . F i g . 2 6 . C r o s s - c h a n n e l p r o f i l e s , l o o k i n g down-channe l , November 1976. (a) upper r e a ch (b) m i d d l e r each (c ) lower reach (d) meander r each a t channe l c r o s s - o v e r s . See F i g . 27 f o r l o c a t i o n s . VO 98 F i g . 27. Sounding t r a n s e c t s f o r p r o f i l e s i n F i g . 26. S e i s m i c p r o f i l e s a c r o s s t h i s r e a c h ( F i g . 28) i n d i c a t e a t h i c k bed of t r u n c a t e d and l a t e r a l l y c o h e r e n t r e f l e c t o r s u n d e r l y i n g the c h a n n e l a x i s . In c o n t r a s t , the i n t e r n a l s t r u c t u r e of the l e v e e s c o m p r i s e s i n c l i n e d , weakly r e f l e c t i n g s t r u c t u r e s . The echo from the pre-mine sediment-water i n t e r f a c e (P) i s d e p r e s s e d beneath the l e v e e s , p r o b a b l y as a r e s u l t of e r o s i o n d u r i n g the i n i t i a l phases of c h a n n e l i z a t i o n . 99 a. F i g . 28. S e i s m i c r e f l e c t i o n p r o f i l e s a c r o s s upper r e a c h : (a) A x i a l L i n e 2, 1977, (b) A x i a l L i n e 2, 1975. See F i g s . 18, 19 and 21 f o r l i n e l o c a t i o n s . 4.3.2 Middle- R e a c h : the Meanders The bottom s l o p e t h r o u g h t h i s r e a c h i s n e a r l y c o n s t a n t a t 0.91° ( F i g . 2 5 ) , a l t h o u g h i t d e c r e a s e s between bends 5 and 6. The meanders were p r e s e n t i n t h r e e s u c c e s s i v e s u r v e y s ( F i g s . 20-22) and, a l l o w i n g f o r the l a r g e p r o b a b l e e r r o r i n the ra d a r f i x e s f o r the s i d e - s c a n l i n e , the i n t e g r i t y of the g e n e r a l shape of the meanders from survey t o survey i s remarkable ( F i g . 29). The number of c h a n n e l - c r o s s i n g s i n the 1977 CSP survey was 100 not s u f f i c i e n t i n i t s e l f t o a l l o w the c h a n n e l a x i s t o be drawn. I n s t e a d , the a x i s was t r a c e d from the i s o p a c h map ( F i g . 2 1 ) , f o r which the i n f l u e n c e of o f f - a x i s p o i n t s i s such t h a t the p o s i t i o n of the c h a n n e l i s w e l l d e f i n e d . The p l a n p o s i t i o n of the l e v e e s o b t a i n e d from the s i d e - s c a n r e c o r d ( F i g . 29b) i s o f f s e t 116 m t o the NE of i t s t r u e p o s i t i o n as per the r a d a r f i x e s . T h i s o f f s e t gave the c l o s e s t s u p e r p o s i t i o n of the two c h a n n e l p r o f i l e s , and i s assumed t o be due t o the (unknown) d i s t a n c e of the t o w - f i s h b e h i n d the s h i p . I t i s i n s t r u c t i v e t o examine the "morphology of the meanders i n c omparison w i t h those i n s u b a e r i a l r i v e r s . A s k e t c h showing the s a l i e n t f e a t u r e s of a r i v e r meander i n p l a n and i n c r o s s -s e c t i o n i s p r e s e n t e d i n F i g . 30. The c h a r a c t e r i s t i c s h o a l s a t c h a n n e l c r o s s - o v e r s and deepening a t the base of the o u t e r (concave) bank i n the v i c i n i t y of bend axes (e . g . L e l i a v s k y , 1966 p.103; D i e t r i c h e t a l , 1979) a r e s u g g ested i n F i g . 25, but a r e not pronounced. Such f e a t u r e s may be p a r t i a l l y masked by e r r o r s i n h e r e n t i n the s u r v e y , such as s i d e - e c h o . 101 Outfall a) November 1976 January 1977 400 400 Scale in metres 800 b) November 1976 January 1977 (side scan) F i g . 29. (a) Channel axes i n J a n u a r y , 1977 ( s o l i d l i n e ) and November, 1976 (dashed l i n e ) . (b) Channel a x i s i n June, 1977 ( s o l i d l i n e s ) and November, 1976 (dashed l i n e ) . Note o f f s e t of s i d e - s c a n p r o f i l e due t o s h i p t o t o w - f i s h s e p a r a t i o n . (See a l s o F i g . 22) 102 C r o s s - s e c t i o n a l p r o f i l e s from t r a v e r s e s c l o s e s t t o the bend axes a r e shown i n F i g . 26b. O v e r s p i l l on the o u t s i d e of each bend r e s u l t i n g from the i n e r t i a of the f l o w i s su g g e s t e d by the asymmetry of the p r o f i l e s . The o u t e r bank i s s t e e p e r and i t s l e v e e h i g h e r than the i n n e r bank, which i s i r r e g u l a r and i n some cas e s w i t h o u t a r e c o g n i z a b l e l e v e e . The i r r e g u l a r p r o f i l e of the i n n e r bank has p o s s i b l e a n a l o g u e s i n the t e r r a c e and s c r o l l bar f o r m a t i o n s i n t e r r e s t r i a l r i v e r s . The former a r e f l a t a r e a s above the l e v e l of the r i v e r s u r f a c e bounded by exposed banks and a r e n o r m a l l y c o n s i d e r e d t o r e s u l t from f l o o d p l a i n e r o s i o n d u r i n g c h a n n e l o v e r f l o w ( L e o p o l d , Wolman and M i l l e r , 1964 p. 458). S c r o l l b ars form on the i n n e r (convex) bank d u r i n g p e r i o d s of h i g h e r than average d i s c h a r g e as a r e s u l t of the d e p o s i t i o n of m a t e r i a l which has been eroded from o u t e r banks upstream and mark t h e h i s t o r y of p o i n t bar m i g r a t i o n (e.g. H i c k i n , 1974). F i g . 30. D e f i n i t i o n s k e t c h of meanders. Based i n p a r t on F i g . 1 i n L e o p o l d and Wolman (1960). 103 The s i d e - s c a n r e c o r d i n F i g . 22 c o n t a i n s l i t t l e i n d i c a t i o n of the p r e s e n c e of e i t h e r t e r r a c e s or s c r o l l b a r s i n the f i r s t f o u r bends of t h i s r e a c h . I n s t e a d t h i s r e c o r d g i v e s the i m p r e s s i o n t h a t the i r r e g u l a r f e a t u r e s on t h e s e p o i n t b a r s ( F i g . 30) a r e e i t h e r the l e v e e s of abandoned and i n f i l l e d c h a n n e l s or r e s u l t from c h a n n e l o v e r s p i l l . The o n l y f e a t u r e s i n F i g . 22 which resemble s c r o l l b a r s a r e on the p o i n t b a r s of bends 5 and 6 but they would n e c e s s a r i l y have had t o be formed b e f o r e the meanders assumed t h i s form, which means b e f o r e November 1976 s u r v e y . T h i s i s i n c o n s i s t e n t w i t h the d e p o s i t i o n r a t e s of 1-2 m y r ~ 1 i n the a r e a (Chapter 5 ) . I t i s suggested t h a t t h e s e too are due t o c h a n n e l o v e r s p i l l . T e r r a c e - l i k e f e a t u r e s a r e p r e s e n t on the p o i n t b a r s of bends 5 ( F i g s . 26b and 31) and 6 ( F i g . 22), and i n the next r e a c h ( F i g . 26c, F i g . 22). N e l s o n e t a l (1978) p r e s e n t a s i d e - s c a n r e c o r d showing a t e r r a c e on the o u t e r bank of a bend i n the La J o l l a f a n - v a l l e y . Two of the 1977 CSP p r o f i l e s happened t o c r o s s the channel v e r y c l o s e t o bend axes and a r e shown i n F i g . 31. Because the h i s t o r y of the m o r p h o l o g i c a l development of the "channel as i t e x i s t e d a t the time i s not known and because of p r o b a b l e c o n t a m i n a t i o n of the sub-bottom r e t u r n s by s i d e - e c h o from the i r r e g u l a r bottom, i t i s d i f f i c u l t t o i n t e r p r e t t h e s e r e c o r d s unambiguously. N e v e r t h e l e s s , CSP 9 appears t o c o n f i r m some e x p e c t a t i o n s . R e f l e c t o r B i n F i g . 31 r i s e s g r a d u a l l y from r i g h t t o l e f t and may be the b u r i e d c h a n n e l bottom, and the shaded a r e a the f i l l on the i n n e r bank as the c h a n n e l m i g r a t e d away from i t s p r e v i o u s p o s i t i o n (C) next .to the r e l i c l e v e e ( L ) . T r u n c a t e d r e f l e c t o r s i n the l e f t l e v e e which would i n d i c a t e 1 04 e r o s i o n of p r e v i o u s l y d e p o s i t e d m a t e r i a l a r e not apparent but c o u l d be masked by s i d e - e c h o from the l e v e e w a l l . In CSP 8 on the o t h e r hand, the sub-bottom r e f l e c t o r s beneath the l e v e e s and above the pre-mine sediment appear t o be conformable w i t h the sediment-water i n t e r f a c e a t the t i m e , i n d i c a t i n g l o c a l a c c u m u l a t i o n w i t h o u t s i g n i f i c a n t l a t e r a l m i g r a t i o n of the c h a n n e l . 1977 CSP 8 10 ms F i g . 31. S e i s m i c p r o f i l e s a c r o s s the meander r e a c h , January 1977, l o o k i n g down-channel. 105 Perhaps the most i n t e r e s t i n g f e a t u r e of the meanders i s the d e c r e a s e i n wavelength and a s l i g h t i n c r e a s e i n a m p l i t u d e w i t h d i s t a n c e down-channel ( F i g . 29, T a b l e V I I I ) b e f o r e t e r m i n a t i n g a b r u p t l y t o form the s t r a i g h t s e c t i o n below the s i x t h bend. L e o p o l d and Wolman (1957, 1960) have shown t h a t the wavelengths (L) of meanders a r e r e l a t e d t o the c h a n n e l w i d t h (w), the l o c a l r a d i u s of c u r v a t u r e ( r ) and the d i s c h a r g e (Q) by L = 10.9w (4.1) L = 4.7r ' (4.2) L = 20Q 1/ 2 (4.3) i n MKS u n i t s . These r e l a t i o n s were based on e m p i r i c a l d a t a f o r meanders i n a l l u v i a l r i v e r s , i n flume e x p e r i m e n t s , i n the G u l f Stream and i n streams on g l a c i e r s , and embrace a range of 5 t o 7 o r d e r s of magnitude i n each parameter. E q u a t i o n s (4.1) and (4.2) c o d i f y the o b s e r v a t i o n t h a t i n p l a n view the geometry of meanders i s independent of s c a l e . The v a l u e s of the parameters f o r our system a r e summarized i n T a b l e V I I I . The second of the above r e l a t i o n s appears t o a p p l y w i t h r e a s o n a b l e a c c u r a c y t o t h i s meander system as w e l l . As s h o u l d be r e a d i l y apparent from F i g . 26b, i t i s v e r y d i f f i c u l t t o d e f i n e a c h a n n e l w i d t h f o r t h i s r e a c h on the b a s i s of the bottom p r o f i l e a t the axes of the bends. The w i d t h of a r i v e r can be d e t e r m i n e d from the c r o s s -stream b r e a d t h of the water s u r f a c e i n p l a n v i e w . T h i s cannot be done h e r e , a l t h o u g h echo-sounding p r o f i l e s which i n d i c a t e the d i s t r i b u t i o n of suspended m a t e r i a l w i t h i n the c h a n n e l , l i k e t h a t i n F i g s . 13 and 14, would be u s e f u l i n t h i s r e g a r d i n any f u t u r e 106 s t u d i e s of systems of t h i s k i n d . A l t e r n a t i v e l y , u s i n g the c h a n n e l w i d t h a t the c r o s s - o v e r s ( F i g . 2 6 d ) , and c o r r e c t i n g f o r the a n g l e between the l i n e and the p e r p e n d i c u l a r t o the c h a n n e l a x i s g i v e s the w i d t h s i n T a b l e V I I I . The mean v a l u e of L/w i s 7.1±0.9, which i s lower than t h a t e x p e c t e d from ( 4 . 2 ) , but the d i f f e r e n c e may be due t o o v e r e s t i m a t i n g w (see F i g . 26d). I t has a l s o been suggested t h a t a t a g i v e n d i s c h a r g e , t h e r e i s a t h r e s h o l d s l o p e such t h a t r i v e r s w i t h s l o p e s l e s s than the t h r e s h o l d a r e s t r a i g h t whereas tho s e w i t h s t e e p e r s l o p e s meander ( A c k e r s and C h a r l t o n , 1970; Schum and Khan, 1972). Above a second, h i g h e r t h r e s h o l d s l o p e , c h a n n e l s a r e b r a i d e d ( L e o p o l d and Wolman, 1960; A c k e r s and C h a r l t o n , 1970; Schum and Kahn, 1972). Ta b l e V I I I . Meander di m e n s i o n s i n m. The meander a m p l i t u d e i s a. The mean v a l u e of L / r i s 3.8±0.4. Bend L r L / r a w L/w (m) (m) (m) (m) 1 518 180 2.9 91 64 8.1 2 475 1 10 4.3 1 02 64 7.4 3 579 207 2.8 1 22 4 536 1 55 3.5 1 10 5 317 82 3.9 101 54 5.9 6 378 76 5.0 1 1 6 54 7.0 4.3.3 Lower Reach The upper p a r t of t h i s r e a c h i s c h a r a c t e r i z e d by a more g r a d u a l bottom s l o p e (0.47°, F i g . 2 5 ) , the absence of meanders ( F i g . 2 0 ) , a s t i l l lower c h a n n e l r e l i e f w i t h no tendency t o widen, and symmetric l e v e e s ( F i g . 2 6 c ) . In l i n e s 15-17 ( F i g . 2 6 c ) , a t e r r a c e - l i k e s t r u c t u r e i s p r e s e n t on t h e r i g h t -hand s i d e of the c h a n n e l . S i m i l a r s t r u c t u r e s are apparent i n the 107 s i d e - s c a n r e c o r d t a k e n seven months l a t e r ( F i g . 22, F i g . 2 9 ) . They suggest a l a t e r a l s h i f t of the c h a n n e l a x i s w i t h o u t meandering i n t h i s p o r t i o n of the r e a c h . The d a t a i n T a b l e V I I i n d i c a t e t h a t t h i s r e a c h i s h i g h l y v a r i a b l e , b o t h as t o the number of c h a n n e l s and t h e i r p o s i t i o n s . I t i s t o be . e x p e c t e d t h a t r e l i c c h a n n e l s would be p r e s e n t i n s e i s m i c p r o f i l e s a c r o s s t h i s p a r t of the i n l e t i f the f i l l m a t e r i a l had a d i f f e r e n t a c o u s t i c impedance than the c h a n n e l banks and bottom. No such f e a t u r e s were o b v i o u s i n the 1977 p r o f i l e s , i n s p i t e of the d i s a p p e a r a n c e of a c h a n n e l a t ICM-14 i n September 1976 which had been q u i t e pronounced e a r l i e r (Table V I I ) . The echo from the b u r i e d c h a n n e l may have been masked by the echo from the sediment-water i n t e r f a c e . I n f i l l i n g of a c h a n n e l i s c l e a r l y i n d i c a t e d , however, i n the 1975 p r o f i l e s i n F i g . 32. T h i s c h a n n e l may have been t h a t o b s e r v e d on the n o r t h s i d e of the i n l e t a t CSP-14 the p r e v i o u s year ( T a b l e V i l a ) . T h i s i n t e r p r e t a t i o n r e q u i r e s a l o c a l d e p o s i t i o n r a t e of about 5 m y r " 1 w h i c h , a l t h o u g h h i g h , i s not out of the q u e s t i o n (see Chapter 5 ) . The lower s e c t i o n of t h i s r e a c h e x h i b i t s a f u r t h e r d e c r e a s e i n s l o p e and a tendency f o r the c h a n n e l t o widen and s h o a l as i t hugs t h e n o r t h w a l l p r i o r t o i t s d i s a p p e a r a n c e e a s t of t h e Hankin P o i n t a r e a . T h i s i s c o n s i s t e n t w i t h the c h a n n e l p a t t e r n o b s e r v e d i n the January 1977 CSP s u r v e y . C S P 12 F i g . 32. S e i s m i c p r o f i l e s a c r o s s the a r e a of the 197 r e a c h i n 1975, l o o k i n g d o w n - i n l e t . 109 4.4 The Apron Regime The next survey was conducted i n September 1978 from the CSS V e c t o r , a t which time the upper r e a c h of the meandering c h a n n e l had c o m p l e t e l y d i s a p p e a r e d under an 'apron' of t a i l i n g ( F i g . 3 3 ) . The meander r e a c h , though p a r t i a l l y i n f i l l e d , was s t i l l d i s c e r n i b l e . T h i s regime was a l s o dominant i n a l a t e r s u r v e y i n l a t e Febuary 1979 ( F i g . 3 4 ) . In both of t h e s e s u r v e y s slump s c a r s or i n c i p i e n t c h a n n e l s marked both the e a s t and west f l a n k s of the a p r o n . A d i f f e r e n c e map ( F i g . 35) was c o n s t r u c t e d from the 1976 and 1978 b a t h y m e t r i c maps, a p p l y i n g the a p p r o p r i a t e sounding speed c o r r e c t i o n i n each c a s e , by r e a d i n g the depth by l i n e a r i n t e r p o l a t i o n between c o n t o u r l i n e s a t the i n t e r s e c t i o n s of an o v e r l a y g r i d . The g r i d i n t e r v a l was 60 m. The p r o b a b l e e r r o r i n a g i v e n d e p t h d i f f e r e n c e i s d i f f i c u l t t o s p e c i f y . S y s t e m a t i c e r r o r s c o u l d a r i s e from the use of a c o n s t a n t c s'/c s , d i f f e r e n c e s between the a c t u a l and the p r e d i c t e d , t i d e s , or an o f f s e t i n the p o s i t i o n of the o v e r l a y g r i d . The c a l c u l a t e d v a l u e of the sounding speed t o 50 m depth d i f f e r e d by 0.3 m s~ 1 or l e s s from t h a t t o 100 m i n both s u r v e y s . U s i n g a c o n s t a n t v a l u e of c5' amounts t o a s y s t e m a t i c e r r o r of 0.02% i n the d e p t h , which i s n e g l i g i b l e . The depths a t most l i n e i n t e r s e c t i o n s agreed t o w i t h i n ±0.2m, and s i n c e such l i n e s were o f t e n run on d i f f e r e n t days, t h i s s h o u l d be a r e a s o n a b l e e s t i m a t e of the composite e r r o r due both t o p o s i t i o n i n g and the t i d a l c o r r e c t i o n . Hand-c o n t o u r i n g the d a t a or a s l i g h t o f f s e t of the map r e l a t i v e t o the d i f f e r e n c e g r i d c o u l d produce l a r g e e r r o r s i n the depth d i f f e r e n c e on s t e e p l y s l o p i n g bottoms. T h i s type of e r r o r i s 110 b e l i e v e d t o be r e s p o n s i b l e f o r the l a r g e n e g a t i v e d i f f e r e n c e s at the west end of the g r i d i n F i g . 35, on the n o r t h s i d e . Large p o s i t i v e d i f f e r e n c e s i n the r e s t of the map are l a r g e l y c o n f i n e d t o the c h a n n e l a x i s . The e s t i m a t e d a c c u m u l a t i o n i s s m a l l and sometimes n e g a t i v e on the l e v e e s both a l o n g the upper r e a c h and near the bend axes i n the m i d d l e r e a c h . A zone of s i g n i f i c a n t n e g a t i v e d i f f e r e n c e s i s p r e s e n t near the o u t f a l l over the former west l e v e e and ex t e n d s down the west f l a n k of the t a i l i n g apron i n the zone marked by the p o s s i b l e slump s c a r s mentioned p r e v i o u s l y . A c c u m u l a t i o n i s pronounced e a s t of the former p o s i t i o n of the upper r e a c h , and appears t o have been g r e a t e r over the e a s t than over the west l e v e e . Johnson (1974) a l s o s u g g ested t h a t t h e main l o b e of the t a i l i n g d e p o s i t a c t e d as a t o p o g r a p h i c b a r r i e r t o the d o w n - i n l e t t r a n s p o r t of mine waste - i n c l u d i n g b oth t a i l i n g and m a t e r i a l from the waste dump. The e x a c t date of the d i s a p p e a r a n c e of the c h a n n e l i s unknown; o n l y t h a t i t was sometime a f t e r 22 December, 1977. A pronounced and p e r s i s t e n t change i n the monthly c h a n n e l p r o f i l e a t ICM 8 ( F i g . 19) was f i r s t o b s e r v e d i n A p r i l 1978 ( H i l l i s , p e r s o n a l c o m m u n i c a t i o n ) , which was unu s u a l because of the s t a b i l i t y of the c h a n n e l p r o f i l e a t t h a t l o c a t i o n over the p r e v i o u s two y e a r s . The change i n t h i s p r o f i l e was not n e c e s s a r i l y s i m u l t a n e o u s w i t h the o b l i t e r a t i o n of the upper r e a c h . 400 0 400 800 . Depth d i f f e r e n c e map, November 1976 - September 1978. P o s i t i v e v a l u e s i o n . N e g a t i v e d i f f e r e n c e s a r e shaded . 113 A g e n e r a l c o l l a p s e of the l e v e e s a l o n g the l e n g t h of the upper re a c h i s not sug g e s t e d by F i g . 35. I f the c h a n n e l had been p i n c h e d o f f by a slump of the west l e v e e near the o u t f a l l , the r e s u l t would s u r e l y have been the d i v e r s i o n of the f l o w down the west f l a n k w i t h o u t f i l l i n g the upper r e a c h . On the o t h e r hand, a bl o c k a g e a t the lower end of t h i s r e a c h would not have been r e a d i l y eroded, and r a p i d d e p o s i t i o n would have o c c u r r e d on i t s upstream f a c e , r e s u l t i n g i n a d e c r e a s e i n the a x i a l s l o p e , d e c c e l e r a t i o n of the f l o w and t h e r e f o r e i n c r e a s e d d e p o s i t i o n throughout the r e a c h . B e f o r e i t s d i s a p p e a r a n c e , the volume of the upper r e a c h was 5.9x10 s m3, the e q u i v a l e n t of 24 days d i s c h a r g e . S i n c e i t i s u n l i k e l y t h a t a l l of the t a i l i n g d i s c h a r g e d would have s e t t l e d i n the upper r e a c h , i t may have taken s e v e r a l months t o f i l l . Such a b l o c k a g e may have been caused by a l e v e e slump, or by a slump from the waste dump. A major slump from the west end of the dump d i d occur i n mid June, 1977, but had no o b v i o u s e f f e c t upon the upper r e a c h ( F i g s . 23 and 2 4 ) . Major slumps o c c u r r e d on 30 J a n . , 11 Mar., and 11 Sept. 1978, but a t the e a s t end of the dump. The f i r s t two of' t h e s e slumps may, i n c o n j u n c t i o n w i t h the 1977 p r e c u r s o r , have caused s u f f i c i e n t d o w n - i n l e t mass-movement of p r e v i o u s l y d e p o s i t e d m a t e r i a l t o cause a bre a c h or c o l l a p s e of the l e v e e a t the p o i n t most s e n s i t i v e t o such movement - the base of the upper r e a c h . P u r s u i n g t h i s h y p o t h e s i s , i t i s sug g e s t e d t h a t a f t e r the apron was formed by f i l l i n g the upper r e a c h , the d i s c h a r g e plume was d i v e r t e d p r i n c i p a l l y down the west but a l s o down the e a s t f l a n k , r e s u l t i n g i n e r o s i o n of p r e v i o u s l y d e p o s i t e d t a i l i n g , 1 1 4 p a r t i c u l a r l y i n the a r e a c l o s e t o the o u t f a l l . The c r e s t of the apron c o i n c i d e d a p p r o x i m a t e l y w i t h the a x i s of the upper r e a c h which i t r e p l a c e d , and a c t e d as a b a r r i e r b e h i n d which t a i l i n g and waste overburden c o n t i n u e d t o c o l l e c t . 4.5 R e c h a n n e l i z e d Regime By August 1979, a second c h a n n e l had d e v e l o p e d on the west f l a n k of the t a i l i n g apron ( F i g . 3 6 ) , the s t e e p e s t s l o p e a v a i l a b l e t o the f l o w . T h i s was a l s o the area t h a t i n 1978 was marked by presumed slump s c a r s ( F i g . 3 3 ) . Even by F e b r u a r y , 1979 t h e r e were i n d i c a t i o n s of a c h a n n e l d e v e l o p i n g i n t h i s a r e a ( F i g . 3 4 ) . The August s u r v e y d i f f e r e d from the o t h e r s i n t h a t i t was c o n d u c t e d from the 5 m UBC l a u n c h w i t h the sounding equipment d i s c u s s e d i n Chapter 3, and i n t h a t p o s i t i o n f i x e s were o b t a i n e d from shore s t a t i o n s w i t h t h e o d o l i t e s . The l a u n c h was g u i d e d a l o n g s t r a i g h t l i n e s towards or away from one s t a t i o n w h i l e c r o s s - a n g l e s were d e t e r m i n e d from t h e second at time i n t e r v a l s (1-2 min.) s i g n a l l e d from the l a u n c h . Communication among the shore s t a t i o n s and the l a u n c h was c o n d u c t e d by r a d i o . A d e t a i l e d survey of the Hankin P o i n t a r e a was made at t h i s t i m e , d e l i n e a t i n g a pronounced s c o u r h o l e i n t o which a v e r y deep and e x t r e m e l y s t e e p - s i d e d c h a n n e l debouched ( F i g . 3 6 ) . T h i s c h a n n e l was not p h y s i c a l l y c o n t i n u o u s w i t h the c h a n n e l o f f the o u t f a l l ( F i g . 37, p r o f i l e s 10-15). The 1979 c h a n n e l system i s d i v i s i b l e i n t o two m o r p h o l o g i c a l l y d i s t i n c t and p h y s i c a l l y s e p a r a t e d r e a c h e s . The upper r e a c h extends from the o u t f a l l d o w n - i n l e t , c u r v i n g t o the r i g h t , w i t h l e v e e s which a r e more or l e s s pronounced ( F i g s . 37a 115 and b ) , and then d i s a p p e a r s b e f o r e the s t a r t of the lower r e a c h . As i n the 1976-77 system, the c h a n n e l r e l i e f and c r o s s - s e c t i o n undergo an i n i t i a l i n c r e a s e near t h e o u t f a l l ( l i n e s 1 and 2 ) , and and then decrease downstream b e f o r e the c h a n n e l d i s a p p e a r s a t l i n e 13. These bottom p r o f i l e s a r e h i g h l y i r r e g u l a r . Some of the f e a t u r e s may be e i t h e r slump s c a r s or c h a n n e l s abandoned by the c o n t i n u o u s f l o w . Note t h a t h o r i z o n t a l r e s o l u t i o n was h i g h e r i n t h i s s u r v e y because of the use of a narrower beam t r a n s d u c e r , and t h a t the h o r i z o n t a l s c a l e i s much c o a r s e r than the p r e v i o u s p r o f i l e s ( F i g s . 24 and 2 6 ) . P r e f e r e n t i a l d e p o s i t i o n on the l e f t l e v e e i s i n d i c a t e d , which i s c o n s i s t e n t w i t h the r i g h t w a r d c u r v a t u r e of the c h a n n e l a x i s and F i g . 13. The r e l i e f of the lower r e a c h i n c r e a s e s downstream ( F i g . 3 7 c ) , a t r a i t o b s e r v e d i n the o t h e r c h a n n e l s o n l y c l o s e t o the o u t f a l l . The w a l l s of the ch a n n e l i n t h i s r e a c h a re p r e c i p i t o u s and no l e v e e s a r e p r e s e n t , i n d i c a t i n g t h a t t h i s c h a n n e l i s an e r o s i o n a l f e a t u r e . F i g . 36. Bathymetry, August 1979. 37. C r o s s - c h a n n e l p r o f i l e s , August 1979, l o o k i n g down-channel, (a) and (b) Upper c h a n n e I ; Lower c h a n n e l . See F i g . 37 f o r l o c a t i o n s . 1 17 F i g . 38. Sounding l i n e s c o r r e s p o n d i n g t o p r o f i l e s i n F i g . 31. Channels are i n d i c a t e d by s o l i d l i n e s . The a x i a l p r o f i l e of the c h a n n e l i s p l o t t e d i n F i g . 39. The s l o p e of the upper r e a c h d e c r e a s e s downstream, w h i l e t h a t of the lower r e a c h i n c r e a s e s . The s l o p e of the upper r e a c h i s comparable t o t h a t of the 1976-77 system, d e c r e a s i n g from 5.77° t o 1.93° i n the f i r s t km, w i t h a r e l a t i v e l y c o n s t a n t v a l u e of .1.24° i n the next 1 km s e c t i o n . The d i s a p p e a r a n c e of the c h a n n e l i s accompanied by a f u r t h e r d e c r e a s e i n s l o p e (0.58°) above the lower r e a c h which b e g i n s a p p r o x i m a t e l y 3 km from the o u t f a l l . I t i s t e m p t i n g t o suggest t h a t the lower r e a c h i s eroded by s u r g e -type t u r b i d i t y c u r r e n t s , and t h a t the a r e a between the two reaches i s f i l l e d by d e p o s i t i o n from the c o n t i n u o u s d i s c h a r g e . Thi.s s u g g e s t i o n i s d i s c u s s e d f u r t h e r i n the f o l l o w i n g c h a p t e r s . 118 AXIAL DISTANCE (km) F i g . 39. Depth of ch a n n e l a x i s , August 1979. A b a t h y m e t r i c map of the Hankin P o i n t a r e a was c o n s t r u c t e d from the 1977 CSP survey and i s p r e s e n t e d i n F i g . 40a, and a depth d i f f e r e n c e map i n F i g . 40b. T h i s i s c l e a r l y an ar e a of d r a m a t i c change i n s e d i m e n t a t i o n regime. I t i s t o be e x p e c t e d t h a t e r o s i v e bottom c u r r e n t s d e v e l o p d u r i n g f l o o d t i d e i n the Hankin P o i n t a r e a as the s a l i n i t y of the deep water i n c r e a s e s d u r i n g the p e r i o d of low r u n o f f from l a t e w i n t e r t o e a r l y f a l l (see Chapter 1). F l o o d t i d e c u r r e n t s as h i g h as 2 m s" 1 have been measured 10 m from the bottom ( S t u c c h i and Farmer, 1976). Heavy r a i n f a l l o c c u r s p r i m a r i l y d u r i n g the autumn months of October t h r o u g h December. I t i s d u r i n g t h i s p e r i o d t h a t d i l u t i o n of the deep water i n the R u p e r t - H o l b e r g b a s i n t a k e s p l a c e , and presumably r e p r e s e n t s a p e r i o d of r e l a t i v e q u i e s c e n c e i n the 119 near-bottom zone. N o t i n g t h a t the 1977 CSP survey was conducted i n e a r l y J a n u a r y , whereas the 1979 survey was i n August, i t seems l i k e l y t h a t the d i f f e r e n c e s i n bathymetry i n t h i s a r e a a r e due t o t h i s s e a s o n a l change i n the a m p l i t u d e of the bottom c u r r e n t s . I t i s a l s o p o s s i b l e t h a t the development of the scour h o l e was a b e t t e d by the reduced t r a n s p o r t of t a i l i n g i n t o the ar e a i m p l i e d by the t r a n s i t i o n from one c h a n n e l i z e d s t a t e t o the n e x t . T h i s t r a n s i t i o n , embodied i n F i g s . 20, 33, 34 and 36, has some i n t e r e s t i n g i m p l i c a t i o n s r e g a r d i n g the development of the l e v e e d c h a n n e l s i n t h i s and s i m i l a r systems. Channels d e v e l o p i n a d i r e c t i o n i n which the downslope component of the g r a v i t a t i o n a l f o r c e a c t i n g on the f l o w i s a maximum. T h i s w i l l be d e t e r m i n e d by a c o m b i n a t i o n of the s t e e p e s t s l o p e and any f e a t u r e i n the bathymetry which i n h i b i t s the l a t e r a l d i v e r g e n c e of the f l o w , p e r m i t t i n g i t t o m a i n t a i n i t s e x c e s s d e n s i t y . I t would appear t h a t slump s c a r s can a c t i n the l a t t e r c a p a c i t y . Having e s t a b l i s h e d an i n c i p i e n t or j u v e n i l e c h a n n e l , l e v e e -b u i l d i n g by p r e f e r e n t i a l d e p o s i t i o n c l o s e t o the c h a n n e l from o v e r s p i l l f l o w s and c h a n n e l - d e e p e n i n g by scour a l o n g the a x i s f u r t h e r i n h i b i t l a t e r a l d i v e r g e n c e l o s s and r e i n f o r c e the i n i t i a l r o u t e . D e p o s i t i o n a l s o o c c u r s w i t h i n the c h a n n e l , and some of the m a t e r i a l d e p o s i t e d on the c h a n n e l w a l l s w i l l s l i d e down t o the c h a n n e l bottom. The i r r e g u l a r f e a t u r e s of the l e v e e w a l l s ' i n the s i d e - s c a n r e c o r d ( F i g . 22) are i n d i c a t i v e of such a p r o c e s s . I f d e p o s i t i o n b a l a n c e s e r o s i o n , the c h a n n e l can be e x p e c t e d t o approach e q u i l i b r i u m f o r a g i v e n d i s c h a r g e - a n d bottom s l o p e . 120 a. b. F i g . 40. (a) B a t h y m e t r y " o f f Hankin P o i n t i n J a n u a r y 1977 and (b) August 1979; (c) Depth d i f f e r e n c e map, Hankin P o i n t a r e a ; J a n u a r y 1977 - August 1979 (Note change i n s c a l e ) . N e g a t i v e v a l u e s a r e shaded and i n d i c a t e e r o s i o n . 121 4.6 Comparison w i t h Deep-Sea F a n - V a l l e y s F a n - v a l l e y s i s s u e from the mouths of submarine canyons, which Daly (1936) suggested were eroded i n t o the c o n t i n e n t a l s h e l f by t u r b i d i t y c u r r e n t s , b oth c o n t i n u o u s and storm-g e n e r a t e d , d u r i n g the lower s e a - l e v e l s t a n d s a s s o c i a t e d w i t h p e r i o d s of g l a c i a t i o n . T h i s c o n c e p t u a l model has been extended t o encompass the e n t i r e canyon, fan and f a n - v a l . l e y system, a l t h o u g h i n t e r m i t t e n t s lump-generated t u r b i d i t y c u r r e n t s a r e u s u a l l y c o n s i d e r e d t o be the p r i m a r y a c t i v e agent. On the b a s i s of the t u r b i d i t e s p r e s e n t i n the g e o l o g i c a l r e c o r d , t h e s e e v e n t s were both more f r e q u e n t and, j u d g i n g from the c o a r s e r m a t e r i a l d e p o s i t e d , more p o w e r f u l d u r i n g the P l e i s t o c e n e than the Holocene. The s u b j e c t of fan and f a n - v a l l e y f o r m a t i o n has been re v i e w e d by Shepard and D i l l (1966), N e l s o n and Kulm (1973), Normark (1974), N e l s o n e t a l (1978) and Normark (1978b). The i d e a l i z e d system c o n s i s t s of a submarine canyon i n the c o n t i n e n t a l s l o p e a t the mouth of which i s a d e p o s i t i o n a l l e v e e d v a l l e y on the s u r f a c e of a fan of l a r g e l y t e r r i g e n o u s s ediments. The presence of the v a l l e y c h a r a c t e r i z e s the upper p a r t of the fan (upper fan) and t e r m i n a t e s i n a system of u n l e v e e d d i s t r i b u t a r y c h a n n e l s on the m i d d l e fan which i n t u r n d i s a p p e a r on the u n c h a n n e l i z e d lower f a n . The Rupert I n l e t system i s not s t r i c t l y comparable t o t h i s because of the l a t e r a l c onfinement imposed by the i n l e t w a l l s and the c o m p l i c a t i o n s i n t r o d u c e d by t i d a l s c o u r i n g of the lower r e a c h i n the Hankin P o i n t a r e a . I t i s a l s o d i f f e r e n t i n t h a t a s t r i c t a n a l o g y t o the canyon i s not p r e s e n t . N e v e r t h e l e s s , a comparison i s made between the canyon and the upper reach,'and between the f a n - v a l l e y and the m i d d l e 122 and lower r e a c h e s . Normark (1978b) f u r t h e r d i s t i n g u i s h e s between the f a n -v a l l e y and meandering or b r a i d e d v a l l e y - f l o o r c h a n n e l s , u s i n g as examples t h e deep-tow r e s u l t s f o r the Navy f a n - v a l l e y ( b r a i d e d v a l l e y - f l o o r c h a n n e l s ) and the A s c e n s i o n f a n - v a l l e y ( i n c i s e d , meandering c h a n n e l ) . The l a t t e r r e p r e s e n t s e r o s i o n a l d o w n c u t t i n g , which i s u n c h a r a c t e r i s t i c of a d e p o s i t i o n a l regime (Hess and Normark, 1976; Normark, 1978b). Such f e a t u r e s may be caused by s m a l l e r s c a l e e v e n t s than the f a n - v a l l e y i t s e l f , perhaps as the r a t e of sediment s u p p l y waned w i t h the r e t r e a t of the g l a c i e r s . In any c a s e , the d i s t i n c t i o n between v a l l e y - f l o o r c h a n n e l s and f a n - v a l l e y s w i l l not be drawn i n t h i s t h e s i s . The phenomenon of meandering i n submarine c h a n n e l s has not r e c e i v e d much a t t e n t i o n . One of the d i f f i c u l t i e s w i t h deep-sea systems i s t h a t the s u r v e y l i n e s a re sometimes not s u f f i c i e n t l y dense t o r e s o l v e a meander. N e v e r t h e l e s s , meanders have been found and t h e i r p resence appears t o depend on the a x i a l s l o p e of the c h a n n e l , as i n Rupert I n l e t . T a b l e IXa i s a l i s t of those f a n - v a l l e y s w i t h a r e a c h c o n t a i n i n g pronounced meanders. The upper r e a c h of the Rupert I n l e t system i s analogous t o a canyon i n t h i s c o n t e x t . The Monterey f a n - v a l l e y (Shepard, 1968; Komar, 1969) has not been i n c l u d e d because i t s meander appears t o t o have been the r e s u l t of c h a n n e l c r o s s - o v e r t o the nearby A s c e n s i o n f a n - v a l l e y (Normark, 1970). The Northwest A t l a n t i c Mid-Ocean Channel does meander (Chough and Hesse, 1976), but the meanders a r e of low a m p l i t u d e (a/L<0.05). The A s t o r i a f a n - v a l l e y ( Nelson e t a l , 1970) e x h i b i t s s i m i l a r l o w - a m p l i t u d e meanders. A l i s t of s t r a i g h t or l o w - a m p l i t u d e meandering f a n - v a l l e y s i s 1 23 g i v e n i n T a b l e IXb. T a b l e I X a . A x i a l s l o p e s ( i n degrees) of submarine c h a n n e l s w i t h a meander r e a c h . Canyon M i d d l e (meander) r e a c h Lower re a c h Amazon Cone 1 0.74 0.42 Bengal f a n 2 0.29 0.09 C o ronado 3 5.7 1 .2 La J o l l a " * 2.3 1.9-0.87 0.65 ** 2.1 0.48 0.48 Navy 5 0.57 0.23 0.06 Redondo 5 2.1 1 .05 1 .95 Rupert I n l e t 2.2 0.91 0.47 * above t r i b u t a r y ** below t r i b u t a r y T a b l e IXb. A x i a l s l o p e s of submarine c h a n n e l s w i t h e i t h e r no meander r e a c h or low a m p l i t u d e meanders. A s t o r i a 7 C a s c a d i a 8 Congo 3 NW A t l a n t i c DOC9 0.95 0.57 0.30 <0.09 0.23 0.04 1Damuth and Kumar < 1 975), 2 C u r r a y and Moore (1971), 3 S h e p a r d and D i l l ( 1966), "Shepard and B u f f i n g t o n (1968), 5Normark and P i p e r (1972), 6Haner (1971), 'Nelson e t a l (1970), " G r i g g s and Kulm (1970), 9Chough and Hesse (1976). On the- b a s i s of t h e s e d a t a , the development of a meander r e a c h appears t o r e q u i r e a s u f f i c i e n t l y s t e e p a x i a l s l o p e . In such c a s e s the s e c t i o n i m m e d i a t e l y upstream i s s t e e p e r and o f t e n l a t e r a l l y c o n s t r i c t e d . A l t h o u g h the Redondo, La J o l l a and Coronado f a n - v a l l e y s e x h i b i t a n e a r l y r i g h t - a n g l e bend ( l e f t w a r d ) near the canyon mouth l i k e the r i g h t w a r d bend of the Rupert I n l e t c h a n n e l , the Amazon, Bengal and Navy f a n - v a l l e y s do n o t . The A s t o r i a f a n - v a l l e y a l s o bends s h a r p l y t o the l e f t near the canyon mouth, but i t s meanders a r e of low a m p l i t u d e . The w i d t h and r e l i e f of most of these f a n - v a l l e y s d e c r e a s e 124 downstream. In the case of the Amazon Cone and the Bengal f a n -v a l l e y , p a r t of t h i s d e c r e a s e may be due t o l o s s t o d i s t r i b u t a r y c h a n n e l s . The Redondo and the C a s c a d i a a r e e x c e p t i o n s , and the b e h a v i o u r of the Coronado i n t h i s r e s p e c t i s not c l e a r . Haner (1971) i n d i c a t e s t h a t a l t h o u g h the r e l i e f of the Redondo d e c r e a s e s downstream, the w i d t h i n c r e a s e s . T h i s f a n - v a l l e y i s a l s o e x c e p t i o n a l i n t h a t the a x i a l s l o p e i n c r e a s e s between the meander and the lower r e a c h e s , a f e a t u r e which i s d i s c u s s e d l a t e r . However, because the sounding g r i d i s r e l a t i v e l y s p a r s e and the l i n e s are not p e r p e n d i c u l a r t o the c h a n n e l t h a l w e g , the apparent i n c r e a s e i n w i d t h i n the meander r e a c h may not be r e a l . The downstream i n c r e a s e i n the r e l i e f of the C a s c a d i a f a n - v a l l e y i s p r o b a b l y due t o the c o n t r i b u t i o n s of i t s s e v e r a l t r i b u t a r i e s , among which i s Vancouver S e a - V a l l e y . Of the systems l i s t e d i n T a b l e IX, the La J o l l a f a n - v a l l e y has r e c e i v e d the d e n s e s t s u r v e y coverage (Shepard and B u f f i n g t o n , 1968). I t i s s t e e p l y s l o p i n g and the meanders decay t o form a s t r a i g h t lower r e a c h as the s l o p e d e c r e a s e s , but d e v e l o p a g a i n downstream of the mouth of a t r i b u t a r y c h a n n e l . The c h a n n e l has t h e r e f o r e been s p l i t i n t o two s e c t i o n s , as i n d i c a t e d i n T a b l e I X a . In the s e c t i o n above the t r i b u t a r y and i m m e d i a t e l y upstream of the s t r a i g h t lower r e a c h , the thalweg meanders w i t h i n a . s t r a i g h t c h a n n e l . The a m p l i t u d e s of the meanders i n the Navy, Redondo, Amazon Cone and Bengal f a n - v a l l e y s i n c r e a s e w i t h d i s t a n c e downstream and then s t o p a b r u p t l y . The Redondo canyon and f a n - v a l l e y system ( F i g . 41) e x h i b i t s some i n t e r e s t i n g p a r a l l e l s t o the Rupert I n l e t c h a n n e l ( F i g s . 20 and 2 5 ) . The s l o p e s of the upper 125 (canyon) and meander reaches a r e v i r t u a l l y the same, but the lower r e a c h of the Redondo i s s t e e p e r and appears t o be b r a i d e d (Haner, 1971). The t r a n s i t i o n from the meandering t o t h e b r a i d e d s t a t e i s accompanied by an i n c r e a s e i n s l o p e from 1° t o 2° (and an i n c r e a s e i n w i d t h ) ; the m e a n d e r i n g - s t r a i g h t t r a n s i t i o n i n Rupert I n l e t by a d e c r e a s e from 1° t o 0.5°. 3 n m J 1 i 5 k m F i g . 41. Redondo canyon and f a n - v a l l e y (adapted from Haner, 1971 ) . F i g . 42 i s a s k e t c h of the t r a j e c t o r i e s of t h e s e two systems i n s l o p e - d i s c h a r g e parameter space, i n which the s t r a i g h t - m e a n d e r i n g and m e a n d e r i n g - b r a i d e d t h r e s h o l d s have been drawn as suggested by Schum and Khan (1972), A c k e r s and C h a r l t o n (1970) and L e o p o l d and Wolman (1960). At a g i v e n s l o p e , the d i s c h a r g e i s assumed t o be p r o p o r t i o n a l t o the c h a n n e l c r o s s -s e c t i o n . Note t h a t the discharge-dependence of the p l a n morphology may e x p l a i n some v a r i a t i o n s i n T a b l e IX. 126 1.0 e UJ 0.1 br 0.01 2.8 x 10* 2.8 x 10 2 2.8 x 10 3 2.8 x 10 4 2.8 BANKFULL DISCHARGE (m 3s _ 1) F i g . 42. H y p o t h e t i c a l submarine c h a n n e l t r a j e c t o r i e s i n s l o p e -d i s c h a r g e space. The broken l i n e i s t h a t s e p a r a t i n g b r a i d e d from meandering and s t r a i g h t r i v e r s ( L e o p o l d and Wolman, 1960). Meander c u r v a t u r e i n c r e a s e s w i t h d e c r e a s i n g s l o p e . The Redondo f a n - v a l l e y i s 10 m deep and 300 m wide i n the meander r e a c h (Haner, 1971), i n d i c a t i n g a c r o s s - s e c t i o n an o r d e r of magnitude g r e a t e r than t h a t i n the Rupert I n l e t c h a n n e l . The upper r e a c h i s c o n f i n e d by the canyon w a l l s ' so no o v e r s p i l l l o s s o c c u r s u n t i l the f l o w e n t e r s the more g e n t l y s l o p i n g meander r e a c h . L o s s e s by o v e r s p i l l a r e assumed t o occur a l o n g the e n t i r e l e n g t h of the Rupert I n l e t c h a n n e l . Because the s l o p e i n c r e a s e s upon l e a v i n g the meander r e a c h i n the Redondo, t h e r e i s a p o t e n t i a l i n c r e a s e i n d i s c h a r g e . The s u g g e s t i o n i s , t h e n , t h a t the p l a n morphology of submarine c h a n n e l s i s c o n t r o l l e d by both the bottom s l o p e and the r a t e of l o s s of m a t e r i a l t h rough both c h a n n e l o v e r s p i l l and a x i a l d e p o s i t i o n . The o b s e r v e d d e c r e a s e i n wavelength and r a d i u s of c u r v a t u r e of t h e Rupert I n l e t meanders w i t h d i s t a n c e downstream i s c o n s i s t e n t w i t h a g r a d u a l l y waning f l o w (see 127 E q u a t i o n s 4.1 t o 4.3). These a r e e f f e c t s of the fundamental d i f f e r e n c e between s u b a e r i a l r i v e r s and c h a n n e l i z e d t u r b i d i t y c u r r e n t s : i n the l a t t e r c a s e , m i x i n g of the f l o w w i t h the o v e r l y i n g f l u i d and the r e s u l t i n g o v e r s p i l l o c c u r s more r e a d i l y , b o t h because of t h e s m a l l e r d e n s i t y d i f f e r e n c e . The t r a j e c t o r i e s i n F i g . 42 a r e s p e c u l a t i v e . The dependence of e i t h e r t h r e s h o l d upon t h e s l o p e and d i s c h a r g e i s not w e l l known even f o r r i v e r s . Because t h e meandering p r o c e s s i t s e l f i s not w e l l u n d e r s t o o d , no t h e o r e t i c a l t h r e s h o l d s a r e a v a i l a b l e . N e i t h e r i s i t o b v i o u s t h a t c h a n n e l s s u b j e c t e d t o the a c t i o n of t u r b i d i t y c u r r e n t s u r g e s s h o u l d be comparable t o r i v e r c h a n n e l s . The r e l a t i v e importance of c o n t i n u o u s and s u r g e - t y p e f l o w s i n the Rupert I n l e t system i s d i s c u s s e d i n Chapter 8. 1 28 CHAPTER 5 SEDIMENTS The s u r f i c i a l sediments were sampled p r i n c i p a l l y t o r e l a t e s p a t i a l v a r i a t i o n s i n g r a i n - s i z e and copper c o n c e n t r a t i o n t o changes i n the s e d i m e n t a t i o n regime i m p l i e d by the morphology of the deposit.. Cores were taken t o e s t a b l i s h the presence of t u r b i d i t e s and t h e r e b y d e t e r m i n e t u r b i d i t y - s u r g e f r e q u e n c i e s . The Cu c o n t e n t of the t a i l i n g b e f o r e d i s c h a r g e i s about 700 ppm (Evans and P o l i n g , 1975), a l t h o u g h i t can v a r y w i t h o r e -type and e x t r a c t i o n e f f i c i e n c y . An a n a l y s i s of d a t a c o l l e c t e d by the mine (Hay, 1978b) i n d i c a t e d t h a t the c o n c e n t r a t i o n of Cu i n the t a i l i n g d e p o s i t d e c r e a s e d w i t h i n c r e a s i n g d i s t a n c e from the o u t f a l l , near which l e v e l s 2-3 times g r e a t e r than 700 ppm were found. I t was d e c i d e d t o e x p l o i t t h i s dependence i n an attempt t o i d e n t i f y c o p p e r - b e a r i n g t u r b i d i t e s w i t h a n e a r - o u t f a l l p o i n t of o r i g i n . Some i r o n d e t e r m i n a t i o n s were a l s o made, p a r t l y because of t h e i r p o t e n t i a l b e a r i n g on the g r a i n - s i z e dependence of the sediment s p e c i f i c g r a v i t y . 5.1 Sampling and L a b o r a t o r y Techniques The s u r f i c i a l sediments were sampled w i t h a Shipek grab i n December 1977, F e b r u a r y 1979 and August 1979. Two 100-150 cm 3 subsamples were taken from each grab by the r e p e a t e d use of a s m a l l p i s t o n c o r e r made from a 50 cm 3 p l a s t i c s y r i n g e . One subsample was s t o r e d a t ambient temperature f o r s i z e a n a l y s i s ; the o t h e r was f r o z e n f o r m e t a l a n a l y s i s (Cu and F e ) . The sediment column was sampled by g r a v i t y c o r e r . Cores were taken d u r i n g the f i r s t c h a n n e l i z e d regime i n November 1976 129 and December 1977. The 1977 c o r e s were used f o r the s t a b i l i t y s t udy by D a v i s (1978). Cores of the apron regime were taken i n F e b r u a r y 1979. No c o r e s were taken d u r i n g the r e c h a n n e l i z e d phase. The sample p o s i t i o n s were d e t e r m i n e d w i t h the T r i s p o n d e r system a t the time of p e n e t r a t i o n , e x c e p t i n g the 1977 c o r e s and c o r e s i n H o l b e r g I n l e t f o r which ra d a r was used. The u n d e r - c o n s o l i d a t e d s t a t e of the upper p a r t of the sediment column i n d e p o s i t s of t a i l i n g mud caused some d i f f i c u l t i e s w i t h the c o r e r . Three t y p e s were used: a K u l l e n b e r g c o r e r i n 1976, a b a r r e l - l e s s c o r e r i n 1977 and a Benthos Boomerang c o r e r , m o d i f i e d f o r use w i t h a winch (Appendix 2 ) , i n 1979. The t o p of the c o r e l i n e r i n the K u l l e n b e r g was 30 cm below the base of the w e i g h t - s t a n d , which meant t h a t i n s o f t sediments the upper 30-50 cm of the sediment column were l o s t . In the Boomerang c o r e r , the e q u i v a l e n t d i s t a n c e i s o n l y 8 cm, and c o r e s were u s u a l l y o b t a i n e d w i t h l i t t l e a pparent l o s s of s u r f a c e sediment and the c o r e c o u l d be m a i n t a i n e d i n a v e r t i c a l o r i e n t a t i o n d u r i n g w i t h d r a w a l from the c o r e r w i t h o u t b r e a k i n g the v a l v e s e a l . T h i s both m i n i m i z e d the d i s t u r b a n c e of the p o o r l y c o n s o l i d a t e d upper p a r t of the c o r e and a l l o w e d removal of the c o r e - c a t c h e r w i t h m i n i m a l l o s s of the h i g h l y p l a s t i c sediment a t the c o r e base. The b a r r e l - l e s s c o r e r used i n 1977 u t i l i z e d an unsupported c o r e l i n e r . The i n s i d e d i a m e t e r s of the l i n e r s f o r the t h r e e c o r e r s were 6.2, 6.6 and 6.6 cm, r e s p e c t i v e l y . A l l c o r e s were s t o r e d i n a v e r t i c a l o r i e n t a t i o n . -the 1976 c o r e s a t 12 °C, the 1977 and 1979 c o r e s a t room temperature - and were a l l o w e d t o c o n s o l i d a t e and dewater f o r a minimum of s i x months. The c o r e s were then X - r a y e d , s p l i t , 1 30 photographed and sampled f o r s i z e and m e t a l a n a l y s e s . 5.1.1 S i z e A n a l y s i s A f t e r manual h o m o g e n i z a t i o n , d i s s o l v e d s a l t s were removed from 30-40 g (dry w e i g h t ) of sediment from the grab subsample by two 0.5 h washes i n 70-80 ml of. d i s t i l l e d w a t e r , and d e c a n t i n g the s u p e r n a t a n t a f t e r c e n t r i f u g a t i o n . T h i s sediment was s p l i t i n t o a c o a r s e (sand) and a f i n e (mud) f r a c t i o n by w e t - s e i v i n g t h r o u g h a 0.0625 mm (4 p h i ) s i e v e . ( P a r t i c l e d i a m e t e r s i n p h i u n i t s a r e g i v e n by the base 2 l o g a r i t h m of the r e c i p r o c a l d i a m e t e r i n mm-1). F o l l o w i n g F o l k (1968) and C a r v e r (1971), the c o a r s e f r a c t i o n was weighed a f t e r o v e n - d r y i n g a t 80-90 °C and s i e v e d t h rough 20.3 cm d i a m e t e r s i e v e s on a Ro-Tap f o r 15 min. To reduce the r a t e of c l o g g i n g of the f i n e r meshes, the s i e v e s were spaced a t 0.25 p h i i n t e r v a l s i n the 3-4 p h i range. O t h e r w i s e the s p a c i n g was 0.5 p h i , and because of the p r o b a b l e o v e r l a p i n the s i z e of the openings of meshes a t c l o s e r s p a c i n g s ( C a r v e r , 1971 p.50), the w e i g h t s were d e t e r m i n e d a t 0.5 p h i i n t e r v a l s . The f i n e r than 4 p h i r e s i d u e was added t o the f i n e f r a c t i o n . The f i n e f r a c t i o n s from the 1977 grab samples were a n a l y z e d by hydrometer. O t h e r w i s e the a n a l y s e s were run on M i c r o m e r i t i c s Model. 5000 and 5000D S e d i g r a p h s . In e i t h e r c a s e , a 5 g 1~ 1 aqueous s o l u t i o n of sodium hexametaphosphate was used as a d i s p e r s a n t and s e t t l i n g medium. The use of 30-40 g of sediment was d i c t a t e d by the need f o r s i g n i f i c a n t q u a n t i t i e s of m a t e r i a l i n the s i e v e s , but p r e s e n t e d a problem f o r the S e d i g r a p h . N o r m a l l y o n l y 2 g of m a t e r i a l i n 25 ml of d i s p e r s a n t a r e used, 131 which would have meant subsampling the f i n e f r a c t i o n . T h i s i n t e r m e d i a t e s t e p and i t s a s s o c i a t e d e r r o r s were a v o i d e d by d e s i g n i n g a sample m i x i n g c e l l which c o u l d accommodate the e n t i r e f i n e f r a c t i o n (Appendix 4 ) . The weight of the f i n e f r a c t i o n was d e t e r m i n e d a f t e r o v e n - d r y i n g a t 80-90 °C and u s i n g the water l o s s t o c o r r e c t f o r the weight of sodium hexametaphosphate. The sediments c o n t a i n e d s i g n i f i c a n t q u a n t i t i e s of m a g n e t i t e which adhered t o the magnetic s t i r - b a r i n the S e d i g r a p h m i x i n g c e l l and t h e r e f o r e c o u l d not be r e l i a b l y a n a l y z e d . Most of t h i s m a t e r i a l was scrubbed from the m i x t u r e by s t i r r i n g w i t h a magnetic s t i r - b a r f o r 5 min. I t s d r y weight was added t o t h a t of the a n a l y z e d f i n e f r a c t i o n , of which i t was 1-7%. The p r e c i s i o n of the s i z e d i s t r i b u t i o n s was ±2% i n the median d i a m e t e r , ±3% i n the p e r c e n t sand (diameters>0,0625 mm), ±1% i n the p e r c e n t s i l t (0.002<diameters<0.0625 mm) and ±13% i n the p e r c e n t c l a y (diameters<0.002 mm), as d e t e r m i n e d from d u p l i c a t e a n a l y s e s of 4 samples w i t h 7-38% sand, 5 6 - 8 6 % . s i l t , 2.6-9% c l a y and 0.033-0.044 mm median d i a m e t e r s . The p r e c i s i o n i n p e r c e n t c l a y i n c r e a s e d w i t h i n c r e a s i n g c l a y c o n t e n t and the o t h e r p e r c e n t a g e components behaved s i m i l a r l y . For g r a i n - s i z e a n a l y s i s .of the c o r e s , because of the s m a l l mass (a maximum of s e v e r a l grams) of t h e samples, t h e e n t i r e sample was run on the S e d i g r a p h w i t h o u t a c o a r s e - f i n e s p l i t . T h i s method was t e s t e d by a n a l y z i n g s m a l l amounts of sediment from grab samples which had a l r e a d y been a n a l y z e d by the p r e v i o u s t e c h n i q u e . The r e s u l t s of t h i s c o m parison a r e p r e s e n t e d i n F i g . 43. I t i s c l e a r t h a t the two t e c h n i q u e s are not 1 32 e q u i v a l e n t . For samples w i t h median d i a m e t e r s g r e a t e r than 0.04 mm, both t h e median d i a m e t e r and the sand p e r c e n t a g e s a re s u b s t a n t i a l l y h i g h e r when the c o a r s e - f i n e s p l i t i s used. Seive & Sedigraph Median Diameter (yjm) F i g . 43. Comparative s i z e a n a l y s e s : S e d i g r a p h a l o n e v e r s u s S e d i g r a p h p l u s s i e v i n g . Because of the advantage of s t u d y i n g t u r b i d i t e s w i t h a method y i e l d i n g s e d i m e n t a t i o n d i a m e t e r s f o r both sand and mud, the c o a r s e - f i n e s p l i t was not used f o r the c o r e a n a l y s e s . The e f f e c t s o f . t h e c o a r s e - f i n e s p l i t on the s i z e - d i s t r i b u t i o n a r e pursued i n Appendix 4. 5.1.2 G r a i n D e n s i t y The s p e c i f i c g r a v i t y of s e v e r a l of the 1977 s u r f i c i a l sediment samples was d e t e r m i n e d u s i n g a p p r o x i m a t e l y 100 g of washed sediment and a 500 ml v o l u m e t r i c f l a s k as a pycnometer, f o l l o w i n g the procedure o u t l i n e d by Lambe (1951). A i r was removed by h e a t i n g w h i l e under e v a c u a t i o n . The sediments were washed and c e n t r i f u g e d t h r e e t o f o u r t i m e s u n t i l the a d d i t i o n of an aqueous s o l u t i o n of s i l v e r n i t r a t e t o the s u p e r n a t a n t no l o n g e r formed a w h i t e p r e c i p i t a t e . The method was s t a n d a r d i z e d 1 33 w i t h Ottawa sand, f o r which the v a l u e of 2.64±0.02 g cm - 3 was o b t a i n e d from f o u r d e t e r m i n a t i o n s . The average of the a b s o l u t e v a l u e of the p e r c e n t a g e d i f f e r e n c e from d u p l i c a t e a n a l y s e s of f i v e samples was 0.9%±0.1%. 5.1.3 M e t a l A n a l y s i s The d r y , unwashed sediment was ground i n a d i a m o n i t e mortar and brushed t h r o u g h a 140 mesh (0.105 mm opening) n y l o n s c r e e n . A mass of about 0.5 g was d i g e s t e d i n a s o l u t i o n of . 4 p a r t s c o n c e n t r a t e d n i t r i c a c i d and 1 p a r t c o n c e n t r a t e d p e r c h l o r i c a c i d at a p p r o x i m a t e l y 200 °C. A f t e r the n i t r i c a c i d had e v a p o r a t e d , the sample was washed through a 0.005 mm nominal pore s i z e Gelman v i n y l membrane f i l t e r and t h e f i l t r a t e made up t o 100 ml w i t h d e i o n i z e d d i s t i l l e d water. A b s o r p t i o n d e t e r m i n a t i o n s were made on a T e c t r o n AA4 Atomic A b s o r p t i o n S p e c t r o p h o t o m e t e r (oxy-a c e t y l e n e flame) a t 324.8 nm f o r Cu and a t 386.0 nm f o r Fe i n the 10-30% absorbance range. S t a n d a r d s were made from Cu and Fe s o l u t i o n s p r e p a r e d by Dr. E.V. G r i l l of the UBC Department of Oceanography. A b l a n k d i g e s t was run w i t h e v e r y s e t of 12 samples. The p r e c i s i o n of the c o n c e n t r a t i o n s was 2.7%±1.1% based upon d u p l i c a t e d i g e s t s of 10 samples w i t h c o n c e n t r a t i o n s r a n g i n g from 340 t o 990 ppm. S y s t e m a t i c e r r o r s due t o i n t e r f e r e n c e by c h e m i c a l s p e c i e s p r e s e n t i n the d i g e s t s but not i n the s t a n d a r d s were d e t e r m i n e d to be l e s s than 3% by measuring the change i n absorbance induced by s p i k i n g a d i g e s t e d sample w i t h a known amount of the element from the s t a n d a r d s o l u t i o n . 134 5.2 S u r f i c i a l Sediments 5.2.1 C h a n n e l i z e d Regime D u r i n g the f i r s t c h a n n e l i z e d phase, the s u r f i c i a l sediments were sampled i n 1977 o n l y . These c o n s i s t e d of Shipek grab samples and the upper 10-15 cm of 5-75 cm l o n g g r a v i t y c o r e s t a k e n from the mine b o a t , the Mac I . The l o n g e r c o r e s were X-rayed and used f o r compaction and shear s t r e n g t h t e s t s i n the s t a b i l i t y s tudy by D a v i s (1978). Samples were taken r e l a t i v e t o the c h a n n e l a x i s by l o w e r i n g the sampler t o a depth 10-20 m from the bottom w h i l e under way and then d r o p p i n g the sampler onto the l e v e e or c h a n n e l bottom. The l o n g - c h a n n e l d i s t a n c e was d e t e r m i n e d by r a d a r . The r e s u l t s of the s i z e , s p e c i f i c g r a v i t y and Cu a n a l y s e s a r e summarized i n F i g . 44 and Appendix 5. These d a t a i n d i c a t e h i g h e r Cu c o n c e n t r a t i o n s and g r a i n - s i z e a l o n g the c h a n n e l a x i s and c l o s e t o the o u t f a l l . The s p e c i f i c g r a v i t y has a mean v a l u e of 2.82±0.05 g cm" 3 and e x h i b i t s no t r e n d e i t h e r l a t e r a l l y or a x i a l l y . W ith the e x c e p t i o n of one sample near the o u t f a l l , t h e s e v a l u e s a re s i g n i f i c a n t l y h i g h e r than t h a t of q u a r t z (2.65 g cm" 3). T a b l e X i s a l i s t of the p r i n c i p a l m i n e r a l s i n the t a i l i n g (from Evans and P o l i n g , 1975), t o g e t h e r w i t h t h e i r s p e c i f i c g r a v i t i e s (Weast, p. B-214). The h i g h e r s p e c i f i c g r a v i t y of the f i n e -g r a i n e d sediments i s p r o b a b l y due t o the presence of m a g n e t i t e and o t h e r i r o n - r i c h m i n e r a l s , as d i s c u s s e d i n 5.2.4. Median Diameter, um •2.82 2 8 8 T 2 . 8 4 2.80* 2.87T C u , ppm SG F i g . 44. S u r f i c i a l s e d i m e n t s , December 1977. (a) Median d i a m e t e r O/tm) (b) Cu c o n c e n t r a t i o n (ppm) (c) S p e c i f i c g r a v i t y . The 1977 channel a x i s i s i n d i c a t e d by t h e dashed l i n e . to tn 1 36 The c o m p a r a t i v e l y lower s p e c i f i c g r a v i t i e s of the c o a r s e r -g r a i n e d a x i a l sediments i s p r o b a b l y due t o g r e a t e r q u a n t i t i e s of q u a r t z augmented s l i g h t l y by m a g n e t i t e and s u l p h i d e m i n e r a l s . T h i s i n t e r p r e t a t i o n i s c o n s i s t e n t w i t h the h i g h e r a x i a l c o n c e n t r a t i o n s of copper which i s p r e s e n t i n the ore-body as c h a l c o p y r i t e ( C u F e S 2 ) . T a b l e X. T a i l i n g m i n e r a l o g y from Evans and P o l i n g (1975) and C a r g i l l ( 1975). M i n e r a l P e r c e n t a g e G r a i n d e n s i t y (g cm" 3) S i l i c a t e s Q u a r t z 50-70 2.65 Carbonate C a l c i t e 25 2.72-2.94 Aluminum-oxides F e l d s p a r s 2-20 A n d e s i n e 1 2.65-2.68 A l b i t e 2 2.63 S h e e t - s i l i c a and C l a y 5-10 B i o t i t e 2.7 -3.3 C h l o r i t e 2.6 -3.3 I r o n o x i d e M a g n e t i t e 2-4 5.18 S u l p h i d e s Pyr i t e 2-4 5.02 C h a l c o p y r i t e 0.2 4.1 -4.3 S p h a l e r i t e 0.02 3.9-4.1 M o l y b d e n i t e 0.01 4.62-4.73 1 ' 2 C a r g i l l (1975) The water c o n t e n t ( r a t i o of the weight of water t o t h a t of the dry sediment) of the s u r f i c i a l sediment ranged from 0.30-0.70 w i t h a mean of 0.50±0.14 ( D a v i s , 1978). The water c o n t e n t d e c r e a s e d w i t h i n c r e a s i n g g r a i n s i z e . These v a l u e s c o r r e s p o n d t o dry b u l k d e n s i t i e s of 0.96-1.54 g cm" 3 and 1.18 g cm" 3 r e s p e c t i v e l y , which not s u r p r i s i n g l y a r e somewhat lower than the v a l u e of 1.37 g cm" 3 d e t e r m i n e d from the compacted sediments i n the s p l i t c o r e s (see Appendix 6 ) . 1 37 5.2.2 S u r f i c i a l Sediments: Apron Regime E x t e n s i v e s a m p l i n g of t h e s u r f a c e sediments was c o nducted i n F e b r u a r y 1979 from the CSS V e c t o r . The r e s u l t s are summarized i n F i g s . 45 t o 48 and Appendix 5. The p r e v i o u s l y n o t e d a s s o c i a t i o n of copper w i t h c o a r s e - g r a i n e d d e p o s i t s i s a g a i n a p p a r e n t . F u r t h e r m o r e , c o a r s e r - g r a i n e d sediments were found on the apron f l a n k s , the c o a r s e s t b e i n g on the west f l a n k , s e p a r a t e d by f i n e - g r a i n e d copper-poor mud a l o n g the apron c r e s t . A d e p o s i t of c o p p e r - r i c h sand was p r e s e n t a t the base of the west f l a n k . These o b s e r v a t i o n s a r e c o n s i s t e n t w i t h the i n t e r p r e t a t i o n of the bathymetry i n S e c t i o n 4.4, i n which i t was s u g g ested t h a t the d i s c h a r g e plume was d e f l e c t e d down e i t h e r f l a n k . The slump-s c a r s and e v e n t u a l c h a n n e l i z a t i o n of the west f l a n k , t o g e t h e r w i t h i t ' s c o a r s e r - g r a i n e d sediment suggest t h a t most of the d i s c h a r g e was d i v e r t e d i n t h i s d i r e c t i o n . The sediments i n the H a nkin P o i n t a r e a were b o t h the c o a r s e s t and c o n t a i n e d the h i g h e s t copper c o n c e n t r a t i o n s a t t h i s t i m e . There were a l s o l a r g e q u a n t i t i e s of s h e l l fragments p r e s e n t , the edges of which were w e l l rounded, presumably the r e s u l t of wear. F i n e t a i l i n g was p r e s e n t i n a l l samples i n H o l b e r g I n l e t . F i g . 46. Sand 1979. c o n t e n t (%) of s u r f i c i a l sediments i n F e b r u a r y , 1 39 F i g . 47. C l a y c o n t e n t (%) of s u r f i c i a l sediments i n F e b r u a r y , 1979. F i g . 48. F e b r u a r y , Cu c o n c e n t r a t i o n 1979. (ppm) i n s u r f i c i a l sediments i n 1 40 5.2.3 S u r f i c i a l Sediments: R e c h a n n e l i z e d Regime• The sediments w i t h i n and a d j a c e n t t o the new c h a n n e l were sampled from the UBC l a u n c h (Appendix 2) i n August 1979. The s a m p l i n g methods were s i m i l a r t o those o u t l i n e d i n S e c t i o n 5.2.1, w i t h the d i f f e r e n c e t h a t a sample l o c a t i o n was f i x e d by s a m p l i n g a l o n g l i n e s d e f i n e d by t e t h e r e d f l o a t s and shore markers, and a c r o s s - a n g l e measured from shore w i t h a t h e o d o l i t e . The r e s u l t s of the a n a l y s e s of these samples a r e p r e s e n t e d i n F i g s . 49 t o 51 and Appendix 5. Copper i s a g a i n a s s o c i a t e d w i t h the c o a r s e - g r a i n e d s e d i m e n t s , which a r e c o n f i n e d t o the c h a n n e l a x i s and do not e x h i b i t downstream-grading. F i g . 49. Grab sample l o c a t i o n s , August 1979. 141 Cu c o n c e n t r a t i o n (ppm) i n s u r f i c i a l s e d i m e n t s , August 142 5.2.4 S u r f i c i a l Sediments: Summary C o a r s e - g r a i n e d , C u - b e a r i n g m a t e r i a l appears t o be c o n c e n t r a t e d a l o n g the c h a n n e l axes. The t r e n d t o s m a l l e r g r a i n -s i z e s w i t h i n c r e a s i n g l a t e r a l d i s t a n c e from the c h a n n e l a x i s i s t y p i c a l of deep-sea submarine c h a n n e l s (Normark, 1978b). F i g . 52 i s a p l o t of the p e r c e n t sand a g a i n s t Cu c o n c e n t r a t i o n i n the 1979 samples, and i n d i c a t e s an a p p r o x i m a t e l y l i n e a r dependence of the Cu c o n c e n t r a t i o n on the amount of sand p r e s e n t . The average Cu c o n c e n t r a t i o n i n mud (samples c o n t a i n i n g no sand) i s about 300 ppm, and r e p r e s e n t s the average background l e v e l of copper found i n the d e p o s i t e d mine waste. The low e s t l e v e l s (60 ppm) were found i n pre-mine sediments sampled by g r a v i t y c o r i n g , as d i s c u s s e d i n the next s e c t i o n . a a <=>-, 03 • - I D CO UJ C J C 3 Q_ + A A A + + A + + + A A U G 79 - F E B 79 A, A fe — i A 1 1 1 0.0 30.0 60.0 90.0 120.0 150.0 COPPER (PPM) (XI0 J ) F i g . 52. P e r c e n t sand v e r s u s Cu c o n c e n t r a t i o n i n the 1979 s u r f i c i a l s e d i m e n t s . 143 C h a l c o p y r i t e i s e x t r a c t e d from the host rock by f r o t h -f l o t a t i o n (Evans and P o l i n g , 1975). The rock i s m i l l e d t o a f i n e powder i n w a t e r . A f t e r a d d i n g s u i t a b l e s u r f a c e - a c t i v e c h e m i c a l s , a i r i s b u bbled upwards t h r o u g h the s l u r r y and the c h a l c o p y r i t e , which s e l e c t i v e l y adheres t o the b u b b l e s , i s c a r r i e d t o the s u r f a c e . Presumably t h i s p r o c e s s i s l e s s e f f i c i e n t f o r l a r g e p a r t i c l e s w i t h s m a l l amounts of c h a l c o p y r i t e on t h e i r s u r f a c e s , because the f o r c e b i n d i n g the p a r t i c l e t o the bubble would be l e s s l i k e l y t o exceed the p a r t i c l e ' s immersed w e i g h t . T h i s p r o b a b l y a c c o u n t s f o r the a s s o c i a t i o n of h i g h Cu v a l u e s w i t h the c o a r s e r - g r a i n e d s ediments. Once d i s c h a r g e d , the copper c o n c e n t r a t i o n i n the c o a r s e -g r a i n e d d e p o s i t s near the o u t f a l l , a l o n g the c h a n n e l a x i s and i n the Hankin P o i n t a r e a c o u l d be f u r t h e r e n r i c h e d due t o the winnowing of low s p e c i f i c g r a v i t y m i n e r a l s and mud from the sediment by bottom c u r r e n t s . The c u r r e n t s i n the c h a n n e l a r e a s s o c i a t e d w i t h the d i s c h a r g e and those i n the Hankin P o i n t a r e a w i t h the t i d a l j e t (see Chapter 1 and S e c t i o n 4.5). The l i n e a r r e l a t i o n s h i p between Cu c o n c e n t r a t i o n and the amount of sand i n the sample ( F i g . 52) s u g g e s t s t h a t Cu behaves c o n s e r v a t i v e l y i n the s u r f i c i a l t a i l i n g , b e i n g d e t e r m i n e d by the r e l a t i v e amounts of c o p p e r - r i c h sand and copper-poor mud. The s c a t t e r i n t h e s e d a t a i s g r e a t e r than the p r o b a b l e e r r o r i n the measurements (±3% i n Cu; ±3% i n p e r c e n t s a n d ) , and c o u l d r e f l e c t v a r i a t i o n s i n the c h a r a c t e r of the ore b e i n g p r o c e s s e d . These samples were a l s o a n a l y z e d f o r Fe and i n F i g . 53 p l o t s of p e r c e n t c l a y and s i l t a g a i n s t i r o n c o n t e n t a r e p r e s e n t e d . A c l e a r d i v i s i o n e x i s t s on average between low c l a y , 1 44 Fe-poor and h i g h c l a y , F e - r i c h s e d i m e n t s . Whereas no t r e n d i s ob v i o u s i n the c l a y - s i z e d m a t e r i a l , w i t h i n t he s c a t t e r of the •data the c o n c e n t r a t i o n of Fe appears t o i n c r e a s e i n p r o p o r t i o n t o the amount of s i l t p r e s e n t . T h i s s u g g e s t s t h a t the h i g h e r s p e c i f i c g r a v i t y of the mud ( S e c t i o n 5.2.1) i s due t o i r o n -b e a r i n g m i n e r a l s l i k e m a g n e t i t e or p y r i t e i n the s i l t - s i z e d m a t e r i a l . * + h* + + + -tf A + A ' A cc LU Q_ • 3 l A + —tS 'A. + + 3.0 3.6 i 1 1 4.2 4.6 IRON (PERCENT) ~ i — 5.4 + + + Jit + ^ * + + + A + A , A -FEB 79 -AUG 79 + 6.0 3.6 4.2 4.8 IRON (PERCENT) -1— 5.4 6.0 F i g . 53. (a) P e r c e n t c l a y and (b) p e r c e n t s i l t v e r s u s Fe c o n c e n t r a t i o n i n the 1979 s u r f i c i a l s e d iments. 5.3 The Sediment Column The c o r e s were taken t o e s t a b l i s h the pre s e n c e of t u r b i d i t e s and the frequ e n c y of o c c u r r e n c e of t u r b i d i t y c u r r e n t s from the number of t u r b i d i t e s per u n i t l e n g t h of c o r e and from the sediment a c c u m u l a t i o n r a t e . A t u r b i d i t e . i s a v e r t i c a l l y - g r a d e d l a y e r of sediment d e p o s i t e d d u r i n g the passage of a s i n g l e s u r g e - t y p e t u r b i d i t y c u r r e n t (Kuenen. and M i g l i o r i n i , 1951). These l a y e r s have been found both i n sed i m e n t a r y r o c k s and i n marine sediments (e.g. 1 45 M i d d l e t o n and Hampton, 1976). There have been few c a s e s i n which b o t h t u r b i d i t e s and t u r b i d i t y c u r r e n t s have been o b s e r v e d c o n c u r r e n t l y . One i n s t a n c e i s the i d e n t i f i c a t i o n by Heezen, E r i c s o n and Ewing (1954) of a 1 m t h i c k v e r t i c a l l y - g r a d e d s u r f i c i a l l a y e r of graded s i l t c o n t a i n i n g s h a l l o w - w a t e r m i c r o f o s s i l s 700 km from the e p i c e n t r e of the 1929 Grand Banks e a r t h q u a k e . T u r b i d i t e s have been found a l o n g the axes and on the l e v e e s of deep-sea c h a n n e l s ( e . g . C a r l s o n and N e l s o n , 1969; G r i g g s and Kulm, 1970; N e l s o n and Kulm, 1973) and s u b l a c u s t r i n e c h a n n e l s (Houbolt and J o n k e r , 1968), "and i n f j o r d sediments ( H o l t e d a h l , 1965; G i l b e r t , 1980). They have not been sought p r e v i o u s l y i n subaqueous m i n e - t a i l i n g d e p o s i t s . Flume e x p e r i m e n t s have shown t h a t v e r t i c a l l y - g r a d e d l a y e r s a r e d e p o s i t e d by t u r b i d i t y s u r ges ( e . g . M i d d l e t o n , 1967). The c h a r a c t e r i s t i c s of a t u r b i d i t e (Bouma, 1962; M i d d l e t o n and Hampton, 1976) a r e : (1) the l a y e r i s graded from c o a r s e a t the base t o f i n e a t the t o p . (2) one or more i n t e r v a l s of the Bouma sequence (see below) i s p r e s e n t . (3) the b a s a l c o n t a c t i s sh a r p and may e x h i b i t f e a t u r e s i n d i c a t i n g e r o s i o n and/or g r a v i t y l o a d i n g of the u n d e r l y i n g s e d i m e n t s . (4) the sediments i n the l a y e r are d i s t i n c t from and u s u a l l y c o a r s e r than those i m m e d i a t e l y above or below. (5) the sediments i n the l a y e r can be i d e n t i f i e d w i t h a sourc e r e g i o n i n s h a l l o w e r w a t e r . The Bouma sequence (Bouma, 1962) co m p r i s e s f i v e i n t e r v a l s l a b e l l e d Ta, Tb, Tc, Td and Te; Ta b e i n g the lowermost and c o a r s e s t - g r a i n e d , Te the uppermost and f i n e s t - g r a i n e d i n t e r v a l . The Ta i n t e r v a l i s u s u a l l y graded w i t h the c o a r s e s t sediment a t 1 46 the base. The Tb and Td i n t e r v a l s a r e p a r a l l e l l a m i n a t e d , the l a t t e r b e i n g much the f i n e r - g r a i n e d . The i n t e r v e n i n g Tc i n t e r v a l i s c u r r e n t r i p p l e - or c o n v o l u t e - l a m i n a t e d . At l e a s t one and r a r e l y a l l of t h e s e i n t e r v a l s a r e p r e s e n t i n any one t u r b i d i t e . I t i s not p o s s i b l e t o demonstrate t h a t e v e r y t u r b i d i t e s a t i s f i e s a l l f i v e c r i t e r i a , p a r t i c u l a r l y a v e r y t h i n l a y e r of f i n e m a t e r i a l l a i d down by a weak event or a t l a r g e d i s t a n c e s from the main p a t h . Such l a y e r s may be too t h i n t o e s t a b l i s h any of the t r a i t s e x cept (4) and perhaps ( 5 ) , so t h a t i n the deep-ocean, mud and s i l t l a y e r s t h i n n e r than 0.5 cm a r e o f t e n not c l a s s i f i e d ( e . g . P i p e r , 1978). The r o l e p l a y e d by (changing) bottom c u r r e n t s i n the f o r m a t i o n of c o a r s e - g r a i n e d l a y e r s i n the deep ocean, t h i n or t h i c k , has r e c e n t l y r e c e i v e d more a t t e n t i o n (see the re v i e w by Stow and L o v e l l , • 1 9 7 8 ) , and i t appears t h a t some d e p o s i t s which have been i d e n t i f i e d as t u r b i d i t e s might now be c a l l e d ' c o n t o u r i t e s ' - formed by the a c t i o n of c o n t o u r - f o l l o w i n g c u r r e n t s (Heezen, H o l l i s t e r and Ruddiman, 1966). In Rupert I n l e t the ambient c u r r e n t s a re t i d a l , and the d e p o s i t i o n r a t e s (1 m y r ~ 1 ) a r e h i g h enough t h a t s e m i - d i u r n a l p e r i o d i c i t y might be r e s o l v e d . D i f f i c u l t i e s a r e t o be expected i n a t t e m p t i n g t o d i s t i n g u i s h such changes from t h o s e i n t r o d u c e d by v a r i a b i l i t y i n the d i s c h a r g e , i n the o r e - t y p e , i n a c t i v i t y a t the waste dump or i n the fr e q u e n c y and magnitude of slump-generated f l o w s . The r e s u l t s from c o r e s taken from the l e v e e s d u r i n g the meandering c h a n n e l regime a r e p r e s e n t e d i n d e t a i l i n the next s e c t i o n , e m p h a s i z i n g the changes i n the sediment column w i t h d i s t a n c e a l o n g the c h a n n e l a x i s . B r i e f l y summarizing, c o a r s e -147 g r a i n e d l a y e r s s a t i s f y i n g c r i t e r i a 1-5 were found i n the c o r e s from the m i d d l e and lower reaches and near the mouth of H o l b e r g I n l e t . A l l c o a r s e - g r a i n e d l a y e r s s a t i s f i e d c o n d i t i o n s (3) and ( 4 ) . In s u f f i c i e n t l y t h i c k l a y e r s , c r i t e r i a (1) and (2) were t e s t e d by g r a i n - s i z e a n a l y s i s and were s a t i s f i e d i n each c a s e . The t h i c k e r c o a r s e - g r a i n e d l a y e r s a l s o had h i g h e r Cu and lower Fe l e v e l s than the i m m e d i a t e l y a d j a c e n t m a t e r i a l . On the b a s i s of the s u r f i c i a l s e d i m e n t s , t h i s i n d i c a t e s a p o i n t of o r i g i n w i t h i n the c h a n n e l and t h e r e f o r e , on p h y s i c a l grounds, i n the upper r e a c h . In S e c t i o n 5.3.2, the c o r e s from the apron regime are d i s c u s s e d b r i e f l y . In S e c t i o n s 5.3.3 t o 5.3.5, the d e p o s i t i o n r a t e s a re used t o e s t i m a t e t u r b i d i t y c u r r e n t f r e q u e n c i e s , time i n t e r v a l s between s m a l l - s c a l e laminae of p r o b a b l e t i d a l o r i g i n , and the time of t r a n s i t i o n t o the apron regime. The p o s s i b i l i t y e x i s t s t h a t some of the f e a t u r e s d e s c r i b e d a r e the r e s u l t of d i s t u r b a n c e s i n t r o d u c e d e i t h e r d u r i n g p e n e t r a t i o n or subsequent h a n d l i n g of the c o r e . Both the upper and lower s e c t i o n s of the c o r e s a r e d i s t u r b e d by m e t a l - f i n g e r c o r e - c a t c h e r s . D i s t u r b a n c e s i n d uced by p i s t o n - c o r i n g i n beds of a l t e r n a t i n g l a y e r s of sand and mud have been documented by Bouma and Boerma (1968) and Stow and Aksu (1977). These r e s u l t p r i m a r i l y from the s u c t i o n d e v e l o p e d by the p i s t o n d u r i n g w i t h d r a w a l a f t e r i n c o m p l e t e - p e n e t r a t i o n , which would not n o r m a l l y o c c u r i n a g r a v i t y c o r e r . 148 5.3.1 The C h a n n e l i z e d Regime The l o c a t i o n s of the 1976 c o r e s a r e shown i n F i g . 54. On s p l i t t i n g the c o r e s , l a y e r s of f i n e sand and s i l t r a n g i n g i n t h i c k n e s s from l e s s than 0.1 cm up t o 20 cm were found ( F i g . 55). The c o a r s e - g r a i n e d l a y e r s i n t h e s e c o r e s a r e d a r k e r . Some of the t h i c k e r l a y e r s ( F i g . 55; A, B and F) e x h i b i t e d d e f o r m a t i o n of t h e i r o t h e r w i s e s h a r p b a s a l c o n t a c t s . Some of the s e (A and B) a r e s i m i l a r t o l o a d - p o c k e t s ; o t h e r s t o l o a d -c a s t e d f l a m e - s t r u c t u r e s ( F ) , b o t h of which a r e found i n l i t h i f i e d t u r b i d i t e s , and both of which a r e thought t o be formed by the g r a v i t a t i o n a l l y u n s t a b l e l o a d i n g of a l i g h t e r p l a s t i c l a y e r of mud by an o v e r l y i n g h e a v i e r l a y e r of u n c o n s o l i d a t e d sand and s i l t ( A l l e n , 1970 pp. 82-86; M i d d l e t o n and Hampton, 1976 pp. 202-203; P o t t e r and P e t t i j o h n , 1977 pp. 198-201). The s t r u c t u r e s a t the b a s a l c o n t a c t of F c o u l d a l s o be f l u t e c a s t s or t o o l marks due t o d e f o r m a t i o n or e r o s i o n of the u n d e r l y i n g s u r f a c e by h i g h speed f l o w . F i g . 54. Core l o c a t i o n s and bathymetry, November 1976. F i g . 55. M o s a i c s o f some o f t h e h a l f - c o r e s from November, 1976. t h e s o l i d c i r c l e s on o p p o s i t e s i d e s o f a c o r e i d e n t i f y t h e l o c a t i o n o f a s p l i c e between two p h o t o g r a p h i c p r i n t s . 76-6 i s a q u a r t e r - c o r e . D i s t u r b a n c e s due t o s p l i t t i n g a r e p r e s e n t a t 5 cm i n 76-3, 33-35 cm and 60-78 cm in 76-4, and 42 cm i n 76-8. S l i g h t b r e a k s i n sand l a y e r s o c c u r a t 22, 36 and 61 cm in 6; 19 and 31 cm i n 7;and 2 cm i n 8. E was gouged by m a t e r i a l a d h e r i n g t o t h e s p l i t t i n g w i r e . O t h e r l a b e l s a r e d i s c u s s e d i n t h e t e x t . 150 Upper Reach Cores 76-1 and 76-2 ( F i g s . 56 and 57) are from t h e e a s t and west l e v e e s of the upper r e a c h , r e s p e c t i v e l y . Both c o n s i s t e d p r i m a r i l y of l a m i n a t e d s i l t and sand, and the c o n c e n t r a t i o n of Cu i n c r e a s e d w i t h depth i n each c o r e . The samples from c o r e 2 a r e c o a r s e r than those from c o r e 1. Both laminae and dark and l i g h t bands encompassing s e v e r a l laminae a r e p r e s e n t ( F i g . 56). The laminae a r e u s u a l l y p a r a l l e l and o f t e n i n c l i n e d ( c o r e 2; 35-50 cm i n c o r e 1 ) , p o s s i b l y r e p r e s e n t i n g the l o c a l bottom s l o p e . The o r i g i n of the l a m i n a t i o n s i n c o r e s from the upper r e a c h i s not c o m p l e t e l y c l e a r . U s i n g the t h i c k n e s s of the t a i l i n g d e p o s i t beneath the l e v e e s ( F i g . 21) t o o b t a i n a rough d e p o s i t i o n r a t e of 3 m y r " 1 , laminae induced by t i d a l c u r r e n t s would be 2 mm t h i c k , which i s not u n l i k e the t h i c k n e s s e s observed i n t h e s e c o r e s . Some laminae may r e p r e s e n t v a r i a b i l i t y i n the d i s c h a r g e . The bands of v a r y i n g shades of grey i n 76-1 (2 cm or more t h i c k ) a r e p r o b a b l y due t o d i f f e r e n c e s i n o r e - t y p e . There a r e two main o r e - t y p e s i n the p i t , and t h a t b e i n g p r o c e s s e d can change as o f t e n as e v e r y 2-4 weeks. One type i s a green-grey a n d e s i t e , the o t h e r a w h i t i s h - g r e y q u a r t z - f e l d s p a r p o r p h y r y . The o t h e r o r e - t y p e s a r e a l t e r a t i o n p r o d u c t s of these two, and are p r i m a r i l y b r e c c i a s . M a g n e t i t e a s s o c i a t e d w i t h the b r e c c i a s can darken the a n d e s i t e ( H i l l i s , p e r s o n a l c o m m u n i c a t i o n ) . 151 7 6 - 1 ( 0 - B O c m ) DIAMETER COPPER 1050 F i g . 56. Core 76-1, showing mosaic of the h a l f - c o r e and s i z e and Cu a n a l y s i s r e s u l t s . Note the l i g h t and dark bands : l i g h t bands are at 12-15, 28-38, 48-52 and 58-60 cm depth. F i n e r laminae a r e i n each band. The down-turning of the laminae a t the edges i s due to f r i c t i o n at the l i n e r w a l l d u r i n g p e n e t r a t i o n . 1 52 76-2 ( 0 - 80 cm ) CORE " 5 I _ a S -" I 10 H 20 H 30 40 H LU O 50 60 70 DIAMETER COPPER (ppm) 20 40 00 250 650 1050 —I J I I I I P F i g . 57. Core 76-2. The dark v e r t i c a l s t r e a k i n the upper 20 cm i s i r o n - o x i d e formed d u r i n g d e w a t e r i n g . The l i g h t s t r e a k s i n the lower 30 cm were formed by m a t e r i a l a d h e r i n g t o the s p l i t t i n g w i r e . Note i n c l i n e d l a m i n a e , and d i s t u r b a n c e i n upper 10 cm. 1 53 M i d d l e Reach Cores 3, 5 and 6 a r e from the o u t e r l e v e e s a t bends i n the meander r e a c h ; c o r e 4 i s f u r t h e s t from the c h a n n e l . They are f i n e r - g r a i n e d than c o r e s 1 and 2, c o n s i s t i n g of l a m i n a t e d and banded mud i n t e r b e d d e d w i t h C u - r i c h s a n d - s i l t l a y e r s w i t h s h a r p b a s a l c o n t a c t s . Core 4 ( F i g . 55) c o n t a i n s the t h i n n e s t and most w i d e l y s e p a r a t e d c o a r s e - g r a i n e d l a y e r s , w i t h some c l o s e l y spaced i n groups (D1-D3), and a sand c l a s t ( C ) . Core 3 ( F i g . 55) c o n t a i n s f r e q u e n t c o a r s e - g r a i n e d l a y e r s 0.5 cm and l e s s i n t h i c k n e s s , and the t h i c k e r l o a d - p o c k e t s d i s c u s s e d p r e v i o u s l y (A and B ) . Core 5 i s from the same bend but f u r t h e r downstream ( F i g . 54) and c o n t a i n s t h i c k e r c o a r s e - g r a i n e d l a y e r s ( F i g . 5 5 ) . These l a y e r s c o n s i s t of C u - r i c h , Fe-poor f i n e sand and s i l t w i t h median d i a m e t e r s r a n g i n g from 0.02-0.06 mm ( F i g s . 58 and 5 9 ) . Note the corres p o n d e n c e between the dark c o a r s e - g r a i n e d l a y e r s and the d a r k e r zones i n the X-ray p o s i t i v e . X-ray a b s o r p t i o n i n th e s e sediments i s g e n e r a l l y h i g h e r i n c o a r s e - g r a i n e d d e p o s i t s p r i m a r i l y because of t h e i r lower p o r o s i t y , s i n c e the g r a i n d e n s i t i e s of the sand and mud a r e v e r y s i m i l a r . The pr e s e n c e of . d i f f e r e n t m i n e r a l s may a l s o have an e f f e c t . The l a y e r w i t h flame s t r u c t u r e s a t i t s base (F i n F i g . 55) i s a t 87-100 cm depth i n F i g . 59. I t c o n s i s t s of two graded l a y e r s s e p a r a t e d by a t h i n l a y e r of i r o n - r i c h c l a y (not v i s i b l e ) . A sand l a y e r a t 113-115 cm depth ( F i g . 59, G i n F i g . 55) i s bounded by a 1 cm t h i c k l a y e r of mud which i s unconformable w i t h the a d j a c e n t l a m i n a e , and may be a sand c l a s t or m u d - b a l l . 1 54 F i g . 58. Core 76-5, upper h a l f . N o t e • d i s t u r b a n c e i n t o p 8 cm. 1 55 MEDIAN 7 6 - 5 (58-130 cm) DIAMETER COPPER IRON (^im) (ppm) (%) F i g . 59.- Core 76-5, lower h a l f . Note p o s s i b l e l o a d - c a s t e d flame s t r u c t u r e s a t 100 cm and mud - b a l l a t 112-115 cm. 1 56 Core 6 ( F i g s . 60 and 61) i s from the o u t e r l e v e e a t bend 4. The dark c o a r s e - g r a i n e d l a y e r s a r e t h i n n e r than i n c o r e 5, and no d e f o r m a t i o n of the b a s a l c o n t a c t i s p r e s e n t . Unconformable l a y e r s are e v i d e n t i n the X - r a d i o g r a p h above and below 54 cm d e p t h . T h i n l a y e r s which a r e r e a d i l y d i s t i n g u i s h e d b oth v i s u a l l y and on the X - r a d i o g r a p h were a l s o e a s i l y r e s o l v e d by s i z e a n a l y s i s ( F i g . 61, 75-76 cm), a l t h o u g h t o o b t a i n s u f f i c i e n t sample the s e c t i o n c o n t a i n i n g the l a y e r had t o be removed from the h a l f - c o r e . T h i s s e c t i o n c o u l d then be s e p a r a t e d a l o n g the l a y e r , and the sample s c r a p e d from the exposed f a c e of each p i e c e . Only v e r y minor i n c r e a s e s i n Cu c o n c e n t r a t i o n were ob s e r v e d i n t h e s e l a y e r s , and the Fe l e v e l s d i d not e x h i b i t a t r e n d : Enhanced Cu and low Fe l e v e l s were obser v e d i n most of the t h i c k e r c o a r s e - g r a i n e d l a y e r s t e s t e d , a l t h o u g h the changes a r e not o f t e n p a r t i c u l a r l y marked i n t h i s c o r e . F u r t h e r m o r e , copper l e v e l s i n the f i n e - g r a i n e d sediments can be v e r y h i g h ( a t 68-73 cm and 86-92 cm). The enhanced l e v e l s i n the mud occur i n the lower p a r t of the c o r e , as i n c o r e 5 ( F i g . 5 9 ) . Cu v a l u e s i n c r e a s i n g towards the base of the c o r e were a l s o o b s e r v e d i n c o r e s 1 and 2 ( F i g s . 56 and 57). 1 57 7 6 - 6 (0-70 cm) MEDIAN DIAMETER COPPER IRON l>m) (ppm) (%) F i g . 60. Upper of the laminae a t p a r t of 54 cm. c o r e 76-6. Note the change i n the s l o p e 159 Lower Reach Cores 7 and 8 are from the levees of the lower reach; core 9 from the Hankin Point area (Fig. 54). In marked contrast to those from the middle reach, the coarse-grained layers comprise most of the core (Figs. 55, 62 and 63). The sand layers are the thickest (up to 20 cm), coarsest (median diameters up to 0.063 mm) and have the highest copper levels (>1200 ppm at the base) of the 1976 cores. The d i s t r i b u t i o n of Cu through the coarse zones p a r a l l e l s that of the grain-size, while Fe levels remain r e l a t i v e l y constant and increase only in the mud. This pattern i s consistent with that in the surface sediments. 7 f t _ 7 MEDIAN — — - DIAMETER COPPER IRON (.pm) (ppm) (%) Sample 2 Q 4 Q 6 0 40Q ggg 12Q0 3.0 4.0 5.0 F i g . 62. Lower section of core 76-7. V e r t i c a l scale of the bargraph i s twice that of the photograph. The horizontal scales for Cu and Fe are di f f e r e n t for thi s core. Note disturbed basal section, and un c l a s s i f i e d structure at 27-28 cm. These layers are v e r t i c a l l y graded and have sharp basal contacts, and together with layer F in core 5 (Figs. 55 and 59) are the only examples of the Ta in t e r v a l of the Bouma sequence .1 60 v e r i f i e d by s i z e a n a l y s i s i n the 1976 c o r e s . They are s e p a r a t e d by t h i n n e r l a y e r s of mud r e p r e s e n t i n g m a t e r i a l d e p o s i t e d a f t e r the passage of the main surge and background d e p o s i t i o n - the Te or p e l l i t i c i n t e r v a l . A sequence of a l t e r n a t i n g s i l t y - s a n d and mud l a y e r s i s p r e s e n t a t the t o p of the Ta i n t e r v a l i n core'9 ( F i g . 62, 7-16 cm) which may be the p a r a l l e l - l a m i n a t e d Tb and Tc i n t e r v a l s . No f o r e - s e t bedding or c o n v o l u t e laminae c h a r a c t e r i s t i c of the Tc i n t e r v a l a r e p r e s e n t . 76 - 9 ( 0 - 38 cm) MEDIAN • DIAMETER COPPER IRON (um) ( ppm) (%) CORF 0 20 40 60 250 650 1050 3 5 7 I 1 0-\ ' 1 | ' I 1 *-F i g . 63. Core 76-9. Note Ta (massive,graded) i n t e r v a l a t 16-34 cm, and p o s s i b l e Tb and Td ( p a r a l l e l l a m i n a t e d ) i n t e r v a l s a t 8-16 cm. The presence of a t u r b i d i t e i n the Hankin P o i n t a rea i s c o m p a t i b l e w i t h the time of year (22 November) at which the core was t a k e n , s i n c e i n autumn the a m p l i t u d e of the near-bottom t i d a l c u r r e n t s s h o u l d be lower because of the p o s i t i v e buoyancy 161 of the t i d a l j e t ( S e c t i o n 1.2.1). F u r t h e r m o r e , the bathymetry 7 weeks a f t e r the c o r e was taken ( F i g . 40a) does not i n d i c a t e the pronounced e r o s i o n e v i d e n t a t o t h e r t i m e s ( F i g s . 40b and c ) . Assuming the c o a r s e l a y e r s i n c o r e s 7 t o 9 a r e t u r b i d i t e s , then t h e s e c o r e s and t h o s e from the m i d d l e r e a c h i n d i c a t e a p r o g r e s s i v e down-channel d e c l i n e i n the importance of overbank d e p o s i t i o n from the c o n t i n u o u s d i s c h a r g e as compared w i t h t h a t from t u r b i d i t y s u r g e s . T h i s r e s u l t has i m p o r t a n t i m p l i c a t i o n s which a r e pursued i n Chapter 8. I t s h o u l d not be c o n f u s e d w i t h the g e n e r a l l y a c c e p t e d downslope d e c r e a s e i n g r a i n - s i z e and t h i c k n e s s of i n d i v i d u a l t u r b i d i t e s ( e . g . Walker, 1967; S c h e i d e g g e r and P o t t e r , 1973). H o l b e r g I n l e t Cores 10 and 11 a r e from H o l b e r g I n l e t ( F i g . 5 4 ) , and both p e n e t r a t e d the pre-mine sediment, which was c h a r a c t e r i z e d by an o l i v e - g r e e n c o l o u r , the odour of hydrogen s u l p h i d e gas and low (<60 ppm) Cu c o n c e n t r a t i o n s ( F i g s . 64 and 6 5 ) . D e t a i l e d bathymetry of H o l b e r g I n l e t i s not a v a i l a b l e west of the c o n t o u r e d a r e a i n F i g . 19, which i s i t s e l f v e r y i r r e g u l a r . The c o r e s i t e s were l o c a t e d a t the deepest p o i n t s of a sounding l i n e a c r o s s the i n l e t (171 m a t s t a t i o n 10 and 118 m a t 11). The CSP s u r v e y s ( d a t a not shown) i n d i c a t e the presence of a mound o f f C o a l Harbour between c o r e s 10 and 11, which may a c t as a b a r r i e r t o the near-bottom t r a n s p o r t of mine t a i l i n g u p - i n l e t . There i s a l s o a c r o s s - i n l e t r i d g e i m m e d i a t e l y west of Hankin P o i n t ( F i g . 40a) which may have impeded the p r o g r e s s of t u r b i d i t y c u r r e n t s up H o l b e r g I n l e t . 162 7 6 - 10 (0 - 55 cm) CORE M o 20 Q_ LU D 30 MEDIAN DIAMETER (^ im ) 20 40 I COPPER IRON ( ppm ) ( % ) 60 250 650 1050 3 5 F i g . 64. Core 76-10. Note m o t t l e s and h o l e s , p a r t i c u l a r l y i n lower h a l f , and dark pre-mine sediment a t base. A l t e r n a t i n g C u - r i c h c o a r s e - g r a i n e d and Fe-poor f i n e - g r a i n e d l a y e r s , s i m i l a r t o those i n c o r e s 7 and 8 ( F i g s . 55 and 6 4 ) , are p r e s e n t o n l y i n the upper h a l f of c o r e 10 ( F i g . 6 4 ) , i n d i c a t i n g t u r b i d i t y c u r r e n t s had not p r e v i o u s l y reached t h i s s i t e . Assuming t h a t the b e g i n n i n g of the t a i l i n g d e p o s i t a t 52 cm r e p r e s e n t s the commencement of d i s c h a r g e i n October 1971, and 1 63 t h a t subsequent d e p o s i t i o n i s c o n s t a n t , then the onset of the a l t e r n a t i n g c o a r s e - f i n e l a y e r s a t 27 cm o c c u r r e d i n M a r c h - A p r i l , 1974. T h i s i s c o n s i s t e n t w i t h the CSP su r v e y s which i n d i c a t e t h a t the development of s i g n i f i c a n t d e p o s i t s of t a i l i n g beyond Hankin P o i n t d i d not b e g i n u n t i l 1975 ( F i g s . 17, 18 and 2 1 ) . C a r r y i n g the assumptions f u r t h e r , the 15-20 c o u n t a b l e t u r b i d i t e s i n t he upper 27 cm g i v e a mean r e c u r r e n c e time of 43-64 days f o r these e v e n t s . M o t t l e s and s m a l l h o l e s due t o b i o t u r b a t i o n permeate c o r e 10. The f a c t t h a t t h e s e h o l e s a r e ob s e r v e d o n l y i n the d i s t a l s e c t o r of the d e p o s i t i s c o n s i s t e n t w i t h the o b s e r v a t i o n s of Moore and S c r u t o n (1957), who found t h a t the ' i n t e n s i t y ' of b i o t u r b a t i o n s t r u c t u r e s i n c r e a s e d w i t h d e c r e a s i n g d e p o s i t i o n r a t e i n submarine d e p o s i t s near r i v e r d e l t a s . 76-11 ( 0 - 30 cm) DIAMETER COPPER IRON ( pm ) ( ppm) ( %) CORE 0 20 40 60 250 650 1050 3 5 7 F i g . 65. Core 76-11. Note copper- and i r o n - p o o r dark pre-mine sediment e x t e n d i n g t o the base of the c o r e (at 42 cm, not shown). 1 64 5.3.2 The Apron Regime: Cores Cores were taken i n F e b r u a r y 1979 w i t h the m o d i f i e d Boomerang c o r e r a t the l o c a t i o n s i n d i c a t e d i n F i g . 45. R e s u l t s a r e t a b u l a t e d i n Appendix 5. The s u r f a c e s of the s p l i t c o r e s a r e shown i n F i g . 66. Only s h o r t c o r e s of sand c o u l d be o b t a i n e d from the f l a n k of the apron (79-4, 79-5, 79-8 and 79-9, l a t t e r two not shown). 79-3 i s from the e a s t f l a n k and c o n s i s t s of 50 cm of l a m i n a t e d mud above a l t e r n a t i n g mud and sand l a y e r s up t o 5 cm t h i c k , t e r m i n a t i n g i n 15 cm of sand. 76-2 and 76-6 a r e l o c a t e d t o the e a s t and west of the apron f l a n k s , and a r e p r i m a r i l y c o m p r ised of l a m i n a t e d mud a l t h o u g h sand l a y e r s s e v e r a l cm t h i c k were p r e s e n t i n 79-2 (e.g. 50 and 113 cm). 79-7 i s from the lower toe of the a p r o n , and c o n t a i n s l a m i n a t e d mud o v e r l y i n g a t h i c k bed of sand a t 62 cm. Cores 79-10 t o 79-12 a r e d o w n - i n l e t " of the a p r o n . 79-10 i s d o m i n a n t l y l a m i n a t e d mud w i t h a 3 cm t h i c k t u r b i d i t e a t 48 cm (H). Both 79-11 and 79-12 have a t h i c k bed of l a m i n a t e d mud o v e r l y i n g beds of a l t e r n a t i n g mud and s a n d - s i l t l a y e r s . A 4 cm t h i c k t u r b i d i t e w i t h a ( g r a v i t a t i o n a l l y ) deformed b a s a l c o n t a c t i s a t 55 cm depth on 79-12. FEBRUARY, 1979 CORES F i g . 66 . C o r e s from February I979. Note t h a t d a r k e r c o l o r a t i o n i m p l i e s c o a r s e r m a t e r i a l e x c e p t f o r pre-mine sediments i n d i c a t e d by t h e c r o s s - h a t c h i n g i n c o r e s IA-IC. 1 66 These c o r e s r e i n f o r c e the s e d i m e n t a t i o n p a t t e r n i m p l i e d by the s u r f i c i a l sediments and the t r a n s i t i o n t o the apron regime: t h a t c o a r s e r - g r a i n e d m a t e r i a l was d i v e r t e d down the ea s t and p r i m a r i l y the west f l a n k s of the apr o n , and t h a t c o a r s e - g r a i n e d m a t e r i a l was not c a r r i e d as f a r d o w n - i n l e t as d u r i n g the c h a n n e l i z e d phase. The l a t t e r i s i n d i c a t e d by the abrupt d i s a p p e a r a n c e of c o a r s e l a y e r s from the upper p a r t s of the c o r e s , p a r t i c u l a r l y 79-7, 79-11 and 79-12 (G1-G3, F i g . 6 6 ) . Note t h a t the lower s e c t i o n s of c o r e s 79-11 and 79-12 a r e comparable i n appearance t o the t u r b i d i t e beds i n 76-7 and 76-8 ( F i g . 5 5). Cores 79-1A, B and C were taken o f f the toe of the waste dump, and c o n t a i n 10-50 cm of mine waste o v e r l y i n g dark o l i v e -green pre-mine sediments. In 79-1B, t h i s m a t e r i a l i s i n t e r b e d d e d w i t h f i n e waste, and i n c o r e 79-1C the two m a t e r i a l s a c t u a l l y i n t e r l e a v e , i m p l y i n g a p r o c e s s which erodes the u n d e r l y i n g m a t e r i a l and mixes i t up i n t o t h a t b e i n g d e p o s i t e d . That such a t h i n l a y e r of mine m a t e r i a l was p r e s e n t so c l o s e t o the dump a f t e r 5.5 y e a r s of o p e r a t i o n i s s u r p r i s i n g , and s u g g e s t s t h a t slumping from the waste dump must be c a p a b l e of d i s p l a c i n g l a r g e q u a n t i t i e s of p r e v i o u s l y d e p o s i t e d m a t e r i a l . T u r b i d i t e s were p r e s e n t i n c o r e s 79-1A and 79-1B ( F i g . 66, A and B ) , the l a t t e r e x h i b i t i n g pronounced d e f o r m a t i o n of the lower c o n t a c t . The m a t e r i a l i n the s e l a y e r s was v i s i b l y c o a r s e r than a n y t h i n g o bserved i n the t a i l i n g d e p o s i t , and i s presumed t o be from the waste dump. The m a t e r i a l i s not d i s t i n g u i s h a b l e from t a i l i n g on the b a s i s of i t s Cu c o n t e n t , however. S i m i l a r h i g h c o n c e n t r a t i o n s , g r a d i n g from 1466 ppm t o 279 ppm a t the t o p were observed i n the s e l a y e r s . 167 5.3.3 D e p o s i t i o n R a t e s : T u r b i d i t y C u r r e n t F r e q u e n c i e s D e p o s i t i o n r a t e s o b t a i n e d from the s e a s o n a l v a r i a t i o n s i n the d i a t o m assemblage w i t h depth i n t h r e e c o r e s a r e comparable to t h o s e o b t a i n e d from water depth and t h i c k n e s s changes (Appendix 6 ) . The l a t t e r may t h e r e f o r e be used a t any c o r e s i t e . P l o t s of t a i l i n g t h i c k n e s s v e r s u s time a t each of the 1976 co r e s i t e s a re g i v e n i n F i g . 67. Note t h a t the minimum r e s o l v a b l e t h i c k n e s s i s 1-1.6 m, and t h a t a speed of sound of 1500 m s " 1 i n the sediments was assumed. Except a t s i t e s 1 and 2, the i n c r e a s e i n t a i l i n g t h i c k n e s s i s r e p r e s e n t e d r e a s o n a b l y w e l l by a s t r a i g h t l i n e . T a b l e XI l i s t s the d e p o s i t i o n r a t e s and t u r b i d i t y c u r r e n t f r e q u e n c i e s a t the s i t e s of each of the 1976 c o r e s . For t h i s purpose e v e r y c o a r s e l a y e r was assumed t o be a t u r b i d i t e . C o u n t i n g the c o a r s e l a y e r s becomes d i f f i c u l t when they a r e v e r y t h i n , and d i s c o u n t i n g the v a l u e f o r c o r e 4 f o r t h i s reason and because i t i s f u r t h e s t from the c h a n n e l , the mean t u r b i d i t y c u r r e n t r e c u r r e n c e i n t e r v a l i n the c h a n n e l v i c i n i t y i s 2-5 days. Table X I . D e p o s i t i o n r a t e s and p r o b a b l e t u r b i d i t y c u r r e n t r e c u r r e n c e i n t e r v a l s from the 1976 c o r e s . Core Rate I n t e r v a l Number Number Rec u r r e n c e of D e n s i t y I n t e r v a l (m y r " 1 ) (cm) L a y e r s (m- 1 ) (d) 76-1 1.3-2.4 2 2.5-4.4 3 2.5 15-90 24 32.0 4.6 4 1 .2 15-150 44 32.6 9.3 5 2.2 10-125 49 42.6 3.9 6 2.0 25-75 1 1 55.6 3.3 82-140 49 7 4.0 8-45 1 7 45.9 2.0 8 1 .8 5-60 57 1 04. 1 .9 10 0.1 0-27 1 5-20 43-64 1972 1973 1974 1975 1976 1977 1972 1973 1974 1975 1976 1977 TIME (year) TIME (year) F i g . 67. T a i l i n g t h i c k n e s s , as d e r i v e d from CSP s u r v e y s , v e r s u s t i m e a t 1976 c o r e s i t e s . CTl CO 169 5.3.4 L a m i n a t i o n Time S c a l e The p r o b a b l e o r i g i n s of the l a m i n a t i o n s i n c o r e s 76-1 and 76-2 have a l r e a d y been d i s c u s s e d ( S e c t i o n 5.3.1). Much f i n e r l a minae were observed i n some of the o t h e r c o r e s . A photograph and X - r a d i o g r a p h of a 1 cm t h i c k s l a b removed from the s u r f a c e of a h a l f - c o r e of 79-6 a r e shown i n F i g . 68. Very f i n e laminae a r e apparent on the X - r a d i o g r a p h whereas they a r e not always v i s i b l e on the s u r f a c e . U s i n g the mean d e p o s t i o n r a t e of 58 + 10 cm y r _ 1 f o r 79-6 (Appendix 6 ) , the time s c a l e of the " f i n e s t r u c t u r e shown i n F i g . 6 8 can be e s t i m a t e d . Two bands of dark laminae were c o u n t e d , each a t depths of 18.9-22 cm and 22.8-24.4 cm, and c o n t a i n i n g 28 and 13 dark laminae r e s p e c t i v e l y , which c o r r e s p o n d t o time i n t e r v a l s of 15-19 hr and 17-22 hr between dark l a m i n a e . Given a p o s s i b l e e r r o r of 25% i n the a c c u m u l a t i o n r a t e e s t i m a t e , i t seems l i k e l y t h a t they a r e due t o the e f f e c t s of t i d a l c u r r e n t s on d e p o s i t i o n . T h i s p o s s i b i l i t y i s pursued i n Chapter 7. 5.3.5 T r a n s i t i o n t o the Apron Regime The time of the d i s a p p e a r a n c e of the upper r e a c h of the meandering c h a n n e l i s not known p r e c i s e l y . A c c o r d i n g t o the b a t h y m e t r i c s u r v e y s , i t o c c u r r e d between 23 December 1977 and September 1978. A major change i n the appearance of the monthly sounding p r o f i l e a t ICM 8 ( F i g . 19) was o b s e r v e d i n May 1978 and p e r s i s t e d s u b s e q u e n t l y ( H i l l i s , p e r s o n a l c o m m u n i c a t i o n ) . U s i n g the d e p o s i t i o n r a t e of 61 cm y r ~ 1 f o r 79-11 from Appendix 6, the t r a n s i t i o n a t G2 o c c u r r e d near 23 May, 1978. T h i s i s a c c e p t a b l y c l o s e t o the time of the change o b s e r v e d i n ICM 8, and t o t h a t 1 70 e x t e n t c o n f i r m s t h i s i n t e r p r e t a t i o n of the G t r a n s i t i o n i n the 8 H E o X 1 8 H »-CL 111 Q 28 H F i g . 68. Photograph ( l e f t ) and X - r a d i o g r a p h ( r i g h t ) of 1 cm t h i c k s l a b from c o r e 79-6. Note congruence i n shades of grey between the two p r i n t s , and the v e r y f i n e laminae i n the X-r a d i o g r a p h . 171 CHAPTER 6 CURRENT MEASUREMENTS 6.1 Taut-Wi r e Moorings: Meandering Channel Regime Aanderaa RCM4 c u r r e n t meters were d e p l o y e d on t a u t - w i r e moorings w i t h s u b s u r f a c e f l o t a t i o n i n August and November, 1976 a t s t a t i o n s 76/1 and 76/2 ( F i g . 6 9 ) . The November 1976 bathymetry i s a l s o shown. The bathymetry a t the time of the August mooring i s unknown. F i g . 69. 1976 mooring l o c a t i o n s , p l u s s t a t i o n J ( l o c a t i o n of Run 2 from Johnson, 1974). 6.1.1 August 1976 The r e c o r d s from the two meters on the August mooring (76/1) a r e shown i n F i g . 70. The meters were 3 and 13 m from the bottom a t 124 m water d e p t h , and the sampl i n g i n t e r v a l was 10 min. a Q. a CNI73I bottom* 13m 1 1 1 1 1 r —r— 1.0 i 1 1— 1.5 2.0 TI MEIDRYS1 ~t 1 a-— l — 2.5 CM98H bottom • 3m ~t 1 r "1 1 1 1 1 -i 1 1 1 1 1 r - i — L.O —l 1 r— 1.5 2.0 TIMEIOAYS) T 1 1 1 1 1 1 ri 1 1.0 1.5 2.0 2.' TIME(DAYS) CM73I bottom»13m F i g . 70 . C u r r e n t meter r e c o r d s a t 7 6 / 1 , 24-26 Augus t 1976. (a) T e m p e r a t u r e , s a l i n i t y , p r e s s u r e and p r e d i c t e d t i d e s ( d o t s ) , d i r e c t i o n (-180°=down-inIet) and s p e e d , (b) A x i a l (u) and c r o s s -i n l e t (v) v e l o c i t y components r e l a t i v e t o an u p - i n l e t d i r e c t i o n o f 70° t r u e . T ime 0 i s 0 h PDT, 24 Augus t 1976. 173 The c u r r e n t s were d o w n - i n l e t even d u r i n g f l o o d ( r i s i n g ) t i d e , except f o r two u p - i n l e t f l o w s a t the b e g i n n i n g and end of the r e c o r d . These appear t o be a s s o c i a t e d w i t h h i g h e r f l o o d t i d e r a n g e s , and r e v e r s e d d i r e c t i o n t o d o w n - i n l e t b e f o r e or a t h i g h water. For t h e r e s t of the r e c o r d , minimum and maximum down-i n l e t speeds were a s s o c i a t e d w i t h f l o o d and ebb t i d e s , r e s p e c t i v e l y . Temperature i n c r e a s e d g r a d u a l l y t h r o u g h o u t the record,, w h i l e s a l i n i t y d e c r e a s e d . The l a t t e r may not be r e a l , s i n c e the suspended- t a i l i n g appear t o a f f e c t " the c o n d u c t i v i t y sensor ( S t u c c h i and Farmer, 1976). 6.1.2 November 1976 F i g s . 71 and 72 a r e t h e r e c o r d s from th e mooring a t s t a t i o n 76/2 ( F i g . 6 9 ) . The meters were 6 and 45 m from the bottom a t 125 m water d e p t h . The s a m p l i n g i n t e r v a l was 20 min. The speed r e c o r d e d by the lower meter remained below t h r e s h o l d (1.5 cm s' 1) a f t e r the t h i r d day ( F i g . 7 1 ) , and i t i s s u s p e c t e d t h a t t a i l i n g f o u l e d the r o t o r . N e v e r t h e l e s s , i t i s c l e a r t h a t the dominant d i r e c t i o n of the c u r r e n t was d o w n - i n l e t . R e v e r s a l t o d o w n - i n l e t f l o w o c c u r r e d b e f o r e h i g h w a t e r . Of the 21 p e r i o d s of u p - i n l e t f l o w , 16 were d u r i n g f l o o d t i d e . F i v e r e v e r s a l s t o u p - i n l e t ' f l o w o c c u r r e d a t or s h o r t l y a f t e r h i g h water. There i s a t r e n d t o lower t e m p e r a t u r e s , and abrupt temperature d e c r e a s e s f o l l o w e d t h e s e 5 p e r i o d s of u p - i n l e t m o t i o n . Toward the end of the r e c o r d , t h e s e e v e n t s r e s u l t e d i n an a c c e l e r a t e d r a t e of c o o l i n g . o in J i u> in o i 1 1 1 1 1 1 I 1 I I ; I 1 1 1 1 I 1 1—:—I I 1 1 1 a 0.0 1.0 2.0 3.0 4.0 S.O 6.0 7.0 8.0 9.0 10.0 11.0 TIME(DAYS) F i g . 71. Record from lower meter a t 76/2, w i t h t h e p r e d i c t e d t i d e . Up-inIet=0°. Time 0 i s 0 h PST, 20 November 1976. The u and v components a r e p a r a i l e i t o and t r a n s v e r s e t o t h e i n l e t a x i s , r e s p e c t i v e l y . Recorded s p e e d . i s z e r o f o r most o f t h e r e c o r d due t o r o t o r f o u l i n g (see t e x t ) . E °" o E 3 a CO in ~i 1 r i r - T" n 1 r 1 1 1 r S.O 6.0 TIME (DATS) -i 1 r F i g . 7 2 . Record f rom upper mete r a t 7 6 / 2 . A x i a l (u) and t r a n s v e r s e (v ) v e l o c i t y components a r e p l o t t e d . cn 1 76 R o t o r f o u l i n g i s not apparent i n the r e c o r d from the upper meter ( F i g . 7 2 ) . The r e s i d u a l f l o w was a l s o d o w n - i n l e t , but more p e r i o d s (29) of s u s t a i n e d u p - i n l e t motion were r e g i s t e r e d . Of t h e s e 19 took p l a c e d u r i n g f l o o d t i d e , u s u a l l y c l o s e t o low w a t e r . The f l o w r e v e r s e d t o d o w n - i n l e t about midway th r o u g h the f l o o d t i d e , and maximum d o w n - i n l e t speed was reached a t or b e f o r e h i g h s l a c k . R e v e r s a l t o u p - i n l e t f l o w d u r i n g ebb t i d e o c c u r r e d 10 t i m e s . A l t h o u g h the t emperature d e c r e a s e d over the d u r a t i o n of the mooring a t t h i s depth as w e l l , the temperature d i d not d r o p e i t h e r as f r e q u e n t l y or a t the same tim e s as a t the deeper meter. N e v e r t h e l e s s , the d e c r e a s e s were a s s o c i a t e d w i t h p e r i o d s of u p - i n l e t m o t i o n . Scale In feet F i g . 73. V e s s e l mooring s t a t i o n s , September 1978. 1 77 6.2 O v e r - t h e - S i d e C u r r e n t Measurements: Apron Regime In September 1978, measurements were made w i t h Aanderaa RCM-4 meters suspended below a f o r e - a n d - a f t moored v e s s e l w i t h a 136 kg l e a d weight a t a d i s t a n c e above the bottom d e t e r m i n e d by an ORE Model 150B 11 kHz p i n g e r (see Appendix 7 ) . F i g . 73 shows the f o r e - a n d - a f t mooring s t a t i o n s . Note t h a t t h e meandering submarine c h a n n e l had d i s a p p e a r e d by t h i s t i m e . Three meters were suspended a t approximate d i s t a n c e s of 2, 4 and 7 m from the bottom. The s a m p l i n g i n t e r v a l was 2 min. S h i p p o s i t i o n s were r e c o r d e d every 2 t o 5 jmin from the T r i s p o n d e r p o s i t i o n i n g system. S h i p v e l o c i t i e s computed from these p o s i t i o n s were s u b t r a c t e d from the measured c u r r e n t v e l o c i t i e s . These d a t a , which a r e summarized i n Appendix 7, may be the o n l y near-bottom c u r r e n t measurements o b t a i n e d over a t i d a l c y c l e from a s h i p at a m u l t i p l e - p o i n t mooring i n a f j o r d . The da t a from s t a t i o n 78/2 a r e p r e s e n t e d i n F i g . 74. The gaps i n the r e c o r d s r e p r e s e n t p e r i o d s when the meters were r a i s e d t o t r a n s f e r the p i n g e r f o r a h y d r o c a s t . The s t e p s i n the p r e s s u r e r e c o r d s (z) r e p r e s e n t changes i n the o v e r b o a r d w i r e l e n g t h t o compensate f o r the t i d a l changes i n water d e p t h . Some r a t h e r a b r u p t changes i n s a l i n i t y and temp e r a t u r e r e l a t e d t o d i r e c t i o n r e v e r s a l s a r e p r e s e n t , and a r e d i s c u s s e d i n the next c h a p t e r . Temperature and s a l i n i t y d e c r e a s e d toward the bottom by 0.0-0.2 °C and 0.05-0.2 ppt between c u r r e n t meters. The s a l i n i t y change i s dominated by a 0.2 ppt o f f s e t of as y e t undetermined o r i g i n (Appendix 7 ) . The d i r e c t i o n was d o m i n a n t l y e i t h e r up-i n l e t (72°) or d o w n - i n l e t (252°), e x c e p t i n g the c r o s s - i n l e t f l o w ( 170°) a t 15.25 d.. T h i s change f o l l o w s the passage of an 1 78 a c o u s t i c a l l y - d e t e c t e d t u r b i d i t y s u r g e ( C h a p t e r 7 ) . The a x i a l and c r o s s - i n l e t components of v e l o c i t y , w i t h s h i p m o t i o n removed, a r e p l o t t e d w i t h t h e p r e d i c t e d t i d e i n F i g . 7 5 . The r e s i d u a l f l o w was d o w n - i n l e t . T r a n s i t i o n t o u p - i n l e t f l o w o c c u r r e d b e f o r e o r a t p r e d i c t e d low w a t e r , t r a n s i t i o n t o down-i n l e t f l o w c l o s e t o m i d - f l o o d , and maximum d o w n - i n l e t f l o w c l o s e t o p r e d i c t e d h i g h w a t e r . A s i m i l a r p a t t e r n was o b s e r v e d a t a l l s t a t i o n s e x c e p t 7 8 / 4 (Ap p e n d i x 7 ) , w h i c h p a t t e r n i s r e a s o n a b l y c o n s i s t e n t w i t h t h e t a u t - w i r e r e s u l t s . Maximum v e l o c i t i e s r a n g e d from -20 t o -40 cm s _ 1 d o w n - i n l e t and from 5 t o 20 cm s " 1 u p - i n l e t , whereas t h o s e from t h e t a u t - w i r e m o o r i n g s r a n g e d from -7 t o - 1 5 cm s " 1 and 0 t o 5 cm s - 1 . The b e s t c u r r e n t measurements u s i n g t h e o v e r b o a r d method were o b t a i n e d d u r i n g p e r i o d s o f low or z e r o wind s p e e d s . Wind-i n d u c e d s h i p m o t i o n c o n s i s t e d p r i m a r i l y of a c o m b i n a t i o n yaw abo u t t h e f o r w a r d a n c h o r , w h i c h had t h e s h o r t e r s c o p e , and l a t e r a l t r a n s l a t i o n w i t h an a p p r o x i m a t e p e r i o d o f two m i n u t e s . Wind was a p r o b l e m o n l y a t 7 8 / 4 , and m a n i f e s t e d i t s e l f a s 2 0 - 4 0 ° f l u c t u a t i o n s i n t h e d i r e c t i o n r e c o r d ( A p p e n d i x 7 ) . The r e s u l t s of t h e b o t t l e c a s t s a t s t a t i o n 7 8 / 2 a r e p l o t t e d i n F i g . 7 6 . The i n c r e a s e i n s a l i n i t y a t m i d - d e p t h due t o up-i n l e t m o t i o n d u r i n g p r e d i c t e d l a t e ebb and e a r l y f l o o d i s q u i t e e v i d e n t . The a b r u p t d r o p i n s a l i n i t y b e f o r e h i g h t i d e i s due t o th e sudden r e v e r s a l t o d o w n - i n l e t f l o w . The c o n c e n t r a t i o n of s u s p e n d e d p a r t i c u l a t e a l s o u s u a l l y d r o p p e d d u r i n g d o w n - i n l e t f l o w . r i o T r _i r CL Q_ o O -~1 Ol 1 m cn i i i i i 1 lu cn L_l L_J r r - i p m li fi 1 5 0 TIMEiDRYS) ~ 1 1 1 5 . 2 5 —i——i 1 i r 1 4 5 1 4 . 7 5 1 5 . 0 TIME(DAYS) 1 5 . 2 5 (If*" M 1 " 1 1 I I i—i 1 4 . 5 1 — 1 * Y 1 4 . / 5 1 5 RJ I 5 . L . ' 5 TIME(DAYS) F i g . 74. C u r r e n t meter r e c o r d s a t f o r e - a n d - a f t mooring s t a t i o n 78/2 and p r e d i c t e d t i d e on 14-15 September, 1978. Arrows i n d i c a t e 0330 h and 0525 h PST. Note t h e absence o f major h i g h f r e q u e n c y f l u c t u a t i o n s i n the d i r e c t i o n r e c o r d s . U p - i n l e t i s 72° t r u e . The p r e s s u r e s e n s o r on t h e BOTTOM meter m a l f u n c t i o n e d d u r i n g t h e f i r s t p a r t o f t h e second c a s t . a 14.5 14.75 15.0 TI ME (DAYS) 15.25 CO o. C_) CD CO o . -fM CJ i o CO >- -A CD co r\j i CD fM CO X o fM CD . LO i r?1 14.5 14.75 15,0 TIME (DAYS) 1 15.25 F i g . 75. (a) T r a n s v e r s e (v) and a x i a l (u) components o f v e l o c i t y a t 78/2 w i t h s h i p motion (b) removed. X and Y a r e e a s t - w e s t and n o r t h - s o u t h d i s p l a c e m e n t s o f t h e s h i p . 181 SEPTEMBER 1978 Station 2 TIME (days) . F i g . 76. Contour p l o t s of s a l i n i t y and suspended p a r t i c u l a t e a t 78/2. 182 6.3 I n t e r p r e t a t i o n These c u r r e n t meter r e c o r d s a r e i n g e n e r a l agreement w i t h those o b t a i n e d by Johnson (1974) a t 1 t o 1.5 m from the bottom i n J u l y , O c t o b e r , November and December, 1973. The d a t a from the J u l y mooring a r e reproduced i n F i g . 77. Except f o r the s t r o n g (70 cm s" 1) u p - i n l e t c u r r e n t s near p r e d i c t e d h i g h water toward the end of the r e c o r d , these a r e s i m i l a r i n a m p l i t u d e and phase t o those p r e s e n t e d e a r l i e r , w i t h maximum v e l o c i t i e s of -40 cm s" 1 d o w n - i n l e t and 10-30 cm s" 1 u p - i n l e t . The h i g h a m p l i t u d e u p - i n l e t f l o w s o c c u r i n c o n j u n c t i o n w i t h the waning s p r i n g t i d e (Johnson, 1974) and appear t o be s u p p r e s s e d when the range of the i m m e d i a t e l y p r e c e d i n g ebb i s much g r e a t e r than t h a t of the f l o o d . R e v e r s a l t o headward motion near p r e d i c t e d h i g h water i s a l s o p r e s e n t i n the r e c o r d from the lower meter a t 76/2 ( F i g . 7 1 ) . F i g . 78 i s a sche m a t i c r e p r e s e n t a t i o n of the unusual a m p l i t u d e and phase r e l a t i o n s h i p of the c u r r e n t regime i n the deep water based upon the two da t a s e t s . A q u a l i t a t i v e e x p l a n a t i o n can be made i n terms of the r e a d j u s t m e n t of the d e n s i t y f i e l d i n response t o the a l t e r n a t e f o r c i n g and r e l a x a t i o n of v e r t i c a l m i x i n g induced by the t i d a l j e t . I t i s e s s e n t i a l l y a f u r t h e r m o d i f i c a t i o n of t h a t g i v e n by Johnson (1974, pp. ' 77-83) who extended e a r l i e r s u g g e s t i o n s by (a) D r i n k w a t e r (1973), t h a t deep-water movement u p - i n l e t d u r i n g ebb t i d e c o u l d o c c u r as a r e s u l t of a r e a d j u s t m e n t of p r e s s u r e g r a d i e n t s f o l l o w i n g p e n e t r a t i o n of the t i d a l j e t t o mid-depth, and (b) by L a z i e r (1963), t h a t a mid-water p e n e t r a t i o n d u r i n g f l o o d - t i d e c o u l d d r i v e d o w n - i n l e t motion i n the deep water . 5 ( H F i g . 77. A x i a l component o f v e l o c i t y a t s t a t i o n J ( F i g . 69) a t 1.0-1.5 m from t h e bottom i n J u l y 1973. T i d a l extrema a r e t h o s e p r e d i c t e d f o r Coal Harbour (adapted from Johnson, 1974). CD CO 1 84 i r Up-lnlet 1 i i • Down-Inlet i 1 i • — F i g . 78. Schematic r e p r e s e n t a t i o n of a x i a l v e l o c i t y component i n the deep water as a f u n c t i o n of the phase and range of the t i d e . D u r i n g f l o o d t i d e , the t i d a l j e t p l u n g e s beneath the f r e s h water o u t f l o w from t h e M a r b l e R i v e r , p r o d u c i n g a zone of t u r b u l e n t m i x i n g about the c o r e of the j e t a t mid-depth. The water i n t r o d u c e d by the j e t must l e a v e the m i x i n g zone and f l o w headward a l o n g i s o p y c n a l s . I f the v e r t i c a l p e n e t r a t i o n of the j e t i s o n l y t o mid-depth a t f u l l f l o o d , a d o w n - i n l e t f l o w i n the deep water i s g e n e r a t e d by a c o m b i n a t i o n of the e n t r a i n m e n t of deep-water a t the base of the j e t and the headward fl o w a t mid-depth due t o t h e outward f l u x of water from the m i x i n g r e g i o n . I f the j e t i s s u f f i c i e n t l y dense, p e n e t r a t i o n i n t o deep water w i l l o c c u r i n the l a t t e r h a l f of the f l o o d ( S t u c c h i and 185 Farmer, 1976), r e s u l t i n g i n a r e v e r s a l t o ( a l o n g i s o p y c n a l ) up-i n l e t f l o w near h i g h water. The depth of p e n e t r a t i o n depends on -both t h e d e n s i t y and momentum of the j e t ( S t u c c h i , 1980). Both i n c r e a s e w i t h the f l o o d t i d e range, but i f the range of the p r e c e d i n g ebb i s s u f f i c i e n t l y g r e a t , the d e n s i t y d u r i n g f l o o d t i d e may remain below t h a t of the deep water. T h i s would e x p l a i n the s u p p r e s s i o n of the h i g h water u p - i n l e t f l o w by an a n t e c e d e n t l a r g e - a m p l i t u d e ebb t i d e . I f the d e n s i t y of the j e t exceeds t h a t of the deep-water, then an u p - i n l e t f l o w would be accompanied by changes i n t e m p e r a t u r e s i m i l a r t o t h o s e o b s e r v e d a t the end of the r e c o r d from the near-bottom meter a t 76/-2 ( F i g . 7 1 ) . The response d u r i n g f l o o d t i d e i s not u n l i k e t h a t t o a s l i g h t l y l e a k y but e l a s t i c b a l l o o n b e i n g f i l l e d by the j e t . D u r i n g f u l l ebb, the s u r f a c e p r e s s u r e g r a d i e n t d r i v i n g the o u t f l o w over the s i l l a l s o causes an i n c l i n a t i o n of the i s o p y c n a l s u r f a c e s upward towards the s i l l . D u r i n g t h e l a t t e r h a l f of the ebb, as the s u r f a c e s l o p e d e c r e a s e s , the p r e s s u r e g r a d i e n t due t o the d e n s i t y f i e l d d r i v e s a headward f l o w . Thus f a r , the p o s s i b l e c o n t r i b u t i o n of the suspended t a i l i n g t o t h e d e n s i t y f i e l d has been i g n o r e d . F or a g i v e n mass c o n c e n t r a t i o n (M) of suspended m a t t e r i n mg l i t r e - 1 , the e x c e s s d e n s i t y of the m i x t u r e i n g c m - 3 i s Ap = ( pj- fe)MxlQ-6 = 6.4x10" 7 M (6.1) where pj = 2.8 g cm" 3 i s the g r a i n d e n s i t y and p„ i s the d e n s i t y of the ambient sea water. R e f e r r i n g t o F i g . 76, • the c o n c e n t r a t i o n of p a r t i c u l a t e sometimes reached 100 mg l i t r e " 1 a t 186 1-2 m from the bottom. T h i s c o r r e s p o n d s t o a d e n s i t y e x c e s s of 0.06 sigma-t u n i t s , which i s s m a l l but c e r t a i n l y not n e g l i g i b l e , e s p e c i a l l y c o n s i d e r i n g t h a t a t t h i s s t a t i o n the t i d a l changes i n s a l i n i t y were o n l y ±0.1 ppt (±0.1 sigma-t u n i t s a t t h e s e t e m p e r a t u r e s ) . N e v e r t h e l e s s , a t d i s t a n c e s 10-20 m from the bottom ( F i g . 7 6 ) , the c o n c e n t r a t i o n of suspended m a t t e r q u i c k l y d rops t o n e g l i g i b l y s m a l l v a l u e s . The d a t a i n F i g . 77 a r e from an i n s t r u m e n t moored a t a d e pth of 108 m on the s o u t h s l o p e of the i n l e t ( F i g . 6 9 ) , where the a x i a l d e p th of the i n l e t was 150 m a t the t i m e . I doubt t h a t the suspended s o l i d s f i e l d c o n t r i b u t e d s i g n i f i c a n t l y t o the c u r r e n t s measured e i t h e r a t t h i s l o c a t i o n or by the upper meter a t 76/2. The o v e r - t h e - s i d e c u r r e n t meter r e c o r d s were examined f o r v e r t i c a l shear i n both speed and d i r e c t i o n as e v i d e n c e of a near-bottom c o n t i n u o u s t u r b i d i t y c u r r e n t . F i g . 79 shows the smoothed ( 5 - p o i n t r u n n i n g average) speed r e c o r d s from the t h r e e meters at 78/2, t o g e t h e r w i t h the d i r e c t i o n r e c o r d s . The speed tended t o d e c r e a s e w i t h d i s t a n c e from the bottom, p a r t i c u l a r l y d u r i n g p e r i o d s of moderate d o w n - i n l e t f l o w . A r e v e r s a l i n the v e l o c i t y g r a d i e n t o c c u r r e d d u r i n g the p e r i o d of u p - i n l e t f l o w a t the end of t h e r e c o r d , and i s d i s c u s s e d i n Chapter 7. D u r i n g d o w n - i n l e t f l o w , t h e r e was an apparent s h i f t i n the d i r e c t i o n of the v e l o c i t y v e c t o r t o the l e f t as the bottom i s approached ( F i g . 8 0 ) . T h i s l e f t w a r d r o t a t i o n of the v e l o c i t y and the i n c r e a s e i n speed toward the bottom d u r i n g d o w n - i n l e t f l o w are a t t r i b u t e d t o a d i s c h a r g e - d r i v e n d e n s i t y c u r r e n t . 187 Q CJ UJ CO CJ o CL CO CO CD LU a I ! CD. CO CO -J o CD CO CO _J 0*" TOP MIDDLE B O T T O M 1 4 . 5 14 .75 • 15.0 TIME(DAYS) 15 .25 F i g . 79. C u r r e n t d i r e c t i o n and smoothed speed from a l l t h r e e meters and the p r e d i c t e d t i d e a t s t a t i o n 78/2, September 14-15 1978. A d i r e c t i o n of 72° i s u p - i n l e t . F i g . 8 0 . A x i a l (u) and t r a n s v e r s e (v) components o f v e l o c i t y , c o r r e c t e d f o r s h i p m o t i o n , a t each o f t h e t h r e e me te r s a t 78/2 on 14-15 Sep tember , 1978. CD CO 189 CHAPTER 7 THE ACOUSTICAL CHARACTER OF THE DISCHARGE PLUME  AND TURBIDITY SURGES I d e a l l y , an o b s e r v a t i o n of a t u r b i d i t y c u r r e n t s h o u l d i n c l u d e e s t i m a t e s of the f o l l o w i n g p a r a m e t e r s : v e l o c i t y , f l o w t h i c k n e s s , e x c e s s d e n s i t y and, i n the case of s u r g e - t y p e f l o w s , the t i m e s of passage of the surge a t s u c c e s s i v e p o i n t s a l o n g i t s p a t h . As so a p t l y s t a t e d by Normark (1978) i n the q u o t a t i o n p r e s e n t e d i n Chapter 1, such o b s e r v a t i o n s have been l i m i t e d a l m o s t e x c l u s i v e l y t o l a b o r a t o r y e x p e r i m e n t s . T h i s i s t e s t i m o n y t o the d i f f i c u l t i e s a s s o c i a t e d w i t h m o n i t o r i n g such i n t e r m i t t e n t and p o t e n t i a l l y d e s t r u c t i v e phenomena. N e v e r t h e l e s s , a number of i m p o r t a n t o b s e r v a t i o n s have been made. Inman et a l (1976) have r e p o r t e d e v e n t s a t t r i b u t e d t o t u r b i d i t y c u r r e n t s i n La J o l l a Canyon w i t h maximum v e l o c i t i e s ( r e g i s t e r e d by c u r r e n t meters) of up t o 190 cm s _ 1 and d u r a t i o n s of up t o 2.5 h. These were a s s o c i a t e d w i t h the passage of s t o r m s , a f t e r which o b s e r v a t i o n by SCUBA showed t h a t the sand d e p o s i t i n the canyon head had been removed. F u r t h e r m o r e , down-canyon surges were not g e n e r a t e d by subsequent storms u n t i l such time as t h e s e d e p o s i t s were r e g e n e r a t e d . Surges presumed t o be t u r b i d i t y c u r r e n t s have a l s o been obse r v e d i n near-bottom c u r r e n t meter r e c o r d s from submarine canyons by Shepard and M a r s h a l l (1973; La J o l l a Canyon), Shepard, M a r s h a l l and M c L o u g h l i n (1975; R i o B a l s a s Canyon); Shepard, M a r s h a l l , M c L o u g h l i n and S u l l i v a n (1979; R i o de l a P l a t a and Abra c a n y o n s ) . In two of t h e s e , La J o l l a and A b r a , the v e l o c i t y was o b s e r v e d t o d e c r e a s e away from the bed w i t h meters a t d i s t a n c e s 190 above bottom of 2 and 4 m, and 3 and 30 m, r e s p e c t i v e l y . The maximum obser v e d v e l o c i t i e s ranged from 50 t o over 70 cm s"' i n the f o u r canyons. The e v e n t s i n Abra and R i o de l a P l a t a canyons were preceded by u n u s u a l l y s t r o n g up-canyon f l o w . The R i o de l a P l a t a was i n f u l l f l o o d , and the Abra Canyon measurements were made d u r i n g the r a i n y season. The event i n R i o B a l s a s Canyon f o l l o w e d a 24 h p e r i o d of heavy s w e l l , and was c h a r a c t e r i z e d by a s e r i e s of 7 p u l s e s of 50-70 cm s~ 1 maximum a m p l i t u d e over a 12 h p e r i o d . The R i o B a l s a s , Abra and R i o de l a P l a t a canyons a r e a l l near the mouths of s e d i m e n t - l a d e n r i v e r s . Gennesseaux a t a l (1971) o b s e r v e d surges a t 1.5 m from the bottom i n the Var Canyon w h i l e the Var R i v e r was i n f l o o d . The e p i s o d e s l a s t e d 0.5-3 h w i t h peak a m p l i t u d e s r a n g i n g from 40 t o 100 cm s _ 1 superimposed on a c o n t i n u o u s down-canyon f l o w of 10-20 cm s - 1 . Johnson (1974) r e p o r t e d s e v e r a l e v e n t s r e g i s t e r e d by a c u r r e n t meter 1-1.5 m above bottom i n Rupert I n l e t w i t h maximum down-i n l e t speeds of up t o 120 cm s _ 1 , some of which may have been t u r b i d i t y c u r r e n t s . F i n a l l y , the breakage of submarine c a b l e s f o l l o w i n g e a r t h q u a k e s has been a t t r i b u t e d t o t u r b i d i t y c u r r e n t s (Heezen and Ewing, 1952, and 1955; Heezen, 1963; Shepard e t a l , 1968; Krause e t a l , 1970). V e l o c i t i e s up t o 27.5 m s" 1 were e s t i m a t e d f o r the event subsequent t o the 1929 Grand Banks earthquake (Heezen and Ewing, 1952). U n d e r f l o w s of s e d i m e n t - l a d e n r i v e r water have been o b s e r v e d i n Lake Geneva, S w i t z e r l a n d ( F o r e l , 1885), Lake Mead, U.S. (Grover and Howard, 1938; B e l l , 1942; Gould, 1951 and 1960) and the Walensee, S w i t z e r l a n d (Lambert e t a l , 1976). These a r e c o n t i n u o u s - f l o w d e n s i t y c u r r e n t s , the speeds of which a r e 191 c o r r e l a t e d w i t h r i v e r d i s c h a r g e (e.g. Lambert e t a l , 1976). In such f l o w s the excess d e n s i t y may be p a r t l y d e t e r m i n e d by tempe r a t u r e d i f f e r e n c e s (e.g. G o u l d , 1951; Houbolt and J o n k e r s , 1968). T h i s i s not a f i n e d i s t i n c t i o n , s i n c e t h e buoyancy of the a d v e c t e d water may s i g n i f i c a n t l y a f f e c t m i x i n g a t the upper i n t e r f a c e , and i s c e r t a i n t o become i m p o r t a n t on s h a l l o w s l o p e s a t d epth as sediment i s d e p o s i t e d . In a slump-generated t u r b i d i t y surge f l o w i n g downslope t h r o u g h a s t a b l y s t r a t i f i e d l a k e or ocean, the a d v e c t e d water w i l l be p o s i t i v e l y buoyant a t depth and may p a r t l y d etermine the e v e n t u a l d i s s i p a t i o n of the surge (Pharo and Carmack, 1978). Measurements of c o n t i n u o u s - f l o w t u r b i d i t y c u r r e n t s i n the v i c i n i t y of mine t a i l i n g o u t f a l l s have been made by Normark and D i c k s o n (1976b) i n Lake S u p e r i o r , and by C a r s t e n s and Tesaker (1972; a l s o i n T e s a k e r , 1975) i n R a n a f j o r d , Norway. The former measurements were made w i t h a c u r r e n t meter moored 5 m above bottom over two p e r i o d s of 5 and 3 months. Downslope f l o w s l a s t i n g 4-328 h w i t h v e l o c i t i e s r a n g i n g from 0.3-13 cm s " 1 (average) and 0.5-30.6 cm s" 1 (peak) were a t t r i b u t e d t o i n t e r m i t t e n t i n c r e a s e s i n the t h i c k n e s s of the c o n t i n u o u s f l o w g e n e r a t e d by the d i s c h a r g e . C a r s t e n s and Tesaker (1972) o b t a i n e d v e l o c i t y and suspended s o l i d s c o n c e n t r a t i o n p r o f i l e s w i t h i n a canyon eroded i n pre-mine sediments by a t a i l i n g d i s c h a r g e plume. Near-bottom c o n c e n t r a t i o n s averaged 130 mg l i t r e " 1 , and peak speeds near the bed were 27 cm s" 1 on a bottom s l o p e of 11°. S a l i n i t y and temperature p r o f i l e s were not r e p o r t e d . The above measurements suggest t h a t by j u d i c i o u s c h o i c e . of 1 92 the l o c a t i o n and time of f i e l d o p e r a t i o n s , n a t u r a l l y o c c u r r i n g or man-made t u r b i d i t y c u r r e n t s may be observ e d w i t h o u t a w a i t i n g s e i s m i c d i s t u r b a n c e s . They a l s o g i v e e s t i m a t e s of t h e v e l o c i t y s c a l e s t o be exp e c t e d i n a v a r i e t y of c i r c u m s t a n c e s . Except f o r those by C a r s t e n s and Tesaker ( 1 9 7 2 ) , however, measurements of one or more of the parameters mentioned a t the b e g i n n i n g of t h i s c h a p t e r were not o b t a i n e d . A c o u s t i c sounding r e c o r d s of c h a n n e l i z e d t u r b i d i t y f l o w s , both c o n t i n u o u s and s u r g e - t y p e , have a l r e a d y been p r e s e n t e d ( f r o n t i s p i e c e , F i g s . 13 and 1 4 ) . The remainder of t h i s c h a p t e r i s d e v o t e d t o a d i s c u s s i o n of thes e and s i m i l a r r e c o r d s . The r e s u l t s a r e a l s o i n c o m p l e t e i n the sense d e s c r i b e d above, but e x e m p l i f y t h e v a l u e of a c o u s t i c sounding f o r m o n i t o r i n g t h e s e p r o c e s s e s . The r e s u l t s f o r c h a n n e l i z e d surge f l o w s a r e complimented by the e x p e r i m e n t s of Bo k u n i e w i c z e t a l ( 1 9 7 8 ) , who o b t a i n e d sonographs of a n n u l a r t u r b i d i t y s u r ges g e n e r a t e d by the dumping of dredge s p o i l s . 7 . 1 The D i s c h a r g e Plume 7 . 1 . 1 . Meandering Channel Regime A 2 0 0 kHz a c o u s t i c sounding r e c o r d of a c r o s s i n g a p p r o x i m a t e l y midway a l o n g the upper r e a c h i s shown i n F i g . 8 1 . The r e c o r d was taken from the CSS V e c t o r w i t h a Ross Model 2 0 0 r e c o r d e r o p e r a t i n g a t a p u l s e l e n g t h of 0 . 1 ms and a beam-width of 5 ° X 1 0 ° . The bottom i s o u t l i n e d by the dark l i n e a t the upper edge of the l i g h t g r e y band, which i s g e n e r a t e d by the 'Fine L i n e ' a m p l i f i e r . T h i s f e a t u r e causes s i g n a l s w i t h a m p l i t u d e s above a t h r e s h o l d s e t t i n g t o be p a i n t e d a u n i f o r m shade of gr e y . LINE 78 West East H 110 m H 193 - 40 50 - 6 0 (fm) F i g . 8 1 . S o n o g r a p h of t h e c h a n n e l a n d d i s c h a r g e p l u m e , l o o k i n g u p s t r e a m , d u r i n g f l o o d t i d e 3.5 h a f t e r l o w w a t e r , 22 November 1976, 1050 h PST. S = s i d e e c h o , P=plume. V e r t i c a l l i n e s i n d i c a t e t i m e s o f p o s i t i o n f i x e s , t a k e n a t 1 min i n t e r v a l s . See F i g . 83 f o r l i n e l o c a t i o n . The c h a n n e l a p p e a r s a s i t w o u l d i f t h e o b s e r v e r were l o o k i n g u p s t r e a m , t h a t i s w i t h t h e h i g h e r w e s t l e v e e on t h e l e f t . L a r g e a m p l i t u d e s c a t t e r e r s ( f i s h ? ) a r e d i s t r i b u t e d t h r o u g h o u t t h e d i s p l a y e d s e c t i o n o f t h e w a t e r c o l u m n . S i d e - e c h o f r o m t h e l e v e e s i s a p p a r e n t b e n e a t h t h e c h a n n e l a x i s , a n d e x t e n d s u p w a r d s i n t o t h e c h a n n e l i t s e l f . Above a nd s u p e r i m p o s e d on t h i s s i d e - e c h o i s t h e b a c k s c a t t e r e d s i g n a l f r o m t h e d i s c h a r g e p l u m e , w h i c h i s s p i l l i n g o u t of t h e c h a n n e l b e y o n d t h e c r e s t o f t h e h i g h e r w e s t l e v e e . The u p p e r edge of t h e c l o u d w i t h i n t h e c h a n n e l i s t i l t e d u p w a r d f r o m e a s t t o w e s t , o r f r o m l e f t t o r i g h t i n t h e d o w n s t r e a m - l o o k i n g s e n s e . T h i s p r o f i l e i s t y p i c a l . F i g . 82 shows o t h e r p r o f i l e s a c r o s s t h e same s e c t i o n o f t h e r e a c h . A l l e x h i b i t t h e same t e n d e n c y on t h e p a r t o f t h e plume t o hug t h e r i g h t bank a n d s p i l l o v e r t h e r i g h t l e v e e . 1 94 LINE 24 1530 h 18 November -180 m-" • i J w - 4 0 - 5 0 ( f m ) LINE 48 2000 h 19 November - 4 0 " - 4 0 # ^ ^ ^ ? - 5 O ( f m ) LINE 54 1330 h 20 November 0920 h 24 November F i g . _ 82. F a c s i m i l e r e c o r d s showing the plume i n the upper reach a t d i f f e r e n t t i m e s , November 1976. From t op to bottom, the runs were made a t 1 h b e f o r e low water, 2 h a f t e r LW, 3.5 h a f t e r HW and a t LW. The F i n e L i n e a m p l i f i e r was s w i t c h e d o f f and the T r i s p o n d e r beacons were not i n p l a c e d u r i n g the bottom r u n . 195 T h i s s u g g e s t s t h a t t h e h i g h e r r i g h t (western) l e v e e i s not due t o a net d o w n - i n l e t t i d a l s t r e s s on the d i s c h a r g e plume, but i n s t e a d t o o t h e r d y n a m i c a l e f f e c t s . In t h i s c o n t e x t Johnson's (1974) o b s e r v a t i o n t h a t t h e maximum t i d a l c u r r e n t s a r e u p - i n l e t i s c r i t i c a l , s i n c e i t means t h a t the net r e s i d u a l t i d a l s t r e s s at the upper i n t e r f a c e , which depends on the c u r r e n t speed squar e d , c o u l d be u p - i n l e t . T h i s i s i m p o r t a n t because i t s u g g e s t s t h a t the h i g h e r r i g h t l e v e e and l e f t - h o o k i n g of t h e c h a n n e l a x i s i n t h i s r e a c h a r e p r o b a b l y due t o p o s i t i v e feedback between the C o r i o l i s and c e n t r i f u g a l a c c e l e r a t i o n s on the one hand and p r e f e r e n t i a l o v e r s p i l l and d e p o s i t i o n on the r i g h t l e v e e on the o t h e r , as s u g g e s t e d by Menard (1955) f o r deep-sea c h a n n e l s . F u r t h e r m o r e , the s l o p e of the i n t e r f a c e i m p l i e s a c r o s s - s t r e a m p r e s s u r e g r a d i e n t which may be s u f f i c i e n t t o b a l a n c e t h e s e a c c e l e r a t i o n s (see Chapter 8 ) . F i g . 83. L o c a t i o n s of t r a n s e c t s c o r r e s p o n d i n g t o the sonographs shown i n F i g . 81 ( l i n e 78) and F i g . 82 ( l i n e s 24, 48 and 54). Outfall ( a ) H*-^ 110 m H East 196 F i g . 8 4 . ( a ) F a c s i m i l e r e c o r d s s h o w i n g t h e p l u m e w i t h i n a n d s p i l l i n g f r o m t h e c h a n n e l a t i n c r e a s i n g d i s t a n c e s f r o m t h e o u t f a l l , 2 2 N o v e m b e r 1 9 7 6 . T h e t i m e s o f t h e p r o f i l e s f r o m t o p t o b o t t o m a r e 1 0 5 0 , 1 1 0 0 a n d 1 1 1 0 P S T . ( b ) P r o f i l e l o c a t i o n s . T h e p r o f i l e s i n F i g . 8 5 a n d i n t h e f r o n t i s p i e c e w e r e o b t a i n e d a l o n g l i n e s 67 a n d T T ' . 197 F i g . 84a i s a s e r i e s o f t h r e e p r o f i l e s s h o w i n g t h e c h a n n e l i z e d plume a t s u c c e s s i v e l y i n c r e a s i n g d i s t a n c e s f r o m t h e o u t f a l l i n t h e u p p e r and meander r e a c h e s . The p o i n t f u r t h e s t d o w n s t r e a m a t w h i c h t h e plume was d e t e c t e d i n November 1976 was l i n e 67 ( F i g . 8 5 ) . T h e s e p r o f i l e s a l l show t h e plume s p i l l i n g o v e r t h e l e v e e o f t h e o u t e r bank ( F i g . 8 4 b ) . L I N E 6 7 F i g . 85. P r o f i l e l o o k i n g d o w n - c h a n n e l a t l i n e 67 ( F i g . 84b) a t 2124 PST on 21 November 1976, s h o w i n g s u s p e n d e d m a t e r i a l a g a i n s t t h e r i g h t b ank. F i n a l l y , F i g . 86 shows two c o n s e c u t i v e a x i a l p r o f i l e s o f t h e u p p e r r e a c h , e a c h s h o w i n g t h e plume i n t h e u p p e r r e a c h and m a t e r i a l s p i l l i n g o v e r t h e c r e s t of t h e s o u t h e r n l e v e e a t bend 1. The plume i s n o t c l e a r l y e v i d e n t w i t h i n t h e c h a n n e l a t t h e b e n d , a n d may be masked by s i d e - e c h o . The p r o f i l e s s u g g e s t t h a t t h e m a t e r i a l c a u s i n g t h e e c h o a b o v e t h e l e v e e c r e s t r o s e some 5-10 m a b o v e i t s d e p t h b e f o r e e n t e r i n g t h e b e n d . T h i s may i n d i c a t e a h y d r a u l i c jump i n i t i a t e d by t h e 1° d e c r e a s e i n a x i a l s l o p e b e t w e e n t h e u p p e r and l o w e r r e a c h e s ( F i g . 2 5 ) , a s Komar ( 1 9 7 1 ) h a s s u g g e s t e d m i g h t o c c u r a t t h e mouths o f s u b m a r i n e c a n y o n s , o r t h e e f f e c t s o f c e n t r i f u g a l a c c e l e r a t i o n o f t h e f l o w i n t h e b e n d , o r b o t h . •160 m-LiNE 59 N •' V.t • j&Wj - 4 5 - 5 5 (fm) b F i g . 86. (a) P r o f i l e s p a r a l l e l i n g t h e upper r e a c h a x i s a t 1935 ( L i n e 58) and 1944 ( L i n e 59) PST on November 21, 1976. (b) P r o f i l e l o c a t i o n s . 03 199 7.1.2 Apron Regime Temperature, s a l i n i t y and suspended, p a r t i c u l a t e p r o f i l e s of the plume a t s t a t i o n 78/2 ( F i g . 73) and the c o r r e s p o n d i n g f a c s i m i l e r e c o r d s a r e p r e s e n t e d i n F i g s . 87 and 88. The deepest samples a r e 1.5-2 m from the bottom. The s a m p l i n g t e c h n i q u e i s d e s c r i b e d e l s e w h e r e (Appendix 6 ) . There i s a c l e a r c o r r e l a t i o n between the near-bottom zone of i n c r e a s e d a c o u s t i c b a c k s c a t t e r and t h a t of i n c r e a s e d suspended s o l i d s which i s the d i s c h a r g e plume. Note t h a t i n the plume, the temperature and s a l i n i t y p r o f i l e s i n d i c a t e t h a t warm f r e s h water i s b e i n g a d v e c t e d t o d e p t h , and b e i n g mixed w i t h the c o l d e r , more s a l i n e (and d e n s e r ) water above. 7.1.3 R e c h a n n e l i z e d Regime The a c o u s t i c r e c o r d s of the plume i n Chapter 3 ( F i g s . 9, 13 and 14) a r e from the r e c h a n n e l i z e d regime. A d d i t i o n a l p r o f i l e s a r e shown i n F i g . 89 which i n d i c a t e t h a t the f e a t u r e marked X i n F i g . 14 i s a s s o c i a t e d w i t h the c h a n n e l . These l i n e s were run w i t h the UBC l a u n c h u s i n g s i n g l e - l i n e t e t h e r e d s u r f a c e f l o a t s d e p l o y e d a l o n g the c h a n n e l a x i s and a shore marker, a l l w i t h l i g h t s , f o r n a v i g a t i o n . L i g h t s were n e c e s s a r y s i n c e , i n o r d e r t o a v o i d c o n t a m i n a t i o n by the d i e l - m i g r a t i n g s c a t t e r i n g l a y e r , the t r a n s e c t s were made a t n i g h t * w h i l e t h i s l a y e r was near the s u r f a c e . The i n d i c a t e d l o c a t i o n s of the l i n e s i s a p p r o x i m a t e . The l i n e s were run i n the o r d e r 2, 3 and then 1. Zones of i n c r e a s e d b a c k s c a t t e r a r e p r e s e n t above or beyond the c h a n n e l i n a l l t h r e e p r o f i l e s . The decrease i n s i g n a l i n t e n s i t y w i t h d e pth does not r e f l e c t a d e c r e a s i n g c o n c e n t r a t i o n of s c a t t e r e r s s i n c e the g a i n was c o n s t a n t . TEMP CO 32 1 S (%o) \ \ / RUP 2 A 13 Sept. 1978 TSP (ma/I) 31.7 318 .eV.' I U TEMP (°C) 32.1 S <%o) RUP 2B »J Sept. 197S .•* 1 TSP (mg/1) i.i TEMP (°C> S (%•> -* I RUP 21 14 Sopf. ;o70 TSP (mg/1) 11.0 31.7 \ \ V ii.a TEMP (°C) 3 M S (%.) —1—A— R U P 2L M Sept. TS7S TSP (mg/l) F i g . 87. Temperature, s a l i n i t y and t o t a l suspended p a r t i c u l a t e (TSP) p r o f i I e s ' from t h e plume d u r i n g t h e apron regime a t 78/2, September 1978. to o o 201 F i g . 88. Sonographs c o r r e s p o n d i n g t o p r o f i l e s i n F i g . 87, Showing the near-bottom t u r b i d zone and the s a m p l i n g b o t t l e s d e s c e n d i n g i n t o and r e m a i n i n g suspended w i t h i n i t . The bottom echo (B) and a f a l s e echo (F) a r i s i n g from i n t e r f e r e n c e w i t h a n o ther sounder are i n d i c a t e d . F i g . ^ 8 9 . ( a ) , (b) and ( c ) P r o f i l e s t a k e n i n September 1979 d u r i n g t h e r e c h a n n e l i z e d r e q i m e. Note t h e c l o u d r i s i n g o u t of t h e c h a n n e l . Depths i n m. (d) P r o f i l e l o c a t i o n s . M o 2 0 3 A s s u m i n g t h a t t h e s e z o n e s a r e a s s o c i a t e d w i t h t a i l i n g i n s u s p e n s i o n , t h e p r o f i l e s i n d i c a t e t h a t t h i s m a t e r i a l r i s e s away from t h e b o t t o m e i t h e r a f t e r e s c a p i n g t h e c h a n n e l ( L i n e 1) o r a t low a x i a l s l o p e s ( L i n e 3 ) . The c l o u d a t t h e w e s t e r n end o f L i n e 2 ( X i n F i g . 14) i s b e l i e v e d t o be an e x t e n s i o n of t h a t above t h e c h a n n e l i n L i n e 3. I t i s s u g g e s t e d t h a t t h e s e f e a t u r e s c o u l d be c a u s e d by b u o y a n t w a t e r c a r r y i n g f i n e p a r t i c l e s and r i s i n g f r o m t h e c h a n n e l as t a i l i n g s e t t l e s o u t o f s u s p e n s i o n and t h e plume l o s e s i t s e x c e s s d e n s i t y . T h i s w o u l d of c o u r s e r e q u i r e t h a t t h e s t r a t i f i c a t i o n be l e s s t h a n t h a t i n September o f t h e p r e v i o u s y e a r ( F i g . 8 7 ) . 7.2 T u r b i d i t y S u r g e s 7.2.1 M e a n d e r i n g C h a n n e l Regime The o n l y s u r g e d e t e c t e d d u r i n g t h e m e a n d e r i n g c h a n n e l phase i s t h a t d e p i c t e d i n t h e f r o n t i s p i e c e , w h i c h i s a t i m e s e r i e s o f 2 0 0 kHz echograms t a k e n a l o n g t h e t r a n s e c t s i n d i c a t e d by TT' i n F i g . 84b. The e v e n t i s i n i t i a l l y c h a r a c t e r i z e d by a r a t h e r s h a r p u p p e r i n t e r f a c e , w h i c h becomes more d i f f u s e w i t h t i m e . The a m p l i t u d e of t h e b o t t o m e c h o i s a t t e n u a t e d a t f i r s t , r e t u r n i n g t o a l e v e l above t h e F i n e L i n e t h r e s h o l d soon a f t e r t h e o n s e t of t h e e v e n t . C h a n n e l o v e r s p i l l i s e v i d e n t from t h e f i r s t , and t h e s p i l l e d m a t e r i a l s p r e a d s l a t e r a l l y away from t h e a x i s w i t h t i m e . In t h e t h i r d p a n e l ( f r o n t i s p i e c e , c ) , t h e r e i s a gap i n t h e c l o u d on t h e s o u t h s i d e o f t h e c h a n n e l . The more s o u t h e r l y c l o u d i s p r o b a b l y t h e r e s u l t of o v e r s p i l l from an u p s t r e a m meander. In a l l , t h e e v e n t was d e t e c t a b l e f o r 1.5 h. The s u r g e was o b s e r v e d a t 107 kHz and 4 2 . 5 kHz as w e l l , 204 a l t h o u g h c o n s i d e r a b l y l e s s d i s t i n c t l y a t the l a t t e r f r e q u e n c y ( F i g . 9 0 ) . These r e c o r d s are a t l a t e r t imes than t h o s e i n the f r o n t i s p i e c e . They a r e not n o r m a l i z e d w i t h r e s p e c t t o t r a n s m i t t e d sound p r e s s u r e l e v e l , so the r e l a t i v e i n t e n s i t y of the b a c k s c a t t e r cannot be i n t e r p r e t e d i n terms of the r e v e r b e r a t i o n mechanism. The r e l a t i v e i n t e n s i t y of the echoes from l a r g e a m p l i t u d e s c a t t e r e r s ( f i s h ? ) t o t h a t from the t u r b i d i t y c u r r e n t , however, a r e much h i g h e r a t 42.5 kHz than a t 107 and 200 kHz. T h i s i s c o n s i s t e n t w i t h the R a y l e i g h s c a t t e r i n g mechanism suggested i n Chapter 3. The mooring a t 76/1 ( F i g . 69) was i n p l a c e d u r i n g the s u r g e , and the v e l o c i t y r e c o r d s from the two meters a r e r e p r o d u c e d i n F i g . 70. V e r t i c a l shear i s e v i d e n t d u r i n g the o c c u r r e n c e . Because t h e changes a r e s m a l l , the c o r r e c t i n t e r p r e t a t i o n i s not o b v i o u s , and i s more d i f f i c u l t s i n c e t h e r e i s a s s u r a n c e n e i t h e r t h a t the mooring was i n the c h a n n e l nor t h a t the bathymetry a t the time was the same as the November 1976 bathymetry i n d i c a t e d i n F i g . 69. The samples i n t h e s e time s e r i e s a r e a t 10 min i n t e r v a l s . The a c t u a l s a m p l i n g i n t e r v a l was 1 min but the speeds were so low t h a t a 10 min i n t e r v a l was needed f o r a measurable i n c r e a s e i n the number of r o t o r c o u n t s . The 1 min t i m e - s e r i e s have been examined f o r changes i n d i r e c t i o n a t the time of the e v e n t , but no s i g n i f i c a n t d i f f e r e n c e s w i t h the 10 min s e r i e s were found. N e i t h e r were t h e r e any changes r e g i s t e r e d i n temperature or c o n d u c t i v i t y . 205 1352 1356 PDT F i g . 90. Sonographs of the 25 August, 1976 t u r b i d i t y c u r r e n t a t (a) 200 kHz (b) 107 kHz and (c) 42.5 kHz. A l l sounders s e t a t 0.1 ms p u l s e l e n g t h and 5°xl0° be amwidth. Note paper take-up problem w i t h the 200 kHz r e c o r d e r ( A ) , and i n t e r f e r e n c e (F) among the sounders. Compare w i t h f r o n t i s p i e c e and see F i g . 84b for t r a n s e c t l o c a t i o n . 206 7.2.2 Apron Regime Three e v e n t s were d e t e c t e d a t 2344h, 0225h and 0525h PST, on September 12, 13 and 15, r e s p e c t i v e l y a t s t a t i o n 78/2 ( F i g . 73). The 107 kHz and 200 kHz echograms a r e shown i n F i g s . 91-93. The 42.5 kHz sounder was not o p e r a t i o n a l . The p r o f i l e s a r e c h a r a c t e r i z e d by i n t e n s e r e v e r b e r a t i o n from the surge d u r i n g the passage of which the a m p l i t u d e of the bottom echo i s a t t e n u a t e d , as i n the f i r s t p a n e l of the f r o n t i s p i e c e . F o l l o w i n g the surge i s a lower a m p l i t u d e echo from a d i f f u s e t a i l . The surge passes the o b s e r v a t i o n p o i n t i n 4-6 min, and the echo from the t a i l p e r s i s t s f o r 1 t o 1.5 h. These time s c a l e s , and the v e r t i c a l l e n g t h s c a l e s (peak surge t h i c k n e s s e s = 2-5 m) a r e s i m i l a r t o those i n the August, 1976 surge ( f r o n t i s p i e c e ) . The growth i n t h i c k n e s s of the t a i l c o u l d i m p ly t h a t the surge was t h i c k e r u p s l o p e , or t h a t the t a i l s i m p l y grew w i t h t i m e , d r i v e n p a r t l y by v e r t i c a l t u r b u l e n t d i f f u s i o n and p a r t l y by the p o s i t i v e buoyancy of the water i n the f l o w . A u n i v e r s a l shape f o r the head of a d e n s i t y surge has been suggested by o t h e r workers ( K e u l e g a n , 1957,1958; M i d d l e t o n , 1966b; Simpson, 1969) on the b a s i s of l a b o r a t o r y e x p e r i m e n t s , i n which the r a t i o x/H 0= 1.5 ( F i g . 9 4 ) . Should t h i s r e l a t i o n h o l d i n t h e p r e s e n t i n s t a n c e , u 0 = 1 . 5H Q / A t (7.1) where u i s the nose v e l o c i t y and t i s the e l a p s e d time between the l e a d i n g edge of the surge and i t s c r e s t on t h e echogram ( 5 -10s). T h i s i m p l i e s nose v e l o c i t i e s r a n g i n g from 30 t o 120- cm • I s F i g . 91. Surge a t 2344 PST on 12 September 1978. (a) 200 kHz (b) 107 kHz. P u l s e lengths=0.5 ms. B a c k s c a t t e r from d i s c h a r g e plume and l a r g e - a m p l i t u d e s c a t t e r e r s a r e a l s o e v i d e n t . S l a n t i n g l i n e s a t 200 kHz (S) a r e 60 Hz i n t e r f e r e n c e . o si I 0230 F i g . 9 2 . Su rge a t 0225 h PST on 13 Sep tember 1978. (a ) 200 kHz (b) 107 k H z . Co F i g . 9 3 . Su rge a t 0525 h PST on 15 Sep tember 1979 . (a ) 200 kHz (b) 107 k H z . © 210 The u s u a l e q u a t i o n f o r t u r b i d i t y surge f l o w i s ( e . g . Komar, 1977) , u 0= 0.75[ g ' H j 1 / 2 (7.2) where g' = ( Ap / f>0 ) g . T h i s g i v e s v a l u e s of Ap r a n g i n g from 8 x 10" 3 t o 50 x 10" 3 g cm" 3 f o r t h e s e e v e n t s . F i g . 94. Two t y p e s of t u r b i d i t y s u r g e : s l u g ( s o l i d l i n e ) , and c o n t i n u o u s source (dashed l i n e , adapted from Komar, 1977). The schematic p r o f i l e of the surge i n F i g . 94 i s d i f f e r e n t from t h a t u s u a l l y assumed f o r t u r b i d i t y c u r r e n t s ( e . g . Komar, 1977; dashed l i n e i n F i g . 9 4 ) , i n which the e n t i r e head, neck and body (o r t a i l ) a re assumed t o be of u n i f o r m d e n s i t y . The l a t t e r i s based upon l a b o r a t o r y e x p e r i m e n t s w i t h s u r g e s f o l l o w e d by a neck and t a i l f e d by a c o n t i n u o u s s o u r c e , whereas a slump-g e n e r a t e d t u r b i d i t y c u r r e n t has a d i s c o n t i n u o u s s o u r c e . E x p e r i m e n t s by Shwartz e t a l (1973) w i t h d e n s i t y s l u g s , however, gave p r o f i l e s s i m i l a r t o t h a t i n F i g . 94, and a m o d i f i e d form of e q u a t i o n ( 7 . 2 ) . T h i s , i s d i s c u s s e d f u r t h e r i n t h e f o l l o w i n g c h a p t e r . The September 15 event ( F i g . 9 3 ) , which gave the weakest echo of the t h r e e , was o b s e r v e d w h i l e the c u r r e n t meters were suspended from the moored v e s s e l . The e v e n t s on September 12 and 13 o c c u r r e d b e f o r e e i t h e r the T r i s p o n d e r p o s i t i o n i n g systems or 21 1 the c u r r e n t meters had been d e p l o y e d . The a p p r o p r i a t e c u r r e n t r e c o r d s f o r September 15 have a l r e a d y been p r e s e n t e d i n F i g s . 74, 75, 79 and 80, on which the time of the event i n q u e s t i o n i s i n d i c a t e d . The d i r e c t i o n r e c o r d s ( F i g . 79) i n d i c a t e a s h i f t from u p - i n l e t t o c r o s s - i n l e t f l o w which i s most pronounced a t the near-bottom meter, and which l a g s the onset of the surge by about 4-6 min (two-minute sampling i n t e r v a l ) . The speed r e c o r d s ( F i g . 79) i n d i c a t e a r e d u c t i o n i n u p - i n l e t speed a t the two lower meters which i s a l s o g r e a t e s t a t the lowermost meter. There i s no ob v i o u s change i n the s a l i n i t y • or temperature r e c o r d s ( F i g . 7 4 ) . The p i n g e r r e c o r d d u r i n g the event i s shown i n F i g . 95. There i s a s l i g h t d e c r e a s e i n p i n g e r - b o t t o m d i s t a n c e f o l l o w i n g the onset a t 0525 h, which i s i n t e r p r e t e d as a r e a l change i n water depth due t o s h i p m o t i o n , s i n c e i t i s a l s o apparent on the echogram ( F i g . 9 3 ) . No r e v e r b e r a t i o n from the t u r b i d i t y c u r r e n t was o b t a i r i e d w i t h the 11 kHz p i n g e r . ' — ~ ~ ~-f-0 5 2 0 c ^ ^ S ^ f ^ m i m ^ ^ ^ ^ 0530 j B :::;,:;:'i?lWI2pa 0530 0540 PST F i g . 95. Record from the 11 kHz p i n g e r , 15 September 1978. A= d i r e c t p u l s e , B= b o t t o m - r e f l e c t e d p u l s e , C= p u l s e s r e f l e c t e d by c u r r e n t meters and weight (W). 212 The change i n the d i r e c t i o n r e c o r d s ( F i g . 79) i s c o n c u r r e n t w i t h a d i s p l a c e m e n t of the s h i p 50 m t o the n o r t h f o l l o w e d by a southward r e t u r n swing ( F i g . 7 5 ) . The peak i n the s h i f t t o southward c r o s s - i n l e t f l o w c o i n c i d e s w i t h the maximum northward d i s p l a c e m e n t (e.g. when the s h i p i s s t a t i o n a r y ) . T h i s , the f a c t t h a t o t h e r e q u a l l y r a p i d d i s p l a c e m e n t s of the s h i p d i d not induce such pronounced changes i n d i r e c t i o n i n the s e and t h e o t h e r r e c o r d s (Appendix 7 ) , the d e c r e a s e i n the a m p l i t u d e of t h e s h i f t w i t h d i s t a n c e from the bottom ( F i g . 79) and the absence of v e r t i c a l shear p r i o r t o the s h i f t ( F i g . 79) a l l suggest t h a t t h e d i r e c t i o n change was not s h i p - i n d u c e d . I f the d i r e c t i o n change was due t o the passage of the su r g e , then the 4-6 min l a g c o u l d be due t o the f i n i t e ' v e r t i c a l and l a t e r a l s e p a r a t i o n s of the meters from the p a t h of the nose. A v o l t a g e c o n t o u r p l o t of the s i g n a l r e c o r d e d d u r i n g the passage of the September 13 event i s p r e s e n t e d i n F i g . 96. T h i s was the o n l y event of the t h r e e f o r which any p a r t of the head r e g i o n was r e c o r d e d on t a p e , and even then the r e c o r d e r was s t a r t e d a f t e r the passage of the nose. The r e c o r d i n g and d i g i t a l p r o c e s s i n g t e c h n i q u e s have been d e s c r i b e d i n Chapter 3. In t h i s c ase the t a p e - r e c o r d i n g o u t p u t of the r e c e i v e r s a t u r a t e d a t 6 v o l t s . F i g . 97 i s a t i m e - s e r i e s of the r e v e r b e r a t i o n r e c o r d s t h r o u g h the co u r s e of the e v e n t . The same g e n e r a l f e a t u r e s a r e p r e s e n t i n the v o l t a g e c o n t o u r p l o t as i n the echogram ( F i g . 9 3 ) . The s h r i n k i n g body r e g i o n and s i m u l t a n e o u s i n c r e a s e i n the a m p l i t u d e of the bottom echo a r e e v i d e n t . CO CO f 1 1 1 1 1 1 1 I I I I 1 0.00 2.94 5.88 8.81 11.75 14.69 17.62 TIME (min) F i g . 96. C o n t o u r p l o t o f d i g i t a l l y - p r o c e s s e d 200 kHz r e v e r b e r a t i o n from t h e s u r g e a t 0225 h PST on 13 September 1978. ( A l s o see F i g . 9 2 ) . Each p o i n t i n t h e c o n t o u r g r i d i s t h e average o f 10 samples v e r t i c a l l y (0.2 ms) and o f 10 c o n s e c u t i v e t r a n s m i s s i o n s (5 s) h o r i z o n t a l l y . Note t h a t t h e 1.0-2.0 v o l t i n t e r v a l i s c r o s s - h a t c h e d n o r m a l l y t o t h e c r o s s - h a t c h i n g i n t h e 0.5-1.0 v o l t i n t e r v a l . 200 kHz: NAV = 0 13 September, 1978 r 0.0 i 2.0 ~l 1 1 4.0 6.0 AMPLITUDE SCALE (volts) x i -0. LU Q h-Z UJ _l I D O LU 146.34 X I-Q. LU Q I-Z 3 o LU 0.S m s 160.0 0.0 0.66 1.33 2.0 3.33 4.0 S.33 6.0 200 kHz: NAV = 0 13 September, 1978 I I I I I I I 0.0 2.0 4.0 6.0 AMPLITUDE SCALE (volts) 9.99 1 1 1 11.32 11.99 —i r 12.65 T " 13.32 TIME (min.) —i r~ i 1 i 13.99 14.65 15.32 1 1 15.99 F i g . 9 7 . V e r t i c a l p r o f i l e s o f t h e s i g n a l b a c k s c a t t e r e d f rom t h e s u r g e i n F i g s . 92 and 9 6 . P u l s e l e n g t h = 0 . 5 ms. No a v e r a g i n g o f t h e s i g n a l . A z e r o v o l t r e f e r e n c e i s p l o t t e d a t t h e b e g i n n i n g and end o f each p r o f i I e . 215 The r e c o r d s u g g e s t s the p o s s i b i l i t y t h a t an e s t i m a t e of the c o n c e n t r a t i o n of suspended m a t e r i a l might be d e r i v e d from the a m p l i t u d e of the bottom echo. The o b v i o u s d i f f i c u l t y w i t h such a method i s t h a t the a c o u s t i c impedance of the bottom i s l i k e l y t o change d u r i n g the passage of the e v e n t . I t i s q u i t e p o s s i b l e t h a t the reason f o r the a p parent a t t e n u a t i o n of the bottom echo d u r i n g the surge i s s i m p l y t h a t the bottom no l o n g e r e x i s t s as an i n t e r f a c e a c r o s s which t h e r e i s a marked change i n a c o u s t i c impedance. Supposing t h a t t h i s i s not the c a s e , and l e t t i n g p and p' r e p r e s e n t the p r e s s u r e a m p l i t u d e of the bottom echo at d i f f e r e n t t i m e s , then p and p' a r e i n t h e r a t i o l o g ( p ' / p ) = 2 ( A - A') (7.3) where A r e p r e s e n t s the v e r t i c a l i n t e g r a l of the a d d i t i o n a l a t t e n u a t i o n c o e f f i c i e n t due t o the presence of suspended matter ( E q u a t i o n 3.3b). Note t h a t (7.3) i s v a l i d o n l y i f the bottom r e f l e c t i o n c o e f f i c i e n t i s c o n s t a n t . From the r e s u l t s of Chapter 2, t h e r m a l a t t e n u a t i o n can be i g n o r e d , l e a v i n g o n l y the c o e f f i c i e n t f o r v i s c o u s a t t e n u a t i o n (<*,; E q u a t i o n 3.4) t o be c o n s i d e r e d . N o t i n g t h a t the v i s c o u s boundary l a y e r t h i c k n e s s ( E q u a t i o n 2.60b) i s about 0.0014 mm a t 200 kHz, the parameter b i n (3.4) i s >>1 as l o n g as i t may be presumed t h a t the p a r t i c l e r a d i i i n the surge a r e comparable t o those i n the t u r b i d i t e s (Chapter 5 ) . In t h i s case the e x p r e s s i o n (3.4) s i m p l i f i e s t o = 0.39 6 /a (7.4) where £ i s the volume f r a c t i o n o c c u p i e d by s o l i d s , a i s the p a r t i c l e r a d i u s i n mm and where a speed and f r e q u e n c y of sound 216 of 1500 m s " 1 and 200 kHz have been assumed. Making the f u r t h e r assumption t h a t e and a are c o n s t a n t i n the v e r t i c a l , then A = 2 ^ H = 3 . 9 € / a (7.5) where a f l o w t h i c k n e s s (H) of 5 m has been used ( F i g . 9 2 ) . From F i g . 97, p and p' a r e p r o p o r t i o n a l t o 2.2 and 4.3 v o l t s r e s p e c t i v e l y , which g i v e s £/a- £'/a' = 0.17 mm"1 F u r t h e r assuming t h a t a=a'=0.03 mm g i v e s £r £'=5.2X10 - 3. The e x c e s s d e n s i t y i s g i v e n by ( pa* - p o) £ . T h i s change i n t h e r e f o r e c o r r e s p o n d s t o a change i n excess d e n s i t y of 8.8X10" 3 g cm" 3. From the change i n mean b a c k s c a t t e r e d s i g n a l i n F i g . 96 between t=0 min j u s t a f t e r the nose and t=4 min, and the p r o p o r t i o n a l i t y of the b a c k s c a t t e r e d s i g n a l t o the square r o o t of suspended s o l i d s c o n c e n t r a t i o n ( F i g . 11), the e x c e s s d e n s i t y of the head i s 16 t i m e s t h a t a t t=4 min, or 0.14 g c m - 3 . U s i n g (7.2) w i t h H<5 =4 m, . t h i s c o r r e s p o n d s t o a nose v e l o c i t y of 1.7 m s " 1 . T h i s i s i n r e a s o n a b l e agreement w i t h the v a l u e of 1.2 m s _ 1 e s t i m a t e d f o r t h i s surge on the assumption of a u n i v e r s a l shape f o r the head. A s m a l l e r p a r t i c l e r a d i u s would have g i v e n a lower v a l u e . At the same t i m e , however, the surge shapes were not c o r r e c t e d f o r s i d e - e c h o , which would cause an u n d e r e s t i m a t e of nose speeds based on the u n i v e r s a l p r o f i l e . 7.3 Other E v e n t s A number of o t h e r e v e n t s of i n t e r e s t were r e c o r d e d on the a c o u s t i c sounders i n September 78, and two of t h e s e are ' 217 mentioned here. The f i r s t i s reproduced i n F i g . 98, which shows a sudden increase i n the concentration of suspended m a t e r i a l in the near bottom zone. This increase occurred at 0330 h PST, 2 h before the September 15 t u r b i d i t y c u r r e n t , and p e r s i s t e d f o r s e v e r a l hours. A simultaneous r e v e r s a l to u p - i n l e t flow took p l a c e , together with a sudden drop i n temperature and increase i n c o n d u c t i v i t y ( F i g . 74). The l a t t e r changes were most pronounced at the upper meter. 0335 0338 PST F i g . 98. T i d a l l y induced change i n the a c o u s t i c backscatter at 200 kHz at 78/2 at 0330 h PST, September 15, 1978. Depths i n fm; 0=50, 20=60 fm. Another event which i s s i m i l a r i n some respects was. detected at 78/1 ( F i g . 73) on September 16 at 0540 h PST, and i s shown i n F i g . 99. A c o u s t i c a l l y , the occurrence i s c h a r a c t e r i z e d by a d i f f u s e cloud of s c a t t e r s , presumably p a r t i c l e s , r i s i n g 30 m from the bottom, and d i s c r e t e large-amplitude s c a t t e r e r s ( f i s h ? ) which e i t h e r r i s e or move away from the bottom as. the cloud abates. S i m i l a r r i s i n g behaviour of large-amplitude 218 s c a t t e r e r s i s o b s e r v e d a t the onset of the event i n F i g . 98. In t h i s second case t o o , the onset i s f o l l o w e d by an apparent i n c r e a s e i n the c o n c e n t r a t i o n of suspended m a t e r i a l on the echogram. The event i s r e f l e c t e d i n s h i f t s t o h i g h e r t e m p e r a t u r e s and lower s a l i n i t i e s which a r e most apparent a t the bottom meter ( F i g . 100), and which a r e f o l l o w e d by t r e n d s t o lower t e m p e r a t u r e s and h i g h e r s a l i n i t i e s . A s u s t a i n e d r e v e r s a l t o u p - i n l e t f l o w d i d not o c c u r a t t h i s t i m e , but t h e r e was an a b r u p t r e v e r s a l a t a l l t h r e e meters, and a s h i f t t o southward f l o w a t the lower two, and no r t h w a r d f l o w a t the upper meter. At the lowermost meter, t h e r e i s an i n i t i a l d e c r e a s e i n speed d u r i n g the r e v e r s a l which i s f o l l o w e d by a g r a d u a l i n c r e a s e as the d i r e c t i o n s h i f t s southward. The d i r e c t i o n r e c o r d of the m i d d l e meter i s p a r t i c u l a r l y n o i s y i n the subsequent time p e r i o d , which i s t o be e x p e c t e d g i v e n the shear i n d i c a t e d by the upper and lower meters. F i g . 101 i s a p l o t of the motion of the s h i p a t i t s mooring. At the time i n q u e s t i o n t h e r e was a r a t h e r r a p i d s h i f t t o the n o r t h , which i s the most l i k e l y e x p l a n a t i o n of the abrupt s h i f t i n d i r e c t i o n t o near 0° r e g i s t e r e d a t a l l t h r e e meters. These t i d a l changes i n the l e v e l of a c o u s t i c b a c k s c a t t e r i n g from the near-bottom zone, t o g e t h e r w i t h the t i d a l p e r i o d i c i t y i n the c o n c e n t r a t i o n of suspended s o l i d s ( F i g . 7 6 ) , suggest t h a t the f i n e - s c a l e laminae o b s e r v e d i n the sediment column (e.g. F i g . 68) may indeed be t i d a l l y i n d u c e d . F i g . 9 9 . T i d a l l y i nduced change i n a c o u s t i c b a c k s c a t t e r a t 7 8 / 1 . c_> 01 o CL to "i r i r tii CD o. MIDDLE BOTTOM ~i 1 ~~r LD 1 I I 1 o~1 1 1 "l 1 1 1 T r ~r~ r i—~i 1 1 n T 1 r n ^ n ~i 1 1 r CL CL r*j - n "i T i—'—r i r i 1 LD LU a —i 1 1 1 15.87 16.12 1G.37 TIME(DAYS) 0540 PST 16.62 15.87 I I I 16.12 16.37 16.62 TIME(DAYS) U l — L j I r 1 1 1 15.87 16 12 16 37 16 S2 TIME(DAYS) F i g . 100. C u r r e n t mete r r e c o r d s a t 78/1 on 15-16 September 1978. to to o 221 O •C\J co CD (X) 15.87 16.12 16.37 TIME (DAYS)" 16.62 F i g . 101. S h i p motion a t 78/1 on 15-16 September 1978. X and Y are e a s t - w e s t and n o r t h - s o u t h d i s p l a c e m e n t s of the s h i p . 222 CHAPTER 8 THE SEDIMENT BUDGET AND CHANNELIZED TURBIDITY FLOW The d i s c u s s i o n now t u r n s t o the f o r m a t i o n and maintenance of the meandering c h a n n e l . In S e c t i o n 4.5, i t was suggested t h a t submarine c h a n n e l s i n i t i a l l y d e v e l o p i n a d i r e c t i o n d e t e r m i n e d by a c o m b i n a t i o n of the s t e e p e s t a c c e s s i b l e s l o p e and l a t e r a l c o n s t r a i n t s imposed by the l o c a l topography. T h i s i m p l i e s t h a t subsequent developments i n the p r o x i m a l zone w i l l depend upon the i n t e r a c t i o n between the c o n t i n u o u s f l o w a s s o c i a t e d w i t h the d i s c h a r g e and the m o b i l e bottom, and - t h a t t h e s e developments w i l l d e t e r m i n e the e v o l u t i o n of the system downstream. At t h e same time i t i s c l e a r t h a t the l e v e e w a l l s i n the upper r e a c h near the o u t f a l l r e p r e s e n t the most u n s t a b l e p a r t of the system, both because of the s t e e p l e v e e s l o p e s ( F i g . 26) and the r a p i d a c c u m u l a t i o n ( F i g . 2 1 ) , and are t h e r e f o r e the most p r o b a b l e < s o u r c e s of slump-generated t u r b i d i t y c u r r e n t s . F u r t h e r m o r e , because m a t e r i a l d i s p l a c e d by s l u m p i n g i s more l i k e l y t o e v o l v e i n t o a t u r b i d i t y c u r r e n t of s i g n i f i c a n t p r o p o r t i o n s on s t e e p e r a x i a l s l o p e s , the most p r o b a b l e source a r e a can be f u r t h e r r e s t r i c t e d t o the t o p end of the upper r e a c h . T h i s i s s u p p o r t e d by the h i g h Cu c o n t e n t of the t u r b i d i t e s i n the m i d d l e and lower reaches ( e . g . F i g s . 59, 62 and 6 3 ) . T h i s s u g g e s t s t h a t the upper r e a c h of the meandering c h a n n e l system r e p r e s e n t s a s t a t e of q u a s i - e q u i 1 i b r i u m between d e p o s i t i o n from the c o n t i n u o u s f l o w and removal of t h i s m a t e r i a l by b e d - l o a d t r a n s p o r t and l e v e e s l u m p i n g . These l a t t e r e v e n t s c o u l d become i n c r e a s i n g l y i m p o r t a n t i n d e t e r m i n i n g the c h a n n e l 223 morphology w i t h i n c r e a s i n g d i s t a n c e from the o u t f a l l as the c o n t i n u o u s f l o w d i s s i p a t e s due t o d e p o s i t i o n and c h a n n e l o v e r s p i l l . T h i s i s s u p p o r t e d by the downstream i n c r e a s e i n the number and t h i c k n e s s of t u r b i d i t e s i n the sediment column ( S e c t i o n 5.3, F i g . 5 5 ) , and p o s s i b l y the reduced a c o u s t i c b a c k s c a t t e r from w i t h i n the c h a n n e l downstream of the f i r s t bend ( S e c t i o n 7.1.1, F i g . 8 4 ) . To s o l v e f o r the e q u i l i b r i u m morphology of the upper r e a c h as d e t e r m i n e d by the i n t e r a c t i v e a d j u s tment of the bed and the c o n t i n u o u s d i s c h a r g e appears t o be r a t h e r d i f f i c u l t . I n s t e a d , i t i s assumed t h a t i n t h o s e reaches of a submarine c h a n n e l formed by u c o n t i n u o u s t u r b i d i t y f l o w on a c o n s t a n t s l o p e , the e q u i l i b r i u m c h a n n e l w i l l be t h a t f o r which the b u l k R i c h a r d s o n number i s c o n s t a n t . T h i s assumption i s d i s c u s s e d i n S e c t i o n 8.2.2. 8.1 Sediment Budget The i s o p a c h maps i n F i g s . 17, 18 and 21 were i n t e g r a t e d by a p l a n i m e t e r t o o b t a i n the volume of d e p o s i t e d t a i l i n g a t the time of each survey ( F i g . 102, T a b l e X I I ) . The t a i l i n g d e p o s i t was a r b i t r a r i l y s e p a r a t e d from waste dump m a t e r i a l by assuming t h a t each sou r c e c o n t r i b u t e d e q u a l l y t o the volume of m a t e r i a l i m m e d i a t e l y a d j a c e n t t o the s a d d l e p o i n t between the two d e p o s i t s , as shown by the l i n e XX' i n these f i g u r e s . Assuming a dry b u l k d e n s i t y of 1.3 g c m - 3 f o r the t a i l i n g (see S e c t i o n 5.2.1), the mass of the t a i l i n g d e p o s i t was computed and compared t o the t o t a l r e p o r t e d d i s c h a r g e . The computed v a l u e s a r e q u i t e s e n s i t i v e t o the v a l u e of the dry b u l k 224 d e n s i t y and, t o a l e s s e r e x t e n t , t o the unknown speed of sound i n the d e p o s i t (1500 m s " 1 was assumed). S i n c e both parameters v a r y w i t h d e p o s i t t h i c k n e s s due t o co m p a c t i o n , the assumption of c o n s t a n t v a l u e s i s not s t r i c t l y v a l i d . F u r t h e r m o r e , the c o n t i n u o u s s e i s m i c p r o f i l e r i s i n s e n s i t i v e t o t a i l i n g d e p o s i t s much l e s s than 1.5 m t h i c k because of a d e c a y i n g o s c i l l a t i o n ( r i n g i n g ) • i n the o u t g o i n g p u l s e . An attempt t o i n c o r p o r a t e t h i s m a t e r i a l i n the t o t a l volume was made by e x t r a p o l a t i n g t o z e r o t h i c k n e s s ( F i g . 102). Good agreement e x i s t s between the v a l u e s f o r t he t o t a l t a i l i n g d e p o s i t e d and the t o t a l t a i l i n g d i s c h a r g e d ( T a b l e X I I ) . 3.0 -, * 1974 o 1975 2.0 -i • 1977 < UJ cc < 1.0 10 15 THICKNESS (m) F i g . 102. Area c o v e r e d by t a i l i n g of a g i v e n t h i c k n e s s f o r d i f f e r e n t CSP s u r v e y s . The t a i l i n g d e p o s i t was d i v i d e d i n t o a p r o x i m a l and a d i s t a l zone s e p a r a t e d by the l i n e YY' a t the lower end of the 225 meander r e a c h ( F i g s . 17, 18 and 21) and the volume of the d e p o s i t was d e t e r m i n e d f o r the p r o x i m a l zone i n the same manner as d e s c r i b e d above. The e q u i v a l e n t mass a c c u m u l a t i o n r a t e was q u i t e c o n s i s t e n t f o r the two p e r i o d s w i t h a mean of 144 kg s _ 1 , l e a v i n g some 240 kg s~ 1 of m a t e r i a l t o be t r a n s p o r t e d out of the p r o x i m a l zone (Table X I I I ) . Assuming t h a t most of t h i s m a t e r i a l i s t r a n s p o r t e d by c h a n n e l i z e d t u r b i d i t y f l o w , the problem remains as t o the r e l a t i v e amounts c a r r i e d by c o n t i n u o u s and -surge-type t u r b i d i t y c u r r e n t s . T a b l e X l l a . Volume of t a i l i n g d e p o s i t from CSP s u r v e y s . Date Volume ( 1 0 6 m 3) 29 Nov. 74 21 Oct. 75 12 J a n . 77 12.58 1 5.64 1 9.82 T a b l e X I I b . Average d i s c h a r g e r a t e s d u r i n g the i n t e r v a l s between CSP s u r v e y s . I n t e r v a l ( y e a r s ) R e p o r t e d Rate (kg s- 1) E s t i m a t e d Rate (kg s " 1) 74- 75 75- 77 420 352 385 348 T a b l e X I 1 1 . Observed mass a c c u m u l a t i o n r a t e s i n the p r o x i m a l zone d u r i n g the i n t e r v a l between CSP s u r v e y s I n t e r v a l ( y e a r s ) A c c u m u l a t i o n Rate (kg s" 1 ) 74- 75 75- 77 1 48 1 40 226 8.2 Two-Dimensional T u r b i d i t y Flow: Theory I t i s assumed t h a t the s o l i d - f l u i d m i x t u r e i n t u r b i d i t y c u r r e n t s can be appro x i m a t e d by a f l u i d of the same b u l k d e n s i t y and a p p r o p r i a t e v i s c o s i t y . Such f l o w s may then be r e g a r d e d as d e n s i t y c u r r e n t s . 8.2.1 Surge Flow For d e n s i t y surges on a h o r i z o n t a l bottom, Benjamin (1968, pp. 241-243) d e r i v e d the r e l a t i o n u c 2 = C 0 2g'H o (8.1) where u 0 i s the nose speed, C 0 a d i m e n s i o n l e s s c o n s t a n t , - H 0 the t h i c k n e s s of the head, g'= Apq/pa , g the a c c e l e r a t i o n due t o g r a v i t y , A^ o the e x c e s s d e n s i t y i n t h e lower l a y e r and f>B the d e n s i t y of the ambient f l u i d ( F i g . 103a). E q u a t i o n (8.1) i s c o n s i s t e n t w i t h the e x p e r i m e n t a l r e s u l t s of Keulegan (1957, 1958) and M i d d l e t o n (1966b), who found t h a t C 0 had an average v a l u e of 0.75 and was r e l a t i v e l y c o n s t a n t f o r s l o p e s up t o 2.3° ( M i d d l e t o n , 1966b). Benjamin's d e r i v a t i o n was f o r a h o r i z o n t a l bottom i n a frame of r e f e r e n c e moving w i t h the nose. In the absence of m i x i n g between the two f l u i d s , the p r e s s u r e i s ta k e n t o be c o n s t a n t a t the l e v e l of the nose ( &H 0, F i g . 103a) w i t h i n the denser l a y e r . E q u a t i o n (8.1) i s o b t a i n e d by i n v o k i n g B e r n o u l l i ' s theorem t o o b t a i n the p r e s s u r e a t . the nose s t a g n a t i o n p o i n t , and assuming the p r e s s u r e t o be h y d r o s t a t i c a t s u f f i c i e n t l y l a r g e d i s t a n c e s b o t h up- and down-stream of the nose and head r e g i o n . I t i s the d i f f e r e n c e i n t h e s e h y d r o s t a t i c p r e s s u r e s which d r i v e s the f l o w and which i s b a l a n c e d by the s t r e s s between the f l u i d s a s s o c i a t e d w i t h t h e . b r e a k i n g head wave. F r i c t i o n a t the bed i s i g n o r e d . 227 F i g . 103. Schematic diagram of a d e n s i t y s u r g e . (a) on a h o r i z o n t a l bottom, (b) on a s l o p i n g bottom. Except f o r the v e l o c i t y p r o f i l e a t x 3 , f o r which the v e l o c i t i e s a r e r e l a t i v e t o the bed, v e l o c i t i e s and c o o r d i n a t e s are r e l a t i v e t o the nose. S i n c e H 0= 2H i n the flume e x p e r i m e n t s , Benjamin (1968) o b t a i n e d Co = (1-25) 1 / 2 (8.2) where S i s the r a t i o of nose h e i g h t t o head t h i c k n e s s ( F i g . 103a). Flume e x p e r i m e n t s a l s o i n d i c a t e d a u n i v e r s a l non-d i m e n s i o n a l shape f o r the p r o f i l e of a d e n s i t y c u r r e n t head (see S e c t i o n 7.2.2), w i t h 8 a p p r o x i m a t e l y e q u a l t o 0.2, g i v i n g C 0= 0.77, which i s v e r y c l o s e t o the e x p e r i m e n t a l v a l u e . T h i s t h e o r y can be extended t o a s l o p i n g bottom. R e f e r r i n g t o F i g . 103b and assuming n o n - l i n e a r , i n v i s c i d t w o - d i m e n s i o n a l f l o w , the downdope. f o r c e p 0gsin^s i s b a l a n c e d by the p r e s s u r e g r a d i e n t due t o the s u r f a c e s l o p e i n the r o t a t e d c o o r d i n a t e system. The p r e s s u r e d i f f e r e n c e between x, and x c i s P, ~ Po = f 0u 0 2/2 (8.3a) from the i n t e g r a l w i t h r e s p e c t t o x of the e q u a t i o n f o r the 228 momentum " component p a r a l l e l t o t h e b e d . The p r e s s u r e d i f f e r e n c e b e t w e e n t h e h y d r o s t a t i c s e c t i o n s ( x 3 a n d x 0 ) up- a n d d o w n - s t r e a m . o f t h e n o s e i s P 3 " Po = Apghcos^S (8.3b) a s s u m i n g t h a t t h e f l o w s p e e d d i f f e r s v e r y l i t t l e f r o m u Q b e t w e e n x„ a n d x3 a t a s u f f i c i e n t h e i g h t a b o v e t h e h e a d . T h i s l i m i t s t h e ar g u m e n t t o c a s e s where H 0 i s much l e s s t h a n t h e w a t e r d e p t h . U n l i k e t h e h o r i z o n t a l c a s e , t h e r e i s now a p r e s s u r e g r a d i e n t p a r a l l e l t o t h e b o t t o m w i t h i n t h e d e n s e r l a y e r , w h i c h i n t h e a b s e n c e o f f r i c t i o n i s g i v e n by t h e component o f g r a v i t y a c t i n g p a r a l l e l t o t h e s l o p e on t h e e x c e s s d e n s i t y , p A - p 3 = A p g s i n ^ ( x z - x 3 ) ( 8 . 3 c ) I f t h e h e a d i s f o l l o w e d by c o n t i n u o u s f l o w f r o m a s t e a d y s o u r c e , t h i s p r e s s u r e g r a d i e n t w i l l be b a l a n c e d by f r i c t i o n a t a s u f f i c i e n t d i s t a n c e f r o m t h e h e a d r e g i o n . S i n c e t h e p r e s s u r e must be c o n t i n u o u s a c r o s s t h e n o s e , p, =p z a n d u 0 2 = • g ' H . f c ' c o s ^ + 2 ^ - x 3 j sin/3 ( 8 . 4 ) where C 0 i s g i v e n by ( 8 . 2 ) a n d x 3 h a s been t a k e n where H=H Q/2. S h w a r t z e t a l ( 1 9 7 3 , p.15) p r e s e n t a s i m i l a r r e s u l t , b u t w i t h o u t e x p l a n a t i o n . T h e i r e x p e r i m e n t s w i t h s a l i n e s l u g s v e r i f i e d t h e f o r m o f t h i s e q u a t i o n up t o s l o p e s o f 16°, w i t h C o z = 0.50 a n d ( x i -x 3 ) / H 0 = 1.6-1.7, w h i c h was c l o s e t o t h e o b s e r v e d r a t i o ( a b o u t 2) of s l u g l e n g t h , s e t e q u a l t o x 2 - x 3 , t o nos e h e i g h t . A l t h o u g h ( 8 . 4 ) i s n o t a new r e s u l t , an e q u a t i o n o f t h e f o r m ( 8 . 1 ) w h i c h i s i n d e p e n d e n t o f s l o p e i s assumed i n most o f t h e g e o l o g i c a l l i t e r a t u r e ( e . g . S c h e i d e g g e r , 1975 p. 218; Komar, 1 9 7 7 ) . I n f a c t , h o w e v e r , e v e n M i d d l e t o n ' s ( 1 9 6 6 b ) r e s u l t s a r e r e p r e s e n t e d r a t h e r w e l l by e q u a t i o n ( 8 . 4 ) , a s i n d i c a t e d i n F i g . 229 104, a l t h o u g h t h i s has not appeared i n the l i t e r a t u r e . M i d d l e t o n ' s e x p e r i m e n t s were made w i t h s a l i n e heads f o l l o w e d by c o n t i n u o u s f l o w . The l i n e a r dependence of u0 on s i n ^ , which i s q u i t e e v i d e n t i n F i g . 104, i s s t r o n g e r than i n the r e s u l t s of Shwartz e t a l (1973) f o r s a l i n e s l u g s . G i v e n (8.4)., t h i s i s not unexpected, s i n c e t h e r a t i o ( x ^ - X j )/H(, c o u l d be l a r g e r f o r a head f o l l o w e d by c o n t i n u o u s f l o w . T h i s r a t i o i s e s s e n t i a l l y the d i m e n s i o n l e s s d i s t a n c e over which the p r e s s u r e g r a d i e n t (8.3c) i s not b a l a n c e d by f r i c t i o n , as i t i s i n the c o n t i n u o u s f l o w . From F i g . 104 i t would appear t h a t t h i s d i s t a n c e d e c r e a s e s w i t h i n c r e a s i n g d i s c h a r g e . 240 cm Js —i 1 1 0.05 0.1 1.05 sin /5 F i g . 104. P l o t s of 2 1 / 2 C 0 v e r s u s bottom s l o p e u s i n g M i d d l e t o n ' s (1966b) r e s u l t s . Those of Shwartz e t a l (1973) a r e shown by s o l i d l i n e s ( a : s a l i n e s l u g s ; b: t u r b i d i t y s l u g s ) . 230 I t has been assumed thus f a r t h a t t h e r e i s no motion i n the head. In the e x p e r i m e n t s , however, i t was shown t h a t pronounced m i x i n g o c c u r s i n the wake of the head. T h i s s e t s up a mean c i r c u l a t i o n i n the denser l a y e r ( F i g . 103) and would d i s s i p a t e the f l o w i n the absence of a c o n s t a n t s u p p l y t o the head from the t r a i l i n g f l o w . In a s e t of flume e x p e r i m e n t s w i t h an a r r e s t e d head on a h o r i z o n t a l bottom moving a t the speed of the mean f l o w (Simpson, 1969, 1972; B r i t t e r and Simpson, 1978), i t has been shown t h a t the m i x i n g i s due p a r t l y t o the f o r m a t i o n of K e l v i n - H e l m h o l t z - l i k e b i l l o w s b e h i n d the head and p a r t l y t o a complex p a t t e r n of l o b e and c l e f t s t r u c t u r e s d r i v e n by the buoyant f l u x of ambient water o v e r r i d d e n by the nose. The s k e t c h of the mean f l o w i n F i g . 103b i s based on F i g . 12 i n Simpson, M a j i s f i e l d and M i l f o r d ( 1 9 77), and i s s i m i l a r t o F i g . 9 i n M i d d l e t o n (1966b). Benjamin (1968) argued t h a t the p r e s s u r e g r a d i e n t s d r i v i n g the c i r c u l a t i o n i n the head would be s m a l l i n comparison t o the d i f f e r e n c e i n h y d r o s t a t i c p r e s s u r e a c r o s s the head and t h e r e f o r e might not s i g n i f i c a n t l y a f f e c t e i t h e r the form of (8.1) or the v a l u e of C 0. Simpson (1972), however, o b t a i n e d the e m p i r i c a l r e l a t i o n s h i p o"=0.61Re-°' 2 3 (8.5) f o r 300<Re<1100 where Re i s the Reynolds number. M i d d l e t o n (1966b) s u g g e s t e d t h a t t h e shape of t h e head might v a r y w i t h Re, and Keulegan (1957, 1958) n o t e d a s l i g h t tendency f o r C e t o i n c r e a s e w i t h Re. A v a l u e of Re of about 5x10 6 i s t o be e x p e c t e d f o r c h a n n e l - f u l l surges i n Rupert I n l e t , and u s i n g (8.2) and ( 8 . 5 ) , C o=0.98, y i e l d i n g a 30% i n c r e a s e i n the v e l o c i t y e s t i m a t e from ( 8 . 1 ) . Simpson's e x p e r i m e n t s , however, were w i t h d e n s i t y 231 c u r r e n t s f o r which HQ was about h a l f the t o t a l d e p th and may not a p p l y t o the case of g r e a t depth b e i n g c o n s i d e r e d . They i n d i c a t e n o n e t h e l e s s t h a t c l a r i f i c a t i o n of the Reynolds number dependence of both C 0 and the shape of the head i s needed. The i m p l i c a t i o n s of the i n t e r n a l c i r c u l a t i o n i n the head t o sediment t r a n s p o r t by t u r b i d i t y s u r ges a r e r e a s o n a b l y c l e a r . In p a r t i c u l a r the upwards mean f l o w b e h i n d the nose, which i s d r i v e n p a r t l y by the v e r t i c a l c o n v e c t i o n of o v e r r i d d e n ambient f l u i d and p a r t l y by e n t r a i n m e n t i n the wake of the -head, may det e r m i n e the maximum g r a i n s i z e which can be t r a n s p o r t e d i n s u s p e n s i o n . A l l e n (1971) has s u g g e s t e d t h a t the i n c o r p o r a t i o n of ambient f l u i d by c o n v e c t i o n a t the base of the nose c o n t r i b u t e s t o the d i l u t i o n of t h e m i x t u r e and s h o u l d be i m p o r t a n t i n the t r a n s f o r m a t i o n of slumps i n t o t u r b i d i t y c u r r e n t s . 8 . 2 . 2 C o n t i n u o u s Flow For c o n t i n u o u s d e n s i t y c u r r e n t f l o w , the e q u a t i o n s of motion a r e w r i t t e n f o r a frame of r e f e r e n c e w i t h the x - a x i s p a r a l l e l t o the bed as i n the body of the surges i n F i g . 104. V e r t i c a l l y i n t e g r a t i n g the l i n e a r i z e d e q u a t i o n f o r the downslope component of momentum g i v e s ?a + * i = ApgHsin/3 (8.6) where ?0 and J\- a re the shear s t r e s s a t the bed and a t the upper i n t e r f a c e . H i s the flo w t h i c k n e s s and Ap the v e r t i c a l l y averaged e x c e s s d e n s i t y . The s t r e s s e s a r e e x p r e s s e d i n terms of drag c o e f f i c i e n t s 7. +rL= ( f . + f i ) pau2/2 = f f . u 2/2 (8.7) where u i s the v e r t i c a l l y - a v e r a g e d downslope speed. The drag 232 c o e f f i c i e n t f 0 i s e q u a l t o one f o u r t h the Darcy-Weisbach f r i c t i o n f a c t o r f o r open c h a n n e l f l o w , which depends on the r e l a t i v e roughness ( r a t i o of roughness h e i g h t t o f l o w t h i c k n e s s ) of the bed, and which can be o b t a i n e d from a Moody diagram f o r p i p e f l o w (Moody, 1944; Harleman , 1961). In an a n a l y s i s of the a v a i l a b l e d a t a , Bo Pederson (1980, p. 38) has c o n c l u d e d t h a t t-L depends o n l y on the Reynolds number. The c o e f f i c i e n t of bottom d r a g , on the o t h e r hand, undergoes a s h a r p i n c r e a s e a f t e r t r a n s i t i o n from s u b c r i t i c a l t o s u p e r c r i t i c a l f l o w as the p o s i t i o n of the maximum i n the n o n - d i m e n s i o n a l v e l o c i t y p r o f i l e s h i f t s c l o s e r t o the bed. T h i s t r a n s i t i o n o c c u r s a t a c r i t i c a l v a l u e of the b u l k R i c h a r d s o n number R i = g'H/u 2 (8.8) which i s u s u a l l y c l o s e t o u n i t y . Both the s u b c r i t i c a l and s u p e r c r i t i c a l f l o w s have d i s t i n c t n o n - d i m e n s i o n a l v e l o c i t y and d e n s i t y p r o f i l e s which a r e independent of the R i c h a r d s o n number. From ( 8 . 6 ) , (8.7) and ( 8 . 8 ) , R i = f / ( 2 s i n ( 3 ) (8.9) so t h a t i t i s c l e a r t h a t depending upon the v a l u e of f ( = f 0 + f ; ), the c r i t i c a l R i c h a r d s o n number w i l l be reached on a s u f f i c i e n t l y s t e e p s l o p e . Assuming R i ( c r i t ) = 1 , Komar (1971) c o n c l u d e d t h a t f l o w would be s u p e r c r i t i c a l i n deep-sea canyons and c h a n n e l s w i t h a x i a l s l o p e s g r e a t e r than 0.5° f o r f=0.02. (See a l s o Hand, 1974 and Komar, 1975 f o r d i s c u s s i o n s . ) The a n a l y s i s by Bo Pedersen (1980, p. 94) i n d i c a t e s t h a t R i ( c r i t ) < 1 , b e i n g between 0.2 and 0.4 f o r f=0.004-0.06, and t h a t f o r t h i s range i n f , t r a n s i t i o n to s u p e r c r i t i c a l f l o w o c c u r s on s l o p e s g r e a t e r t h a n 0.6-6°. The t r a n s i t i o n p o i n t depends on the r e l a t i v e roughness 233 of the bed. E q u a t i o n (8.6) i s i n c o m p l e t e because the f l u x of low momentum f l u i d i n t o the d e n s i t y c u r r e n t a t i t s upper boundary has been n e g l e c t e d . When e n t r a i n m e n t i s i n c l u d e d , the e q u i v a l e n t of (8.9) becomes (Bo Pedersen, 1980, p.92) R i = f + w,r u (8.10) 2sin jS where we i s the e n t r a i n m e n t v e l o c i t y and F i s a f a c t o r which depends upon the shape of the v e l o c i t y p r o f i l e ; t h a t i s , whether the f l o w i s s u b c r i t i c a l or s u p e r c r i t i c a l . For s u b c r i t i c a l f l o w , we /u = 0.072sin i6 (8.11) and t h e second term i n the numerator i s u n i m p o r t a n t , and (8.10) r e d u c e s t o ( 8 . 9 ) . R e a r r a n g i n g e q u a t i o n (8.9) g i v e s u 2= _2_ [ g'Hsin/3 ] (8.12) f which i s a Chezy-type e q u a t i o n . The q u e s t i o n a r i s e s as t o the a p p l i c a b i l i t y of e q u a t i o n s (8.1) or (8.3) and (8.11) t o t u r b i d i t y c u r r e n t s . There has been o n l y one m o d i f i c a t i o n of t h e s e e q u a t i o n s t o account f o r the p o s s i b l e e f f e c t t h a t p a r t i c l e s e t t l i n g might have on the dynamics of the f l o w . T h i s m o d i f i c a t i o n i s the a u t o s u s p e n s i o n t h e o r y f o r c o n t i n u o u s t u r b i d i t y f l o w d e r i v e d by Bagnold (1962) and m o d i f i e d by Inman (1963). Very b r i e f l y , the p a r t i c l e i s assumed t o move w i t h the mean f l o w p a r a l l e l t o t h e bed, and would n o r m a l l y s e t t l e toward the bed at a r a t e W j c o s ^ where ws i s the p a r t i c l e s e t t l i n g v e l o c i t y . The g r a v i t a t i o n a l a c c e l e r a t i o n g s i n p p a r a l l e l t o the bed and a c t i n g on the p a r t i c l e does work on t h e f l u i d , and i n stead y f l o w t h i s work must be b a l a n c e d by t h a t done a g a i n s t f r i c t i o n a t the bed and a t the upper i n t e r f a c e 234 and t o m a i n t a i n the p a r t i c l e i n s u s p e n s i o n . The r e s u l t i s + JI = ApgHt sin,a -w s/u ] (8.13) which i s a m o d i f i e d form of (8.6) and i m p l i e s t h a t f o r a c o n t i n u o u s t u r b i d i t y c u r r e n t t o e x i s t the i n e q u a l i t y ws < usin/3 (8.14) must be s a t i s f i e d . N e i t h e r t h i s c o n d i t i o n nor the v a l i d i t y of the r e l a t i o n (8.13) have been v e r i f i e d e x p e r i m e n t a l l y . E x p e r i m e n t s w i t h c o n t i n u o u s f l o w t u r b i d i t y c u r r e n t s have u s u a l l y been conducted w i t h s u s p e n s i o n s of c l a y p a r t i c l e s w i t h n e g l i g i b l y s m a l l s e t t l i n g v e l o c i t i e s . A s h i d a and E g a s h i r a (1976) , however, have s u c c e s s f u l l y g e n e r a t e d c o n t i n u o u s t u r b i d i t y c u r r e n t s w i t h 0.03> mm d i a m e t e r q u a r t z p a r t i c l e s (w=0.08 cm s" 1) on s l o p e s of 1°. (U=15 cm s - 1 ; u sin|3= 0.26 cm s _ 1 ) . T h e i r ' s appear t o be the o n l y measurements of v e l o c i t y and d e n s i t y p r o f i l e s w i t h i n a c o n t i n u o u s f l o w t u r b i d i t y c u r r e n t c o m p r i s e d of l a r g e p a r t i c l e s . These p r o f i l e s a r e i n q u a l i t a t i v e agreement w i t h Bo Pedersen's u n i v e r s a l p r o f i l e s f o r s u b c r i t i c a l d e n s i t y c u r r e n t f l o w . W i t h r e g a r d t o ( 8 . 1 3 ) , i t i s c l e a r t h a t i f w/u i s s u f f i c i e n t l y s m a l l then the c o r r e c t i o n term can be i g n o r e d . The t h e o r y has been c r i t i c i z e d by M i d d l e t o n (1966a) and by Chu, P i l k e y and P i l k e y (1979), but t h i s c r i t i c i s m has not been s p e c i f i c , perhaps because of the d i f f i c u l t i e s e n c o u n t e r e d when a t t e m p t i n g t o improve upon (8.13) by i n c o r p o r a t i n g the s e t t l i n g v e l o c i t y i n the momentum e q u a t i o n s . . In the remainder of t h i s c h a p t e r , s u b c r i t i c a l c o n t i n u o u s t u r b i d i t y f l o w w i l l be d e s c r i b e d by e q u a t i o n s (8.6) th r o u g h ( 8 . 9 ) , p r o v i d e d (8;14) i s s a t i s f i e d . T h i s p r o c e d u r e i s s u p p o r t e d by the r e s u l t s of A s h i d a and 235 E g a s h i r a (1975). 8.3 T u r b i d i t y Flow and the Meandering Chan n e l . The r e s u l t s of the p r e v i o u s s e c t i o n w i l l now be a p p l i e d t o f l o w i n the meandering c h a n n e l , w i t h the i n t e n t i o n of d e t e r m i n i n g the r e l a t i v e c o n t r i b u t i o n s of c o n t i n u o u s and s u r g e -type t u r b i d i t y c u r r e n t f l o w t o the t r a n s p o r t of t a i l i n g a l o n g the lower r e a c h . 8.3.1 . Upper Reach: Mean Flow R e f e r r i n g t o the c r o s s - c h a n n e l p r o f i l e s i n F i g . 26 and the a x i a l s l o p e i n F i g . 25, the i n c r e a s e i n c r o s s - s e c t i o n a l a r e a of the c h a n n e l between l i n e s 1 and 2 i n d i c a t e s a h i g h r a t e of e n t r a i n m e n t , which t o g e t h e r w i t h the s t e e p s l o p e i n t h i s upper s e c t i o n s u g g e s t s t h a t the f l o w i s s u p e r c r i t i c a l a t the o u t f a l l and may undergo a h y d r a u l i c jump. In c o n t r a s t , the s l o p e i s r e l a t i v e l y c o n s t a n t i n the i n t e r m e d i a t e s e c t i o n of the upper r e a c h , and below l i n e 2 the c h a n n e l c r o s s - s e c t i o n tends t o d e c r e a s e downstream. Both the c r o s s - c h a n n e l changes i n r e l i e f ( F i g . 26) and the a c o u s t i c -s o u n d i n g runs i n the neighbourhood of l i n e 5 ( F i g s . 81 and 82) suggest t h a t t h e r e may be a c r o s s - s t r e a m momentum ba l a n c e between the i n e r t i a l ( C o r i o l i s and c e n t r i p e t a l ) a c c e l e r a t i o n s of the f l o w on the one hand and the p r e s s u r e g r a d i e n t due t o the i n t e r f a c i a l s l o p e on the o t h e r . That i s , f o r a l e f t w a r d - c u r v i n g c h a n n e l w i t h u p o s i t i v e i n the downstream d i r e c t i o n , f*u + u 2 / r = g'aH/W (8.15) where f * i s the C o r i o l i s parameter (1.1x10'* s _ 1 ) , r i s the 236 c h a n n e l r a d i u s of c u r v a t u r e (1300 m) and AH/W i s the s l o p e of the i n t e r f a c e (about 0.11 and upward t o the r i g h t ; see F i g s . 81 and 8 2 ) . Komar (1969) used a s i m i l a r t r a n s v e r s e f o r c e b a l a n c e t o e s t i m a t e t u r b i d i t y c u r r e n t v e l o c i t i e s i n a meander of t h e Monterey Deep-Sea Channel by e s t i m a t i n g the i n t e r f a c i a l s l o p e from the c r o s s - c h a n n e l d i f f e r e n c e i n l e v e e h e i g h t s . For a g i v e n mass c o n c e n t r a t i o n M of t a i l i n g i n s u s p e n s i o n , t h e e x c e s s d e n s i t y of the m i x t u r e i n a f l u i d of d e n s i t y w i l l be Af> = ^p:-p0^ M - . (8.16) where pj i s the g r a i n d e n s i t y (2.7 g cm' 3; a l s o see E q u a t i o n 6.1). S u b s t i t u t i o n of v a r i o u s v a l u e s of u i n (8.15) and u s i n g (8.16) g i v e s the v a l u e s f o r the v e r t i c a l l y - a v e r a g e d c o n c e n t r a t i o n (M), volume t r a n s p o r t Q 0(=uA; A=450 m2 a t l i n e 5) and sediment mass t r a n s p o r t Q'a (=uAM) a t l i n e 5 g i v e n i n T a b l e X l V a (p. 239). The a c t u a l v e r t i c a l l y - a v e r a g e d speed must be between about 0.4 and 0.8 m s " 1 i n o r d e r t h a t the c a l c u l a t e d v a l u e s of M be s i m i l a r t o the o b s e r v e d mean c o n c e n t r a t i o n s ( e.g. F i g . 11), and t h a t the mass t r a n s p o r t Qd not exceed the r a t e of t a i l i n g d i s c h a r g e (about 380 kg s " ' ) . F o r t h i s range of v e l o c i t i e s the R i c h a r d s o n number (8.8) ranges from 0.095 t o 0.082 f o r H=10 m, and from ( 8 . 9 ) , f ranges from 0.0073 t o 0.0063 f o r sin/? = 0.038 (T a b l e X l V a ) . These v a l u e s a r e c o n s i s t e n t w i t h s u b c r i t i c a l f l o w (Bo Pedersen, 1980 p. 9 4 ) . A mean f l o w speed i n the range 0.4 to.0.8 m s - 1 i s a l s o r e a s o n a b l y c o n s i s t e n t w i t h the s i z e of m a t e r i a l c o n s t i t u t i n g the bed .from the v i e w p o i n t of the t h r e s h o l d v e l o c i t y f o r g r a i n movement ( e . g . M i l l e r , McCave and Komar, 1977). F i n a l l y , t hese 237 v e l o c i t i e s c o r r e s p o n d t o Reynolds' numbers of 3.1x10 s t o 1 . 2 x l 0 7 . From Bo Pedersen (1980, p.38), a r e a s o n a b l e range of v a l u e s f o r f t r a n g i n g from 0.004-0.002. The f r i c t i o n c o e f f i c i e n t a t the bed ( f 0 ) i s t h e r e f o r e about 0.004, g i v i n g a r e l a t i v e roughness of 0.0004. T h i s i s 50 t o 100 t i m e s g r e a t e r than the r a t i o of the g r a i n - s i z e of the bed m a t e r i a l t o the f l o w t h i c k n e s s , and s u g g e s t s t h a t the s c a r r i n g of t h e l e v e e w a l l s ( F i g . 22) c o n t r i b u t e s an e f f e c t i v e r o u g h n e s s - h e i g h t of 4 mm. The v a l u e s of t0 and f j a r e s i m i l a r i n r a t i o t o , but s m a l l e r by a f a c t o r of 2-3 than those of 0.01 and 0.009 assumed by Komar (1971) f o r t u r b i d i t y f l o w i n submarine canyons. Komar (1969) assumed f„=0.007 f o r f l o w i n Monterey Deep-Sea C h a n n e l , which i s c l o s e r t o the v a l u e o b t a i n e d h e r e . Because of the d i f f e r e n c e i n s c a l e between deep-sea systems and the Rupert I n l e t c h a n n e l , the g e n e r a l agreement among these f r i c t i o n c o e f f i c i e n t s s u g g ests t h a t the f l o w parameters and r o u g h n e s s - h e i g h t s s c a l e s i m i l a r l y . Flow a t C o n s t a n t R i c h a r d s o n Number The assumption of c o n s t a n t R i i s based on the o b s e r v a t i o n t h a t s t e a d y , t w o - d i m e n s i o n a l d e n s i t y c u r r e n t s on an i n c l i n e of c o n s t a n t s l o p e tend r a p i d l y t o a c o n s t a n t b u l k R i c h a r d s o n number (Bo P e d e r s e n , 1980 p. 103)'. S i n c e the f l u x of e x c e s s d e n s i t y /jpH p a r a l l e l t o the bed i s c o n s t a n t f o r f l o w i n t h i s s t a t e , the v e l o c i t y u, and t h e r e f o r e Ap H must a l s o be c o n s t a n t . The s l o p e i s a p p r o x i m a t e l y c o n s t a n t i n the upper r e a c h below l i n e 2 ( F i g . 25, i n s e t ) , as i s the c h a n n e l depth ( F i g . 26) and presumably, t h e r e f o r e , the f l o w t h i c k n e s s (H). As a r e s u l t the assumption t h a t R i = c o n s t a n t i m p l i e s t h a t Ap i s a l s o 238 c o n s t a n t . In the presence of e n t r a i n m e n t a t the upper boundary and d e p o s i t i o n on the bed, t h i s s t a t e can be m a i n t a i n e d o n l y i f the c h a n n e l c r o s s - s e c t i o n d e c r e a s e s downstream, which i s o b s e r v e d ( F i g . 2 6 ) . F u r t h e r m o r e i t i s r e a d i l y shown by c o n s i d e r i n g c o n s e r v a t i o n of volume and sediment t h a t under t h e s e c o n d i t i o n s the volume r a t e of e n t r a i n m e n t (Q e) must be l e s s than the volume r a t e of o v e r s p i l l ( Q 5 ) , i r r e s p e c t i v e of the s o l i d s c o n c e n t r a t i o n i n the s p i l l e d m a t e r i a l , and t h a t Q5 -Qe = (Q; +Q^)/M (8.17) where Q'6 and a r e the mass r a t e s of d e p o s i t i o n and o v e r s p i l l , r e s p e c t i v e l y . F o r R i c o n s t a n t on a c o n s t a n t s l o p e , the d i s t a n c e i n which a t w o - d i m e n s i o n a l d e n s i t y c u r r e n t would double i t s t h i c k n e s s i s g i v e n by X =uH/w = H/(0.072 s i n ^ ) (8.18) from e q u a t i o n ( 8 . 1 1 ) . The d o u b l i n g l e n g t h s f o r the upper, m i d d l e , and lower reaches a r e 3.6, 6.1, and 8.4 km, r e s p e c t i v e l y . From F i g . 25, the r a t i o of the l e n g t h of the c o n s t a n t s l o p e s e c t i o n t o the d o u b l i n g l e n g t h i s 0.14, 0.21, and 0.25, i n the upper, middle and lower reaches r e s p e c t i v e l y . T h i s i n d i c a t e s t h a t i f these reaches were p e r f e c t l y s t r a i g h t and of u n i f o r m c r o s s - s e c t i o n , f l o w s t h i c k e r than 0.86, 0.79 and 0.75 of the l e v e e h e i g h t i n each r e a c h would o v e r s p i l l because of e n t r a i n m e n t . 239 T a b l e X l V a . C o n t i n u o u s - f l o w parameters i n the upper r e a c h a t l i n e 5 ( l o c a t i o n g i v e n i n F i g . 2 7 ) . Bottom s l o p e = 2.2°, c r o s s -s e c t i o n a l area=450 m2. u m s" 1M* mg 1" 1 m3 s" 1 kg s" 1R i * * f/2 *** x1 0 3 0.2 80.2 90 7.2 0. 120 4.60 0.3 1 55 1 35 21 0. 1 03 3.96 0.4 254 180 46 0.095 3.64 0.5 376 225 85 0.090 3.45 0.6 521 270 141 0.087 3.32 0.7 690 315 217 0.084 3.23 0.8 882 360 318 0.082 3.16 0.9 1098 405 445 0.081 3.11 1.0 1337 450 602 0.080 3.07 * from (8.15) and (8. ** H=10 m; from (8.8) *** from (8.9) 16) T a b l e XIVb. T r a n s p o r t s by c o n t i n u o u s f l o w i n the upper reach between l i n e s 2 and 5 ( l o c a t i o n i n F i g . 2 7 ) . C r o s s - s e c t i o n a l a r e a s a t l i n e s 2 and 5 a r e 700 and 450 m2, r e s p e c t i v e l y . The Q and Q' a r e i n u n i t s of m3 s " 1 and kg s ~ 1 , r e s p e c t i v e l y . u m s" 1Q* Q** Q' +Q* 0.4 280 180 29 1 29 71 46 25 0.5 350 225 36 161 1 32 85 47 0.6 420 270 43 1 93 219 141 78 0.7 490 315 50 225 338 217 121 0.8 560 360 57 257 494 318 176 * from (8.11) ** Q s= Q.+Qe-Qc, 8.3.2 En t r a i n m e n t and Sediment T r a n s p o r t i n the Upper Reach The t r a n s p o r t s of volume (Q 0) and mass {Ql) a t l i n e 5 de t e r m i n e d from (8.15) a r e g i v e n i n T a b l e X l V a . The e q u i v a l e n t parameters a t l i n e 2 {Q• and Q') can be c a l c u l a t e d u s i n g the same v a l u e s of u and M s i n c e R i i s assumed c o n s t a n t . S i m i l a r l y , the volume r a t e of e n t r a i n m e n t (Q e) between l i n e s 2 and 5 i s de t e r m i n e d from e q u a t i o n (8. 11 ) , the l i n e s e p a r a t i o n (260 m) and 240 the mean c h a n n e l w i d t h a t the i n t e r f a c e (100 m). The sediment l o s s r a t e Q^+Q'^can then be o b t a i n e d from ( 8 . 1 7 ) . E s t i m a t e s of the t r a n s p o r t s i n - a n d out of the s e c t i o n between l i n e s 2 and 5 a r e p r e s e n t e d i n Table X l V b . S i n c e the mass t r a n s p o r t of s o l i d s a t l i n e 2 (CV) cannot exceed the r a t e of d i s c h a r g e , the mean speed must be l e s s than 0.8 m s ~ 1 . Now assume t h a t the r a t e of l o s s by. d e p o s i t i o n and o v e r s p i l l i s c o n s t a n t a l o n g the 600 m s e c t i o n of t h e upper r e a c h beween the o u t f a l l and l i n e 5. The s o l i d s l o s s r a t e s between the o u t f a l l and l i n e 5, 600 (QJ +Q^ )/260,„ must b a l a n c e CV and the r a t e of d i s c h a r g e . T h i s o c c u r s c l o s e t o u-0.6 m s ~ 1 ( T a b l e X l V b ) , f o r which the t o t a l l o s s of s o l i d s by o v e r s p i l l and d e p o s i t i o n i s 180 kg s _ 1 . Because the i n c r e a s e i n the t h i c k n e s s of the t a i l i n g d e p o s i t tended t o be a l i n e a r f u n c t i o n of time ( F i g . 67 and Appendix 6 ) , rough e s t i m a t e s of the r a t e s of a c c u m u l a t i o n on the l e v e e s and on the c h a n n e l bed i n the upper r e a c h can be made from F i g . 21. Assuming a d r y b u l k d e n s i t y of 1.3 g c m - 3 f o r the d e p o s i t , r a t e s of 31 kg s _ 1 on the l e v e e s and 2 kg s ~ 1 on the bed were o b t a i n e d i n the 900 m l e n g t h of the upper r e a c h , not i n c l u d i n g the l a r g e d e p o s i t on the s o u t h s i d e of the f i r s t bend. A c c o r d i n g l y o n l y some 22 kg s " 1 (=600x33/900) can account f o r the net a c c u m u l a t i o n i n two zones, each 100 m wide and c e n t e r e d on the l e v e e c r e s t s , between the o u t f a l l and l i n e 5. I f another 22 kg s " 1 i s c a r r i e d ( l a t e r a l l y ) beyond t h i s zone, then f o r a s o l i d s d i s c h a r g e r a t e of 390 kg s " 1 , 225 kg s " 1 must be t r a n s p o r t e d out of t h i s s e c t i o n by slump-generated f l o w . G i v e n the entr a i n m e n t r a t e , the s a l i n i t y of the water i n 241 the plume can be c a l c u l a t e d t o det e r m i n e the e f f e c t of the f r e s h water on the plume d e n s i t y . Because Rupert I n l e t i s o f t e n n e a r l y v e r t i c a l l y homogeneous below 15-50 m (see D r i n k w a t e r and Osborn, 1975 ) , f o r the purpose of t h i s argument the temperature and t h e s a l i n i t y i n the i n l e t a r e s e t a t t h e i r a n n u a l mean v a l u e s of 9 °C .and 3 0 . 5 p p t . The d i s c h a r g e i s 10% s o l i d s , 40% f r e s h water and 50% sea-water' by volume, and under i s o t h e r m a l c o n d i t i o n s the l i q u i d phase would have a sigma-t of 13.06 (Cox e t a l , 1 9 7 0 ) . The volume t r a n s p o r t of f r e s h water a t the o u t f a l l i s — 0 . 5 4 m3 s"1, w h i l e t h e volume t r a n s p o r t of water p a s t l i n e 2 a t a mean speed of 0 .6 m s~ 1 i s Q^= 420 m3 s " 1 . The s a l i n i t y of t h i s water i s g i v e n by S= 3 0 . 5 ( Q j " 0 . 5 4 ) / Q - = 30 .46 ppt which c o r r e s p o n d s t o a sigma-t of 2 3 . 6 1 , w h i l e t h a t of the ambient sea water i s 2 3 . 6 4 . The v a l u e of S i s c o n s i s t e n t w i t h the o b s e r v e d drop i n s a l i n i t y w i t h depth i n the plume (Chapter 7, F i g . 8 7 ) , a l b e i t t h a t t h e s e o b s e r v a t i o n s were taken d u r i n g the u n c h a n n e l i z e d phase. The v a l u e s of sigma-t i n d i c a t e t h a t the e x c e s s d e n s i t y of t h e plume i s dominated by suspended s o l i d s p r o v i d e d M > 47 mg 1 ~ 1 . 8 . 3 . 3 Lower Reach The s l o p e i n the lower r e a c h i s 0 . 4 7 ° , w i t h a c h a n n e l - f u l l f l o w t h i c k n e s s of 5 m and a maximum c r o s s - s e c t i o n a l a r e a of 200 m2. From Bo Pedersen (1980 , F i g . 5 . 1 4 ) , R i s h o u l d be between 0 .28 and 4 . 0 a t t h i s s l o p e f o r h i s su g g e s t e d range of v a l u e s of the drag c o e f f i c i e n t f ( 0 . 0 0 4 - 0 . 0 6 ) . From ( 8 . 1 2 ) and an assumed average c o n c e n t r a t i o n of 400 mg l " 1 , u= 0 . 0 5 5 - 0 . 2 1 m s " 1 , g i v i n g 242 4-17 kg s" 1 f o r the mass t r a n s p o r t by c o n t i n u o u s f l o w . S i n c e i t was e s t i m a t e d i n S e c t i o n 8.2 from the volume of a c c u m u l a t e d t a i l i n g t h a t the t o t a l mass t r a n s p o r t t h r o u g h t h i s r e a c h must be about 240 kg s " 1 , then 223-236 kg s" 1 must be t r a n s p o r t e d by mechanisms o t h e r than c o n t i n u o u s f l o w . The 225 kg s " 1 of m a t e r i a l e s t i m a t e d t o be t r a n s p o r t e d out of the upper r e a c h by slump-generated t u r b i d i t y c u r r e n t s a c c o u n t s f o r t h e d i f f e r e n c e r e a s o n a b l y w e l l . 8.3.4 The Frequency of T u r b i d i t y Surges The mean r e c u r r e n c e i n t e r v a l of t u r b i d i t y c u r r e n t s has been e s t i m a t e d a t 2-5 d from the t u r b i d i t e d e p o s i t s i n c o r e s from the l e v e e s i n the m i d d l e r e a c h ( S e c t i o n 5.3.3). Assuming t h a t the t u r b i d i t y surges a r e of the s l u g - t y p e ( F i g . 9 4 ) , and t h a t the nose v e l o c i t y ( 8 . 1 ) , w i t h C o=0.75, c h a r a c t e r i z e s the motion of the s l u g as a whole on low s l o p e s , the mass t r a n s p o r t of sediment by the surge i s g i v e n by Q'= FMu 0 TA (8.19) A i s the c h a n n e l c r o s s - s e c t i o n , F i s the f r e q u e n c y of o c c u r r e n c e of t u r b i d i t y c u r r e n t s and T i s a time s c a l e r e p r e s e n t i n g the l e n g t h of time f o r the head and the main p a r t of the f o l l o w i n g f l o w t o pass a g i v e n p o s i t i o n . The t a i l of the c u r r e n t , which i s p r o b a b l y governed by ah e q u a t i o n s i m i l a r t o ( 8 . 9 ) , i s assumed not t o c o n t r i b u t e s i g n i f i c a n t l y t o the t r a n s p o r t . From the f a c s i m i l e r e c o r d s i n the p r e v i o u s c h a p t e r ( F i g s . 91-93), T i s about 15 min. I t remains t o e s t i m a t e Ap i n the head. Bagnold (1962) has s u g g e sted t h a t a t suspended sediment c o n c e n t r a t i o n s g r e a t e r than 243 9% by volume, g r a i n - g r a i n c o n t a c t causes a much g r e a t e r r a t e of i n c r e a s e i n v i s c o s i t y w i t h i n c r e a s e d c o n c e n t r a t i o n . Note t h a t t h i s i s a p p r o x i m a t e l y the same c o n c e n t r a t i o n a t which the a t t e n u a t i o n of sound i n s u s p e n s i o n s becomes n o n - l i n e a r due t o m u l t i p l e - s c a t t e r i n g (Chapter 3 ) , and t h a t i t c o r r e s p o n d s t o a b u l k d e n s i t y of 1.18 g c m - 3 , compared t o the v a l u e of 1.12 g c m - 3 i n f e r r e d from the r e c o r d e d b a c k s c a t t e r from the most pronounced surge ( F i g s . 96 and 9 7 ) . F o l l o w i n g Komar (1969), 9% i s t a k e n as an upper l i m i t t o the c o n c e n t r a t i o n i n t u r b i d i t y s u r g e s . W i t h Q' = 223-236 kg s'1, the surge f r e q u e n c y i s F=3.5-3.7 x 10' 6 s~ 1, from e q u a t i o n ( 8 . 1 9 ) . The r e c u r r e n c e i n t e r v a l , t h e r e f o r e , i s of the o r d e r of 3.1-3.2 days, w h i c h i s w i t h i n the i n t e r v a l d e t e r m i n e d from the c o r e s . 244 CHAPTER 9 SUMMARY AND CONCLUSIONS A time s e r i e s of b a t h y m e t r i c , s i d e - s c a n and s e i s m i c r e f l e c t i o n s u r v e y s over a t h r e e year p e r i o d show t h a t the t a i l i n g d e p o s i t e v o l v e d through t h r e e s u c c e s s i v e m o r p h o l o g i c a l regimes: (a) the i n i t i a l meandering c h a n n e l , (b) the t a i l i n g apron and (c) the r e c h a n n e l i z e d s t a t e . The f o c u s has been th e i n i t i a l regime, and i n f o r m a t i o n from the subsequent phases has been used t o c l a r i f y c e r t a i n a s p e c t s of t h i s problem. A p r i m a r y p a r t of the r e s e a r c h c o n c e r n s the use of a c o u s t i c sounders f o r the remote d e t e c t i o n of suspended sediments i n g e n e r a l , and t u r b i d i t y c u r r e n t s i n p a r t i c u l a r , i n c l u d i n g the c o n t i n u o u s f l o w a s s o c i a t e d w i t h t h e t a i l i n g d i s c h a r g e . These l a t t e r phenomena i n v o l v e h i g h suspended sediment l o a d s , a t which the a d d i t i o n a l a t t e n u a t i o n of the sound waves, both i n c i d e n t and s c a t t e r e d , t hrough a b s o r p t i o n p r o c e s s e s a t the w a t e r - p a r t i c l e i n t e r f a c e must be c o n s i d e r e d . E x p l i c i t e x p r e s s i o n s a p p l i c a b l e t o the l o n g - w a v e l e n g t h ( R a y l e i g h ) r e g i o n a r e o b t a i n e d f o r the s c a t t e r e d wave as m o d i f i e d by t h e s e p r o c e s s e s , t o g e t h e r w i t h a r e l a t i o n e x p r e s s i n g the r e l a t i v e magnitudes of v i s c o u s and t h e r m a l a b s o r p t i o n . T h i s r a t i o i s shown t o be c o n s i s t e n t w i t h e x i s t i n g e x p e r i m e n t a l e v i d e n c e , and i s used t o demonstrate t h a t t h e r m a l a b s o r p t i o n can be n e g l e c t e d f o r most s o l i d p a r t i c l e s of m i n e r a l o r i g i n , which s i m p l i f i e s the c a l c u l a t i o n of the a d d i t i o n a l l o s s e s c o n s i d e r a b l y . The t h e o r y of a c o u s t i c remote s e n s i n g of R a y l e i g h s c a t t e r e r s i s p r e s e n t e d . I t i s shown t h a t a t h i g h f r e q u e n c i e s , at which the background n o i s e of an i d e a l t r a n s d u c e r i s due t o 245 t h e r m a l m o l e c u l a r motion i n the w a t e r , t h e r e e x i s t s an o p t i m a l c h o i c e of f r e q u e n c y f o r a g i v e n s c a t t e r e r range. No q u a n t i t a t i v e s t u d y of the f r e q u e n c y dependence of the b a c k s c a t t e r e d s i g n a l was c o n d u c t e d . Q u a l i t a t i v e comparisons a t 42.5, 107 and 200 kHz, however, a r e c o n s i s t e n t w i t h e x p e c t a t i o n s ( e . g . F i g . 9 0 ) . An e m p i r i c a l r e l a t i o n between s i g n a l l e v e l and suspended s o l i d s c o n c e n t r a t i o n i s p r e s e n t e d and shown t o be c o n s i s t e n t i n form w i t h R a y l e i g h s c a t t e r i n g t h e o r y ( F i g . 11). F u r t h e r m o r e , the s i g n a l l e v e l r e l a t i v e t o a s t a n d a r d t a r g e t i s a l s o c o n s i s t e n t w i t h t h e o r y . The e m p i r i c a l r e l a t i o n i s used t o e x t r a c t a c r o s s -s e c t i o n a l p r o f i l e of the c h a n n e l i z e d d i s c h a r g e plume from the t a p e - r e c o r d e d s i g n a l ( F i g . 13). Such p r o f i l e s a r e based on the a ssumption t h a t the s i z e d i s t r i b u t i o n of the suspended p a r t i c l e s does not change shape s i g n i f i c a n t l y , e i t h e r i n the v e r t i c a l or the h o r i z o n t a l , over the range of s i z e s r e s p o n s i b l e f o r the r e v e r b e r a t i o n . The use of t a r g e t spheres as p r i m a r y c a l i b r a t i o n s t a n d a r d s i s not recommended. Such t a r g e t s a r e u s e f u l as secondary s t a n d a r d s , p a r t i c u l a r l y i n s h e l t e r e d e nvironments where t h e r e i s g r e a t e r p r o b a b i l i t y of p l a c i n g a t a r g e t on the a c o u s t i c a x i s . The c h a n n e l i s d i v i s i b l e i n t o t h r e e r e a c h e s , which are m o r p h o l o g i c a l l y d i s t i n c t i n p l a n and both a x i a l and t r a n s v e r s e p r o f i l e s . The upper r e a c h hooks t o the l e f t , a p p a r e n t l y due t o t r a n s v e r s e C o r i o l i s and c e n t r i f u g a l a c c e l e r a t i o n s (the l a t t e r b e i n g the more i m p o r t a n t of the t w o ) , as Menard (1955) has s u g g e sted f o r deep-sea c h a n n e l s . The meanders of the m i d d l e r e a c h a r e g e o m e t r i c a l l y s i m i l a r t o meanders i n s u b a e r i a l r i v e r s , and t h e i r p resence appears t o depend upon the a x i a l s l o p e and 246 d i s c h a r g e , as w i t h r i v e r s . In the subaqueous c a s e , however, e n t r a i n m e n t a t the upper i n t e r f a c e , and m a t e r i a l (and c o n s e q u e n t l y p o t e n t i a l energy) l o s s e s t h r o u g h d e p o s i t i o n and c h a n n e l o v e r s p i l l must be c o n s i d e r e d . There i s e v i d e n c e t o suggest t h a t t h e s e p r o c e s s e s induce m o r p h o l o g i c a l changes which can be r e c o g n i z e d and un d e r s t o o d ( e . g . F i g . 4 2 ) . S u r f i c i a l sediment samples i n d i c a t e t h a t c o a r s e d e p o s i t s are r e s t r i c t e d t o the c h a n n e l a x i s ( F i g s . 44 and 5 0 ) . A l t h o u g h i t i s p r o b a b l e t h a t the c o a r s e s t sediments a r e a l s o r e s t r i c t e d t o the n e a r - o u t f a l l a r e a i n some " s p a t i a l l y a v eraged sense, c o a r s e r d e p o s i t s were found f u r t h e r downstream ( F i g s . 46 and 50). The c o n c e n t r a t i o n of Cu i n a d e p o s i t i n c r e a s e s a p p r o x i m a t e l y l i n e a r l y w i t h the amount of sand p r e s e n t ( F i g . 52). The s u g g e s t i o n i s t h a t the f r o t h - f l o t a t i o n p r o c e s s by which c h a l c o p y r i t e i s e x t r a c t e d from the g r i n d i s l e s s e f f i c i e n t f o r l a r g e r p a r t i c l e s . The c o n c e n t r a t i o n of i r o n i s lo w e s t f o r the c o a r s e s t s e d i m e n t s , and h i g h e r i n d e p o s i t s w i t h l a r g e r f r a c t i o n s of c l a y ( F i g . 5 3 ) , p r o b a b l y because of the a s s o c i a t i o n of i r o n w i t h the s o f t e r m i n e r a l s and, t h e r e f o r e , the f i n e r p a r t i c l e s . T u r b i d i t e s c o n t a i n i n g the Ta, Te, and p o s s i b l y the Tb and Td i n t e r v a l s of the Bouma sequence were found i n the sediment column. These d e p o s i t s were v e r t i c a l l y graded i n b o t h t e x t u r e and c opper, and had s h a r p c o n t a c t s w i t h the u n d e r l y i n g mud, some of which e x h i b i t e d f e a t u r e s s i m i l a r t o l o a d - p o c k e t s and l o a d -c a s t e d flame s t r u c t u r e s . The use of copper and i r o n as c h e m i c a l t r a c e r s of such d e p o s i t s shows c o n s i d e r a b l e promise i n t h i s t y p e of environment. The frequ e n c y and t h i c k n e s s of the s e d e p o s i t s 247 r e l a t i v e t o the i n t e r v e n i n g mud d e c r e a s e d w i t h l a t e r a l d i s t a n c e from t h e c h a n n e l a x i s , but i n c r e a s e d w i t h d i s t a n c e downstream. T h i s l a t t e r o b s e r v a t i o n i s a t complete v a r i a n c e w i t h the e x i s t i n g l i t e r a t u r e on t u r b i d i t e s , but i s not n e c e s s a r i l y a c o n t r a d i c t i o n . I t may r e f l e c t the l a c k of c o r e s from the c h a n n e l a x i s i n the p r e s e n t s t u d y , due t o the d i f f i c u l t y i n m a i n t a i n i n g p o s i t i o n over the c h a n n e l and i n p e n e t r a t i n g sand w i t h our c o r i n g a p p a r a t u s . D e p o s i t i o n r a t e s are e s t a b l i s h e d from the changes i n t a i l i n g t h i c k n e s s d e r i v e d from s e i s m i c p r o f i l e s , changes i n water depth and the down-core v a r i a t i o n s i n the c o n c e n t r a t i o n of the f r u s t u l e s of l a r g e d i a t o m s . A c c u m u l a t i o n r a t e s r a n g i n g from 0.3 t o s e v e r a l meters per year were o b t a i n e d , and were used t o i n f e r the f r e q u e n c y of t u r b i d i t y surges from the number of t u r b i d i t e s per u n i t l e n g t h of c o r e . Recurrence i n t e r v a l s of 2-5 d were o b t a i n e d f o r the meandering c h a n n e l phase, a l t h o u g h a t l a r g e d i s t a n c e s from the o u t f a l l (8.3 km), t h i s v a l u e i n c r e a s e d t o 43-64 d. D u r i n g the subsequent apron regime, t u r b i d i t e s were v i r t u a l l y absent from the sediment column d o w n - i n l e t from the apron, i n d i c a t i n g t h a t both the f r e q u e n c y of o c c u r r e n c e of t u r b i d i t y surges and the d i s t a n c e s t o which they propagate a r e g r e a t e r i n the presence of a l e v e e d c h a n n e l . F a c s i m i l e r e c o r d s a r e p r e s e n t e d showing t h e a c o u s t i c b a c k s c a t t e r from the d i s c h a r g e plume d u r i n g the meandering c h a n n e l regime. They i l l u s t r a t e : (a) the plume s p i l l i n g over the l e v e e f o r m i n g the o u t e r (concave) bank i n bends, (b) an i n t e r f a c e s l o p i n g upward t o the r i g h t i n a bend c u r v i n g t o the l e f t i n the downstream-looking sense, and (c) t h a t the d i s c h a r g e 248 plume extended a t l e a s t p a r t way a l o n g the meander r e a c h . The l o s s of s i g n a l a t g r e a t e r a x i a l d i s t a n c e s may have been p a r t l y due t o i n c r e a s e d a t t e n u a t i o n over the l o n g e r r e t u r n p a t h s i n deeper water . The s l o p e of the i n t e r f a c e i s c o n s i d e r a b l y s t e e p e r than might be e x p e c t e d from the d i f f e r e n c e i n l e v e e h e i g h t a c r o s s the c h a n n e l . In the upper r e a c h the i n t e r f a c i a l s l o p e d i d not change s i g n i f i c a n t l y w i t h the phase of the t i d e , i n d i c a t i n g t h a t the c r o s s - s t r e a m t i d a l s t r e s s was not s i g n i f i c a n t a t these t i m e s . The deep water c u r r e n t s i n t h i s i n l e t e x h i b i t an u n u s u a l r e l a t i o n s h i p t o the phase of the t i d e . Flow i s u s u a l l y u p - i n l e t from a p p r o x i m a t e l y mid-ebb t o m i d - f l o o d and d o w n - i n l e t from mid-f l o o d t o mid-ebb, a l t h o u g h r e v e r s a l t o u p - i n l e t f l o w can occur c l o s e t o h i g h water, p a r t i c u l a r l y i f the f l o o d t i d e range i s s u f f i c i e n t l y h i g h . T h i s p a t t e r n appears t o be d e t e r m i n e d by the r a t e and depth of d e s c e n t of the t i d a l j e t through the water column i n the Hankin P o i n t a r e a d u r i n g f l o o d t i d e . The c u r r e n t r e c o r d s c o n t a i n e v i d e n c e of the passage of t u r b i d i t y s u r g e s . The s i g n a t u r e i s by no means o b v i o u s , however. A t o t a l of f o u r surges were d e t e c t e d w i t h the a c o u s t i c sounders, d u r i n g two of which c u r r e n t meters were i n p l a c e . Without the a c o u s t i c r e c o r d s i t i s u n l i k e l y t h a t the events c o u l d have been i d e n t i f i e d by the c u r r e n t changes. Nose v e l o c i t i e s of 30-120 cm s" 1 were e s t i m a t e d from the surge p r o f i l e by i n v o k i n g the u n i v e r s a l shape f o r d e n s i t y c u r r e n t heads. The h i g h e s t e s t i m a t e c o r r e s p o n d e d t o t h a t event w i t h the s t e e p e s t l e a d i n g edge, most of which was r e c o r d e d on tape-. A second e s t i m a t e o t 170cm s"' c o r r e s p o n d i n g t o an e x c e s s d e n s i t y 249 of 0.12 g cm" 3 was o b t a i n e d a f t e r d i g i t a l l y p r o c e s s i n g t h i s r e c o r d , and by assuming (a) t h a t the mean p a r t i c l e s i z e of the s u s p e n s i o n d i d not change d u r i n g the f i r s t 6 min, or over a l e n g t h of 400-600 m a t the e s t i m a t e d v e l o c i t i e s , and (b) t h a t t h e bottom r e f l e c t i o n c o e f f i c i e n t was u n a f f e c t e d by the f l o w d u r i n g a 2 min i n t e r v a l from 4-6 min a f t e r the o n s e t . F i n a l l y , a s y n t h e s i s of t h i s m a t e r i a l i s a c h i e v e d t h rough a sediment budget based on the s e i s m i c p r o f i l e s and a s i m p l e a n a l y t i c a l model, i n c l u d i n g e n t r a i n m e n t , of c o n t i n u o u s f l o w w i t h i n the c h a n n e l . The c r o s s - s e c t i o n a l a r e a of the c h a n n e l i n c r e a s e s w i t h i n the f i r s t 100-200 m of the o u t f a l l and then d e c r e a s e s u n t i l i t d i s a p p e a r s . Assuming t h a t t h i s b e h a v i o u r i s a r e f l e c t i o n of the p r o p e r t i e s of the f l o w w i t h i n the c h a n n e l , i t i s s u g g e s t e d t h a t the d e c r e a s e i n c r o s s - s e c t i o n i s p r i m a r i l y due t o e n t r a i n m e n t and consequent l o s s of m a t e r i a l and p o t e n t i a l energy t h r o u g h c h a n n e l o v e r s p i l l , w h i l e the i n c r e a s e i n the near o u t f a l l r e g i o n may i n d i c a t e the p r e s ence of a h y d r a u l i c jump. The t a i l i n g d e p o s i t i s d i v i d e d i n t o a p r o x i m a l and a d i s t a l zone a t the end of the meander r e a c h . The change i n volume of the t a i l i n g d e p o s i t i n the two zones g i v e s a f i g u r e of 240 kg s"' f o r the mass t r a n s p o r t of t a i l i n g out of the p r o x i m a l zone. Of t h i s , 12-44 kg s " 1 are e s t i m a t e d t o be c a r r i e d by c o n t i n u o u s f l o w . The remainder i s assumed t o be c a r r i e d by t u r b i d i t y s u r g e s , g i v i n g an e s t i m a t e d r e c u r r e n c e i n t e r v a l f o r t h e s e e v e nts of 6-7 d. T h i s i s c o n s i s t e n t w i t h the 2-5 d range of v a l u e s o b t a i n e d from the c o r e s , and w i t h the amount of m a t e r i a l which must be removed from the l e v e e s of the upper r e a c h t o account f o r the o b s e r v e d r a t e s of a c c u m u l a t i o n t h e r e . 250 B i b l i o q r a p h y A c k e r s , P. and F. G. C h a r l t o n (1970) The s l o p e and r e s i s t a n c e of s m a l l meandering c h a n n e l s . I n s t i t u t i o n of C i v i l E n g i n e e r s , London. P r o c . S u p p l . XV, paper 7362 S. A l l e g r a , J.R. and S.A. Hawley (1972) A t t e n u a t i o n of sound i n s u s p e n s i o n s and e m u l s i o n s : t h e o r y and e x p e r i m e n t s . J_^ _ A c o u s t . Soc. Am. , 51, 1545-1564. A l l e n , J . R. L. (1970) P h y s i c a l P r o c e s s e s i n S e d i m e n t a t i o n . E l s e v i e r , New York, 248 pp. A l l e n , J . R. L. (1971 ) M i x i n g a t t u r b i d i t y c u r r e n t heads, and i t s g e o l o g i c a l i m p l i c a t i o n s . Sed. P e t . , 41, 97-113. A s h i d a , K. and S. E g a s h i r a (1975) B a s i c study on t u r b i d i t y c u r r e n t s . Jap. Soc. C i v . Eng.,  T r a n s a c t i o n s , 7, 83-86. B a g n o l d , R. A. (1962) A u t o s u s p e n s i o n of t r a n s p o r t e d s e d i m e n t s : T u r b i d i t y c u r r e n t s . P r o c . Roy. Soc. A., 265, 315-319.. B a t c h e l o r , G . K . (1967) An I n t r o d u c t i o n t o F l u i d Dynamics. Cambridge U n i v e r s i t y P r e s s , Cambridge, U.K., 615 pp. B a t t a r b e e , R.W. (1978) O b s e r v a t i o n s on the r e c e n t h i s t o r y of Lough Neagh and i t s d r a i n a g e b a s i n , P h i l o s o p h i c a l T r a n s a c t i o n s of the R o y a l  S o c i e t y (London), S e r i e s B, 281, 303-345. Beamish, P. C. (1969) Quant i t a t i v e Measurements of Mar i n e A c o u s t i c S c a t t e r i n g  from Z o o p l a n k t o n i c Organisms. Ph. D. T h e s i s , u n p u b l . , U n i v e r s i t y of B r i t i s h C o lumbia, 89 pp. Beamish, P. C. (1971) Q u a n t i t a t i v e measurements of a c o u s t i c b a c k s c a t t e r i n g from z o o p l a n k t o n i c o r g anisms. Deep-Sea Res., J_8, 811-822. B e l l , H. S. (1942) D e n s i t y c u r r e n t s as agents f o r t r a n s p o r t i n g sediment. J .  G e o l . , 50, 512-547. Benjamin, T. B. (1968) G r a v i t y c u r r e n t s and r e l a t e d phenomena. Jj _ F l u i d Mech. , 31 , 209-248. Bergman, P. G. and A. Yaspan (eds.) (1968) The P h y s i c s of Sound i n the Sea. P a r t I . T r a n s m i s s i o n . Gordon and B r e a c h , I n c . , New York, 235 pp. 251 B i e n f a n g , P.K. (1979) A new p h y t o p l a n k t o n s i n k i n g r a t e method s u i t a b l e f o r f i e l d use. Deep-Sea R e s e a r c h , 26, 719-729. B l u e , J . E. and E. G. McLeroy (1968) A t t e n u a t i o n of sound i n s u s p e n s i o n s and g e l s . J ^ A c o u s t .  Soc. Am., 44, 1145-1148. Bo P e d e r s e n , F. (1980) A Monograph on T u r b u l e n t E n t r a i n m e n t and F r i c t i o n i n Two- l a y e r S t r a t i f i e d Flow. I n s t , of Hydrodynamics and H y d r a u l i c Eng., T e c h n i c a l U n i v e r s i t y of Denmark, 397 pp. B o k u n i e w i c z , H. J . , J . G e b e r t , R. B. Gordon, J . L. H i g g i n s , P. Kaminsky, C. C. P i l b e a m , M. Reed and C. T u t t l e (1978) F i e l d study of the mechanics of the placement of dredged m a t e r i a l a t open-water d i s p o s a l s i t e s . T e c h n i c a l Report D-78-7, U.S. Army E n g i n e e r Waterways Experiment S t a t i o n , V i c k s b u r g , M i s s . Bouma, A. H. (1962) A n c i e n t and r e c e n t t u r b i d i t e s . G e o l . en Mijnbouw, 43, 375-379. • Bouma, A. H. and J . A. K. Boerma (1968) V e r t i c a l d i s t u r b a n c e s i n p i s t o n c o r e s . Mar. G e o l . , 6_, 231 — 241 . B r a i t h w a i t e , H. (1974) Some measurements of a c o u s t i c c o n d i t i o n s i n r i v e r s . J .  Sound and V i b . , 37, 557-563. B r i t t e r , R. E. and J . E. Simpson (1978) E x p e r i m e n t s on the dynamics of a g r a v i t y c u r r e n t head. J .  F l u i d Mech., 88, 223-240. Busby, J . and E. G. R i c h a r d s o n (1956) The p r o p a g a t i o n of u l