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Flood control and sediment transport study of the Vedder River McLean, David George 1980

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FLOOD CONTROL AND SEDIMENT TRANSPORT STUDY OF THE VEDDER RIVER by DAVID GEORGE McLEAN .A.Sc., U n i v e r s i t y of B r i t i s h Columbia, 1975 \ THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES The Department of C i v i l E n g i n e e r i n g We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1980 (5) David George McLean In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Brit ish Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Cim / moo^i^y The University of Brit ish Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 E-6 B P 75-51 1 E ABSTRACT The C h i l l i w a c k R i v e r flows through the Cascade Mountains u n t i l r e a c h i n g a narrow gorge near Vedder C r o s s i n g where i t flows onto the F r a s e r Lowlands and e v e n t u a l l y meets the F r a s e r R i v e r . Below Vedder C r o s s i n g , the r i v e r i s a c t i v e l y b u i l d i n g an a l l u v i a l fan by depos-i t i n g i t s sediment load of g r a v e l and sand. T h i s d e p o s i -t i o n has r e s u l t e d i n frequent channel s h i f t s over the fan s u r f a c e w i t h the most r e c e n t m i g r a t i o n o c c u r r i n g around 1894 when the r i v e r s h i f t e d down Vedder Creek. Over the l a s t century the Vedder River has been undergoing very complex changes i n response to changes i n the i n c i d e n c e of severe f l o o d s , changes i n sediment supply and i n t e r f e r e n c e from r i v e r t r a i n i n g . E x t e n s i v e c h a n n e l i z a t i o n works c a r r i e d out i n the 1960's induced temporary deg r a d a t i o n over p a r t of the channel which was accompanied by r a p i d ag g r a d a t i o n i n the reach immediately downstream. T h i s r a p i d channel adjustment ceased i n l e s s than 10 y e a r s . In 1975 a f l o o d having a r e t u r n p e r i o d of about 10 years "deposited 260,000 c u b i c yards of sediment onto the fan which i n c r e a s e d the mean b e d l e v e l by n e a r l y 1 f o o t . By comparison, the average annual d e p o s i t i o n r a t e was estimated to be 7 2,000 c u b i c yards per year. Based on bedload t r a n s p o r t c a l c u l a t i o n s , approximately 700 ,,000 c u b i c yards of sediment c o u l d be d e p o s i t e d by a 50 year r a i n s t o r m f l o o d . In order to p r o v i d e long term f l o o d c o n t r o l , e i t h e r the upstream sediment supply w i l l have to be reduced or dredging w i l l have to be c a r r i e d out on the lower r i v e r . I t i s not f e a s i b l e to e l i m i n a t e aggradation by t r a n s p o r t -i n g the incoming bedload through the system and i n t o the F r a s e r R i v e r . Some s t r a t e g i e s are c o n s i d e r e d which, by c o n t r o l l e d dredging and t r a i n i n g would m a i n t a i n the channel permanently i n i t s p r e s e n t p o s i t i o n . More severe f l o o d s would be con-t a i n e d by set-back d i k e s . I t i s thought t h a t , w i t h c a r e , these measures c o u l d be c o n s i s t e n t w i t h salmon h a b i t a t requirements. iv TABLE OF CONTENTS CHAPTER PAGE ABSTRACT i i TABLE OF CONTENTS • i v LIST OF'TABLES VI LIST OF FIGURES V i i i ACKNOWLEDGEMENTS c Xi I INTRODUCTION 1 I I HISTORY OF RIVER ACTIVITY 6 2.1 S i t e L o c a t i o n 6 2.2 E a r l y H i s t o r y and Settlement 6 2.3 R i v e r T r a i n i n g and F l o o d i n g Along the Vedder R i v e r 12 I I I HYDROLOGY. . . . 24 3.1 Ba s i n C h a r a c t e r i s t i c s 24 3.2 Climate 25 3.3 Streamflow Data 25 3.4 B a s i n Runoff 26 3.5 F l o o d Hydrology 27 3.6 Fl o o d Frequency A n a l y s i s 34 IV GEOLOGY AND PHYSIOGRAPHY 4 5 4.1 Physiography 45 4.2 G l a c i a l H i s t o r y 47 4.3 Formation o f the C h i l l i w a c k R i v e r Fan 49 V RIVER PROCESSES UPSTREAM OF VEDDER CROSSING 53 5.1 Data A v a i l a b l e 54 5.2 A n a l y s i s o f R i v e r Processes . . . . . 58 5.3 The Sediment Supply of the C h i l l i w a c k R i v e r 78 V. CHAPTER PAGE V I CHANNEL PROCESSES BELOW VEDDER CROSSING 8 3 6.1 D a t a A v a i l a b l e 8 3 6.2 C h a n n e l P a t t e r n o f t h e V e d d e r R i v e r 86 6.3 C h a n n e l H y d r a u l i c s 92 6.4 B e d M a t e r i a l C h a r a c t e r i s t i c s 99 V I I SEDIMENT TRANSPORT 10 5 7.1 S u s p e n d e d L o a d 105 7.2 B e d l o a d . 106 V I I I AGGRADATION ON THE VEDDER RIVER 118 8.1 The P r o c e s s o f A g g r a d a t i o n 118 8.2 H i s t o r i c a l D e p o s i t i o n R a t e s o n t h e C h i l l i w a c k R i v e r 121 8.3 A g g r a d a t i o n D u r i n g t h e 1975 F l o o d 132 8.4 P r e d i c t i o n o f F u t u r e A g g r a d a t i o n 135 I X FLOOD CONTROL ON THE VEDDER RIVER 141 9.1 Some E x a m p l e s o f F l o o d C o n t r o l P r a c t i c e 141 9.2 F l o o d C o n t r o l on t h e V e d d e r R i v e r 14 6 X CONCLUSIONS 162 BIBLIOGRAPHY 16 6 TABLES 174 FIGURES 207 APPENDIX 1 266 v i LIST OF TABLES TABLE TITLE PAGE 1 SUMMARY OF FLOOD CONTROL WORK ON THE VEDDER RIVER 17 5 2 BASIN RUNOFF CHARACTERISTICS 17 8 3 MAJOR FLOODS ON CHILLIWACK RIVER. 179 4 SUMMARY OF SEASONAL FLOOD DATA. . . . . . . . 181 5 FLOOD FREQUENCY FLOWS 18 3 6 MAXIMUM INSTANTANEOUS FLOOD FREQUENCY ESTIMATES 18 4 7 FREQUENCY OF HISTORICAL FLOODS 18 5 8 SUMMARY OF MAPS/AIRPHOTOS ABOVE VEDDER CROSSING 18 6 9 BED MATERIAL DATA ABOVE VEDDER CROSSING 187 10 SUMMARY OF HYDROLOGIC DATA ALONG CHILLIWACK RIVER 18 8 11 SUMMARY OF GEOMORPHIC FEATURES ALONG CHILLIWACK RIVER 18 9 12 SUMMARY OF CHANNEL HYDRAULICS ALONG CHILLIWACK RIVER 190 13 INCIPIENT MOTION FOR BED MATERIAL ALONG CHILLIWACK RIVER 191 14 SUMMARY OF WIDTH CHANGES ABOVE VEDDER CROSSING 19 2 15 SUMMARY OF CHANNEL CHANGES AND SEDIMENT EROSION ABOVE VEDDER CROSSING. . . . 193 16 SUMMARY OF CROSS SECTION DATA BELOW VEDDER CROSSING 194 v i i TABLE TITLE PAGE 17 WATER SURFACE SLOPE SURVEYS 196 18 BANKFULL PROPERTIES OF BRAIDED SUB-CHANNELS ALONG THE VEDDER RIVER 19 7 19 COMPOSITE BED MATERIAL SIZE DISTRIBUTION ALONG VEDDER RIVER 198 20 DOWNSTREAM BED MATERIAL CHANGES ON GRAVEL RIVERS 199 21 SUMMARY OF SUSPENDED LOAD DATA ON VEDDER RIVER 200 22 SUMMARY OF BEDLOAD MEASUREMENTS COLLECTED ON VEDDER RIVER 201 23 SUMMARY OF AGGRADATION ESTIMATES PRIOR TO 1975 FLOOD 203 24 BEDLOAD TRANSPORT FOR VARIOUS FLOOD EVENTS 204 25 SUMMARY OF CHANNEL DATA ON FOUR RIVER CONTROL PROJECTS. 205 26 REGIME EQUATIONS FOR ACTIVE GRAVEL RIVERS 206 A . l SUMMARY DESCRIPTION OF MEASUREMENT SITES 279 v i i i LIST OF FIGURES FIGURE TITLE PAGE 1 Site Location 208 2 Study Area Below Vedder Crossing 209 3 Chilliwack River Channels Below Vedder Crossing 210 4 Channel Pattern of the Vedder River 1930-1976 211 5 Flood Paths Along Vedder River i n 1951, 1975 214 6 Chilliwack River Basin 215 7 Monthly Met Data for Chilliwack Basin 216 8 Summary of Stream Gauging Operations Along Chilliwack River 217 9 Monthly Flows Along Chilliwack River 218 10 H i s t o r i c a l Occurrences of Past Floods 219 11 Comparison of Two Snowmelt and Rainstorm Floods 220 12 Correlation Between Nooksack River and Chilliwack River Floods 221 13 Predicted and Recorded 1975 Flows 222 14 Predicted Flood Hydrographs for 1932 and 1951 223 15 Time Series of Annual Floods at Vedder Crossing 224 16 Flood Frequency Analysis at Vedder Crossing 225 i x FIGURE TITLE PAGE 17 Stream P r o f i l e of C h i l l i w a c k R i v e r 226 18 Fan P r o f i l e s 227 19 Channel C r o s s - S e c t i o n s Above Vedder C r o s s i n g 228 2 0 H y d r a u l i c Geometry a t Hydrometric Gauges Above Vedder C r o s s i n g 229 21 Channel Reach D e s c r i p t i o n s . . . . 230 22 Comparative A i r p h o t o s — V e d d e r C r o s s i n g to Liumchen Creek 235 2 3 Channel P a t t e r n Upstream of Vedder C r o s s i n g 236 24 Channel Changes Near Vedder C r o s s i n g 239 25 Conceptual Bedload Movement Above Vedder C r o s s i n g . . . . . . . 242 26 Approximate L o c a t i o n of Vedder R i v e r S e c t i o n s 243 27 C r o s s - S e c t i o n s Along Vedder R i v e r 244 28 S e c t i o n s Showing F l o o d p l a i n and Channel Topography 24 7 29 E f f e c t of F r a s e r and Vedder R i v e r Flows on the Stage i n the Vedder Canal 248 30 H y d r a u l i c Geometry a t Yarrow and Vedder C r o s s i n g 249 31 Comparison of R e s i s t a n c e Formulas Using Yarrow Data 250 32 Downstream Changes i n Bed M a t e r i a l S i z e Along Vedder R i v e r 251 33 Bedload G r a i n S i z e Measured a t Yarrow 252 X FIGURE TITLE PAGE 34 Bedload S i z e D i s t r i b u t i o n Curves a t D i f f e r e n t Flow C o n d i t i o n s 253 35 Bedload T r a n s p o r t a t Yarrow 254 36 Comparison of Measured and Computed Bedload a t Yarrow 255 37 Bedload Estimates at Vedder C r o s s i n g 256 38 T h e o r e t i c a l Aggradation P r o f i l e s 257 39 Comparison of Mean B e d l e v e l s , 1963-1975 258 40 E f f e c t of C h a n n e l i z a t i o n on Channel Geometry 259 41 S p e c i f i c Gauge Record Near Yarrow 260 42 S p e c i f i c Gauge Record a t Vedder C r o s s i n g 261 4 3 V a r i a t i o n i n D e p o s i t i o n Along Vedder R i v e r 2 62 44 Derived Hydrographs f o r Snowmelt and Rainstorm Floods 26 3 45 Wide Vedder R i v e r F l o o d C o n t r o l 264 46 P o s s i b l e Set-Back Dike and R i v e r T r a i n i n g Alignment 265 A . l Comparison of Bedload Formulas on Vedder R i v e r 280 A.2 Comparison of Bedload Formulas on Elbow R i v e r 281 A.3 Comparison of Bedload Formulas on North Saskatchewan R i v e r 282 A.4 Comparison of Bedload Formulas on Clearwater R i v e r 28 3 A.5 Comparison of Bedload Formulas on Snake R i v e r 284 x i ACKNOWLEDGEMENTS The a u t h o r i s v e r y g r a t e f u l t o t h e f i n a n c i a l s u p -p o r t and e n c o u r a g e m e n t g i v e n by h i s s u p e r v i s o r , P r o f e s s o r M. C. Q u i c k . A l s o , he w o u l d l i k e t o t h a n k D r . S. 0. R u s s e l l a n d D r . M. C h u r c h f o r t h e i r many h e l p f u l d i s c u s -s i o n s . A p p r e c i a t i o n i s a l s o e x t e n d e d t o t h e s t a f f o f W a t e r S u r v e y o f C a n a d a a nd t h e B.C. W a t e r R e s o u r c e s S e r v i c e who p r o v i d e d u n p u b l i s h e d d a t a t h a t was u s e d i n t h i s s t u d y . F i n a l l y , t o my w i f e , C a t h y . T h i s t h e s i s c o u l d n o t hav e b e e n c o m p l e t e d w i t h o u t y o u r p a t i e n c e a n d s u p p o r t . 1 CHAPTER I INTRODUCTION The C h i l l i w a c k R i v e r r i s e s i n t h e C a s c a d e M o u n t a i n s 100 m i l e s e a s t o f V a n c o u v e r , B r i t i s h C o l u m b i a and f l o w s f o r 2 5 m i l e s t h r o u g h a r u g g e d , m o u n t a i n o u s v a l l e y . N e a r t h e t o w n o f V e d d e r C r o s s i n g t h e r i v e r e m erges f r o m a n a r -row c a n y o n and f l o w s a c r o s s t h e F r a s e r L o w l a n d u n t i l j o i n -i n g t h e F r a s e r R i v e r n e a r C h i l l i w a c k . D o w n s t r e a m o f V e d d e r C r o s s i n g t h e C h i l l i w a c k R i v e r h a s b u i l t a c o n i c a l a l l u v i a l f a n by d e p o s i t i n g i t s s e d i -ment l o a d o f s a n d and g r a v e l , p e r i o d i c a l l y c a u s i n g t h e r i v e r c h a n n e l t o s h i f t a c r o s s a w i d e a r e a . B e l o w V e d d e r C r o s s i n g t h e r i v e r i s known as t h e V e d d e r R i v e r , s i n c e t h e l a s t m a j o r c h a n n e l s h i f t d i v e r t e d t h e C h i l l i w a c k R i v e r down V e d d e r C r e e k . C o n t i n u e d c h a n n e l a g g r a d a t i o n i n r e c e n t t i m e s h a s c o n t r i b u t e d t o f r e q u e n t f l o o d i n g t o f a r m s and t o w n s l o c a t e d n e a r t h e r i v e r . I n December 1975 f l o o d i n g on t h e V e d d e r R i v e r c a u s e d a p p r o x i m a t e l y 260,000 c u b i c y a r d s o f g r a v e l t o be d e p o s i t e d o v e r a d i s t a n c e o f a p p r o x -i m a t e l y t h r e e m i l e s . P a s t a t t e m p t s a t f l o o d c o n t r o l h a v e p r o d u c e d s t r o n g c r i t i c i s m f r o m e n v i r o n m e n t a l g r o u p s and f i s h e r i e s a g e n c i e s due t o d e s t r u c t i o n o f s p a w n i n g and r e a r i n g a r e a s f o r s a l -mon a n d s t e e l h e a d t r o u t . The V e d d e r R i v e r s u p p o r t s i m p o r -t a n t c o m m e r c i a l p i n k a n d chum s a l m o n r u n s a s w e l l a s a s p o r t f i s h e r y f o r c o h o and s t e e l h e a d . 2 Th i s c o n f l i c t between f l o o d c o n t r o l and f i s h e r i e s management i l l u s t r a t e s the need f o r long term p l a n n i n g o f development along the Vedder R i v e r . I d e a l l y , any d e s i g n of f l o o d c o n t r o l measures should r e c o g n i z e the c h a r a c t e r -i s t i c morphologic and sediment t r a n s p o r t processes occur-r i n g on the r i v e r . U n f o r t u n a t e l y , r i v e r e n g i n e e r i n g i s i n a r e l a t i v e l y p r i m i t i v e stage of development compared to many other e n g i n e e r i n g d i s c i p l i n e s . At p r e s e n t , r i v e r processes are o n l y p o o r l y understood and the e f f e c t s o f i n t e r f e r i n g w i t h these processes cannot always be pre -d i c t e d a c c u r a t e l y . As a r e s u l t , many examples have been recorded where a l t e r i n g a r i v e r ' s regime has caused ad-verse environmental consequences and unexpected changes to the e a r l i e r p a t t e r n o f r i v e r .behaviour (Parker and Andres, 1976). T h e r e f o r e , u n t i l c o n s i d e r a b l e advances have been made i n understanding b a s i c r i v e r p r o c e s s e s , engineers i n v o l v e d i n r i v e r problems must r e l y on records of p a s t experiences and on sy s t e m a t i c o b s e r v a t i o n s o f r i v e r behaviour. Although a l l u v i a l fans occur throughout the world, most p r e v i o u s s t u d i e s have been c a r r i e d out i n s e m i - a r i d or a r i d environments ( B u l l , 1962, 1964; Denny, 1965; Hooke, 1967; L u s t i g , 1965; L u s t i g and Busch, 1967). There has been c o n s i d e r a b l y l e s s documentation o f a l l u v i a l fans l o c a t e d i n temperate, mountainous environments. S t u d i e s have been c a r r i e d out i n the A l b e r t a Rockies (McPherson 3 and Hurst, 1972; Smith, 1972; NHCL, 1979), i n B r i t i s h Columbia (Ryder, 1970, 1971; NHCL, 1975, 1976) and i n the A r c t i c (Legget e t a l , 1966; Anderson and Hussey, 1962). In a d d i t i o n M a l c o v i s h (1974) c a r r i e d out a number of model experiments t o i l l u s t r a t e some g e n e r a l p r i n c i p l e s of a l l u v i a l f an behaviour. In order to understand the nature of the sedimenta-t i o n and f l o o d i n g processes on the Vedder R i v e r , a number of key q u e s t i o n s must be answered. Some of the most important a r e : 1. What are the magnitudes and a s s o c i a t e d f r e q u e n c i e s of f l o o d s on the r i v e r ? 2. What i s the volume of sediment t h a t can be d e p o s i t e d on the fan d u r i n g these f l o o d s ? 3. Where does most sediment d e p o s i t i o n occur? What f a c t o r s govern the p a t t e r n of d e p o s i t i o n along the r i v e r ? 4. How has past c h a n n e l i z a t i o n and f l o o d c o n t r o l a c t i v i t i e s a l t e r e d the p a t t e r n of sedimentation? 5. What have been the most important l a t e r a l and v e r t i c a l a c t i v i t i e s on the r i v e r , and how do these a f f e c t the present-day and f u t u r e r i v e r p rocesses? 6. Can a p a r t i c u l a r channel alignment be found t h a t w i l l p r o v i d e long term f l o o d p r o t e c t i o n and a t the same time p r o v i d e a s u i t a b l e spawning h a b i t a t f o r the salmon? 4 7 . Wha t a r e t h e m a i n s e d i m e n t s o u r c e s i n t h e C h i l l i w a c k R i v e r b a s i n a n d c a n s e d i m e n t a t i o n p r o b l e m s o n t h e f a n b e s o l v e d b y u p s t r e a m s e d i m e n t c o n t r o l ? The o b j e c t i v e o f t h i s s t u d y i s t o t r y t o p r o v i d e a n s w e r s t o m o s t o f t h e s e q u e s t i o n s . U n f o r t u n a t e l y , m o s t o f t h e s e c a n o n l y be a n s w e r e d i n c o m p l e t e l y o r i n a q u a l i -t a t i v e f a s h i o n . H o w e v e r , i t i s h o p e d t h a t t h i s s t u d y w i l l c o n t r i b u t e t o u n d e r s t a n d i n g t h e n a t u r e o f t h e f l o o d i n g p r o b l e m o n t h e V e d d e r R i v e r a n d , a s w e l l , p r o v i d e some g e n e r a l o b s e r v a t i o n s o n s e d i m e n t a t i o n p r o c e s s e s o n g r a v e l r i v e r s . T h i s s t u d y h a s b e e n s u b d i v i d e d i n t o n i n e s e c t i o n s . C h a p t e r 2 p r o v i d e s h i s t o r i c a l a n d b a c k g r o u n d i n f o r m a t i o n o n t h e f l o o d c o n t r o l p r o b l e m o n t h e V e d d e r R i v e r . Two o f t h e m o s t i m p o r t a n t f a c t o r s g o v e r n i n g c h a n n e l m o r p h o l o g y a r e t h e h y d r o l o g i c a l c h a r a c t e r i s t i c s a n d g e o -m o r p h i c s e t t i n g o f t h e b a s i n . T h e s e t o p i c s a r e d i s c u s s e d i n C h a p t e r s 3 a n d 4 r e s p e c t i v e l y . I n o r d e r t o u n d e r s t a n d t h e d e p o s i t i o n a l p r o c e s s e s o n t h e f a n , t h e m o r p h o l o g i c a l p r o c e s s e s g o i n g o n u p s t r e a m o f V e d d e r C r o s s i n g m u s t a l s o be c o n s i d e r e d . T h e r e f o r e , a b r i e f o v e r v i e w o f t h e 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 o f t h e C h i l l i w a c k R i v e r b e t w e e n V e d d e r C r o s s i n g a n d C h i l l i w a c k L a k e i s p r e s e n t e d i n C h a p t e r 5 . C h a p t e r s 6 a n d 7 o u t l i n e t h e m o s t i m p o r t a n t h y d r a u l i c a n d s e d i m e n t t r a n s p o r t c h a r a c t e r i s t i c s o f t h e V e d d e r R i v e r 5 while Chapter 8 d e s c r i b e s the d e p o s i t i o n a l processes t h a t have o c c u r r e d on the fan over the l a s t c e n t u r y . F i n a l l y , Chapter 9 mentions some p o s s i b l e methods of p r o v i d i n g f l o o d c o n t r o l on the fan and makes some comments on t h e i r long term e f f e c t i v e n e s s . R e l a t i v e l y l i t t l e d i s c u s s i o n has been made on the f i s h e r i e s r e s o u r c e s of the Vedder R i v e r i n t h i s study. T h i s i s because the main emphasis of t h i s t h e s i s i s to document the p h y s i c a l processes on the r i v e r . However, f u r t h e r d i s c u s s i o n of the impact of v a r i o u s f l o o d c o n t r o l measures of the salmon stocks i n the Vedder R i v e r i s con-t a i n e d i n the study by P e t e r s (1978). 6 CHAPTER I I HISTORY OF RIVER A C T I V I T Y 2.1 S i t e L o c a t i o n A l a r g e s c a l e map i n d i c a t i n g t h e l o c a t i o n o f t h e C h i l l i w a c k R i v e r r e l a t i v e t o V a n c o u v e r i s shown on F i g u r e 1. I n a d d i t i o n , a s i t e p l a n s h o w i n g m o s t o f t h e p r o m i n e n t g e o g r a p h i c a l f e a t u r e s d o w n s t r e a m o f V e d d e r C r o s s i n g h a s a l s o b e e n i n c l u d e d i n F i g u r e 2. F e a t u r e s on t h i s p l a n w i l l be r e f e r r e d t o f r e q u e n t l y t h r o u g h o u t t h i s c h a p t e r and i n s u b s e q u e n t s e c t i o n s . 2.2 E a r l y H i s t o r y and S e t t l e m e n t The f i r s t w h i t e man t o e n t e r t h e C h i l l i w a c k R i v e r b a s i n was S i m o n F r a s e r d u r i n g h i s e x p l o r a t i o n o f t h e F r a s e r R i v e r i n 1808. H o w e v e r , some o f t h e e a r l i e r n a t u r a l h i s t o r y o f t h e C h i l l i w a c k R i v e r i s r e c o r d e d i n t h e t r a d i -t i o n s and l e g e n d s o f t h e C h i l l i w a c k I n d i a n t r i b e s , whose l i v e s w e r e c o n s t a n t l y a f f e c t e d by t h e r i v e r ' s b e h a v i o u r . Some o f t h i s e a r l y h i s t o r y i s c o n t a i n e d i n r e p o r t s by D u f f ( 1 9 5 2 ) , W e l l s (1965) and Ramsey ( 1 9 7 5 ) . A c c o r d i n g t o l e g e n d a t one t i m e t h e C h i l l i w a c k r i v e r f l o w e d w e s t b e l o w V e d d e r C r o s s i n g i n t o Sumas L a k e ( F i g u r e 2 ) . D u r i n g a l a r g e f l o o d t h e r i v e r l e f t i t s c o u r s e and f l o w e d n o r t h , r e a c h i n g t h e F r a s e r R i v e r up-s t r e a m f r o m C h i l l i w a c k M o u n t a i n . E v e n t u a l l y new c h a n n e l s 7 were formed as the mouth of the r i v e r worked westward, down the F r a s e r R i v e r (Duff, 1952). The S t a l o Indians who i n h a b i t e d the F r a s e r V a l l e y a t t h i s time named t h i s channel "Thewlnum" meaning " r i v e r t h a t changed i t s course." By the time s e t t l e r s a r r i v e d i n 1850 the r i v e r was s p l i t i n t o two channels below Vedder C r o s s i n g : the C h i l l i w a c k R i v e r with i t s mouth near C h i l l i w a c k Mountain and Luck-a-Kuck Creek (Duff, 1952). U n f o r t u n a t e l y , the date of t h i s major channel s h i f t i s unknown. However, e x p l o r a t i o n s by F r a n c o i s Annance i n 1828 i n d i c a t e d a s i n g l e major channel d i d not flow i n t o Sumas Lake (Ramsey, 1975) s u g g e s t i n g the channel s h i f t preceded h i s v i s i t . By 18 6 6 settlements had been e s t a b l i s h e d a t C h i l l i w a c k , Sumas and S a r d i s . In 1873 a second major channel s h i f t commenced when p a r t of the C h i l l i w a c k R i v e r found i t s way i n t o Vedder Creek and flowed i n t o Sumas Lake. In 1875 a very severe f l o o d caused the C h i l l i w a c k R i v e r t o abandon i t s channel and the main flow was d i -v e r t e d down Luck-a-Kuck Creek (LeBaron, 19 08). A c c o r d i n g to Ramsey (197 5) the channel of the Luck-a-Kuck i n c r e a s e d i t s width from 30 f e e t to 200 f e e t almost o v e r n i g h t washing out a l l b r i d g e s spanning the creek. E v e n t u a l l y the channel s h i f t e d again and Vedder Creek began to cap-t u r e most o f the flow u n t i l both the Luck-a-Kuck and the o l d C h i l l i w a c k channels were abandoned (LeBaron, 1908). 8 F i g u r e 3 shows a r e p r o d u c t i o n of an e a r l y map of the C h i l l i w a c k area prepared by the Royal M i l i t a r y Engineers between 1868 and 1903, d u r i n g t h i s p e r i o d of channel s h i f t i n g . T h i s map shows the r i v e r s p l i t i n t o three channels w i t h the Luck-a-Kuck channel a p p a r e n t l y t a k i n g most of the flow. In 18 94 the main channel began to s h i f t once more down Luck-a-Kuck Creek u n t i l a l o g jam formed p r e v e n t i n g f u r t h e r d i v e r s i o n . Residents from Sumas who l i v e d near the banks of Vedder Creek t r i e d t o break the jam but were prevented by the C h i l l i w a c k s e t t l e r s so t h a t the Vedder Channel became the s o l e o u t l e t of the C h i l l i w a c k R i v e r . Although popular accounts of t h i s p e r i o d suggest r e s i d e n t s from C h i l l i w a c k a i d e d i n the i r i v e r ' s d i v e r s i o n down Vedder Creek ( S i n c l a i r , 1961; Ramsey, 1975), h i s t o r i c a l r e p o r t s i n d i c a t e the channel s h i f t s were probably e n t i r e l y n a t u r a l p r o c e s s e s . For example, a summary of the r e p o r t on the f l o o d i n g by C o l o n e l Baker, P r o v i n c i a l S e c r e t a r y , s t a t e d "A l o g jam had formed i n Luck-a-Kuck Creek which prevented the main flow of the Vedder waters from going down the Luck-a-Kuck i n t o S a r d i s . The Sumas people t r i e d to break up the jam but were stopped by the C h i l l i w a c k people. F e e l i n g s ran high and both s i d e s threatened t o use f o r c e of arms." (Annual r e p o r t of the Lands S e r v i c e f o r 1946) A f t e r the f l o o d i n g of 18 94 the P r o v i n c i a l Government t r i e d t o s t a b i l i z e the Vedder R i v e r by b u i l d i n g a rock f i l l e d c r i b and revetment across the o l d entrance to 9 Luck-a-Kuck Creek (LeBaron, 1908). Since t h i s time the r i v e r has been maintained i n the Vedder Channel so t h a t downstream of Vedder C r o s s i n g the C h i l l i w a c k R i v e r i s r e f e r r e d t o as "Vedder R i v e r . " A s i d e from wi n t e r f l o o d i n g by the C h i l l i w a c k R i v e r , e a r l y s e t t l e r s were faced with frequent f l o o d i n g by the F r a s e r R i v e r . During the summer f r e s h e t the F r a s e r R i v e r f l o o d e d the lowlands between Sumas and C h i l l i w a c k Mountain, backing water up i n t o Sumas Lake, Sumas R i v e r and the Vedder R i v e r . A f t e r severe f l o o d i n g i n 1894, s e t t l e r s p e t i t i o n e d the p r o v i n c i a l government t o r e c l a i m Sumas Lake f o r farmland and to c o n s t r u c t d i k e s along the F r a s e r R i v e r . Almost a l l engineers i n v o l v e d i n r e c l a m a t i o n s t u d i e s agreed the key problem was to convey the Vedder River s e c u r e l y and permanently ac r o s s Sumas P r a i r i e to the F r a s e r R i v e r . P r i o r to 1908 a l l schemes i n v o l v e d d i v e r t i n g the r i v e r back down Luck-a-Kuck Creek, thereby t a k i n g the r i v e r completely out of the d i k i n g d i s t r i c t . Although t h i s p l a n would have s i m p l i f i e d the r e c l a m a t i o n of Sumas Lake, o p p o s i t i o n from r e s i d e n t s l i v i n g i n S a r d i s (near the o l d Luck-a-Kuck channel) prevented the p l a n from being accepted. L a t e r plans by B r i c e and Smith (1913) and S i n c l a i r (1918) proposed t o d i v e r t the r i v e r from i t s course about one h a l f m i l e e a s t o f Sumas Lake and c o n f i n e i t i n an excavated channel n o r t h a c r o s s Sumas P r a i r i e and i n t o the F r a s e r R i v e r west of C h i l l i w a c k 10 Mountain ( S i n c l a i r , 1961). E v e n t u a l l y the S i n c l a i r p l a n was adopted and c o n s t r u c t i o n commenced on the r e c l a m a t i o n of Sumas Lake i n 1919. The o b j e c t i v e s of the p r o j e c t were t h r e e f o l d : (1) t o shut out the F r a s e r R i v e r d u r i n g f r e s h e t from the Sumas V a l l e y and a d j o i n i n g lowlands (2) t o d r a i n Sumas Lake i n order t o i n c r e a s e the area a v a i l a b l e f o r a g r i c u l t u r e i n the d i s t r i c t (3) t o c h a n n e l i z e the Vedder and Sumas R i v e r along t h e i r r o utes a c r o s s Sumas P r a i r i e to the F r a s e r R i v e r The S i n c l a i r p l a n i n c l u d e d a s e r i e s o f stream d i v e r s i o n s to dispose of i n t e r n a l drainage and c o n s t r u c t i o n o f the no r t h and south Vedder d i k e s , extending on both s i d e s of the Vedder R i v e r t o the B.C. E l e c t r i c Railway b r i d g e 1 embankment near Yarrow ( S i n c l a i r , 1961). The n o r t h Vedder dike t i e d i n t o a d i k e running along the F r a s e r R i v e r t o C h i l l i w a c k Mountain while the south Vedder di k e extended to a c o n t r o l dam on Sumas R i v e r . T h i s dam prevented the F r a s e r R i v e r backwater from p e n e t r a t i n g up the Sumas Riv e r d u r i n g the s p r i n g f r e s h e t . Under normal c o n d i t i o n s the Sumas R i v e r was passed through s l u i c e gates w h i l e d u r i n g f l o o d s the r i v e r was pumped over the dam. In a d d i t i o n a s m a l l e r dam and pumphouse were c o n s t r u c t e d on M c G i l l i v a r y Creek to dispose of i n t e r n a l drainage from the East Sumas P r a i r i e . 11 The major requirements of the Vedder Canal have been: (1) t o c o n t a i n the F r a s e r R i v e r backwater which extends up the Vedder R i v e r d u r i n g the s p r i n g f r e s h e t (2) t o pass f l o o d flows on the Vedder R i v e r w i t h -out s c o u r i n g i t s banks or to l o s e channel c a p a c i t y due to e x c e s s i v e sediment aggrad a t i o n Although the c a n a l was planned to be s e l f - s c o u r i n g , S i n c l a i r a n t i c i p a t e d t h a t movement of g r a v e l i n the Vedder R i v e r would make i t necessary t o remove g r a v e l bars from time to time near the entrance of the c a n a l ( S i n c l a i r , 1961). The f i n a l c a n a l design c a l l e d f o r a channel excav-ated approximately seven f e e t i n t o Sumas P r a i r i e , with d i k e s spaced 500 f e e t a p a r t a t the c r e s t , and a channel slope o f approximately 0.00028. The c a n a l was excavated with an e l e c t r i c powered s u c t i o n dredge while the d i k e s . were c o n s t r u c t e d from the h y d r a u l i c f i l l pumped from the channel. The S i n c l a i r p l a n was completed i n 1924 at a f i n a l c o s t o f $3,4 00,000. The t o t a l area r e c l a i m e d by the pro-j e c t was approximately 33,000 a c r e s , s u b d i v i d e d as f o l l o w s : E a s t Sumas P r a i r i e 5,000 acres Sumas Lake Area 10,000 acres West Sumas P r a i r i e 15,000 acres Area i n Washington S t a t e 3,000 acres 12 2.3 R i v e r T r a i n i n g and F l o o d i n g Along the Vedder R i v e r Although the o r i g i n a l Sumas d i k i n g and drainage pro-j e c t was completed i n 1924, the n o r t h and south Vedder _dikes which border the Vedder Canal were never extended pas t the B.C. E l e c t r i c Railway b r i d g e . T h e r e f o r e , a l -though Yarrow has been given some degree of f l o o d p r o t e c -t i o n (provided the d i k e s and r a i l w a y embankment are not overtopped), the land upstream of the town has remained r e l a t i v e l y u nprotected. As a r e s u l t , t h i s l a n d has been s u b j e c t to frequent f l o o d i n g by the Vedder R i v e r . In the past, much of t h i s land remained undeveloped or was used f o r a g r i c u l t u r a l purposes so t h a t a c t u a l f l o o d damages have remained low. However, i n r e c e n t times there has been a t r e n d towards i n c r e a s e d r e s i d e n t i a l development along the r i v e r so t h a t demands f o r improved f l o o d pro-t e c t i o n have i n c r e a s e d . Attempts at c o n t r o l l i n g f l o o d i n g above Yarrow have r e l i e d mainly on c o n s t r u c t i o n of r i p - r a p p e d bank p r o t e c -t i o n and on p e r i o d i c channel maintenance. T h i s work has been conducted by the f e d e r a l government (Unemployment R e l i e f d u r i n g the d e p r e s s i o n ) , P r o v i n c i a l Department of P u b l i c Works, Department of Highways, P r o v i n c i a l Water Resources S e r v i c e and D i s t r i c t M u n i c i p a l i t y of C h i l l i w a c k (Marr, 1964). For the most p a r t work has been done on an emergency b a s i s whenever f l o o d problems arose or whenever money was made a v a i l a b l e f o r f l o o d c o n t r o l works. T h i s 13 has r e s u l t e d i n very l i t t l e e f f e c t i v e long term f l o o d p r o t e c t i o n upstream of the r a i l w a y b r i d g e . In the e a r l y years of channel maintenance most a c t i v i t y went towards p r e v e n t i n g the C h i l l i w a c k R i v e r from reoccupying one of i t s abandoned channels near Vedder C r o s s i n g . A permanent r o c k - f i l l e d c r i b and revetment was c o n s t r u c t e d across the entrance to the Luck-a-Kuck Channel i n order to s t a b i l i z e the r i v e r i n a s i n g l e channel. The l a r g e s t f l o o d recorded a t the Water Survey of Canada gauge at Vedder C r o s s i n g o c c u r r e d on December 29, 1917 and reached 27,000 c f s (mean d a i l y f l o w ) . However, i t appears t h i s f l o o d caused l i t t l e damage except f o r washing out the highway b r i d g e near Vedder C r o s s i n g . In f a c t , o l d newspaper accounts of the f l o o d d i d not mention any damage to the towns of Yarrow or Sumas: "The water i s higher i n the Vedder R i v e r than i t has been f o r many years and although the t r a f f i c b r i d g e on the trunk road i s s t i l l s t a n d i n g . . . t h e r e was j u s t as much water sweeping pas t the b r i d g e as under i t . " (The Vancouver Sun, January 1, 1918) "B.C. E l e c t r i c o f f i c i a l s were g l a d to l e a r n the (railway) b r i d g e c r o s s i n g the Vedder R i v e r was damaged to o n l y an i n s i g n i f i c a n t e x t e n t . " (The Vancouver Sun, January 4, 1918) Marr (1964) r e p o r t e d t h a t the Vedder R i v e r over-topped the n o r t h end of the r a i l w a y embankment i n 1932, washed out 1,000 f e e t of t r a c k and f l o o d e d Sumas East P r a i r i e . F o l l o w i n g t h i s f l o o d , the n o r t h Vedder Dike was 14 extended about 5,000 f e e t i n order to p a r a l l e l the r a i l w a y embankment. Ac c o r d i n g to h i s t o r i c a l accounts, e x t e n s i v e f l o o d i n g took p l a c e i n the Sumas-Yarrow area i n 1935, 1948 and 1951 ( S i n c l a i r , 1961; Marr, 1964). The f l o o d of January 1935 was one of the most severe i n the h i s t o r y of the F r a s e r V a l l e y and r e s u l t e d i n l a r g e areas of Sumas P r a i r i e t o be under water (The Vancouver P r o v i n c e , January 25, 1935). However, i t appears most of the f l o o d damage was caused by the Sumas R i v e r and not the Vedder R i v e r . A c c o r d i n g to Bruce Dixon, P r o v i n c i a l D i k i n g Commissioner at t h a t time, the 1935 f l o o d was due mainly t o : (1) d r i f t s of s i x to e i g h t f e e t of snow on Sumas P r a i r i e f o l l o w e d by r a i n and r a p i d thaw (2) an i c e jam on the Sumas R i v e r sent water over i t s bank and t o r e away 300 f e e t of Sumas dike (3) the Sumas pumping s t a t i o n was put out of com-mi s s i o n when the e l e c t r i c power f a i l e d . (The Vancouver P r o v i n c e , January 22, 19 35) Marr (1964) r e p o r t e d the r a i l w a y embankment was over-topped again i n 194 8. Based on a i r p h o t o s taken on J u l y 4 and on newspaper accounts, most of the f l o o d i n g t h i s time was caused by the r e c o r d flows on the F r a s e r R i v e r . Accord-I i n g t o S i n c l a i r (1961), h i g h water l e v e l s on the F r a s e r R i v e r overtopped i t s dikes and inundated much of the low rec l a i m e d Sumas Lake area. High water l e v e l s i n the F r a s e r 15 R i v e r would have c r e a t e d a high backwater c o n d i t i o n i n c. the Vedder R i v e r which c o u l d have extended w e l l p a s t the r a i l w a y b r i d g e a t Yarrow. T h e r e f o r e , t h i s backwater may have been an important f a c t o r i n the ove r t o p p i n g of the r a i l w a y embankment. The f l o o d of February 10, 1951 was t r i g g e r e d by heavy r a i n s , t o t a l l i n g over 11 inches i n three days and by m i l d temperatures which reached up to 54°F a t C h i l l i w a c k . The Vedder R i v e r broke out of i t s banks a t s e v e r a l l o c a -t i o n s (Figure 5) between Vedder C r o s s i n g and the r a i l w a y b r i d g e , w i t h the overbank flow e v e n t u a l l y d i r e c t e d back i n t o the main channel by the r a i l w a y embankment. Ac c o r d i n g t o newspaper r e p o r t s : "The hardest h i t p o i n t was a t Yarrow where a l o g jam sent the Vedder R i v e r o f f i t s course over homes, f i e l d s and roads. At noon the RCMP broadcast a s p e c i a l a l e r t t o the 1,200 c i t i z e n s of Yarrow t e l l i n g them t o be pre -pared t o evacuate t h e i r homes." (The Vancouver Sun, February 10, 1951) However, the t h r e a t to Yarrow was eased when "the B.C. E l e c t r i c r a i l embankment n o r t h of the town was dynamited to get the Vedder c l o s e r t o i t s proper course" (The Vancouver Sun, February 12, 1951). As a r e s u l t , only minor f l o o d damage was r e p o r t e d along the n o r t h s i d e of the r i v e r (Marr, 1964). F o l l o w i n g the f l o o d of 1951, p r o p o s a l s were made f o r a comprehensive f l o o d c o n t r o l p r o j e c t along the Vedder R i v e r . In 1952, the P r o v i n c i a l P u b l i c Works 16 Department proposed t o c o n s t r u c t a 240 f o o t wide s t r a i g h t channel, bordered by 12 f o o t h i g h d i k e s extending from Vedder C r o s s i n g to the B.C. E l e c t r i c Railway b r i d g e . The c o s t of t h i s p r o j e c t was estimated to be about $500,000 with the p r o v i n c i a l government o f f e r i n g a 50-50 c o s t s h a r i n g agreement with the D i s t r i c t M u n i c i p a l i t y of C h i l l i w a c k . Although the m u n i c i p a l i t y supported the p r o j e c t , l a c k of funds caused the e v e n t u a l abandonment of the scheme. A m o d i f i e d p r o p o s a l was presented again i n 1964 (Marr, 1964), however t h i s p r o j e c t was a l s o aban-doned due to l a c k of f i n a n c i n g . Although a comprehensive f l o o d c o n t r o l p r o j e c t was never c a r r i e d out on the Vedder R i v e r , annual channel maintenance continued under c o o p e r a t i o n between the p r o v i n c i a l government and the D i s t r i c t M u n i c i p a l i t y of C h i l l i w a c k . A summary of some of the work c a r r i e d out on the Vedder R i v e r between 1951 and 1974 i s shown i n Table 1. During t h i s p e r i o d channel maintenance seemed to be r e q u i r e d most f r e q u e n t l y i n three areas: - o p p o s i t e Peache Road about one m i l e downstream of Vedder C r o s s i n g - o p p o s i t e Browne and Lickman Roads - near the B.C. E l e c t r i c Railway b r i d g e . Two main methods of channel maintenance were used on the Vedder R i v e r . During low water i n f a l l or w i n t e r , snags were removed and b u l l d o z e r s were used to p i l e g r a v e l 17 a l o n g t h e b a n k s i n o r d e r t o e s t a b l i s h a w e l l d e f i n e d c h a n n e l . T h i s t a c t i c was o f t e n u n s u c c e s s f u l a s t h e r i v e r f r e q u e n t l y a d o p t e d a new c h a n n e l u p s t r e a m i n w h i c h c a s e t h e w o r k was c o m p l e t e l y b y p a s s e d . A l t e r n a t i v e l y , d u r i n g e m e r g e n c y c o n d i t i o n s , r o c k w i n g dams w e r e o f t e n c o n s t r u c t e d i n o r d e r t o d i v e r t t h e r i v e r c u r r e n t away f r o m e r o d i n g b a n k s . U n f o r t u n a t e l y w i n g dams w e r e l i a b l e t o i n i t i a t e e r o s i o n o n t h e o p p o s i t e r i v e r b a n k a n d a l s o a r o u s e d p r o -t e s t s f r o m f i s h e r i e s o f f i c i a l s . P r o b a b l y o n e o f t h e e a r l i e s t c a s e s w h e r e f i s h e r i e s a g e n c i e s i n t e r v e n e d i n f l o o d c o n t r o l o p e r a t i o n s o c c u r r e d o n S e p t e m b e r 2 4 , 1 9 5 6 . A t t h i s t i m e t h e D e p a r t m e n t o f F i s h e r i e s d e m a n d e d t h e r e m o v a l o f a w i n g dam n e a r B r o w n e R o a d i n o r d e r t o a l l o w s a l m o n a c c e s s t o a s i d e c h a n n e l . The n e x t m a j o r c o n f r o n t a t i o n o c c u r r e d i n 1964 when g r a v e l was d r e d g e d f r o m t h e r i v e r ' s m a i n c h a n n e l i n o r d e r t o b u i l d d i k e s a l o n g H o p e d a l e S l o u g h . A c c o r d i n g t o f i s h e r i e s o f f i c i a l s , t h e d r e d g i n g was c a r r i e d o u t i n a n a r e a w h e r e a p p r o x i m a t e l y 1 0 , 0 0 0 chum a n d o v e r 2 5 , 0 0 0 p i n k s a l m o n h a d s p a w n e d , a n d a t a t i m e when many o f t h e e g g s w e r e s t i l l i n t h e g r a v e l . The d i f f e r e n t a t t i t u d e s t o w a r d s f l o o d c o n t r o l a n d e n v i r o n m e n t a l p r o t e c t i o n e x p r e s s e d b y t h e D e p a r t m e n t o f F i s h e r i e s a n d M u n i c i p a l i t y o f C h i l l i w a c k i s i l l u s t r a t e d b e l o w : "I w i s h t o b r i n g t o y o u r a t t e n t i o n a r e c e n t d e v e l o p m e n t w h i c h h a s r e s u l t e d i n t h e l o s s o f many m i l l i o n s o f chum s a l m o n a n d p i n k 18 salmon eggs. T h i s has been the d i r e c t r e s u l t of f l o o d c o n t r o l measures i n the lower Vedder R i v e r . " W. R. Hourston Department of F i s h e r i e s March 16, 1964 ( l e t t e r to the Reeve of the D i s t r i c t M u n i c i p a l i t y of C h i l l i w a c k ) "When I t h i n k of t h i s r i v e r i n spate on i t s mad t e r r i f y i n g plunge through our area, I thank the Almighty f o r the p r o t e c t i o n works c a r r i e d out." W. G. R. Simpson Reeve, Township of C h i l l i w a c k March 17, 1964 ( r e p l y to W. R. Hourston) A f t e r 1964 the Department of F i s h e r i e s appears t o have taken a more a c t i v e r o l e i n a l l f l o o d c o n t r o l works on the Vedder R i v e r . For example, i n 1967 F i s h e r i e s r e f u s e d to permit the M u n i c i p a l i t y to dredge 6,000 c u b i c yards of g r a v e l from the r i v e r near Hopedale Road. Due t o F i s h e r i e s r e s t r i c t i o n s , most f l o o d c o n t r o l work s i n c e 1964 has i n v o l v e d p l a c i n g r i p r a p along the r i v e r banks i n s t e a d of channel e x c a v a t i o n . F i s h e r i e s a l s o r e s t r i c t e d commercial g r a v e l removal o p e r a t i o n s on the Vedder R i v e r a t t h i s time. P r i o r to 1964 s e v e r a l p r i v a t e companies excavated g r a v e l from an area approximately 1 m i l e down-stream of the r a i l w a y b r i d g e (P. Heptner, p e r s o n a l com-munication) . At p r e s e n t , F i s h e r i e s has granted o n l y one l i c e n s e to remove 5,000 c u b i c yards of g r a v e l per year near the head of the Vedder Canal. Over the l a s t 2 5 years c o n s t r u c t i o n of bank pro-t e c t i o n and i n c r e a s e d f l o o d p l a i n encroachment has induced 19 many obvious changes to the Vedder R i v e r (Figure 4). Some of the most common r e s u l t s of these developments have been: - c u t o f f of s i d e channels and sloughs from the main channel - g e n e r a l r i v e r s t r a i g h t e n i n g by e l i m i n a t i o n of meanders or bends - r e d u c t i o n i n channel width due to c o n s t r u c t i o n of bank p r o t e c t i o n . Probably the most d r a s t i c m o d i f i c a t i o n s to the Vedder R i v e r have o c c u r r e d between the r a i l w a y b r i d g e and Ford Road. In t h i s 1% m i l e reach c o n s t r u c t i o n o f bank p r o t e c t i o n has r e s u l t e d i n a r e d u c t i o n i n channel width from an average of 670 f e e t i n 1956 to 350 f e e t i n 1969, r e p r e s e n t i n g a l o s s of approximately 75 acres of r i v e r channel. T h i s r e c l a m a t i o n of r i v e r bottom land has come about through an unusual s e t of circumstances s t a r t i n g back i n 1875 when the C h i l l i w a c k R i v e r s h i f t e d i t s course down Vedder Creek. Since most of Sumas had been d i v i d e d i n t o l o t s by 1858, many p r o p e r t y owners l o s t c o n s i d e r a b l e areas of land when the C h i l l i w a c k R i v e r s h i f t e d . Rather than s e l l t h i s l a n d back t o the government, some r e s i -dents r e t a i n e d p o s s e s s i o n of land occupied by the r i v e r , i n the hope t h a t t h e i r p r o p e r t y c o u l d some day be r e -claimed. T h e r e f o r e r e s i d e n t s have t r i e d i n the past t o 20 r e g a i n a s much l a n d a s p o s s i b l e b y b u i l d i n g b a n k p r o t e c -t i o n t o c o n s t r i c t t h e r i v e r . T h i s p o l i c y s e e m e d t o r e -c e i v e u n o f f i c i a l a p p r o v a l f r o m t h e p r o v i n c i a l g o v e r n m e n t ( K i e r a n s , 1959) a n d t h e W a t e r I n v e s t i g a t i o n s B r a n c h ( M a r r , 1 9 6 4 ) . F o r e x a m p l e , o n e o f t h e d e s i g n c r i t e r i a a d o p t e d i n a p r o p o s e d r i v e r p r o t e c t i o n p r o j e c t f o r t h e V e d d e r R i v e r i n 1964 w a s : " t o c o n f i n e t h e r i v e r w i t h i n a n a r r o w s t r i p o f l a n d a n d p o s s i b l y r e c l a i m l a n d w i t h i n t h e p r e s e n t e r o s i o n b e l t . " ( M a r r , 1964 ) A l t h o u g h t h i s p r o j e c t e n v i s i o n e d a s e r i e s o f g r o i n s t o c o n f i n e t h e c h a n n e l a n d was n e v e r c a r r i e d o u t due t o l a c k o f f u n d i n g , p a r t s o f t h e V e d d e r R i v e r h a v e g r a d u a l l y e v o l v e d t o t h e g e n e r a l o u t l i n e s u g g e s t e d i n t h i s s t u d y . The f l o o d o f D e c e m b e r 3 , 19 75 r e a c h e d a max imum i n s t a n t a n e o u s d i s c h a r g e o f 2 7 , 8 0 0 c f s , c o r r e s p o n d i n g t o r o u g h l y a o n e i n t e n y e a r e v e n t . F l o o d w a t e r s o v e r -t o p p e d t h e r i v e r b a n k s i n t w o m a i n a r e a s - n e a r W e b s t e r R o a d o n t h e n o r t h b a n k a n d n e a r t h e r a i l w a y b r i d g e o n t h e s o u t h b a n k ( F i g u r e 5 ) . A l t h o u g h a f e w homes w e r e f l o o d e d b e t w e e n W e b s t e r a n d L i c k m a n R o a d , m o s t o f t h e w a t e r i n t h i s a r e a was d i v e r t e d b a c k i n t o t h e V e d d e r R i v e r b y t h e n o r t h e r n e n d o f t h e r a i l w a y e m b a n k m e n t . On t h e s o u t h b a n k , f l o o d w a t e r s o v e r t o p p e d t h e b a n k n e a r H o p e d a l e R o a d a n d p o n d e d b e h i n d t h e r a i l w a y e m b a n k m e n t . When t h e e m b a n k m e n t f a i l e d , w a t e r p o u r e d t h r o u g h t h e t o w n o f Y a r r o w a n d e n t e r e d Sumas P r a i r i e , 2 1 f o r c i n g the e v a c u a t i o n of about 160 people and c a u s i n g about $770,000 damage (The Vancouver Sun, December 5, 1975) . Surveys conducted by the Water I n v e s t i g a t i o n s Branch i n d i c a t e d t h a t approximately 250,000 c u b i c yards of g r a v e l had been d e p o s i t e d between Vedder C r o s s i n g and the B.C. Railway b r i d g e , and t h a t the channel bed had aggraded on average 1 to 2 f e e t d u r i n g the f l o o d (Tempest, 1976) . As a r e s u l t of the 1975 f l o o d i n g , e x t e n s i v e f l o o d c o n t r o l measures were c a r r i e d out by the p r o v i n c i a l government. A f t e r c o n s u l t a t i o n s between the Water I n v e s t i g a t i o n s Branch, the P r o v i n c i a l F i s h and W i l d l i f e Branch, F e d e r a l F i s h e r i e s S e r v i c e and F r a s e r R i v e r J o i n t A d v i s o r y Board, a three-phase f l o o d c o n t r o l program was adopted i n March 1976. The f i r s t phase of t h i s program was to be completed be f o r e the 197 6 s p r i n g f r e s h e t and c o n s i s t e d of r a i s i n g e x i s t i n g banks by'three f e e t , r e -moving g r a v e l from exposed bars above the water l i n e and p r o v i d i n g r i p - r a p p r o t e c t i o n where r e q u i r e d . Work c a r -r i e d out under the phase I program was intended to pro-v i d e a channel c a p a c i t y o f 19,000 c f s a t b a n k f u l l stage. The phase I I program was c a r r i e d out i n August 1976 and c o n s i s t e d of i n - c h a n n e l e x c a v a t i o n of 750,000 c u b i c yards of g r a v e l i n order to i n c r e a s e the channel c a p a c i t y to approximately 30,000 c f s . The t h i r d phase of the f l o o d 22 c o n t r o l program c o n s i s t e d of a recommendation t h a t s e t -back d i k e s be c o n s t r u c t e d along the Vedder R i v e r i n order to p r o v i d e p r o t e c t i o n a g a i n s t f l o o d s r e a c h i n g 44,000 c f s (200 year f l o o d ) . I t was a l s o suggested t h a t p e r i o d i c g r a v e l removal o p e r a t i o n s would be r e q u i r e d from year to year i n order to prevent d e t e r i o r a t i o n o f the channel c a p a c i t y due to sediment aggradation. The Phase I and I I measures were completed at a c o s t of roughly $1,300,000 (Peters, 1978), while a t the time of w r i t i n g , the Phase I I I program has not been implemented. The f l o o d c o n t r o l measures t h a t were adopted pro-duced s t r o n g c r i t i c i s m from environmental groups who were concerned t h a t the Phase I I dredging would cause severe damage to the f i s h e r i e s r esources of the r i v e r (B.C. Outdoors Magazine, 1976). Although p r e v i o u s channel-i z a t i o n and dredging o p e r a t i o n s c a r r i e d out i n the 1950's and 1960's had undoubtedly reduced the escapement of the r i v e r , the Vedder was s t i l l an important salmon and s t e e l -head stream. The environmental o r g a n i z a t i o n s contended t h a t the most s a t i s f a c t o r y s o l u t i o n t o p r o v i d i n g f l o o d c o n t r o l along the r i v e r w h i le s t i l l p r o t e c t i n g the f i s h -e r i e s r e s o u r c e was t o : (1) c o n s t r u c t set-back d i k e s along the r i v e r up-stream of the r a i l w a y b r i d g e 23 (2) allow the r i v e r to r e t u r n to a more n a t u r a l c o n d i t i o n by removing some of the bank pro-t e c t i o n t h a t had c u t o f f former s i d e channels and had c o n s t r u c t e d the channel. I t was f e l t t h a t i f the channel upstream of the r a i l w a y b r i d g e was widened to i t s former c o n d i t i o n , then the need f o r e x t e n s i v e channel dredging would be minimized (B.C. Outdoors Magazine, 1976). At prese n t the f e a s i b i l i t y of c a r r y i n g out such a program has not been confirmed. P e t e r s (1978) has d e s c r i b e d an a n a l y s i s to d e t e r -mine the e f f e c t of v a r i o u s f l o o d c o n t r o l a l t e r n a t i v e s on the pink and chum salmon escapement. I t i s hoped t h a t t h i s p r e s e n t study w i l l p r o v i d e some answers on the e f f e c t of f l o o d c o n t r o l measures on the p a t t e r n of s e d i -mentation and f l o o d l e v e l s along the r i v e r . 24 CHAPTER I I I HYDROLOGY 3'.1 B a s i n C h a r a c t e r i s t i c s The C h i l l i w a c k R i v e r b a s i n h a s an a r e a o f 474 s q u a r e m i l e s a b o v e V e d d e r C r o s s i n g a n d a t o t a l l e n g t h o f a b o u t 45 m i l e s . The r i v e r f l o w s i n a w e s t e r l y d i r e c t i o n t h r o u g h t h e n o r t h e r n C a s c a d e M o u n t a i n s w h i c h f r e q u e n t l y e x c e e d 8,000 f e e t i n e l e v a t i o n , a n d e n t e r s t h e F r a s e r R i v e r a t an e l e v a t i o n o f o n l y a b o u t 10 f e e t a b o v e s e a l e v e l . A p p r o x -i m a t e l y one h a l f o f t h e b a s i n a r e a i s a b o v e an e l e v a t i o n o f 3,700 f e e t a n d n e a r l y 2 5 % l i e s a b o v e 4,500 f e e t . M o s t o f t h e u p l a n d s i n t h e b a s i n a r e m a n t l e d by v e r y t h i n s o i l s o v e r l y i n g b e d r o c k and b a r e r o c k i s e x p o s e d f r e q u e n t l y a l o n g t h e h i g h e r r i d g e s a n d m o u n t a i n p e a k s . B e l o w an e l e v a t i o n o f a b o u t 6,000 f e e t t h e b a s i n i s c o v e r e d by s t a n d s o f m i x e d c o n i f e r o u s t i m b e r . A b o v e V e d d e r C r o s s i n g s e v e r a l l a r g e t r i b u t a r i e s f l o w t h r o u g h s t e e p m o u n t a i n o u s v a l l e y s i n t o t h e C h i l l i w a c k R i v e r ( F i g u r e 6 ) . P r o c e e d i n g u p s t r e a m t h e l a r g e s t t r i b u -t a r i e s i n c l u d e L i u m c h e n C r e e k , Tamahi C r e e k , S l e s s e C r e e k , F o l e y C r e e k , C e n t r e C r e e k a nd N e s a k w a t c h C r e e k . The b a s i n a l s o i n c l u d e s two m a j o r l a k e s - C h i l l i w a c k L a k e w h i c h i s l o c a t e d a b o u t 30 m i l e s u p s t r e a m o f V e d d e r C r o s s i n g , a n d C u l t u s L a k e w h i c h d r a i n s i n t o t h e C h i l l i w a c k R i v e r one h a l f m i l e u p s t r e a m o f V e d d e r C r o s s i n g t h r o u g h S w e l t z e r R i v e r . 25 3.2 C l i m a t e The c l i m a t e i s c h a r a c t e r i z e d b y warm d r y summers and c o o l m o i s t w i n t e r s . The mean a n n u a l p r e c i p i t a t i o n r e -c o r d e d n e a r C e n t r e C r e e k ( E l . 1,600 f e e t ) i s 61.67 i n c h e s and t h e a n n u a l w i n t e r s n o w f a l l i s 8 9.1 i n c h e s . The m o n t h l y v a r i a t i o n i n p r e c i p i t a t i o n a n d t e m p e r a t u r e i s shown i n F i g u r e 7. S i n c e a l l o f t h e m e t e o r o l o g i c a l s t a t i o n s i n t h e C h i l l i w a c k b a s i n a r e l o c a t e d i n t h e v a l l e y b o t t o m , i t i s d i f f i c u l t t o e s t i m a t e o r o g r a p h i c e f f e c t s i n t h e w a t e r s h e d . However, s i n c e t h e mean a n n u a l d i s c h a r g e a t V e d d e r C r o s s i n g i s 2,440 c f s , t h e c o r r e s p o n d i n g a n n u a l d e p t h o f r u n o f f i s a p p r o x i m a t e l y 70 i n c h e s / y e a r . A s s u m i n g an a n n u a l e v a p o -t r a n s p i r a t i o n o f r o u g h l y 20 i n c h e s / y e a r , t h e mean a n n u a l b a s i n p r e c i p i t a t i o n i s p r o b a b l y c l o s e t o 90 i n c h e s / y e a r . 3.3 S t r e a m f l o w D a t a The l o c a t i o n o f a l l s t r e a m f l o w s t a t i o n s i n t h e C h i l l i w a c k b a s i n i s shown i h F i g u r e 6 and a summary o f t h e i r p e r i o d o f o p e r a t i o n i s shown i n F i g u r e 8. A l t h o u g h a g a u g i n g s t a t i o n h a s o p e r a t e d n e a r V e d d e r C r o s s i n g a s e a r l y a s 1 9 1 1 , t h e r e i s a gap i n t h e r e c o r d f o r a p e r i o d o f 23 y e a r s , e x t e n d i n g f r o m 1932 t o 1950. U n f o r t u n a t e l y i t i s known t h a t a number o f l a r g e f l o o d s o c c u r r e d d u r i n g t h i s t i m e . S i n c e 1951 t h e V e d d e r C r o s s i n g gauge h a s o p e r a t e d c o n t i n u o u s l y a n d a t o t a l o f 44 y e a r s 26 o f r e c o r d s a r e a v a i l a b l e a t t h i s s t a t i o n . G a u g i n g s t a t i o n s h ave a l s o o p e r a t e d on t h e C h i l l i w a c k R i v e r b e l o w S l e s s e C r e e k , a b o v e S l e s s e C r e e k and a t t h e o u t l e t o f C h i l l i w a c k L a k e . 3.4 B a s i n R u n o f f Some s t a t i s t i c s on t h e d i s c h a r g e s r e c o r d e d a l o n g t h e C h i l l i w a c k R i v e r a r e s u m m a r i z e d i n T a b l e 2. B a s e d on t h i s d a t a , t h e l o n g t e r m mean d i s c h a r g e v a r i e s f r o m 2,440 c f s a t V e d d e r C r o s s i n g t o 679 c f s a t t h e o u t l e t o f C h i l l i w a c k L a k e , w h i c h c o r r e s p o n d s t o a v e r y u n i f o r m r u n o f f o f a b o u t 7 0 i n c h e s / y e a r t h r o u g h o u t t h e e n t i r e b a s i n . The l o n g t e r m m o n t h l y f l o w s r e c o r d e d a t t h e f o u r m a i n s t r e a m g a u g i n g s t a t i o n s a r e i l l u s t r a t e d i n F i g u r e 9. The m o n t h l y f l o w r e g i m e i s t y p i c a l o f many c o a s t a l s t r e a m s i n B r i t i s h C o l u m b i a , s h o w i n g f o u r d i s t i n c t p e r i o d s : - s p r i n g f r e s h e t , e x t e n d i n g f r o m A p r i l t o J u n e and d e r i v e d m a i n l y f r o m s n o w m e l t - summer r e c e s s i o n , u s u a l l y b e g i n n i n g i n J u l y and r e a c h i n g a minimum i n S e p t e m b e r - autumn r i s e due t o i n c r e a s e d p r e c i p i t a t i o n a n d m i l d t e m p e r a t u r e s e x t e n d i n g f r o m O c t o b e r t o December - w i n t e r r e c e s s i o n b e g i n n i n g u s u a l l y i n J a n u a r y a n d r e a c h i n g a minimum i n M a r c h due t o d e c r e a s e d p r e c i p -i t a t i o n a n d c o l d e r t e m p e r a t u r e s . 27 A comparison of the flow r e c o r d s a t the four gauging s t a -t i o n s on the C h i l l i w a c k R i v e r shows a very c o n s i s t e n t run-o f f d i s t r i b u t i o n along the b a s i n with about 40% of the annual r u n o f f o c c u r r i n g between A p r i l - J u n e , 25% between July-September, 20% between October-December and 15% be-tween January-March. 3.5 F l o o d Hydrology 3.5.1 F l o o d Generation Extreme hi g h flows g e n e r a l l y occur on the C h i l l i w a c k River i n two p e r i o d s - between October-February and between A p r i l - J u n e (Figure 10). Autumn and winter f l o o d s are caused by heavy r a i n s t o r m s which develop from warm, moist P a c i f i c low p r e s s u r e systems. G e n e r a l l y o r o g r a p h i c e f f e c t s cause p r e c i p i t a t i o n to i n c r e a s e s h a r p l y with e l e v a t i o n i n the b a s i n due to the moist a i r being f o r c e d to r i s e over the steep mountains which surround the F r a s e r V a l l e y . Often, a d d i t i o n a l r u n o f f may be generated by m e l t i n g o f the w i n t e r snowpack due to the sudden temperature r i s e accompanying these storms. G e n e r a l l y winter r a i n s t o r m s cause c h a r a c t e r i s t i c a l l y " f l a s h y " f l o o d s , having a h i g h i n t e n s i t y but s h o r t d u r a t i o n l a s t i n g o n l y one or two days. S p r i n g f l o o d s have o c c u r r e d most f r e q u e n t l y i n June and u s u a l l y r e s u l t from r a p i d snowmelt due to r i s i n g tem-p e r a t u r e s . However, i n some years such as i n 1968 combined r a i n s t o r m and snowmelt f l o o d i n g have a l s o o c c u r r e d . 28 The peak d i s c h a r g e from snowmelt i s governed mainly by the s p r i n g snowpack d i s t r i b u t i o n i n the b a s i n and on the sequence of d a i l y temperatures d u r i n g the c r i t i c a l melt p e r i o d . The snowmelt f l o o d hydrograph g e n e r a l l y shows a much more gr a d u a l r i s e and r e c e s s i o n than r a i n s t o r m gener-ated f l o o d s w i t h high water i n some years l a s t i n g f o r s e v e r a l weeks. However, although the d i s c h a r g e volume a s s o c i a t e d w i t h snowmelt f l o o d s i s g e n e r a l l y much g r e a t e r than r a i n s t o r m f l o o d s , the peak flows have been c o n s i d e r a b l y lower. For example, based on d i s c h a r g e r e c o r d s a t Vedder C r o s s i n g , the l a r g e s t recorded s p r i n g f l o o d reached 15,400 c f s i n 1968, whereas at l e a s t seven wi n t e r r a i n s t o r m f l o o d s have exceeded t h i s d i s c h a r g e . In order to compare the flow regimes f o r the two f l o o d types, the m e t e o r o l o g i c a l c o n d i t i o n s and d i s c h a r g e hydrographs from a t y p i c a l r a i n s t o r m and snowmelt gener-ated f l o o d are i l l u s t r a t e d i n F i g u r e 11. 3.5.2 Record of Floods a t Vedder C r o s s i n g Table 3 l i s t s a l l of the major f l o o d s t h a t are known to have o c c u r r e d on the Vedder R i v e r . U n f o r t u n a t e l y s e v e r a l l a r g e f l o o d s o c c u r r e d e i t h e r b e f o r e the gauge at Vedder C r o s s i n g was e s t a b l i s h e d or d u r i n g the p e r i o d between 1932-1952 when the gauge was not maintained. Although h i s t o r i c a l accounts were found d e s c r i b i n g the l a r g e f l o o d s i n 1875 and 1898, i t appears no d i s c h a r g e 29 estimates were made of these e a r l y f l o o d s . A l s o s i n c e the r a i n f a l l a s s o c i a t e d w i t h these f l o o d s i s not known, i t i s not p o s s i b l e to estimate the flows from the meteor-o l o g i c a l data. However, i t was c o n s i d e r e d t h a t s u f f i c i e n t data was a v a i l a b l e to a t l e a s t roughly estimate the magni-tude of some of the ungauged f l o o d s which o c c u r r e d between 1932 and 1952. Based on h i s t o r i c a l accounts, and examination of m e t e o r o l o g i c a l data and some i n t e r m i t t e n t stage r e c o r d s at Vedder C r o s s i n g , i t was concluded t h a t h i g h flows o c c u r r e d i n the f o l l o w i n g years (see Table 3): 19 32 (probably on November 12) 1948 (June 7) 194 9 (November 27) 1951 (February 10) B a s i c a l l y , two main procedures were used t o estimate the ungauged flows: (1) by d e v e l o p i n g a simple c o r r e l a t i o n with f l o o d flows recorded on the Nooksack R i v e r i n Washington State (2) by e s t i m a t i n g the flows on the C h i l l i w a c k R i v e r from recorded m e t e o r o l o g i c a l data. The Nooksack R i v e r was chosen f o r d e v e l o p i n g a flow c o r r e -l a t i o n because i t i s the o n l y nearby b a s i n w i t h comparable p h y s i c a l and h y d r o l o g i c a l c h a r a c t e r i s t i c s as the C h i l l i w a c k R i v e r . The Nooksack R i v e r d r a i n s the Cascade Mountains 30 immediately south of the C h i l l i w a c k b a s i n and appears to have a roughly s i m i l a r exposure and geology, although the r e l i e f i s somewhat g r e a t e r . The f l o o d flow c o r r e l a t i o n was developed by u s i n g d i s c h a r g e records c o l l e c t e d a t the U.S. G e o l o g i c a l Survey gauging s t a t i o n near Deming, Washington. The Nooksack R i v e r has a drainage area of 58 0 square m i l e s a t t h i s s i t e and has been gauged con-t i n u o u s l y s i n c e 1937. F i g u r e 12 shows the r e l a t i o n between annual extreme flows recorded a t Vedder C r o s s i n g and Deming. For each of the years shown on t h i s graph, the peak flows on both r i v e r s o c c u r r e d l e s s than two days a p a r t . U n f o r t u n a t e l y , the recorded flows do not show a unique r e l a t i o n s h i p but i n s t e a d p l o t as an envelope curve. T h e r e f o r e , f o r a given d i s c h a r g e on the Nooksack R i v e r o n l y the approximate upper l i m i t to the flows on the C h i l l i w a c k R i v e r can be estimated. T h i s suggests t h a t many of the p a s t storms i n t h i s area have been q u i t e l o c a l i z e d , and have not always extended i n t o both b a s i n s . The U.B.C. watershed model was used f o r s i m u l a t i n g f l o o d d i s c h a r g e s from m e t e o r o l o g i c a l data recorded at C h i l l i w a c k . T h i s model has been d e s c r i b e d i n d e t a i l by Quick and Pipes (1976). The computer program attempts to mathematically model the p h y s i c a l r u n o f f processes i n a watershed from recorded d a i l y p r e c i p i t a t i o n and temper-ature data. I t was r e c o g n i z e d t h a t good flow s i m u l a t i o n J 31 would be d i f f i c u l t to achieve on the C h i l l i w a c k R i v e r due to the very mountainous nature of the b a s i n and to the h i g h l y v a r i a b l e p r e c i p i t a t i o n t h a t c o u l d r e s u l t . However, i t was decided the r e s u l t s from the model would p r o v i d e a u s e f u l comparison to the c o r r e l a t i o n a n a l y s i s . The model was c a l i b r a t e d from ten months of meteor-o l o g i c a l and d i s c h a r g e data recorded between March and December 1966. The c a l i b r a t i o n parameters used i n the model were then kept constant f o r a l l remaining c a l c u l a -t i o n s . In order to check the c o n s i s t e n c y of the c a l i b r a -t i o n , the model was then used to simulate the December 1975 f l o o d . F i g u r e 13 shows the p r e d i c t e d and recorded d i s c h a r g e s a t Vedder C r o s s i n g throughout the month of December. I t can be seen t h a t the model tended to under-estimate the flows s l i g h t l y , w i t h the f l o o d peak estimated a t about 17,100 c f s while the recorded peak was 18,700 c f s (McLean, 1975). However, i n g e n e r a l , these r e s u l t s were c o n s i d e r e d very s a t i s f a c t o r y given the mountainous nature of the b a s i n . The model was f i r s t a p p l i e d to the f l o o d of November 1932 u s i n g m e t e o r o l o g i c a l data recorded a t C u l t u s Lake. The p r e d i c t e d hydrograph and the c o r r e s p o n d i n g temperature and r a i n f a l l data are summarized i n F i g u r e 14. The p r e -d i c t e d peak flow of 14,000 c f s (mean d a i l y ) seems low con-s i d e r i n g the e x t e n t of the damages r e p o r t e d by Marr (1964). U n f o r t u n a t e l y , the gauge on the Nooksack R i v e r was not 32 o p e r a t i n g a t t h i s time so t h a t the c o r r e l a t i o n r e s u l t s cannot be used as an independent check on the model pr e -d i c t i o n s . The f i n a l a p p l i c a t i o n o f the watershed model was to simulate the f l o o d o f February 1951. As mentioned p r e -v i o u s l y , t h i s f l o o d was t r i g g e r e d by heavy r a i n s t o t a l l i n g over 11 inches i n three days and by u n u s u a l l y m i l d temper-a t u r e s . The p r e d i c t e d hydrograph and cor r e s p o n d i n g me-t e o r o l o g i c a l data are again summarized on F i g u r e 14. A l s o shown are stage measurements c o l l e c t e d a t Vedder C r o s s i n g . U n f o r t u n a t e l y s i n c e the gauge had been s h i f t e d p r i o r t o the 1951 f l o o d and was subsequently washed out, i t i s imp o s s i b l e t o r e l a t e these measurements to d i s c h a r g e v a l u e s . The p r e d i c t e d f l o o d peak reached 20,000 c f s on February 9th or one day before the r e p o r t e d maximum stage a t Vedder C r o s s i n g . The Nooksack R i v e r r e c e i v e d major f l o o d i n g d u r i n g t h i s storm w i t h the mean d a i l y d i s c h a r g e r e a c h i n g 34,900 c f s a t Deming on February 10th. Based on the r e s u l t s o f F i g u r e 14, t h i s would correspond t o a d i s c h a r g e of around 18,500 c f s at Vedder C r o s s i n g which i s q u i t e c l o s e t o the watershed model r e s u l t s . T h e r e f o r e i t was concluded t h a t the f l o o d o f 1951 was probably at l e a s t as l a r g e as the f l o o d o f December 1975. The watershed model was not a p p l i e d to the f l o o d s i n 1948 and 194 9 due to a l a c k of time and because i t was o r i g i n a l l y f e l t t h a t the flows o c c u r r i n g i n these years 33 were not as g r e a t as i n 1932 and 1951. A c c o r d i n g t o the stage measurements at Vedder C r o s s i n g , the f l o o d s i n 194 8 and 1949 were about 1.3 f e e t and 0.6 f e e t below the 1951 stage. Based on c u r r e n t s t a g e - d i s c h a r g e data a t Vedder C r o s s i n g and assuming the 1951 f l o o d reached about 20,000 c f s , the 1948 and 1949 flows would have been roughly 5,000 c f s and 2,500 c f s lower. However, t h i s assumes the channel c o n t r o l at Vedder C r o s s i n g remained s t a b l e through-out t h i s p e r i o d which does not seem very l i k e l y . The recorded flows on the Nooksack R i v e r were not used to estimate the 194 8 summer snowmelt f l o o d s i n c e the c o r r e -l a t i o n r e s u l t s shown i n F i g u r e 12 were based o n l y on r a i n -f a l l f l o o d d a ta. However, the Nooksack R i v e r reached a peak flow of 24,400 c f s on November 27, 1949 which sug-gests the f l o o d on the C h i l l i w a c k R i v e r was probably below 15,000 c f s . In summary, based on the r e s u l t s from the U.B.C. watershed model, on comparison w i t h flows recorded on the Nooksack R i v e r , and on an examination of h i s t o r i c a l accounts, h i g h flows probably o c c u r r e d on the Vedder R i v e r i n the f o l l o w i n g y e a r s : 19 32 November 12 probably l e s s than 15,000 c f s 194 8 June 7 unknown, probably l e s s than 1949 f l o o d 194 9 November 2 7 probably l e s s than 15,000 c f s 1951 February 10 about 20,000 c f s 34 I t should be noted t h a t a l l o f these flows r e f e r t o mean d a i l y d i s c h a r g e v a l u e s and t h a t the maximum i n s t a n -taneous valu e s c o u l d be as much as 50% to 100% g r e a t e r (see S e c t i o n 3.6). 3.6 F l o o d Frequency A n a l y s i s Before c a r r y i n g out a frequency a n a l y s i s of f l o o d s on the C h i l l i w a c k R i v e r , i t was decided t o f i r s t assess the accuracy o f the r e p o r t e d flows and to examine some of the s t a t i s t i c a l assumptions t h a t are r e q u i r e d i n the ana-l y s i s . 3.6.1 Accuracy o f Reported Flows Although a number of l a r g e f l o o d s have been recorded a t the Vedder C r o s s i n g gauge, i t i s d i f f i c u l t t o assess the accuracy of these measurements. Water Survey of Canada r a t e s the q u a l i t y o f the gauge re c o r d s from t h i s s t a t i o n as o n l y " f a i r . " A comparison of a l l a v a i l a b l e gauge r a t -i n g t a b l e s a t Vedder C r o s s i n g showed t h a t a new stage-d i s c h a r g e r e l a t i o n was determined a f t e r any major f l o o d and o f t e n f o r each year. T h e r e f o r e , i t i s l i k e l y t h a t changes i n channel c o n t r o l due to s h i f t i n g o f the r i v e r bed c o u l d make d i s c h a r g e estimates of major f l o o d s q u i t e u n r e l i a b l e . Unless a c t u a l d i s c h a r g e measurements are c a r r i e d out d u r i n g the course of a f l o o d , i t i s not pos-s i b l e t o determine when t h i s s h i f t i n c o n t r o l has oc c u r r e d . 35 U n f o r t u n a t e l y , very few r a t i n g measurements have been c a r r i e d out d u r i n g high flows a t Vedder C r o s s i n g and very o f t e n long e x t r a p o l a t i o n s o f the st a g e - d i s c h a r g e r e l a t i o n have been r e q u i r e d . In f a c t , p r i o r t o 1968, no r a t i n g measurements had been c a r r i e d out a t flows g r e a t e r than 10,000 c f s , which i s almost o n e - t h i r d o f the r e p o r t e d f l o o d of r e c o r d . By simply examining the shape of the stag e - d i s c h a r g e curves at Vedder C r o s s i n g and the magni-tude of some of the past r a t i n g s h i f t s , i t seems l i k e l y t h a t some of the r e p o r t e d f l o o d s c o u l d be i n e r r o r by as much as -25%. Another problem wi t h the gauge r e c o r d s i s t h a t p r i o r to 1968 the r i v e r stage was not recorded c o n t i n u o u s l y at Vedder C r o s s i n g but was read manually from a s t a f f guage. Although a l l o f the recorded f l o o d flows b e f o r e t h i s time have been r e p o r t e d as mean d a i l y d i s c h a r g e s , i n f a c t , o n l y spot readings may have been measured on the day of the f l o o d . T h e r e f o r e the r e p o r t e d flows are probably i n s t a n -taneous measurements which may not correspond to the maxi-mum d a i l y or the maximum instantaneous d i s c h a r g e . I f the C h i l l i w a c k R i v e r were not such a " f l a s h y " stream, there would not be a s i g n i f i c a n t d i f f e r e n c e between the i n s t a n -taneous and d a i l y flows. However, d u r i n g the f l o o d of December 1975, which was one of the few f l o o d s to be r e -corded c o n t i n u o u s l y , the maximum instantaneous d i s c h a r g e (27,800 c f s ) was n e a r l y 50% g r e a t e r than the maximum d a i l y 36 flow (18,700 c f s ) . I t i s b e l i e v e d t h a t such a wide range i n flows over a s i n g l e day i s t y p i c a l of most w i n t e r f l o o d s on the r i v e r . A good example of the d i f f i c u l t y i n i n t e r p r e t i n g the recorded flow data can be found by examining the f l o o d of r e c o r d which o c c u r r e d i n December 1917. T h i s f l o o d i s r e p o r t e d t o have reached a maximum d a i l y d i s c h a r g e of 27,000 c f s , which was a r r i v e d a t by e x t r a p o l a t i n g the stage-d i s c h a r g e curve f o r 1917 to the r e p o r t e d gauge h e i g h t o f 11.5 f e e t . However, the l a r g e s t flow measurement used to e s t a b l i s h the r a t i n g curve was onl y 5,84 0 c f s , having a gauge h e i g h t of 5.2 f e e t . U n f o r t u n a t e l y , even the gauge r e a d i n g of 11.5 f e e t i s onl y a rough estimate s i n c e the gauge was washed out on the day of the f l o o d . T h e r e f o r e , the f l o o d of r e c o r d must be c o n s i d e r e d very approximate. U n f o r t u n a t e l y , the source of e r r o r s j u s t d e s c r i b e d seem t y p i c a l of most f l o o d data a t Vedder C r o s s i n g . 3.6.2 F l o o d Frequency A n a l y s i s K i t e (1977) has o u t l i n e d some of the most important assumptions t h a t must be made i n c a r r y i n g out a f l o o d frequency a n a l y s i s . These a r e : (1) a l l of the data must d e s c r i b e independent, random events (2) the f l o o d s e r i e s should not e x h i b i t any long term trends over the p e r i o d of r e c o r d and must be c o n s i d e r e d s t a t i o n a r y with r e s p e c t to time 37 (3) a l l of the recorded f l o o d events should be from the same p o p u l a t i o n and can be used to estimate the p o p u l a t i o n mean, v a r i a n c e and skewness. The f i r s t assumption r e g a r d i n g independence i s prob-a b l y v a l i d s i n c e o n l y annual maximum flows were used i n the a n a l y s i s . However, the second assumption of long term s t a t i o n a r i t y may not be as reasonable. In order to i l l u s -t r a t e the long term p a t t e r n of annual f l o o d s on the C h i l l i w a c k R i v e r , a l l of the annual f l o o d s at Vedder C r o s s i n g were p l o t t e d as a time s e r i e s (Figure 15). Exam-i n a t i o n of t h i s r e c o r d shows very c l e a r l y t h a t few l a r g e f l o o d s have o c c u r r e d i n the l a s t 25 years compared to the number i n p r e v i o u s y e a r s . In f a c t , the f l o o d i n 1975 was the only f l o o d t o exceed 18,000 c f s s i n c e 1951, while t h i s flow was exceeded at l e a s t seven times between 1906 and 1951. Sporns (1962) noted a s i m i l a r p a t t e r n i n the occur-rence of severe r a i n s t o r m s i n the F r a s e r V a l l e y , w i t h un-u s u a l l y i n t e n s e storm a c t i v i t y o c c u r r i n g i n the w i n t e r of 1931/32, 1934/35 and 1950/51. Sporns a l s o concluded t h a t "Storms are not evenly d i s t r i b u t e d from year to year and . . . a marked c y c l i c a l t r e n d i n the frequency of occurrence of severe storms seems to be i n d i c a t e d i n the p e r i o d under study." T h e r e f o r e , the f l u c t a t i o n s e x h i b i t e d by the f l o o d r e c o r d probably r e f l e c t s a s h o r t term c l i m a t i c c y c l e which appears to be c h a r a c t e r i s t i c of the F r a s e r V a l l e y . I t has been 38 assumed t h a t such c y c l e s do not r e p r e s e n t a permanent change i n the behaviour o f the watershed so t h a t the com-p l e t e f l o o d r e c o r d was i n c l u d e d i n the frequency a n a l y s i s . However, these s h o r t term c y c l e s may cause p e r i o d s of hig h f l o o d a c t i v i t y , a l t e r n a t i n g w i t h r e l a t i v e l y " q u i e t " p er-io d s l a s t i n g a few decades and t h i s p a t t e r n cannot be p r e -d i c t e d . The f i n a l assumption r e g a r d i n g a s i n g l e p o p u l a t i o n of f l o o d events i s u n l i k e l y t o be s t r i c t l y c o r r e c t . I t has been mentioned p r e v i o u s l y t h a t two types of f l o o d s may occur on the C h i l l i w a c k R i v e r - f a l l or w i n t e r r a i n -storm f l o o d s and s p r i n g snowmelt f l o o d s . Since p a s t r a i n -storm and snowmelt f l o o d s have e x h i b i t e d very d i f f e r e n t c h a r a c t e r i s t i c s , i t was b e l i e v e d t h a t the two f l o o d types r e p r e s e n t d i f f e r e n t p o p u l a t i o n s . In order t o decide whether the two f l o o d types have s i g n i f i c a n t l y d i f f e r e n t c h a r a c t e r i s t i c s , a s t a t i s t i c a l t e s t was c a r r i e d out u s i n g the procedure d e s c r i b e d by K i t e (1977) . A " N u l l h y p o t h e s i s " and an " A l t e r n a t i v e h y p o t h e s i s " were s t a t e d as f o l l o w s : " n u l l : The r a i n s t o r m and snowmelt f l o o d peaks are from the same p o p u l a t i o n o f f l o o d events. a l t e r n a t i v e : The r a i n s t o r m and snowmelt f l o o d s are d e r i v e d from d i f f e r e n t p o p u l a t i o n s . " The l e v e l of s i g n i f i c a n c e of the t e s t was computed u s i n g the Mann and Whitney t e s t ( K i t e , 1977). The r e s u l t s 39 i n d i c a t e d the " N u l l h y p o t h e s i s " c o u l d be r e j e c t e d a t a s i g n i f i c a n c e l e v e l of b e t t e r than 5% so t h a t i t was con-cluded the d i f f e r e n c e s between the two f l o o d types were l a r g e enough to i n d i c a t e two d i f f e r e n t p o p u l a t i o n s e x i s t . T h e r e f o r e , i t was decided to compute a separate f l o o d frequency r e l a t i o n f o r each f l o o d type and then determine the annual f l o o d frequency by combining the two r e l a t i o n s . D a i l y flow records a t Vedder C r o s s i n g were examined and the maximum d a i l y d i s c h a r g e o c c u r r i n g i n each year between A p r i l 1 - J u l y 31 and August 1 - March 31 were t a b u l a t e d (Table 4). The estimated value f o r the ungauged f l o o d s i n 1951 was i n c l u d e d i n order t o extend the r e c o r d , g i v i n g 45 years of r a i n s t o r m events and 4 4 years of snow-melt events. Each s e t of data was f i t t e d t o l o g Pearson I I I f r e -quency d i s t r i b u t i o n from the computed sample mean, s t a n -dard d e v i a t i o n and skewness u s i n g the f o l l o w i n g r e l a t i o n : l o g Q = X + kS where Q = d i s c h a r g e c o r r e s p o n d i n g to the s p e c i f i e d f l o o d frequency N Y _ £ l o g Q. X " 1 * N £ l o g Q 2 v 2 S = N " X N - l k = a frequency f a c t o r depending on the sample skewness and the p r o b a b i l i t y of exceedance 40 Although a number of frequency d i s t r i b u t i o n s have been used i n f l o o d frequency a n a l y s i s , the l o g Pearson I I I d i s t r i b u t i o n has been found to be one of the most r e l i a b l e methods a v a i l a b l e and i s c u r r e n t l y recommended by the U.S. Water Resources C o u n c i l (W.R.C., 1977). The l o g Pearson I I I d i s t r i b u t i o n s i m p l i f i e s to a log-normal d i s t r i b u t i o n when the sample skewness approaches zero (W.R.C., 1977). The l o g normal d i s t r i b u t i o n has a l s o been o f t e n used i n f l o o d frequency a n a l y s i s and i n some cases may g i v e more r e l i a b l e e stimates than the l o g Pearson I I I d i s t r i b u t i o n when used on mountainous streams ( S t o l t e and Dumontier, 1977). However, s i n c e the computed sample skewness was found to be q u i t e low f o r both the snowmelt and r a i n s t o r m f l o o d data, i t was f e l t t h a t the r e s u l t s from the two d i s t r i b u t i o n s would be n e a r l y i d e n t i c a l . The d e r i v e d frequency r e l a t i o n s f o r the r a i n s t o r m and snowmelt data are shown on F i g u r e 16. As expected, the r a i n s t o r m f l o o d s were found to be s i g n i f i c a n t l y l a r g e r than the snowmelt f l o o d s f o r n e a r l y a l l p r o b a b i l i t i e s . For example, the 10 0 year r a i n s t o r m f l o o d was estimated to be 32,000 c f s which was over twice the c o r r e s p o n d i n g snowmelt f l o o d of 15,000 c f s . However, the two frequency r e l a t i o n s tend to converge at lower r e t u r n p e r i o d s and, f o r f l o o d s w i t h r e t u r n p e r i o d s l e s s than 1.25 y e a r s , the snowmelt events were s l i g h t l y l a r g e r than the correspond-i n g r a i n s t o r m f l o o d s . 41 In order to determine the annual f l o o d frequency r e l a t i o n , the two seasonal f l o o d frequency curves were combined u s i n g the method suggested by K i t e (197 7). I f a d i s c h a r g e Q has a p r o b a b i l i t y of exceedance P r ( r a i n s t o r m flood) and P g (snowmelt f l o o d ) , then the p r o b a b i l i t y of Q not being e q u a l l e d or exceeded i s (1 - P ) • (1 - P ). T h e r e f o r e , the p r o b a b i l i t y of Q being e q u a l l e d or exceeded d u r i n g the year i s : 1 - ( (1 - P s) • (1 - P r) ) The r a i n s t o r m and snowmelt frequency r e l a t i o n s were combined i n t h i s manner to d e r i v e the annual f l o o d f r e -quency r e l a t i o n shown i n F i g u r e 16 and summarized i n Table 5. I t can be seen t h a t the annual frequency curve l i e s very c l o s e to the r a i n s t o r m f l o o d curve f o r f l o o d s exceeding about 15,000 c f s . T h i s i s because snowmelt f l o o d s become so r a r e a t t h i s magnitude t h a t the annual p r o b a b i l i t y of exceedance i s n e a r l y the same as the prob-a b i l i t y o f the r a i n s t o r m f l o o d s . The p r e c e d i n g a n a l y s i s r e q u i r e s c o n s i d e r a b l y more work than a standard f l o o d frequency a n a l y s i s s i n c e c l o s e to 5 0 years of d a i l y flow r e c o r d s must be examined i n order to p i c k out the snowmelt and r a i n s t o r m f l o o d occur-r i n g i n each year. In order to check whether t h i s a d d i -t i o n a l e f f o r t i s j u s t i f i e d , a standard f l o o d frequency a n a l y s i s was c a r r i e d out u s i n g the annual f l o o d s e r i e s with no attempt made to d i s t i n g u i s h between d i f f e r e n t 42 p o p u l a t i o n s . The data analyzed c o n s i s t e d of 45 years o f rec o r d s i n c l u d i n g the estimated f l o o d i n 1951 and, as be f o r e , the data was f i t t e d t o a l o g Pearson I I I frequency d i s t r i b u t i o n . The f l o o d frequency r e l a t i o n computed from the annual maximum d a i l y d i s c h a r g e records was compared with annual frequency d i s t r i b u t i o n d e r i v e d by combining the r a i n s t o r m and snowmelt r e l a t i o n s . I t was found t h a t between r e t u r n p e r i o d s of 2 to 10 years the two r e l a t i o n s were e s s e n t i a l l y i d e n t i c a l . However, f o r more extreme events, the standard frequency a n a l y s i s underestimated the f l o o d flows. For example, u s i n g the standard frequency a n a l y s i s , the 100 year f l o o d was estimated a t 28,000 c f s which i s about 10% lower than the estimate of 32,000 c f s us i n g the combined snowmelt and r a i n s t o r m frequency r e l a -t i o n s . T h i s d i f f e r e n c e i s not very g r e a t c o n s i d e r i n g the l a r g e u n c e r t a i n t i e s and i n a c c u r a c i e s a s s o c i a t e d with the flow data. On the oth e r hand, the comparison shows t h a t a n a l y z i n g the r a i n s t o r m and snowmelt f l o o d s s e p a r a t e l y and then combining the r e s u l t s may le a d to higher estimates of extreme f l o o d v a l u e s than i n d i c a t e d by a standard a n a l y s i s of the annual f l o o d r e c o r d s . A l l o f the estimated f l o o d d i s c h a r g e s d i s c u s s e d so f a r have been mean d a i l y d i s c h a r g e s s i n c e maximum i n s t a n -taneous flows have on l y been recorded at Vedder C r o s s i n g s i n c e 1968. During t h i s p e r i o d the r a t i o o f maximum i n -stantaneous t o mean d a i l y d i s c h a r g e has v a r i e d from about 43 1.5 f o r the f l o o d o f December 3, 1975 to about 1.04 f o r the f l o o d o f May 24, 196 9. Since there i s not very much data a v a i l a b l e on the C h i l l i w a c k R i v e r , i t was deci d e d t o examine r e c o r d s from nearby streams between Vancouver and Hope. The r a t i o of instantaneous to d a i l y d i s c h a r g e was found t o vary from about 1.1 to 1.8 f o r r a i n s t o r m f l o o d s and from 1.04 to 1.7 f o r snowmelt f l o o d s . The Nooksack R i v e r a t Deming, Washington has a long p e r i o d of instantaneous and mean d a i l y f l o o d flow measure-ments and was used e a r l i e r i n t h i s study t o estimate mis-s i n g f l o o d r e c o rds a t Vedder C r o s s i n g . A comparison of f l o o d frequency r e l a t i o n s based on instantaneous and mean d a i l y flows on the Nooksack R i v e r showed the r a t i o v a r i e d from about 1.3 f o r the 100 year f l o o d t o about 1.5 a t the mean annual f l o o d . Based on a l l o f the above i n f o r m a t i o n , the maximum instantaneous flows on the C h i l l i w a c k R i v e r were estimated by a r b i t r a r i l y a s s i g n i n g a r a t i o o f 1.5 to the mean d a i l y flow d a t a . The f i n a l adopted maximum i n -stantaneous flows are summarized i n Table 6. With the d e r i v e d f l o o d frequency r e l a t i o n , i t i s now p o s s i b l e t o estimate the frequency of some of the l a r g e h i s t o r i c a l f l o o d s on the C h i l l i w a c k R i v e r (Table 7). I t can be seen t h a t the December 1917 f l o o d of r e c o r d (27,000 c f s ) probably had a r e t u r n p e r i o d o f about 4 0 y e a r s . By comparison, the f l o o d of December 1975 (18,700 c f s ) was on l y a ten year event. Although the f l o o d of 197 5 cannot 4 4 be c o n s i d e r e d an extreme event, i t was the l a r g e s t f l o o d t o occur i n the l a s t 25 y e a r s . However, the l a c k o f ex-treme f l o o d s i n r e c e n t times should be c o n s i d e r e d an un-u s u a l l y f o r t u n a t e circumstance. In f a c t , the p r o b a b i l i t y of not r e c e i v i n g a f l o o d equal t o or g r e a t e r than the 1975 magnitude i n a 25 year p e r i o d can be estimated as f o l l o w s : Q = (1 " P ) n where n = 25 years p = p r o b a b i l i t y o f occurrence i n one year Q = p r o b a b i l i t y of non-occurrence i n n years Given t h a t the r e t u r n p e r i o d of the 1975 f l o o d was about 10 ye a r s , the p r o b a b i l i t y of not r e c e i v i n g a t l e a s t one f l o o d i n 25 years i s on l y about 0.07. T h e r e f o r e , the encroachment which has taken p l a c e along the Vedder R i v e r i n the l a s t 25 years has o c c u r r e d i n an unusual p e r i o d c h a r a c t e r i z e d by very low f l o o d a c t i v i t y . However, i f severe storm a c t i v i t y f o l l o w s the c y c l i c a l p a t t e r n des-c r i b e d by Sporns (1962), then i t seems not too u n l i k e l y t h a t a sequence of very severe f l o o d s c o u l d occur i n a r e l a t i v e l y s h o r t p e r i o d of time i n the f u t u r e . 45 CHAPTER I V GEOLOGY AND PHYSIOGRAPHY The s u r f i c i a l g e o l o g y o f t h e C h i l l i w a c k v a l l e y i s c o m p l e x a nd h a s r e c e i v e d o n l y c u r s o r y s t u d y by g e o l o g i s t s . H owever, some r e l e v a n t i n f o r m a t i o n was o b t a i n e d f r o m t h e f o l l o w i n g s o u r c e s : - g e o l o g i c a l m a p p i n g o f t h e F r a s e r v a l l e y by' A r m s t r o n g (1959) - g e o l o g i c a l m a p p i n g o f t h e C o l u m b i a v a l l e y a n d C u l t u s L a k e by E a s t e r b r o o k (1975) - u n p u b l i s h e d B.A.Sc. t h e s e s on t h e g e o m o r p h o l o g y o f t h e C h i l l i w a c k v a l l e y by Chubb (1966) a n d Munshaw (1975) - u n p u b l i s h e d s t u d i e s on s u r f i c i a l d e p o s i t s i n t h e C h i l l i w a c k v a l l e y by V i c k e r s o n and M a r k s . 4.1 P h y s i o g r a p h y The C h i l l i w a c k R i v e r f l o w s t h r o u g h two m a j o r p h y s i o -g r a p h i c d i v i s i o n s - t h e C a s c a d e M o u n t a i n s a n d t h e F r a s e r L o w l a n d s . The n o r t h e r n C a s c a d e s f o r m a r u g g e d m o u n t a i n r a n g e t h r o u g h o u t t h e b a s i n w i t h p e a k s f r e q u e n t l y e x c e e d -i n g 7,000 f e e t i n e l e v a t i o n . B e d r o c k c o n s i s t s p r e d o m i n -a t e l y o f g r a n o d i o r i t e i n t h e e a s t e r n p o r t i o n o f t h e w a t e r -s h e d w h i l e w e s t o f C e n t r e C r e e k a c o m p l e x s e q u e n c e o f s a n d s t o n e s , l i m e s t o n e s a n d c o n g l o m e r a t e i s f o u n d . T h r o u g h -46 o u t t h e u p l a n d s b e d r o c k i s i n t e r m i t t e n t l y e x p o s e d o v e r w i d e s p r e a d a r e a s o r c o v e r e d by a t h i n l a y e r o f g l a c i a l d r i f t . A l o n g t h e v a l l e y b o t t o m u n c o n s o l i d a t e d f l u v i a l g l a c i a l a n d r e c e n t f l u v i a l d e p o s i t s may be f o u n d up t o d e p t h s o f s e v e r a l h u n d r e d f e e t ( A r m s t r o n g , 195 9 ) . The C h i l l i w a c k v a l l e y a n d some o f t h e l a r g e r t r i b -u t a r y v a l l e y s show a c l a s s i c " U " - s h a p e d c r o s s - s e c t i o n i n d i c a t i n g t h e i n f l u e n c e o f p a s t g l a c i a t i o n s . The m a i n -s t r e a m v a l l e y h a s a b r o a d f l a t f l o o r a n d s t e e p w a l l s w i t h an a v e r a g e d e p t h o f 4,000 f e e t a n d a w i d t h f r o m r i m t o r i m o f n e a r l y f o u r m i l e s . D o w n s t r e a m o f C h i l l i w a c k L a k e t h e v a l l e y c r o s s - s e c t i o n shows i n c r e a s e d m o d i f i c a t i o n by s t r e a m a c t i v i t y . A b o v e Chipmunk C r e e k t h e g l a c i a t e d , " U " - s h a p e d v a l l e y s e c t i o n i s m o s t a p p a r e n t a n d t h e r i v e r f l o w s on t o p o f a b r o a d f l a t a p p r o x i m a t e l y o n e - h a l f m i l e w i t h b e d r o c k b l u f f s f o r m i n g t h e v a l l e y s i d e s . D o w n s t r e a m o f Chipmunk C r e e k t h e C h i l l i w a c k R i v e r h a s c u t t h r o u g h t h i s p l a i n l e a v i n g a s e r i e s o f f l a t t o p p e d , d i s c o n t i n u o u s b e n c h e s p r e d o m i n a t e l y a l o n g t h e n o r t h s i d e o f t h e v a l l e y up t o 30 0 f e e t a b o v e r i v e r l e v e l . B e t w e e n Tamahi C r e e k and V e d d e r C r o s s i n g a s e c o n d d i s c o n t i n u o u s t e r r a c e l e v e l i s f o u n d a b o u t 50 f e e t a b o v e t h e r i v e r l e v e l a n d t h e f l o o d p l a i n w i d t h i n c r e a s e s u n t i l n e a r C u l t u s L a k e i t r e a c h e s a maximum o f 7,500 f e e t . 47 4.2 G l a c i a l H i s t o r y The l a s t c o n t i n e n t a l g l a c i a t i o n i n s o u t h w e s t B r i t i s h C o l u m b i a , r e f e r r e d t o a s t h e F r a s e r G l a c i a t i o n , o c c u r r e d b e t w e e n 12,000 and 25,000 y e a r s ago ( A r m s t r o n g , 1 9 5 9 ) . T h i s p e r i o d h a s b e e n d i v i d e d i n t o t h r e e i n t e r v a l s o f g l a c i a l a d v a n c e s ( s t a d e s ) a nd one n o n - g l a c i a l i n t e r v a l ( i n t e r s t a d e ) ; c h r o n o l o g i c a l l y t h e E v a n s C r e e k S t a d e , V a s h o n S t a d e , E v e r s o n I n t e r s t a d e a n d Sumas S t a d e ( A r m s t r o n g , 1 9 5 9 ) . The e a r l i e s t g l a c i a l a d v a n c e s w i d e n e d a n d s t e e p -e n e d t h e C h i l l i w a c k v a l l e y a n d d e p o s i t e d a t h i n l a y e r o f t i l l t h r o u g h o u t t h e u p l a n d s . D u r i n g t h e E v e r s o n I n t e r s t a d e , v a l l e y i n f i l l i n g o c c u r r e d u n t i l i c e r e a d v a n c e d t h r o u g h o u t s o u t h w e s t e r n B r i t i s h C o l u m b i a when t h e Sumas G l a c i a t i o n commenced a p p r o x i m a t e l y 11,000 y e a r s ago. M o s t d e p o s i t s i n t h e C h i l l i w a c k v a l l e y a s s o c i a t e d w i t h t h e Sumas G l a c i a t i o n a r e r e c e s s i o n a l , b e i n g l a i d down d u r i n g t h e r e t r e a t o f t h e v a l l e y g l a c i e r . D u r i n g t h i s p e r i o d up t o 150 f e e t o f s a n d a n d g r a v e l was d e p o s i t e d u p s t r e a m o f T a m a h i C r e e k o v e r t o p o f e a r l i e r E v e r s o n I n t e r s t a d e s e d i m e n t s . A c c o r d i n g t o E a s t e r b r o o k ( 1 9 7 5 ) , o u t w a s h d e p o s i t s o f s a n d a nd g r a v e l o v e r 400 f e e t t h i c k w e r e a l s o l a i d down t h r o u g h o u t t h e C o l u m b i a V a l l e y i n W a s h i n g t o n S t a t e d u r i n g t h i s r e c e s s i o n a l p e r i o d a s m e l t w a t e r f r o m a n i c e -l o b e n e a r C u l t u s L a k e f l o w e d s o u t h i n t o W a s h i n g t o n S t a t e . I t i s a l s o t h o u g h t t h a t C h i l l i w a c k L a k e was f o r m e d a t 48 t h i s t i m e when a g l a c i a l dam o n P o s t C r e e k b u r s t , c a r r y -i n g l a r g e q u a n t i t i e s o f b o u l d e r s down t h e c r e e k damming t h e C h i l l i w a c k v a l l e y (Munshaw, 1 9 7 5 ) . E x t e n s i v e b o u l d e r d e p o s i t s f o u n d i n t h e c h a n n e l o f t h e C h i l l i w a c k R i v e r s h o w i n g a r o u g h s o r t i n g w i t h b o u l d e r s i z e d e c r e a s i n g d o w n s t r e a m a r e p r o b a b l y d e r i v e d f r o m t h i s e v e n t . The e nd o f t h e Sumas G l a c i a t i o n h a s n o t b e e n a c c u -r a t e l y d a t e d . H owever, A r m s t r o n g (195 9) s u g g e s t e d t h a t t h e Sumas I c e f i n a l l y d i s a p p e a r e d f r o m t h e F r a s e r V a l l e y a p p r o x i m a t e l y 10,000 y e a r s a g o . F o l l o w i n g t h e end o f t h e Sumas G l a c i a t i o n , i t i s b e l i e v e d t h e c l i m a t e s h i f t e d , b e c o m i n g warmer a n d d r i e r t h a n a t p r e s e n t ( E a s t e r b r o o k a n d Rahm, 1 9 7 0 ) . T h i s p e r i o d , t e r m e d t h e " A l t i t h e r m a l P e r i o d , " l a s t e d u n t i l a b o u t 3,000 y e a r s a g o . I n r e s p o n s e t o t h e warmer, d r i e r c l i m a t e a n d t h e e v e n t u a l d e c r e a s e i n s e d i m e n t s u p p l y , t h e r i v e r d i s s e c t e d t h e p o s t - g l a c i a l v a l l e y f i l l s e d i m e n t s and f o r m e d a s e r i e s o f t e r r a c e s . D e g r a d a t i o n a p p e a r s t o h a v e b e e n a r r e s t e d n e a r Chipmunk C r e e k by o u t c r o p p i n g b e d r o c k w h i c h h a s f o r m e d a k n i c k p o i n t i n t h e s t r e a m p r o f i l e ( F i g u r e 1 7 ) . A s a r e -s u l t , u p s t r e a m o f Chipmunk C r e e k t h e r i v e r f l o w s on t o p o f t h e v a l l e y f i l l s e d i m e n t s w h e r e a s d o w n s t r e a m o f t h i s p o i n t t h e r i v e r d r o p s t h r o u g h a s t e e p c a n y o n a n d t h e n f l o w s i n an e n t r e n c h e d c h a n n e l c o n f i n e d by h i g h t e r r a c e s . The u p p e r t e r r a c e l e v e l ( T l o n F i g u r e 17) i s up t o 400 49 f e e t a b o v e t h e p r e s e n t r i v e r l e v e l a n d e x t e n d s d o w n s t r e a m f r o m Chipmunk C r e e k t o n e a r T a m a h i C r e e k . Remnants o f a s e c o n d l o w e r t e r r a c e (T2 on F i g u r e 1 7 ) , a p p r o x i m a t e l y 4 0 f e e t a b o v e t h e p r e s e n t r i v e r l e v e l , a r e a l s o f o u n d n e a r T a m a h i C r e e k a n d n e a r t h e s o u t h e n d o f C u l t u s L a k e . 4.3 F o r m a t i o n o f t h e C h i l l i w a c k R i v e r F a n A c c o r d i n g t o A r m s t r o n g ( 1 9 5 9 ) , t h e F r a s e r R i v e r f l o w e d t h r o u g h t h e p r e s e n t d a y Sumas V a l l e y p r i o r t o t h e Sumas G l a c i a t i o n . The F r a s e r was p r o b a b l y d i v e r t e d i n t o i t s p r e s e n t c h a n n e l when t h e a d v a n c i n g g l a c i e r b l o c k e d t h e c h a n n e l a n d f o r c e d t h e r i v e r t o f l o w w e s t a r o u n d Sumas M o u n t a i n . A f t e r t h e Sumas i c e r e t r e a t e d , t h e C h i l l i w a c k R i v e r was f r e e t o f l o w t h r o u g h t h e gap a t V e d d e r C r o s s i n g and b e g a n d e p o s i t i n g i t s l o a d o f g r a v e l a n d s a n d o n t o p o f t h e o l d e r f l o o d p l a i n d e p o s i t s . T h e r e f o r e , t h e C h i l l i w a c k R i v e r f a n i s l e s s t h a n 10,000 y e a r s o l d . The p r e s e n t C h i l l i w a c k f a n h a s a r o u g h l y c o n i c a l s h a p e a nd e x t e n d s o v e r an a r e a o f a p p r o x i m a t e l y 27 s q u a r e m i l e s b e t w e e n Sumas M o u n t a i n a n d C h i l l i w a c k M o u n t a i n ( F i g u r e 2 ) . The h e a d o f t h e f a n a t V e d d e r C r o s s i n g i s a t an e l e v a t i o n o f 100 f e e t a b o v e s e a l e v e l o r a b o u t 90 f e e t a b o v e t h e F r a s e r R i v e r f l o o d p l a i n . H o wever, t h e l o w t e r -r a c e n e a r C u l t u s L a k e a t an e l e v a t i o n o f 14 0 f e e t a b o v e 50 s e a l e v e l p r o v i d e s s t r o n g e v i d e n c e t h a t a t o n e t i m e t h e f a n h e a d was a p p r o x i m a t e l y 30 f e e t h i g h e r t h a n a t p r e s e n t . I t i s b e l i e v e d t h a t t h e p r o f i l e o f a n a l l u v i a l f a n r e f l e c t s t h e h i s t o r y o f e r o s i o n a n d d e p o s i t i o n w h i c h h a s t a k e n p l a c e i n t h e p a s t ( B u l l , 1 9 6 4 ) . F i g u r e 18 s h o w s a n u m b e r o f r a d i a l p r o f i l e s m e a s u r e d down t h e C h i l l i w a c k f a n f r o m V e d d e r C r o s s i n g t o t h e F r a s e r R i v e r f l o o d p l a i n . T h e s e p r o f i l e s w e r e p r e p a r e d f r o m 1 m e t e r c o n t o u r o r t h o -p h o t o g r a p h s a n d 5 f o o t c o n t o u r t o p o g r a p h i c m a p s . The s u r f a c e s h o w s a g e n t l y c o n c a v e p r o f i l e w h i c h i s t y p i c a l o f many a l l u v i a l f a n s ( B u l l , 1 9 6 4 ; H o o k e , 1 9 6 7 ; M a l c o v i s h , 1 9 7 4 ) . B a s e d o n a s i m p l e r e g r e s s i o n a n a l y s i s , i t was f o u n d t h a t t h e f a n p r o f i l e c o u l d be f i t t e d t o t h e e x p o n -e n t i a l e q u a t i o n : y = 140 e - 8 - 7 5 X l 0 " 5 x w h e r e y = f a n s u r f a c e e l e v a t i o n ( f e e t ) x = d i s t a n c e f r o m V e d d e r C r o s s i n g r 2 = 0 . 9 7 I t c a n be s e e n f r o m F i g u r e 18 t h a t t h e f a n p r o f i l e s show a n a b r u p t c h a n g e i n s l o p e a p p r o x i m a t e l y o n e - h a l f m i l e b e l o w V e d d e r C r o s s i n g . I t i s b e l i e v e d t h a t t h i s c h a n g e i n t h e p r o f i l e i s r e l a t e d t o p a s t p e r i o d s o f d o w n -c u t t i n g b y t h e C h i l l i w a c k R i v e r . When t h e C h i l l i w a c k R i v e r f l o w e d a t t h e l e v e l o f t h e l o w t e r r a c e n e a r C u l t u s L a k e , t h e f a n h e a d w o u l d h a v e b e e n g r a d e d t o a p p r o x i m a t e l y 51 t h i s l e v e l . T h e r e f o r e , when the r i v e r began i t s down-c u t t i n g , the fan head would have been d i s s e c t e d and the d e p o s i t i o n would have s h i f t e d from above Vedder C r o s s i n g to a p o i n t f u r t h e r downstream. A d d i t i o n a l evidence of fan d i s s e c t i o n such as remnants of the o l d fan head near Vedder C r o s s i n g cannot be found, p o s s i b l y because the pre s e n t day r i v e r has occupied channels a c r o s s the e n t i r e fan s u r f a c e . I t i s p o s s i b l e to estimate the average long term sedimentation r a t e on the C h i l l i w a c k fan by measuring the volume of sediment l a i d down i n the time i n t e r v a l of d e p o s i t i o n . The sediment volume was determined by d e f i n i n g the fan's extent from s u r f i c i a l geology maps (Armstrong, 195 9) and a i r p h o t o s , and then p l a n i m e t e r i n g the area from topograhpic maps. U n f o r t u n a t e l y , the p e r i o d of a c t i v e sedimentation cannot be a c c u r a t e l y determined. I t i s b e l i e v e d t h a t the l a s t g l a c i a t i o n ended approximately 10,000 years ago (Armstrong, 1959). However, Church and Ryder (1972) suggested t h a t most p o s t - g l a c i a l sedimenta-t i o n took p l a c e i n the p e r i o d immediately f o l l o w i n g g l a -c i a t i o n when the supply of sediment from g l a c i a l d r i f t was much g r e a t e r than the normal sediment supply d u r i n g n o n - g l a c i a l p e r i o d s . Ryder (1971) suggested t h a t most p o s t - g l a c i a l sedimentation i n s o u t h - c e n t r a l B r i t i s h Columbia o c c u r r e d w i t h i n a 4,000 year p e r i o d between 10,000 and 6,000 years ago. Using t h i s time p e r i o d and 52 assuming a fan head e l e v a t i o n o f 14 0 f e e t , the average r a t e of sedimentation on the C h i l l i w a c k fan was estimated a t 250,000 c u b i c yards per ye a r . T h i s f i g u r e probably r e p r e s e n t s a minimum estimate s i n c e the F r a s e r R i v e r f l o o d p l a i n probably aggraded d u r i n g t h i s p e r i o d so t h a t fan d e p o s i t s below the prese n t f l o o d p l a i n l e v e l were excluded from the est i m a t e . I t i s assumed t h a t d u r i n g the A l t i t h e r m a l p e r i o d (which l a s t e d u n t i l about 3,000 years ago) a c t i v e s e d i -mentation on the fan was low due to the decrease i n pr e -c i p i t a t i o n o c c u r r i n g around t h i s time. The p r e s e n t day sedimentation on the fan w i l l be the s u b j e c t of much of the remaining chapters i n t h i s t h e s i s . At t h i s time i t i s worth mentioning t h a t a g g r a d a t i o n has recommenced i n modern times although at c o n s i d e r a b l y lower r a t e s than i n e a r l y post g l a c i a l times. T h i s can be i l l u s t r a t e d by comparing the long term d e p o s i t i o n r a t e i n post g l a c i a l times w i t h the d e p o s i t i o n t h a t o c c u r r e d d u r i n g the r e c e n t f l o o d i n December 1975. A c c o r d i n g to surveys c a r r i e d out by the B.C. Water Resources S e r v i c e , approximately 2 6 0,000 cu b i c yards of sediment was d e p o s i t e d on the fan d u r i n g the December 197 5 f l o o d which corresponds c l o s e l y t o the long term post g l a c i a l average. However, the f l o o d o f 1975 was an extreme event w i t h a r e t u r n p e r i o d of about once i n ten y e a r s . T h e r e f o r e , the average p r e s e n t day d e p o s i t i o n r a t e i s l i k e l y to be much lower than the amount o c c u r r i n g i n 1975. 53 CHAPTER V R I V E R P R O C E S S E S UPSTREAM OF VEDDER CROSSING B e f o r e t h e r i v e r p r o c e s s e s o n t h e V e d d e r f a n c a n be d i s c u s s e d , i t i s i m p o r t a n t t o h a v e a t l e a s t a q u a l i t a t i v e u n d e r s t a n d i n g o f t h e r i v e r ' s b e h a v i o u r u p s t r e a m o f V e d d e r C r o s s i n g . T h i s i s b e c a u s e i n t h e l o n g t e r m t h e r e a c h b e t w e e n C h i l l i w a c k L a k e a n d V e d d e r C r o s s i n g g o v e r n s t h e q u a n t i t y a n d n a t u r e o f t h e s e d i m e n t s u p p l i e d t o t h e f a n . F o r t h i s r e a s o n t h e c u r r e n t p a t t e r n o f s e d i m e n t a t i o n o n t h e f a n may be r e l a t e d t o m o r p h o l o g i c a l p r o c e s s e s o c c u r -r i n g much f u r t h e r u p s t r e a m i n t h e b a s i n . T h i s c h a p t e r a t t e m p t s t o d i s c u s s , m a i n l y i n a q u a l -i t a t i v e f a s h i o n , t h e r e g i m e o f t h e C h i l l i w a c k R i v e r . Some o f t h e m o s t i m p o r t a n t q u e s t i o n s t h a t r e q u i r e a n s w e r -i n g i n c l u d e : 1 . Wha t a r e t h e m a j o r s e d i m e n t s o u r c e s t o t h e C h i l l i w a c k R i v e r f a n ? I s s e d i m e n t d e r i v e d m a i n l y f r o m t r i b u t a r i e s s o u r c e s , f r o m e r o s i o n o f v a l l e y w a l l s a n d f l o o d p l a i n d e p o s i t s o r f r o m s c o u r o f c h a n n e l b e d m a t e r i a l ? 2. Wha t a r e t h e m o s t i m p o r t a n t r i v e r p r o c e s s e s o c c u r r i n g o n t h e C h i l l i w a c k R i v e r a b o v e V e d d e r C r o s s i n g a t t h e p r e s e n t t i m e ? What a r e t h e m o s t i m p o r t a n t f a c t o r s w h i c h g o v e r n t h e m o r p h o l o g y o f t h e r i v e r ? 3 . How f a r d o e s s e d i m e n t move t h r o u g h t h e b a s i n d u r i n g a s i n g l e f l o o d e v e n t ? C a n s e d i m e n t s i n k s ( w h i c h 54 i n d i c a t e t e m p o r a r y s t o r a g e a r e a s f o r s e d i m e n t ) be i d e n t i -f i e d a l o n g t h e r i v e r ? 4. Has t h e s e d i m e n t y i e l d o f t h e b a s i n b e e n s i g -n i f i c a n t l y a l t e r e d by a c t i v i t i e s s u c h a s l o g g i n g a n d r o a d c o n s t r u c t i o n ? U n f o r t u n a t e l y , t h e s e q u e s t i o n s c a n o n l y be p a r t i a l l y a n s w e r e d i n t h i s s t u d y . 5.1 D a t a A v a i l a b l e T h i s d i s c u s s i o n i s b a s e d m a i n l y on o b s e r v a t i o n s a n d f i e l d d a t a c o l l e c t e d d u r i n g a number o f f i e l d t r i p s b e -t w e e n May 1976 and J u n e 1977. D u r i n g t h i s p e r i o d n e a r l y t h e e n t i r e l e n g t h o f r i v e r b e t w e e n V e d d e r C r o s s i n g a n d C h i l l i w a c k L a k e was v i s i t e d . I n a d d i t i o n , f i e l d t r i p s w e r e made t o m o s t o f t h e m a j o r t r i b u t a r y c r e e k s i n c l u d i n g T amahi C r e e k , S l e s s e C r e e k , Chipmunk C r e e k , N e s a k w a t c h C r e e k and C e n t r e C r e e k . F i n a l l y , a r e c o n n a i s s a n c e was made o f t h e e n t i r e l e n g t h o f r i v e r f r o m an a i r p l a n e i n J u n e 1977. A d d i t i o n a l d a t a was p r o v i d e d f r o m p a s t r e p o r t s p u b l i s h e d by t h e B.C. W a t e r R e s o u r c e s S e r v i c e ( M a r r , 1964; G o o d y e a r , 1957) and f r o m W a t e r S u r v e y o f C a n a d a G a u g i n g S t a t i o n r e c o r d s . Maps and A i r p h o t o s o f R i v e r F i g u r e 6, r e f e r r e d t o p r e v i o u s l y , shows t h e e n t i r e l e n g t h o f t h e C h i l l i w a c k R i v e r b e l o w C h i l l i w a c k L a k e 55 a l o n g w i t h p r i n c i p a l t r i b u t a r i e s and h y d r o m e t r i c s t a -t i o n s . M o s t o f t h e r i v e r a b o v e V e d d e r C r o s s i n g was s t u d i e d by u s i n g t o p o g r a p h i c maps a n d h i g h l e v e l a i r p h o t o g r a p h s , f o l l o w e d by s e v e r a l f i e l d t r i p s t o i n s p e c t a r e a s o f i n -t e r e s t a n d t o p r o v i d e " g r o u n d t r u t h " f o r t h e o f f i c e s t u d y . However,., i t was d e c i d e d t o c a r r y o u t a more d e t a i l e d s t u d y b e t w e e n L i u m c h e n C r e e k a nd V e d d e r C r o s s i n g due t o t h e r a p i d c h a n n e l s h i f t i n g t h a t h a d o c c u r r e d t h r o u g h o u t t h i s r e a c h i n t h e p a s t . T h e r e f o r e , a number o f c h a n n e l o v e r l a y s w e r e p r e p a r e d i n t h i s r e a c h u s i n g s u c c e s s i v e y e a r s o f a i r p h o t o g r a p h s f l o w n b e t w e e n 1940 and 1976. F u r t h e r d i s c u s s i o n o f t h e s e o v e r l a y s i s c o n t a i n e d i n s e c t i o n 5.6. A l i s t o f a l l maps a n d a i r p h o t o s u s e d i n t h i s s t u d y i s s u m m a r i z e d i n T a b l e 8. C h a n n e l G e o m e t r y The u p p e r C h i l l i w a c k R i v e r i s g e n e r a l l y a f a s t f l o w i n g s h a l l o w s t r e a m t h a t c a n n o t be e a s i l y waded e v e n d u r i n g v e r y l o w f l o w s . T h e r e f o r e , c h a n n e l c r o s s - s e c t i o n s w e r e n o t s u r v e y e d by t h e a u t h o r e x c e p t a t c o n v e n i e n t b r i d g e c r o s s i n g s a n d on some o f t h e t r i b u t a r y c r e e k s . A d d i t i o n a l d a t a was o b t a i n e d f r o m e a r l i e r s u r v e y s by t h e B.C. W a t e r R e s o u r c e s S e r v i c e a n d f r o m c u r r e n t m e t e r m e a s u r e m e n t s a t some o f t h e W a t e r S u r v e y o f C a n a d a g a u g i n g s t a t i o n s . A summary o f t h e a v a i l a b l e d a t a i s a s f o l l o w s : 56 - 4 c r o s s - s e c t i o n s s u r v e y e d by t h e B.C. W a t e r R e s o u r c e s S e r v i c e b e t w e e n V e d d e r C r o s s i n g a n d L i u m c h e n C r e e k ( M a r r , 1964) - 2 c r o s s - s e c t i o n s s u r v e y e d by t h e a u t h o r f r o m b r i d g e s a c r o s s t h e C h i l l i w a c k R i v e r n e a r C e n t r e C r e e k a n d N e s a k w a t c h C r e e k - 6 c r o s s - s e c t i o n s s u r v e y e d by t h e a u t h o r a t T a m a h i C r e e k and S l e s s e C r e e k - c r o s s - s e c t i o n s a n d v e l o c i t y m e a s u r e m e n t s a t t h e f o l l o w i n g W a t e r S u r v e y o f C a n a d a g a u g i n g s t a t i o n s : C h i l l i w a c k R i v e r a b o v e S l e s s e C r e e k (8MH103) C h i l l i w a c k R i v e r b e l o w S l e s s e C r e e k (8MH55) S l e s s e C r e e k (8MH56) Some o f t h e s e s e c t i o n s h a v e b e e n shown on F i g u r e 19 and t h e gauge r a t i n g m e a s u r e m e n t s a r e s u m m a r i z e d on F i g u r e 20. S l o p e S u r v e y s C h a n n e l s l o p e s u r v e y s w e r e c a r r i e d o u t by t h e a u t h o r by l e v e l l i n g a l o n g t h e w a t e r ' s edge a t s e v e r a l s i t e s a l o n g t h e r i v e r . T h e s e s u r v e y s w e r e c a r r i e d o u t on S e p t e m b e r 1, 1976 when t h e d i s c h a r g e a t V e d d e r C r o s s i n g was 2,550 c f s ( a b o u t t h e l o n g t e r m mean). I n a d d i t i o n , a l o n g i t u d i n a l s t r e a m p r o f i l e was p r e -p a r e d b e t w e e n V e d d e r C r o s s i n g and C h i l l i w a c k L a k e u s i n g a number o f c o n t o u r maps p r e p a r e d by t h e B.C. W a t e r R e s o u r c e s S e r v i c e ( G o o d y e a r , 1 9 5 7 ) , h a v i n g s c a l e s o f 57 1:7,2 00 and c o n t o u r i n t e r v a l s o f 10 f e e t a s w e l l a s 1 : 2 5 , 0 0 0 N a t i o n a l T o p o g r a p h i c S e r i e s maps. T h i s p r o f i l e , r e f e r r e d t o p r e v i o u s l y , i s shown i n F i g u r e 1 7 . B e d M a t e r i a l S a m p l e s A t o t a l o f 36 bed m a t e r i a l s a m p l e s w e r e c o l l e c t e d by t h e a u t h o r b e t w e e n V e d d e r C r o s s i n g a n d C h i l l i w a c k L a k e d u r i n g t h e summer and f a l l o f 1 9 7 6 . M o s t s a m p l e s w ere m e a s u r e d e i t h e r by u s i n g t h e p h o t o g r a p h i c g r i d o r t a p e m e t hod w h i c h h a v e b e e n o u t l i n e d by K e l l e r h a l s ( 1 9 7 3 ) . B r i e f l y , t h e two method s o f s a m p l i n g w e re as f o l l o w s : P h o t o g r a p h i c g r i d : A s q u a r e g r i d w i t h 50 mm s p a c -i n g s was p l a c e d o v e r t h e a r e a t o be s a m p l e d a n d a p h o t o -g r a p h was t h e n t a k e n . The s t o n e u n d e r l y i n g e a c h g r i d p o i n t was m e a s u r e d f r o m t h e p h o t o g r a p h . Tape: A 50 f o o t t a p e s u r v e y t a p e was s t r e t c h e d a l o n g t h e s a m p l e s i t e a n d s t o n e s u n d e r l y i n g e a c h f o o t mark on t h e t a p e w e r e m e a s u r e d . F o r e a c h m e t h o d t h e i n t e r m e d i a t e a x i s o f e a c h s t o n e was m e a s u r e d a nd t h e r e s u l t s w e r e p r e s e n t e d a s a c u m u l a -t i v e f r e q u e n c y - b y - n u m b e r s i z e d i s t r i b u t i o n . A l s o i t s h o u l d be n o t e d t h a t b o t h o f t h e s e m e t h o d s d e s c r i b e o n l y t h e s u r f a c e b e d m a t e r i a l s i z e d i s t r i b u t i o n s i n c e o n l y t h e t o p l a y e r o f s t o n e s was s a m p l e d . I n g e n e r a l , much o f t h e b e d i s a r m o u r e d , w i t h s a n d a n d f i n e g r a v e l f o u n d t o u n d e r l i e t h e s u r f a c e l a y e r o f c o b b l e s . 58 In a d d i t i o n a s m a l l e r number of bulk s i e v e samples were c o l l e c t e d i n order to p r o v i d e a comparison with the s u r f a c e samples. Bulk samples were obtained by removing the s u r f a c e armoured l a y e r of g r a v e l and then c o l l e c t i n g approximately 20 pounds of the u n d e r l y i n g bed m a t e r i a l . The samples were analyzed by s i e v i n g and the r e s u l t s were presented as a cumulative frequency by weight s i z e d i s -t r i b u t i o n . A summary of the bed m a t e r i a l data i s presented i n Table 9. 5.2 A n a l y s i s of R i v e r Processes Even a b r i e f i n s p e c t i o n of a i r photographs shows the C h i l l i w a c k R i v e r undergoes s e v e r a l abrupt changes i n channel c h a r a c t e r i s t i c s between C h i l l i w a c k Lake and Vedder C r o s s i n g . The most apparent changes may be seen i n the v a r i a t i o n of channel p a t t e r n and bed m a t e r i a l s i z e along the r i v e r . I t i s b e l i e v e d t h a t such v a r i a -t i o n s may r e f l e c t changes i n geomorphic s e t t i n g , s e d i -ment supply or d i s c h a r g e regime - the major f a c t o r s which tend to govern r i v e r morphology ( K e l l e r h a l s , Church and Bray, 1976). In order to s i m p l i f y t h i s d i s c u s s i o n , the C h i l l i w a c k R i v e r has been s u b d i v i d e d i n t o f i v e reaches, each d i s -p l a y i n g roughly c o n s i s t e n t channel c h a r a c t e r i s t i c s . I t i s assumed t h a t s i n c e the morphology i s reasonably 59 constant i n these reaches, the f a c t o r s governing r i v e r behaviour are a l s o r e l a t i v e l y c o n s t a n t ( K e l l e r h a l s , Church and Bray, 1976). The f i v e reaches t h a t have been i d e n t i f i e d are as f o l l o w s : C h i l l i w a c k Lake - Chipmunk Creek Chipmunk Creek - S l e s s e Creek S l e s s e Creek - Tamahi Creek Tamahi Creek - Ryder Creek Ryder Creek - Vedder C r o s s i n g The e x t e n t of each reach i s shown on the long pro-f i l e i n F i g u r e 17, while some of the most prominent mor-p h o l o g i c a l f e a t u r e s have been i l l u s t r a t e d on the s e r i e s of maps shown on F i g u r e s 21.1 to 21.5. In a d d i t i o n , some of the key h y d r o l o g i c , geomorphic and h y d r a u l i c data t h a t have been determined f o r each reach are summarized i n Tables 10 to 12 r e s p e c t i v e l y . C h i l l i w a c k Lake to Chipmunk Creek Throughout t h i s reach the C h i l l i w a c k R i v e r flows over a s t a b l e boulder bed which i s c h a r a c t e r i s t i c of many lake o u t l e t streams. The r i v e r flows i n a s i n g l e channel and has degraded i n t o i t s former v a l l e y f l o o r so t h a t i t i s c o n t i n u o u s l y c o n f i n e d by low wooded banks. The channel p a t t e r n i s very i r r e g u l a r i n t h i s reach with the r i v e r o f t e n d e f l e c t e d across the v a l l e y bottom wherever the channel impinges a g a i n s t the v a l l e y w a l l s . 60 Bars and islands are generally very infrequent except i n l o c a l i z e d areas where the channel width i n -creases abruptly. Although major t r i b u t a r i e s such as Centre Creek, Nesakwatch Creek and Chipmunk Creek flow into the river, i n t h i s reach a l l u v i a l fans have not b u i l t out into the mainstream. Between Chilliwack Lake and Chipmunk Creek the bed material consists predominately of angular boulders and more rounded cobbles (Table 9 ). Based on l i t h o l o g y and size i t seems l i k e l y these boulders are derived from the debris which has dammed the western end of Chilliwack Lake. It i s also l i k e l y that much of present channel consists of r e l a t i v e l y stable "lag deposits" which are not transported except possibly i n very extreme floods. Therefore, although the r i v e r capacity for sediment transport i s very large due to the high slope, the r i v e r probably c a r r i e s a r e l a t i v e l y small bedload of gravel and cobbles. This i s because the supply of sediment that can be transported under e x i s t i n g hydraulic conditions i s quite low, being derived mainly from t r i b u t a r i e s . In summary, in t h i s reach the Chilliwack River i s flowing on a slope that has been imposed by the g l a c i a l history of the v a l l e y . Also most of the channel deposits which make up the r i v e r ' s bed material are not derived from present day channel processes but from early post g l a c i a l events. At present the channel i s generally « 61 s t a b l e i n t h i s reach with the major channel processes r e -s t r i c t e d to e r o s i o n of fan d e p o s i t s s u p p l i e d by t r i b u t a r y c r e e k s . Bank e r o s i o n may a l s o occur a l o n g the C h i l l i w a c k R i v e r where log-jams have c r e a t e d major o b s t r u c t i o n s to the flow. • Chipmunk Creek - S l e s s e Creek Below Chipmunk Creek the C h i l l i w a c k R i v e r has d i s -s e c t e d i t s former v a l l e y f l o o r , l e a v i n g t e r r a c e s up to 4 00 f e e t above the p r e s e n t r i v e r l e v e l (Figure 17). Close t o Chipmunk Creek the r i v e r i s n e a r l y c o n t i n u o u s l y c o n f i n e d by these t e r r a c e s , however w i t h i n c r e a s i n g d i s -tance downstream the v a l l e y widens and a fragmentary v a l l e y f l a t can be r e c o g n i z e d . At Chipmunk Creek, the r i v e r r i s e s to i t s former v a l l e y f l o o r l e v e l i n a steep bedrock canyon. This canyon r e p r e s e n t s a s t a b l e " k n i c k p o i n t " i n the stream-p r o f i l e and can be i d e n t i f i e d on the l o n g i t u d i n a l p r o f i l e and on F i g u r e 21.2. Throughout t h i s reach the r i v e r d i s p l a y s a very i r r e g u l a r channel p a t t e r n , r e f l e c t i n g the i n f l u e n c e of the v a l l e y w a l l s which n e a r l y c o n t i n u o u s l y c o n f i n e s the stream. The r i v e r flows i n a s i n g l e channel throughout the reach and v e r y few i s l a n d s or bars are e v i d e n t . In g e n e r a l , the r i v e r flows i n a cobble and b o u l d e r channel with h e a v i l y f o r e s t e d g r a v e l and cobble banks. A random sampling of 2 5 b o u l d e r s upstream of the S l e s s e Creek 62 confluence i n d i c a t e d stones up to 1100 mm (b-axis) are present i n the channel w h i l e the average s i z e was found to be about 500 mm. The r i v e r slope was found to average around 0.018 between Chipmunk Creek and S l e s s e Creek and the channel top w idth ranged from about 70 f e e t - 90 f e e t . The o n l y h y d r a u l i c data a v a i l a b l e was d e r i v e d from the Water Survey of Canada gauging s t a t i o n l o c a t e d about 6800 f e e t below Chipmunk Creek and i s summarized i n Table 12 and F i g u r e 20. Although these measurements are probably not r e p r e s e n t a t i v e of the e n t i r e r each, they a t l e a s t p r o v i d e a rough i d e a of the h y d r a u l i c c o n d i t i o n s i n the r i v e r . These r e s u l t s were used to estimate the t h r e s h o l d c o n d i t i o n s f o r bed movement by means of N e i l l ' s competent v e l o c i t y curves ( N e i l l 1967, RTAC 1978) (See Table 13). Based on N e i l l ' s r e l a t i o n a f l o o d of 4700 c f s (2 year r e t u r n period) having a mean v e l o c i t y o f 7.5 f t / s and a mean depth o f 8.5 f t should be a b l e to t r a n s p o r t stones up to about 5 0 mm i n diameter. A more extreme f l o o d of 6500 c f s should be com-petent to move stones up t o about 80 mm. Since the bed m a t e r i a l c o n t a i n s a c o n s i d e r a b l e amount of m a t e r i a l t h a t i s much l a r g e r than the c a l c u l a t e d s i z e s (by as much as an order of magnitude) i t seems l i k e l y t h a t much of the bed w i l l remain s t a b l e even d u r i n g severe f l o o d e v ents. There-f o r e the channel d e p o s i t s i n t h i s reach do not c o n s t i t u t e a major source of m a t e r i a l t h a t i s r e a d i l y a v a i l a b l e f o r 63 t r a n s p o r t a s b e d l o a d . . C o n s e q u e n t l y , i t i s e x p e c t e d t h a t t h e b e d l o a d t r a n s p o r t r a t e i s r e l a t i v e l y l o w . The magor p r o c e s s e s w i t h i n t h i s r e a c h a p p e a r s t o be w i d e n i n g o f t h e v a l l e y f l o o r b y e r o s i o n o f t e r r a c e s w h i c h f r e q u e n t l y c o n f i n e t h e c h a n n e l . T h i s e r o s i o n h a s r e s u l t e d i n some f a i r l y l a r g e l a n d s l i d e s i n t h e n o r t h a n d s o u t h v a l l e y w a l l s u p s t r e a m o f S l e s s e C r e e k ( F i g u r e 21.2) . T h i s s l i d e m a t e r i a l c o n s i s t s p r e d o m i n a t e l y o f s a n d a n d some f i n e g r a v e l a n d w o u l d be r a p i d l y r e m o v e d b y r i v e r e r o s i o n . S l e s s e C r e e k t o Tamahi C r e e k S l e s s e C r e e k i s t h e l a r g e s t s i n g l e t r i b u t a r y i n t h e C h i l l i w a c k b a s i n a n d h a s a m a j o r i n f l u e n c e on t h e h y d r o l o g y a n d m o r p h o l o g y o f t h e C h i l l i w a c k R i v e r . One o f t h e m o s t n o t i c e a b l e e f f e c t s o f t h e i n c r e a s e d d i s c h a r g e b e l o w S l e s s e C r e e k i s t h e C h i l l i w a c k R i v e r ' s s u d d e n i n c r e a s e i n c h a n n e l w i d t h . W h i l e t h e a v e r a g e c h a n -n e l w i d t h u p s t r e a m o f S l e s s e C r e e k r a n g e s f r o m 70 - 100 f e e t , b e t w e e n S l e s s e C r e e k a n d Tamahi C r e e k t h e w i d t h v a r i e s f r o m a b o u t 130 - 150 f e e t . I n t h i s r e a c h t h e C h i l l i w a c k R i v e r b e g i n s t o d e v e l o p a more c o n t i n u o u s v a l l e y f l a t w h i c h i s c omposed o f g r a v e l a n d c o b b l e f l o o d p l a i n d e p o s i t s . However i n some a r e a s s u c h as n e a r B o r d e r C r e e k t h i s v a l l e y f l a t d i s a p p e a r s a n d t h e r i v e r i s c o n t i n u o u s l y c o n f i n e d b y b e d r o c k . 6 4 A s h o r t d i s t a n c e d o w n s t r e a m o f S l e s s e C r e e k t h e C h i l l i w a c k R i v e r a l s o b e g i n s t o d e v e l o p m e a n d e r s . T h i s p a t t e r n v a r i e s f r o m r e g u l a r c o n f i n e d m e a n d e r s d o w n s t r e a m o f S l e s s e C r e e k t o v e r y i r r e g u l a r , a l m o s t t o r t u o u s m e a n d e r s a b o v e S l e s s e C r e e k . T h i s v a r i a t i o n i n p a t t e r n seems t o r e f l e c t d i f f e r e n c e s i n bank m a t e r i a l p r o p e r t i e s - n e a r l y S l e s s e C r e e k t h e r i v e r i s f r e q u e n t l y c o n f i n e d by t h e v a l l e y w a l l , w h e r e a s d o w n s t r e a m o f B o r d e r C r e e k t h e r i v e r f l o w s a g a i n s t r e l a t i v e l y e r o d i b l e t e r r a c e d e p o s i t s composed o f s i l t y - c l a y . F r e q u e n t g r a v e l d i a g o n a l b a r s and p o i n t b a r s a r e f o u n d i n t h i s r e a c h , r e f l e c t i n g t h e i n p u t o f s e d i m e n t f r o m S l e s s e C r e e k . The m o s t p r o m i n e n t c h a n n e l d e p o s i t s c a n be f o u n d a p p r o x i m a t e l y t w o m i l e s u p s t r e a m o f T a mahi C r e e k w h e r e v e r y l a r g e f i n e g r a v e l p o i n t b a r s h a v e d e v e l o p e d . T hese b a r s a r e i l l u s t r a t e d i n F i g u r e 2 1 . 3 . R e s u l t s o f t h e b e d m a t e r i a l s a m p l i n g p r o g r a m i n d i c a t e t h e b e d s i z e d e c r e a s e s s h a r p l y i n t h i s r e a c h ( T a b l e 9 ) . An a v e r a g e o f a l l s a m p l e s on t h e l a r g e p o i n t b a r s a b o v e Tamahi C r e e k i n d i c a t e d a D , _ Q s i z e o f 7 0 mm w h i l e m e a s u r e -m e n t s o f t h e c o n f l u e n c e o f S l e s s e C r e e k g a v e a c o r r e s p o n d i n g s i z e o f 1 4 0 mm. E s t i m a t e s o f h y d r a u l i c p a r a m e t e r s m e a s u r e d a t t h e W a t e r S u r v e y o f C a n a d a gauge b e l o w S l e s s e C r e e k (8MH55) a r e s u m m a r i z e d i n T a b l e 1 2 . T h e s e r e s u l t s a r e p r o b a b l y r e a s o n a b l y r e p r e s e n t a t i v e o f t h e u p p e r p a r t o f t h e r e a c h 65 n e a r S l e s s e C r e e k b u t n o t o f t h a t p a r t d o w n s t r e a m o f B o r d e n C r e e k . A c o m p a r i s o n o f t h e s e m e a s u r e m e n t s w i t h t h e r e s u l t s f r o m t h e gauge a b o v e S l e s s e C r e e k (8MH10 3) i n d i c a t e s t h a t f o r t h e same f l o o d r e t u r n p e r i o d t h e C h i l l i -wack R i v e r b e l o w S l e s s e C r e e k f l o w s w i t h i n a w i d e r , s h a l l o w e r c h a n n e l a t a h i g h e r v e l o c i t y ( h e n c e h i g h e r f r o u d e n u m b e r ) . E s t i m a t e s o f minimum s t o n e s i z e f o r i n c i p i e n t b e d move-ment a r e s u m m a r i z e d i n T a b l e 1 3 . T h e s e c a l c u l a t i o n s show s t o n e s up t o a b o u t 80 mm c a n be moved d u r i n g f l o o d s h a v i n g a r e t u r n p e r i o d o f two y e a r s w h i l e c o b b l e s up t o a b o u t 150 mm c a n be moved d u r i n g more e x t r e m e f l o o d s w i t h r e -t u r n p e r i o d s o f 20 y e a r s . T hese s i z e s a p p e a r r o u g h l y c o m p a r a b l e t o t h e s i z e o f t h e b e d m a t e r i a l m e a s u r e d t h r o u g h o u t t h i s r e a c h . T h e r e f o r e t h e b e d p r o b a b l y becomes a c t i v e f a i r l y f r e q u e n t l y - a t l e a s t w h e n e v e r f l o w s e x c e e d t h e two y e a r f l o o d l e v e l . T h i s i s q u i t e d i f f e r e n t f r o m t h e u p s t r e a m r e a c h e s w h e r e much o f t h e b e d i s composed o f s t a b l e l a g d e p o s i t s w h i c h do n o t move e x c e p t p o s s i b l y d u r i n g v e r y e x t r e m e f l o o d s . I n t e r m s o f p r e s e n t d a y p r o c e s s e s i n t h i s r e a c h , t h e C h i l l i w a c k R i v e r a p p e a r s t o be c o n t i n u i n g t o w i d e n i t s v a l l e y f l o o r as shown by t h e e r o s i o n and s l u m p i n g a l o n g t h e v a l l e y w a l l s . A l s o i n some a r e a s , n o t a b l y n e a r S l e s s e C r e e k , o l d c h a n n e l s c a r s c a n be i d e n t i f i e d i n d i c a t i n g l a t e r a l p r o g r e s s i o n o f t h e m e a n d e r s h a s t a k e n p l a c e i n t h e p a s t . The p r e s e n c e o f f r e q u e n t g r a v e l b a r s i n t h i s r e a c h 66 r e f l e c t s the i n c r e a s e d supply of sediment t o the r i v e r from t r i b u t a r i e s - w i t h S l e s s e Creek the most important s i n g l e s o urce. The v e r y e x t e n s i v e g r a v e l p o i n t bars e v i -dent upstream of Tamahi Creek r e p r e s e n t the o n l y major channel d e p o s i t s to be found i n the upper C h i l l i w a c k R i v e r . These d e p o s i t s can probably be c o n s i d e r e d as an important storage area f o r g r a v e l - s i z e sediment i n the b a s i n . Tamahi Creek to Ryder Creek Approximately 700 f e e t upstream of Tamahi Creek the C h i l l i w a c k R i v e r undergoes another very abrupt change i n c h a r a c t e r . Near t h i s p o i n t the r i v e r changes from a g r a v e l bed meandering channel and begins to narrow, forming a s e r i e s of steep r a p i d s c o n t a i n i n g v e r y l a r g e angular b o u l -ders up to 1 metre i n s i z e . T h i s t r a n s i t i o n i s i l l u s -t r a t e d on the photo i n F i g u r e 21.4 which shows s t a n d i n g waves and r a p i d s j u s t upstream of Tamahi Creek. These boulders may be found i n the r i v e r channel f o r a t l e a s t lk m i l e s below Tamahi Creek although both the frequency and s i z e of the boulders tends to decrease w i t h d i s t a n c e downstream. By Osborne Road the channel appears once more to be composed o f g r a v e l and cobbles and b o u l d e r d e p o s i t s can not be found. Bed m a t e r i a l samples were taken a t the confluence of Tamahi Creek and downstream near Osborne Road. At Tamahi Creek the boulder d e p o s i t s were sampled by measuring 67 the i n t e r m e d i a t e a x i s of 25 stones. The average boulder s i z e was found to be about 0.9m with the l a r g e s t stone up to 1.85 m. In a d d i t i o n a standard tape g r i d sample was a l s o made on the Tamahi Creek d e l t a near i t s c o n f l u e n c e with the C h i l l i w a c k R i v e r (Sample 64). T h i s sample gave a D,-Q s i z e o f 150 mm and a Dg Q s i z e of 220 mm. By Osborne Road the D ,_Q s i z e had decreased to 120 mm and the D^g s i z e was 160 mm (Table 9). The source o f these l a r g e b o u l d e r s i s not e v i d e n t , however there are a number of p o s s i b i l i t i e s such as: 1. Moraine d e p o s i t s 2. Debris c a r r i e d down Tamahi Creek e i t h e r by a l a r g e s l i d e or by r e l e a s e of an i c e dam. The a c t u a l mechanism i s probably not too important f o r the purposes o f t h i s study. The main p o i n t i s t h a t a l a r g e "plug" o f b o u l d e r s e x i s t s near Tamahi Creek and paves the bed of the r i v e r f o r a c o n s i d e r a b l e d i s t a n c e downstream. These d e p o s i t s a l s o account f o r the i n c r e a s e i n slope i n t h i s reach, which averages 0.0086. The C h i l l i w a c k R i v e r channel appears to be q u i t e s t a b l e i n t h i s reach due to the paving e f f e c t of the l a r g e b o u l d e r s . However a comparison o f a i r p h o t o s i n d i c a t e d Tamahi Creek s h i f t e d about 250 f e e t d u r i n g the f l o o d of 1975. Surveys of the d e l t a show t h a t the o l d channel was completely f i l l e d - i n w i t h cobbles and g r a v e l and a new channel was c r e a t e d . I t i s l i k e l y t h a t s e v e r a l thousand 68 c u b i c yards of cobbles and g r a v e l would have been dumped i n t o the C h i l l i w a c k R i v e r d u r i n g t h i s f l o o d . Ryder Creek to Vedder C r o s s i n g Downstream of Ryder Creek the C h i l l i w a c k R i v e r g r a d u a l l y transforms from a s t a b l e c o n f i n e d s i n g l e channel and becomes much wider, d e v e l o p i n g a s p l i t or b r a i d e d channel p a t t e r n . T h i s change becomes most n o t i c e a b l e downstream o f Liumchen Creek where a number of g r a v e l bars f i r s t become e v i d e n t i n the channel. Opposite C u l t u s Lake the C h i l l i w a c k R i v e r flows i n a s h i f t i n g , l a t e r a l l y u n s table channel with a v a l l e y f l a t n e a r l y h a l f a m i l e i n width. The souths v a l l e y w a l l e f f e c t i v e l y c o n f i n e s the C h i l l i w a c k R i ver u n t i l j u s t west of Liumchen Creek. West of t h i s p o i n t the v a l l e y w a l l turns to the south and even-t u a l l y forms a steep b l u f f along the e a s t e r n shore of C u l t u s Lake. Therefore downstream of Liumchen Creek the r i v e r has been f r e e t o migrate l a t e r a l l y over a v e r y wide area. D e t a i l e d examination shows three t e r r a c e l e v e l s can be i d e n t i f i e d i n t h i s reach: 1. G l a c i a l outwash d e p o s i t s which c o n f i n e the chan-n e l along the south bank above Liumchen Creek. These de-p o s i t s extend up to about 500 f e e t above the p r e s e n t r i v e r l e v e l . 69 2. A small t e r r a c e about 50 f e e t above the p r e s e n t r i v e r l e v e l found along the n o r t h s i d e of C u l t u s Lake. This probably corresponds to a former l e v e l of the C h i l -l i w a c k R i v e r i n p o s t - g l a c i a l times p r i o r t o r i v e r down-c u t t i n g (see Chapter 4 - Geology). 3. A very widespread low t e r r a c e of the C h i l l i w a c k River approximately 10 f e e t above the p r e s e n t day f l o o d -p l a i n . Many o l d channel s c a r s v i s i b l e between the e x i s t i n g channel and C u l t u s Lake suggest t h a t t h i s l e v e l was aban-doned i n very r e c e n t times. The e x i s t i n g channel has a w e l l developed v a l l e y f l a t t h a t i s f o r e s t e d w i t h young c o n i f e r s and cottonwoods and appears to be s u b j e c t t o frequent f l o o d i n g . A number of bed m a t e r i a l samples were c o l l e c t e d by the author i n t h i s r each (Table 9) and although c o n s i d e r a b l e s i z e v a r i a t i o n was found between samples, no systematic downstream trends c o u l d be d e t e c t e d . Based on these samples, the average D^.,- g r a i n s i z e i n t h i s reach was around 60 mm and the corresponding D^Q s i z e was about 40 mm. A l l o f these samples were c o l l e c t e d from g r a v e l bars (mainly d i a g o n a l and mid-channel bars) and are probably r e p r e s e n -t a t i v e of the m a t e r i a l t h a t i s b e i n g t r a n s p o r t e d by the c h a n n e l . C o n s i d e r a b l y c o a r s e r sediments c o u l d be seen to l i e i n the main channel however these were not sampled. The bank m a t e r i a l was found to c o n s i s t mainly of p o o r l y s o r t e d sand and g r a v e l s roughly s i m i l a r i n s i z e t o the 70 present bed m a t e r i a l . The main d i f f e r e n c e between the bed and bank m a t e r i a l s seemed to be i n the g r e a t e r p r o p o r t i o n of f i n e r g r a v e l s and sands (and g r e a t e r range of s i z e s ) i n the banks. The average water s u r f a c e slope a t low water between Vedder C r o s s i n g and Liumchen Creek was found to be about 0.0063, d e c r e a s i n g t o 0.005 near Vedder C r o s s i n g . U n f o r t u n a t e l y the o n l y c r o s s s e c t i o n s a v a i l a b l e to the author i n t h i s reach were surveyed by the B.C. Water Resources S e r v i c e i n 1958 and again i n 1963. Since c o n s i d e r a b l e channel s h i f t i n g has o c c u r r e d s i n c e t h i s time these s e c t i o n s are not r e p r e s e n t a t i v e of p r e s e n t channel c o n d i t i o n s . However i t was f e l t t h a t t h i s data c o u l d at l e a s t be used t o p r o v i d e a v e r y rough estimate of b a n k f u l l flow i n the reach. In a d d i t i o n s i n c e a water s u r f a c e p r o f i l e was o b t a i n e d i n 1963 d u r i n g a moderately h i g h flow (6880 c f s ) i t was f e l t t h a t reasonable e s t i m a t e s c o u l d be made of the slope the channel roughness. There-fore the f o l l o w i n g a n a l y s i s was c a r r i e d out: 1. The water s u r f a c e slope was computed and found t o v a r y between 0.0052 and 0.0065. T h i s agrees w i t h the surveys c a r r i e d out by the author i n 1976 a t low flow. 2: Using the surveyed water l e v e l s and the d i s c h a r g e of 6880 c f s Manning's "n" v a l u e s were computed a t each sec-t i o n and were found to vary between 0.00 35 - 0.0042. 3. The c r o s s - s e c t i o n s were then s u b d i v i d e d i n t o main 11 c h a n n e l a n d o v e r b a n k s u b - s e c t i o n s . O v e r b a n k s e c t i o n s w e r e a s s i g n e d r o u g h n e s s v a l u e s o f b e t w e e n 0.06 - 0.10 .(based on s u r v e y d e s c r i p t i o n s and a i r p h o t o i n s p e c t i o n ) w h i l e a v a l u e o f 0.038 was u s e d f o r a l l t h e m a i n c h a n n e l s e c t i o n s . 4. The d i s c h a r g e was t h e n c o m p u t e d f r o m t h e M a n n i n g ' s 2/3 1/2 e q u a t i o n Q = 1.49 AR S f o r v a r i o u s r i v e r s t a g e s n a s s u m i n g u n i f o r m f l o w . The c a l c u l a t i o n s i n d i c a t e d t h a t t h e b a n k f u l l d i s -c h a r g e was b e t w e e n 9000 - 11000 c f s , w h i c h c o r r e s p o n d s t o a f l o o d w i t h a r e t u r n p e r i o d o f a r o u n d two y e a r s . T h e s e r e s u l t s a r e i n g e n e r a l a g r e e m e n t w i t h o t h e r s t u d i e s on g r a v e l b e d r i v e r s ( H e n d e r s o n , 1966; B r a y , 1 9 7 2 ) . I t was a l s o f o u n d t h a t o n c e t h e b a n k f u l l l e v e l i s e x c e e d e d t h e r i v e r s t a g e - d i s c h a r g e r e l a t i o n becomes v e r y f l a t , w i t h o n l y a s l i g h t i n c r e a s e i n s t a g e f o r e v e n s e v e r e f l o o d s . T h i s i s b e c a u s e o n c e b a n k f u l l s t a g e i s e x c e e d e d , t h e c h a n -n e l w i d t h becomes v e r y l a r g e t h e r e b y i n c r e a s i n g t h e c h a n n e l a r e a . As a r e s u l t , i t a p p e a r s t h a t t h e r i v e r s t a g e d o e s n o t e x c e e d t h e l e v e l o f t h e l o w t e r r a c e i n t h i s r e a c h e v e n d u r i n g e x t r e m e f l o o d s . The r e s u l t s f r o m t h e s e c a l c u -l a t i o n a r e s u m m a r i z e d i n T a b l e 1 2 . A c o m p a r i s o n b e t w e e n t h e 1958 a n d 1963 c r o s s s e c -t i o n s showed t h a t c o n s i d e r a b l e c h a n n e l s h i f t i n g o c c u r r e d a r o u n d t h i s t i m e , w i t h some t e n d e n c y t o w a r d s d e p o s i t i o n ( F i g u r e 1 9 ) . The a v e r a g e b e d l e v e l c h a n g e was c o m p u t e d a t e a c h s e c t i o n a s f o l l o w s : 72 1. The n e t a r e a b e t w e e n t h e c h a n n e l b o t t o m i n 1958 a n d 196 3 was p l a n i m e t e r e d . 2. The a v e r a g e b e d l e v e l c h a n g e was t h e n t a k e n a s t h e n e t a r e a d i v i d e d b y t h e b o t t o m w i d t h . The r e s u l t i n d i c a t e d t h a t t h r e e o u t o f f o u r s e c t i o n s show n e t a g g r a d a t i o n h a d o c c u r r e d i n t h i s p e r i o d , w i t h o n l y t h e v e r y n a r r o w s e c t i o n n e a r V e d d e r C r o s s i n g s h o w i n g n e t d e g r a d a t i o n . As f a r as t h e a u t h o r i s a w a r e , no c r o s s s e c t i o n s were s u r v e y e d i n t h i s r e a c h f o l l o w i n g t h e 1974 f l o o d . H owever, b a s e d on some f i e l d o b s e r v a t i o n s a n d a i r p h o t o c o m p a r i s o n s , i t a p p e a r e d t h a t many new g r a v e l b a r s w e re f o r m e d as a r e s u l t o f t h i s f l o o d . T h e r e f o r e , t h e r e i s some e v i d e n c e ( a l t h o u g h n o t c o n c l u s i v e ) t o i n d i c a t e t h a t t h e r i v e r may be now s l o w l y a g g r a d i n g i n t h i s r e a c h . The l a t e r a l i n s t a b i l i t y o f t h i s r e a c h i s m o s t m a r k e d b e t w e e n V e d d e r C r o s s i n g and L i u m e l e n C r e e k and i s c h a r a c -t e r i z e d by s u d d e n c h a n n e l s h i f t s t e r m e d " a v u l s i o n s " . T h e s e c h a n n e l s h i f t s w e r e d o c u m e n t e d b y c o m p a r i n g h i s -t o r i c a l maps and a i r p h o t o g r a p h s . The e a r l i e s t map o f t h i s r e a c h was d a t e d 1886 a n d was o b t a i n e d f r o m t h e a r c h i v e s o f t h e B.C. E l e c t r i c Com-pa n y . A l t h o u g h , t h e g e n e r a l r i v e r a l i g n m e n t a p p e a r s t o h a v e b e e n c l o s e t o p r e s e n t d a y c h a n n e l , t h e map d i d n o t show s u f f i c i e n t d e t a i l s t o make any f u r t h e r c o n c l u s i o n s . O t h e r o l d maps w e r e f o u n d i n t h e B.C. E l e c t r i c 7 3 Company a r c h i v e s d a t i n g back t o 1905, and 1910, drawn a t s c a l e s of 1 i n = 5880 f e e t and 1 i n c h - 1320 f e e t r e s p e c -t i v e l y . These maps showed the C h i l l i w a c k R i v e r had roughly the same alignment as a t p r e s e n t , although the channel may have been wider. For example, the 19 05 map showed the C h i l l i w a c k R i v e r i n the v i c i n i t y of Sweltzer Creek had a width o f 1200 f e e t , w h i l e the 1910 map showed t h a t near Liumchen Creek the width v a r i e d between 2100 f e e t and 1000 f e e t . Although the present-day channel i s com-para b l e to the 1905 map near Sweltzen R i v e r , i t i s now roughly h a l f the width shown on the 1910 map near Liumchen Creek. The e a r l i e s t a i r p h o t o s ;obtained by the author were flown i n 1940, w i t h a d d i t i o n a l coverage f o l l o w i n g i n 1952, 1958, 1966, 1969, 1971 and 1976. Some of these photos have been reproduced i n F i g u r e 22 i n order to i l l u s t r a t e some of the channel changes t h a t have o c c u r r e d throughout t h i s r e a c h. In a d d i t i o n , maps were made from each of the photos a t a common s c a l e of 1 i n c h = 1300 f e e t and these are shown i n F i g u r e s 24. The average a c t i v e channel width was computed from each map over a d i s t a n c e o f 10,000 f e e t e x t e n d i n g from Vedder C r o s s i n g t o Near Liumchen Creek. The average channel width was determined by p l a n i m e t e r i n g the o u t l i n e of the channel bottom i n t h i s r e ach and then d i v i d i n g by the t o t a l reach l e n g t h . R e s u l t s of these computations are shown i n Table 1.4. 74 Two n o t i c e a b l e c h a n g e s h a v e o c c u r r e d s i n c e 1 9 4 0 . 1. O v e r t h e y e a r s t h e a c t i v e c h a n n e l w i d t h h a s n a r r o w e d a p p r e c i a b l y i n t h i s r e a c h , d e c r e a s i n g f r o m 760 f e e t i n 1940 t o 560 f e e t i n 1 9 6 8 . T h i s t r e n d was p a r t i a l l y r e v e r s e d b y t h e f l o o d i n 1975 w h i c h c a u s e d c o n s i d e r a b l e l o c a l bank e r o s i o n a l o n g t h e n o r t h s i d e o f t h e r i v e r . M o s t o f t h i s n a r r o w i n g h a s r e s u l t e d f r o m a p p a r e n t f l o o d -p l a i n r e - c o n s t r u c t i o n on t h e s o u t h s i d e o f t h e r i v e r , w i t h l a r g e a r e a s f o r m e r l y o c c u p i e d by c h a n n e l s b e c o m i n g v e r y d e n s e l y v e g e t a t e d . 2. The c h a n n e l p a t t e r n h a s c h a n g e d f r o m an e s s e n -t i a l l y b r a i d e d c h a n n e l t o a s p l i t c h a n n e l w i t h f r e q u e n t wooded i s l a n d s . T h i s p a t t e r n c h a n g e i s m o s t n o t i c e a b l e by c o m p a r i n g t h e a i r p h o t o s o f 1940 a n d 1971 ( F i g u r e 2 2 ) . The e x p l a n a t i o n f o r t h i s a p p a r e n t c h a n g e i n r i v e r c h a r a c t e r i s t i c s i s n o t known. H o w e v e r , t h e s e c h a n g e s may r e f l e c t t h e c h a n g i n g p a t t e r n o f f l o o d i n g t h a t h a s o c c u r r e d o v e r t h e l a s t 80 y e a r s . I t h a s b e e n m e n t i o n e d p r e v i o u s l y t h a t t h e r e h a s b e e n a number o f s e v e r e f l o o d s i n t h e f i r s t h a l f o f t h i s c e n t u r y , f o l l o w e d by an u n u s u a l l y l o w i n c i -d i n c e i n t h e l a s t 30 y e a r s . I n f a c t , b e t w e e n 1951 a n d 197 3 when m o s t o f t h e c h a n n e l c h a n g e s t o o k p l a c e , t h e two l a r g e s t f l o o d s t o o c c u r i n t h i s p e r i o d h a d r e t u r n p e r i o d s o f o n l y a b o u t 5- y e a r s . I t i s e x p e c t e d t h a t a l o n g d u r a t i o n w i t h o u t l a r g e f l o o d s c o u l d a l l o w f o r m e r c h a n n e l a r e a s t o become r e - v e g e t a t e d 75 w i t h h e a v y b r u s h a n d w i l l o w s a n d e v e n t u a l l y become p a r t o f t h e f l o o d p l a i n o r d e v e l o p i n t o wooded i s l a n d s . As a r e s u l t t h e f l o w w o u l d t e n d t o become c o n c e n t r a t e d i n two o r t h r e e m a i n c h a n n e l s c a u s i n g t h e r i v e r t o become somewhat i n c i s e d and t o d e v e l o p a more s p l i t a p p e a r a n c e . I n a d d i -t i o n when b a n k f u l l c o n d i t i o n s w e r e e x c e e d e d i t i s e x p e c t e d t h a t a t l e a s t some o f t h e s u s p e n d e d l o a d w o u l d be t r a p p e d by t h e new v e g e t a t i o n and d e p o s i t e d o v e r b a n k . S u c h c h a n n e l c h a n g e s c a n c e r t a i n l y n o t be r u l e d o u t a f t e r c o m p a r i n g t h e c r o s s s e c t i o n s s u r v e y e d i n 1958 and 1963 ( F i g u r e 19) w h i c h seem t o show o v e r b a n k d e p o s i t i o n g o i n g on i n c o n j u n c -t i o n w i t h t h a l w e g d e p e n i n g . The maps shown i n F i g u r e 2 3 w e r e u s e d t o p r e p a r e o v e r l a y s i n o r d e r t o c ompute t h e a r e a s o f a p p a r e n t f l o o d -p l a n r e c o n s t r u c t i o n a n d e r o s i o n . T hese o v e r l a y s a r e shown i n F i g u r e 24, w h i l e t h e r e s u l t s o f t h e c o m p a r i s o n s a r e s u m m a r i z e d i n T a b l e 15. I t s h o u l d be m e n t i o n e d t h a t t h e a r e a s g i v e n as " f l o o d -p l a i n r e c o n s t r u c t i o n " s h o u l d n o t be c o n s i d e r e d as a r e a s o f d e p o s i t i o n . T h e s e a r e a s w e r e d e l i n e a t e d s i m p l y b y n o t i n g w h e re v e g e t a t i o n h a d become e s t a b l i s h e d on t h e f o r m e r c h a n -n e l s u r f a c e . T h e r e f o r e , t h i s d o e s n o t n e c e s s a r i l y i m p l y t h a t a c t u a l s e d i m e n t d e p o s i t i o n h a s t a k e n p l a c e i n t h e s e a r e a s . On t h e o t h e r h a n d , i t a p p e a r s t h a t m o s t o f t h e a r e a s o f a p p a r e n t e r o s i o n o c c u r r e d i n t e r r a c e o r b a n k d e p o s i t s s o t h a t l a r g e q u a n t i t i e s o f s e d i m e n t w o u l d h a v e 76 b e e n r e m o v e d d u r i n g t h e s e c h a n n e l s h i f t s . I n g e n e r a l , t h e l a t e r a l s h i f t i n g on t h e C h i l l i w a c k R i v e r h a s f o l l o w e d a s y s t e m a t i c p a t t e r n , w i t h a p p a r e n t f l o o d p l a i n r e c o n s t r u c t i o n on t h e s o u t h bank a n d e r o s i o n on t h e n o r t h b a n k . The maximum o b s e r v e d e r o s i o n r a t e s e s t i m a t e d f r o m t h e o v e r l a y s r a n g e d f r o m 620 f e e t b e t w e e n 1958 a n d 1971 ( a v e r a g i n g 48 f e e t / y e a r ) t o 300 f e e t b e t w e e n 1971 and 1976 w i t h m o s t o f t h i s e r o s i o n o c c u r r i n g d u r i n g t h e 1975 f l o o d . I n t e r m s o f a r e a s o f l a n d e r o d e d , b e t w e e n 1940 a n d 1951 t h e a v e r a g e a n n u a l e r o s i o n r a t e was a b o u t 2.5 t o 3.0 a c r e s p e r y e a r . T h i s c o r r e s p o n d s t o a t o t a l o f a b o u t 91 a c r e s o f l a n d l o s t b e t w e e n V e d d e r C r o s s i n g and L i u m c h e n C r e e k d u r i n g t h i s p e r i o d . By c o m p a r i s o n , b e t w e e n 1971 and 19 76 a b o u t 4 7 a c r e s o f l a n d was l o s t , w i t h p r o b a b l y n e a r l y a l l o f t h i s o c c u r r i n g d u r i n g t h e 1975 f l o o d . I t i s p o s s i b l e t o r o u g h l y e s t i m a t e t h e v o l u m e o f m a t e r i a l e r o d e d f r o m t h i s r e a c h i f an a v e r a g e bank h e i g h t c a n be a s s i g n e d t o t h e ^ e r o d e d l a n d a r e a s . B a s e d on an e x a m i n a t i o n o f p r e s e n t l y e r o d i n g b a n k s a n d o n t h e c r o s s s e c t i o n s s u r v e y e d i n 1958 and 196 3 i t was d e c i d e d a r e a s o n a b l e h e i g h t i w o u l d be a b o u t 10 f e e t . The r e s u l t i n g s e d i m e n t v o l u m e s shown i n T a b l e 15 s h o u l d p r o b a b l y be c o n s i d e r e d o r d e r o f m a g n i t u d e e s t i m a t e s . T h i s i s b e c a u s e t h e r e a r e c l e a r l y l a r g e u n c e r t a i n t i e s i n v o l v e d b o t h i n p r e p a r i n g t h e o r i g i n a l o v e r l a y s a n d i n 77 a s s i g n i n g a r e p r e s e n t a t i v e bank h e i g h t . Regardless of these u n c e r t a i n t i e s , i t i s b e l i e v e d the e s t i m a t e s are reasonable and can be used t o at l e a s t roughly i n d i c a t e the amount of sediment t h a t has been eroded by the r i v e r i n t h i s reach. I t should a l s o be noted t h a t the volumes and areas shown i n Table 15 were computed from o v e r l a y s which extended o n l y to Liumchen Creek. T h e r e f o r e , any e r o s i o n o c c u r r i n g upstream of t h i s p o i n t has not been i n c l u d e d . The r e s u l t s i n Table 15 show t h a t between 1940 and 1971 the e r o s i o n r a t e averaged about 50,000 c u b i c yards per year, and t h a t approximately 6 37,000 c u b i c yards of m a t e r i a l was eroded between 1971 - 1976. By comparison, surveys by the B.C. Water Resources S e r v i c e i n d i c a t e d about 258,000 c u b i c yards of sediment was d e p o s i t e d between Vedder C r o s s i n g and the B.C. E l e c t r i c Railway b r i d g e d u r i n g the 19 75 f l o o d . Therefore the amount of m a t e r i a l eroded i n the two m i l e reach above Vedder C r o s s i n g d u r i n g 19 75 was approximately twice the amount d e p o s i t e d onto the f a n . T h i s may i n d i c a t e t h a t some of the m a t e r i a l was re-depo-s i t e d upstream o f Vedder C r o s s i n g or was t r a n s p o r t e d down-stream of the r a i l w a y b r i d g e i n t o the Vedder Canal. A l t e r -n a t e l y , t h i s d i s c r e p a n c y may r e f l e c t the i n a c c u r a c i e s i n v o l v e d i n p r e p a r i n g the o v e r l a y s and i n a s s i g n i n g a r e p r e -s e n t a t i v e bank h e i g h t . However, these r e s u l t s demonstrate t h a t bank e r o s i o n immediately upstream of Vedder C r o s s i n g 78 c o n s t i t u t e s o n e o f t h e m o s t i m p o r t a n t s o u r c e s o f s e d i m e n t t o t h e f a n . 5 . 3 The S e d i m e n t S u p p l y o f t h e C h i l l i w a c k R i v e r A l t h o u g h b a n k e r o s i o n i n t h e r e a c h a b o v e V e d d e r C r o s s i n g i s c l e a r l y a n i m p o r t a n t s e d i m e n t s o u r c e , t h e r e a r e o t h e r i m p o r t a n t s o u r c e s i n t h e b a s i n . M o s t o f t h e s e d i m e n t d e p o s i t e d o n t h e f a n i s p r o -b a b l y d e r i v e d f r o m t h r e e s o u r c e s : 1 . T r i b u t a r y c r e e k s 2. L a n d s l i d e s i n t e r r a c e d e p o s i t s 3 . B a n k e r o s i o n o f c h a n n e l a n d f l o o d p l a i n d e p o s i t s B a s e d o n f i e l d o b s e r v a t i o n s a n d a i r p h o t o i n t e r p r e -t a t i o n i t a p p e a r s S l e s s e C r e e k i s t h e t a r g e t t r i b u t a r y s o u r c e i n t h e C h i l l i w a c k b a s i n . The e f f e c t o f t h i s s e d i -m e n t i n f l u x on t h e C h i l l i w a c k R i v e r i s v e r y a p p a r e n t , w i t h t h e r i v e r ' s b e d m a t e r i a l s i z e c h a n g i n g f r o m b o u l d e r s t o c o b b l e s a n d g r a v e l a n d p r o m i n e n t p o i n t b a r s o c c u r r i n g . O t h e r i m p o r t a n t c r e e k s s u p p l y i n g s e d i m e n t t o t h e C h i l l i w a c k R i v e r p r o b a b l y i n c l u d e N e s a k w a t c h C r e e k , T a m a h i C r e e k a n d L i u m c h e n C r e e k . S e v e r a l l a r g e l a n d s l i d e s h a v e o c c u r r e d i n t h e h i g h t e r r a c e s a l o n g t h e C h i l l i w a c k R i v e r u p s t r e a m o f S l e s s e C r e e k . T h e s e t e r r a c e s a r e c o m p o s e d p r e d o m i n a t e l y o f s a n d s o t h i s m a t e r i a l w o u l d be r a p i d l y e r o d e d b y t h e r i v e r a n d c o u l d p r o b a b l y b e c a r r i e d i n s u s p e n s i o n . S i n c e t h e v o l u m e 79 o f some s l i d e s h a s b e e n i n t h e o r d e r o f h u n d r e d s o f t h o u -s a n d s o f c u b i c y a r d s , t h e s e e v e n t s c o u l d c o n s t i t u t e i m -p o r t a n t s o u r c e s o f s a n d s i z e m a t e r i a l when t h e y o c c u r . I t w o u l d a p p e a r s i m p l y f r o m v i s u a l o b s e r v a t i o n s , t h a t some o f t h e s e s l i d e s h a v e b e e n a g g r a v a t e d b y l o g g i n g r o a d c o n -s t r u c t i o n . As m e n t i o n e d p r e v i o u s l y m o s t a c t i v e bank e r o s i o n o c c u r s b e t w e e n V e d d e r C r o s s i n g a n d L i u m c h e n C r e e k . Much o f t h e r i v e r a b o v e L i u m c h e n C r e e k i s f l o w i n g o n t o p o f v e r y c o a r s e b o u l d e r d e p o s i t s w h i c h a p p e a r t o be s t a b l e e v e n d u r i n g m a j o r f l o o d s . T h e r e f o r e , e x c e p t f o r t h e r e a c h i m m e d i a t e l y u p s t r e a m o f V e d d e r C r o s s i n g , t h e s u p p l y o f s e d i m e n t s f r o m bank a n d c h a n n e l e r o s i o n i s l i k e l y t o be r e l a t i v e l y s m a l l . I n d e t e r m i n i n g t h e r e l a t i v e i m p o r t a n c e o f t h e s e s e d i m e n t s o u r c e s , i t i s i m p o r t a n t t o s p e c i f y t h e t i m e f r a m e b e i n g c o n s i d e r e d . I n t h e s h o r t t e r m ( s a y a s i n g l e f l o o d e v e n t ) i t seems l i k e l y t h a t b a n k e r o s i o n f r o m t h e r e a c h i m m e d i a t e l y u p s t r e a m o f V e d d e r C r o s s i n g i s t h e s i n g l e m o s t i m p o r t a n t s o u r c e o f s e d i m e n t s f o r t h e f a n . The s i m p l e c a l c u l a t i o n s p r e s e n t e d e a r l i e r c l e a r l y d e m o n s t r a t e t h a t t h e v o l u m e o f m a t e r i a l e r o d e d i n t h i s r e a c h i s c o m p a r a b l e w i t h t h e amount o f d e p o s i t i o n t h a t h a s o c c u r r e d d o w n s t r e a m o f V e d d e r C r o s s i n g . I t s h o u l d a l s o be n o t e d t h a t d u r i n g a s i n g l e f l o o d e v e n t , t r a n s p o r t o f t h e g r a v e l a n d c o b b l e s i z e b e d l o a d may 30 p e r s i s t f o r a r e l a t i v e l y s h o r t p e r i o d o f t i m e , r a n g i n g f r o m p e r h a p s a f e w h o u r s t o s e v e r a l d a y s p e r y e a r . T h i s c a n be c o n f i r m e d by r e v i e w i n g t h e c a l c u l a t i o n s o f t h r e s h o l d c o n d i t i o n s f o r s e d i m e n t movement w h i c h were p r e s e n t e d e a r l i e r ( T a b l e 1 3 ) . F o r e x a m p l e , b a s e d on N e i l l ' s com-p e t e n t v e l o c i t y c u r v e s i t was f o u n d t h a t b e l o w S l e s s e C r e e k f l o w s o f 6500 c f s ( c o r r e s p o n d i n g t o a two y e a r f l o o d ) c o u l d move g r a v e l up t o a b o u t 80 mm. By e x a m i n i n g t h e d a i l y f l o w r e c o r d s i n t h i s r e a c h i t a p p e a r s on a v e r a g e s u c h f l o w s may o c c u r t h r e e t o f o u r d a y s p e r y e a r . S i n c e b e d l o a d moves i n t e r m i t t e n t l y , a t much s l o w e r s p r e a d s t h a n t h e w a t e r v e l o c i t y i t seems d o u b t f u l t h a t c o a r s e m a t e r i a l c o u l d move f r o m t h e u p p e r p a r t s o f t h e b a s i n t o t h e f a n i n a s i n g l e f l o o d e v e n t . More l i k e l y , c o a r s e s e d i m e n t p r o -b a b l y moves a f e w m i l e s i n e a c h f l o o d , w i t h s e d i m e n t b e i n g d e p o s i t e d i n l o c a l i z e d r e a c h e s a l o n g t h e r i v e r . The e x -t e n s i v e g r a v e l b a r s t h a t h a v e d e v e l o p e d a t t h e m e a n d e r s u p s t r e a m o f T a m a h i C r e e k may c o r r e s p o n d t o one o f t h e s e t e m p o r a r y s e d i m e n t " s i n k s " . T h i s c o n c e p t o f l o c a l i z e d s e d i m e n t t r a n s p o r t a n d d e p o s i t i o n f r o m r e a c h t o r e a c h i s i l l u s t r a t e d i n F i g u r e 25. T h e r e i s l i t t l e d i r e c t q u a n t i t a t i v e d a t a t o c o n f i r m t h i s m o d e l o f s e d i m e n t movement. Ho w e v e r , e x p e r i m e n t s h a v e b e e n c o n d u c t e d on o t h e r g r a v e l r i v e r s w h i c h p r o v i d e some s u p p o r t . F o r e x a m p l e , M o s l e y (1978) c a r r i e d o u t t r a c e r s t u d i e s on t h e T a m a k i R i v e r i n New Z e a l a n d and 81 concluded t h a t the r a t e of movement of a s l u g of bed m a t e r i a l was q u i t e slow, w i t h the peak t r a v e l l i n g about 1.75 km/year. Of course the f i n e r sand and s i l t s i z e d m a t e r i a l w i l l move i n suspension and may be swept through the b a s i n i n a s i n g l e f l o o d event. Over a time frame l a s t i n g years or decades, s e d i -ment from the upper reaches of the C h i l l i w a c k River w i l l move through the b a s i n and be d e p o s i t e d below Vedder C r o s s i n g . T h i s long term p a t t e r n sediment movement w i l l determine whether the reach d i r e c t l y upstream of Vedder C r o s s i n g undergoes d e g r a d a t i o n or a g g r a d a t i o n . For example i f the supply o f sediment from upstream does not balance the q u a n t i t y of m a t e r i a l removed from channel and bank e r o s i o n i n t h i s reach then d e g r a d a t i o n w i l l take p l a c e . In summary the a c t u a l p a t t e r n of sediment movement between the upper reaches o f the C h i l l i w a c k R i v e r , the reach immediately upstream of Vedder C r o s s i n g and the fan below Vedden C r o s s i n g i s o b v i o u s l y very c o m p l i c a t e d . For example, i t has been shown p r e v i o u s l y t h a t when major f l o o d s are absent the bank e r o s i o n r a t e s decrease, some of the channel d e p o s i t s t e n t to become vegetated and the r i v e r p a t t e r n shows a tendency to develop a more i n -c i s e d , s p l i t channel. As shown i n Table 15, d u r i n g the p e r i o d between 1952 and 19 71 the volume o f m a t e r i a l eroded i n the two m i l e reach above Vedder C r o s s i n g averaged about 30,000 c u b i c y a r d s / y e a r . During t h i s p e r i o d i t i s l i k e l y 82 t h a t o t h e r s e d i m e n t was s u p p l i e d t o t h e f a n f r o m u p s t r e a m s o u r c e s a n d f r o m s c o u r a s s o c i a t e d w i t h t h e c h a n n e l i n c i -s i o n t h a t o c c u r r e d i n t h i s r e a c h . D u r i n g m a j o r f l o o d s , s u c h a s i n 1 9 7 5 , v e r y l a r g e v o l u m e s o f s e d i m e n t a r e made a v a i l a b l e f o r t r a n s p o r t due t o ^ b a n k e r o s i o n a n d c h a n n e l s h i f t i n g n e a r V e d d e n C r o s s i n g . The s e d i m e n t t r a n s p o r t c a p a c i t y o f t h e r i v e r t h e n d e t e r -m i n e s how much o f t h i s m a t e r i a l w i l l be t r a n s p o r t e d b e l o w V e d d e r C r o s s i n g o n t o t h e f a n and how much w i l l be r e - d e -p o s i t e d u p s t r e a m . I n a d d i t i o n some s e d i m e n t f r o m u p s t r e a m s o u r c e s may be t r a n s p o r t e d t h r o u g h t h i s r e a c h o n t o t h e f a n , a n d some may be d e p o s i t e d a b o v e V e d d e r C r o s s i n g i n t h e c h a n n e l s t h a t have b e e n a b a n d o n e d d u r i n g t h e s h i f t s . S i n c e much o f t h e e r o s i o n o c c u r r i n g i n t h i s r e a c h a p p e a r s t o be a g g r a v a t e d by l o g jams i t i s i m p o s s i b l e t o e s t i m a t e t h e q u a n t i t y o f m a t e r i a l t h a t w i l l be s u p p l i e d t o t h e r i v e r d u r i n g a g i v e n f l o o d . H o w e v e r , t h e t r a n s p o r t c a p a c i t y o f t h e r i v e r a t V e d d e r C r o s s i n g , w h i c h g o v e r n s t h e amount o f s e d i m e n t t h a t w i l l be t r a n s p o r t e d o n t o t h e f a n , c a n be e s t i m a t e d b y s e d i m e n t t r a n s p o r t t h e o r y . Much o f t h e r e -m a i n i n g c h a p t e r s o f t h i s s t u d y w i l l be d e v o t e d t o t h i s s u b j e c t . 83 CHAPTER V I CHANNEL PROCESSES BELOW VEDDER CROSSING The V e d d e r R i v e r h a s b e e n s t u d i e d b y s e v e r a l a g e n c i e s o v e r t h e l a s t two d e c a d e s . S i n c e much o f t h e d a t a c o l -l e c t e d d u r i n g t h e s e p a s t i n v e s t i g a t i o n s h a s b e e n u s e d i n t h i s p r e s e n t s t u d y , a b r i e f d i s c u s s i o n o f t h e d a t a i s w a r r a n t e d . 6 1 D a t a A v a i l a b l e • Maps a n d A i r p h o t o s Many o f t h e h i s t o r i c a l maps and a i r p h o t o s m e n t i o n e d i n C h a p t e r V a l s o show p o r t i o n s o f t h e V e d d e r R i v e r . The e a r l i e s t map o f t h e r i v e r was s u r v e y e d b e t w e e n 186 3 a n d 1902 a n d h a s b e e n p r e s e n t e d i n C h a p t e r I I ( F i g u r e 3 ) . The a i r p h o t o c o v e r a g e o f t h e V e d d e r R i v e r i s e x c e l -l e n t , w i t h t h e e a r l i e s t p h o t o s d a t i n g b a c k t o 1 9 3 0 . The r i v e r h a s b e e n r e f l o w n f r e q u e n t l y s i n c e t h i s t i m e , i n 1940, 1 9 4 8 , 1 9 5 2 , 1 9 5 8 , 1 9 6 6 , 1968, 1 9 6 9 , 1 9 7 1 , 1 9 7 4 , and 1976. Some o f t h e s e p h o t o s h a v e b e e n s u m m a r i z e d i n F i g u r e 4. Two s e t s o f d e t a i l e d t o p o g r a p h i c maps o f t h e s u r -r o u n d i n g f l o o d p l a i n w e r e u s e d i n t h i s s t u d y . The e a r l i e s t map f r o m M a r r 1 s 1964 r e p o r t showed s p o t e l e v a t i o n s t o t h e n e a r e s t f o o t . I n a d d i t i o n a 19 76 o r t h o p h o t o g r a p h was 84 obtained from the B.C. Water Resources S e r v i c e , having a contour i n t e r v a l o f 0.5 metres. Channel Surveys R i v e r c r o s s s e c t i o n s have been surveyed by the B.C. Water Resources S e r v i c e i n 1958, 1959 and 196 3. Twelve of these s e c t i o n s , s i t u a t e d between the o u t l e t o f the Vedder Canal and Vedder C r o s s i n g were o b t a i n e d from M a r r 1 s 19 64 r e p o r t . In a d d i t i o n surveys were c a r r i e d out i n 1975 and 1976 however most of these were made a t d i f f e r e n t l o c a t i o n s from the e a r l i e r s u r v e y s . The data made a v a i l -a ble to the author c o n s i s t e d o f : - 12 s e c t i o n s surveyed, i n the l a t e summer o f 19 75 and s h o r t l y a f t e r the December f l o o d i n g , l o c a t e d between the r a i l w a y b r i d g e and Vedder C r o s s i n g . - 20 s e c t i o n s surveyed a f t e r completion o f the Phase I f l o o d c o n t r o l program. A d d i t i o n a l c r o s s s e c t i o n s were surveyed by the Water Survey of Canada between 19 71 and 19 75 as p a r t o f t h e i r sedimen-t a t i o n study on the r i v e r . U n f o r t u n a t e l y , none of these s e c t i o n s were a l i g n e d with any o f the B.C. Water Resources surveys. The surveys between 19 71-19 73 were o b t a i n e d from p r e l i m i n a r y r e p o r t s by Tywoniuk (1971, 1972, 1973). In 1975 16 a d d i t i o n a l surveys were made, a l l downstream o f the r a i l w a y b r i d g e . 85 In o r d e r to a v o i d c o n f u s i o n , a l l of the s e c t i o n s have been given a mileage d e s i g n a t i o n , measured upstream from the Trans-Canada highway c r o s s i n g of the Vedder Canal near i t s c onfluence with the F r a s e r R i v e r . The l o c a t i o n o f the s e c t i o n s are shown on F i g u r e 26 and a l l o f the s e c t i o n s are summarized i n Table 16. A few r e p r e s e n t a t i v e s e c t i o n s have been shown i n F i g u r e 27. - Water L e v e l Data The c r o s s s e c t i o n surveys can be used to c o n s t r u c t water s u r f a c e p r o f i l e s along the r i v e r . However most of these surveys were c a r r i e d out a t r e l a t i v e l y low flows (around the l o n g term mean), wit h the e x c e p t i o n of a 196 3 B.C. Water Resources water s u r f a c e p r o f i l e which was s u r -veyed d u r i n g a flow of 6880 c f s (Marr, 1964) . The author c a r r i e d out a number of slope surveys d u r i n g flows which ranged between 4000 c f s and 6000 c f s . However these were made around the time when dredging was being c a r r i e d out which c o u l d have a f f e c t e d the water p r o f i l e s . The r e s u l t s of these surveys and the estimates from the agency c r o s s s e c t i o n s are summarized i n Table 17. Aside from surveys, water l e v e l s have been recorded a t three Water Survey of Canada gauging s t a t i o n s . These s t a t i o n s are - Vedder C r o s s i n g (stage and discharge) - below the r a i l w a y b r i d g e near Yarrow (stage 1952-1974) 86 - Sumas Ri v e r near S a r d i s (stage 1951-1972) Although these s t a t i o n s are not s u f f i c i e n t t o determine a water s u r f a c e p r o f i l e along the r i v e r , they p r o v i d e a con-s i d e r a b l e amount of data on f l o o d l e v e l s and h y d r a u l i c p r o c e s s e s . s Bed M a t e r i a l Data Bed m a t e r i a l data has been c o l l e c t e d by Water Survey of Canada (W.S.C.) as p a r t of t h e i r sediment i n v e s -t i g a t i o n on the Vedder R i v e r and by the author. The Water Survey o f Canada data was c o l l e c t e d i n 1973 and 1975 and c o n s i s t e d o f 6 3 bulk samples taken between the Vedder Canal and Vedder C r o s s i n g . Most samples ranged between 12-25 pounds and a l l were taken on W.S.C. c r o s s s e c t i o n l i n e s . The l o c a t i o n o f each sample on the cross s e c t i o n was s p e c i f i e d i n most cases. In a d d i t i o n the author c o l l e c t e d 21 samples i n order to supplement the Water Survey of Canada data. Most of these were tape g r i d o r photographic g r i d samples although a few bulk samples were a l s o c o l l e c t e d . 6.2 Channel P a t t e r n of the Vedder R i v e r In comparison to most r i v e r s i n B.C., the Vedder R i v e r i s a v e r y new stream - b e i n g o n l y about one c e n t u r y o l d . Therefore throughout most o f i t s l i f e the Vedder 87 c h a n n e l h a s p r o b a b l y b e e n i n a s t a t e o f t r a n s i t i o n a s i t t r i e d t o a d j u s t t o t h e new f l o w r e g i m e a n d s e d i m e n t l o a d i m p o s e d on i t . The map o f t h e C h i l l i w a c k a r e a p r e p a r e d a r o u n d t h e t u r n o f t h e c e n t u r y ( F i g u r e 3) shows t h e C h i l l i w a c k R i v e r s p l i t i n t o t h r e e m a j o r c h a n n e l s a s h o r t d i s t a n c e b e l o w V e d d e r C r o s s i n g , w i t h t h e L u c k - a - K u c k a n d C h i l l i w a c k c h a n n e l s a p p e a r i n g t o c a r r y m o s t o f t h e f l o w . A t t h i s t i m e t h e V e d d e r R i v e r h a d a r e l a t i v e l y s t r a i g h t c h a n n e l , f r e q u e n t l y s p l i t by b a r s o r i s l a n d s , w i t h a w i d t h v a r y i n g f r o m a maximum o f a b o u t 400 f e e t n e a r V e d d e r C r o s s i n g t o b e t w e e n 75-100 f e e t n e a r Sumas L a k e . I t i s b e l i e v e d t h i s map was p r e p a r e d o n l y a few y e a r s a f t e r t h e C h i l l i w a c k R i v e r b e g a n i t s m a i n p e r i o d o f c h a n n e l s h i f t i n g i n 18 75. Le B a r o n , i n 19 08, d e s c r i b e d t h e V e d d e r R i v e r a s : " h a v i n g a w i d t h v a r y i n g f r o m 60 f e e t t o 400 f e e t a t l o w w a t e r a n d f u l l o f r a p i d s a n d g r a v e l b a n k s . I t i s a l s o much c h o k e d b y f a l l e n t r e e s a n d l o g s w h i c h a p p e a r t o h a v e b e e n u p r o o t e d when t h e r i v e r b r o k e o u t i n t o i t s p r e s e n t c h a n n e l a b o u t 15 y e a r s a g o . Hermon a n d B u r w e l l , C i v i l E n g i n e e r s s t a t e . . . t h e r i v e r i s c o n t i n u a l l y w i d e n i n g . " By 1930 t h e r i v e r h a d a v e r y b r a i d e d u n s t a b l e c h a n n e l w i t h a n a c t i v e c h a n n e l w i d t h v a r y i n g f r o m a b o u t 4 50 f e e t n e a r t h e r a i l w a y b r i d g e t o a b o u t 1600 f e e t o p p o s i t e W e b s t e r Road (two m i l e s b e l o w V e d d e r C r o s s i n g ) . The u p p e r two m i l e s o f t h e c h a n n e l a p p e a r e d m o s t u n s t a b l e , w h i l e t o w a r d s t h e r a i l w a y b r i d g e t h e c h a n n e l a p p e a r e d r e l a t i v e l y i n c i s e d . 88 T h i s d o w n s t r e a m d e c r e a s e i n w i d t h i s m o s t a p p a r e n t on t h e J u n e 194 8 a i r p h o t o w h i c h t a k e n a t c l o s e t o b a n k f u l l c o n -d i t i o n ( F i g u r e 4 ) . A c o m p a r i s o n o f t h e 19 30 a n d 1948 p h o t o s shows t h e o v e r a l l c h a n n e l a l i g n m e n t h a d r e m a i n e d q u i t e c o n s t a n t i n t h i s p e r i o d . T h e r e f o r e t h e c h a n n e l w i d e n i n g r e f e r r e d t o i n L e B a r o n ' s 190 8 d e s c r i p t i o n a p p e a r s t o h a v e c e a s e d a p p r o x -i m a t e l y f i f t y y e a r s a f t e r t h e C h i l l i w a c k R i v e r a v u l s i o n . However l o c a l i z e d bank e r o s i o n c o n t i n u e d a n d i s m o s t e v i d e n t b e t w e e n 194 8 a n d 1951 where i n some a r e a s a l o n g t h e s o u t h bank t h e c h a n n e l s h i f t e d up t o 470 f e e t . I t i s b e l i e v e d m o s t o f t h i s e r o s i o n o c c u r r e d d u r i n g t h e F e b r u a r y 1 0 t h , 1951 f l o o d . B e t w e e n 195 2 a n d 19 75 two m a i n c h a n n e l c h a n g e s a r e a p p a r e n t : - e x t e n s i v e c h a n n e l i z a t i o n o f t h e r i v e r b e t w e e n t h e r a i l w a y b r i d g e and F o r d Road; - f l o o d p l a i n r e c o n s t r u c t i o n b e t w e e n W e b s t e r Road and V e d d e r C r o s s i n g . A l s o , t h e r i v e r a p p e a r s t o h a v e c h a n g e d f r o m a v e r y u n s t a b l e b r a i d e d c h a n n e l t o a more i n c i s e d s p l i t c h a n n e l . The c h a n n e l i z a t i o n o f t h e r i v e r h a s b e e n d e s c r i b e d p r e v i o u s l y i n C h a p t e r I I . T h i s w o r k , c a r r i e d o u t i n t h e l a t e 1 9 5 0 ' s a n d 1 9 6 0 ' s r e s u l t e d i n a l o s s o f c h a n n e l a r e a o f a b o u t 75 a c r e s . As a r e s u l t t h e a c t i v e c h a n n e l w i d t h 89 decreased from 6 70 f e e t to 35 0 f e e t between the r a i l w a y b r i d g e and Ford Road. The channel changes near Vedder C r o s s i n g appear to be mainly n a t u r a l although some r i v e r t r a i n i n g o c c u r r e d i n t h i s area as w e l l . T h i s change i n channel p a t t e r n may i n d i c a t e the r i v e r had begun t o " s e t t l e down" a f t e r a l o n g p e r i o d of channel i n s t a b i l i t y f o l l o w i n g the i n i t i a l channel s h i f t i n 1875. The long p e r i o d of r e l a t i v e l y moderate f l o o d s s t a r t i n g i n the e a r l y 1950 "s and extending up to 1975 would probably have a l s o c o n t r i b u t e d to t h i s change i n p a t t e r n . Therefore the e x i s t i n g channel p a t t e r n o f the Vedder R i v e r can be d e s c r i b e d as b e i n g s t r a i g h t , s p l i t or s l i g h t l y b r a i d e d a l o n g i t s upper h a l f becoming con-f i n e d to a s i n g l e channel through i t s c h a n n e l i z e d reach and the Vedder Ca n a l . S e v e r a l d i f f e r e n t bar types could.be d i s t i n g u i s h e d along the r i v e r i n c l u d i n g l a r g e midchannel b a r s , s i d e bars and d i a g o n a l b a r s . The d i a g o n a l bars f o r a r e g u l a r s e r i e s o f " r i f f l e s " which extend through the c h a n n e l i z e d reach above the r a i l w a y b r i d g e (Figure 4 ) . These r i f f l e s appear t o be spaced roughly four channel widths a p a r t (based on 1971 a i r p h o t o s ) . Throughout the Vedder Canal a very s t r i k i n g sequence o f a l t e r n a t i n g s i d e bars can be seen d u r i n g low flow c o n d i t i o n s . The "wavelength" of these bars was found t o average 19 30 f e e t over the l e n g t h o f the 90 c a n a l which corresponds t o about 12 b a n k f u l l channel widths. Therefore the spa c i n g between c r o s s - o v e r p o i n t s i s h a l f of t h i s amount. These a l t e r n a t i n g bars i n the c a n a l and di a g o n a l bars i n the c o n s t r i c t i o n tend to produce a sinuous flow p a t t e r n d u r i n g low flows and suggest the channel i s attempting to develop meanders. I t i s apparent t h a t the channel p a t t e r n of the Vedder R i v e r has not remained co n s t a n t over the p a s t cen-t u r y , nor i s i t cons t a n t over the e n t i r e r i v e r l e n g t h . The upper h a l f of the r i v e r from above the r a i l w a y b r i d g e to Vedder C r o s s i n g has d i s p l a y e d a l a t e r a l l y unstable channel with p o o r l y d e f i n e d banks and fre q u e n t i s l a n d s and bar s . Th i s type o f b r a i d e d p a t t e r n i s commonly a s s o c i a t e d with two c o n d i t i o n s : - streams t r a n s p o r t i n g h i g h sediment loads on steep s l o p e s (Henderson, 1966) . Such channels may develop because of the high shear on the banks which can cause channel widening and sub-sequent d e p o s i t i o n i n the c e n t r e of the stream. - d e l t a i c environments and a l l u v i a l fans where the sediment t r a n s p o r t c a p a c i t y decreases i n a down-stream d i r e c t i o n (Church, 1972) . Leopold! and Wolman (1957) a l s o a s s o c i a t e d b r a i d i n g with chan-n e l a g g r a d a t i o n . In b r a i d e d channels i t i s o f t e n d i f f i c u l t t o d i s t i n g u i s h 91 t h e b a n k f u l l l e v e l o f t h e c h a n n e l f r o m t h e i n a c t i v e f l o o d -p l a i n a n d f r o m l o w t e r r a c e s . T e r r a c e s a r e r e m n a n t s o f f o r m e r r i v e r d e p o s i t i o n t h a t h a v e b e e n s u b s e q u e n t l y a b a n -d o n e d by r i v e r d o w n - c u t t i n g . As a r e s u l t t e r r a c e s may n o t be f l o o d e d e v e n d u r i n g e x t r e m e f l o o d s . I n a c t i v e f l o o d p l a i n s a r e o f t e n s c a r r e d w i t h o l d a b a n -d o n e d c h a n n e l s and f o r m e r b a r s , h o w e v e r t h e y a r e o f t e n c o v e r e d b y d e n s e v e g e t a t i o n . I n a c t i v e f l o o d p l a i n may b e -come r e o c c u p i e d d u r i n g f l o o d s a s a r e s u l t o f c h a n n e l s h i f t i n g . I n t h e c a s e o f t h e V e d d e r R i v e r , n e a r l y t h e e n t i r e s u r f a c e o f t h e a l l u v i a l f a n c o u l d be c o n s i d e r e d i n a c t i v e f l o o d p l a i n . I n b r a i d e d r i v e r s t h e a c t i v e c h a n n e l c a n be v e r y w i d e and s h a l l o w . I n t h i s c a s e t h e b a n k f u l l l e v e l n o r m a l l y c o r r e s p o n d s t o t h e t o p o f t h e a c t i v e b a r s . T a b l e 8 l i s t s some p r o p e r t i e s o f t h e b r a i d e d c h a n n e l s on t h e V e d d e r R i v e r . M o s t o f t h i s d a t a was d e r i v e d f r o m t h e 195 8 a n d 1963 c r o s s s e c t i o n s u r v e y s s i n c e a t t h i s t i m e , t h e c h a n n e l was r e l a t i v e l y u n a l t e r e d by human a c t i v i t i e s . A few c r o s s s e c t i o n s s u r v e y e d i n 19 75 n e a r P e a c h e Road w e r e a l s o i n -c l u d e d s i n c e t h i s l o c a t i o n h a s r e m a i n e d r e l a t i v e l y u n d i s -t u r b e d . I n a l l c a s e s o n l y t h e m a j o r s u b c h a n n e l s a t e a c h s e c t i o n were a n a l y s e d . T h e s e r e s u l t s show t h e a v e r a g e b a n k f u l l d e p t h was o n l y a b o u t 3.1 f e e t . I t was a l s o f o u n d t h a t t h e i n a c t i v e f l o o d p l a i n , w h i c h i s c u r r e n t l y b e i n g d e v e l o p e d a n d b u i l t o n , i s a t n e a r l y t h e same e l e v a t i o n 92 as t h e t o p s o f t h e b a r s i n t h e a c t i v e c h a n n e l . T h i s f e a t u r e i s i l l u s t r a t e d on some o f t h e f a n c r o s s s e c t i o n s shown i n F i g u r e 2 8 . D o w n s t r e a m o f t h e r a i l w a y b r i d g e t h e r i v e r f l o w s i n a s i n g l e c h a n n e l w i t h f e w i s l a n d s o r b a r s . T h i s r e a c h h a s b e e n so a l t e r e d by c h a n n e l i z a t i o n a n d d i k e c o n s t r u c t i o n t h a t i t i s v e r y d i f f i c u l t t o d e t e r m i n e t h e r i v e r ' s n a t u r a l c h a n n e l p a t t e r n , a l t h o u g h e a r l y maps showed t h e r i v e r t o be m e a n d e r i n g . L e o p o l d and Wolman (1957) d e t e r m i n e d an e m p i r i c a l r e l a t i o n t o d i s c r i m i n a t e b e t w e e n b r a i d i n g a n d m e a n d e r i n g on t h e b a s i s o f s l o p e and d i s c h a r g e : - 0 44 S = 0.06 Q I f t h e o b s e r v e d s l o p e was f o u n d t o be g r e a t e r t h a n t h e c o m p u t e d v a l u e , t h e c h a n n e l was f o u n d t o be b r a i d e d , w h e r e a s i f t h e m e a s u r e d s l o p e was l e s s t h a n t h i s v a l u e t h e c h a n n e l was f o u n d t o m eander. U s i n g a mean a n n u a l f l o o d as a d o m i n a n t d i s c h a r g e , t h e c r i t i c a l s l o p e b e t w e e n b r a i d i n g a n d m e a n d e r i n g was e s t i m a t e s t o be a b o u t 0.001. T h i s w o u l d c o r r e s p o n d t o a l o c a t i o n somewhere b e t w e e n t h e r a i l w a y b r i d g e a n d t h e h e a d o f t h e c a n a l w h i c h a g r e e s r e a s o n a b l y c l o s e l y t o t h e o b s e r v e d t r a n s i t i o n . 6 . 3 C h a n n e l H y d r a u l i c s The r i v e r s u r v e y s r e p o r t e d p r e v i o u s l y show t h e s l o p e 93 o f t h e c h a n n e l i s r e l a t i v e l y u n i f o r m f r o m V e d d e r C r o s s i n g t o n e a r W e b s t e r Road a n d a v e r a g e s a r o u n d 0.005. Down-s t r e a m f r o m t h i s p o i n t t h e p r o f i l e g r a d u a l l y f l a t t e n s o u t , a v e r a g i n g a r o u n d 0.0 0 35 n e a r F o r d Road and 0.002 n e a r t h e r a i l w a y b r i d g e . The V e d d e r C a n a l i s s u b j e c t t o b a c k w a t e r f r o m t h e F r a s e r R i v e r s o t h e s l o p e i n t h i s r e a c h i s v a r i a b l e . To make m a t t e r s more c o m p l i c a t e d , t i d a l i n f l u e n c e s c a n e x t e n d up t h e F r a s e r R i v e r p a s t C h i l l i w a c k M o u n t a i n , s o d i u r n a l f l u c t u a t i o n s c a n o c c u r i n t h e c a n a l a t some f l o w s . I n a d d i t i o n , t h e Sumas R i v e r e n t e r s t h e V e d d e r C a n a l a n d t h e r e f o r e h a s some i n f l u e n c e o n t h e r i v e r ' s s t a g e . As m e n t i o n e d e a r l i e r g e o d e t i c w a t e r l e v e l s h a v e b e e n r e c o r d e d n e a r t h e o u t l e t o f t h e V e d d e r C a n a l b e t w e e n 1951 a n d 1 9 7 2 . The s t a g e m e a s u r e m e n t s i n t h e c a n a l w e re c o r r e l a t e d w i t h d i s c h a r g e s r e c o r d e d on t h e C h i l l i w a c k R i v e r a t V e d d e r C r o s s i n g a n d t h e F r a s e r R i v e r a t Hope ( F i g u r e 2 9 ) . T h e s e r e s u l t s show t h a t f o r a d i s c h a r g e o f 10,000 c f s a t V e d d e r C r o s s i n g , t h e s t a g e i n t h e c a n a l c a n v a r y b y o v e r 15 f e e t , d e p e n d i n g on t h e f l o w s i n t h e F r a s e r R i v e r . F u r t h e r m o r e , d u r i n g t h e w i n t e r t h e F r a s e r R i v e r i s g e n e r a l l y l o w and i n s e n s i t i v e t o w i n t e r r a i n s t o r m s . T h e r e f o r e d u r i n g a w i n t e r f l o o d on t h e C h i l l i w a c k R i v e r , a s t e e p drawdown t y p e p r o f i l e s h o u l d o c c u r t h r o u g h o u t t h e c a n a l . 94 In the summer, when the F r a s e r R i v e r f r e s h e t occurs the high water l e v e l s a t the c a n a l o u t l e t should cause a c l a s s i c "M-1" type backwater p r o f i l e i n the c a n a l and lower Vedder R i v e r . The e f f e c t o f these water l e v e l f l u c t u a t i o n s on the s l o p e through the canal can be roughly determined by com-p a r i n g the water l e v e l s recorded a t the r a i l w a y b r i d g e and the c a n a l . Two extreme combinations i n the p e r i o d o f r e c o r d were c o n s i d e r e d : High flow on C h i l l i w a c k R i v e r (15,900 c f s ) Low flow on F r a s e r R i v e r (110,000 c f s ) average slope = 0.00058 Low flow on C h i l l i w a c k River (5,170 c f s ) High flow on F r a s e r R i v e r (408,000 c f s ) average slope = 0.0001 The e x t e n t o f the backwater i n the Vedder Canal w i l l . depend on the flow i n the Vedder R i v e r and i n the F r a s e r R i v e r . The stage r e c o r d s near the r a i l w a y b r i d g e were scanned and i t was determined t h a t when the flow a t Vedder C r o s s i n g was 5,000 c f s , the water l e v e l s a t the r a i l w a y guage were not a f f e c t e d by the F r a s e r R i v e r even when flows a t Hope reached 400,000 c f s . Therefore except perhaps under very r a r e c o n d i t i o n s , i t can be concluded the F r a s e r R i v e r backwater does not extend past the r a i l w a y 95 b r i d g e . H y d r a u l i c measurements have been c a r r i e d o u t a t o n l y two s i t e s a l o n g t h e V e d d e r R i v e r : - a t t h e g a u g i n g s t a t i o n n e a r V e d d e r C r o s s i n g - a t t h e c a b l e w a y j u s t b e l o w t h e r a i l w a y b r i d g e n e a r Y a r r o w . A l l o f t h i s d a t a was o b t a i n e d f r o m Water S u r v e y o f Canada and t h e a v e r a g e c h a n n e l p r o p e r t i e s ( t o p w i d t h , mean d e p t h a n d mean v e l o c i t y ) were p l o t t e d a g a i n s t d i s c h a r g e as shown i n F i g u r e 30. The d a t a was f o u n d t o p l o t as s t r a i g h t l i n e s on l o g - l o g p a p e r so t h a t t h e h y d r a u l i c g e o m e t r y c o u l d be e x p r e s s e d a s power law r e l a t i o n s . The d e r i v e d e x p r e s -r a i l w a y b r i d g e V e d d e r C r o s s i n g T h e s e r e s u l t s were d e r i v e d f r o m d i s c h a r g e s r a n g i n g between 3,070 c f s and 12,400 c f s a t t h e r a i l w a y b r i d g e and 1,770 c f s and 18,800 c f s a t V e d d e r C r o s s i n g . The maximum v e l o c i t y r e p o r t e d by W a t e r S u r v e y o f Canada was 14 f t / s e c s i o n s were v = 0.044 Q 0.55 0.123 Q 0.05 0.40 W = 185 Q V = ,183 O 0 .430 d = 0.041 Q W = 134.3 Q 0.559 0 .011 96 a t V e d d e r C r o s s i n g w i t h a c o r r e s p o n d i n g F r o u d e number o f a b o u t 0.75 a n d 6.8 f t / s e c a t t h e r a i l w a y b r i d g e , w i t h a F r o u d e number o f 0.55. The e x p o n e n t s o f t h e p o w e r l a w e q u a t i o n s i n d i c a t e s t h e v a r i a b i l i t y o f e a c h p a r a m e t e r w i t h d i s c h a r g e ( L e o p o l d , V7olman and M i l l e r , 1964) . A t b o t h s i t e s t h e w i d t h i s v e r y i n s e n s i t i v e t o d i s c h a r g e w h i l e t h e v e l o c i t y i n c r e a s e s t h e m o s t r a p i d l y a t t h e r a i l w a y b r i d g e a n d d e p t h i n c r e a s e s most r a p i d l y a t V e d d e r C r o s s i n g . T h e s e r e s u l t s c a n be u s e d t o i n d i c a t e how t h e c h a n n e l r e s i s t a n c e c h a n g e s w i t h d i s c h a r g e . S i n c e M a n n i n g ' s c o e f f i c i e n t s h o u l d be p r o p o r t i o n a l t o 2/3 • . d , t h e power l a w e q u a t i o n s i n d i c a t e : v n a Q * ( b e l o w t h e r a i l w a y b r i d g e ) n a Q~° * 0 6 ( a t V e d d e r C r o s s i n g ) T h i s shows t h e c h a n n e l r e s 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 n e a r t h e r a i l w a y b r i d g e , b u t i s n e a r l y c o n s t a n t a t V e d d e r C r o s s i n g . V a l u e s o f M a n n i n g ' s c o e f f i c i e n t e s t i -m a t e d f r o m t h e h y d r a u l i c m e a s u r e m e n t s c o n f i r m t h e s e t r e n d s . A t t h e r a i l w a y b r i d g e " n " v a l u e s w e r e f o u n d t o d e c r e a s e f r o m a b o u t 0.034 a t 5000 c f s t o a b o u t 0.025 a t 12,500 c f s . A t V e d d e r C r o s s i n g t h e c o m p u t e d n v a l u e s s c a t t e r e d b e t w e e n 0.04-0.045 a n d showed no c o n s i s t a n t v a r i a t i o n . C h a n n a l r e s i s t a n c e n o r m a l l y r e s u l t s f r o m two f a c t o r s : - " s k i n " r e s i s t a n c e due t o t h e r o u g h c h a n n e l b o u n d a r y - " f o r m " r e s i s t a n c e due t o b a r s , c h a n g e s i n c h a n n e l 97 a l i g n m e n t o r c h a n n e l o b s t r u c t i o n s . I n g r a v e l r i v e r s f o r m l o s s e s a r e n o r m a l l y c o n s i d e r e d t o be s m a l l ( R o u s e , 1965) . F o r h y d r a u l i c a l l y r o u g h f l o w s s k i n r e s i s t a n c e c a n be e s t i m a t e d f r o m t h e b e d m a t e r i a l c o m p o s i t i o n by means o f S t r i c k l e r ' s e m p i r i c a l r e l a t i o n ( H e n d e r s o n , 1966) . n = 0.034 D 9 Q 1 / 6 w h e r e D^Q r e p r e s e n t s t h e b e d m a t e r i a l r o u g h n e s s h e i g h t . T h i s e x p r e s s i o n i n d i c a t e s t h e minimum e x p e c t e d M a n n i n g ' s n v a l u e s w o u l d be a r o u n d 0.026 a t t h e r a i l w a y b r i d g e a n d a r o u n d 0.029 a t V e d d e r C r o s s i n g . I f t h e e x p r e s s i o n f o r M a n n i n g ' s c o e f f i c i e n t i s s u b -2/3 1/2 s t i t u t e d i n t o M a n n i n g ' s e q u a t i o n V = 1.49 d S a n d i m e n s i o n l e s s r e s i s t a n c e f o r m u l a c a n be d e r i v e d : V = 8.4 d _ 1 / 6 V * D 9 0 -Two o t h e r r e s i s t a n c e e q u a t i o n s w h i c h c a n be e x p r e s s e d i n a s i m i l a r d i m e n s i o n l e s s f o r m a r e K e u l e g a n ' s l o g r i t h m i c f o r m u l a (Burkham a n d Dawdy , 19 76) a n d L i m e r i n o s ' m o d i f i c a t i o n o f t h i s f o r m u l a ( L i m e r i n o s , 1970). These a r e , r e s p e c t i v e l y : V = 6 . 2 5 + 5 . 7 5 l o g ,d_ V * D 90 V = 3.28 + 5.75 l o g ,R_ > V * D 84 A l l t h r e e o f t h e s e e x p r e s s i o n s h a v e b e e n p l o t t e d i n 98 F i g u r e 3 1 , a l o n g w i t h t h e m e a s u r e m e n t s made b e l o w t h e r a i l w a y b r i d g e . The m e a s u r e d d a t a s c a t t e r s a r o u n d t h e L i m e r i n o s e q u a t i o n , h o w e v e r i t a p p e a r s t o p l o t a t a s t e e p e r s l o p e t h a n a n y o f t h e e q u a t i o n s p r e d i c t . T h e s e r e s u l t s show t h a t f o r l o w d e p t h / g r a i n s i z e r a t i o s t h e m e a s u r e d c h a n n e l r e s i s t a n c e was h i g h e r t h a n t h e p r e d i c t e d v a l u e s , i n d i c a t i n g t h a t s i g n i f i c a n t f o r m l o s s e s w e r e p r e s e n t . When t h e ^—; r a t i o e x c e e d e d a b o u t 15 t h e m e a s u r e d v a l u e s 9 0 be g a n t o a p p r o a c h t h e t h e o r e t i c a l r e s u l t s i n d i c a t i n g f o r m l o s s e s w e r e d e c r e a s i n g . T h i s i s q u i t e r e a s o n a b l e s i n c e a t h i g h f l o w s many o f t h e b a r s a n d c h a n n e l i r r e g u l a r i t i e s w o u l d be "drowned o u t " . C h u r c h (1972) showed t h a t d u r i n g v e r y h i g h f l o w s t h e c h a n n e l r e s i s t a n c e c o u l d become much l o w e r t h a n t h e t h e o r -e t i c a l p r e d i c t i o n s w o u l d i n d i c a t e . T h i s was a t t r i b u t e d p a r t i a l l y t o " l i v e b e d " c o n d i t i o n s w h i c h a p p a r e n t l y c a u s e d s m o o t h i n g o u t o f t h e b e d . The V e d d e r R i v e r d a t a was n o t c o l l e c t e d o v e r a s u f f i c i e n t l y l a r g e f l o w r a n g e t o make any c o n c l u s i o n s on t h e s e o b s e r v a t i o n s . I n summary, n e a r Y a r r o w t h e c h a n n e l r e s i s t a n c e seems t o d e c r e a s e a t h i g h f l o w s a s t h e f o r m r e s i s t a n c e i s "drowned cl o u t " . A t f l o w s a r o u n d 12,000 c f s ( — - 15) t h e r e s i s t a n c e D 9 0 a p p r o a c h e s v a l u e s w h i c h c o r r e s p o n d t o s k i n r e s i s t a n c e a l o n e . A t V e d d e r C r o s s i n g t h e r e s i s t a n c e a p p e a r s t o r e m a i n r e a s o n a b l y c o n s t a n t o v e r a w i d e f l o w r a n g e , p r o b a b l y 99 b e c a u s e t h e c h a n n e l a l i g n m e n t i s v e r y i r r e g u l a r i n t h i s r e a c h , c a u s i n g s t a n d i n g waves a n d e d d i e s t o d e v e l o p a t h i g h f l o w s . 6.4 B e d M a t e r i a l C h a r a c t e r i s t i c s S e d i m e n t s i z e s c a n v a r y w i d e l y on t h e V e d d e r R i v e r , b o t h i n t h e d o w n s t r e a m d i r e c t i o n and a c r o s s t h e c h a n n e l . G e n e r a l l y i t was f o u n d t h a t t h e c o a r s e s t s e d i m e n t s ( g r a v e l and c o b b l e s ) w e re f o u n d i n t h e m a i n c h a n n e l o f t h e r i v e r , f o r m i n g a s u r f a c e l a y e r i n w h i c h s a n d a n d f i n e r g r a v e l s was v i r t u a l l y a b s e n t . T h i s s u r f a c e l a y e r has b e e n t e r m e d "pavement" by B r a y ( 1 9 7 2 ) . When t h i s s u r f a c e l a y e r was r e m o v e d , l a r g e q u a n t i t i e s o f c o a r s e s a n d a n d f i n e g r a v e l was f o u n d u n d e r n e a t h . On most o f t h e b a r s a s u r f a c e p a v e -ment was a l s o e v i d e n t a l t h o u g h i n g e n e r a l t h i s was n o t as o b v i o u s a s t h e m a i n c h a n n e l . Oh many b a r s l a r g e a r e a s o f f i n e g r a v e l s a n d s a n d c o u l d be f o u n d on t h e s u r f a c e . The l a r g e v a r i a b i l i t y o f s e d i m e n t s i z e s i n g r a v e l r i v e r s makes t h e c o l l e c t i o n o f r e p r e s e n t a t i v e b e d m a t e r i a l s a m p l e s v e r y d i f f i c u l t . I n a d d i t i o n , t h e n a t u r a l p a v i n g w h i c h c a n be f o u n d i n d i c a t e s t h e g r a v e l b e d c a n c o n s i s t o f two s e p a r a t e p o p u l a t i o n s - t h e s u r f a c e l a y e r and t h e u n d e r -l y i n g m a t e r i a l ( K e l l e r h a l s , 1 9 7 1 ) . I f a s i m p l e b u l k s a m p l e i s c o l l e c t e d t h e n t h e two p o p u l a t i o n s w i l l be m i x e d t o g e t h e r and t h e r e s u l t i n g s a m p l e w i l l n o t be r e p r e s e n t a t i v e 100 o f t h e p a v e m e n t o r o f t h e u n d e r l y i n g m a t e r i a l . P a s t s t u d i e s h a v e shown t h a t t h e m a t e r i a l f o u n d o n b a r s i s r e p r e s e n t a t i v e o f t h e s e d i m e n t b e i n g moved a s b e d -l o a d ( L e o p o l d , Wolman a n d M i l l e r , 1 964; M o s l e y , 1 9 7 8 ) . T h e r e f o r e i t seems r e a s o n a b l e t o u s e b u l k s a m p l e s o f t h e s u b s u r f a c e b e d m a t e r i a l t o d e s c r i b e t h e c o m p o s i t i o n o f t h e b e d l o a d . A l t e r n a t e l y , i t h a s b e e n g e n e r a l l y a c c e p t e d t h a t t h e s u r f a c e p a v e m e n t i s a n i m p o r t a n t f a c t o r i n d e t e r -m i n i n g c h a n n e l r o u g h n e s s ( K e l l e r h a l s , 1 9 7 0 ; C h u r c h a n d K e l l e r h a l s , 19 7 9 ) . The o n l y p r a c t i c a l m e t h o d t o s a m p l e t h i s s u r f a c e l a y e r i s t o u s e one o f t h e g r i d m e t h o d s d e s -c r i b e d p r e v i o u s l y i n C h a p t e r V. The p r o c e d u r e s d e s c r i b e d a b o v e w e r e u s e d f o r a l l o f t h e t w e n t y one s a m p l e s c o l l e c t e d b y t h e a u t h o r . The W a t e r S u r v e y o f Canada d a t a w e re a l l b u l k s a m p l e s , h o w e v e r m o s t o f t h e s e w e r e c o l l e c t e d o n b a r s w h e r e t h e s u r f a c e p a v i n g was g e n e r a l l y n o t p r o m i n e n t . T h e r e f o r e t h e s e s a m p l e s w e re u s e d t o e s t a b l i s h t h e s i z e o f t r a n s p o r t e d m a t e r i a l . I n o r d e r t o o v e r c o m e some o f t h e s p a t i a l v a r i a b i l i t y i n b e d m a t e r i a l s s i z e , t h e r i v e r was s u b - d i v i d e d i n t o s i x r e a c h e s and t h e s a m p l e s w i t h i n e a c h r e a c h w e r e c o m p o s i t e d . T h e s e r e a c h e s w e r e as f o l l o w s : V e d d e r C a n a l ( m i l e 1.45-2.42) h e a d o f c a n a l ( m i l e 2.42-3.52) r a i l w a y b r i d g e ( m i l e 3.52-4.43) 101 c o n s t r i c t i o n ( m i l e 4.43-5.61) F o r d Road t o P e a c h e Road ( m i l e 5.61-6.56) V e d d e r C r o s s i n g ( m i l e 6.56-7.75) The a v e r a g e s u r f a c e and s u b s u r f a c e b e d m a t e r i a l c o m p o s i t i o n o f e a c h r e a c h i s s u m m a r i z e d i n T a b l e 19. T h e s e r e s u l t s show t h a t t h e m e d i a n s i z e o f t h e s u r f a c e l a y e r was g e n e r a l l y a r o u n d 1.5 t o 3.0 t i m e s t h e s i z e o f t h e u n d e r l y i n g m a t e r i a l . I n a d d i t i o n , v a l u e s o f T r a s k 1 s f a c e m a t e r i a l a n d 2.25-3.3 f o r t h e u n d e r l y i n g b e d m a t e r i a l . T h i s shows t h a t t h e s u r f a c e l a y e r i s b e t t e r s o r t e d w h i c h r e f l e c t s t h e l o s s o f f i n e m a t e r i a l i n t h e p a v e m e n t . The a v e r a g e b e d m a t e r i a l c o m p o s i t i o n s u m m a r i z e d i n T a b l e 19 shows a t r e n d t o w a r d s d e c r e a s i n g g r a i n s i z e down t h e V e d d e r R i v e r . F o r e x a m p l e , t h e m e d i a n b e d s i z e was f o u n d t o d e c r e a s e b y h a l f i n t h e f i r s t 3 1/2 m i l e s down-s t r e a m f r o m V e d d e r C r o s s i n g . D o w n s t r e a m c h a n g e s i n g r a i n s i z e h a v e b e e n s t u d i e d b y many g e o m o r p h o l o g i s t s a n d e n g i n e e r s ( M a c k i n , 194 8; Y a t s u , 1955; S c h u l i t s , 1 9 4 1 ; S i m o n s , 1 9 7 1 ; C h u r c h and K e l l e r h a l s , 1 9 7 9 ) . I n i t i a l l y , s e d i m e n t g r a d a t i o n was a t t r i b u t e d t o a b r a s i o n . F o l l o w i n g t h e w o r k o f S t e r n b e r g , L e l i a v s k y (19 55) p r e s e n t e d d a t a f r o m t h e R h i n e R i v e r w h i c h showed t h e w e i g h t o f p e b b l e s d e c r e a s e d e x p o n e n t i a l l y w i t h d i s t a n c e . w h i c h m e a s u r e t h e s p r e a d o f t h e s i z e d i s t r i b u t i o n , v a r i e d b e t w e e n 1.5-1.7 f o r t h e s u r -102 Using stone s i z e i n s t e a d o f weight, t h i s can be expressed as: D = D e d where "a-," i s a s i z e r e d u c t i o n c o e f f i c i e n t o d x i s the d i s t a n c e along the r i v e r However g r a d a t i o n may be a l s o caused by s e l e c t i v e t r a n s p o r t o f d i f f e r e n t bed m a t e r i a l s i z e s along a r i v e r Scheidegger (1961) . This s e l e c t i v e t r a n s p o r t can occur i n both a g g r a d a t i o n and e r o s i o n p r o c e s s e s . In the case o f a g g r a d a t i o n a l s i t u a t i o n s such as on a l l u v i a l fans, sediment s o r t i n g may occur when the t r a n s p o r t c a p a c i t y o f the channel decreases with d i s t a n c e downstream. T h i s can cause the coarse f r a c t i o n of the sediment l o a d t o be s e l e c t i v e l y de-p o s i t e d near the head o f the fan. Sediment s o r t i n g on aggrading streams has been d e s c r i b e d by L u s t i g (1963); B l i s s e n b a c h (1952) and Church (1972). Sediment s o r t i n g can a l s o occur i n e r o s i o n a l s i t u a t i o n s where the f i n e r m a t e r i a l i n the bed i s s e l e c t i v e l y removed and the c o a r s e r immobile m a t e r i a l i s l e f t b ehind. I t was decided to c a r r y out a simple r e g r e s s i o n a n a l y s i s on the coarse f r a c t i o n o f the bed m a t e r i a l sample c o l l e c t e d on the Vedder R i v e r . In order to reduce some o f the v a r i a b i l i t y o f the samples a l l o f the f i n e m a t e r i a l ( l e s s than 8 mm) was removed from the samples. I t was reasoned t h a t t h i s f i n e m a t e r i a l should not show s i g n i f i c a n t s o r t i n g over the l e n g t h o f the fan . s i n c e i t can probably 103 be t r a n s p o r t e d t h r o u g h t h e e n t i r e s y s t e m . However i n some a r e a s l a r g e q u a n t i t i e s o f f i n e s e d i m e n t c a n be t e m p o r a r i l y d e p o s i t e d o n b a r s . T h i s s e d i m e n t c a n i n t r o d u c e a l a r g e amount o f s c a t t e r i n t h e b e d m a t e r i a l s a m p l e s u n l e s s t h e s a m p l i n g s i t e s a r e s e l e c t e d c a r e f u l l y t o a v o i d t h i s m a t e r i a l . R e s u l t s o f t h e a n a l y s i s , b a s e d on a t o t a l o f 58 s a m p l e s showed t h e m e d i a n s e d i m e n t s i z e c o u l d be e x p r e s s e d a s : D c „ = 65 e " 0 , 1 9 3 x r 2 = 0.63 x = d i s t a n c e i n m i l e s As shown i n F i g u r e 32 t h e o v e r a l l s c a t t e r i s v e r y l a r g e w h i c h i n d i c a t e s t h a t a l t h o u g h a t r e n d i s c l e a r l y p r e s e n t , t h e r e i s a g r e a t d e a l o f v a r i a b i l i t y t h a t i s n o t a c c o u n t e d f o r by t h e r e g r e s s i o n . Some o f t h i s s c a t t e r i s p r o b a b l y due t o p o o r c h o i c e o f s a m p l i n g s i t e s , a n d p o o r s a m p l i n g t e c h n i q u e s . F o r c o m p a r i s o n p u r p o s e s , some d a t a on d o w n s t r e a m c h a n g e s o f b e d m a t e r i a l s i z e r e p o r t e d b y Simons (19 71) h a s b e e n s u m m a r i z e d i n T a b l e 20. T h e s e r e s u l t s show t h e c o e f f i c i e n t o f s i z e r e d u c t i o n (a^) r a n g e d b e t w e e n 0.15 m i l e s - 1 t o 0.01 m i l e s - 1 . I n t h e c a s e o f most r e a s o n a b l y c o m p e t e n t r o c k , a b r a s i o n c a n n o t a c c o u n t f o r l a r g e v a l u e s o f a ^ . F o r e x a m p l e B r a d l e y e t a l (19 72) c o n c l u d e d t h a t f o r t h e K n i k R i v e r i n A l a s k a s o r t i n g p r o c e s s e s a c c o u n t e d f o r 90 t o 95% o f t h e r e d u c t i o n i n g r a v e l s i z e , w i t h t h e b a l a n c e 104 a t t r i b u t a b l e t o a b r a s i o n . A l t h o u g h t h e l i t h o l o g y o f t h e V e d d e r R i v e r s e d i m e n t s was n o t s t u d i e d . i n d e t a i l i t was f o u n d t h a t t h e g r a v e l s w e r e composed p r i m a r i l y o f , l i m e s t o n e , c o n g l o m e r a t e s a n d g r a n -o d i o r i t e . M o s t o f t h e r o c k a p p e a r e d c o m p e t e n t . S i n c e t h e c o e f f i c i e n t o f s i z e r e d u c t i o n was e v e n l a r g e r o n t h e V e d d e r R i v e r t h a n o b s e r v e d b y B r a d l e y on t h e K n i k R i v e r i t i s c o n c l u d e d t h e s e l e c t i v e d e p o s i t i o n i s t h e o n l y s i g -n i f i c a n t f a c t o r c a u s i n g t h e d e c r e a s e i n b e d m a t e r i a l s i z e b e t w e e n V e d d e r C r o s s i n g a n d t h e V e d d e r C a n a l . 105 CHAPTER V I I SEDIMENT TRANSPORT 7 .1 S u s p e n d e d L o a d S u s p e n d e d l o a d d a t a h a s b e e n c o l l e c t e d b y W a t e r S u r v e y o f C a n a d a r o u t i n e l y s i n c e 1965 . T h e s e m e a s u r e m e n t s h a v e b e e n made a t t h e c a b l e w a y j u s t b e l o w t h e r a i l w a y b r i d g e . Some s t a t i s t i c s d e r i v e d f r o m t h e W a t e r S u r v e y o f C a nada m e a s u r e m e n t s a r e shown i n T a b l e 2 1 . The maximum r e c o r d e d s e d i m e n t c o n c e n t r a t i o n was m e a s u r e d o n December 3, 19 75 a n d r e a c h e d 4,000 mg/1 w h i c h c o r r e s p o n d s t o a l o a d o f 202,000 t o n s / d a y . By c o m p a r i s o n , t h e a v e r a g e a n n u a l l o a d b e t w e e n 1965-1977 h a s b e e n o n l y 146,000 t o n s / y e a r . T h e r e h a s b e e n v e r y few m e a s u r e m e n t s t o d e t e r m i n e t h e s i z e c o m p o s i t i o n o f t h e s u s p e n d e d l o a d . However d u r i n g t h e 19 75 f l o o d i t was r e p o r t e d t h a t t h e m e d i a n g r a i n s i z e was a b o u t 0.05 mm a n d t h a t 90% o f t h e s u s p e n d e d l o a d was f i n e t h a n 0.2 5 mm. The s u s p e n d e d l o a d c o n s i s t s o f two c o m p o n e n t s - t h e s u s p e n d e d b e d m a t e r i a l l o a d a n d t h e wash l o a d . Wash l o a d i s t h a t p a r t o f t h e s e d i m e n t l o a d c o n s i s t i n g o f g r a i n s i z e s f i n e r t h a n t h o s e f o u n d i n t h e s t r e a m b e d . The t r a n s p o r t o f t h i s s e d i m e n t i s n o t g o v e r n e d b y t h e h y d r a u l i c p r o p o r t i e s o f t h e c h a n n e l b u t by t h e s e d i m e n t s u p p l y t h r o u g h o u t t h e w a t e r s h e d . T h i s i s b e c a u s e t h e t r a n s p o r t c a p a c i t y o f t h e 106 channel always exceeds the supply of t h i s f i n e sediment. E i n s t e i n (1950) suggested t h a t the l i m i t i n g s i z e f o r wash-l o a d can be c o n s i d e r e d as the g r a i n diameter f o r which 10% of the bed m a t e r i a l i s f i n e r . T h i s s i z e f r a c t i o n c o r r e s -ponds to between 0.4 mm-1.0:mmin the Vedder Canal and 0.5 mm-2.0 mm a t the r a i l w a y b r i d g e . Since the composi-t i o n of the suspended l o a d was c o n s i d e r a b l y f i n e r than these s i z e s , v i r t u a l l y a l l of the suspended l o a d can be c o n s i d e r e d as washload. Therefore although the q u a n t i t y of the suspended l o a d may be q u i t e l a r g e i t i s simply washed through the Vedder River, without having a major impact on the sedimentation p r o c e s s e s . 7.2 Bedload Bedload i s t h a t p a r t of the sediment l o a d t h a t moves i n c o n t a c t w i t h the channel bottom - by s l i d i n g , r o l l i n g or s a l t a t i n g . The Vedder R i v e r i s one o f the few r i v e r s i n the country where a c o n c e n t r a t e d e f f o r t has been made to c o l l e c t bedload t r a n s p o r t measurements. Other g r a v e l r i v e r s where bedload data has been c o l l e c t e d i n c l u d e the Elbow R i v e r ( H o l l i n g s h e a d , 1968, 1971) and the North Saskat-chewan River (Samide, 1971). In a d d i t i o n , r e c e n t l y s e v e r a l s t u d i e s have been c a r r i e d out on some American g r a v e l r i v e r s i n c l u d i n g the Tanana R i v e r (Emmett e t a l , 1978) the Snake Ri v e r and the Clearwater R i v e r (Emmett, 1976). 1 0 7 The bedload measurements on the Vedder R i v e r were c o l l e c t e d a t the cableway below the B.C. E l e c t r i c r a i l w a y b r i d g e by the Water Survey o f Canada between 19 71 and 1975. This data, f o r the most p a r t unpublished, was made a v a i l a b l e by the Sediment Survey S e c t i o n of Environment Canada. Some a d d i t i o n a l data was e x t r a c t e d from the r e p o r t by Jonys (1976). A t o t a l o f 44 measurements were made, under flow c o n d i t i o n s r a n g i n g from 3., 37.0 c f s t o 13,120 c f s . For each measurement u s u a l l y s e v e r a l samples were c o l l e c t e d a cross the r i v e r c r o s s s e c t i o n i n order t o d e f i n e the width of bedload movement. Most o f the measurements were made w i t h e i t h e r a basket sampler o r a h a l f s i z e VUV sampler,from the c a b l e -way. The basket sampler c o n s i s t e d o f a r e c t a n g u l a r frame with an open-ended 1/4 i n c h mesh basket f i t t e d i n to c o l l e c t the bedload. Jonys (19 76) r e p o r t e d the bask e t opening was two f e e t wide. I t was assumed t h a t the e f f i c i e n c y of the basket sampler was about 33% which i s i n agreement with e s t i -mates r e p o r t e d by H o l l i n g s h e a d (1971) . The h a l f s i z e VUV sampler i s a pressure d i f f e r e n c e type sampler (Graf, 1971) w i t h an opening of about 8 1/2 in c h e s . In the VUV sampler sediment i s c o l l e c t e d i s a metal pan so t h a t the sand s i z e d m a t e r i a l should be r e -t a i n e d . The e f f i c i e n c y o f the VUV sampler has been found to equal 60% (Gibbs and N e i l l , 1973). 108 I t i s b e l i e v e d t h a t t h e b e d l o a d t r a n s p o r t i s t h e m a i n f a c t o r g o v e r n i n g a g g r a d a t i o n a n d d e g r a d a t i o n p r o c e s s e s o f t h e V e d d e r R i v e r . I n t h e v a s t m a j o r i t y o f g r a v e l r i v e r s e d i m e n t a t i o n p r o b l e m s , i n f o r m a t i o n on b e d l o a d i s d e t e r -m i n e d i n d i r e c t l y - u s u a l l y b y r e l y i n g on h i g h l y e m p i r i c a l t h e o r i e s t h a t h a v e o f t e n b e e n b a s e d o n l y on l a b o r a t o r y s t u d i e s . F r e q u e n t l y , f o r m u l a s h a v e b e e n d e r i v e d f o r s a n d bed c h a n n e l s b u t have b e e n a p p l i e d t o g r a v e l s t r e a m s w i t h -o u t p r o p e r v e r i f i c a t i o n . T h e r e f o r e , t h e b e d l o a d d a t a c o l l e c t e d on t h e V e d d e r R i v e r b y W a t e r S u r v e y o f C a n a d a p r o v i d e s a u n i q u e o p p o r t u n i t y t o l e a r n a b o u t t h e s e d i m e n t t r a n s p o r t p r o c e s s e s on t h e r i v e r a n d t o t e s t o u t some o f t h e p r e d i c t i v e m ethods t h a t a r e c u r r e n t l y a v a i l a b l e . The Y a r r o w c a b l e w a y c r o s s s e c t i o n w h ere a l l o f t h e b e d l o a d m e a s u r e m e n t s were made i s shown i n F i g u r e 2 7 . I n a d d i t i o n , t h e b e d l o a d d a t a and c o r r e s p o n d i n g h y d r a u l i c d a t a c o l l e c t e d a t t h e t i m e o f t h e s a m p l i n g i s s u m m a r i z e d i n T a b l e 22. A f e w o b s e r v a t i o n s on some f e a t u r e s o f t h e m e a s u r e m e n t s a r e a s f o l l o w s . F i r s t l y , t h e b e d l o a d t r a n s p o r t a p p e a r e d t o be v e r y e r r a t i c a n d s u b j e c t t o w i d e f l u c t u a t i o n s i n m a g n i t u d e . J o n y s (19 7 6 ) r e p o r t s m e a s u r e m e n t s made i n 1974 a t a s i n g l e l o c a t i o n w h ere t h e t r a n s p o r t r a t e f l u c t u a t e d b e t w e e n 0.2 5 kg/m/minute (0.17 l b / f t / m i n u t e ) t o 14.11 kg/ m / m i n u t e (9.46 l b / f t / m i n u t e ) i n a s p a c e o f 12 m i n u t e s u n d e r a p p r o x i m a t e l y 10 9 steady flow c o n d i t i o n s . Such l a r g e f l u c t u a t i o n s i n t r a n s -p o r t have a l s o been r e p o r t e d by Graf (19 71) . These f l u c -t u a t i o n s mean t h a t a l a r g e number of bedload samples must be c o l l e c t e d to estimate the average t r a n s p o r t r a t e . At present, there are no g u i d e l i n e s a v a i l a b l e to i n d i c a t e how many samples are r e q u i r e d to make a r e a l i a b l e estimate of the average t r a n s p o r t r a t e . Secondly, bedload movement d i d not u s u a l l y occur over the e n t i r e channel but was r e s t r i c t e d to a s t r i p of about 125 f e e t i n width. Jonys (1976) r e p o r t e d t h a t most t r a n s -p o r t o c c u r r e d along the n o r t h bank o f the channel over a submerged bar and t h a t very l i t t l e movement o c c u r r e d i n the deepest p a r t of the channel. A n a l y s i s o f the bedload s i z e d i s t r i b u t i o n showed th a t f o r flows under about 8,000 c f s the sediment l o a d was composed predominately o f sand. Under these c o n d i t i o n s g r a v e l - s i z e d m a t e r i a l ( u s u a l l y l e s s than 4 mm) o f t e n com-p r i s e d l e s s than 5% o f the t o t a l bedload. However, when the d i s c h a r g e exceeded about 8,000-9,000 c f s the bedload s i z e i n c r e a s e d very s h a r p l y and g r a v e l made up the l a r g e s t f r a c t i o n of the sediment l o a d . In order to i l l u s t r a t e t h i s change i n bedload g r a i n s i z e with d i s c h a r g e , the median p a r t i c l e s i z e was p l o t t e d a g a i n s t discharge i n F i g u r e 33. In a d d i t i o n a few of the bedload s i z e d i s t r i b u t i o n curves have been p l o t t e d i n F i g u r e 34, along w i t h the average 110 bed m a t e r i a l d i s t r i b u t i o n a t the r a i l w a y b r i d g e . These curves show t h a t when the flows exceeded about 8 , 0 0 0 - 9 , 0 0 0 c f s the bedload and bed m a t e r i a l g r a i n s i z e d i s t r i b u t i o n s were very s i m i l a r . T h i s i n d i c a t e s t h a t d u r i n g high flows a l l o f the g r a i n s i z e s i n the bed are a c t i v e . Using S h i e l d ' s r e l a t i o n f o r i n c i p i e n t motion the maximum p a r t i c l e s i z e moved at a flow of 8 ,000 c f s would be about 70umm, which corresponds to roughly the DgQ s i z e o f the s u r f a c e bed m a t e r i a l . I t appears t h a t u n t i l t h i s s u r f a c e l a y e r i s s e t i n motion the bedload c o n s i s t s mainly of sand moving over an immobile g r a v e l bed. However, once the s u r f a c e l a y e r i s "broken" a much l a r g e r range of g r a v e l and sand s i z e d m a t e r i a l i s made a v a i l a b l e f o r t r a n s p o r t . F i g u r e 35 shows the r e l a t i o n between bedload t r a n s -p o r t r a t e and d i s c h a r g e . Although c o n s i d e r a b l e s c a t t e r i s e v i d e n t on the l o g - l o g p l o t there appears to be a reasonably c o n s i s t a n t r e l a t i o n s h i p , with sediment l o a d p r o p o r t i o n a l to the f i f t h power o f d i s c h a r g e . T h i s i l l u s t r a t e s the very n o n - l i n e a r nature o f bedload t r a n s p o r t and i n d i c a t e s how the m a j o r i t y of the annual t r a n s p o r t may occur d u r i n g a few days o f h i g h f l o w s . The h i g h e s t flow a t which bedload was measured was around 13 ,000 c f s . Therefore a r a t h e r l a r g e e x t r a p o l a t i o n I l l i s r e q u i r e d t o a p p l y t h i s d a t a t o e x t r e m e f l o o d c o n d i t i o n s . As a r e s u l t , i t was d e c i d e d t o t r y t o p r e d i c t t h e b e d l o a d w i t h a v a i l a b l e t r a n s p o r t f o r m u l a s and use t h e m e a s u r e m e n t s t o v e r i f y t h e r e s u l t s . T h e r e h a s b e e n v e r y l i t t l e s u c c e s s i n e s t i m a t i n g b e d -l o a d f r o m s e d i m e n t t r a n s p o r t t h e o r y . B l e n c h (1969) s t a t e d t h a t p r e d i c t e d b e d l o a d r a t e s s h o u l d be c o n s i d e r e d o n l y a s o r d e r o f m a g n i t u d e e s t i m a t e s . W h i t e , M i l l i a n d C r a b b e (19 75) c o m p a r e d s e v e r a l b e d l o a d f o r m u l a s u s i n g o v e r a t h o u s a n d f l u m e a n d f i e l d m e a s u r e m e n t s . The f o r m u l a s o f A c k e r s a n d W h i t e , E n g e l u n d and H a n s e n and R o t t n e r w e r e f o u n d t o be t h e m o s t r e l i a b l e e q u a t i o n s . F o r t h e s e t h r e e f o r m u l a s , b e t t e r t h a n h a l f o f t h e c o m p u t e d v a l u e s w e r e f o u n d t o l i e w i t h i n 50% t o 200% o f t h e m e a s u r e d t r a n s p o r t r a t e s . H o w e v e r , t h e v a s t m a j o r i t y o f d a t a u s e d t o v e r i f y t h e s e f o r m u l a r e l a t e d t o s a n d b e d s t r e a m s . C h u r c h (19 76) c o m p a r e d t h e S c h o c k l i t s c h , M e y e r - P e t e r , M e y e r - P e t e r a n d M u l l e r , S h i e l d s , K a l i n s k e and E i n s t e i n f o r m u l a u s i n g t h e b e d l o a d m e a s u r e m e n t s r e p o r t e d by H o l l i n g s h e a d (1968) on t h e E l b o w R i v e r . C h u r c h recommended t h a t t h e p e r f o r m a n c e o f t h e E i n s t e i n e q u a t i o n c o u l d be i m p r o v e d b y m a k i n g a s l i g h t m o d i f i c a t i o n t o some o f t h e h y d r a u l i c c a l c u l a t i o n s t h a t a r e u s e d i n t h e o r i g i n a l m e t h o d . B a s i c a l l y , C h u r c h recommended t h a t m e a s u r e d h y d r a u l i c d a t a s h o u l d be u s e d t o c a l c u l a t e b e d l o a d i n s t e a d o f r e l y i n g on t h e o r e t i c a l 112 p r o c e d u r e s w h i c h a t t e m p t t o compute t h e v e l o c i t y a n d c h a n n e l r e s i s t a n c e . C h u r c h ' s u n p u b l i s h e d r e p o r t i s one o f t h e few s t u d i e s t o c o n c e n t r a t e on t h e p r o b l e m o f p r e -d i c t i n g b e d l o a d i n g r a v e l r i v e r s . I n o r d e r t o d e t e r m i n e w h i c h t h e o r i e s c o u l d g i v e t h e b e s t b e d l o a d p r e d i c t i o n s on t h e V e d d e r R i v e r , t h e a u t h o r c o m p a r e d t h r e e f o r m u l a t h a t h a v e c l a i m e d t o be a p p l i c a b l e t o g r a v e l r i v e r s - t h e E i n s t e i n (1950) f o r m u l a , M e y e r -P e t e r a n d M u l l e r ' s f o r m u l a a n d A c k e r s a n d W h i t e ' s e q u a t i o n . T h ese t h e o r i e s w e r e v e r i f i e d u s i n g b e d l o a d m e a s u r e m e n t s f r o m f i v e g r a v e l r i v e r s : - E l b o w R i v e r a t B r a g g C r e e k ( H o l l i n g s h e a d , 1968, 1969) - N o r t h S a s k a t c h e w a n R i v e r ( S a m e d i , 19 7 ) - Snake a n d C l e a r w a t e r R i v e r s (Emmett, 19 76) - V e d d e r R i v e r n e a r Y a r r o w (W.S.C. 1 9 7 1 - 1 9 7 3 , J o n y s , 1976) A d e s c r i p t i o n o f t h e f i v e s i t e s a n d r e s u l t s o f t h e c o m p a r i s o n s h a s b e e n i n c l u d e d i n A p p e n d i x I . The E i n s t e i n (1950) f o r m u l a u s i n g t h e m o d i f i c a t i o n s u g g e s t e d b y C h u r c h was f o u n d t o g i v e t h e c l o s e s t a g r e e m e n t t o t h e f i e l d m e a s u r e m e n t s . However o n l y a b o u t one t h i r d o f t h e c o m p u t e d v a l u e s l a y w i t h i n 50% t o 200% o f t h e mea-s u r e d d a t a . N e i t h e r t h e M e y e r - P e t e r a nd M u l l e r f o r m l a n o r t h e A c k e r s a n d W h i t e m e t h o d c o u l d p r o d u c e s a t i s f a c t o r y r e s u l t s e v e n when s l i g h t m o d i f i c a t i o n s w e r e made t o t h e 1 1 3 i n p u t d a t a . F i g u r e 35 a n d 36 compare t h e t h r e e f o r m u l a a n d t h e m e a s u r e d r e s u l t s on t h e V e d d e r R i v e r . The A c k e r s and W h i t e f o r m u l a e s t i m a t e d t h r e s h o l d c o n d i t i o n s s a t i s f a c t o r i l y h o w e v e r i t t e n d s t o o v e r e s t i m a t e t h e t r a n s p o r t a t h i g h f l o w s by a f a c t o r o f t e n . The M e y e r - P e t e r a n d M u l l e r f o r m u l a w h i c h i s o f t e n c o n s i d e r e d t o be s u i t a b l e f o r g r a v e l r i v e r s g a v e v e r y p o o r r e s u l t s on t h e V e d d e r R i v e r . When t h e o r i -g i n a l v e r s i o n o f t h e f o r m u l a was t r i e d t h e b e d l o a d was o v e r e s t i m a t e d b y a f a c t o r o f 50. A f t e r a m o d i f i c a t i o n was made t o t h e e s t i m a t i o n o f t h r e s h o l d c o n d i t i o n s ( s e e A p p e n -d i x I ) t h e c o m p u t e d r e s u l t s i n t e r s e c t e d t h e m e a s u r e m e n t s , h o w e v e r t h e t r a n s p o r t r a t e s w e r e s t i l l u n d e r e s t i m a t e d a t l o w f l o w s and o v e r e s t i m a t e d a t h i g h f l o w s . I n v i e w o f t h e v e r y p o o r p e r f o r m a n c e o f t h e A c k e r s a n d W h i t e a nd t h e M e y e r - P e t e r a n d M u l l e r f o r m u l a , o n l y t h e E i n s t e i n r e l a t i o n was c o n s i d e r e d a p p l i c a b l e t o t h e V e d d e r R i v e r . U n f o r t u n a t e l y , e v e n t h e E i n s t e i n r e l a t i o n was f o u n d t o r e q u i r e c a r e f u l u s e a g e . A s e n s i t i v i t y a n a l y s i s showed t h a t s m a l l c h a n g e s i n some o f t h e i n p u t d a t a c o u l d c a u s e d r a s t i c c h a n g e s i n t h e c o m p u t e d t r a n s p o r t r a t e , e s p e -c i a l l y n e a r t h r e s h o l d c o n d i t i o n s ( s e e A p p e n d i x I ) . The two most s e n s i t i v e p a r a m e t e r s w e r e f o u n d t o be t h e mean v e l o c i t y a n d t h e e f f e c t i v e b e d r o u g h n e s s h e i g h t ( D ^ g r a i n s i z e ) . C h a n g i n g t h e s e v a l u e s b y o n l y 10% c o u l d c h a n g e 114 the sediment l o a d by 50% to 250%. Therefore i f reasonable bedload e s t i m a t e s are to be made f i e l d - d e t e r m i n e d h y d r a u l i c data (mean depth, mean v e l o c i t y , width and slope) should be used i n s t e a d o f e s t i m a t e s based on Manning's equation or o t h e r formulas. H o l l i n g s h e a d (19 70) a l s o noted the impor-tance of u s i n g a c t u a l h y d r a u l i c measurements. The o n l y other l o c a t i o n on the Vedder R i v e r where r o u t i n e h y d r a u l i c data has been c o l l e c t e d i s a t the Vedder C r o s s i n g gauging s t a t i o n . Since t h i s s i t e a l s o c o r r e s -ponds to the head o f the fan i t was c o n s i d e r e d important to estimate the sediment t r a n s p o r t a t t h i s l o c a t i o n i n order to determine the sediment i n f l o w to the fan. The bedload t r a n s p o r t a t Vedder C r o s s i n g was c a l c u -l a t e d from the f o l l o w i n g data: - h y d r a u l i c geometry measurements from gauge 8MH01 (Figure 30) - surveyed slope = 0.006 - bed m a t e r i a l samples c o l l e c t e d from bars ustream of Vedder C r o s s i n g g i v i n g a D^^ s i z e of 32 mm. I t was decided to use bed m a t e r i a l samples from the reach immediately upstream of Vedder C r o s s i n g i n the c a l c u -l a t i o n s r a t h e r than the data c o l l e c t e d at Vedder C r o s s i n g and r e p o r t e d i n Table 19. I t was f e l t t h a t the f i n e r samples c o l l e c t e d on the bars above Vedder C r o s s i n g were more r e p r e -s e n t a t i v e o f the m a t e r i a l being t r a n s p o r t e d than the h i g h l y 115 p a v e d s a m p l e s c o l l e c t e d f r o m t h e n a r r o w , c o n s t r i c t e d r e a c h . The c o a r s e r s a m p l e s f o u n d b e l o w V e d d e r C r o s s i n g r e p r e s e n t t h e s e d i m e n t t h a t t h e r i v e r h a s b e e n i n c a p a b l e o f t r a n s p o r t i n g , w h i l e t h e f i n e r s e d i m e n t s on t h e b a r s u p s t r e a m o f V e d d e r C r o s s i n g r e p r e s e n t s t h e m a t e r i a l t h a t i s t r a n s p o r t e d t h r o u g h t h i s n a r r o w gap o n t o t h e f a n b e l o w . The r e s u l t s o f t h e c a l c u l a t i o n s a r e s u m m a r i z e d on F i g u r e 37 a l o n g w i t h t h e e s t i m a t e d b e d l o a d t r a n s p o r t r e l a -t i o n a t t h e r a i l w a y b r i d g e . The t h r e s h o l d f o r s e d i m e n t t r a n s p o r t a t V e d d e r C r o s s i n g was i n t h e same r a n g e as a t t h e r a i l w a y b r i d g e ( r o u g h l y 5,000 c f s ) , h o w e v e r f o r f l o w s e x c e e d i n g 10,000 c f s t h e t r a n s p o r t a t V e d d e r C r o s s i n g was -to i n t h e o r d e r o f 20 t o 50 t i m e s t h e t r a n s p o r t n e a r Y a r r o w . I t i s p o s s i b l e t o c h e c k t h e a c c u r a c y o f t h e p r e d i c t e d V e d d e r C r o s s i n g b e d l o a d r e l a t i o n b y a t t e m p t i n g t o r e p r o d u c e t h e c h a n n e l d e p o s i t i o n r e s u l t i n g f r o m t h e December, 1975 f l o o d . As m e n t i o n e d p r e v i o u s l y , B.C. W a t e r R e s o u r c e s o f f i -c i a l s d e t e r m i n e d t h a t 258,000 c u b i c y a r d s o f s e d i m e n t was d e p o s i t e d b e t w e e n t h e r a i l w a y b r i d g e a n d V e d d e r C r o s s i n g d u r i n g t h i s f l o o d ( T e m p e s t , 19 7 6 ) . M o s t o f t h i s s e d i m e n t w o u l d h a v e b e e n t r a n s p o r t e d d u r i n g t h e p e r i o d b e t w e e n December 1 s t a n d 1 0 t h when mean d a i l y f l o w s e x c e e d e d 5,000 c f s . T h e r e f o r e t h e t o t a l amount o f s e d i m e n t d e p o -s i t e d b e t w e e n Y a r r o w a n d V e d d e r C r o s s i n g was e x p r e s s e d a s 10 V = Z (G - G ) w h e r e G = t r a n s p o r t a t V e d d e r v c y v c c C r o s s i n g 116 w h e r e G = t r a n s p o r t a t Y a r r o w A s s u m i n g t h e b e d l o a d s e d i m e n t h a s a u n i t w e i g h t o f 100 l b / f t 3 ( H o l l i n g s h e a d , 1 9 7 1 ) , t h e t o t a l v o l u m e o f s e d i m e n t d e p o s i t e d i n t h e r e a c h was e s t i m a t e d a t 155,000 c u b i c y a r d s o r a b o u t 60% o f t h e m e a s u r e d q u a n t i t y . S i n c e t h e t o t a l s e d i m e n t o u t f l o w a t Y a r r o w was l e s s t h a n 10% o f t h e i n f l o w m o s t o f t h e e r r o r i n t h i s c a l c u l a t i o n m ust have b e e n i n u n d e r e s t i m a t i n g t h e l o a d a t V e d d e r C r o s s i n g . C o m p u t i n g t h e b e d l o a d t o w i t h i n a f a c t o r o f two i s p r o b a b l y a l l t h a t c a n be e x p e c t e d , g i v e n t h e e x p e r i e n c e w i t h t h e p r e d i c t i o n s a t t h e r a i l w a y b r i d g e a n d on o t h e r g r a v e l r i v e r s w h e r e m e a s u r e m e n t s h a v e b e e n o b t a i n e d . The s i t e a t V e d d e r C r o s s i n g i s e s p e c i a l l y d i f f i c u l t t o c a r r y o u t c a l c u l a t i o n s b e c a u s e t h e r e a c h i s v e r y n o n - u n i f o r m w i t h t h e f l o w m a k i n g a s h a r p b e n d a n d c o n t r a c t i n g v e r y a b r u p t l y . As a r e s u l t t h e s l o p e may c h a n g e d u r i n g v e r y h i g h f l o w s . I n v i e w o f t h e h i g h s e n s i t i v i t y o f t h e E i n s t e i n b e d -l o a d e q u a t i o n i t w o u l d be e a s y t o i m p r o v e t h e b e d l o a d p r e -d i c t i o n b y a d j u s t i n g one o f t h e i n p u t p a r a m e t e r s s u c h a s t h e s l o p e , v e l o c i t y o r g r a i n s i z e . H o w e v e r , i t was d e c i d e d t h a t t h e b e d l o a d - d i s c h a r g e r e l a t i o n s h i p a t V e d d e r C r o s s i n g c o u l d be e s t i m a t e d more d i r e c t l y b y u s i n g t h e r e s u l t s o f t h e 19 75 f l o o d s u r v e y s a n d t h e d e r i v e d b e d l o a d r e l a t i o n a t t h e r a i l w a y b r i d g e n e a r Y a r r o w . I t was a s s u m e d t h a t t h e t h r e s h o l d c o n d i t i o n s a t V e d d e r C r o s s i n g w e r e p r e d i c t e d I l l a p p r o x i m a t e l y c o r r e c t by t h e E i n s t e i n e q u a t i o n . T h e r e f o r e t h e e n d p o i n t o f t h e b e d l o a d f u n c t i o n shown on F i g u r e 37 was f i x e d and t h e s l o p e o f t h e r e l a t i o n was a d j u s t e d b y t r i a l a n e r r o r u n t i l t h e c o m p u t e d d e p o s i t i o n on t h e f a n e x a c t l y m a t c h e d t h e s u r v e y e d q u a n t i t y . T h i s f i n a l a d o p t e d t r a n s p o r t r e l a t i o n h a s a l s o b e e n shown on F i g u r e 3 7 . U s i n g t h i s m o d i f i e d r e l a t i o n s h i p , t h e t r a n s p o r t a t V e d d e r C r o s s i n g was e s t i m a t e d t o be i n t h e o r d e r o f 20 t o 100 t i m e s t h e t r a n s p o r t b e l o w t h e r a i l w a y b r i d g e f o r f l o w s e x c e e d i n g 10,000 c f s . I n f a c t , d u r i n g t h e 1975 f l o o d t h e t o t a l v o l u m e o f s e d i m e n t t r a n s p o r t e d p a s t t h e r a i l w a y b r i d g e and i n t o t h e h e a d o f t h e V e d d e r C a n a l was p r o b a b l y o n l y a b o u t 5% o f t h e t o t a l s e d i m e n t i n f l o w a t V e d d e r C r o s s i n g . T h e r e f o r e t h e " t r a p e f f i c i e n c y " o f t h e f a n b e t w e e n V e d d e r C r o s s i n g a n d t h e r a i l w a y b r i d g e was p r o b a b l y c l o s e t o 9 5 % . I t s h o u l d be e m p h a s i z e d t h a t t h i s c a l c u l a t i o n i s b a s e d m a i n l y on f i e l d m e a s u r e m e n t s : - t h e b e d l o a d r e l a t i o n s h i p a t Y a r r o w w h i c h was d e t e r -m i n e d b y b e d l o a d m e a s u r e m e n t s a n d e x t e n d e d b y c a l c u l a t i o n s - t h e d e p o s i t i o n c o m p u t e d f r o m t h e 1975 f l o o d s u r v e y s . T h e r e f o r e i t i s b e l i e v e d t h i s e s t i m a t e i s r e a s o n a b l y a c c u r -a t e a s s u m i n g t h a t t h e d e p o s i t i o n r e p o r t e d by Tempest (1976) i s c o r r e c t . 118 CHAPTER V I I I AGGRADATION ON THE VEDDER RIVER 8.1 The Process o f Aggradation A l l u v i a l fans are d i s t i n c t i v e l a n d forms t h a t are normally a s s o c i a t e d w i t h sediment aggr a d a t i o n . The f a n below Vedder C r o s s i n g i s t y p i c a l of many streams i n B r i t i s h Columbia t h a t flow out of the mountains onto a f l a t a l l u v i a l p l a i n . U s u a l l y sediment d e p o s i t i o n on fans i s a t t r i b u t e d to a decrease i n stream competence due to the c h a r a c t e r i s -t i c decrease i n sl o p e which occurs along the channel ( L u s t i g , 1965; Hooke, 1967; M a l c o v i s h , 1974). D e p o s i t i o n can a l s o occur when the flow s p i l l s overbank and spreads over the fan s u r f a c e . G e s s l e r (1971) c a r r i e d out t h e o r e t i c a l s t u d i e s of aggradation and de g r a d a t i o n p r o c e s s e s . G e s s l e r showed t h a t r a i s i n g or lowering of the streambed was r e l a t e d to the change i n sediment t r a n s p o r t r a t e along the r i v e r a c c o r d i n g t o the sediment c o n t i n u i t y e q u a t i o n : 3G _ - c 3 z 3 x 3 t where t = time z = bed l e v e l x = d i s t a n c e along channel G = sediment t r a n s p o r t r a t e 119 G e s s l e r s t u d i e s a simple case of a flume s e t a t a s l o p e where the bed m a t e r i a l i n the channel was j u s t at the t h r e s h o l d of movement. Then a constant supply of sediment was f e d i n t o the upstream end of the channel. The r e s u l t i n g v a r i a t i o n i n bed l e v e l over time i s sum-marized i n F i g u r e 38. The a g g r a d a t i o n developed as a wedge of sediment which e v e n t u a l l y progressed downstream w i t h time. A l s o the bed developed a concave p r o f i l e which appears to be c h a r a c t e r i s t i c of aggrading c o n d i t i o n s ( G e s s l e r , 1971). E v e n t u a l l y , as a r e s u l t o f the p r o g r e s s i v e b u i l d up of the bed, a new e q u i l i b r i u m s l o p e was e s t a b l i s h e d which was steeper than the i n i t i a l one. At t h i s time a l l of the i n f l o w i n g sediment was t r a n s p o r t e d through the channel and the aggradation ceased. The processes d e s c r i b e d by G e s s l e r are comparable to d e p o s i t i o n on an a l l u v i a l fan except f o r the f a c t t h a t fans are f r e e t o s h i f t l a t e r a l l y over a wide area. T h e r e f o r e l o c a l i z e d a ggradation d u r i n g a f l o o d event can cause the flow to s p i l l out of i t s channel and cause a sudden channel s h i f t o r a v u l s i o n . As a r e s u l t , the l o c u s of d e p o s i t i o n may change over the e n t i r e f a n s u r f a c e . Aggradation on fans can be i n t e r r u p t e d f o r s e v e r a l reasons. For example, aggradation may cease when the 120 s e d i m e n t s u p p l y f r o m t h e u p s t r e a m w a t e r s h e d i s r e d u c e d . R y d e r (1970) showed t h a t many f a n s i n s o u t h - c e n t r a l B r i t i s h C o l u m b i a a r e no l o n g e r a c t i v e l y a g g r a d i n g due t o c l i m a t i c c h a n g e s a nd t o r e d u c t i o n i n t h e a v a i l a b i l i t y o f s e d i m e n t . Hooke (1967) n o t e d t h a t i n c i s i o n o f t h e f a n h e a d c o u l d o c c u r on m o d e l f a n s when t h e l o c u s o f d e p o s i t i o n s h i f t e d t o a p l a c e t h a t h a d n o t r e c e i v e d s e d i m e n t f o r s e v e r a l e p i s o d e s o f c h a n n e l s h i f t i n g . When a s h i f t t o one o f t h e s e t o p o g r a p h i c l o w s t o o k p l a c e , d e g r a d a t i o n o c c u r r e d n e a r t h e f a n h e a d i n r e s p o n s e t o t h e s u d d e n i n c r e a s e i n s l o p e . T h i s d e g r a d a t i o n l a s t e d u n t i l t h e l o w a r e a was b u i l t up t o t h e l e v e l o f t h e s u r r o u n d i n g f a n . M a l c o v i s h (1974) c a r r i e d o u t a number o f m o d e l s t u d i e s t o d e t e r m i n e t h e e f f e c t o f c o n s t r u c t i n g b r i d g e s and g u i d e b a n k s a c r o s s f a n s . When g u i d e b a n k s w e r e p l a c e d on t h e f a n t o r e s t r i c t t h e l a t e r a l s h i f t i n g o f t h e c h a n n e l , a c h a n g e i n t h e d e p o s i t i o n a l p a t t e r n was n o t e d . I n i t i a l d o w n c u t t i n g o c c u r r e d w i t h i n t h e c o n s t r u c t i o n w h i l e a d i s t i n c t i v e c o n i c a l f a n segment was f o r m e d b e l o w t h e b r i d g e c r o s s i n g . A c c o r d i n g t o M a l c o v i s h , t h i s z o n e o f d e p o s i t i o n s e r v e d as a h i n g e p o i n t f o r f u r t h e r up-s t r e a m a g g r a d a t i o n , s o t h a t t h e i n i t i a l d e g r a d a t i o n w i t h -i n t h e g u i d e b a n k s was e v e n t u a l l y o f f s e t by d e p o s i t i o n . I n v i e w o f t h e c o n s i d e r a b l e c h a n n e l i z a t i o n w o r k t h a t h a s 1 2 1 b e e n c a r r i e d o u t on t h e l o w e r V e d d e r R i v e r , M a l c o v i s h ' s o b s e r v a t i o n s a r e v e r y r e l e v a n t . A l t h o u g h some o f t h e p r o c e s s e s g o v e r n i n g a g g r a d a -t i o n a r e w e l l u n d e r s t o o d , s u c h a s t h e s e d i m e n t c o n t i n u i t y r e l a t i o n s h i p , t h e r e a r e s t i l l many d i f f i c u l t i e s i n v o l v e d ' i n m a k i n g q u a n t i t a t i v e p r e d i c t i o n s . The m a i n d i f f i c u l t y l i e s i n d e f i n i n g a s e d i m e n t t r a n s p o r t r e l a t i o n s h i p a l o n g t h e c h a n n e l . As was shown i n t h e p r e v i o u s c h a p t e r , e v e n w i t h m e a s u r e d h y d r a u l i c g e o m e t r y d a t a , e s t i m a t e s o f b e d -l o a d may be i n e r r o r by a t l e a s t a f a c t o r o f t w o . A n o t h e r m a j o r c o m p l i c a t i o n i s t h a t v e r y l i m i t e d s t u d y h a s gone i n t o t h e u n s t e a d y n a t u r e o f s e d i m e n t movement a n d a g g r a -d a t i o n . F o r e x a m p l e , d o e s m o s t s e d i m e n t d e p o s i t i o n o c c u r on t h e f a l l i n g l i m b o f a f l o o d o r i s i t c o i n c i d e n t w i t h t h e f l o o d p e a k ? U n t i l a d v a n c e s a r e made i n s e d i m e n t t r a n s p o r t t h e o r y , q u a n t i t a t i v e p r e d i c t i o n s o f a g g r a d a -t i o n w i l l be d i f f i c u l t t o make and w i l l r e l y t o a l a r g e d e g r e e on s y s t e m a t i c o b s e r v a t i o n s o f c h a n n e l b e h a v i o u r . 8.2 H i s t o r i c a l D e p o s i t i o n R a t e s on t h e V e d d e r R i v e r O v e r t h e l a s t f ew d e c a d e s s e v e r a l d i f f e r e n t a g e n -c i e s h a v e made e s t i m a t e s o f t h e r a t e o f d e p o s i t i o n on t h e V e d d e r R i v e r . T h e s e g r o u p s h a v e i n c l u d e d t h e B.C. W a t e r R e s o u r c e s S e r v i c e ( M a r r , 1964; T e m p e s t , 1 9 7 6 ) , W a t e r S u r v e y o f C a n a d a (W.S.C., 1971-1975) a nd t h e I n t e r n a t i o n a l P a c i f i c S a l m o n C o m m i s s i o n ( I . P . S . C . , 1 9 7 7 ) . The e s t i m a t e d 122 d e p o s i t i o n r a t e s t h a t h a v e b e e n r e p o r t e d o r c a n be com-p u t e d f r o m d a t a s u p p l i e d by t h e s e a g e n c i e s i s s u m m a r i z e d i n T a b l e 23. T h e s e e s t i m a t e s a r e a l l f o r t h e p e r i o d b e f o r e t h e December 1975 f l o o d . On t h e b a s i s o f r i v e r s u r v e y s c a r r i e d o u t i n 1958 and 1 9 6 3 , M a r r (1964) c o n c l u d e d t h a t w h i l e c o n s i d e r a b l e c h a n g e s o c c u r r e d a t e a c h s e c t i o n , t h e r e was no c o n s i s t e n t p a t t e r n a l o n g t h e V e d d e r C a n a l o r t h e r i v e r t o e s t a b l i s h an a g g r a d i n g c o n d i t i o n . M a r r a l s o c a r r i e d o u t some b e d -l o a d t r a n s p o r t c a l c u l a t i o n s and c o n c l u d e d t h a t t h e a v e r -age a n n u a l t r a n s p o r t on t h e f a n was a b o u t 139,000 c u b i c y a r d s p e r y e a r . F u r t h e r m o r e , i t was c o n c l u d e d t h a t a l l o f t h i s m a t e r i a l was t r a n s p o r t e d t h r o u g h t h e c a n a l and d e p o s i t e d i n t h e F r a s e r R i v e r . M a r r ' s c a l c u l a t i o n s w e r e b a s e d on h y d r a u l i c c o n d i t i o n s on t h e u p p e r p a r t o f t h e f a n a n d i t was n o t e s t a b l i s h e d w h e t h e r t h e c a n a l h a d t h e c a p a c i t y t o t r a n s p o r t t h i s s e d i m e n t l o a d t o t h e F r a s e r . A l s o , no m e n t i o n was made o f t h e s e d i m e n t s o r t i n g w h i c h o c c u r s a l o n g t h e r i v e r i n d i c a t i n g t h a t s e l e c t i v e d e p o s i -t i o n i s t a k i n g p l a c e . W a t e r S u r v e y o f C a n a d a r e s u r v e y e d 11 c r o s s s e c t i o n s l o c a t e d b e t w e e n t h e c a n a l a n d V e d d e r C r o s s i n g s e v e r a l t i m e s b e t w e e n 1971 and 1975. The c r o s s s e c t i o n s showed b o t h s c o u r a n d f i l l c o u l d o c c u r f r o m one y e a r t o t h e n e x t , h o w e v e r , o v e r t h e e n t i r e p e r i o d n e t a g g r a d a t i o n o c c u r r e d a t mo s t l o c a t i o n s . No e s t i m a t e o f t h e v o l u m e 1 2 3 o f s e d i m e n t a t i o n was made, p r o b a b l y b e c a u s e t h e s e c t i o n s w e r e s p a c e d t o o f a r a p a r t t o a c h i e v e r e a s o n a b l y a c c u r a t e r e s u l t s . T e m p e s t (1976) r e p o r t e d t h a t a b o u t 258,000 c u b i c y a r d s o f s e d i m e n t was d e p o s i t e d b e t w e e n t h e r a i l w a y b r i d g e and V e d d e r C r o s s i n g d u r i n g t h e 1975 f l o o d . F u r t h e r m o r e , i t was e s t i m a t e d t h a t a b o u t 235,000 c u b i c y a r d s was d e p o s -i t e d i n t h i s same a r e a b e t w e e n 1972 and J u l y 1 975. I n c o m p a r i s o n , t h e I n t e r n a t i o n a l P a c i f i c S a l m o n C o m m i s s i o n ( I . P . S . C . ) e s t i m a t e d t h a t 370,000 c u b i c y a r d s was d e p o s -i t e d b e t w e e n t h e r a i l w a y b r i d g e a n d P e a c h e Road ( a b o u t one m i l e b e l o w V e d d e r C r o s s i n g ) b e t w e e n 1957 and 1976. T h i s was b a s e d on 12 s e c t i o n s s u r v e y e d b y t h e I . P . S . C . i n 1957 and 13 s e c t i o n s s u r v e y e d by t h e B.C. W a t e r R e s o u r c e s S e r v i c e (B.C.W.R.S.) i n J a n u a r y 1976. I t was a l s o s t a t e d t h a t t h e a v e r a g e b e d l e v e l r o s e 1.6 f e e t i n 19 y e a r s . I f . t h e 1975/1976 d e p o s i t i o n b e t w e e n t h e r a i l -way b r i d g e a n d P e a c h e Road r e p o r t e d by Tempest (197 6) i s s u b t r a c t e d f r o m t h e c o r r e s p o n d i n g 1957/1976 d e p o s i -t i o n , t h e n t h e n e t d e p o s i t i o n i n t h i s 2.6 m i l e r e a c h b e t w e e n 1957 and J u l y 1975 i s o n l y 192,000 c u b i c y a r d s . T h i s a v e r a g e s o n l y a b o u t 10,000 c u b i c y a r d s p e r y e a r w h i c h i s l e s s t h a n o n e - t h i r d o f t h e r a t e e s t i m a t e d by Tempest b e t w e e n 1972-1975 i n t h e 1.6 m i l e r e a c h b e t w e e n t h e r a i l -way b r i d g e a n d F o r d Road. 124 The o n l y d i r e c t c o m p a r i s o n o f c r o s s s e c t i o n s b e l o w t h e r a i l w a y b r i d g e t h a t c a n be made i s f r o m t h e e i g h t 1958/1963 s e c t i o n s r e p o r t e d b y M a r r (1964) a nd t h e s i x 1971/1975 s e c t i o n s r e p o r t e d by t h e W a t e r S u r v e y o f C a n a d a . C o m p a r i s o n o f t h i s d a t a showed t h e mean b e d l e v e l r o s e 0.2 f e e t b e t w e e n 1958-1963 a nd 0.5 f e e t b e t w e e n 1971 and 1975. The c o r r e s p o n d i n g v o l u m e s d e p o s i t e d i n t h e s e p e r i o d s c a n n o t be e s t i m a t e d b e c a u s e o f t h e v e r y w i d e s p a c i n g b e t w e e n c r o s s s e c t i o n s . B a s e d on t h e d a t a a v a i l a b l e , i t was c o n c l u d e d t h a t a l l o f t h e a g g r a d a t i o n e s t i m a t e s p r i o r t o 1975 a r e v e r y a p p r o x i m a t e . T h e r e h a s b e e n no s y s t e m a t i c l o n g t e r m o b s e r v a t i o n s on t h e r i v e r a n d mos t o f t h e s u r v e y s c a r r i e d o u t by t h e d i f f e r e n t a g e n c i e s o v e r t h e y e a r s h a v e n o t b e e n c o o r d i n a t e d . As a r e s u l t , o n l y c h a n n e l c h a n g e s o v e r r e l a t i v e l y s h o r t p e r i o d s o f t i m e c a n be e s t a b l i s h e d ( 1 9 5 8 -1963 , 1 9 7 1 - 1 9 7 5 ) . I n t h e c a s e o f t h e I . P . S . C . e s t i m a t e s , i t seems u n l i k e l y t h a t t h e 1957 c r o s s s e c t i o n s e s t a -b l i s h e d by t h e I . P . S . C . w o u l d a l i g n e x a c t l y w i t h t h e 1975-1976 s e c t i o n s e s t a b l i s h e d by t h e B.C.W.R.S. i n v i e w o f t h e m a j o r c h a n g e s i n c h a n n e l a l i g n m e n t t h a t o c c u r r e d o v e r t h e y e a r s . A n o t h e r p r o b l e m w i t h some o f t h e e s t i -m a t e s i s t h a t p r i o r t o 1964 a c o n s i d e r a b l e amount o f d r e d g i n g t o o k p l a c e on t h e l o w e r r i v e r . U n f o r t u n a t e l y , t h e r e a p p e a r s t o be no way t o e s t i m a t e t h e amount o f s e d i m e n t t h a t was r e m o v e d f r o m t h e r i v e r a r o u n d t h i s 125 t i m e . F i n a l l y , some e s t i m a t e s o f d e p o s i t i o n do n o t a c c o u n t f o r s y s t e m a t i c c h a n g e s i n t h e d e p o s i t i o n p a t t e r n w h i c h h a v e o c c u r r e d b o t h a l o n g t h e r i v e r a n d o v e r t i m e . F o r e x a m p l e , t h e 1957-1975 e s t i m a t e i n d i c a t e s o n l y t h e n e t d e p o s i t i o n b e t w e e n t h e r a i l w a y b r i d g e a n d P e a c h e Road. H o w e v e r , a s s u b s e q u e n t d a t a w i l l show, a l a r g e amount o f d e g r a d a t i o n o c c u r r e d d u r i n g a p o r t i o n o f t h i s p e r i o d s o t h a t t h e t o t a l amount o f s e d i m e n t t r a n s p o r t e d i n t o t h i s r e a c h was much g r e a t e r t h a n t h e e s t i m a t e w o u l d i n d i c a t e . S i n c e i t d o e s n o t a p p e a r p o s s i b l e t o d i r e c t l y com-p a r e t h e e a r l y c r o s s s e c t i o n s , i t was d e c i d e d t o p l o t p r o f i l e s s h o w i n g t h e mean b ed e l e v a t i o n s o f e a c h s u r v e y . The mean b e d l e v e l was c o m p u t e d f o r a l l o f t h e a g e n c y c r o s s s e c t i o n s ( e x c e p t I . P . S . C , 1957) a c c o r d i n g t o t h e f o l l o w i n g d e f i n i t i o n : E = EE.Ax w h e r e E. i s t h e a v e r a g e b e d e l e v a -1 x 3 ~ t i o n f o r t h e c h a n n e l i n c r e m e n t Ax. x X i s t h e a c t i v e c h a n n e l w i d t h . The b e d p r o f i l e s c o m p u t e d f r o m M a r r ' s 1963 d a t a and f r o m t h e W.S.C. and B.C.W.R.S. 1975 d a t a a r e p l o t t e d i n F i g u r e 39. C o m p a r i s o n o f t h e s e p r o f i l e s shows t h r e e m a i n f e a t u r e s : - r e l a t i v e l y l i t t l e c h a n g e o c c u r r e d on t h e u p p e r p a r t o f t h e f a n b e t w e e n P e a c h e Road a n d V e d d e r C r o s s i n g . 126 - d e g r a d a t i o n o c c u r r e d b e t w e e n t h e r a i l w a y b r i d g e n e a r Y a r r o w a n d F o r d Road. - a g g r a d a t i o n o c c u r r e d d o w n s t r e a m o f t h e r a i l w a y b r i d g e t o n e a r t h e h e a d o f t h e V e d d e r C a n a l . The d e g r a d a t i o n i n t h e 1.6 m i l e r e a c h b e t w e e n t h e r a i l w a y b r i d g e and F o r d Road r a n g e d f r o m b e t w e e n 2.0 f e e t a nd 4.5 f e e t . I t i s b e l i e v e d t h i s d e g r a d a t i o n was c a u s e d by t h e e x t e n s i v e c h a n n e l i z a t i o n t h a t was c a r r i e d o u t a b o v e t h e r a i l w a y b r i d g e b e t w e e n 1964 and 1968. S i n c e t h e a c t i v e c h a n n e l w i d t h was r e d u c e d by a s much a s 50 p e r c e n t , t h e c h a n n e l v e l o c i t i e s c o u l d h a v e b e e n n e a r l y d o u b l e d i n t h i s r e a c h s h o r t l y a f t e r c h a n n e l i z a t i o n . As a r e s u l t t h e s e d i m e n t t r a n s p o r t c a p a c i t y w o u l d h a v e b e e n i n c r e a s e d i n t h e n a r r o w c h a n n e l a n d w o u l d h a v e e x c e e d e d t h e s e d i m e n t i n f l o w f r o m t h e u p p e r p a r t o f t h e f a n . F i g u r e 4 0 c o m p a r e s a c h a n n e l c r o s s s e c t i o n s u r v e y e d n e a r H o p e d a l e Road i n 1975 w i t h a c r o s s s e c t i o n s u r v e y e d i n 1963 a t t h e same l o c a t i o n . T h i s shows t h a t when t h e c h a n n e l w i d t h was r e d u c e d f r o m a b o u t 700 f e e t t o 350 f e e t , t h e mean b e d l e v e l d r o p p e d a b o u t 4.6 f e e t w h i l e t h e e l e v a t i o n o f t h e d e e p e s t p o r t i o n o f t h e c h a n n e l ( t h e t h a l w e g ) d r o p p e d a b o u t 9.0 f e e t . A v e r y r o u g h o r d e r o f m a g n i t u d e e s t i m a t e o f t h e d e g r a d a t i o n i n t h i s r e a c h i s a p p r o x i m a t e l y 300,000 c u b i c y a r d s , a s s u m i n g t h e a v e r a g e c h a n n e l w i d t h i n 1975 was a b o u t 300 f e e t . The t i m e r e q u i r e d t o d e v e l o p t h i s 127 d e g r a d a t i o n c a n n o t be e s t i m a t e d p r e c i s e l y , h o w e v e r , t h e W.S.C. s u r v e y s b e t w e e n 1971 and 1975 show t h i s r e a c h was s t a b l e o r p o s s i b l y a g g r a d i n g . T h e r e f o r e , m o s t d e g r a d a t i o n p r o b a b l y o c c u r r e d s o o n a f t e r c h a n n e l i z a t i o n b e g a n and e n d e d by a b o u t 1970. B e t w e e n 1964 and 1970 t h e l a r g e s t f l o w r e a c h e d o n l y 15,400 c f s on J u n e 2 n d , 1968, and t h e d a i l y d i s c h a r g e e x c e e d e d 10,000 c f s on o n l y s i x d a y s . The a g g r a d a t i o n b e l o w t h e r a i l w a y b r i d g e a p p e a r s t o be i n t h e f o r m o f a wedge o f s e d i m e n t e x t e n d i n g a b o u t 1.25 m i l e s i n l e n g t h and h a v i n g a maximum h e i g h t o f a b o u t 3.8 f e e t j u s t b e l o w t h e b r i d g e . T h i s wedge o f s e d i m e n t c r e a t e s an o b v i o u s "hump" i n t h e s t r e a m b e d p r o f i l e ( F i g u r e 3 9 ) . A v e r y r o u g h c a l c u l a t i o n shows t h a t t h e a p p r o x i m a t e v o l u m e o f s e d i m e n t d e p o s i t e d i n t h i s a r e a was a b o u t 150,000 t o 200,000 c u b i c y a r d s . S i n c e d r e d g i n g i s known t o h a v e o c c u r r e d b e l o w t h e r a i l w a y b r i d g e i n t h e m i d -1960' s, t h e a c t u a l amount o f m a t e r i a l d e p o s i t e d i n t h i s r e a c h c o u l d h a v e b e e n c o n s i d e r a b l y g r e a t e r . I t i s a p p a r e n t t h a t t h e m a t e r i a l d e p o s i t e d b e l o w t h e b r i d g e was d e r i v e d f r o m t h e d e g r a d a t i o n o c c u r r i n g i n t h e c h a n n e l i z e d r e a c h i m m e d i a t e l y u p s t r e a m . T h i s s u g -g e s t s t h e s e d i m e n t was s w e p t t h r o u g h t h e c h a n n e l i z e d r e a c h and was d e p o s i t e d i n t h e f i r s t a r e a w h e r e t h e c h a n -n e l w i d t h e x p a n d e d . As t h i s wedge o f s e d i m e n t f o r m e d b e l o w t h e b r i d g e and as t h e c h a n n e l l o w e r e d i n t h e c o n -s t r i c t i o n , t h e s l o p e t h r o u g h t h e s e two r e a c h e s w o u l d h a v e 128 g r a d u a l l y c h a n g e d . T h i s w o u l d h a v e l e d t o a d e c r e a s e i n s e d i m e n t t r a n s p o r t t h r o u g h t h e c o n s t r i c t i o n , c e a s i n g o f d e g r a d a t i o n a n d e v e n t u a l r e e s t a b l i s h m e n t o f a g g r a d a t i o n u p s t r e a m o f t h e b r i d g e . T h i s i s s i m i l a r t o t h e l a b o r a -t o r y o b s e r v a t i o n s r e p o r t e d by M a l c o v i s h ( 1 9 7 4 ) . I f t h e b e d l o a d t r a n s p o r t r e l a t i o n e s t a b l i s h e d b y t h e W a t e r S u r v e y o f C a n a d a ' s m e a s u r e m e n t p r o g r a m b e t w e e n 1971-1975 i s c o m p a r e d w i t h t h e q u a n t i t y o f s e d i m e n t d e p o s i t e d b e l o w t h e r a i l w a y b r i d g e b e t w e e n 1963 and 1975, t h e r e i s an o b v i o u s d i s c r e p a n c y . U s i n g t h i s b e d l o a d r e l a t i o n , t h e r e i s no p o s s i b l e way f o r 150,000-20 0,000 c u b i c y a r d s t o be t r a n s p o r t e d p a s t t h e Y a r r o w c a b l e w a y and d e p o s i t e d n e a r t h e h e a d o f t h e c a n a l . I n f a c t u n d e r t h e f l o w c o n d i t i o n s t h a t e x i s t e d b e t w e e n 1963 and 1975 t h e p r e d i c t e d d e p o s i t i o n amount t o a b o u t 10% o f t h e e s t i -m a t e d v a l u e . A l t h o u g h b o t h t h e b e d l o a d m e a s u r e m e n t s and t h e c o m p u t e d d e p o s i t i o n v o l u m e may be s u b j e c t t o c o n s i d -e r a b l e e r r o r s , i t i s b e l i e v e d t h e s e a r e n o t s u f f i c i e n t t o a c c o u n t f o r s u c h a l a r g e d i f f e r e n c e . I t i s much more l i k e l y t h a t t h e s e d i m e n t t r a n s p o r t c a p a c i t y a t t h e b r i d g e g r a d u a l l y r e d u c e d a s t h e s l o p e a n d t r a n s p o r t c a p a c i t y i n t h e c o n s t r i c t i o n a l s o c h a n g e d . A l s o , when d e g r a d a t i o n was f i r s t g o i n g on i n t h e c o n s t r i c t i o n , t h e h i g h v e l o c i t y f l o w e m e r g i n g f r o m t h e b r i d g e m u s t h a v e r e s e m b l e d a j e t and t h i s w o u l d a l s o h a v e t e n d e d t o sweep some o f t h e s e d i m e n t c o n s i d e r a b l y f u r t h e r d o w n s t r e a m t h a n m i g h t 129 o r d i n a r i l y be p r e d i c t e d . There i s one f i n a l source o f data t h a t can p r o v i d e a d d i t i o n a l i n f o r m a t i o n on h i s t o r i c a l channel changes on the Vedder R i v e r . These are the gauge r e c o r d s c o l l e c t e d at Yarrow and Vedder C r o s s i n g which can be used t o d e t e r -mine whether any s y s t e m a t i c changes have o c c u r r e d i n the st a g e - d i s c h a r g e r e l a t i o n s at the two s i t e s . In order to determine whether systematic trends e x i s t , the water l e v e l c o r r e s p o n d i n g to a s p e c i f i c d i s c h a r g e was p l o t t e d over the p e r i o d of the gauge r e c o r d . The r e s u l t i n g p l o t of stage vs. time i s termed a s p e c i f i c gauge r e c o r d and a c c o r d i n g to Blench (1969) i t i s one of the most power-f u l s i n g l e t e s t s to determine whether a r i v e r i s " i n -regime." F i g u r e 41 shows the s p e c i f i c gauge p l o t a t the Yarrow gauge. T h i s was e s t a b l i s h e d from continuous stage measurements between 1952-1972 and m i s c e l l a n e o u s measure-ments between 197 3-1977. T h i s p l o t shows t h a t the r i v e r has been aggrading n e a r l y c o n t i n u o u s l y except f o r a s h o r t p e r i o d between 1960-1964. The aggrada t i o n r a t e between 1964-1975 t o t a l l e d about 3.6 f e e t o r about 0.30 f e e t / y e a r . T h i s i s n e a r l y i d e n t i c a l to the mean bed r i s e e s t i m a t e d from the 1963/1975 channel surveys. I t i s b e l i e v e d t h a t the apparent bed lo w e r i n g i n d i -cated between 1960-1964 r e f l e c t s the l a r g e amount of dredging and channel c l e a r i n g work t h a t was c a r r i e d out 130 a r o u n d t h i s t i m e ( T a b l e 1 ) . When t h e d r e d g i n g was s t o p p e d i n 1964 and t h e c h a n n e l i z a t i o n w ork commenced u p s t r e a m o f t h e r a i l w a y b r i d g e , t h e c h a n n e l a t t h e gauge l o c a t i o n r o s e 2.0 f e e t i n one y e a r . I t i s u n f o r t u n a t e t h a t t h e Y a r r o w gauge h ad b e e n d i s c o n t i n u e d a t t h e t i m e o f t h e 1975 f l o o d . H o w e v e r , t h e a u t h o r s u r v e y e d t h e w a t e r l e v e l a t t h e gauge s i t e i n 1976 a n d 1977 i n o r d e r t o d e t e r m i n e t h e i m p a c t o f t h e f l o o d a n d t h e s u b s e q u e n t d r e d g i n g o p e r a t i o n s . The gauge l e v e l was f o u n d t o i n c r e a s e by a b o u t 0.4 f e e t b e t w e e n J.uly 1975 and May 1976, w h i c h i s n o t v e r y d i f f e r e n t f r o m t h e l o n g t e r m a v e r a g e r i s e . H o w e v e r , t h e P h a s e I l i m i t e d d r e d g i n g p r o g r a m h a d b e e n c a r r i e d o u t i n b e t w e e n t h i s t i m e w h i c h c o u l d h a v e r e d u c e d t h e w a t e r l e v e l s s l i g h t l y . The l a r g e d r o p o f a b o u t 3.3 f e e t b e t w e e n 1976-1977 r e f l e c t s t h e m a s s i v e P h a s e I I d r e d g i n g p r o g r a m t h a t was c a r r i e d o u t i n 1976. C o n s i d e r i n g t h a t t h e Y a r r o w gauge p r o v i d e d t h e o n l y c o n t i n u o u s l o n g t e r m r e c o r d o f a g g r a d a t i o n on t h e V e d d e r R i v e r , i t seems v e r y p o o r p l a n n i n g t o h a v e d i s c o n t i n u e d i t s o p e r a t i o n . The s p e c i f i c gauge p l o t a t V e d d e r C r o s s i n g e x t e n d s f r o m b e t w e e n 1918-1929 a nd 1951-1975 ( F i g u r e 4 2 ) . How-e v e r , due t o a s h i f t i n t h e g a u g e ' s l o c a t i o n , t h e two s e t s o f r e c o r d s c a n n o t be r e l a t e d . The e a r l i e s t p a r t o f t h e r e c o r d shows t h e gauge l e v e l d r o p p e d n e a r l y 4.0 131 f e e t i n t h e f i v e y e a r p e r i o d b e t w e e n 1 9 1 8 - 1 9 2 3 . T h i s c h a n g e o c c u r r e d o n l y one y e a r a f t e r t h e f l o o d o f r e c o r d i n 1917 and o n l y a b o u t 25 y e a r s a f t e r t h e p e r i o d o f m a j o r c h a n n e l s h i f t i n g i n 1894. I t i s n o t known w h e t h e r t h e a p p a r e n t b e d - l o w e r i n g r e s u l t e d f r o m c o n s t r u c t i o n a c t i v i t y w h i c h was c a r r i e d o u t t o p r e v e n t t h e r i v e r f r o m s h i f t i n g down one o f i t s f o r m e r c h a n n e l s o r f r o m n a t u r a l d e g r a d a -t i o n . M a r r (1964) showed an e a r l y map n e a r V e d d e r C r o s s i n g i n d i c a t i n g t h a t a s t o n e r e v e t m e n t was i n - p l a c e b y 1916 a l o n g t h e n o r t h b a n k . M a r r a l s o m e n t i o n e d t h a t f u r t h e r w o r k was c a r r i e d o u t a f t e r t h e 1917 f l o o d b e t w e e n 1 9 2 1 -1928. A s shown by t h e c r o s s s e c t i o n s i n F i g u r e 2 8 , t h e c h a n n e l n e a r V e d d e r C r o s s i n g i s c l o s e t o b e i n g e n t r e n c h e d , w i t h t h e b a n k f u l l d e p t h i n t h e o r d e r o f 15 f e e t . I n a d d i t i o n a l o w t e r r a c e a p p r o x i m a t e l y 10 f e e t a b o v e t h e s u r r o u n d i n g f l o o d p l a i n c a n a l s o be i d e n t i f i e d i m m e d i a t e l y u p s t r e a m o f V e d d e r C r o s s i n g . T h e s e f e a t u r e s s u g g e s t t h a t r e c e n t d e g r a d a t i o n h a s o c c u r r e d n e a r t h e h e a d o f t h e f a n and f o r some d i s t a n c e u p s t r e a m a s w e l l . Some d e g r a d a t i o n c o u l d p r o b a b l y be e x p e c t e d when t h e e n t i r e C h i l l i w a c k R i v e r f l o w was f o r c e d down V e d d e r C r e e k i n s t e a d o f b e i n g s p l i t i n t o t h r e e c h a n n e l s a s i t was p r i o r t o t h e t u r n o f t h e c e n t u r y . T h e r e f o r e , i n some r e s p e c t s , t h i s e a r l y d e g r a d a t i o n w o u l d h a v e d e v e l o p e d u n d e r s i m i l a r c o n d i t i o n s a s t h e d e g r a d a t i o n i n t h e c h a n n e l i z e d r e a c h a b o v e t h e r a i l w a y b r i d g e . 132 B e t w e e n 1951 t o t h e p r e s e n t t h e gauge a t V e d d e r C r o s s i n g showed a s l o w a l t e r n a t i n g p a t t e r n o f s c o u r and f i l l , w i t h a g g r a d a t i o n o c c u r r i n g b e t w e e n 1951-1958 and d e g r a d a t i o n o c c u r r i n g b e t w e e n 1959-1968. I t w o u l d be v e r y i n t e r e s t i n g t o know how t h e r i v e r was b e h a v i n g up-s t r e a m o f V e d d e r C r o s s i n g t h r o u g h o u t t h i s p e r i o d . Un-f o r t u n a t e l y , t h e o n l y d a t a a v a i l a b l e i s t h r e e c r o s s s e c t i o n s s u r v e y e d i n 1958 and 1963 ( M a r r , 1 9 6 4 ) . A l l t h r e e s e c t i o n s showed n e t a g g r a d a t i o n b e t w e e n 1958-1963 d u r i n g t h e p e r i o d when t h e f a n h e a d was s l o w l y l o w e r i n g . T h i s may i n d i c a t e t h a t s e d i m e n t was b e i n g t r a p p e d a b o v e V e d d e r C r o s s i n g d u r i n g t h i s p e r i o d so t h a t t h e a c t u a l s u p p l y t o t h e f a n was v e r y l o w . T h e n , when a m a j o r f l o o d s u c h as i n 1975 o c c u r r e d , t h i s s e d i m e n t i s w a s h e d t h r o u g h t h e n a r r o w gap a t V e d d e r C r o s s i n g a nd t r a n s p o r t e d on t h e f a n . 8.3 A g g r a d a t i o n D u r i n g t h e 1975 F l o o d The d e p o s i t i o n r e s u l t i n g f r o m t h e December 1975 f l o o d h a s a l r e a d y b e e n m e n t i o n e d a number o f t i m e s i n t h i s c h a p t e r a nd i n e a r l i e r c h a p t e r s a s w e l l . T e m p e s t (1976) e s t i m a t e d t h e d e p o s i t i o n b e t w e e n t h e r a i l w a y b r i d g e and V e d d e r C r o s s i n g was d i s t r i b u t e d a s f o l l o w s : r a i l w a y b r i d g e - Browne Rd. (1.1 mi) = 72,000 c u . y d s . Browne Rd. - F o r d Rd. (0.5 mi) = 52, 000 c u . y d s . 133 F o r d Rd. - P e a c h e Rd. (1.0 mi) = 58,000 c u . y d s . P e a c h e Rd. - V e d d e r C r o s s i n g (1.1 mi) = 80,000 c u . y d s . T h i s e s t i m a t e was b a s e d on c r o s s s e c t i o n s s u r v e y e d i n J u l y 19 75 and J a n u a r y 1976. However, i t a p p e a r s t h a t a c e r t a i n amount o f e x t r a p o l a t i o n was r e q u i r e d t o d e t e r -m i n e t h i s d e p o s i t i o n s i n c e t h e 1975 c r o s s s e c t i o n s d i d n o t e x t e n d t h r o u g h o u t t h e e n t i r e r e a c h . F o r t h e p u r p o s e s o f t h i s s t u d y , t h e numbers w i l l be a c c e p t e d a s r e a s o n a b l y a c c u r a t e e s t i m a t e s . I n o r d e r t o d e t e r m i n e how t h e a g g r a d a t i o n v a r i e d a l o n g t h e r i v e r , t h e n e t a r e a o f d e p o s i t i o n o r s c o u r a n d t h e mean b e d l e v e l c h a n g e w e r e c o m p u t e d f o r e a c h o f t h e 13 c r o s s s e c t i o n s p r o v i d e d by t h e B.C.W.R.S. T h e s e r e -s u l t s i n d i c a t e d t h e a v e r a g e b e d l e v e l r i s e was a b o u t 0.75 f e e t and r a n g e d f r o m v i r t u a l l y no c h a n g e t o a b o u t 2.0 f e e t . F i g u r e 43 shows a p l o t o f t h e n e t c h a n n e l a r e a c h a n g e , mean b e d l e v e l c h a n g e and c h a n n e l w i d t h a l o n g t h e r i v e r . The m o s t i n t e r e s t i n g f e a t u r e o f t h i s g r a p h i s t h e a p p a r e n t r e l a t i o n s h i p b e t w e e n c h a n n e l d e p o s i t i o n a n d b o t t o m w i d t h . The g r e a t e s t d e p o s i t i o n c o n s i s t e n t l y o c c u r r e d i n r e a c h e s w h e r e t h e w i d t h i n c r e a s e d a b r u p t l y w h i l e t h e c h a n n e l showed v i r t u a l l y no n e t c h a n g e i n some o f t h e c o n t r a c t i o n s . The z o n e s w h e r e t h e d e p o s i t i o n was g r e a t e s t i n c l u d e d : 134 - t h e v e r y w i d e a r e a o f b a r s a n d i s l a n d s n e a r P e a c h e Rd. - t h e b r a i d e d r e a c h n e a r F o r d Rd. - n e a r H o p e d a l e Rd. w here t h e c h a n n e l w i d t h i n c r e a s e s f r o m a b o u t 200 f e e t t o 330 f e e t . A l l o f t h e s e r e a c h e s c o u l d be c h a r a c t e r i z e d a s f l o w e x -p a n s i o n s w h i c h show a b r u p t i n c r e a s e s i n w i d t h o v e r r e l a -t i v e l y s h o r t d i s t a n c e s . The a r e a s w h i c h r e m a i n e d r e l a t i v e l y s t a b l e a f t e r t h e f l o o d i n c l u d e d : - t h e s h o r t r e a c h u p s t r e a m o f F o r d Rd. w h e r e t h e c h a n n e l f l o w s i n a s i n g l e c h a n n e l - i n t h e c e n t r e o f t h e c h a n n e l i z e d r e a c h w h e r e t h e w i d t h h a s b e e n r e d u c e d t o a b o u t 20 0 f e e t . The r e s u l t s shown i n F i g u r e 43 s u g g e s t s t h a t d e p o s i t i o n d e p e n d e d more on w h e t h e r t h e f l o w was e x p a n d i n g o r c o n -t r a c t i n g t h a n t h e a b s o l u t e w i d t h . A s a r e s u l t , p r o v i d i n g a n a r r o w c h a n n e l w i l l n o t n e c e s s a r i l y i n s u r e t h e r i v e r w i l l r e m a i n s e l f - s c o u r i n g d u r i n g a m a j o r f l o o d . When t h e c h a n n e l c h a n g e s s u r v e y e d by t h e W a t e r S u r v e y o f C a n a d a b e t w e e n 19 71 a n d 197 5 w e r e p l o t t e d i n a s i m i l a r f a s h i o n a s F i g u r e 4 3 , t h e r e s u l t s a p p e a r e d e x a c t l y o p p o s i t e t o t h e p a t t e r n o b s e r v e d i n 1 9 7 5 - 1 9 7 6 . B e t w e e n 1971-1975 m o s t d e p o s i t i o n o c c u r r e d i n t h e n a r -r o w e r r e a c h e s and r e l a t i v e l y l i t t l e c h a n g e o c c u r r e d i n t h e w i d e r a r e a s . T h e r e f o r e , t h e p a t t e r n o f d e p o s i t i o n 135 d u r i n g t h e 1975 f l o o d may n o t be c o n s i s t e n t f r o m y e a r t o y e a r . 8.4 P r e d i c t i o n o f F u t u r e A g g r a d a t i o n The d e p o s i t i o n t h a t o c c u r r e d d u r i n g t h e 1975 f l o o d c a u s e d c o n s i d e r a b l e d i s r u p t i o n t o t h e V e d d e r c h a n n e l and was p a r t i a l l y r e s p o n s i b l e f o r t h e h i g h w a t e r l e v e l s a l o n g t h e r i v e r . H o wever, t h e 1975 f l o o d was r e a l l y a m i n o r e v e n t h a v i n g a r e t u r n p e r i o d o f o n l y a b o u t 10 y e a r s . I f a 50 o r 100 y e a r f l o o d o c c u r r e d , t h e maximum i n s t a n t a n e o u s d i s c h a r g e c o u l d p r o b a b l y r e a c h 4 0,000-50,000 c f s and t h e q u a n t i t y o f s e d i m e n t d e p o s i t e d a l o n g t h e r i v e r c o u l d p o s -s i b l y be much l a r g e r t h a n t h e 258,000 c u b i c y a r d s t h a t was e s t i m a t e d f o r t h e 1975 f l o o d . The c o m p u t e d b e d l o a d t r a n s p o r t r a t e s a t t h e r a i l w a y b r i d g e a n d a t V e d d e r C r o s s i n g d e r i v e d i n C h a p t e r V I I c a n be u s e d t o e s t i m a t e t h e d e p o s i t i o n r e s u l t i n g f r o m v a r i o u s f l o o d c o n d i t i o n s . H owever, i n o r d e r t o compute t h e t o t a l d e p o s i t i o n t h a t may o c c u r , t h e s h a p e and d u r a t i o n o f t h e f l o o d h y d r o g r a p h m u s t be known as w e l l a s t h e f l o o d p e a k . The p e a k s n o w m e l t a n d r a i n s t o r m f l o o d s w e r e e s t i -m a t e d f o r d i f f e r e n t p r o b a b i l i t i e s o f o c c u r r e n c e i n C h a p t e r I I I a n d w e r e s u m m a r i z e d i n T a b l e 5. The h y d r o g r a p h s c o r r e s p o n d i n g t o t h e s e f l o o d s w e r e e s t i m a t e d a s f o l l o w s . A d i m e n s i o n l e s s s n o w m e l t and r a i n s t o r m f l o o d h y d r o g r a p h 136 was d e v e l o p e d f r o m h i s t o r i c a l d a t a by p l o t t i n g : Q t v s . t , w h e r e = p e a k f l o o d Q p Q t = f l o w o n d a y " t " D i s c h a r g e s r e c o r d e d i n 1914, 1 9 1 7 , 1 9 2 1 , 1924, 1928 a n d 1975 w e r e u s e d t o e s t a b l i s h t h e r a i n s t o r m h y d r o g r a p h s . D u r i n g t h e s e y e a r s t h e p e a k d a i l y d i s c h a r g e r a n g e d b e -t w e e n 17,200 c f s a n d 27,000 c f s . The d i m e n s i o n l e s s snow-m e l t h y d r o g r a p h s w e r e p l o t t e d f r o m f l o o d s r e c o r d e d i n 1 9 6 1 , 1 9 6 7, 1 9 7 1 , 1972 and 1976. D u r i n g t h e s e y e a r s t h e maximum d a i l y f l o w s r a n g e d f r o m 8,800 c f s t o 12,600 c f s . The o r d i n a t e s o f t h e f l o o d h y d r o g r a p h s w e r e t h e n d e t e r m i n e d a s s i m p l e r a t i o s o f t h e p e a k mean d a i l y f l o o d d i s c h a r g e . The r e s u l t i n g s n o w m e l t a n d r a i n s t o r m " d e s i g n " h y d r o g r a p h s a r e shown i n F i g u r e 44. The m a i n d i f f e r e n c e b e t w e e n t h e s n o w m e l t and r a i n -s t o r m h y d r o g r a p h s i s t h e much more g r a d u a l r i s e a n d r e -c e s s i o n o f t h e s n o w m e l t f l o o d s . A s a r e s u l t , f o r t h e same p e a k d i s c h a r g e , t h e s n o w m e l t f l o o d s c o u l d t r a n s p o r t c o n s i d e r a b l y more s e d i m e n t t h a n a r a i n s t o r m f l o o d b e c a u s e t h e d u r a t i o n o f h i g h f l o w s i s much g r e a t e r . H owever, an e x t r e m e s n o w m e l t f l o o d i s i n t h e o r d e r o f 12,000 c f s t o 15,000 c f s w h i l e r a i n s t o r m f l o o d s c a n e a s i l y r e a c h t w i c e t h e s e f l o w s . T h e r e f o r e , o v e r a l o n g p e r i o d o f t i m e , i t i s b e l i e v e d t h a t t h e r a i n s t o r m f l o o d s w i l l p r o d u c e t h e d o m i n a n t e f f e c t on s e d i m e n t a t i o n on t h e V e d d e r R i v e r . 137 The e x p e c t e d d e p o s i t i o n b e t w e e n t h e r a i l w a y b r i d g e and V e d d e r C r o s s i n g was e s t i m a t e d f o r v a r i o u s f l o o d f r e -q u e n c i e s on t h e b a s i s o f t h e s e d i m e n t t r a n s p o r t r e l a t i o n s shown i n F i g u r e 37 and t h e h y d r o g r a p h s shown i n F i g u r e 44. The r e s u l t s , w h i c h a r e s u m m a r i z e d i n T a b l e 24, c o n f i r m t h a t f o r e x t r e m e e v e n t s t h e w i n t e r r a i n s t o r m f l o o d s w i l l p r o d u c e much g r e a t e r d e p o s i t i o n t h a n t h e s n o w m e l t f l o o d s . The d e p o s i t i o n p r e d i c t e d f o r a p e a k d a i l y w i n t e r f l o o d o f 27,500 c f s ( h a v i n g a r e t u r n p e r i o d o f 50 y e a r s ) was c l o s e t o 600,000 c u b i c y a r d s o r a b o u t 2.5 t i m e s t h e d e p o -s i t i o n t h a t was r e p o r t e d i n 1 9 7 5. T h e s e f i g u r e s r e p r e -s e n t minimum e s t i m a t e s s i n c e t h e s e d i m e n t t r a n s p o r t r a t e s w e r e a l l c o m p u t e d f o r mean d a i l y f l o w s a n d no a t t e m p t was made t o a c c o u n t f o r t h e f a c t t h a t t h e maximum i n s t a n t a -n e o u s f l o w c o u l d be a s much as 50% h i g h e r . H o w e v e r , e v e n d e p o s i t i o n o f 600,000 c u b i c y a r d s o f s e d i m e n t c o u l d p r o -d u c e l o c a l a g g r a d a t i o n o f s e v e r a l f e e t a n d c o u l d p r o b a b l y c r e a t e c o n s i d e r a b l e c h a n n e l s h i f t i n g and l a t e r a l i n s t a -b i l i t y . I n a d d i t i o n t o k n o w i n g t h e d e p o s i t i o n r e s u l t i n g f r o m a s i n g l e f l o o d e v e n t , i t i s e q u a l l y i m p o r t a n t t o ha v e a n e s t i m a t e o f t h e a v e r a g e a n n u a l d e p o s i t i o n r a t e . T h i s h a s b e e n e s t i m a t e d f o r two a r e a s — d o w n s t r e a m o f t h e r a i l w a y b r i d g e a n d b e t w e e n t h e r a i l w a y b r i d g e a n d V e d d e r C r o s s i n g . 138 The t r a n s p o r t i n t o the reach below the r a i l w a y b r i d g e was e s timated from the W.S.C. bedload measurements and t h e o r e t i c a l c a l c u l a t i o n s presented p r e v i o u s l y . The average annual t r a n s p o r t was then estimated by means of a f l o w - d u r a t i o n curve which was determined from d a i l y flow r e c o r d s a t Vedder C r o s s i n g . Only flows exceeding 5,000 c f s were i n c l u d e d i n the a n a l y s i s s i n c e the t r a n s -p o r t r a t e i s very s m a l l below t h i s v a l u e . The r e s u l t i n g c a l c u l a t i o n showed the t r a n s p o r t below the b r i d g e was l e s s than 4,000 c u b i c yards per year. The sediment i n -flow a t the r a i l w a y b r i d g e has been very low so i t i s no wonder t h a t the grade of the Vedder Canal has not changed a p p r e c i a b l y over the years (Marr, 1964; S i n c l a i r , 1961). T h i s c a l c u l a t i o n does not i n c l u d e the l a r g e d e p o s i -t i o n t h a t o c c u r r e d below the r a i l w a y b r i d g e between 1963-1970, which was brought on by d e g r a d a t i o n i n the c o n s t r i c t e d reach immediately upstream. I t i s b e l i e v e d t h i s l a r g e d e p o s i t i o n was a t r a n s i e n t f e a t u r e t h a t i s not r e p r e s e n -t a t i v e of the long term t r a n s p o r t r a t e . On the other hand, the bedload measurements between 1971-1975 were made a f t e r the upstream d e g r a d a t i o n had ceased which suggests a rough e q u i l i b r i u m c o n d i t i o n had been achieved. 139 The a v e r a g e a n n u a l t r a n s p o r t a t V e d d e r C r o s s i n g was e s t i m a t e d f r o m t h e same f l o w d u r a t i o n r e l a t i o n u s e d i n t h e p r e v i o u s c a l c u l a t i o n and t h e p r e d i c t e d b e d l o a d r e s u l t s shown i n F i g u r e 37. T h i s c a l c u l a t i o n i n d i c a t e d an a n n u a l t r a n s p o r t o f a b o u t 100,000 c u b i c y a r d s p e r y e a r . S i n c e p r e d i c t e d a n n u a l t r a n s p o r t was o n l y 4% o f t h i s e s t i m a t e , t h e n e t d e p o s i t i o n b e t w e e n t h e r a i l w a y b r i d g e and V e d d e r C r o s s i n g c a n a l s o be t a k e n a s a r o u n d 100,000 c u b i c s y a r d s / y e a r . I t i s p o s s i b l e t o e s t i m a t e t h e d e p o s i t i o n i n t h i s r e a c h f r o m o t h e r s o u r c e s i n o r d e r t o p r o v i d e a c o m p a r i s o n w i t h t h e b e d l o a d c a l c u l a t i o n s . T h e s e s o u r c e s i n c l u d e : - e s t i m a t e s o f bank e r o s i o n u p s t r e a m o f V e d d e r C r o s s i n g w h i c h w e r e p r e s e n t e d i n C h a p t e r 5. The t o t a l e r o s i o n b e t w e e n 1940-1976 i n t h e r e a c h b e -t w e e n L i u m c h e n C r e e k a n d V e d d e r C r o s s i n g was a b o u t 2,200,000 c u b i c y a r d s w h i c h a v e r a g e s 60,000 c u b i c y a r d s / y e a r . - e s t i m a t e d d e p o s i t i o n r e p o r t e d by I . P . S . C . (1977) b e t w e e n 1 9 5 7 - 1 9 7 6 . The e s t i m a t e d 1963-1970 d e g r a -d a t i o n i n t h e c o n s t r i c t i o n (300,000 c u b i c y a r d s ) s h o u l d be a d d e d t o t h e I . P . S . C . f i g u r e o f 370,000 c u b i c y a r d s n e t d e p o s i t i o n i n o r d e r t o a r r i v e a t t h e t o t a l s e d i m e n t i n f l o w a t V e d d e r C r o s s i n g . T h i s f i g u r e t o t a l s 670,000 c u b i c y a r d s b e t w e e n 1957-1976 o r 46,000 c u b i c y a r d s / y e a r . 140 - estimated 1972-1976 net d e p o s i t i o n of 493,000 c u b i c yards r e p o r t e d by Tempest (1976). Account-in g f o r the sediment outflow a t the r a i l w a y b r i d g e , the t o t a l i n f l o w a t Vedder C r o s s i n g averaged about 100,000 c u b i c yards/year. A simple average of these f o u r estimates i n d i c a t e s the average annual t r a n s p o r t a t Vedder C r o s s i n g i s i n the order of 76,000 c u b i c yards/year. T h e r e f o r e , the average d e p o s i t i o n between Vedder C r o s s i n g and the r a i l w a y b r i d g e i s i n the order of 72,000 c u b i c yards/year. Since the f o u r estimates were made over d i f f e r e n t p e r i o d s of time, computing a simple average i s not s t r i c t l y c o r r e c t . However, the e r r o r i n t r o d u c e d from t h i s f a c t i s probably s m a l l compared t o the i n a c c u r a c i e s of the i n i t i a l c a l c u l a t i o n s . The average d e p o s i t i o n r a t e i s probably most r e p r e -s e n t a t i v e of the flow c o n d i t i o n s e x i s t i n g over the l a s t 20 years which has had u n u s u a l l y low f l o o d s compared to e a r l i e r y e a r s . T h e r e f o r e , i f data was a v a i l a b l e f o r a much longer p e r i o d the annual d e p o s i t i o n r a t e would probably be c o n s i d e r a b l y h i g h e r - perhaps by even a f a c t o r of two. In a d d i t i o n i t must be remembered t h a t the d e p o s i t i o n from a s i n g l e extreme f l o o d might exceed the average by a f a c t o r of t e n . 141 CHAPTER I X FLOOD CONTROL ON THE VEDDER RIVER P r o v i d i n g f l o o d c o n t r o l on s t r e a m s t h a t a r e a c t i v e l y -a g g r a d i n g i s one o f t h e m o s t d i f f i c u l t p r o b l e m s i n r i v e r e n g i n e e r i n g . T h i s i s b e c a u s e t h e c h a n n e l s c a n become v e r y u n s t a b l e d u r i n g f l o o d s and s u b j e c t t o e r r a t i c s h i f t s . A l s o , due t o t h e p r o g r e s s i v e r i s e i n t h e b e d l e v e l , b a n k -f u l l c o n d i t i o n s a r e u s u a l l y e x c e e d e d f r e q u e n t l y and a l a r g e p o r t i o n o f t h e t o t a l f l o w may be c a r r i e d by t h e f l o o d p l a i n . 9.1 Some E x a m p l e s o f F l o o d C o n t r o l P r a c t i c e Some o f t h e m o s t i n t e r e s t i n g e x a m p l e s o f r i v e r s t a b i l i z a t i o n p r o b l e m s a r e f o u n d on some o f t h e l a r g e s t r i v e r s i n t h e w o r l d i n c l u d i n g t h e M i s s i s s i p p i R i v e r ( W i n k l e y , 1 9 7 7 ) , t h e Y e l l o w R i v e r i n C h i n a (Chou, 1 9 7 6 ) , t h e K o s i R i v e r i n I n d i a ( G o l e e t a l , 1966) and t h e B r a h m a p u t r a R i v e r i n P a k i s t a n ( L a t i f , 1 9 6 9 ) . Some o f t h e h i s t o r i c a l c h a n n e l s h i f t s on t h e s e r i v e r s h a v e b e e n immense ( t h e Y e l l o w R i v e r s h i f t e d 310 m i l e s i n 1194 A.D.) and h a v e r e s u l t e d i n v e r y h i g h damages and l o s s o f i l i f e . H o w e ver, t h e s e r i v e r s a r e so l a r g e and o f s u c h d i f f e r e n t c h a r a c t e r t h a n t h e V e d d e r R i v e r t h a t t h e m e t h o d s d e v e l o p e d t o p r o v i d e f l o o d c o n t r o l a r e n o t v e r y c o m p a r a b l e . 142 T h e r e f o r e , i t was d e c i d e d t o t r y t o f i n d some c a s e h i s -t o r i e s o f s t a b i l i z a t i o n p r o b l e m s on s t r e a m s t h a t c o u l d be c o n s i d e r e d c o m p a r a b l e t o t h e V e d d e r R i v e r . The f o u r e x a m p l e s t h a t w i l l be d e s c r i b e d i n c l u d e : - S n a k e R i v e r n e a r J a c k s o n H o l e , Wyoming ( J o n e s , 1966) - R h i n e R i v e r n e a r L a k e C o n s t a n c e ( E i n s t e i n , 197 3) - W a i m a k a r i r i R i v e r , New Z e a l a n d ( H e n d e r s o n , 1960) - S o u t h e r n C a l i f o r n i a a l l u v i a l f a n s (Wong and R o b l e s , 1971) Some o f t h e g e n e r a l c h a r a c t e r i s t i c s o f t h e s e r i v e r s a r e s u m m a r i z e d i n T a b l e 25. 9.1.1 S n a k e R i v e r , Wyoming A c c o r d i n g t o J o n e s ( 1 9 6 6 ) , t h e S n a k e R i v e r i s a b r a i d e d , g r a v e l s t r e a m t h a t i s a c t i v e l y a g g r a d i n g . The maximum r e c o r d e d f l o o d i s 40,000 c f s and t h e two y e a r f l o o d i s a b o u t 20,000 c f s . The c h a n n e l s l o p e was r e p o r t e d t o be 19 f e e t / m i l e o r a b o u t 0.0036. P r i o r t o r i v e r t r a i n i n g , e x t e n s i v e c h a n n e l c h a n g e s e n d a n g e r e d l a r g e a r e a s o f r a n c h l a n d . The m e thod o f b ank s t a b i l i z a t i o n was t o c o n s t r u c t e a r t h a n d g r a v e l l e v e e s p r o t e c t e d by r i p r a p w h i c h e x t e n d e d up t o t h e l e v e l o f a n n u a l f l o o d d i s c h a r g e (15,000 c f s ) . The t o p o f t h e l e v e e s e x t e n d e d a b o u t 3 f e e t a b o v e t h e p r o j e c t d e s i g n f l o o d w h i c h was 45,000 c f s . The d i s t a n c e b e t w e e n l e v e e s 143 was e s t a b l i s h e d a t 1,000 f e e t , which was the width e s t i -mated to m a i n t a i n the channel without aggradation or d e g r a d a t i o n . At the time of t h i s r e p o r t , the p r o j e c t had o n l y been completed two years so i t s long term performance c o u l d not be e v a l u a t e d . 9.1.2 Rhine R i v e r , S w i t z e r l a n d E i n s t e i n (1973) d e s c r i b e d a very e x t e n s i v e i n v e s t i -g a t i o n of sediment aggrad a t i o n and r i v e r t r a i n i n g t h a t was c a r r i e d out on the Rhine R i v e r above Lake Constance i n the 1930's. The r i v e r i s d e s c r i b e d as a mountain stream w i t h a g r a v e l bed. The r i v e r appears to have a steep s l o p e of about 0.01 and the maximum d i s c h a r g e was r e p o r t e d to be 3,000 m3/s (106,000 c f s ) . E x t e n s i v e bed-l o a d measurements were made on the r i v e r and the annual t r a n s p o r t was r e p o r t e d to be 90,000 tonnes/year (99,000 tons/year) which i s probably i n the same order as the Vedder R i v e r . The main problem on the Rhine R i v e r was channel aggradation which was brought on by e x t e n s i v e d i k e c o n s t r u c t i o n f u r t h e r upstream. T h i s c h a n n e l i z a t i o n caused the c o a r s e r sediment to be t r a n s p o r t e d to the reach below and be d e p o s i t e d . The s o l u t i o n t o t h i s prob-lem was to reduce the bottom width of the aggrading reach i n order to i n c r e a s e i t s t r a n s p o r t c a p a c i t y . A c c o r d i n g to E i n s t e i n , as a r e s u l t of a continuous dredging pro-gram and channel narrowing, the r i v e r has remained s t a b l e 144 o v e r t h e y e a r s . No m e n t i o n was made w h e t h e r t h i s c h a n -n e l i z a t i o n w o r k c r e a t e d a g g r a d a t i o n p r o b l e m s f u r t h e r d o w n s t r e a m on t h e r i v e r . 9.1.3 W a i m a k a r i r i R i v e r , New Z e a l a n d The W a i m a k a r i r i R i v e r f l o w s i n a m o u n t a i n o u s v a l l e y u n t i l r e a c h i n g t h e C a n t e r b u r y P l a i n s w h e r e i t f l o w s f o r a b o u t 36 m i l e s b e f o r e r e a c h i n g t h e o c e a n . I n t h i s l o w e r r e a c h i t c h a n g e s i t s c h a n n e l p a t t e r n f r o m h i g h l y b r a i d e d t o s p l i t a n d e v e n t u a l l y becomes a s i n g l e m e a n d e r i n g c h a n -n e l . I n a d d i t i o n , t h e s l o p e and b e d m a t e r i a l s i z e a l s o d e c r e a s e s d o w n s t r e a m w i t h t h e r i v e r b e d c h a n g i n g f r o m g r a v e l t o s a n d and t h e s l o p e d r o p p i n g f r o m 0.005 t o 0.00038. I n g e n e r a l t e r m s t h e W a i m a k a r i r i R i v e r f l o o d c o n -t r o l scheme r e l i e d on t h r e e c o m p o n e n t s — c h a n n e l e x c a v a -t i o n t o c o n t r o l a g g r a d a t i o n , a m a i n c h a n n e l w h i c h was s u p p o s e d t o c a r r y t h e s e d i m e n t t o t h e s e a and h a v e a c a p a c i t y f o r l o w f l o o d s ( l e s s t h a n 2 y e a r s ) a n d s e t - b a c k d i k e s l o c a t e d a c o n s i d e r a b l e d i s t a n c e f r o m t h e c h a n n e l t o c o n t a i n t h e o v e r b a n k f l o w s . H e n d e r s o n ' s s t u d y was i n t e n d e d t o e v a l u a t e t h e l o n g t e r m m e t h o d s o f p r o v i d i n g f l o o d c o n t r o l on t h e r i v e r a nd t o recommend p o s s i b l e a l t e r n a t i v e s o l u t i o n s . The m a i n r e c o m m e n d a t i o n s i n c l u d e d : 1. c o n s t r u c t bank p r o t e c t i o n i n t h e u p p e r r e a c h e s o f '  14 5 t h e r i v e r t o r e d u c e e r o s i o n and t h e r e b y d e c r e a s e t h e s u p p l y o f s e d i m e n t t o t h e a g g r a d i n g r e a c h . 2. remove l o c a l c o n s t r i c t i o n s i n t h e f l o w w h i c h c a u s e d i n c r e a s e d w a t e r l e v e l s and c o n t r i b u t e d t o down-s t r e a m a g g r a d a t i o n . 3. m a i n t a i n c h a n n e l d r e d g i n g a t a l e v e l t h a t e q u a l l e d o r e x c e e d e d t h e a v e r a g e a n n u a l s e d i m e n t t r a n s p o r t on t h e l o w e r p a r t o f t h e r i v e r . 4. c a r r y o u t l i m i t e d r i v e r t r a i n i n g i n t h e a g g r a d i n g r e a c h i n o r d e r t o i m p r o v e i t s t r a n s p o r t c a p a c i t y . 5. A f t e r t h e a b o v e s t e p s w e r e c o m p l e t e d , a c a r e f u l m o n i t o r i n g p r o g r a m was s u g g e s t e d t o s e e w h e t h e r a g g r a d a t i o n was i n c r e a s i n g o r d e c r e a s i n g . I f t h e b e d l e v e l s p e r s i s t e d t o r i s e a f t e r a 5 t o 10 y e a r p e r i o d , f u r t h e r s t u d i e s w e r e recommended t o d e t e r -m i n e w h e t h e r a d d i t i o n a l c h a n n e l i z a t i o n o r d r e d g i n g s h o u l d be c a r r i e d o u t . 9.1.4 C a l i f o r n i a C o a s t a l S t r e a m s Wong a n d R o b l e s (1971) d e s c r i b e some o f t h e e x t e n -s i v e f a c i l i t i e s t h a t h a v e b e e n c o n s t r u c t e d i n s o u t h e r n , C a l i f o r n i a t o c o n t r o l f l o o d i n g f r o m d e b r i s - l a d e n m o u n t a i n s t r e a m s t h a t f l o w o n t o t h e v a l l e y a r e a s and c a u s e w i d e -s p r e a d d e s t r u c t i o n . The m a i n f a c i l i t i e s t h a t h a v e b e e n b u i l t i n c l u d e d e b r i s b a s i n s a t t h e h e a d w o r k s o f f l o o d c o n t r o l c h a n n e l s , f l o o d c o n t r o l b a s i n s t o r e d u c e f l o o d 146 peaks and concrete l i n e d channels to c a r r y water and s e d i -ment. The d e b r i s b a s i n s were designed to p r o v i d e storage f o r g r a v e l bedload and had c a p a c i t i e s i n the order of 100,000-200,000 c u b i c y a r d s . They were c o n s t r u c t e d by e x c a v a t i n g a bowl shaped p i t i n t o the s u r f a c e of the a l l u v i a l fan and p l a c i n g an embankment around the down-stream rim of the p i t which t i e s i n t o h i g h ground. The e x t e n s i v e s t r u c t u r a l f l o o d c o n t r o l works i n C a l i f o r n i a have been b u i l t a t a c o s t of many m i l l i o n s of d o l l a r s over a p e r i o d of 30 y e a r s . Much of t h i s work c o u l d prob-a b l y o n l y be j u s t i f i e d because o f the l a r g e p o p u l a t i o n i n t h i s area and the h i g h f l o o d damages i n v o l v e d . There-f o r e , most of the f l o o d c o n t r o l measures are probably not a p p l i c a b l e to the Vedder R i v e r . 9.2 F l o o d C o n t r o l on the Vedder R i v e r On the Vedder R i v e r the main requirements of f l o o d c o n t r o l should be: 1. prevent the r i v e r from undergiong a r a d i c a l s h i f t down one of i t s former channels or d e v e l o p i n g a completely new route to the F r a s e r R i v e r . 2. p r o v i d e f l o o d p r o t e c t i o n to Yarrow and some of the land upstream of the r a i l w a y b r i d g e . 3. p r o v i d e an optimum channel alignment t h a t w i l l minimize the e f f e c t s of a g g r a d a t i o n and p r o t e c t 147 a g a i n s t bank e r o s i o n and c h a n n e l s h i f t i n g . 4. a d o p t f l o o d c o n t r o l schemes t h a t a r e c o m p a t i b l e w i t h s a l m o n s p a w n i n g r e q u i r e m e n t s and w i t h p o s s i b l e s a l m o n e n h a n c e m e n t p r o j e c t s . F o l l o w i n g t h e 1975 f l o o d , t h r e e m a i n f l o o d c o n t r o l d e v e l o p m e n t s w e r e c a r r i e d o u t . T h e s e i n c l u d e d : - r e m o v a l o f a p p r o x i m a t e l y one m i l l i o n c u b i c y a r d s o f g r a v e l b e w t e e n t h e h e a d o f t h e c a n a l and P e a c h e Road ( I . P . S . C . , 1 9 7 7 ) . A s a r e s u l t , t h e b o t t o m e l e v a t i o n o f t h e c h a n n e l was r e d u c e d by s e v e r a l f e e t . - b a n k p r o t e c t i o n i n t h e c h a n n e l i z e d r e a c h u p s t r e a m o f t h e r a i l w a y b r i d g e was r a i s e d t o p r o v i d e c a p a -c i t y f o r a 24,000 c f s f l o o d w i t h 2 f e e t o f f r e e -b o a r d ( I . P . S . C , 1 9 7 7 ) . - a p p r o v a l was r e c e i v e d f o r e a r t h f i l l s e t - b a c k d i k e s w h i c h w o u l d be l o c a t e d u p s t r e a m o f t h e r a i l w a y b r i d g e and p r o t e c t a g a i n s t a 200 y e a r f l o o d . When s e t - b a c k d i k e s a r e c o n s t r u c t e d , t h e p o t e n t i a l f o r s e r i o u s f l o o d i n g on t h e V e d d e r R i v e r s h o u l d be r e d u c e d . I f t h e d i k e s e x t e n d f a r e n o u g h u p s t r e a m and t i e i n t o h i g h g r o u n d , t h e n t h e c h a n c e o f t h e r i v e r m a k i n g a s u d d e n s h i f t a c r o s s i t s f a n s h o u l d be g r e a t l y r e d u c e d . A t p r e -s e n t , t h e m o s t l i k e l y l o c a t i o n f o r s u c h a s h i f t i s t h e o l d A t c h e l i t z c h a n n e l , w i t h f l o o d w a t e r b r e a k i n g o u t o f t h e V e d d e r c h a n n e l d o w n s t r e a m o f t h e Army b a s e , b e l o w 148 V e d d e r C r o s s i n g . The l o n g t e r m e f f e c t i v e n e s s o f t h e m a s s i v e d r e d g i n g and bank r a i s i n g a l o n g t h e V e d d e r R i v e r i s more q u e s t i o n -a b l e . A l t h o u g h a l a r g e q u a n t i t y o f s e d i m e n t was r e m o v e d , u n l e s s r e g u l a r d r e d g i n g i s c a r r i e d o u t , t h e c h a n n e l w i l l g r a d u a l l y f i l l i n and r e t u r n t o t h e c o n d i t i o n s e x i s t i n g i n 1975. The s p e c i f i c gauge r e c o r d n e a r Y a r r o w shown i n F i g u r e 42 i n d i c a t e s how r a p i d l y t h e c h a n n e l c a n f i l l i n o n c e d r e d g i n g i s d i s c o n t i n u e d . V i n c e n t (1968) c a r r i e d o u t f i e l d a n d m o d e l s t u d i e s t o d e t e r m i n e t h e e f f e c t o f d e e p e n i n g t h e c h a n n e l o f t h e Danube R i v e r on u p s t r e a m r i v e r l e v e l s and s e d i m e n t t r a n s -p o r t p r o c e s s e s . The s t u d i e s showed t h a t t h e b e d l o a d t r a n s p o r t i n t o t h e d r e d g e d r e a c h i n c r e a s e d s h a r p l y a b o v e t h e n o r m a l r a t e t h a t h a d b e e n m e a s u r e d p r i o r t o d r e d g i n g . As a r e s u l t , t h e h o l e f i l l e d i n r a p i d l y and d e g r a d a t i o n was i n d u c e d i n t h e u p s t r e a m r e a c h due t o an i n c r e a s e i n s l o p e . A s i m i l a r s i t u a t i o n c o u l d a l s o o c c u r on t h e V e d d e r R i v e r , w i t h r a p i d a g g r a d a t i o n d e v e l o p i n g f i r s t b e l o w t h e r a i l w a y b r i d g e and t h e n p r o g r e s s i n g u p s t r e a m i n t o t h e c o n s t r i c t e d r e a c h . The t i m e r e q u i r e d f o r t h i s f i l l i n g w i l l d e p e n d on t h e s e q u e n c e o f f l o w s t h a t o c c u r o v e r t h e n e x t f e w y e a r s . I f f l o o d c o n d i t i o n s r e m a i n c l o s e t o t h e l o n g t e r m a v e r a g e , t h e n t h e t i m e r e q u i r e d c o u l d p r o b a b l y be o n l y 10-15 y e a r s . I f a s e q u e n c e o f v e r y h i g h f l o w s 149 o c c u r r e d , p o s s i b l y l e s s t h a n 5 y e a r s w o u l d be r e q u i r e d . I t i s c l e a r t h a t r e g u l a r m a i n t e n a n c e w i l l be r e -q u i r e d on t h e V e d d e r R i v e r e v e n when s e t - b a c k d i k e s a r e c o n s t r u c t e d . As a r e s u l t , i t i s f a i r t o e x a m i n e p o s s i b l e a l t e r n a t i v e s t o t h e e x i s t i n g c h a n n e l a l i g n m e n t . I n t h e p r e v i o u s s e c t i o n , f o u r v e r y d i f f e r e n t m e t h o d s o f p r o v i d i n g f l o o d c o n t r o l on a g g r a d i n g g r a v e l r i v e r s w e r e d e s c r i b e d . T h e s e m e t h o d s i n c l u d e d : - w i d e l y s p a c e d a r m o u r e d l e v e e s (Snake R i v e r , Wyoming) - r i v e r n a r r o w i n g a nd u p s t r e a m d r e d g i n g ( R h i n e R i v e r ) - u p s t r e a m bank p r o t e c t i o n t o r e d u c e s e d i m e n t s u p p l y , s e t - b a c k d i k e s t o c o n t a i n o v e r b a n k f l o w s , r i v e r t r a i n i n g a n d d r e d g i n g t o c o n t r o l s e d i m e n t a g g r a d a -t i o n ( W a i m a k a r i r i R i v e r ) - c o n s t r u c t i o n o f d e b r i s b a s i n s , e x t e n s i v e c h a n n e l -i z a t i o n ( s o u t h e r n C a l i f o r n i a a l l u v i a l f a n s ) . A l t h o u g h e a c h r i v e r h a s i t s own u n i q u e c h a r a c t e r -i s t i c s w h i c h d e t e r m i n e t h e t y p e o f f l o o d c o n t r o l w o r k s t h a t w i l l be m o s t a p p r o p r i a t e , i t i s i n t e r e s t i n g t o n o t e t h a t m o s t o f t h e schemes l i s t e d a b o v e h a v e i n p a r t o r i n w h o l e b e e n s u g g e s t e d f o r t h e V e d d e r R i v e r . T h e r e f o r e , a t t h i s t i m e some a l t e r n a t i v e m e t h o d s o f p r o v i d i n g f l o o d c o n t r o l w i l l be r e v i e w e d . 150 9.2.1 Upstream Sediment C o n t r o l Reducing the supply of the g r a v e l bedload above Vedder C r o s s i n g c o u l d , i n the long term, p r o v i d e an e f f e c -t i v e method of r e d u c i n g sedimentation on the Vedder R i v e r . As d i s c u s s e d i n Chapter 5, probably the most important source of t h i s sediment i s produced from bank e r o s i o n i n the l a t e r a l l y u n s t a b l e reach between Vedder C r o s s i n g and Liumchen Creek. The I.P.S.C. suggested t h a t c o n t r o l l i n g e r o s i o n i n t h i s reach would be b e n e f i c i a l i n r e d u c i n g aggradation on the Vedder R i v e r . I t was a l s o concluded t h a t l o g jams and d e b r i s c o n t r i b u t e d to t h i s e r o s i o n ( I . P . S . C , 1977). U n f o r t u n a t e l y , c o n t r o l l i n g bank e r o s i o n c o u l d be-come very expensive even i f t h i s work were c o n f i n e d to the most un s t a b l e reach which extends about 10,000 f e e t above Vedder C r o s s i n g . I f a continuous revetment were c o n s t r u c t e d , probably 50,000-75,000 c u b i c yards of heavy r i p - r a p would be r e q u i r e d which c o u l d c o s t w e l l over one m i l l i o n d o l l a r s . T h i s scheme would not be e n t i r e l y e f f e c t i v e s i n c e most of the l a r g e i s l a n d s and bars would s t i l l be s u b j e c t to e r o s i o n . Probably a cheaper approach would be to c o n s t r u c t a number o f s h o r t spurs or "plugs." T h e i r purpose would be to prevent the r i v e r from r e -occupying o l d abandoned s i d e channels by encouraging them to s i l t up and become s t a b i l i z e d w i t h v e g e t a t i o n . S p e c i a l 151 c a r e w o u l d h a v e t o be t a k e n t o i n s u r e t h a t t h e s e s t r u c -t u r e s d i d n o t e n c o u r a g e new e r o s i o n o r i n c r e a s e c h a n n e l s c o u r . I t i s u n l i k e l y t h a t a n y e r o s i o n c o n t r o l s c h e m e c o u l d r e d u c e t h e s e d i m e n t s u p p l y t o t h e V e d d e r R i v e r e n -t i r e l y . H o w e v e r , e v e n a r e d u c t i o n o f 2 0 - 3 0 % c o u l d p r o v e t o be v e r y i m p o r t a n t d u r i n g a m a j o r f l o o d . P r o b a b l y t h e b e s t a p p r o a c h t o t a k e w o u l d be t o c a r r y o u t a l i m i t e d p r o g r a m t o b e g i n w i t h — f o r e x a m p l e , c o m p l e t e m e a s u r e s t o p r o t e c t t h e r o a d r u n n i n g a l o n g t h e n o r t h b a n k ( F i g u r e 2 2 ) , t h e n w a i t a f e w y e a r s a n d s e e how t h e p r o t e c t i o n i s p e r f o r m i n g . A t t h i s t i m e d e t a i l e d s u r v e y s w o u l d be made d o w n s t r e a m o f V e d d e r C r o s s i n g t o d e t e r m i n e w h e t h e r t h e r a t e o f a g g r a d a t i o n was b e i n g r e d u c e d . I t i s u n l i k e l y t h a t a u t h o r i t i e s w o u l d c o n s i d e r a n y e r o s i o n c o n t r o l m e a s u r e s a t t h e p r e s e n t t i m e b e c a u s e o f t h e e x p e n s e i n v o l v e d a n d b e c a u s e i t i s d i f f i c u l t t o q u a n -t i f y t h e e f f e c t i v e n e s s . H o w e v e r , a s r e s i d e n t i a l d e v e l o p -m e n t i n t e n s i f i e s a b o v e V e d d e r C r o s s i n g , t h e j u s t i f i c a t i o n f o r e r o s i o n c o n t r o l s h o u l d i n c r e a s e . 9 . 2 . 2 S e d i m e n t T r a p s L a r g e e x c a v a t i o n s c o u l d be made i n t h e c h a n n e l t o h e l p t r a p s e d i m e n t a n d l o c a l i z e s e d i m e n t d e p o s i t i o n . B a s e d o n t h e p a t t e r n o f a g g r a d a t i o n t h a t h a s b e e n o b -s e r v e d o n t h e r i v e r , t h r e e l o c a t i o n s a l r e a d y a p p e a r t o 152 f u n c t i o n i n t h i s manner and c o u l d be d e v e l o p e d r e l a t i v e l y e a s i l y . T h e s e a r e a s a r e : - t h e w i d e b r a i d e d r e a c h n e a r P e a c h e Road - t h e w i d e a r e a n e a r F o r d Road - i m m e d i a t e l y d o w n s t r e a m o f t h e r a i l w a y b r i d g e . A l l t h r e e o f t h e s e s i t e s a r e a r e a s w h e r e t h e w i d t h i n c r e a s e s a b r u p t l y , c a u s i n g a s u d d e n f l o w e x p a n s i o n . An e x c a v a t i o n 2,000 f e e t l o n g by 600 f e e t w i d e by 5 f e e t d e e p m i g h t be a b l e t o t r a p a b o u t 200,000 c u b i c y a r d s o f g r a v e l . T h e r e f o r e , t h e s e d i m e n t t r a p s w o u l d be m o s t e f f e c t i v e i n c o n t r o l l i n g t h e a v e r a g e a n n u a l s e d i m e n t d e p o s i t i o n b u t d u r i n g a m a j o r f l o o d t h e y w o u l d p r o b a b l y be c o m p l e t e l y o v e r w h e l m e d . One d i s a d v a n t a g e o f t h e s e t r a p s i s t h a t d r e d g i n g w o u l d be c a r r i e d o u t i n a r e a s t h a t m i g h t be p r i m e spawn-i n g a r e a s f o r s a l m o n ( f o r e x a m p l e F o r d R o a d ) . H o w e v e r , i t i s p o s s i b l e t h a t much o f t h e e x c a v a t i o n c o u l d be c a r r i e d o u t on d r y b a r s i n t h e s e w i d e , b r a i d e d r e a c h e s w h i c h c o u l d m i n i m i z e d i s t u r b a n c e s . A l s o , i t i s p o s s i b l e t h a t i f p e r m a n e n t s e d i m e n t t r a p s w e r e c o n s t r u c t e d , some f o r m o f o v e r h e a d c a b l e e x c a v a t i o n s y s t e m c o u l d be d e v e l o p e d . T h e r e a p p e a r s t o be no p o i n t i n c o n s t r u c t i n g a l a r g e t r a p a b o v e V e d d e r C r o s s i n g , as t h e r e a r e no s u i t a b l e l o c a t i o n s u n l e s s m a j o r c h a n g e s w e r e made t o t h e c h a n n e l . The m a j o r g o a l o f s e d i m e n t c o n t r o l i n t h i s a r e a s h o u l d be c h a n n e l s t a b i l i z a t i o n , n o t r e m o v a l . 153 9.2.3 Wide V e d d e r R i v e r w i t h A r m o u r e d D i k e s T h i s scheme w o u l d l e a v e t h e r i v e r a b o v e F o r d Road i n i t s e x i s t i n g f o r m , w i t h t h e a d d i t i o n o f r i p - r a p p e d d i k e s t o c o n t a i n o v e r b a n k f l o w s . B e l o w F o r d Road t h e e x i s t i n g bank p r o t e c t i o n w o u l d be r e m o v e d and t h e c h a n n e l w o u l d be a l l o w e d t o d e v e l o p w i t h i n a w i d t h o f a b o u t 1,00 0 f e e t b e t w e e n t h e d i k e s . A p o s s i b l e a l i g n m e n t o f t h e s e d i k e s i s shown i n F i g u r e 45 w h i c h i s r e p r o d u c e d f r o m P e t e r s , (197 8). The a d v a n t a g e o f t h i s scheme w o u l d be p r i m a r i l y an i m p r o v e m e n t t o t h e s p a w n i n g a n d r e a r i n g a r e a s f o r t h e V e d d e r R i v e r f i s h e r i e s . P e t e r s (1978) showed t h i s c o u l d s i g n i f i c a n t l y i n c r e a s e t h e p r o d u c t i o n o f chum s a l m o n f r o m t h e l o w e r r i v e r . A s e c o n d a d v a n t a g e o f a w i d e n e d V e d d e r R i v e r i s t h a t t h e s t o r a g e a r e a a v a i l a b l e f o r s e d i m e n t d e p o s i t i o n w o u l d be g r e a t l y i n c r e a s e d . I f t h e r i v e r was r e t u r n e d t o i t s 1958 a l i g n m e n t b e t w e e n t h e r a i l w a y b r i d g e and F o r d R o a d , t h e b o t t o m a r e a w o u l d be n e a r l y d o u b l e d . T h e r e f o r e , d u r i n g a m a j o r f l o o d t h e b e d l e v e l r i s e due t o s e d i m e n t a -t i o n m i g h t be l e s s t h a n i n t h e e x i s t i n g a l i g n m e n t . T h e r e a r e s e v e r a l d i s a d v a n t a g e s t o t h i s scheme. F i r s t , t h e a r m o u r e d d i k e s w o u l d h a v e t o c a r r y o u t two d i f f e r e n t f u n c t i o n s — p r e v e n t i o n o f m a j o r c h a n n e l s h i f t i n g a n d c o n t a i n m e n t o f o v e r b a n k f l o w s . As a r e s u l t , t h e y c o u l d e n d up n o t h a n d l i n g e i t h e r r o l e v e r y e f f e c t i v e l y . 154 I f t h e d i k e s w e r e s p a c e d a b o u t 1,000 f e e t a p a r t , t h e r i v e r w o u l d p r o b a b l y e v e n t u a l l y r e t u r n t o a v e r y b r a i d e d c h a n n e l p a t t e r n a s shown on t h e 1930 a i r p h o t o i n F i g u r e 4. As a r e s u l t , t h e r i v e r w o u l d become v e r y s h a l -l o w w i t h l a r g e q u a n t i t i e s o f s e d i m e n t a d d e d t o t h e c h a n -n e l f r o m bank e r o s i o n . T h i s i n t u r n w o u l d p r o b a b l y c o n t r i b u t e t o f u r t h e r a g g r a d a t i o n d u r i n g m a j o r f l o o d s and e r r a t i c a l i g n m e n t s h i f t s . An e x a m p l e o f t h i s t y p e o f s h i f t i n g o c c u r r i n g d u r i n g t h e F e b r u a r y , 1951 f l o o d when a l a r g e amount o f e r o s i o n o c c u r r e d a l o n g t h e s o u t h bank n e a r Browne Road ( F i g u r e 4 ) . A l s o , i n o r d e r t o a c h i e v e some f o r m o f r i v e r t r a i n -i n g , t h e a r m o u r e d d i k e s w o u l d p r o b a b l y h a v e t o be s i t u -a t e d c l o s e r t o t h e r i v e r t h a n t h e s e t - b a c k d i k e scheme. As a r e s u l t , t h e r e w o u l d be c o m p a r a t i v e l y l e s s o v e r b a n k a r e a t o c a r r y t h e f l o w o v e r t h e f l o o d p l a i n . I n t h i s c a s e t h e "Wide R i v e r " scheme may a c t u a l l y n o t i n c r e a s e t h e c h a n n e l c o n v e y a n c e v e r y much. I f a w i d e c h a n n e l scheme was a d o p t e d , t h e r e w o u l d n o t be much a d v a n t a g e i n t r y i n g t o c o n s t r u c t s e d i m e n t t r a p s — i n t h i s c o n f i g u r a t i o n t h e e n t i r e c h a n n e l i s t h e s e d i m e n t t r a p . T h e r e f o r e , d r e d g i n g w o u l d be r e q u i r e d o v e r t h e e n t i r e r e a c h . T h i s w o u l d p r o b a b l y be c o n s i d e r e d a d v a n t a g e o u s t o t h e f i s h e r i e s s i n c e d r e d g i n g c o u l d p r o b -a b l y be c o n c e n t r a t e d on t h e t o p s o f d r y g r a v e l b a r s and i n - c h a n n e l e x c a v a t i o n c o u l d be a v o i d e d . 9.2.4 R i v e r T r a i n i n g w i t h S e t - B a c k D i k e s T h i s scheme i s r o u g h l y e q u i v a l e n t t o t h e p l a n a d o p t e d by t h e B.C. W a t e r R e s o u r c e s S e r v i c e . The s e t -b a c k d i k e s w o u l d be c o n s t r u c t e d o f e a r t h - f i l l a n d w o u l d be s p a c e d r o u g h l y 1,000-1,500 f e e t a p a r t . The r i v e r t r a i n i n g w o u l d be a c c o m p l i s h e d by a c o n -t i n u o u s r e v e t m e n t a l o n g t h e m a i n l o w - w a t e r c h a n n e l . I t i s e x p e c t e d t h a t t h e e x i s t i n g c h a n n e l a l i g n m e n t u p s t r e a m o f F o r d Road w o u l d be m a i n t a i n e d . I f f u r t h e r r i v e r n a r r o w i n g was c a r r i e d o u t on t h e u p p e r h a l f o f t h e f a n , t h e r e i s no d o u b t a s t o t h e o u t c o m e . A g g r a d a t i o n w o u l d i n c r e a s e d r a s t i c a l l y on t h e l o w e r r e a c h n e a r Y a r r o w w h i c h c o u l d t h r e a t e n t h e s t a b i l i t y o f t h e c h a n n e l . The m a i n a d v a n t a g e o f t h i s scheme i s t h a t f l o o d c o n t r o l w o u l d n o t r e l y on a s i n g l e f a c i l i t y a s i n t h e "Wide R i v e r " scheme. The p u r p o s e o f t h e s e t - b a c k d i k e s w o u l d be t o c o n t r o l o v e r b a n k f l o w on t h e f l o o d p l a i n and t o d i r e c t t h i s b a c k i n t o t h e m a i n c h a n n e l b e l o w t h e r a i l -way b r i d g e . T h e r e f o r e , t h e d i k e s c o u l d be d e s i g n e d so t h a t d u r i n g v e r y e x t r e m e f l o o d s a l a r g e p a r t o f t h e f l o w c o u l d be c a r r i e d by t h e f l o o d p l a i n . The r e v e t m e n t w o u l d l i m i t bank e r o s i o n and r e d u c e t h e i n f l u x o f s e d i m e n t on t h e u p p e r p a r t o f t h e f a n . On t h e l o w e r h a l f o f t h e f a n , t h e m a i n o b j e c t o f t h e b a n k p r o t e c t i o n w o u l d be t o h e l p m a i n t a i n s t a b l e c h a n n e l t h a t c o u l d t r a n s p o r t i t s a v e r a g e a n n u a l s e d i m e n t l o a d w i t h o u t 156 e x c e s s i v e a g g r a d a t i o n . The m a i n d i s a d v a n t a g e o f t h i s s c h e m e i s t h a t t h e s p a w n i n g h a b i t a t o n t h e l o w e r r i v e r w o u l d s u f f e r f r o m m o s t o f t h e p r o b l e m s t h a t a l r e a d y e x i s t . T h e s e p r o b l e m s i n c l u d e l i m i t e d a r e a a v a i l a b l e f o r s p a w n i n g , d e s t r u c t i o n o f e g g s d u e t o c h a n n e l s c o u r d u r i n g f l o o d s , p o o r r e a r i n g a r e a s due t o h i g h v e l o c i t i e s a n d p o s s i b l e d i s r u p t i o n f r o m i n - c h a n n e l d r e d g i n g . Some o f t h e s e e f f e c t s c o u l d be p a r t i a l l y o v e r c o m e b y r e h a b i l i t a t i n g some o f t h e o l d s i d e c h a n n e l s o n t h e s o u t h b a n k w h i c h a r e l o c a t e d b e t w e e n t h e b a n k p r o t e c t i o n a n d t h e s e t - b a c k d i k e s . A s e c o n d d i s a d v a n t a g e o f t h i s scheme w o u l d be t h a t r e a s o n a b l y f r e q u e n t m a i n t e n a n c e w o u l d b e r e q u i r e d t o t h e b a n k p r o t e c t i o n . A l s o , s e d i m e n t r e m o v a l f r o m b e l o w t h e r a i l w a y b r i d g e , F o r d R o a d a n d P e a c h e R o a d w o u l d p r o b a b l y be a v e r y i m p o r t a n t c o m p o n e n t o f t h i s f l o o d c o n t r o l s c h e m e . T h e r e f o r e , i f l o c a l i z e d , i n t e n s i v e d r e d g i n g was p r e v e n t e d , i t w o u l d be d i f f i c u l t t o make t h i s a p p r o a c h w o r k . 9 . 3 D e s i g n i n g a F l o o d C o n t r o l Scheme f o r t h e V e d d e r R i v e r The g e n e r a l c o n c e p t o f p r o v i d i n g b a n k p r o t e c t i o n t o s t a b i l i z e t h e V e d d e r c h a n n e l a n d s e t - b a c k d i k e s t o c o n t a i n t h e o v e r b a n k f l o w a p p e a r s t o be t h e s o u n d e s t m e t h o d o f p r o v i d i n g l o n g t e r m f l o o d c o n t r o l o n t h e V e d d e r 157 R i v e r . U n f o r t u n a t e l y , t h i s may n o t r e p r e s e n t t h e b e s t a l t e r n a t i v e a s f a r a s t h e f i s h e r i e s r e s o u r c e s a r e c o n -c e r n e d . On t h e o t h e r h a n d , t h i s scheme d o e s n o t n e c e s -s a r i l y e n s u r e t h a t t h e r i v e r m ust be t u r n e d i n t o a c h a n n e l i z e d d i t c h , n o r d o e s i t r u l e o u t some p o s s i b l e s a l m o n e n h a n c e m e n t a l t e r n a t i v e s . T h e r e f o r e , a g e n e r a l p l a n f o r d e v e l o p i n g t h i s f l o o d c o n t r o l scheme w i l l be d i s c u s s e d . The m a i n q u e s t i o n s t h a t n e e d t o be a n s w e r e d i n -c l u d e : 1. What s h o u l d t h e m a i n c h a n n e l a l i g n m e n t b e ? 2. How s h o u l d d r e d g i n g be i n c o r p o r a t e d i n t o t h e p l a n ? 3. What s h o u l d be t h e c a p a c i t y o f t h e m a i n c h a n n e l ? I n an e a r l y p r o p o s a l p r e s e n t e d by M a r r ( 1 9 6 4 ) , i t was s u g g e s t e d t h a t a c h a n n e l c o u l d be c o n s t r u c t e d s o t h a t t h e e n t i r e s e d i m e n t i n f l o w c o u l d be t r a n s p o r t e d t h r o u g h t h e s y s t e m a n d d e p o s i t e d i n t h e F r a s e r R i v e r w i t h o u t p r o d u c i n g a g g r a d a t i o n . The s e d i m e n t t r a n s p o r t c a l c u l a t i o n s a t Y a r r o w and V e d d e r C r o s s i n g a l o n g w i t h t h e a n a l y s i s o f s e d i m e n t s o r t i n g o n t h e f a n h a s shown t h i s t o be e n t i r e l y i m p o s s i b l e . T h e r e f o r e , i n o r d e r t o c o n t r o l a g g r a d a t i o n , s e d i m e n t r e m o v a l w i l l be r e q u i r e d . The d e p o s i t i o n a l p a t t e r n o b s e r v e d d u r i n g t h e 1975 f l o o d showed t h a t d e p o s i t i o n t e n d e d t o be l o c a l i z e d i n t h e a b r u p t f l o w e x p a n s i o n s w h i l e m o s t o f t h e c o n t r a c t i o n s r e m a i n e d more s t a b l e . T h i s f e a t u r e s u g g e s t s a p o s s i b l e 158 c h a n n e l a l i g n m e n t t h a t c o u l d t e n d t o l o c a l i z e t h e s e d i -ment d e p o s i t i o n i n p a r t i c u l a r s i t e s w h i l e a l l o w i n g a s i g n i f i c a n t p o r t i o n o f t h e c h a n n e l t o r e m a i n s t a b l e . S i n c e m o s t d e p o s i t i o n w o u l d o c c u r i n t h e w i d e b r a i d e d r e a c h e s , s e d i m e n t r e m o v a l c o u l d p r o b a b l y be a c c o m p l i s h e d by e x c a v a t i n g d r y b a r s w h i c h w o u l d m i n i m i z e f i s h e r i e s o b j e c t i o n s . A p o s s i b l e s c h e m a t i c a l i g n m e n t i s i l l u s t r a t e d i n F i g u r e 46. A b o v e F o r d Road t h e e x i s t i n g c h a n n e l w o u l d n o t be g r e a t l y m o d i f i e d e x c e p t f o r p r o v i d i n g f o r s e d i m e n t r e m o v a l n e a r P e a c h e Road. No r i v e r n a r r o w i n g w o u l d be made i n t h i s r e a c h . The two o t h e r d e p o s i t i o n z o n e s w o u l d be d e v e l o p e d n e a r F o r d Road a n d b e l o w t h e r a i l w a y b r i d g e . As a r e s u l t , t h e V e d d e r R i v e r w o u l d be d e v e l o p e d i n t o an a l t e r n a t i n g s e q u e n c e o f t r a n s p o r t r e a c h e s a n d d e p o s i t i o n r e a c h e s s p a c e d r o u g h l y one m i l e a p a r t . I n o r d e r t o p r e -v e n t a g g r a d a t i o n d e v e l o p i n g i n t o t h e t r a n s p o r t r e a c h e s , o v e r t h e l o n g t e r m , t h e a n n u a l s e d i m e n t l o a d d e p o s i t e d on t h e f a n w o u l d h a v e t o be r e m o v e d by d r e d g i n g . B a s e d on c a l c u l a t i o n s p r e s e n t e d e a r l i e r , t h i s w o u l d p r o b a b l y a v e r a g e a b o u t 7 0,000 c u b i c y a r d s p e r y e a r . I t i s e x p e c t e d t h a t u n d e r a v e r a g e f l o o d c o n d i t i o n s , t h e a l t e r n a t i n g c h a n n e l p a t t e r n w o u l d s t a y s t a b l e f o r many y e a r s . H owever, d u r i n g e x t r e m e f l o o d s t h e c h a n n e l c o u l d be c h a n g e d e x t e n s i v e l y s o t h a t a new p a t t e r n w o u l d h a v e t o be e s t a b l i s h e d a f t e r w a r d s . 159 Once a c h a n n e l a l i g n m e n t i s s e l e c t e d , t h e f l o o d c a p a c i t y o f t h e m a i n c h a n n e l must be d e c i d e d . I f o v e r -t o p p i n g was a l l o w e d t o o c c u r v e r y f r e q u e n t l y , t h e n s u c h a l a r g e p o r t i o n o f t h e f l o w w o u l d be c a r r i e d by t h e f l o o d p l a i n t h a t t h e t r a n s p o r t c a p a c i t y o f t h e c h a n n e l w o u l d be g r e a t l y r e d u c e d . A l t e r n a t e l y , i f o v e r t o p p i n g i s n e v e r a l l o w e d , v e r y h i g h c h a n n e l v e l o c i t i e s w o u l d o c c u r a l o n g w i t h s c o u r and p o s s i b l e bank e r o s i o n . I n H e n d e r s o n ' s s t u d y o f t h e W a i m a k a r i r i R i v e r , i t was recommended t h a t t h e b e s t a p p r o a c h f o r e s t a b l i s h i n g t h e b a n k f u l l c a p a c i t y o f t h e m a i n c h a n n e l was t o f i n d o u t t h e f r e q u e n c y o f o v e r b a n k f l o o d i n g on n a t u r a l r i v e r s . B a s e d on d a t a c o l l e c t e d on New Z e a l a n d , E u r o p e a n a n d A m e r i c a n r i v e r s , H e n d e r s o n a d o p t e d a d e s i g n f l o w w i t h a n a n n u a l r e t u r n p e r i o d o f a b o u t 1.5 y e a r s . B r a y (1972) c a r r i e d o u t a s i m i l a r s t u d y u s i n g d a t a f r o m 72 A l b e r t a r i v e r s a n d c o n c l u d e d b a n k f u l l c o n d i t i o n s u s u a l l y h a d a r e t u r n p e r i o d o f b e t w e e n 2 and 10 y e a r s . . F u r t h e r m o r e , i t was c o n c l u d e d t h a t a r e t u r n p e r i o d o f 2 y e a r s p r o -v i d e d t h e b e s t e s t i m a t e o f a " d o m i n a n t " o r c h a n n e l f o r m -i n g d i s c h a r g e ( B r a y , 1975). A two y e a r maximum i n s t a n t a n e o u s f l o o d on t h e V e d d e r R i v e r h a s a d i s c h a r g e o f a b o u t 15,000 c f s . T h e r e -f o r e , t h i s f i g u r e was a d o p t e d f o r e s t a b l i s h i n g t h e c a p a -c i t y o f t h e m a i n c h a n n e l . 160 The f i n a l d e c i s i o n i s to estimate the width of the main channel below Ford Road. T h e o r e t i c a l l y the i n f l o w -i n g sediment lo a d at Peache Road c o u l d be computed and the channel c o u l d then be designed to match t h i s r a t e . However, the i n a c c u r a c i e s i n v o l v e d i n c a r r y i n g out t h i s c a l c u l a t i o n are probably so l a r g e t h a t i t i s not worth t r y i n g . An a l t e r n a t i v e approach i s to t r e a t the channel as i f i t were a n a t u r a l , s e l f - f o r m e d r i v e r t h a t has a d j u s t e d to i t s bed m a t e r i a l , sediment i n f l o w and d i s c h a r g e . T h i s assumption would be completely i n v a l i d on an aggrading a l l u v i a l fan but i n t h i s h y p o t h e t i c a l a l t e r n a t i n g t r a n s p o r t and d e p o s i t i o n channel t h i s assumption may not be too i n c o r r e c t . Parker (1979) c o n s i d e r e d the case of s e l f - f o r m e d r i v e r s w i t h g r a v e l bed and banks t r a n s p o r t i n g low s e d i -ment loads and d e r i v e d a number of r a t i o n a l regime equa-t i o n s to compute the h y d r a u l i c geometry o f these channels. The equations developed by Parker are summarized i n Table 27. For a b a n k f u l l d i s c h a r g e of 15,000 c f s and a rep-r e s e n t a t i v e bed m a t e r i a l s i z e of 45 mm, these equations i n d i c a t e the s t a b l e bed width should be about 32 0 f e e t and the maximum channel depth would be about 6.5 f e e t . T h i s i s s l i g h t l y wider than some p a r t s of the 1976 chan-n e l which reached about 250 f e e t i n some p l a c e s . 161 I t i s b e l i e v e d t h i s approach would have a reason-a b l e chance of success d u r i n g "average" f l o o d c o n d i t i o n s . During a c a t a s t r o p h i c f l o o d which might exceed 40,000-50,000 c f s would probably have r e l a t i v e l y l i t t l e e f f e c t on the flows and i t i s l i k e l y t h a t channel widening might occur and some of the o l d side - c h a n n e l s would be re - o c c u p i e d . T h e r e f o r e under these flow c o n d i t i o n s t h i s scheme would not a c t much d i f f e r e n t l y than the wide r i v e r scheme. However, care would have to..be taken to i n s u r e t h a t the set-back d i k e s were s i t u a t e d f a r enough away from the si d e - c h a n n e l s so t h a t e r o s i o n d i d not take p l a c e . 162 CHAPTER X CONCLUSIONS F l o o d H y d r o l o g y The C h i l l i w a c k R i v e r i s t y p i c a l o f many m o u n t a i n o u s s t r e a m s i n s o u t h w e s t e r n B r i t i s h C o l u m b i a . Two s e p a r a t e t y p e s o f f l o o d s c a n o c c u r — s p r i n g s n o w m e l t a n d w i n t e r r a i n s t o r m f l o o d s . A f r e q u e n c y a n a l y s i s was c a r r i e d o u t f o r e a c h f l o o d - t y p e a n d t h e r e s u l t s w e r e t h e n c o m b i n e d t o d e t e r m i n e t h e a n n u a l f l o o d f r e q u e n c y . I t was f o u n d t h a t f o r e x t r e m e f l o o d s t h e w i n t e r r a i n s t o r m e v e n t s a r e d o m i n a n t . A n a l y s i s o f t h e o c c u r r e n c e o f f l o o d i n g o v e r t h e l a s t 70 y e a r s showed t h a t t h e i n c i d e n c e o f m a j o r f l o o d s h a s b e e n u n u s u a l l y l o w s i n c e 1 9 5 0 . T h i s was a t t r i b u t e d t o s h o r t t e r m c l i m a t i c c y c l e s . The Regime o f t h e C h i l l i w a c k R i v e r A b o v e V e d d e r C r o s s i n g t h e C h i l l i w a c k R i v e r f l o w s i n a g l a c i a t e d v a l l e y t h a t h a s b e e n s u b s e q u e n t l y m o d i f i e d by r i v e r p r o c e s s e s . F o r much o f i t s l e n g t h , t h e r i v e r f l o w s on an i m p o s e d s l o p e t h r o u g h - b o u l d e r d e p o s i t s . T h e s e " l a g " d e p o s i t s become m o b i l e v e r y i n f r e q u e n t l y . T h r o u g h o u t m o s t o f t h i s r e a c h t h e r i v e r i s f r e q u e n t l y c o n f i n e d by t e r r a c e s o r v a l l e y w a l l s . 163 I n t h e two m i l e r e a c h b e t w e e n L i u m c h e n C r e e k and V e d d e r C r o s s i n g , t h e r i v e r h a s b e e n f r e e t o d e v e l o p a w i d e a l l u v i a l p l a i n , a n d t h e c h a n n e l p a t t e r n h a s a l t e r -n a t e d b e t w e e n b e i n g b r a i d e d o r s p l i t w i t h l a r g e wooded i s l a n d s . T h i s r e a c h i s v e r y u n s t a b l e l a t e r a l l y a n d d u r i n g f l o o d s bank e r o s i o n p r o v i d e s t h e m a i n s o u r c e o f s e d i m e n t t h a t i s t r a n s p o r t e d o n t o t h e f a n b e l o w V e d d e r C r o s s i n g . C h a n n e l C h a n g e s on t h e V e d d e r R i v e r The V e d d e r c h a n n e l i s o n l y a b o u t one c e n t u r y o l d , a n d s i n c e t h e i n i t i a l c h a n n e l s h i f t a r o u n d t h e t u r n o f t h e c e n t u r y , i t h a s b e e n i n a c o n s t a n t s t a t e o f t r a n s i -t i o n . S h o r t l y a f t e r t h e s h i f t , d e g r a d a t i o n a p p e a r s t o h a v e t a k e n p l a c e n e a r t h e h e a d o f t h e f a n w h i l e r a p i d c h a n n e l w i d e n i n g o c c u r r e d f u r t h e r d o w n s t r e a m . M a j o r c h a n g e s w e r e i n d u c e d b y c h a n n e l i z a t i o n on t h e l o w e r p a r t o f t h e f a n i n t h e m i d - 1 9 6 0 ' s . T h i s c h a n -n e l i z a t i o n i n i t i a l l y c a u s e d d e g r a d a t i o n a b o v e t h e r a i l -way b r i d g e and r a p i d a g g r a d a t i o n i n t h e r e a c h i m m e d i a t e l y d o w n s t r e a m . E v e n t u a l l y a g g r a d a t i o n s p r e a d u p s t r e a m i n t o t h e c h a n n e l i z e d r e a c h . S e d i m e n t T r a n s p o r t o n t h e V e d d e r R i v e r C o m p a r i s o n w i t h b e d l o a d m e a s u r e m e n t s c o l l e c t e d on t h e V e d d e r R i v e r and o t h e r g r a v e l r i v e r s showed t h e 164 o r i g i n a l E i n s t e i n b e d l o a d e q u a t i o n , w i t h s l i g h t m o d i f i -c a t i o n , c o u l d p r o v i d e r e a s o n a b l y a c c u r a t e e s t i m a t e s o f s e d i m e n t t r a n s p o r t . A b o u t o n e - t h i r d o f t h e e s t i m a t e s f e l l w i t h i n o n e - h a l f t o two t i m e s t h e m e a s u r e d r e s u l t s . I t i s b e l i e v e d t h e E i n s t e i n r e l a t i o n w o r k s b e t t e r t h a n o t h e r f o r m u l a s b e c a u s e i t s e m p i r i c a l c o e f f i c i e n t s w e r e d e r i v e d f r o m f l u m e s t u d i e s w i t h g r a v e l s e d i m e n t . A l s o , i t i s t h e o n l y r e l a t i o n t h a t c o m p u t e s b e d l o a d by s i z e f r a c t i o n r a t h e r t h a n d e p e n d i n g on a r e p r e s e n t a t i v e o r D^ Q s i z e . The r e s u l t s o f c a l c u l a t i o n s showed t h a t f o r t h e c h a n n e l g e o m e t r y e x i s t i n g b e t w e e n 1 9 7 1 - 1 9 7 5 , n e a r l y a l l o f t h e s e d i m e n t i n f l o w t h r o u g h V e d d e r C r o s s i n g was d e p o -s i t e d a b o v e t h e r a i l w a y b r i d g e . F l o o d C o n t r o l on t h e V e d d e r R i v e r B a s e d on t h e b e d l o a d t r a n s p o r t c a l c u l a t i o n s a n d on t h e o b s e r v e d s e d i m e n t s o r t i n g t h a t i s a p p a r e n t , t h e r e i s no c h a n c e o f c o n s t r u c t i n g a c h a n n e l t h a t w i l l " s l u i c e " a l l o f t h e s e d i m e n t i n f l o w a t V e d d e r C r o s s i n g t h r o u g h t h e V e d d e r R i v e r a n d i n t o t h e F r a s e r R i v e r . T h e r e f o r e , t o a c h i e v e l o n g - t e r m s t a b i l i z a t i o n o f t h e r i v e r , e i t h e r up-s t r e a m s e d i m e n t c o n t r o l o r d r e d g i n g b e l o w V e d d e r C r o s s i n g w i l l be r e q u i r e d , r e g a r d l e s s o f t h e c h a n n e l a l i g n m e n t o f t h e l o w e r r i v e r . I t was c o n c l u d e d t h a t p r o v i d i n g s e t - b a c k d i k e s t o c o n t r o l o v e r b a n k f l o o d i n g and r i v e r t r a i n i n g t o s t a b i l i z e 165 t h e V e d d e r C h a n n e l c o u l d p r o v i d e l o n g - t e r m f l o o d p r o t e c -t i o n i f c o m b i n e d w i t h s e d i m e n t c o n t r o l o r s e d i m e n t r e m o v a l . I t was a l s o c o n c l u d e d t h a t a m a i n c h a n n e l a l i g n m e n t c o u l d p r o b a b l y b e e s t a b l i s h e d w h i c h w o u l d t e n d t o l o c a l i z e d e p o s i t i o n i n w i d e r e a c h e s a l o n g t h e r i v e r . T h e r e f o r e , s e d i m e n t c o u l d b e r e m o v e d f r o m t h e s e z o n e s , w h i l e t h e c h a n n e l i n - b e t w e e n c o u l d r e m a i n r e l a t i v e l y s t a b l e . I t was s u g g e s t e d t h a t t h e m a i n c h a n n e l s h o u l d be a b l e t o c o n t a i n m o d e r a t e f l o o d s h a v i n g r e t u r n ^ p e r i o d s o f a b o u t two y e a r s (maximum i n s t a n t a n e o u s ) . T h i s w o u l d c o r r e s p o n d r o u g h l y t o a f i v e y e a r maximum d a i l y f l o o d . F o r more e x t r e m e f l o o d s , t h e f l o w s h o u l d be a l l o w e d t o s p i l l o v e r b a n k a n d be c a r r i e d b y t h e s i d e c h a n n e l s a n d f l o o d p l a i n i n s i d e t h e s e t - b a c k d i k e s . 1 6 6 BIBLIOGRAPHY Ackers, P., White, W., "Sediment T r a n s p o r t : New Approach and A n a l y s i s " , Proc. A.S.C.E., V o l . 99, 1973, pp. 2041-2060. Anderson, G. S., Hussey, K. M., " A l l u v i a l Fan Development at F r a n k l i n B l u f f s , A l a s k a " , Proc. Iowa Acad. S c i . , V o l . 69, 1962, pp. 310-322. 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Union Trans., V o l . 36, 1955. 174 TABLES TABLE 1 SUMMARY OF FLOOD CONTROL WORK ON THE VEDDER RIVER Year L o c a t i o n Work C a r r i e d Out Approximate Cost R e f e r e n c e 1921 Vedder C r o s s i n g 1922- Vedder R i v e r 192 4 below Yarrow 19 30 Downstream of B.C. Railway b r i d g e 1951 Near B.C. Railway b r i d g e 1952 One mile west of Vedder C r o s s i n g 1952 Near Browne Road 1953 Vedder R i v e r 195 4 Browne Road to Lickman Road 1955 K e i t h Wilson Road Peache Road 1956 Browne Road v •.: Vedder ^Crossing c o n s t r u c t i o n of a rock c r i b $ hear Vedder C r o s s i n g Marr, 196 4 c o n s t r u c t i o n of Vedder Canal, n o r t h and south Vedder dykes, $3,400,000 S i n c l a i r , 1961 Sumas dam and drainage works - c u t o f f meander bend - channel c l e a r i n g - bank p r o t e c t i o n - g r a v e l removal - channel c l e a r i n g - channel c l e a r i n g channel improvement, bank p r o t e c t i o n wing dam ^ bank p r o t e c t i o n $ - S i n c l a i r , 1961 $ 7,338 Township of C h i l l i w a c k $ 1,722 Township of C h i l l i w a c k $ - Township of C h i l l i w a c k $ 2,756 Township of C h i l l i w a c k $ 4,5 37 Township of C h i l l i w a c k $ 13,15 2 Township of C h i l l i w a c k $ 14,852 Township of C h i l l i w a c k Year L o c a t i o n TABLE 1 (cont'd) Work C a r r i e d Out Approximate Cost Reference 195 7 Vedder R i v e r 195 8 Lickman-Webster Road 1961 Peache Road,-Lickman Road NeSr Hopedale Road Browne Road Above Vedder C r o s s i n g 1962 B.C. Railway b r i d g e t o Ford Road 196 3 B.C. Railway b r i d g e t o Ford Road 1964 Browne Road 1965 Near B.C. Railway b r i d g e 196 7 Hopedale Road 196 8 Near B.C. Railway b r i d g e 1969 Near B.C. Railway b r i d g e g r a v e l removal $ bank p r o t e c t i o n $ 2,000 f e e t of bank p r o t e c t i o n bank p r o t e c t i o n ^ bank p r o t e c t i o n channel c l e a r i n g bank p r o t e c t i o n and dyke c o n s t r u c t i o n bank p r o t e c t i o n and dyke c o n s t r u c t i o n dyking and g r a v e l removal bank p r o t e c t i o n - dyke extended from railway b r i d g e t o Hopedale Road - bank p r o t e c t i o n - bank p r o t e c t i o n Township of C h i l l i w a c k Township of C h i l l i w a c k Township of C h i l l i w a c k $ 14,800 Township of C h i l l i w a c k $ 25,726 Township of C h i l l i w a c k $ 40,000 Township of C h i l l i w a c k $ 3,6 30 Township of C h i l l i w a c k $ 10,135 Township of C h i l l i w a c k $ 15,000 Township of C h i l l i w a c k $ 15,000 Township of C h i l l i w a c k H TABLE 1 (cont'd) Year L o c a t i o n Work C a r r i e d Out Approximate Cost Reference 19 74 Peache Road 19 75 Vedder R i v e r 19 76 Vedder R i v e r 19 76 Vedder R i v e r - r i p r a p c o n s t r u c t i o n - channel c l e a r i n g of d e b r i s Phase I F l o o d C o n t r o l Works - s c a l p i n g of g r a v e l bars - r a i s i n g banks Phase I I F l o o d C o n t r o l Works - dredging of 750,000 cubi c yards of g r a v e l $ - Township of C h i l l i w a c k $ 100,000 B.C. VJater Resources S e r v i c e , 19 76 $ 473,000 B.C. VJater Resources S e r v i c e , 19 76 $ 682,000 P e t e r s , 1978 TABLE 2 BASIN RUNOFF CHARACTERISTICS Gauge L o c a t i o n Gauge D r a i n a g e L o n g Term # A r e a ( m i 2 ) Mean ( c f s ) B a s i n Y i e l d ( i n / y r ) Maximum R e c o r d e d Minimum R e c o r d e d D a i l y D i s c h a r g e D a i l y D i s c h a r g e ( c f s ) ( c f s ) V e d d e r C r o s s i n g 8MH1 B e l o w S l e s s C r e e k 8MH55 Above S l e s s C r e e k 8MH103 C h i l l i w a c k L a k e O u t l e t 8MH16 474 323 249 127 2,440 1,500 1,350 679 69.8 65.0 73.6 72.6 27,000 17/12/17 9,000 02/12/58 10,000 04/12/75 4,100 10/06/72 280 30/11/52 359 22/01/60 256 5/11/74 104 21/10/25 —i co TABLE 3 MAJOR FLOODS ON CHI] Year 1875 1898 1906 1917 1921 1924 1928 1932 1935 Date unknown unknown Oct Dec 29 Dec 12 Feb 12 Jan 12 unknown Jan 2 6 194 8 Jun 7 1949 Nov 27 1951 Feb 10 1955 Nov 3 Discharge at Vedder C r o s s i n g (cfs) unknown unknown 19,000 27,000 19,000 17,600 17,200 unknown unknown G.H. = 12.2 f t (2) G.H. = 12.9 f t (2) G.H. = 13.5 f t (2) 15,400 Max. One Day P r e c i p i t a t i o n (inches) unknown unknown unknown 1.1/3.11 (4) Nov 12 3.50 Jan 26 snowmelt f l o o d 1.47 Nov 27 4.55 Feb 3 4.56 Nov 2 RIVER Remarks channel s h i f t e d down Vedder Creek major s h i f t i n g reported r e p o r t e d by Le Baron (1908) bridge a t Vedder C r o s s i n g destroyed no damage r e p o r t e d no damage r e p o r t e d no damage r e p o r t e d r a i l w a y embankment overtopped (Marr, 1964) ext e n s i v e f l o o d i n g to Sumas r e p o r t e d r a i l w a y embankment overtopped (Marr, 1964) no damage r e p o r t e d b r i d g e a t Vedder C r o s s i n g destroyed no damage r e p o r t e d TABLE 3 MAJOR FLOODS ON CHILLIWACK RIVER (CONTINUED) Discharge a t Max. One Day Vedder C r o s s i n g P r e c i p i t a t i o n Year Date (cfs) (inches) Remarks 1968 Jun 2 15,900 2.77 no damage r e p o r t e d Jun 1 1975 Dec 3 18,700 4.05 r a i l w a y embankment f a i l e d , Yarrow f l o o d e d Dec 1 Note: (1) A l l d i s c h a r g e s are mean d a i l y flows. (2) Gauge h e i g h t s shown f o r 1948, 1949 and 1951 were recorded at Vedder C r o s s i n g . (3) A l l p r e c i p i t a t i o n v a l u e s except 1932 recorded at C h i l l i w a c k . (4) P r e c i p i t a t i o n v a l u e s shown f o r 1932: 1.10 inches a t C h i l l i w a c k 3.11 inches a t Cu l t u s Lake CO o 181 TABLE 4 SUMMARY OF SEASONAL FLOOD DATA C h i l l i w a c k R i v e r a t V e d d e r C r o s s i n g W i n t e r F l o o d S p r i n g F l o o d Y e a r ( c f s ) D a t e ( c f s ) D a t e 1976/77 10,200 18/01/77 5 ,730 07/06/77 1975/76 18,700 03/12/75 9 ,490 19/06/76 1974/75 5,780 21/12/74 9 r380 05/06/75 1973/74 8,440 16/01/74 12 r800 19/06/74 1972/73 7,840 26/12/72 6 ,620 18/05/73 1971/72 7,590 17/03/72 12 ,700 09/06/72 1970/71 12,600 31/01/71 8 F800 13/0 5 / 7 1 1969/70 5,240 23/09/69 7 ,680 03/06/70 1968/69 8,800 17/09/68 9 ,540 24/05/69 1967/68 12,000 31/10/67 15 ,400 02/06/68 1966/67 11,600 16/12/66 10 ,400 20/06/67 1965/66 5,240 04/11/65 6 ,510 17/06/66 1964/65 7,030 02/10/64 6 ,200 11/06/65 1963/64 13,000 26/11/63 8 ,860 10/06/64 1962/63 7,660 20/11/62 4 ,870 12/06/63 1961/62 9,280 03/01/62 5, ,740 25/06/62 1960/61 9,310 15/01/61 9 240 18/06/61 1959/60 8,930 24/11/59 6, 570 02/06/60 1958/59 8,810 10/10/58 9 970 29/04/59 1957/58 4,760 17/01/58 8, 150 28/05/58 1956/57 9,300 20/10/56 6 970 08/05/57 1955/56 15,900 03/11/55 9, 700 10/06/56 1954/55 10,600 22/11/54 9, 720 12/06/55 1953/54 12,400 31/10/53 9, 800 02/07/54 1952/53 5,930 12/01/53 7, 190 13/06/53 1951/52 3,730 20/10/51 6, 770 17/05/52 1950/51 -20,000 10/02/51 6, 320 23/05/51 182 TABLE 4 SUMMARY OF SEASONAL FLOOD DATA C h i l l i w a c k R i v e r a t V e d d e r C r o s s i n g (CONTINUED) W i n t e r F l o o d S p r i n g F l o o d Y e a r ( c f s ) D a t e ( c f s ) D a t e 1929/30 10,800 10/02/30 6,330 10/06/30 1928/29 8,090 09/10/29 6,160 22/05/29 1927/28 17 ,200 12/01/28 10,080 23/05/28 1926/27 4,430 10/12/26 11,000 07/06/27 1925/26 6,790 11/12/25 3,720 27/05/26 1924/25 16,900 12/12/24 11,600 20/05/25 1923/24 17,600 12/02/24 10,700 12/05/24 1922/23 10,700 24/12/22 9,340 09/06/23 1921/22 19,000 12/12/21 12,100 03/06/22 1920/21 10,600 05/10/20 10,400 07/06/21 1918/19 - - 10,100 23/05/19 1917/18 27,000 29/12/17 8,170 09/06/18 1916/17 4,870 09/11/16 8,000 16/06/17 1915/16 9,350 28/10/15 - -1914/15 5,000 11/11/14 8,700 03/04/15 1913/14 20,000 06/01/14 5,800 15/05/14 1912/13 10,000 17/02/13 12 ,200 02/06/13 1911/12 3,650 25/01/12 10,500 20/06/12 1906/07 19,000 unknown - -N o t e : W i n t e r f l o o d p e r i o d S e p t e m b e r 1 - M a r c h 31 S p r i n g f l o o d p e r i o d A p r i l 1 - J u l y 31 A l l d i s c h a r g e s a r e mean d a i l y f l o w s TABLE 5 FLOOD FREQUENCY FLOWS C h i l l i w a c k R i v e r a t V e d d e r C r o s s i n g R e t u r n P e r i o d ( Y e a r s ) P r o b a b i l i t y o f E x c e e d a n c e (%) Mean Snowmelt ( c f s ) D a i l y D i s c h a r g e R a i n s t o r m A n n u a l ( c f s ) ( c f s ) 100 1 15,000 32,000 32,000 50 2 14 ,200 27,500 27,500 20 5 13,000 22,500 22,500 10 10 12,000 18,700 18,800 5 20 10,800 15,000 15,100 2 50 8,600 9,800 11,200 1.25 80 6 ,700 6,400 8,600 N o t e : S nowmelt f l o o d s c o n s i d e r e d t o o c c u r b e t w e e n A p r i l 1 - J u l y 3 1 . R a i n s t o r m f l o o d s c o n s i d e r e d t o o c c u r b e t w e e n A u g u s t 1 - M a r c h 31. A n n u a l f l o o d f r e q u e n c y d e t e r m i n e d by c o m b i n i n g t h e two s e a s o n a l r e l a t i o n s . 184 T A B L E 6 MAXIMUM INSTANTANEOUS FLOOD FREQUENCY E S T I M A T E S C h i l l i w a c k R i v e r a t V e d d e r C r o s s i n g R e t u r n P e r i o d ( Y e a r s ) P r o b a b i l i t y o f F l o w E x c e e d a n c e (%) S n o w m e l t F l o o d Mean M a x . D a i l y I n s t , ( c f s ) ( c f s ) R a i n s t o r m F l o o d Mean M a x . D a i l y I n s t , ( c f s ) ( c f s ) 100 1 1 5 , 0 0 0 2 2 , 5 0 0 3 2 , 0 0 0 4 8 , 0 0 0 50 2 1 4 , 2 0 0 2 1 , 3 0 0 2 7 , 5 0 0 4 1 , 3 0 0 20 5 1 3 , 0 0 0 1 9 , 5 0 0 2 2 , 5 0 0 3 3 , 8 0 0 10 10 1 2 , 0 0 0 1 8 , 0 0 0 1 8 , 7 0 0 2 8 , 1 0 0 5 20 1 0 , 8 0 0 1 6 , 2 0 0 1 5 , 0 0 0 2 2 , 5 0 0 2 50 8 , 6 0 0 1 2 , 9 0 0 9 , 8 0 0 1 4 , 7 0 0 1 . 2 5 80 6 , 7 0 0 1 0 , 1 0 0 6 , 4 0 0 9 , 6 0 0 185 TABLE 7 FREQUENCY OF HISTORICAL FLOODS Mean D a i l y A n n u a l P r o b a b i l i t y A n n u a l D i s c h a r g e o f E x c e e d a n c e R e t u r n P e r i o d Y e a r D a t e ( c f s ) (%) ( y e a r s ) 1975 Dec 3 18,700 10 10 1955 Nov 3 15,900 17 6 1928 J a n 12 17,200 13 7.7 1924 Feb 12 17,600 12.5 8 1921 Dec 12 19,000 9.5 10. 5 1917 Dec 29 27,000 2X ^50 4 o 1914 J a n 6 20,000 8 12.5 TABLE 8 SUMMARY OF MAPS/AIRPHOTOS ABOVE VEDDER CROSSING E x t e n t D a t e S c a l e V e d d e r C r o s s i n g — L i u m c h e n C r . 1886 - map V e d d e r C r o s s i n g - L i u m c h e n C r . 1905 1: 70560 map L i u m c h e n C r . - T a m a h i C r . 1910 1: 15840 map V e d d e r C r o s s i n g - T a m a h i C r . J u l y 15, 1940 1: 20676 BC 209 / P h o t o V e d d e r C r o s s i n g - T a m a h i C r . S e p t . 1952 1: 39600 BC 1622 / P h o t o V e d d e r C r o s s i n g - Tamahi C r . O c t . 24, 1958 1: 6000 BC 5005 / P h o t o V e d d e r C r o s s i n g - T a m a h i C r . 1961 1: 25000 map V e d d e r C r o s s i n g - C h i l l i w a c k L a k e 1964 1: 50000 map V e d d e r C r o s s i n g - C h i l l i w a c k L a k e S e p t . 4, 1966 1: 38520 BC 5217 / P h o t o V e d d e r C r o s s i n g - T a m a h i C r . May 1 8, 1968 1: 17124 BC 7057 / P h o t o V e d d e r C r o s s i n g - L i u m c h e n C r . M a r c h 1 1 , 1969 1: 11556 BC 5318 / P h o t o V e d d e r C r o s s i n g - L i u m c h e n C r . M a r c h 19, 1971 1: 33432 BC 5406 / P h o t o V e d d e r C r o s s i n g - L i u m c h e n C r . J u n e 19, 1976 1: 19400 BC 5714 / P h o t o TABLE 9 BEDMATERIAL DATA ABOVE VEDDER CROSSING Distance From Vedder Crossing Sample Sample T o r a t i o n Bridge (feet) Number Type Location 2 50 29 P Right side bar near Vedder Crossing 2 50 30 P Right side bar near Vedder Crossing 7 50 22 P Right side bar near Vedder Crossing 1 o 50 23 P Large i s l a n d near Vedder Crossing o 1 1 00 26 P Large i s l a n d near Vedder Crossing X X 1 ? 00 25 P Large i s l a n d near Vedder Crossing J . £. 15 00 24 P L e f t bank near Sweltzer Creek 00 5 P Right bank side bar J - J + 00 6 P Mid-channel bar O X 31 + 50 8 B Right bank side bar 14 + 00 7 P Mid-channel bar j i 55 + 50 32 P Mid-channel bar 55 + 50 31 P Mid-channel bar 73 + 50 37 P Diagonal near mobile home development / -> 7 fl 50 42 P D/S end of side bar / o 78 + 50 42A B D/Send of side bar 81 + 00 41 P Middle of side bar Rl 50 40 P Middle of side bar O X R 1 00 39 P Upstream end of side bar O X 104 + 00 34 P Small mid-channel bar near Liumchen Creek 1 ? S 00 36 P Right side bar near Liumchen Creek X ^ -J 260 + 50 58 T Right bank Osborne Rd. 14 S 25 64 T Tamahi Creek confluence J 4 J 445 + 00 48 T Point bar 1.2 miles above Tamahi Creek 445 + 00 48A T Point bar 1.2 miles above Tamahi Creek A A Q 00 45 P U/S end of point bar 1.25 miles U/S Tamah: 4 4 3 c >in I nn 59 T At Borden Creek confluence 7 yl A 4. u u nn 60 T At Slesse Creek confluence 1 f* *J 7 4 yl I 4. u u0 0 61 T Slesse Creek confluence / HH 1 9 £ E i ' 00 62 T Near Centre Creek X / D 0 63 T Near Post Creek Notation: 1. Sample type P = Photographic g r i d T = Tape g r i d B = Bulk sample 2. D/S = downstream U/S = upstream Grain Size D i s t r i b u t i o n D90 °65 D50 D35 D15 (mm) 85 61 50 37 18 30 20 17 14 11 48 33 25 17 12 77 55 44 33 14 68 55 44 37 25 47 32 25 22 12 55 42 37 31 20 60 40 32 25 16 65 40 33 23 14 55 24 15 9 1.5 100 70 52 32 13 63 43 36 31 24 78 58 48 37 22 37 26 20 16 13 26 16 12 8 -30 15 8 4 1.2 45 34 29 22 15 65 36 20 15 12 95 70 47 42 17 47 33 25 17 10 87 62 50 35 14 160 125 120 112 95 220 180 150 100 70 188 110 94 71 47 157 89 66 53 38 87 62 49 35 19 200 157 130 110 80 500 180 150 130 90 200 140 130 100 75 260 180 150 120 90 400 300 260 160 100 00 TABLE 10 SUMMARY OF HYDROLOGIC DATA ALONG CHILLIWACK RIVER Reach Lake Outlet to Chipmunk Cr. Chipmunk Cr. to Slesse Cr. Slesse Cr. to Tamahi Cr. T.imahi Cr. to Ryder Cr. Ryder Cr. to Vedder Crossing Reach Length (mi) 10.7 4.0 7.7 2.1 4.5 Drainage Area at D/S end of Reach (mi 2) 234 262 355 415 474 Major T r i bu t a r i e s i n Reach Post Cr. Centre Cr. Nesakwatch Cr. Chipmunk Cr. Slesse Cr. Borden Cr. Tamahi Cr. Ryder Cr. Liumchen Cr. Sweltzer R. Gauging S ta t i on i n Reach Drainage Area at Gauge (ml2) Period of Record Long Term Mean Fl ow (c f s ) Flood Frequency Estimates (Mean Dai ly) 2 y r 5 yr 10 y r 20 yr Maximum Recorded Flow ( c f s ) / Date Minimum Recorded Flow ( c f s ) / Date 8MH16 127 1923-1978 680 2300 2900 3200 3400 4100 10/06/72 104 21/10/25 8MH103 249 1963-1978 1350 4700 5600 6100 6500 10000 04/12/75 256 05/11/74 8MH55 323 1956-1962 1710 6500 7800 8600 9500 9000 02/12/58 359 22/01/60 None 8MH01 474 1911-1978 2440 11200 15100 27800 03/12/75 280 30/11/52 18800 22500 TABLE 11 SUMMARY OF GEOMORPHIC FEATURES Reach Lake Outlet to Chipmunk Cr. Chipmunk Cr. to S lesse Cr. Va l ley Descr ipt ion broad g l ac i a ted mountain v a l l e y extensive v a l l e y t r a i n on v a l l e y f l o o r deep stream-cut in mountain val ley Terraces v a l l e y t r a i n may be low ter race 1 continuous 1 evel corresponds to v a l l e y t r a i n Width of Va l ley F loor (mi) 0.5 0.2 Descr ipt ion of Va l ley F lat i n d e f i n i t e i n d e f i n i t e S lesse Cr. to Tamahi Cr. deep stream-cut in mountain v a l l e y 2 fragmentary l e v e l s one corresponds to v a l l e y t r a i n 0.2 fragmentary very i r r e g u l a r Tamahi Cr. to Ryder Cr. stream cut i n d e f i n i t e 0.3 fragmentary narrow forested Ryder Cr. to Vedder Crossing wide a l l u v i a l p l a i n on south bank 2 continuous l e v e l s lowest l e ve l appears recent 0.7 continuous and broad forested CHILLIWACK RIVER Relat ion of Channel to Va l ley has degraded in to v a l l e y t r a i n continuously confined Channel Bed angular boulders and cobbles entrenched and confined shallow boulder deposits over l y ing bedrock f requent ly confined by bedrock or terraces shallow gravel s over l y ing bedrock Channel Banks angular boulders and cobbles Per Cent A l l u v i a l Left Bank/ Right Bank 5 5 bedrock or. cobbles gravel 10 10 bedrock or c lay cobbles gravel 60 40 channel flows angular boulders 60 over boulder boulders, or g r a ve l , debr is cobbles cobbles 50 f requent ly 9 r a v e l confined occas iona l l y predominately predominately 90 confined gravel gravel along north 100 bank f ree on south bank TABLE 12 SUMMARY OF CHANNEL HYDRAULICS ALONG CHILLIWACK RIVER Reach Lake Outlet to Chipmunk Cr Chipmunk Cr to Slesse Cr Channel Pattern i r regu lar s l i g h t l y sinuous s i ng le channel i r r e g u l a r s i ng le channel Channel Features Ava i l ab le Hydraul ic Data Islands few none Bars few none Latera l A c t i v i t y s tab le s tab le Average Channel Slope 0.017 0.015 Channel Geometry: Discharge (c f s ) 1350 4700 5600 Top Width ( f t ) 68 73 77 long term mean 2 y r f lood 5 y r f lood Mean Depth ( f t ) 6.0 8.5 9.0 Mean Ve loc i t y ( f t/sec) 3.3 7.5 8.1 Data Source Number of Cross Sections gauge ra t i ng curve 1 Slesse Cr to Tamahi Cr Tamahi Cr to Ryder Cr Ryder Cr to Vedder Crossing confined meanders s i ng le channel i r regu la r s i ng le channel s p l i t / braided few few frequent wooded i s l ands prominent point bars diagonal bars r i f f l e s eros ion causing slumps in v a l l e y wal l s tab le frequent frequent mid-channel i r r e g u l a r diagonal bars s h i f t s , avuls ions 0.011 0.020 0.0063 1710 6500 7800 2440 11200 15100 105 115 116 217 358 370 4.8 6.6 7.1 2.1 3.9 4.5 3.4 8.5 9.5 5.4 8.0 9.0 gauge ra t ing curve 1 B.C. W.R.S. sect ions 4 O Table 13 INCIPIENT MOTION FOR BED MATERIAL ALONG CHILLIWACK RIVER L o c a t i o n Flow C o n d i t i o n D i s c h a r g e Mean Mean F r o u d e Maximum P a r t i c l e ( c f s ) V e l o c i t y D e p t h Number S i z e Moved ( f t / s ) ( f t ) (mm) C h i l l i w a c k R i v e r above Sle s s e Cr. gauge 8MH10 3 mean d a i l y 2 y r f l o o d 5 y r f l o o d 10 y r f l o o d 20 y r f l o o d 1350 4700 5600 6100 6500 3.3 7 .5 8.1 8.6 8.9 6, 8, 9, 9. 9. 0 .24 0.45 0.48 0 .50 0.51 5 50 65 75 80 C h i l l i w a c k R i v e r below Sl e s s e Cr. gauge 8MH55 mean d a i l y 2 y r f l o o d 5 y r f l o o d 10 y r f l o o d 2 0 y r f l o o d 1710 6500 7800 8600 9500 3.4 8.5 9 .5 10.2 11.0 4 , 6 7 7, 7, 6 1 2 32 0, 0, 0 0 . 0 27 58 63 65 72 6 82 90 96 103 Note: Slope a t gauge 8MH10 3 assumed 0.015 Slope a t gauge 8MH55 assumed 0.017 I n c i p i e n t motion computed using c r i t i c a l v e l o c i t y r e l a t i o n of N e i l l (1976, 1978) 192 TABLE 14 SUMMARY OF WIDTH CHANGES ABOVE VEDDER CROSSING A v e r a g e A c t i v e C h a n n e l W i d t h Y e a r ( f e e t ) 1940 790 1952 660 1958 660 1968 560 1971 430 1976 610 N o t e : C h a n n e l w i d t h m e a s u r e d b e t w e e n V e d d e r C r o s s i n g a n d L i u m c h e n C r e e k TABLE 15 SUMMARY OF CHANNEL CHANGES AND SEDIMENT EROSION ABOVE VEDDER CROSSING A p p r o x i m a t e A p p a r e n t F l o o d p l a i n A p p a r e n t S e d i m e n t Volume R e c o n s t r u c t i o n E r o s i o n E r o d e d Y e a r ( A c r e s ) ( A c r e s ) ( c u b i c y a r d s ) 1940-1952 1952-1958 1958-1971 1971-1976 92 21 91 N i l 39 22 34 47 634,000 356,000 541,000 637,000 N o t e : (1) m e a s u r e d b e t w e e n V e d d e r C r o s s i n g a n d L i u m c h e n C r e e k (2) bank h e i g h t o f e r o d e d m a t e r i a l assumed t o be 10 f e e t Table 16 SUMMARY OF CROSS SECTION DATA BELOW VEDDER CROSSING l e c t i o n Surveyed O r i g i n a l Date o f :ignation by D e s i g n a t i o n Survey BCWRS 1 1958, 59, 63 0.39 BCWRS 2 1958, 59, 63 0.98 BCWRS 3 1958, 59, 63 1.45 WSC 11 1971, 72, 73 1.57 BCWRS 4 1958, 59, 63 2.00 WSC 10 1971, 72, 73 2.05 BCWRS 28 1975 2.13 BCWRS 27 1975 2.22 BCWRS 26 1975 2. 32 BCWRS 5 1958, 59, 63 2.34 WSC 9 1971, 72, 73 2.42 WSC 25 1975 2.51 WSC 24 1975 2.61 WSC 23 1975 2.70 WSC 22 1975 2. 70 BCWRS 6 1958, 59, 63 2.77 WSC 8 1971,' 72, 73 2. 84 WSC 21 1975 2.92 WSC 20 1975 3 .02 WSC 19 1975 3.14 WSC 18 1975 3.24 WSC 17 1975 3.30 BCWRS 7 1958, 59, 63 3. 36 WSC 16 1975 3.44 WSC 7 1971, 72, 73 3.52 WSC 15 1975 3.61 WSC 14 1975 3.69 WSC 13 1975 L o c a t i o n below Hwy 1 b r i d g e Vedder Canal Vedder Canal Head of can a l Table 16 (continued) S e c t i o n Surveyed D e s i g n a t i o n by 3 .84 WSC 3 .84 BCWRS 3.91 WSC 4 .00 BCWRS 4.07 BCWRS 4 .14 BCWRS 4.23 BCWRS 4.43 BCWRS 4.43 WSC 4.50 BCWRS 4 .76 VCWRS 4 .83 BCWRS 4 .96 BCWRS 5 .00 WSC 5.13 BCWRS 5 .32 BCWRS 5.52 BCWRS 5 .61 BCWRS 5 .61 WSC 5 .75 BCWRS 5 .88 BCWRS 6.20 BCWRS 6.43 BCWRS 6 .56 WSC 6 .61 BCWRS 6.68 BCWRS 6 .95 BCWRS 7.40 BCWRS 7.58 BCWRS 7.70 BCWRS 7.70 WSC 7.75 O r i g i n a l Date o f Des i g n a t i o n Survey 12 1975 8 1958 , 59, 6 1971, 72, 5 1976 6 1976 7 1976 8 1975, 76 9 1975 , 76 5 1971, 72, 10 1975 , 76 11 1975 , 76 9 1958, 63 12 1975, 76 4 1971, 72, 13 1975, 76 14 1975, 76 15 1975, 76 10 ••: 1958, 63 3 1971, 72, 16 1975 , 76 17 1975 , 76 18 1975 , 76 19 1975 , 76 2 1971, 72, 20 1975 , 76 11 1958, 59, 21 1976 23 1976 24 1976 25 1976 1 1971, 72, 73 L o c a t i o n Cableway Railway Bridge Hopedale Road Browne Road Ford Road Peache Road Vedder C r o s s i n g Road bridge T a b l e 17 WATER SURFACE SLOPE SURVEYS Reach M i l e a g e D ate o f S u r v e y / D i s c h a r g e ( c f s ) Nov. 196 3 A p r i l 19 71 May 1 1 , 19 77 6880 1900 4000 V e d d e r C r o s s i n g - 7.75- 0.0042 0.0049 0.006 W e b s t e r Road 6.12 W e b s t e r Road 6.12- 0.0048 0.0032 F o r d Road 5.61 F o r d Road 5.61- 0.0036 0.0043 0.0031 Browne Road 5.02 Browne Road 5.02- 0.0026 0.0016 0.00226 R a i l w a y B r i d g e 4.00 R a i l w a y B r i d g e 4.00- 0.0016 0.0020 Head o f C a n a l 2.70 V e d d e r C a n a l 2.70- 0.00032 0.0009 0.39 H <D 197 TABLE 18 BANKFULL PROPERTIES OF BRAIDED SUB-CHANNELS ALONG THE VEDDER RIVER R i v e r M i l e a g e I n a c t i v e B a n k f u l l Mean Mean F l o o d p l a i n . L e v e l B e d L e v e l D e p t h ( f t ) 4.83 41 40.1 36.9 3.6 5.68 55 53.5 51.4 2.1 5.88 60 60 57.5 2.5 6.20 69 69 64.6 4.4 6.43 71 70 67.8 2.2 6 .61 77 76 72.8 3.2 6.68 • 82 80 76.5 3.5 TABLE 19 COMPOSITE BED MATERIAL SIZE DISTRIBUTION ALONG VEDDER RIVER Reach Vedder Canal 1.45-2 .42 Number o f Samples Used D 90 12 bars 45 12 pavement 54 D 65 15 32 D 5 0 (mm) 8.8 21 D 35 4.5 15 15 0.8 10 D '75 25 3. 30 1. 71 Canal Head 2.51-3.52 14 bars 35 4 pavement 6 7 16 43 9.5 32 5.0 25 1.0 16 3.09 1.56 Railway Bridge 3.61-4.43 10 bars 54 7 pavement 8 0 31 60 21 46 13 38 2.5 20 2.31 1.47 C o n s t r i c t i o n 5.0-5.61 6 bars 94 6 pavement 100 50 60 34 45 20 34 3.5 17.5 ,, 2.36 1.74 Ford Rd-Peache Rd 5.70-6 .56 4 bars 88 5 pavement 100 41 54 24 48 12 37 2.1 23 3.19 1.51 Vedder C r o s s i n g 7.1-7 .75 8 bars 95 9 pavement 120 70 77 52 63 32 49 7.5 31 2.25 1.51 199 TABLE 20 DOWNSTREAM BED MATERIAL CHANGES ON GRAVEL RIVERS R i v e r Range o f C o e f f i c i e n t D i s t a n c e R e q u i r e d P a r t i c l e o f S i z e Re- t o Reduce G r a i n S i z e s (mm) d u c t i o n (a.) s i z e by 50% ( m i l e s - 1 ) ( m i l e s ) P e a c e — 0.008-0.010 86 .6-69 R h i n e 50 -160 0.018 32.5 Mur 34 - 83 0.031 22 .5 I l l e r 50 -140 0 .0135 5 1 . 3 K i n u 20 - 70 0.0407 17.0 W a t r a s e 30 - 80 0 .067 10. 3 T e n r y u 15 - 50 0.0856 8.1 K i s o 35 - 70 0.0520 13.3 N a g a r a 25 - 40 0 .0718 9.7 Sho 20 - 50 0.0464 14 .9 Abe 15 - 90 0.1150 6.0 M a k i t a 100 -200 0 .180 3.9 K n i k 30 -400 0 .130 5.3 V e d d e r 0.193 3.6 D = D e " a d x o A l l d a t a e x c e p t K n i k , P e a c e , a n d V e d d e r R i v e r s : \. r e p o r t e d by Simons (19 7 1 ) . K n i k R i v e r d a t a r e p o r t e d by B r a d l e y e t a l (19 72) P e a c e R i v e r d a t a r e p o r t e d b y C h u r c h a n d K e l l e r h a l s , 19 78 200 TABLE 21 SUMMARY OF SUSPENDED SEDIMENT DATA ON VEDDER RIVER P e r i o d Maximum Maximum Minimum Average o f Recorded Load C o n c e n t r a t i o n Annual Record C o n c e n t r a t i o n (tons/day) (mg/1) Load (mg/1) (tons/yr) 1965-77 4,000 Dec. 3, 19 75 202,000 0 146,000 Dec. 3, 1975 Oct. 13, 1970 TABLE 22 SUMMARY OF BEDLOAD MEASUREMENTS COLLECTED ON VEDDER RIVER Date Discharge Mean Mean Sampler Bedload V e l o c i t y Depth Type (Tons/da ( f t / s e c ) ( f t ) June 1, 1971 5 ,400 5.42 3.91 basket 0 June 2, 1971 5 ,690 5.11* 3.91 basket 0 June 7, 1971 6,710 5.89* 4.17 basket 0 June 22, 1971 7,640 6.01* 4 .40 VUV 41.4 June 2 3, 1971 8.040 6.20* 4.49 VUV 54.3 J une 2 3, 1971 8,040 6.20* 4.49 basket 9.3 June 24, 1971 6,990 5.73* 4 .24 basket 0 June 24, 1971 6,990 5.73* 4 .24 VUV 29.1 June 2 5, 1971 6 ,970 5.73* 4 .24 VUV 43.5 May 26, 1972 5, 210 5.34 3.5 VUV 9.6 May 29, 1972 11,220 7.85 4.6 basket 1062 May 30, 1972 12,480 7,52 5.3 basket 453 May 31, 1972 11,640 7.23 5.2 basket 27.9 May 31, 19 72 11,300 7.02 5.2 VUV 33.9 June 1, 1972 9,630 6.46' 4.8 basket 2.7 June 1, 1972 9,630 6.46 4.8 VUV 18.3 June 2, 1972 8, 250 5.98 4.5 VUV 22 .5 June 5, 1972 8, 330 6 .04 4.5 VUV 24 .6 June 6, 1972 9,400 6 .48 4 . 7 basket 0 June 6, 1972 9,350 6.45 4.7 VUV 15.6 June 7, 1972 10,800 6.92 5.0 VUV 98.7 June 7, 1972 10,800 6.92 5.0 basket 120 June 8, 1972 11,020 6.89 5.1 basket 287 June 9, 1972 13,120 7. 72 5.3 basket 22 .2 June 13, 1972 7,400 5.29 4.5 VUV 29.1 June 15, 1972 6, 200 4.92 4.4 VUV 6.0 o TABLE 22 (continued) Date Discharge Mean Mean Sampler Bedload V e l o c i t y Depth Type (Tons/da;; ( f t / s e c ) (ft) June 2 3, 1972 5,860 4 .92 4.3 VUV 16 .5 June 30, 1972 7, 360 5 .53 4.3 VUV 6. 3 May 17, 1973 5,400 5 .09 3.9 basket 0 May 17, 1973 5 ,730 5.26 3.9 VUV 20 .5 May 17, 1973 5,900 5. 36 3.9 basket 3.1 May 18, 1973 6,080 5.43 3.9 basket 1.1 May 18, 1973 6 ,010 5.41 3.9 VUV 31.5 May 23, 1973 3,370 3.95 3.1 VUV 8.3 May 24, 1973 5,440 5.13 3.8 VUV 20 .8 May 24, 1973 6 ,500 5.60 4.0 basket 0 May 25 , 1973 4,900 4.85 3.6 VUV 16 .2 June 22 , 1973 5,000 4 .90 3.7 VUV 17.0 June 3, 1974 7,560 basket 43.5 June 4, 1974 7,700 basket 53.9 June 12, 1974 9,080 basket 280 June 13, 1974 10 ,600 basket 790.6 June 14, 1974 11,700 basket 286.9 June 15, 1974 12,600 basket 1292 .6 Note: A l l bedload data o b t a i n e d from Water Survey of Canada, Sediment Survey S e c t i o n *estimated by i n t e r p o l a t i o n of Stage-discharge measurements TABLE 23 SUMMARY OF AGGRADATION ESTIMATES PRIOR TO 1975 FLOOD Length Reach (mi) P e r i o d r a i l w a y b r i d g e - 2.6 1957 -Peache Road J u l y 1975 Peache Road - 1.1 1957 -Vedder C r o s s i n g J u l y 1975 r a i l w a y b r i d g e - 1.6 1972 -Ford Road J u l y 1975 Ford Road - 2.1 1972 -Vedder C r o s s i n g J u l y 1975 r a i l w a y b r i d g e - 2.6 1958 -Peache Road 1963 Peache Road - 1.1 1958 -Vedder C r o s s i n g 1963 r a i l w a y b r i d g e - 2.6 1971 -Peache Road 1975 Peache Road - 1.1 1971 -Vedder C r o s s i n g 1975 T o t a l D e p o s i t i o n (yd3) 192,000 130,000 135,000 100,000 17,000 80,000 84,000 Average Annual D e p o s i t i o n (yd3/yr) 10,100 6,800 33,800 25,000 3,400 16,000 16,800 Source I.P.S.C. I.P.S.C. (1) (1) B.C.W.R.S. B.C.W.R.S. Marr (1964) Marr (1964) (2) W.S.C, W.S.C. (2) Notes: (1) Based on 1957-1976 estimate made by I.P.S.C, adjus t e d f o r 1975-1976 d e p o s i t i o n ^ r e p o r t e d by Tempest (1976). o (2) Based on net channel area changes at 6 s e c t i o n s r e p o r t e d by W.S.C. Estimates are 0 0 very approximate and f o r comparison purposes o n l y . TABLE 24 BEDLOAD TRANSPORT FOR VARIOUS FLOOD EVENTS P r o b a b i l i t y o f E x c e e d a n c e i n P e r i o d I n d i c a t e d P e a k D a i l y D i s c h a r g e ( c f s ) T o t a l B e d l o a d T r a n s p o r t ( t o n s ) V e d d e r C r o s s i n g R a i l w a y B r i d g e T o t a l D e p o s i t i o n ( t o n s ) T o t a l D e p o s i t i o n ( c u . y d s . ) 0.50 0.10 0.05 0.02 8,600 12,000 13,000 14 ,200 S p r i n g Snowmelt F l o o d s 49,000 158,000 209,000 290,000 300 3,000 5, 000 8,000 48,700 155,000 204,000 282,000 36,000 115,000 151,000 210,000 W i n t e r R a i n s t o r m F l o o d s 0.50 0.10 0.05 0.02 9,800 18,700 22,500 27,500 30,000 254,000 451,000 855,000 400 12,000 29,000 61,000 29,600 242,000 422,000 794,000 22,000 180,000 313,000 645,000 N o t e : S p r i n g s n o w m e l t p e r i o d : A p r i l 1 - J u l y 31 W i n t e r r a i n s t o r m p e r i o d : S e p t . 1 - Mar. 31 F l o o d h y d r o g r a p h s u s e d t o compute b e d l o a d t r a n s p o r t shown i n F i g u r e o TABLE 2 5 SUMMARY OF CHANNEL DATA ON FOUR RIVER CONTROL PROJECTS Ri v e r Snake R i v e r Wyoming Rhine R i v e r S w i t z e r l a n d Waimakariri R i v e r New Zealand C a l i f o r n i a fans Design Discharge (cfs) 45,000 106,000 167,000 Slope 0.0036 = 0.01 0.0024 Dso Bed S i z e (mm) 20 9 -38 Channel Width (f t ) 1,000 1, 000 Channel P a t t e r n b r a i d e d s i n g l e channel s p l i t / b r a i d e d Problems aggradation bank e r o s i o n aggradation aggradation f l o o d s d e b r i s mudflows C o n t r o l Scheme levees upstream dredging, c o n s t r i c t i o n r i v e r t r a i n i n g dredging stop banks d e b r i s b a s i n s f l o o d channels K> o TABLE 2 6 REGIME EQUATIONS FOR ACTIVE GRAVEL RIVERS from Parker (1979) H C/D 5 Q = 0.253 Q U ' * ± D S = 0.223 Q ~ 0 - 4 1 0 B/D 5 ( ) = 4.4 Q °- 5 where Q = Q/ (1.65g D 5 Q D ^ 2 H c = c e n t r e l i n e channel depth S = slope B = top width Q = dominant d i s c h a r g e 207 FIGURES F I G U R E 1. S i t e L o c a t i o n FIGURE 2. Study Area Below Vedder C r o s s i n g o L u c k - a - K u c k C r e e k Sumas L a k e V e d d e r C r o s s i n g R e p r o d u c e d f r o m 0 5000 f e e t D e p a r t m e n t o f t h e I n t e r i o r T o p o g r a p h i c a l S u r v e y s B r a n c h Map TS26 ..East o f C o a s t M e r i d i a n FIGURE 3. C h i l l i w a c k R i v e r C h a n n e l s B e l o w V e d d e r C r o s s i n g A r o u n d 1902 L e g e n d 1975 f l o o d p a t h 1951 f l o o d p a t h FIGURE 5. F l o o d P a t h s A l o n g V e d d e r R i v e r i n 1 9 5 1 , 1975 I—' lb. 2 1 6 CM O 70 + 604-CD U 5 50 + rd u CD e 40 + 0) E-i 30 10 CD u o •H -P rrj +>• •H •H u CD S-l P-i 5 + N e a r G i b s o n Road M A M A S O N C h i l l i w a c k R i v e r a t C e n t r e C r e e k M A M A S 0 N D FIGURE 7. M o n t h l y Met D a t a f o r t h e C h i l l i w a c k B a s i n 217 1900 1920 1980 A t V e d d e r C r o s s i n g V e d d e r R i v e r n e a r Y a r r o w B e l o w S l e s s e C r e e k Above S l e s s e C r e e k C h i l l i w a c k L a k e O u t l e t S l e s s e C r e e k L e g e n d : J d i s c h a r g e I s t a g e o n l y FIGURE 8. Summary o f S t r e a m G a u g i n g O p e r a t i o n s A l o n g C h i l l i w a c k R i v e r 218 tn u U O W 3000 2000 1000 3000. 2000 1000 3000 2000 1000 5000 4000 3000 2000 1000 C h i l l i w a c k L a k e O u t l e t M A M J J A S A b o v e S l e s s e C r e e k M A M J J A S B e l o w S l e s s e C r e e k M A M J A A t V e d d e r C r o s s i n g M A M O N O N D O N D J A O N D F I G U R E 9 . M o n t h l y F l o w s A l o n g C h i l l i w a c k R i v e r . r a i n s t o r m s n o w m e l t 20 1 10 + O l O c t N D M M Sep FIGURE 10. H i s t o r i c a l O c c u r r e n c e o f P a s t F l o o d s 220 20,000 S 10,000 Max lnst:27,800cfs Max Daily 18,700 Winter Rainstorm Flood December 1975 26 28 30 1 3 S 7 9 11 13 15 17 19 2 a- n n u. 5 0 \ a <° I 30 *~ 20 26 28 30 1 3 5 November December 7 9 11 13 15 17 19 20,000 Ol 10,000 Summer Snowmelt Flood June 1972 A Max Inst - 15,100cfs - \ M a x Daily 12,700cfs -I I I L__J I L_ 27 29 31 1 3 5 May June 7 9 11 13 15 17 19 801 u_ 70 o 60 50 a. £ 40J-27 29 31 1 3 5 7 May 9 11 13 15 17 19 J une F i g u r e 11. Comparison o f Two Rainstorm and Snowmelt Floods 25.000r 20000 15000 10000 S 5000 1965 196 • 1953 <il966 1968 < 1 9 5 4 •1959 .1956 • 1958 • 1969 1975 '1955 10000 20000 30000 Nooksack River at Deming (cfs) FIGURE 12. C o r r e l a t i o n Between Nooksack River and C h i l l i w a c k R i v e r Floods 222 , maximum instantaneous C h i l l i w a c k R i v e r a t I — i — i — » — , — i — i — i — i — i — i — h — i — i — i — i — i — i — i — i — i — i — i — i — i — i 26 28 30 1 3 5 7 9 11 13 15 17 19 November December Climate data at C h i l l i w a c k in tn u-t xi G O •H C rd -H 4--3.. 2.. r-50 O. 40 % 30. ^ 20 JZL FIGURE 13. P r e d i c t e d and Recorded 1975 Flows 223 20000 r 4-1 u <u 10000 tji rd Xi U cn P r e d i c t e d Discharge j i ' • 10 12 14 16 18 20 Pu tn • H 0) u xi O) o SH c OH - H CU EH 10 12 14 16 18 20 November 19 32 4H o CU 20000 £ 10000 I rd Xi o CQ • H Q -rH CU O 43 oj o u a CM - H P r e d i c t e d Discharge recorded stage 4 . 0 L 10 5 fe 60 Pu e CD EH 40 20 February 1951 10 12 14 16 FIGURE 14 . P r e d i c t e d F l o o d Hydrographs f o r 1932 and 1951 25000 20000 tn 4-1 u TJ O O •H r H c < 15000 10000 5000 1910 1920 ungauged average of 1911-1975 Note: A l l flows are mean d a i l y d i s c h a r g e s recorded at Vedder C r o s s i n g j _ _ i _ 1930 1940 1950 1960 1970 J 1980 NJ NJ FIGURE 15. Time S e r i e s of Annual Floods a t Vedder C r o s s i n g ~i r ~i 1 1 r 30,000 tn S> 20,0001 Q - 10,000| c o a> 5,000 " Snowmelt Note: r e l a t i o n s d e r i v e d from mean d a i l y flows • Apri I l - Aug 31 • Sept 1 - March 31 J L _ i _ J L J L 99 95 90 80 50 20 Probability of Exceedance ( %) 10 5 2 1 0.5 FIGURE 16. F l o o d Frequency A n a l y s i s a t Vedder C r o s s i n g NJ Ln E l e v a t i o n (feet) to it* o o o o o o M r— 1 H (-• M K> CO O 00 O o O O O o O O o H O O O 1 o O O 1 0 Vedder C r o s s i n g Liumchen Cr. Ryder Cr. Tamahi Cr S l e s s e Cr. Chipmunk Cr. Nesakwatch Cr. Centre Cr. Post Cr. tr1 ro fD n M r-1 9c! 2 rt O rt i-i fD H-i-i tr tr" i-i tr c PJ PJ fD rt rV o Cu fD fD ro ry M o fD o < i-i fD (D M fD 150 1.2 mi above Vedder C r o s s i n g D i s t a n c e ( f t ) 185 165 2.5 mi above Vedder C r o s s i n g ii o t e : a l l data from Marr(1964) _ i i i i i 200 400 600 800 1000 1200 1400 1600 1800 Di s t a n c e ( f t ) 4-» m 215 c 0 •H -P rrj > 205 rH W 195 \ i \ i \ i \ i ,-' X 1958 ,' \ / IN , ^ l v V . ' N ' •I I \ I A 3.6 mi above Vedder Crossing f V ~1 t_ _ l 1_ i i -1 I : I 200 400 600 800 1000 1200 1400 1600 1800 Distanc e ( f t ) FIGURE 19. Channel C r o s s - s e c t i o n s Above Vedder C r o s s i n g 229 Chi l l iwack River Above Slesse Creek 1 I : 1 1 i l I 1000 2000 5000 10,000 Discharge (cfs) Ch i l l iwack River Below Slesse Creek 1" 1 1 1 J I 1000 2000 5000 10,000 Discharge (cfs) F i g u r e 20. H y d r a u l i c M e a s u r e m e n t s a t W a t e r S u r v e y o f C a n a d a Gauges a b o v e V e d d e r C r o s s i n g Chipmunk C r s c a l e 1" = 5 4 0 0 f t K n i c k p o i n t C h i l l i w a c k L a k e t o C h i p m u n k C r , FIGURE 21.1 C h a n n e l R e a c h D e s c r i p t i o n s C h i l l i L a k e to O S c a l e = 4 1 6 7 f t M e a n d e r s a b o v e T a m a h i C r . S l e s s e C r . t o T a m a h i C r . to FIGURE 21.3 C h a n n e l R e a c h D e s c r i p t i o n s M 233 Ryder Cr. \ Tamahi Cr. to Ryder Cr. FIGURE 21.4 Channel Reach D e s c r i p t i o n s FIGURE 21.5 Channel Reach D e s c r i p t i o n s 235 J u l y 15, 1940 Scale lin=1723 f t (Approx) Vedder C r o s s i n g May 18, 1968 S c a l e lin=1430 f t (Approx) Discharge=4230 c f s June 19, 1976 S c a l e lin=1617 f t (Approx) Discharge=9490 c f s F i g u r e 22 Comparative A i r p h o t o s - Vedder C r o s s i n g t o Liumchen Creek September 1952 FIGURE 23.1. Channel P a t t e r n Upstream of Vedder C r o s s i n g to 1958 Bars 0 1000 2000 f e e t Wooded I s l a n d s r " " " * " * ^ 1 1 ™ 1 ™ ^ June 1968 FIGURE 23.2. Channel P a t t e r n Upstream of Vedder C r o s s i n g CO road FIGURE 2 3.3. Channel P a t t e r n Upstream of Vedder C r o s s i n g M CO CO 1940 C h a n n e l i i n i m t i i IMIII< >•>• l l l l l l l l l l t l l l l l l l l l l A p p a r e n t e r o s i o n A p p a r e n t F l o o d p l a i n r e c o n s t r u c t i o n 1000 2000 f e e t V e d d e r C r o s s i n g FIGURE 2 4 . 1 . C h a n n e l Changes N e a r V e d d e r C r o s s i n g 1940-1958 t o CO ,'V:>iV.;.>i-i. 1958 Channel FIGURE 24.2. Channel Changes Near Vedder C r o s s i n g 1958-1971 O 1971 C h a n n e l A p p a r e n t e r o s i o n 1000 2000 f e e t FIGURE 24 . 3 . C h a n n e l Changes N e a r V e d d e r C r o s s i n g 1971-19 P o i n t S e d i m e n t S o u r c e s xi o -p rrj M rd co CD S3 CD CO CO CD r-i CO 5H TTTT T e r r a c e E r o s i o n T e m p o r a r y S e d i m e n t S t o r a g e u u CD x o £• •H •H CO CQ O U U T e m p o r a r y S e d i m e n t S t o r a g e Vedder R i v e r to to FIGURE 25. C o n c e p t u a l B e d l o a d Movement Above V e d d e r C r o s s i n g 2 4 4 J 1 1 1 1 1 1 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 D i s t a n c e ( f t ) FIGURE 2 7 . 1 C r o s s - s e c t i o n s Along Vedder R i v e r 245 FIGURE 27.2 C r o s s - s e c t i o n s Along Vedder R i v e r M i l e 7.40 ( n e a r V e d d e r C r o s s i r 100 200 ;. D i s t a n c e ( f t ) 300 £ 110 I M i l e 7.58 ( n e a r V e d d e r C r o s s i n g ) 100 200 300 D i s t a n c e ( f t ) M i l e 7.70 ( a t V e d d e r C r o s s i n g ) 100 200 D i s t a n c e ( f t ) 300 n o t e : a l l s e c t i o n s s u r v e y e d b y B.C.W.R.S. i 9 7 6 FIGURE 27.3 C r o s s - s e c t i o n s A l o n g V e d d e r R i v e r Near Vedder C r o s s i n g — i 4000 4-100 fl o -P -P rd m > — CD 1000 2000 3000 Dis t a n c e ( f t ) 5000 approx 1975 fcbood stage J ^ • — 0 Near Ford Rd 1000 2600 3000 Dis t a n c e ( f t ) 4000 5000 -p m o •H 1 50g CD w 40 Railway Bridge 0 1000, 2000 Di s t a n c e ( f t ) 3000 4000 FIGURE 28. S e c t i o n s Showing F l o o d p l a i n and Channel Topography r 40 -P m fl o t 3 0 -H rd > 20 « w NJ 30 25 20 15 Legend C h i l l i w a c k River discharge (cfs) • < 5000 + 5000-7500 o 7500-10000 A 10000-12500 x 12500-15000 * > 15000 10 approximate range observed _i i_ 100000 200000 300000 400000 Discharge - F r a s e r River at Hope (cfs) FIGURE 2 9 . E f f e c t of F r a s e r and Vedder River Flows on the Stage i n the Vedder Canal co 249 FIGURE 30. H y d r a u l i c 'Geometry a t Yarrow and Vedder C r o s s i n g R e s i s t a n c e Equations 1 M a n n i n g - S t r i c k l e r V/V* = 8.4(d/D 9 Q) 2 Keulegan V/V* = .6.25+5.751og(d/D 9 Q) 3 Limerinos V/V* = 3.28+5.751og(d/D q n) 20 15 10 5 4 10 20 50 R e l a t i v e Roughness (d/D n n) y o FIGURE 31. Comparison of R e s i s t a n c e Formulas Using Yarrow Data 100 (JI O 252 N o t e : A l l d a t a d e r i v e d f r o m W.S.C. mea-s u r e m e n t s 1971-75 4000 6000 8000 Discharge 10,000 12,000 F i g u r e 3 3 . B e d l o a d G r a i n S i z e M e a s u r e d n e a r Y a r r o w 0 . 5 1 2 5 1 0 2 0 5 0 1 0 0 G r a i n S i z e of Bedload (mm) cn .. „ " . Co FIGURE 3 4 . Bedload S i z e D i s t r i b u t i o n a t D i f f e r e n t Flow C o n d i t i o n s 254 2000 D i s c h a r g e ( c f s ) FIGURE 35. Bedload T r a n s p o r t a t Yarrow 255 3 0 T Tj 0) -p fd u •H 13 C H 20 OJ a H o\° E i n s t e i n (1950) 1/4 1/2 1 8 16 32 64 30r OJ -P rd O -H Tj C 20 QJ rji § 10 Pi o\o 60+ TJ 0) +J rd U •H TJ c H QJ rji rd 40 2 0 1 AckersSe White 1/8 1/4 1/2 1 8 16 32 64 note: Discrepancy Ratio= Predicted Value Observed Value Meyer-PeterSMuller t 1 ITS—1/4 1 / 2 1 T 4"—cT l b 2 6T Discrepancy Ratio FIGURE 36. Comparison of Measured and Computed Bedload at Yarrow 256 5000001 R i v e r Discharge (cfs) FIGURE 3 7 . Bedload Estimates at Vedder C r o s s i n g 257 H o r i z o n t a l D i s t a n c e based on a n a l y s i s by Gessler(1971) FIGURE 38. T h e o r e t i c a l Aggradation P r o f i l e s FIGURE 39. C o m p a r i s o n o f M e a n " B e d l e v e l s A l o n g V e d d e r R i v e r 259 ,0 l q o o f t C r o s s - s e c t i o n a t M i l e 4.43 / / V 1 1 1 1 1 1 r 0 200 400 600 D i s t a n c e ( f t ) FIGURE 40. E f f e c t of C h a n n e l i z a t i o n on Channel Geometry FIGURE 41. S p e c i f i c Gauge Record Near Yarrow FIGURE 42. S p e c i f i c Gauge Record a t Vedder C r o s s i n g 262 -p 2.0 3.0 4.0 5.0 6.0 7.0 Distanc e Along Vedder'River '(-mL) FIGURE 43. V a r i a t i o n i n D e p o s i t i o n Along Vedder R i v e r Due to 1975 Elo o d 263 F i g u r e 44. D e r i v e d H y d r o g r a p h s f o r S nowmelt and R a i n s t o r m F l o o d s Ford Rd S e t - B a c k D i k e •FIGURE 4 6 P o s s i b l e S e t - B a c k D i k e and R i v e r T r a i n i n g A l i g n m e n t 266 APPENDIX 1 267 APPENDIX 1 PERFORMANCE OF BEDLOAD FORMULA ON GRAVEL RIVERS The p e r f o r m a n c e o f a v a i l a b l e b e d l o a d f o r m u l a e w e re t e s t e d u s i n g f i e l d m e a s u r e m e n t s f r o m f i v e g r a v e l r i v e r s . S e v e r a l p a s t s t u d i e s h a v e e v a l u a t e d t h e f e a t u r e s o f t r a n s -p o r t f o r m u l a u s i n g f l u m e d a t a a n d f i e l d m e a s u r e m e n t s f r o m s a n d b e d s t r e a m s (ASCE S e d i m e n t a t i o n M a n u a l , 1975; R a u d k i v i , 1967; W h i t e , M i l l i a n d C r a b b e , 1 9 7 5 ) . However e x c e p t f o r r e p o r t s b y C h u r c h (1976) a nd H o l l i n g s h e a d ( 1 9 6 8 , 1971) v e r y l i t t l e e f f o r t has b e e n made t o t e s t t h e u s e -f u l n e s s o f t h e s e f o r m u l a on g r a v e l r i v e r s . R a t h e r t h a n t r y i n g t o e x h a u s t i v e l y t e s t e v e r y f o r m u l a a v a i l a b l e , o n l y m e t h o d s t h a t have p r o v e n r e a s o n a b l y r e l i a b l e i n t h e p a s t o r h ave b e e n d e v e l o p e d f r o m c o n d i t i o n s r e p r e s e n t a t i v e o f g r a v e l r i v e r s w e r e u s e d . I n t h i s s t u d y t h r e e b e d l o a d e q u a t i o n s were s e l e c t e d f o r t e s t i n g : M e y e r P e t e r & M u l l e r (1948) E i n s t e i n (1950) A c k e r s - W h i t e (1972) F i e l d m e a s u r e m e n t s o f b e d l o a d t r a n s p o r t i n g r a v e l r i v e r s a r e s t i l l r e l a t i v e l y s c a r c e due t o t h e t e c h n i c a l d i f f i c u l t i e s i n v o l v e d a n d t h e h i g h c o s t o f s a m p l i n g . T h e r e f o r e , c o n c l u s i o n s drawn f r o m t h i s s t u d y may n e e d t o be m o d i f i e d a s more d a t a a n d b e t t e r s a m p l i n g t e c h n i q u e s become a v a i l a b l e . A l t h o u g h c o n s i d e r a b l y more d a t a may 268 e x i s t , o n l y d a t a f r o m t h e f o l l o w i n g g r a v e l r i v e r s w e r e u s e d f o r e v a l u a t i n g t h e b e d l o a d f o r m u l a e : E l b o w R i v e r n e a r B r a g g C r . A l b e r t a ( H o l l i n g s h e a d 1 9 68, 1971) N. S a s k a t c h e w a n R i v e r a t N o r d e g g , A l b e r t a ( S a m e d i , 19 71) V e d d e r R i v e r a t Y a r r o w (Water S u r v e y o f C a n a d a , 19 7 1 , 1 9 7 2 , 1973) Snake R i v e r n e a r A n a t o n e W a s h i n g t o n (Emmett 19 76) C l e a r w a t e r R i v e r n e a r S p a l d i n g I d a h o (Emmett 19 76) The m e t h o d s u s e d t o c o l l e c t b e d l o a d , h y d r a u l i c and b e d m a t e r i a l d a t a a r e s u m m a r i z e d i n T a b l e A l . S i n c e t h e b e d l o a d m e a s u r i n g t e c h n i q u e s a s w e l l a s t h e t y p e o f i n p u t d a t a i n t h e t r a n s p o r t e q u a t i o n s v a r i e d f r o m s i t e t o s i t e a b r i e f d e s c r i p t i o n o f t h e m e t h o d s u s e d a t e a c h r i v e r a r e i n c l u d e d . B e d l o a d M e a s u r e m e n t s ; B e d l o a d m e a s u r e m e n t s on t h e E l b o w R i v e r , N. S a s k a t -chewan R i v e r , and V e d d e r R i v e r w e re made u s i n g b o t h 1/4" a n d 1/2" mesh b a s k e t s a m p l e r s . From t h e l i m i t e d d a t a a v a i l a b l e a n o v e r a l l t r a p e f f i c i e n c y o f 0.31 was a p p l i e d t o t h e m e a s u r e d d i s c h a r g e r a t e s . T h i s f a c t o r was e s t i m a t e d by H o l l i n g s h e a d (1971) a f t e r c o m p a r i n g t h e b e d l o a d d e p o -s i t e d i n an e x c a v a t e d p i t w i t h m a t e r i a l c a u g h t i n a s a m p l e r . T r a p e f f i c i e n c y w i l l v a r y w i t h d i s c h a r g e and s e d i m e n t s i z e , h o w e v e r no i n f o r m a t i o n i s i a v a i l a b l e y e t t o a c c o u n t f o r t h e s e e f f e c t s . On t h e V e d d e r R i v e r , a h a l f s i z e VUV s a m p l e r 269 was u s e d n e a r t h r e s h o l d l e v e l s a l o n g w i t h t h e b a s k e t s a m p l e r . The r e s u l t s showed t h a t t h e b a s k e t s a m p l e r s w e r e n o t s u i t a b l e f o r m e a s u r i n g b e d l o a d a t l o w f l o w s due t o t h e l o s s o f f i n e s t h r o u g h t h e c o a r s e mesh. B e d l o a d s a m p l e r s u s e d on t h e Snake a n d C l e a r w a t e r R i v e r s w e r e o f t h e H e l l e y - S m i t h t y p e a n d a r e d e s c r i b e d f u r t h e r b y Emmett ( 1 9 7 6 ) . The H e l l e y - S m i t h s a m p l e s h a v e n o t b e e n f u l l y c a l i b r a t e d h o w e v e r , p r e l i m i n a r y f i e l d t e s t i n g b y Emmett (1975) i n d i c a t e d t h e e f f i c i e n c y may a p p r o a c h 100% . The p r a c t i c a l p r o b l e m s i n v o l v e d i n m e a s u r i n g b e d l o a d a r e o u t l i n e d c l e a r l y b y S a m e d i (1971) and H o l l i n g s h e a d (1968) . B e s i d e s t h e p u r e l y t e c h n i c a l p r o b l e m s i n v o l v e d , t h e d i f f i c u l t y i n a s s e s s i n g a s a m p l e r e f f i c i e n c y f a c t o r and t h e i n h e r e n t u n s t e a d y n a t u r e o f s e d i m e n t t r a n s p o r t i n t r o d u c e s c o n s i d e r a b l e u n c e r t a i n t y i n t o a n y b e d l o a d m e a s u r e -ment. T h e r e f o r e , i n t h i s s t u d y t h e d i f f e r e n c e b e t w e e n m e a s u r e d and p r e d i c t e d b e d l o a d r a t e s s h o u l d n o t be c o n -s i d e r e d a s t h e e r r o r a s s o c i a t e d w i t h t h e f o r m u l a . I n f a c t , p r o b a b l y b o t h t h e m e a s u r e m e n t s and t h e p r e d i c t i o n s v a r y c o n s i d e r a b l y f r o m t h e " t r u e " t r a n s p o r t r a t e - i f s u c h a v a l u e h a s any r e a l m e a n i n g . H y d r a u l i c D a t a : ' The q u a n t i t y a n d t y p e o f h y d r a u l i c d a t a r e p o r t e d X f r o m e a c h s i t e v a r i e d c o n s i d e r a b l y . D a t a c o l l e c t e d f r o m 270 t h e E l b o w R i v e r a n d N o r t h S a s k a t c h e w a n R i v e r w e r e r e d u c e d t o mean h y d r a u l i c g e o m e t r y r e l a t i o n s f r o m a com-p o s i t e c r o s s - s e c t i o n r e p r e s e n t a t i v e o f t h e t e s t r e a c h . F o r e x a m p l e , a t E l b o w R i v e r t w e n t y c r o s s - s e c t i o n s w e re s u r v e y e d w i t h i n a l e n g t h o f 3400 f e e t a t s e v e r a l s t a g e i n t e r v a l s t o o b t a i n a v e r a g e c h a n n e l p r o p e r t i e s . I n c o n t r a s t Emmett (19 76) r e p o r t e d mean h y d r a u l i c c o n d i t i o n s a t one s e c t i o n r e c o r d e d d u r i n g s a m p l i n g on t h e Snake a n d C l e a r w a t e r R i v e r . I n t h i s c a s e , b e d l o a d r e s u l t s were c o m p u t e d u s i n g t h e a c t u a l r e c o r d e d d a t a m e a s u r e d a t a s i n g l e s t a t i o n . The p o s s i b i l i t y t h a t a s i n g l e c r o s s -s e c t i o n may n o t be r e p r e s e n t a t i v e o f t h e r i v e r r e a c h makes t h i s t y p e o f d a t a l e s s d e s i r a b l e f o r u s e i n p r e d i c t i n g b e d l o a d . B e d M a t e r i a l D a t a The f i n a l i n p u t r e q u i r e d f o r a l l b e d l o a d c a l c u -l a t i o n s i s t h e b e d m a t e r i a l s g r a i n s i z e d i s t r i b u t i o n . The c h o i c e o f s a m p l i n g p r o c e d u r e and s a m p l e l o c a t i o n may d r a s t i c a l l y a l t e r t h e s e d i m e n t t r a n s p o r t r a t e p r e d i c t e d f r o m f o r m u l a . T h i s i s e s p e c i a l l y t r u e f o r g r a v e l r i v e r s w here l a r g 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 , c h a n n e l p a v i n g a n d i m b r i c a t i o n o f t e n o c c u r . U n f o r t u n a t e l y , e x c e p t f o r d a t a f r o m V e d d e r R i v e r a n d E l b o w R i v e r o n l y a s i n g l e r e p r e s e n t a t i v e b e d m a t e r i a l s i z e d i s t r i b u t i o n c u r v e were a v a i l a b l e . A t E l b o w R i v e r 10 p i t s a m p l e s e x c a v a t e d 2 7 1 a t l e a s t t o t h e l a r g e s t e x p o s e d p a r t i c l e w e r e u s e d t o e s t a -b l i s h t h e b e d m a t e r i a l a v a i l a b l e f o r t r a n s p o r t ( H o l l i n g s h e a d 1 9 7 1 ) . A t V e d d e r ' R i v e r 16 p i t s a m p l e s w e r e c h o s e n i n t h e v i c i n i t y o f t h e t e s t r e a c h t o d e f i n e t h e b e d m a t e r i a l . A d d i t i o n a l s u r f a c e s a m p l e s w e r e t a k e n b y u s i n g a p h o t o -g r a p h i c g r i d m e t h o d ( K e l l e r h a l s & B r a y 1971) t o e s t a b l i s h t h e b e d r o u g h n e s s s i z e . P r e d i c t i o n R e s u l t s E i n s t e i n E q u a t i o n (1950) The o r i g i n a l 1950 E i n s t e i n p r o c e d u r e was u s e d i n t h i s s t u d y w i t h two m i n o r v a r i a t i o n s . I n t h e o r i g i n a l m e t h o d t h e mean v e l o c i t y , h y d r a u l i c r a d i u s a n d d i s c h a r g e w ere c o m p u t e d d i r e c t l y u s i n g a r e s i s t a n c e e q u a t i o n p r o -p o s e d b y E i n s t e i n and B a r b a r o s s a ( 1 9 5 2 ) . The r e d u c t i o n i n b e d s h e a r due t o f o r m l o s s e s was c o n s i d e r e d b y d i v i d i n g t h e h y d r a u l i c r a d i u s ( r ) i n t o two c o m p o n e n t s : r ' : h y d r a u l i c r a d i u s due t o b e d r o u g h n e s s r " : h y d r a u l i c r a d i u s due t o f o r m l o s s e s s o t h a t t h e s h e a r s t r e s s c o n t r i b u t i n g t o b e d l o a d movement i s : t 1 = T r ' S f . When E i n s t e i n ' s p r e d i c t e d h y d r a u l i c p a r a m e t e r s w e r e d. c o m p a r e d w i t h a c t u a l f i e l d m e a s u r e m e n t s t h e r e s u l t s showed c o n s i d e r a b l e d i s c r e p a n c i e s o n b o t h t h e V e d d e r a n d E l b o w R i v e r s . I n b o t h c a s e s E i n s t e i n ' s m e t h o d o v e r e s t i m a t e d 272 the mean depth and underestimated the mean v e l o c i t y . Since the flow r e s i s t e n c e was overestimated the p r e d i c t e d bed-l o a d r a t e s were g r e a t l y reduced. In t h i s study, known val u e s of mean v e l o c i t y , h y d r a u l i c r a d i u s and wetted p e r i -meter were used as i n p u t i n the bedload equation t o e l i m i -nate t h i s source o f e r r o r . A l s o , the h y d r a u l i c r a d i u s r due t o g r a i n roughness ( r 1 ) was computed d i r e c t l y from the Manning S t r i c h l e r e q u a t i o n . I- *•*<> < r - > 1 / 6 * s i n s t e a d of from the "bar r e s i s t a n c e graph" proposed by E i n s t e i n . The M a n n i n g - S t r i c h l e r e q u a t i o n was developed from l a b experiments by Nikuradse and from f i e l d e x p e r i -ments i n g r a v e l streams by S t r i c h l e r . I t i s a p p l i c a b l e o n l y f o r the case o f f u l l y rough t u r b u l e n t flow - a con-d i t i o n n ormally encountered i n g r a v e l r i v e r s . R e s u l t s from the E i n s t e i n equation appear to be q u i t e good c o n s i d e r i n g the l a r g e s c a t t e r o f t e n d i s p l a y e d by the f i e l d measurements. P r e d i c t i o n s on the Elbow R i v e r , Vedder R i v e r and Snake R i v e r tend t o agree with the g e n e r a l t r e n d o f the measurements throughout the range of flows en-countered d u r i n g sampling. On the N. Saskatchewan R i v e r t h r e s h o l d c o n d i t i o n s were e s t i m a t e d c l o s e l y however t r a n s -p o r t r a t e s were underestimated at hi g h e r f l o w s . The po o r e s t performance of the E i n s t e i n equation was on the Clearwater R i v e r where t h r e s h o l d c o n d i t i o n s were g r o s s l y o v e r e s t i m a t e d . 273 F o r e x a m p l e , a t a d i s c h a r g e o f 6 0,000 c f s m e a s u r e m e n t s i n d i c a t e d a t r a n s p o r t r a t e o f a p p r o x i m a t e l y 250 t o n s / d a y w h i l e t h e e s t i m a t e d t r a n s p o r t was o n l y 25 t o n s / d a y . W i t h i n c r e a s e d d i s c h a r g e t h e m e a s u r e d and p r e d i c t e d t r a n s -p o r t r a t e s t e n d t o c o n v e r g e h o w e v e r a g r e e m e n t was s t i l l p o o r . The r a t i o o f p r e d i c t e d t o m e a s u r e d t r a n s p o r t r a t e s w e r e c o m p u t e d u s i n g a l l d a t a e x c e p t f o r m e a s u r e m e n t s on t h e C l e a r w a t e r R i v e r . O n l y a b o u t one t h i r d o f t h e mea-s u r e m e n t s f e l l w i t h i n one h a l f t o two t i m e s t h e p r e d i c t e d t r a n s p o r t r a t e s . T h i s r a t i o r e p r e s e n t s a v e r y p e s s i m i s t i c e s t i m a t e o f t h e E i n s t e i n e q u a t i o n ' s p e r f o r m a n c e b e c a u s e t h e f i e l d m e a s u r e m e n t s d i s p l a y e d a l a r g e amount o f s c a t t e r . I t i s q u i t e l i k e l y t h a t a c o n s i d e r a b l e p o r t i o n o f t h i s s c a t t e r c a n be a t t r i b u t e d t o m e a s u r e m e n t e r r o r s a nd i n a c c u r -a c i e s a n d t o f l u c t u a t i o n s i n b e d l o a d t r a n s p o r t a s s o c i a t e d w i t h t u r b u l e n c e . A b e t t e r e s t i m a t i o n o f t h e e q u a t i o n s r e l i a b i l i t y was made by p l o t t i n g t h e m e a s u r e d t r a n s p o r t r a t e s a g a i n s t d i s c h a r g e on l o g - l o g p a p e r . P r e d i c t e d b e d -l o a d r a t e s were t h e n c o m p a r e d w i t h " b e s t f i t " s t r a i g h t l i n e r e l a t i o n s d e r i v e d f r o m t h e m e a s u r e m e n t s . I n t h i s c a s e , u s i n g t h e E l b o w R i v e r d a t a t h e d i s c r e p a n c y r a t i o . P r e d i c t e d T r a n s p o r t , v a r i e d f r o m 1.0 t o 1.2 5 w h i l e t h e M e a s u r e d T r a n s p o r t Snake R i v e r r e s u l t s showed a v a r i a t i o n b e t w e e n 1.0 a n d 2.5. P o o r e s t c o r r e l a t i o n o c c u r r e d on t h e C l e a r w a t e r R i v e r w h e r e 274 t h e d i s c r e p a n c y r a t i o v a r i e d f r o m 0.01 t o 0.45. M e y e r P e t e r & M u l l e r T h i s f o r m u l a was d e v e l o p e d f r o m f l u m e e x p e r i m e n t s u s i n g s e d i m e n t a s c o a r s e as 28.65 mm. The f i n a l f o r m u l a s u g g e s t e d b y M e y e r - P e t e r & M u l l e r (1948) was: S \ _ n rt A -7 I ^, \ — n T C ^^-/^ \ „ 2/3 T(^) -0.047 ( y s - y ) D 5 0 = 0 . 2 5 ( p ^ " ) g r s gs ( s u b m e r g e d b e d l o a d r a t e / p e r u n i t w i d t h ) k 3/2 The t e r m T (J-^-) r e p r e s e n t s t h e s h e a r s t r e s s on t h e b e d r w h i l e 0.047(Y G- Y)D^q i s t h e c r i t i c a l s t r e s s r e q u i r e d t o i n i t i a t e p a r t i c l e movement. U n l i k e e a r l i e r e q u a t i o n s b a s e d o n e x c e s s s h e a r s u c h as t h e duBoys e q u a t i o n , t h e M e y e r -P e t e r & M u l l e r f o r m u l a a c c o u n t s f o r t h e r e d u c t i o n i n b e d s h e a r due t o f o r m l o s s e s b y u s i n g a r e s i s t a n c e c o e f f i c i e n t k b 3 / 2 (£—) . T h x s t e r m i s t h e r a t i o o f t o t a l r e s i s t a n c e t o g g r a i n r e s i s t a n c e a nd i s c a l c u l a t e d u s i n g S t r i c h l e r ' s f o r m u l a a n d M a n n i n g ' s c o e f f i c i e n t . k, = 1.49/n b k, = 48 g I n g e n e r a l t h e M e y e r - P e t e r & M u l l e r f o r m u l a t e n d e d t o s i g -n i f i c a n t l y o v e r e s t i m a t e t h r e s h o l d c o n d i t i o n s , r e s u l t i n g i n v e r y p o o r a g r e e m e n t w i t h m e a s u r e m e n t s a t l o w e r f l o w s . On t h e V e d d e r R i v e r t h r e s h o l d c o n d i t i o n s w e r e e s t i m a t e d t o o c c u r a t 9200 c f s w h i l e m e a s u r e m e n t s showed s i g n i f i c a n t 275 sediment t r a n s p o r t commenced near 600 c f s . S i m i l a r l y , one the Snake R i v e r , t h r e s h o l d was e s t i m a t e d to be near 76,000 c f s while measurements i n d i c a t e d a value of 35,000 c f s was more l i k e l y . The Meyer-Peter & M u l l e r formula c a l c u l a t e s t h r e s h o l d c o n d i t i o n s from S h i e l d s formula x = 0.04 7. Reducing t h i s value from 0.04 7 ( Y s " Y ) D 5 0 to 0.0 3 s i g n i f i c a n t l y improved the p r e d i c t i o n s near t h r e s -h o l d however i n s u f f i c i e n t data i s a v a i l a b l e t o t e s t t h i s f u r t h e r . At h i g h e r flows the formula may tend to overestimate bedload. T h i s was e s p e c i a l l y true on the Elbow and Snake Ri v e r where the e s t i m a t e d bedload exceeded the measured va l u e s by over f i v e times. Ackers-White A c c o r d i n g t o White e t a l (19 75) the Ackers-White formula i s one o f the most r e l i a b l e bedload equations a v a i l a b l e a t p r e s e n t . For a p p l i c a t i o n to g r a v e l r i v e r s the formula s i m p l i f i e s t o : G = 0.025 D Q y (F - 1 . 0 ) 1 ' 5 s s x ' gr d 1.0 where F - V . g r 7 D ( s - l ) /32. l o g /lOd. 9 x ( — ) x O r i g i n a l l y the authors suggested using as the r e p r e -s e n t a t i v e g r a i n s i z e i n the t r a n s p o r t equation, however b e t t e r agreement with measurements o c c u r r e d when the D ^ Q 276 s i z e was u s e d . U n f o r t u n a t e l y r e s u l t s f r o m t h e A c k e r s -W h i t e e q u a t i o n w e r e s t i l l q u i t e d i s s a p p o i n t i n g . A l t h o u g h t h r e s h o l d c o n d i t i o n s w e r e e s t i m a t e d w e l l t h e f o r m u l a g e n e r a l l y o v e r e s t i m a t e d b e d l o a d r a t e s a t h i g h e r f l o w s . T h i s was e s p e c i a l l y n o t i c e a b l e o n t h e E l b o w R i v e r , V e d d e r R i v e r a n d p o s s i b l y t h e N. S a s k a t c h e w a n R i v e r . C o m p a r i n g t h e p r e -d i c t e d b e d l o a d r a t e s w i t h b e s t f i t m e a s u r e d r e l a t i o n s i n d i c a t e d t h e d i s c r e p a n c y r a t i o v a r i e d f r o m 32 t o 56 u s i n g V e d d e r R i v e r d a t a t o b e t w e e n 1.9 a n d 3.6 o n t h e Snake R i v e r . The r e a s o n f o r s u c h l a r g e d i f f e r e n c e s may be due t o t h e f o r m u l a ' s f a i l u r e t o a c c o u n t f o r f o r m l o s s e s a d e q u a t e l y . A l t h o u g h p a s t s t u d i e s h a v e f o u n d t h e A c k e r s - W h i t e f o r m u l a r e l i a b l e i t d o e s n o t a p p e a r t o be a p p l i c a b l e f o r g r a v e l r i v e r s when mean h y d r a u l i c g e o m e t r y a r e u s e d a s t h e i n p u t d a t a . L i m i t a t i o n s o f B e d l o a d T h e o r i e s i n G r a v e l R i v e r s A l t h o u g h b e d l o a d f o r m u l a o f t e n h a v e b e e n d e r i v e d f r o m d i f f e r e n t t h e o r i e s , many f o r m u l a s h a r e v e r y s i m i l a r d e f i c i e n c i e s . F o r e x a m p l e , a l l f o r m u l a e e x c e p t t h e E i n s t e i n e q u a t i o n u s e a r e p r e s e n t a t i v e g r a i n s i z e s u c h as o r D ^ Q t o d e s c r i b e t h e b e d m a t e r i a l c o m p o s i t i o n . I n t h e c a s e o f s a n d b e d s t r e a m s s u c h an a s s u m p t i o n may be r e a s o n a b l e , h o w e v e r i t d o e s n o t seem v a l i d i n t h e c a s e o f g r a v e l r i v e r s . B e s i d e s t h e much g r e a t e r s i z e r a n g e d i s p l a y e d i n g r a v e l r i v e r s , v a r i a t i o n s i n t h e s h a p e o f t h e g r a i n s i z e d i s t r i b u t i o n 277 c u r v e may a l s o be p r o n o u n c e d . A n o t h e r common f e a t u r e o f many b e d l o a d e q u a t i o n s i n c l u d i n g t h e M e y e r - P e t e r & M u l l e r a n d A c k e r s - W h i t e m e t h o d i s t h a t t h e y c a n be r e d u c e d t o t h e f o r m : G s = k 1 ( X 1 - X 2 ) N T h i s t y p e o f r e l a t i o n i s v e r y s u s c e p t i b l e t o e r r o r s when X^ •> X^j w h i c h n o r m a l l y c o r r e s p o n d s t o t h r e s h o l d c o n d i t i o n s . F o r e x a m p l e , i n t h e M e y e r P e t e r & M u l l e r f o r m u l a b e d l o a d t r a n s p o r t i s p r o p o r t i o n a l t o : k1 ( T ( 1 ! k ) 3 / 2 " o.047 ( y s " Y ) D 5 0 ) 3 / 2 k g The f a c t o r 0 . 0 4 7 ( Y _ Y ) D r „ was t a k e n f r o m S h i e l d 1 s r e l a t i o n ' s ' 50 ( ( y — I ^ T ) 0 ) = 0-047 t o d e s c r i b e t h e b e g i n n i n g o f p a r t i c l e movement. C o n s i d e r i n g t h e c o m p l i c a t i n g f a c t o r s o f b e d i m b r i -c a t i o n , a n d p a r t i c l e s h a p e i t i s l i k e l y t h e v a l u e o f 0.047 may v a r y c o n s i d e r a b l y i n a c t u a l r i v e r s . H o w e v e r , any s m a l l e r r o r i n t h i s f a c t o r w i l l be m u l t i p l i e d c o n s i d e r a b l y i n t h e e q u a t i o n . One m a j o r f a c t o r n o t c o n s i d e r e d by p r e s e n t day t h e o r y i s t h e v a r i a t i o n i n b e d c o m p o s i t i o n o v e r a f l o o d . To d a t e a l l t h e o r i e s assume t h e i n i t i a l b e d m a t e r i a l s i z e r e m a i n s c o n s t a n t . I n g r a v e l r i v e r s t h i s i s n o t l i k e l y t o o c c u r . A t l o w f l o w s t h e c o a r s e f r a c t i o n o f t h e b e d d o e s n o t move. Ho w e v e r , d u r i n g a f l o o d t h e c o a r s e r m a t e r i a l 278 w i l l e v e n t u a l l y b e g i n t o move, t h e a r m o u r e d l a y e r w i l l b r e a k up a n d f i n e r s e d i m e n t w i l l be e n t r a i n e d . T h i s c o u l d c a u s e a n i n c r e a s e i n t r a n s p o r t a s t h e c o u r s e r g r a v e l b e -comes b u r i e d by t h e f i n e r m a t e r i a l . Summary and C o n c l u s i o n s : 1. The E i n s t e i n e q u a t i o n was f o u n d t o be t h e m o s t r e l i a b l e f o r m u l a a v a i l a b l e f o r p r e d i c t i n g b e d l o a d on t h e f i v e g r a v e l r i v e r s e x a m i n e d . When i n d i v i d u a l m e a s u r e m e n t s w e r e com-p a r e d w i t h p r e d i c t e d v a l u e s o n l y one t h i r d o f t h e m e a s u r e -ments f e l l w i t h one h a l f t o two t i m e s t h e p r e d i c t e d v a l u e s . When " b e s t f i t " s t r a i g h t l i n e r e l a t i o n s w e r e e s t a b l i s h e d f r o m t h e m e a s u r e m e n t s c o n s i d e r a b l y b e t t e r a g r e e m e n t was f o u n d . 2. The A c k e r s - W h i t e a p p e a r s t o be r e l i a b l e n e a r t h r e s h o l d c o n d i t i o n s b u t o v e r e s t i m a t e d t h e b e d l o a d r a t e a t h i g h f l o w s on a l l f i v e r i v e r s e x a m i n e d . 3. The M e y e r - P e t e r & M u l l e r f o r m u l a d i d n o t p e r f o r m w e l l n e a r t h r e s h o l d c o n d i t i o n s i n t h i s t e s t . H o wever, a t h i g h e r f l o w s i t seemed t o c o n v e r g e t o w a r d s t h e m e a s u r e d r e s u l t s . 4. The p e r f o r m a n c e o f any e q u a t i o n i s r e l a t e d t o t h e q u a l i t y o f t h e i n p u t d a t a . A t p r e s e n t , i t a p p e a r s b e t t e r t o u s e mean h y d r a u l i c g e o m e t r y w h i c h i s r e p r e s e n t a t i v e o f t h e r i v e r r e a c h r a t h e r t h a n d a t a f r o m a s i n g l e c r o s s s e c -t i o n . TABLE A . l SUMMARY DESCRIPTION OF MEASUREMENT SITES Mean Flows Bed Number of R i v e r Data Source Annual Flood (cfs) During Sampling (cfs) Channel Slope M a t e r i a l S i z e ( D 5 Q mm) Measurements per Sample/ Type Elbow R i v e r H o l l i n g s h e a d (1968, 1971) 2000 1370 -3850 0.0075 25.0 24 basket N. Saskatchewan Ri v e r Samide (1971) 15000 6169 -10358 0.00158 17.0 15 basket Vedder R i v e r WSC (1971, 1972, 1973) 10000 5400 -12300 0.00195 21. 5 35 basket and % s i z e VUV Snake R i v e r „.Emmett (1976) - 32000 -133000 0.00066-0.0011 32. 0 28 He l l e y - S m i t h Clearwater Emmett (1976) - 21984 123930 0.00068-0.00011 32.0 29 Hel l e y - S m i t h K5 —1 V e d d e r R i v e r n e a r Y a r r o w d a t a p r o v i d e d b y W.S.C. ' l 10 100 TOTJO IuOOO M B e d l o a d T r a n s p o r t ( t o n s / d a y ) o FIGURE A . l C o m p a r i s o n o f B e d l o a d F o r m u l a s on V e d d e r R i v e r E l b o w R i v e r n e a r B r a g g d a t a f r o m H o l l i n g s h e a d C r . (1968) 1 : : — i i 10 100 1000 10000 B e d l o a d T r a n s p o r t ( t o n s / d a y ) FIGURE A.2 C o m p a r i s o n o f B e d l o a d F o r m u l a s o n E l b o w R i v e r North Saskatchewan River a t Nordegg data from Samedi (1971) 10000 4-5000 1 w o cu d 2000 u (0 xi m 1000 •H Q Legend: Einstein(1950) Meyer-Peter&Muller — Ackers&White Regression from measured da.ta _L 10000 FIGURE A.3 Comparison of Bedload Formulas on N. Saskatchewan River 100 1000 Bedload Transport (tons/day) 00 NJ Cleafewater R i v e r a t Spalding Washington data from Emmett (1976) in 3 lOOOOrO CD U jS 5000(| o cn •H P a> 2000Q). > •H saooo Legend: Einstein(1950) Meyer-PeterSMuller Ackers&White Regression from measured data 10 100 1000 Bedload Transport (tons/day) FIGURE A.4 Comparison of Bedload Formulas on Clearwater River 10000 S n a k e R i v e r n e a r A n a t o n e W a s h i n g t o n d a t a f r o m Emmett(1976) iSlOOOOOj. tn Irj 50000| J3 o (A -H Q 200001. L e g e n d : E i n s t e i n (1950) M e y e r - P e t e r & M u l l e r A c k e r s & W h i t e R e g r e s s i o n f r o m m e a s u r e d d a t a j 100 1000 10000 B e d l o a d T r a n s p o r t ( t o n s / d a y ) FIGURE A.5 C o m p a r i s o n o f B e d l o a d F o r m u l a s o n Snake R i v e r 100000 

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