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A preliminary study of the regional groundwater flow in the Meager Mountain geothermal area, British… Jamieson, Gordon Reginald 1981

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A PRELIMINARY STUDY OF THE REGIONAL GROUNDWATER FLOW IN THE MEAGER MOUNTAIN GEOTHERMAL AREA, BRITISH COLUMBIA by GORDON REGINALD JAMIESON B . S c , The U n i v e r s i t y of W a t e r l o o , 1979 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES DEPARTMENT OF GEOLOGICAL SCIENCES We ac c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA May 1981 © Gordon R e g i n a l d Jamieson, 1981 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agr e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f ert-b&tett/ -^£s^<J<?i^& The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date Iff/  DR-fi 12/79) ABSTRACT The Meager Mountain geothermal area i s s i t u a t e d 160 km n o r t h - n o r t h w e s t of Vancouver, B r i t i s h Columbia. V a r i o u s t y p e s of e x i s t i n g and f i e l d - g e n e r a t e d g e o l o g i c a l and hydro-g e o l o g i c a l d a t a were employed t o f u l l y e v a l u a t e the groundwa-t e r f l o w regime of the study s i t e . M a t h e m a t i c a l m o d e l l i n g was c a r r i e d out t o determine the f e a s i b l e range of r e g i o n a l groundwater f l o w c h a r a c t e r i s t i c i n the a r e a . Meager Mountain i s a v o l c a n o comprised m a i n l y of ande-s i t e and d a c i t e f l o w s , b r e c c i a s and ash. I t became a c t i v e i n the P l i o c e n e , f r a c t u r i n g the T e r t i a r y and o l d e r g r a n i t i c basement r o c k s through which i t e r u p t e d . Subsequent a l p i n e g l a c i a t i o n has d e p o s i t e d u n c o n s o l i d a t e d d e p o s i t s of v a r i a b l e t h i c k n e s s i n the v a l l e y bottom. I t can be shown t h a t the most l i k e l y p o s i t i o n f o r the water t a b l e i s a t an i n t e r m e d i a t e e l e v a t i o n i n the mountain system. A p a r t from a v e r y few s p r i n g s at h i g h e r e l e v a t i o n s , the d i s c h a r g e area i s b e l i e v e d t o be c o n f i n e d t o the p o r t i o n of the v a l l e y c o v e r e d by u n c o n s o l i d a t e d d e p o s i t s . Meager Creek H o t s p r i n g s and Pebble Creek H o t s p r i n g s a r e both l o c a t e d i n t h i s suggested d i s c h a r g e a r e a near stream l e v e l . Water b a l a n c e c a l c u l a t i o n s f o r the L i l l o o e t R i v e r b a s i n and b a s e f l o w d e t e r m i n a t i o n s i n the Meager Creek b a s i n i n d i -c a t e t h a t 14.5 t o 17% of the t o t a l p r e c i p i t a t i o n e n t e r s the groundwater system. M a t h e m a t i c a l m o d e l l i n g i n d i c a t e t h a t the amount of groundwater d i s c h a r g e i s dependent on t h e h y d r a u l i c c o n d u c t i -v i t y d i s t r i b u t i o n and water t a b l e c o n f i g u r a t i o n but indepen-dent of the depth of the f l o w r e g i o n . The pe r c e n t a g e of t o t a l p r e c i p i t a t i o n e n t e r i n g the groundwater zone i s c a l c u -l a t e d t o be 14-18%, c o r r e l a t i n g w e l l w i t h the water b a l a n c e and b a s e f l o w c a l c u l a t i o n s . The s i m u l a t i o n s were used t o e s -t i m a t e the h y d r a u l i c c o n d u c t i v i t y of the v a r i o u s m a t e r i a l s i n the Meager Mountain system. The r e p r e s e n t a t i v e h y d r a u l i c c o n d u c t i v i t i e s were found t o be 1 0 " 2 t o 10" 5 m/s f o r the u n c o n s o l i d a t e d d e p o s i t s , 10" 7 t o 10" 8 m/s f o r the basement rock and 10" 4 , 5 t o 10" 8 m/s f o r the v o l c a n i c s . The v e r t i c a l h y d r a u l i c c o n d u c t i v i t y may be as much as 5 times g r e a t e r than the h o r i z o n t a l i n the basement r o c k s . The h o r i z o n t a l h y d r a u l i c c o n d u c t i v i t y may be as much as 5 t i m e s g r e a t e r than the v e r t i c a l i n the v o l c a n i c s r o c k s . S i m i l a r v e r t i c a l h y d r a u l i c c o n d u c t i v i t y v a l u e s p r o b a b l y e x i s t i n the v o l c a n i c s and i n the basement. Recommendations f o r f u t u r e work a t the Meager Mountain g e o t h e r m a l a r e a i n c l u d e the i n i t i a t i o n of a d e t a i l e d water b a l a n c e i n the so u t h r e s e r v o i r a r e a , a f r a c t u r e survey of the v o l c a n i c r o c k s , c o n t i n u e d m a t h e m a t i c a l m o d e l l i n g , and hydrau-l i c c o n d u c t i v i t y measurements i n deep d r i l l h o l e s . TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i LIST OF ILLUSTRATION v i ACKNOWLEDGEMENTS x 1. INTRODUCTION ..1 O b j e c t i v e s 1 L o c a t i o n And A c cess 4 P r e v i o u s Work 9 B.C. Hydro And Power A u t h o r i t y 12 Energy Mines & Resources Canada 13 2. PHYSICAL SETTING 16 R e g i o n a l Geology 16 L o c a l Geology 18 P h y s i o g r a p h y 23 Thermal S p r i n g s 25 C o l d S p r i n g s 28 3. FUNDAMENTALS OF GROUNDWATER FLOW 31 D a r c y ' s Law 31 The P o r o s i t y R e l a t i o n s h i p With H y d r a u l i c C o n d u c t i v i t y 35 Homogeneity And H e t e r o g e n e i t y Of H y d r a u l i c C o n d u c t i v i t y 36 I s o t r o p y And A n i s o t r o p y Of H y d r a u l i c C o n d u c t i v i t y ...38 Water T a b l e 40 Flow Nets 40 Recharge A r e a s , D i s c h a r g e A r e a s , And Groundwater D i v i d e s 42 Steady S t a t e Flow Vs T r a n s i e n t Flow 43 The E f f e c t Of The H y d r o g e o l o g i c Environment On The Groundwater Regime 46 4. PRELIMINARY WATER BALANCE 50 P r e c i p i t a t i o n And Temperature 51 E v a p o t r a n s p i r a t i o n 54 Runoff 55 Water B a l a n c e 57 5. HYDRAULIC CONDUCTIVITY OF FRACTURED ROCK 63 F r a c t u r e Mapping And Data P r o c e s s i n g Methods 64 Meager Mountain F r a c t u r e Survey 67 R e s u l t s 67 D i s c u s s i o n 70 P u b l i s h e d F r a c t u r e P e r m e a b i l i t i e s Of V a r i o u s Rock Types 75 6. HYDROGEOLOGY 80 Water T a b l e C o n f i g u r a t i o n 82 H y d r a u l i c C o n d u c t i v i t i e s Of The G e o l o g i c M a t e r i a l s ..84 E s t i m a t e s Of Groundwater Recharge 88 7. GROUNDWATER MODELLING 92 The Computer Program 93 S i m u l a t i o n S t r a t e g y 95 Region Of Flow 95 E q u a t i o n Of Flow 97 Boundary C o n d i t i o n s 97 H y d r a u l i c C o n d u c t i v i t y D i s t r i b u t i o n 99 F i n i t e Element Method 101 Input Data 103 S e n s i t i v i t y A n a l y s e s With FOPS 104 FREESURF1 M o d e l l i n g 108 V a r i a b l e Parameters . 108 F i n i t e Element Mesh 109 R e s u l t s 110 I n t e r p r e t a t i o n 125 8. CONCLUSIONS AND RECOMMENDATIONS 128 Summary And C o n c l u s i o n 128 Geography .• 128 Geology 129 Hydrogeology 130 M a t h e m a t i c a l M o d e l l i n g 132 Recommendations 133 APPENDIX I : GLACIAL BASAL MELT FLUX CALCULATIONS IN THE MEAGER CREEK BASIN 136 APPENDIX I I : CONTOURED-POLE PLOTS OF FRACTURE DATA ..138 APPENDIX I I I : RIVER STAGE MEASUREMENTS AT MEAGER CREEK HOTSPRINGS BRIDGE, 1979 152 APPENDIX IV: DISCHARGE CALCULATION AT THE MEAGER CREEK STAGE SITE, DEC. 10, 1979 156 APPENDIX V: DECEMBER DAILY DISCHARGES OF THE LILLOOET RIVER NEAR PEMBERTON (1977-1979) 158 REFERENCES , 160 v i LIST OF TABLES Tab l e Page 4.1 P r e c i p i t a t i o n and temperature d a t a a t Pemberton Meadows and B r a l o r n e 53 5.1 O r i e n t a t i o n v a r i a t i o n s of j o i n t s e t s 70 5.2 Average o r i e n t a t i o n of j o i n t s e t s 71 5.3 J o i n t s p a c i n g and a p e r t u r e v a r i a t i o n s 72 5.4 Average s p a c i n g and a p e r t u r e 72 5.5 Summary of measured h y d r a u l i c c o n d u c t i v i t y v a l u e s f o r v a r i o u s rock types 78 7.1 Summary of s e n s i t i v i t y a n a l y s i s s i m u l a t i o n s 106 7.2 H y d r a u l i c c o n d u c t i v i t y d i s t r i b u t i o n s used i n FREESURF1 s i m u l a t i o n s 112 7.3 Recharge and h y d r a u l i c con-d u c t i v i t y d i s t r i b u t i o n s w i t h a s e t d i s c h a r g e i n FREESURF1 s i m u l a t i o n s 124 v i i LIST OF ILLUSTRATION I l l u s t r a t i o n Page 1.1 L o c a t i o n of Meager Mountain geothermal area 5 1.2 R i v e r , g l a c i e r , and mountain peak d e s i g n a t i o n 6 1.3 Photograph of Meager and P l i n t h peaks 7 1.4 H o t s p r i n g s and r e s e r v o i r l o c a t i o n s 9 1.5 D r i l l h o l e l o c a t i o n s 11 2.1 R e g i o n a l geology and l o c a t i o n of t h e r m a l s p r i n g s i n s o u t h w e r s t e r n B r i t i s h Columbia 17 2.2 L o c a l geology of the Meager Mountain a r e a 20 2.3 Photograph of the Meager Creek v a l l e y i n the South R e s e r v o i r a r e a 24 2.4 Photograph of the r a p i d l y e r o d i n g v o l c a n i c s 24 2.5 L o c a t i o n of major v e n t s a t Meager Creek H o t s p r i n g s 27 2.6 L o c a t i o n of major v e n t s a t pebble c r e e k H o t s p r i n g s 27 2.7 C o l d s p r i n g l o c a t i o n s 29 3.1 E x p e r i m e n t a l a p p a r a t u s f o r the i l l u s t r a t i o n of D arcy's law 32 3.2 H y d r a u l i c head, p r e s s u r e head and e l e v a t i o n head f o r a l a b o r a t o r y manometer 32 3.3 L a y e r e d h e t e r o g e n e i t y and t r e n d i n g h e t e r o g e n e i t y 37 3.4 Four p o s s i b l e c o m b i n a t i o n s of h e t e r o g e n e i t y and a n i s o t r o p y 37 v i i i 3.5 R e l a t i o n s h i p between l a y e r e d h e t e r o g e n e i t y and a n i s o t r o p y 41 3.6 groundwater f l o w a t v a r i o u s b o u n d a r i e s 41 3.7 Two-dimensional groundwater fl o w net 44 3.8 E f f e c t of topograph on groundwater f l o w p a t t e r n s 44 3.9 E f f e c t of geology on groundwater f l o w p a t t e r n s 47 4.1 L o c a t i o n of d a t a g a t h e r i n g s t a t i o n s i n the L i l l o o e t R i v e r a r e a 52 4.2 H y d r o m e t e o r o g i c a l regime of the L i l l o o e t R i v e r and v a l l e y bottom 56 4.3 Mean of mean d a i l y d i s c h a r g e f o r L i l l o o e t R i v e r 61 5.1 L o c a t i o n of f r a c t u r e s u r v e y s i t e s 68 6.1 G e n e r a l groundwater f l o w i n Meager Mountain 81 6.2 Water t a b l e e l e v a t i o n and seepage f a c e development 83 6.3 E q u i v a l e n t h y d r a u l i c c o n d u c t i v i t y i n l a y e r e d v o l c a n i c s 87 6.4 C r o s s - s e c t i o n of Meager Creek at stage l o c a t i o n 87 6.5 Summary of hydrogeology on the s o u t h side- of Meager Mountain 91 7.1 Region of f l o w f o r m a t h e m a t i c a l m o d e l l i n g 96 7.2 L i n e of s e c t i o n f o r r e g i o n of flo w 96 7.3 G e o l o g i c a l c o n f i g u r a t i o n s s i m u l a t e d 100 7.4 groundwater movement i n the rock and i n the u n c o n s o l i d a t e d m a t e r i a l 102 7.5 Geometries used i n FOPS s i m u l a t i o n s 105 7.6 F i n i t e element mesh used i n FREESURF1 i x s i m u l a t i o n s 110 7.7 E q u i p o t e n t i a l p a t t e r n f o r FREESURF IA and FREESURF IB c a s e s 113 7.8 E q u i p o t e n t i a l p a t t e r n f o r FREESURF IC cases 114 7.9 E q u i p o t e n t i a l p a t t e r n f o r FREESURF 2 cases 115 7.10 E q u i p o t e n t i a l p a t t e r n f o r FREESURF 3 c a s e s 116 7.11 E q u i p o t e n t i a l p a t t e r n f o r FREESURF 4 cases 117 7.12 P r e s s u r e vs depth graph of minimum water t a b l e e l e v a t i o n examples 121 7.13 P r e s s u r e vs depth graph of maximum water t a b l e e l e v a t i o n examples 122 X ACKNOWLEDGEMENTS I would l i k e t o e x p r e s s my deep a p p r e c i a t i o n t o Dr. A l l a n F r e e z e f o r h i s s u p p o r t and guidance throughout the c o u r s e of t h i s s tudy and f o r h i s c r i t i c a l r e v i ew of the manu-s c r i p t . I a l s o acknowledge the support of Dr. B i l l Mathews and Dr. Tom Brown f o r t h e i r r e v i e w of t h i s m a n u s c r i p t and f o r t h e i r p a r t i c i p a t i o n on the t h e s i s e x a m i n a t i o n committee. I w i s h t o thank Dr. Jack Souther of the G e o l o g i c a l Survey of Canada f o r h i s s u p p o r t and i n v a l u a b l e i n f o r m a t i o n he g r a c i o u s l y s u p p l i e d d u r i n g the e a r l y s t a g e s of t h i s s t u d y . I g r a t e f u l l y acknowledge the k i n d and h e l p f u l c o o p e r a t i o n and a s s i s t a n c e i n the f i e l d of John Reader, B r i a n F a i r b a n k , and S t u C r o f t of Nev i n S a d l i e r - B r o w n and Goodbrande L t d . I would l i k e t o thank Joe Stauder of the B r i t i s h Columbia Hydro and Power A u t h o r i t y f o r s u p p l i n g my room and board i n t h e f i e l d . F u r t h e r m o r e , I would l i k e t o acknowledge the h e l p f u l a d v i c e and i n f o r m a t i o n s u p p l i e d by Dr. Olav Slaymaker, Dr. P e t e r Read and Dr. Gary C l a r k e . I would l i k e t o extend my thanks t o Roberta Crosby f o r her k i n d a s s i s t a n c e and c o u n s e l on the t r i a l s and t r i b u l a -t i o n s of t y p i n g a t h e s i s on the computer. The e x c e l l e n t d r a -f t i n g i n t h i s r e p o r t was drawn by Gord Hodge. H i s work i s g r a t e f u l l y acknowledged. x i I w i s h t o thank a good f r i e n d and c o l l e a g u e Grant Garven, f o r h i s h e l p f u l s u g g e s t i o n s and a s s i s t a n c e t h r o u g h o u t t h i s study and my acedemic program a t The U n i v e r s i t y of B r i t i s h Columbia. A s p e c i a l word of thanks goes t o L i n d a Mah, f o r t y p i n g the m a n u s c r i p t . Her c o n s t a n t a s s i s t a n c e i n the f i n a l p r e -p a r a t i o n of t h i s t h e s i s has make i t s c o m p l e t i o n by t h i s date a r e a l i t y . 1 1 Chapter 1. INTRODUCTION T h i s t h e s i s i s an e v a l u a t i o n of the h y d r o g e o l o g y of the Meager Mountain geothermal a r e a . The work done i s a s m a l l p a r t of a j o i n t study of Meager Mountain b e i n g c a r r i e d out by the B.C. Hydro and Power A u t h o r i t y and Energy, Mines and R e s o u r c e s , Canada i n o r d e r t o a s s e s s the geothermal r e s o u r c e p o t e n t i a l of the a r e a . O b j e c t i v e s The main purpose of t h i s study i s t o d e v e l o p a p r e l i m i -nary m a t h e m a t i c a l model of the r e g i o n a l groundwater f l o w i n the Meager Mountain geothermal a r e a . The m a t h e m a t i c a l model w i l l p r o v i d e o n l y an a p p r o x i m a t i o n of the r e a l system, be-cause of the s i m p l i f y i n g assumptions t h a t must be made i n the model and the l i m i t e d knowledge of the s u b s u r f a c e g e o l o g i c a l and h y d r o g e o l o g i c a l c o n d i t i o n s a t Meager Mountain. However, i t i s f e l t t h a t the m a t h e m a t i c a l model can prove v a l u a b l e , d e s p i t e the l i m i t e d amount of f i e l d i n f o r m a t i o n . The i n t e n t here i s t o d e v e l o p t h r o u g h m o d e l l i n g a range of groundwater f l o w c h a r a c t e r i s t i c s t h a t i s both r e a s o n a b l e and p h y s i c a l l y p o s s i b l e , t h e r e b y r e d u c i n g the i n f i n i t e range of p o s s i b i l i -t i e s t o a s u i t e of f e a s i b l e f l o w f i e l d s . As more groundwater i n f o r m a t i o n becomes a v a i l a b l e i n the f u t u r e the s u i t e can be f u r t h e r r e f i n e d . I t must be s t r e s s e d t h a t t h i s i s a r e g i o n a l study of 2 groundwater f l o w i n the e n t i r e mountain and not a gebthermal r e s o u r c e study at a l o c a l s c a l e . B e f o r e one can f o c u s on a s p e c i f i c a r e a , the system as a whole must be u n d e r s t o o d . The i n c o r p o r a t i o n of heat f l o w i n the groundwater model i s beyond the scope of t h i s r e p o r t . Heat f l o w would s l i g h t l y a l t e r the s u b s u r f a c e f l o w paths but no s u b s t a n t i a l change i n the g e n e r a l f l o w c h a r a c t e r i s t i c s would be e x p e c t e d . I t i s suggested t h a t f u t u r e m a t h e m a t i c a l m o d e l l i n g s h o u l d c o u p l e the heat f l o w w i t h the groundwater f l o w . . In Chapter 1, the p r e v i o u s work undertaken i n the Meager Mountain a r e a by the B r i t i s h Columbia Hydro and Power A u t h o r i t y and the G e o l o g i c a l Survey of Canada w i l l be d i s -c u s s e d . Numerous g e o l o g i c a l , g e o c h e m i c a l and g e o p h y s i c a l s u r v e y s have been completed s i n c e 1973. In Chapter 2, the p h y s i o g r a p h y and the complex l o c a l and r e g i o n a l geology are examined. The p h y s i o g r a p h i c n a t u r e and l o c a t i o n of the Meager Mountain hot and c o l d s p r i n g s are a l s o c o n s i d e r e d . In Chapter 3, the b a s i c p h y s i c s of groundwater f l o w i s d i s c u s s e d . The m a t e r i a l i s c o v e r e d i n g r e a t e r d e t a i l than i s normal i n h y d r o g e o l o g i c a l r e p o r t s i n an attempt t o g e n e r a t e an u n d e r s t a n d i n g of groundwater f l o w a c r o s s the i n t e r d i s c i p -l i n a r y b o u n d a r i e s of the Meager Mountain geothermal p r o j e c t . In Chapter 4, the c l i m a t i c c o n d i t i o n s and the amount of r u n o f f out of the L i l l o o e t R i v e r b a s i n are d i s c u s s e d and a 3 c a l c u l a t i o n of a p r e l i m i n a r y water b a l a n c e f o r the b a s i n i s made. The o b j e c t i v e i s t o e s t i m a t e the p e r c e n t a g e of the t o t a l p r e c i p i t a t i o n t h a t e n t e r s the groundwater system. The c h a r a c t e r i s t i c s of the s u b s u r f a c e f l o w regime are dependent on the amount of water e n t e r i n g the system. In Chapter 5, s p e c i a l a t t e n t i o n i s p a i d t o the h y d r a u l i c c o n d u c t i v i t y of f r a c t u r e d r o c k . F r a c t u r e mapping and d a t a p r o c e s s i n g methods are c o n s i d e r e d . The r e s u l t s and s i g n i f i -cance of the Meager Mountain f r a c t u r e s u r v ey a r e d i s c u s s e d . To check the v a l i d i t y of the s u r v e y , the r e s u l t s a re compared w i t h p u b l i s h e d d a t a on the f r a c t u r e p e r m e a b i l i t y of v a r i o u s rock t y p e s . In Chapter 6, a s p e c t s of the hydrogeology are examined i n c l u d i n g the water t a b l e c o n f i g u r a t i o n and h y d r a u l i c conduc-t i v i t y of the d i f f e r e n t g e o l o g i c m a t e r i a l s . The amount of groundwater r e c h a r g e i n the Meager Creek b a s i n i s c a l c u l a t e d and compared w i t h the amount d e t e r m i n e d by the water b a l a n c e , f o r the e n t i r e L i l l o o e t R i v e r b a s i n . In Chapter 7, a d i s c u s s i o n of the groundwater m o d e l l i n g i s p r e s e n t e d t o i l l u s t r a t e t h a t a s h a l l o w f l o w system on the o r d e r of 2 km deep or l e s s , r a t h e r than a d e e p e r - s e a t e d s y s -tem, i s more l i k e l y t o produce the t o t a l d i s c h a r g e of water observed i n the mountain d i s c h a r g e a r e a s . 4 L o c a t i o n and Access The Meager Mountain v o l c a n i c complex i s l o c a t e d 160 km n o r t h - n o r t h w e s t of Vancouver, B r i t i s h Columbia and a p p r o x i -m a t e l y 60 km northwest of Pemberton ( F i g . 1.1). Most of the mountain complex and the area of concern l i e south of the L i l l o o e t R i v e r and n o r t h of Meager Creek ( F i g . 1.2). Acc e s s t o the mountain complex i s by paved highway from Vancouver t o 20 km northwe s t of Pemberton where g r a v e l l e d F o r e s t r y Development and p r i v a t e l o g g i n g roads c o n t i n u e t o the mountain a r e a . A ccess w i t h i n the a r e a i s by l o g g i n g road or r e c e n t l y b u i l t by B.C. Hydro roads ( F i g . 1.2). Meager Mountain has a number of v o l c a n i c peaks i n c l u d i n g P l i n t h Peak, Mount Meager, Mount Job, C a p r i c o r n Mountain and P y l o n Peak. F i g u r e 1.3 i s a view of the Meager and P l i n t h peaks from the L i l l o o e t R i v e r v a l l e y . The mountain a r e a i s capped by an e x t e n s i v e system of g l a c i e r s t h a t s e a s o n a l l y feeds many of the h i g h g r a d i e n t streams on the mountain s i d e . The streams f e e d i n g Meager Creek i n c l u d e D e v a s t a t i o n Creek, Boundary Creek, No Good Creek, A n g e l , Camp, Canyon and C a p r i c o r n Creek. Mosaic Creek, A f f l i c t i o n , Job and F a l l Creek a l l fe e d i n t o the L i l l o o e t R i v e r o f f the n o r t h and e a s t f l a n k s of the mountain. The major h o t s p r i n g s i n the a r e a s a r e the Meager Creek and Pebble Creek H o t s p r i n g s ( F i g . 1.4). The Meager Creek H o t s p r i n g s a re a p p r o x i m a t e l y 6 km from the c o n f l u e n c e of 5 F i g u r e 1.2 R i v e r , g l a c i e r and mountain peak names i n t h e Meager Mou n t a i n a r e a . 7 F i g u r e 1.3 Meager and P l i n t h peaks. 8 Meager Creek w i t h the L i l l o o e t R i v e r . The Pebble Creek H o t s p r i n g s a r e l o c a t e d on the northwest s i d e of the L i l l o o e t R i v e r , 7.5 km upstream from i t s i n t e r s e c t i o n w i t h Meager Creek. The two most p r o m i s i n g a r e a s f o r geothermal development, as d e t e r m i n e d by r e s i s t i v i t y s u r v e y s , are o u t l i n e d i n F i g u r e 1.4. The r e g i o n a l o n g the L i l l o o e t R i v e r i n c l u d i n g the Pebble Creek H o t s p r i n g s has been d e s i g n a t e d the N o r t h R e s e r v o i r . The area n o r t h of Meager Creek i n c l u d i n g No Good and Angel Creek i s c a l l e d the South R e s e r v o i r . In g e o l o g y , the term r e s e r v o i r i n d i c a t e s t h e r e has been an a c c u m u l a t i o n of f l u i d i n a permeable g e o l o g i c u n i t under adequate t r a p c o n d i t i o n s . Trap c o n d i t i o n s a r e not e s s e n t i a l t o e x p l a i n the presence of hot water i n the basement r o c k . A more p l a u s i b l e e x p l a n a t i o n i s t h a t r e g i o n a l groundwater f l o w t h r o u g h the more permeable zones or a q u i f e r s i n t h e rock i s s u p p l y i n g a c o n s t a n t f l o w of hot water to the a r e a . T h i s e x p l a n a t i o n w i l l become c l e a r l a t e r i n the r e p o r t . To be c o n s i s t e n t w i t h p r e v i o u s r e p o r t s the terms N o r t h and South R e s e r v o i r w i l l be used, t o r e f e r t o the two a r e a s as they a r e o u t l i n e d i n F i g . 1.2. Most of the f i e l d work d i s c u s s e d i n the next s e c t i o n has been c o n c e n t r a t e d on the South R e s e r v o i r due t o i t s e a s i e r a c c e s s i b i l i t y and i t s more p r o m i s i n g , i n i t i a l g e o p h y s i c a l and d r i l l i n g r e s u l t s . 9 F i g u r e 1.4 H o t s p r i n g s and r e s e r v o i r l o c a t i o n s i n the Meager Mountain a r e a . 10 P r e v i o u s Work In 1973 the Department of Energy, Mines and Resources Canada t h r o u g h the G e o l o g i c a l Survey of Canada and the E a r t h P h y s i c s Branch began t o a s s e s s the geothermal r e s o u r c e p o t e n -t i a l of western Canada. The l o c a t i o n and age of Q u a t e r n a r y v o l c a n i c s and h i g h l e v e l p l u t o n s were c a t a l o g u e d and t h i s study was f o l l o w e d by a g e o c h e m i c a l survey of t h e r m a l s p r i n g s to i d e n t i f y the waters most l i k e l y t o have been a t much h i g h e r t e m p e r a t u r e s a t depth. As a r e s u l t of t h i s work the Meager Mountain area was chosen as the most f a v o u r a b l e r e g i o n f o r more d e t a i l e d i n v e s t i g a t i o n (Lewis and S o u t h e r , 1978). S i n c e 1973 v a r i o u s s u r v e y s i n the Meager Mountain a r e a have been conducted by the G e o l o g i c a l Survey of Canada and the E a r t h P h y s i c s Branch of Energy Mines and Resources Canada and by N e v i n , S a d l i e r - B r o w n , Goodbrande L t d . , and t h e i r sub-c o n t r a c t o r s f o r the B r i t i s h Columbia Hydro and Power A u t h o r i t y . Much of the e a r l y work i n v o l v e d g e o p h y s i c a l s t u -d i e s such as r e s i s t i v i t y , s e l f - p o t e n t i a l , s e i s m i c and magne-t o t e l l u r i c s u r v e y s . E x t e n s i v e g e o l o g i c mapping of the r e g i o n and g e o c h e m i s t r y of the t h e r m a l and c o l d waters has been com-p l e t e d . In r e c e n t y e a r s a g r e a t e r amount of d r i l l i n g has been undertaken i n the p r o m i s i n g a r e a s d e l i n e a t e d by the i n i -t i a l g e o p h y s i c a l work. The l o c a t i o n of these d r i l l h o l e s i s i l l u s t r a t e d i n F i g u r e 1.5. The f o l l o w i n g summary of work completed i s d i v i d e d i n t o two l i s t s , one f o r each of the two main p a r t i c i p a n t s i n the 11 Glacier Logging Road Drill Hole F i g u r e 1.5 D r i l l h o l e DRILL HOLES 1. E M R - 1 2. E M R - 2 3. M1 - 7 4 D 4. M 2 - 7 5 D 5. M 3 - 7 5 D 6. M 4 - 7 5 D 7. L1 - 7 8 D 8. M 5 - 7 8 D l o c a t i o n s i n t h e Meager Mountain a r e a . 9. M 6 - 7 9 D 10. M 7 - 7 9 D 11. M 8 - 7 9 D 12. M 9 - 8 0 D 13. M 1 0 - 8 0 D 14. M11 - 8 0 D 15. M 1 2 - 8 0 D 16. L 2 - 8 0 D 17. L 3 - 8 0 D 12 p r o j e c t . A p o r t i o n of t h i s summary i s taken from F a i r b a n k et a l . (1979). B.C. Hydro and Power A u t h o r i t y 1974 G e o l o g i c a l , g e o c h e m i c a l and g e o p h y s i c a l s u r v e y s were i n i t i a t e d . 1975 D i p o l e - d i p o l e r e s i s t i v i t y s u r v e y s , diamond d r i l l i n g and water g e o c h e m i s t r y s t u d i e s were performed on the south s i d e of the mountain area i n the Meager Creek v a l l e y . T h i s work d e f i n e d the South R e s e r v o i r as a t a b u l a r shaped body open t o the n o r t h under Meager Mountain. 1976 A s e l f - p o t e n t i a l ( S P ) g e o p h y s i c a l s u r v e y on the n o r t h s i d e of the mountain was i n c o n c l u s i v e . 1977 A r e s i s t i v i t y low was d e l i n e a t e d near the c o n f l u e n c e of the L i l l o o e t R i v e r and Pebble Creek u s i n g a p o l e -p o l e r e s i s t i v i t y s u r v e y . 1978 P o l e - p o l e r e s i s t i v i t y work on the n o r t h and south s i d e of the mountain f u r t h e r d e l i n e a t e d the r e s e r v o i r r e -gimes. A minor d i p o l e - d i p o l e survey was undertaken i n the N o r t h R e s e r v o i r a r e a . Two e x p l o r a t o r y h o l e s were d r i l l e d , one i n the N o r t h R e s e r v o i r and one i n the South R e s e r v o i r . Twelve p e r c u s s i o n d r i l l h o l e s were sunk a l o n g Meager Creek and near the L i l l o o e t R i v e r a p p r o x i m a t e l y 1 km n o r t h of i t s c o n f l u e n c e w i t h Meager Creek. G e o l o g i c mapping was a c c o m p l i s h e d , m o s t l y i n the South R e s e r v o i r a r e a . Radon gas and 13 mercury s u r v e y s were undertaken i n an attempt t o de-l i n e a t e geothermal water pathways t o the s u r f a c e . 1979 The d i p o l e - d i p o l e r e s i s t i v i t y s urvey was c o n t i n u e d i n the N o r t h R e s e r v o i r a r e a . Three e x p l o r a t i o n h o l e s were d r i l l e d i n the South R e s e r v o i r . G e o l o g i c map-p i n g of the South R e s e r v o i r a rea was c o n t i n u e d . A r e c o n n a i s s a n c e study of basement-rock a l t e r a t i o n was i n i t i a t e d t o de t e r m i n e i f t h e r e i s a h y d r o t h e r m a l a l t e r a t i o n p a t t e r n a s s o c i a t e d w i t h the i n f e r r e d n o r t h - s o u t h s t r u c t u r a l zone i n e i t h e r the N o r t h or South R e s e r v o i r ( F a i r b a n k et a l . , 1980). 1980 F i v e e x p l o r a t i o n h o l e s were d r i l l e d i n the South R e s e r v o i r . G e o l o g i c mapping was c o n t i n u e d i n the N o r t h and South R e s e r v o i r a r e a s . A f r a c t u r e survey of the basement g r a n d i o r i t e s was undertaken i n the South R e s e r v o i r . Energy Mines & Resources Canada 1973 Two 50 m diamond d r i l l h o l e s were bored a t the Meager Creek H o t s p r i n g s . 1974 M i c r o s e i s m i c i t y s t u d i e s were completed i n the Meager Mountain a r e a . 1976 S e i s m i c p r o f i l i n g was undertaken i n the upper L i l l o o e t V a l l e y , m a g n e t o t e l l u r i c s u r v e y s were e x e c u t e d between Meager Creek and Pemberton Meadows i n the L i l l o o e t V a l l e y . Diamond d r i l l i n g and s t u d i e s of temperature g r a d i e n t s were undertaken i n the L i l l o o e t and 14 Squamish v a l l e y s by Lewis (1977) of the E a r t h P h y s i c s Branch. A water g e o c h e m i s t r y study of Pebble and Meager Creek H o t s p r i n g s and s u r f a c e waters was done by Hammerstrom and Brown (1977) a t the Department of G e o l o g i c a l S c e i n c e s , U n i v e r s i t y of B r i t i s h Columbia and found no e v i d e n c e t h a t the water had been heated above 80°C. 1977 D e t a i l e d g e o l o g i c a l and s t r a t i g r a p h i c mapping of the Meager Mountain v o l c a n i c complex was i n i t i a t e d by Read (1977) f o r the G e o l o g i c a l Survey of Canada. M i c h e l and F r i t z (1977) of the U n i v e r s i t y of W a t e r l o o , Department of E a r t h S c i e n c e performed an i s o t o p e study of stream water, s p r i n g water and snow samples i n the Meager Mountain a r e a t o i n t e r p r e t the o r i g i n , h i s t o r y , f l o w and c h e m i s t r y of the n a t u r a l d i s c h a r g i n g groundwater. 1978 Read c o n t i n u e d t o map the v o l c a n i c complex. Lewis and Souther (1978) r e l e a s e d a summary and i n t e r p r e t a t i o n of the i n f o r m a t i o n o b t a i n e d a t Meager Mountain t o date w i t h r e s p e c t ot i t s geothermal r e s o u r c e p o t e n -t i a l . 1979 Read (1979) c o n t i n u e d mapping and r e l e a s e d a g e o l o g i -c a l map of the Meager Mountain a r e a . C l a r k (1980) of the U n i v e r s i t y of W a t e r l o o , Dept. of E a r t h S c i e n c e s , undertook an i s o t o p e h y d r o geology and geothermometry study of the t h e r m a l waters a t Meager Mountain and found no e v i d e n c e t h a t the waters were heated above 140°C. With the f a m i l a r i z i n g i n t r o d u c t o r y m a t e r i a l a t hand, the p h y s i c a l s e t t i n g of the Meager Mountain a r e a can now be de-s c r i b e d i n d e t a i l . 16 Chapter 2. PHYSICAL SETTING In an attempt t o i n t e r p r e t the hydrogeology of an a r e a one must f i r s t have an u n d e r s t a n d i n g of the m a t e r i a l t h r o u g h which the water i s f l o w i n g and of the l o c a t i o n s where the water i s d i s c h a r g i n g from the m a t e r i a l . I t i s t h e r e f o r e es-s e n t i a l t h a t the geology of an a r e a and the s p r i n g l o c a t i o n s a r e known, i f r e a s o n a b l e h y d r o g e o l o g i c a l i n t e r p r e t a t i o n s a re t o be made. T h i s c h a p t e r d i s c u s s e s the geology of the Meager Mountain a r e a and the p h y s i c a l s e t t i n g of the hot and c o l d s p r i n g s . R e g i o n a l Geology Meager Mountain i s s i t u a t e d i n the Coast Mountains near the a x i s of the Coast P l u t o n i c Complex, a n o r t h w e s t e r l y t r e n -d i n g b e l t of T e r t i a r y and o l d e r g r a n i t i c and metamorphic r o c k s . The n o r t h w e s t e r l y t r e n d i n g Pemberton B e l t of l a t e T e r t i a r y and Quaternary p l u t o n s , and the G a r i b a l d i B e l t of n o r t h - s o u t h t r e n d i n g Q u a t e r n a r y v o l c a n o e s , i n t e r s e c t w i t h i n the Coast P l u t o n i c Complex a t the S a l a l P l u t o n near Meager Creek ( F i g . 2.1) (.Lewis and Souther , 1978) . P o tassium-argon d a t e s suggest t h a t the p l u t o n s of the Pemberton B e l t range from 7.9 t o 18 Ma o l d . The v o l c a n o e s of the G a r i b a l d i B e l t a r e much younger, g i v i n g p o t a s s i u m - a r g o n ages of 4 Ma t o l e s s than 100,000 y e a r s . The Pemberton B e l t i s b e l i e v e d t o con-s i s t of s u b v o l c a n i c r o o t s of a Miocene v o l c a n i c f r o n t r e l a t e d 17 F i g u r e 2.1 R e g i o n a l geology and the l o c a t i o n o f t h e r m a l s p r i n g s i n s o u t h w e s t e r n B r i t i s h Columbia ( a f t e r Lewis and S o u t h e r , 1978) 18 t o the s u b d u c t i o n of the Juan de Fuca P l a t e (Lewis and S o u t h e r , 1 9 7 8 ) . The s i x a n d e s i t e - d a c i t e v o l c a n o e s of the G a r i b a l d i B e l t are a l s o c o n s i d e r e d t o be r e l a t e d t o t h i s sub-d u c t i o n , and a r e b e l i e v e d t o be an e x t e n s i o n of the H i g h Cascades i n the western U n i t e d S t a t e s , which i n c l u d e Mount Baker, Mount S t . H e l e n s , and o t h e r v o l c a n i c c e n t r e s ( C l a r k , 1 9 8 0 ) . In the Meager Mountain a r e a the C o a s t a l P l u t o n i c complex c o n s i s t s of northwest t r e n d i n g d i s c o n t i n u o u s s t r i p s of meta-v o l c a n i c s and metasediments surrounded by q u a r t z d i o r i t e s and g r a n o d i o r i t e s and a l l o v e r l a i n by i s o l a t e d p a t c h e s of younger v o l c a n i c r o c k s . The S a l a l Creek P l u t o n , a q u a r t z monzonite, c u t s the o l d e r p l u t o n i c and metamorphic r o c k s near the head of the L i l l o o e t R i v e r . Some s m a l l e r s a t e l l i t e b o d i e s of the p l u t o n u n d e r l i e p a r t of the n o r t h p o r t i o n of Meager Mo u n t a i n . The S a l a l Creek P l u t o n i s p a r t of the Pemberton B e l t of h i g h l e v e l p l u t o n s . L o c a l Geology The Meager Mountain V o l c a n i c Complex was o r i g i n a l l y mapped by Anderson (1975) f o r a B.Sc. t h e s i s a t the U n i v e r s i t y of B r i t i s h Columbia. More r e c e n t l y Read (1977, 1979) mapped the a r e a i n g r e a t e r d e t a i l under c o n t r a c t t o the G e o l o g i c a l Survey of Canada. The o l d e r p o r t i o n of the complex c o m p r i s e s m a i n l y wides-pread a n d e s i t e and i s best exposed i n the s o u t h . The younger 19 n o r t h h a l f i s composed of d a c i t e f l o w s and l a v a domes o v e r -l y i n g the o l d e r a n d e s i t e f l o w s . Read (1979) i n i t i a l l y broke the complex i n t o n i n e v o l -c a n i c assemblages. With f u r t h e r mapping and age d a t i n g Read (1979) s u b d i v i d e d the complex f u r t h e r i n t o 18 v o l c a n i c assem-b l a g e s , f o u r i n the P l i o c e n e and 14 i n Qu a t e r n a r y t i m e . Lewis and Souther (1978) grouped the assemblages of Read (1977) i n t o f o u r main u n i t s or phases which w i l l be d i s c u s s e d below. The bottom of the v o l c a n i c p i l e c o n s i s t s of b a s a l b r e c -c i a w h ich has i n c o r p o r a t e d b l o c k s of basement i n a t u f f a c e o u s m a t r i x , e x c e e d i n g 300 m i n t h i c k n e s s a l o n g the s o u t h e r n s i d e of the complex (Read,1977). T h i s i n d i c a t e s t h a t the i n i t i a l e r u p t i o n was e x p l o s i v e , l e a d i n g t o e x t e n s i v e f r a c t u r i n g of the l o c a l basement r o c k . D i r e c t l y o v e r l y i n g the b r e c c i a i s a sequence c o n s i s t i n g of d a c i t e f l o w s and up t o 500 m of a c i d t u f f . The b r e c c i a , f l o w s and t u f f are a l l p a r t of u n i t 1 ( F i g . 2.2). The p o r p h y r i t i c a n d e s i t e s and minor h y p a b y s s a l i n t r u -s i o n s of u n i t 2 make up the main mass of the complex. Potassium-argon d a t e s r e p o r t e d by Lewis and Souther (1978) range from 4.2 ± 0.3 Ma t o 2.1 ± 0.2 Ma s u g g e s t i n g a l o n g p e r i o d of i n t e r m i t t e n t a n d e s i t i c v o l c a n i s m . The youngest r o c k s of the complex, u n i t 3, a r e d a c i t e f l o w s , b r e c c i a s , t u f f s and h y p a b y s s a l i n t r u s i v e s . The u n i t 20 F i g u r e 2.2. Geology o f t h e Meager Mountain a r e a ( a f t e r Lewis and S o u t h e r , 1979) . 21 i s up t o 600 m t h i c k . The Meager, C a p r i c o r n , Job and P l i n t h summits a l o n g w i t h a l a r g e p o r t i o n of the c e n t r a l and n o r t h -e a s t p a r t of the complex a r e comprised of u n i t 3. The most r e c e n t v o l c a n i c a c t i v i t y a t Meager Mountain o c c u r r e d 2440 ± 140 y e a r s ago w i t h the d i s c h a r g e of the B r i d g e R i v e r ash (Nasmith e t a l . , 1967) which c o v e r e d an ar e a as f a r e a s t as Ba n f f .Park, A l b e r t a . D e p o s i t s of the ash near the mountain a r e up t o 30 m t h i c k and c o n s t i t u t e the youngest p o r t i o n of the B r i d g e R i v e r u n i t . The Meager Creek and L i l l o o e t v a l l e y s , s u r r o u n d i n g Meager Mountain , have been f i l l e d w i t h v a r y i n g t h i c k n e s s e s of u n c o n s o l i d a t e d g l a c i a l d e p o s i t s . In L i l l o o e t v a l l e y d r i l l h o l e L1-78D ( F i g . 1.4) encountered 47 m of outwash sands and g r a v e l s w i t h i n t e r b e d d e d b o u l d e r y t i l l l a y e r s . The d r i l l h o l e i s s i t u a t e d near the c o n t a c t between the v a l l e y f i l l and th e rock s l o p e s . The u n c o n s o l i d a t e d d e p o s i t s a r e thought t o be much deeper c l o s e r t o the r i v e r a x i s . D r i l l h o l e M5-78D i n the Meager Creek v a l l e y was sunk 250m and f a i l e d t o i n t e r s e c t e d bedrock. Outwash sands and g r a v e l s , i n t e r b e d d e d zones of l a r g e b o u l d e r s and r a r e t h i n g l a c i o l a c u s t r i n e c l a y l a y e r s were e n c o u n t e r e d . F a r t h e r down stream a t d r i l l h o l e EMR73-1 and EMR73-2 the overburden t h i n s t o 18 m or l e s s , p a r t l y because of a bedrock h i g h and v a l l e y n a r r o w i n g i n the a r e a . The g r a n i t i c basement i n the Meager Mountain a r e a i s 22 h i g h l y j o i n t e d and f r a c t u r e d because of the e x p l o s i v e n a t u r e of the i n i t i a l Meager Mountain e r u p t i o n s . A f r a c t u r e survey r e v e a l e d t h a t t h e r e are 2 dominant j o i n t s e t s and two subor-d i n a t e s e t s i n the South R e s e r v o i r a r e a . More d e t a i l s of the f r a c t u r e s u r v e y w i l l f o l l o w i n Chapter 5. The v o l c a n i c r o c k s a r e a l s o h i g h l y j o i n t e d . An e x t e n -s i v e f r a c t u r e survey was not c a r r i e d out i n the v o l c a n i c s but s t e e p l y d i p p i n g s e t s appear t o dominate. The groundwater movement i n the basement and v o l c a n i c r o c k s w i l l be m a i n l y a l o n g the f r a c t u r e s i n the r o c k . The amount of water t h a t moves through the r e l a t i v e l y impermeable rock m a t r i x s h o u l d be e s s e n t i a l l y n e g l i g i b l e . In the v o l -c a n i c r o c k s the f r a c t u r e p a t t e r n s a re t h e r e f o r e much more imp o r t a n t than the l i t h o l o g y w i t h r e s p e c t t o groundwater mo-vement. In the h y d r o g e o l o g i c m o d e l l i n g which i s d e s c r i b e d i n Cha p t e r 7 , the v o l c a n i c s a r e lumped i n t o one h y d r o g e o l o g i c u n i t . B e f o r e d e s c r i b i n g the p h y s i o g r a p h y of the hot and c o l d s p r i n g s a t Meager Mountain, a b r i e f d e s c r i p t i o n of the b a s i c p h y s i o g r a p h y of the area i s i n o r d e r . 23 P h y s i o g r a p h y The i m p r e s s i v e geology of the Meager Mountain a r e a i s s u r p a s s e d o n l y by i t s s p e c t a c u l a r p h y s i o g r a p h y . The r e l i e f a t Meager Mountain i s more than 2300 m w i t h the e l e v a t i o n r a n g i n g from 425 m t o over 2700 m above sea l e v e l . The topography i s v e r y rugged w i t h e l e v a t i o n changes of more than 2000 m i n l e s s than 5 km h o r i z o n t a l d i s t a n c e . The L i l l o o e t R i v e r v a l l e y and the Meager Creek v a l l e y range i n e l e v a t i o n from 425 m a t t h e i r c o n f l u e n c e t o 900 m i n t h e i r upper r e a c h e s . F i g u r e 2.3 d e p i c t s a p o r t i o n of the Meager Creek v a l l e y i n the South R e s e r v o i r a r e a . The mountain peaks i n c l u d i n g P l i n t h , P y l o n , Meager, C a p r i c o r n and Job range be-tween 2450 t o 2700 m i n e l e v a t i o n . The ruggedness of Meager and P l i n t h peaks i s i l l u s t r a t e d i n F i g u r e 1.3. The s t e e p s l o p e s and the low r e s i s t a n c e of the v o l c a n i c s t o w e a t h e r i n g , a l o n g w i t h the h i g h p r e c i p i t a t i o n i n the a r e a , l e a d s t o v e r y r a p i d e r o s i o n of the v o l c a n i c p i l e . F i g u r e 2.4 i l l u s t r a t e s one of the many d e e p l y i n c i s e d v a l l e y s and canyons d i s i n t e g r a t i n g a t a r a t e t o o r a p i d f o r v e g e t a t i o n t o t a k e h o l d . The mountain i s capped by an e x t e n s i v e g l a c i e r system ( F i g . 1.2) t h a t t e r m i n a t e s at the headwaters of a'number of streams. Many of the g l a c i e r s have a q u i r e d the same name as the streams to which they s u p p l y m e l t w a t e r s , such as M o s a i c , A f f l i c t i o n , D e v a s t a t i o n , Job and C a p r i c o r n g l a c i e r s . 24 Figure 2.4 Rapid erosion of the volcanic rock. 25 The g r a d i e n t of the streams on Meager Mountain i s ex-t r e m e l y h i g h a t a p p r o x i m a t e l y 0.3 t o 0.4. The h i g h g r a d i e n t and deep, s t e e p - s i d e d v a l l e y s a r e c h a r a c t e r i s t i c of streams i n t h e i r young stage of development. The stream p a t t e r n ( F i g u r e 1.4) from D e v a s t a t i o n Creek c o u n t e r c l o c k w i s e t o Manatee Creek, i s a r a d i a l p a t t e r n , t y p i c a l of a v o l c a n i c mountain. F i r , hemlock and cedar t r e e s dominate the s u b a l p i n e f o r e s t below 1500 t o 1800 m. A l p i n e meadows e x i s t above the t r e e l i n e , i n a r e a s were e r o s i o n i s slow enough t o a l l o w f o r t h e i r development. Thermal S p r i n g s The hot s p r i n g s of s o u t h w e s t e r n B r i t i s h Columbia can be d i v i d e d i n t o two groups. The f i r s t group i s a s s o c i a t e d w i t h the Pemberton B e l t ( F i g . 2.1) and i n c l u d e s w e l l known hot s p r i n g s such as H a r r i s o n and S l o q u e t . I t appears t h a t the f a u l t system of the Pemberton B e l t has s u p p l i e d the f r a c t u r e p e r m e a b i l i t y needed t o a l l o w f o r the deep c i r c u l a t i o n of me-t e o r i c w aters and t h e i r consequent h e a t i n g . The second group of hot s p r i n g s are a s s o c i a t e d w i t h Q u a t ernary v o l c a n i s m i n the Meager Mountain and Mount C a y l e y a r e a s ( F i g . 2.1). The two h o t s p r i n g a r e a s of i n t e r e s t t o t h i s r e s e a r c h are the Pebble Creek h o t s p r i n g s and Meager Creek h o t s p r i n g s l o c a t e d a t Meager Mountain ( F i g . 1.2, 2.2). 26 Meager Creek h o t s p r i n g s i s s u e from c o a r s e f l u v i a l sand and g r a v e l d e p o s i t s a p p r o x i m a t e l y 6 km from the c o n f l u e n c e of Meager Creek w i t h the L i l l o o e t R i v e r . More than 30 s p r i n g s and seeps i s s u e from a 1200 square meter a r e a ( F i g . 2.5) w i t h a t o t a l d i s c h a r g e of a p p r o x i m a t e l y 40 1/s, a t te m p e r a t u r e s of 45-55°C (Lewis and S o u t h e r , 1 9 7 8 ) . I t i s b e l i e v e d t h a t the l o c a t i o n of the h o t s p r i n g s i s c o n t r o l l e d by an u n d e r l y i n g bedrock t o p o g r a p h i c h i g h . In F i g u r e 1.4 the o u t l i n e of the South R e s e r v o i r shows a tongue e x t e n d i n g down the Meager Creek v a l l e y t o the Meager Creek H o t s p r i n g s . Thermal waters p r o b a b l y e n t e r the v a l l e y f i l l , t r a v e l down g r a d i e n t and e x i t s a t the p r e s e n t hot s p r i n g s s i t e . The r i s e i n the bedrock causes a t h i n n i n g of the v a l l e y f i l l , which i n t u r n , g i v e s r i s e t o hot water s u r f a c i n g a t the p r e s e n t p o s i t i o n of the Meager Creek H o t s p r i n g s . One k i l o m e t e r upstream from Meager Creek H o t s p r i n g s i s the P l a c i d H o t s p r i n g s , d i s c h a r g i n g from a g r a v e l bank of Meager Creek a t an e s t i m a t e d r a t e of 2 1/s a t 45°C. F i v e k i l o m e t e r s f a r t h e r upstream i s the No Good Warm S p r i n g s i s -s u i n g 20-40°C water from a g r a s s y sandy bank on the n o r t h s i d e of Meager Creek a t a r a t e of 5 1/s. The warm s p r i n g s r e p r e s e n t the most w e s t e r l y d i s c h a r g e of t h e r m a l waters found at Meager Creek. The Pebble Creek H o t s p r i n g s a re l o c a t e d on the n o r t h e a s t s i d e of the L i l l o o e t R i v e r , 7.5 km upstream from i t s c o n f -lu e n c e w i t h Meager Creek. The two main v e n t s occur on, a 20 m 27 0 20 40 mir r t i M E A G E R C R E E K H O T S P R I N G S THERMAL DISCHARGE SINTER LINED POOL OlAMONO DRILL HOLE F i g u r e 2.5 L o c a t i o n o f major v e n t s a t the Meager Creek h o t s p r i n g s s i t e ( a f t e r C l a r k , 1980). MAINWENT P E B B L E C R E E K H O T S P R I N G S / T H E R M A L OlS f 'v; SINTER DEPOS r r m T i 7 T LILLOOET 20 40 m t t r i t F i g u r e 2.6 L o c a t i o n o f major v e n t s a t the P e b b l e Creek h o t s p r i n g s s i t e ( a f t e r C l a r k , 1980). 28 h i g h bench, s i t u a t e d on the bank of the r i v e r ( F i g . 2.6). The t h e r m a l waters d e p o s i t c a l c i t e t u f a , s t a i n e d deep ochre i n the a r e a of the v e n t s . A d d i t i o n a l seeps i s s u e from the q u a r t z monzonite bedrock, u n c o n s o l i d a t e d d e p o s i t s and p y r o c -l a s t i c d e b r i s o u t c r o p p i n g on the f a c e of the bench near the r i v e r . The Pebble Creek H o t s p r i n g s i s s u e d i r e c t l y from bedrock, u n l i k e the Meager Creek H o t s p r i n g s which i s s u e from v a l l e y f i l l . C o l d S p r i n g s A number of c o l d s p r i n g s e x i s t i n the Meager Mountain complex, r a n g i n g i n a l t i t u d e from 580 m t o 1850 m. F i g u r e 2.7 shows the l o c a t i o n of the major c o l d s p r i n g s d i s c o v e r e d t o d a t e . The s p r i n g s a r e found i n the basement r o c k , v o l -c a n i c rock and the u n c o n s o l i d a t e d m a t e r i a l . The s i t e s of s p r i n g s i n the u n c o n s o l i d a t e d m a t e r i a l are g e n e r a l l y c o n t r o l l e d by the s t r a t i g r a p h y of the d e p o s i t s . The s p r i n g s and seeps are u s u a l l y found at c o n t a c t s between s i l t or c l a y and c o a r s e a l l u v i u m exposed on the s t e e p s i d e s of V-shaped stream v a l l e y s . The water t r a v e l l i n g i n the p e r -meable a l l u v i u m i n t e r s e c t s the c l a y l a y e r and cannot pene-t r a t e i t . The water i s , t h e r e f o r e , f o r c e d t o t r a v e l a l o n g the c o n t a c t and i s s u e as a s p r i n g . c A number of c o l d s p r i n g s a t h i g h e l e v a t i o n s d i s c o v e r e d Glacier Logging Road • Cold Spring COLD SPRINGS 1. Devastation 2. Boundary 3. CaC0 3 4. Moria 5. Rivendell 6. Angel Cirque 7. Problem 8. Logger 9. Fall Creek 10. 78-H-1 11. Job 12. Job West 13. Affliction 14. Mt. Athelstan F i g u r e 2.7 L o c a t i o n o f t h e c o l d s p r i n g s i n t h e Meager Moun t a i n a r e a . 30 by Read (1979) and C l a r k (1980) are a l s o s t r a t i g r a p h i c a l l y c o n t r o l l e d . The s p r i n g s d i s c h a r g e a t g e o l o g i c c o n t a c t s be-tween v o l c a n i c l a y e r s , v o l c a n i c - b a s e m e n t c o n t a c t s and v o l c a n i c - u n c o n s o l i d a t e d - d e p o s i t b o u n d a r i e s . The a u t h o r , d u r i n g h i s f i e l d w o r k , d i d not o b s e r ve a l l 14 c o l d s p r i n g s marked on F i g u r e 2.7. The s p r i n g s i n v e s t i g a t e d had d i s c h a r g e r a t e s of 2 t o 25 1/s. C a l c u l a t i o n s , t h a t w i l l be d i s c u s s e d i n Chapter 6, show t h a t the c o l d s p r i n g s c o n t r i -bute a maximum of o n l y 2 t o 3 p e r c e n t of the t o t a l groundwa-t e r d i s c h a r g e observed i n the Meager Creek B a s i n . The amount of groundwater r e l e a s e d by the c o l d s p r i n g s i s t h e r e f o r e , thought t o be i n s i g n i f i c a n t . I t s h o u l d be noted t h a t most of the c o l d s p r i n g s and a l l of the h o t s p r i n g s e x i s t i n l o c a l , l o w - e l e v a t i o n a r e a s near c r e e k s and streams. In the f o l l o w i n g c h a p t e r , r e g i o n a l groundwater fl o w systems w i l l be d i s c u s s e d . I t w i l l be shown t h a t water e n t e r s the system at h i g h e r e l e v a t i o n s and d i s -charges out of the system i n the l o w - l y i n g a r e a s . The s p r i n g s n a t u r a l l y occur i n the l o w - l y i n g d i s c h a r g e a r e a s . Now t h a t the p h y s i c a l s e t t i n g has been d i s c u s s e d , the h y d r o l o g i c and h y d r o g e o l o g i c a s p e c t s of the Meager Mountain a r e a can be examined. B e f o r e t h i s e x a m i n a t i o n , background i n f o r m a t i o n of the b a s i c p h y s i c s of groundwater f l o w w i l l be c o n s i d e r e d i n Chapter 3. 31 Chapter 3. FUNDAMENTALS OF GROUNDWATER FLOW T h i s c h a p t e r d i s c u s s e s the b a s i c p h y s i c s of groundwater f l o w i n an attempt t o ge n e r a t e an u n d e r s t a n d i n g of hydrogeo-l o g i c e nvironments a c r o s s t h e i n t e r d i s c i p l i n a r y b o u n d a r i e s of the Meager Mountain geothermal p r o j e c t . Readers w i t h a hy-d r o g e o l o g i c a l background may want t o move d i r e c t l y t o Chapter 4. The m a j o r i t y of the m a t e r i a l i n t h i s c h a p t e r was taken from F r e e z e and Ch e r r y (1979). The i n t e r e s t e d r e a d e r may wish t o r e f e r t o t h i s t e x t i f more d e t a i l i s d e s i r e d . D a r c y ' s Law The s c i e n c e of groundwater h y d r o l o g y began i n 1856 when Henry Darcy p u b l i s h e d a r e p o r t on h i s l a b o r a t o r y experiment a n a l y z i n g the flo w of water through sands. Darcy's e x p e r i -ment was s e t up as i n F i g u r e 3.1. A c i r c u l a r c y l i n d e r of c r o s s s e c t i o n A i s f i l l e d w i t h sand, s t o p p e r e d a t each end, and equipped w i t h i n f l o w and o u t f l o w tubes and a p a i r of manometers. Water i s a l l o w e d t o f l o w t h r o u g h the sand u n t i l t he i n f l o w r a t e Q i s e q u a l t o the o u t f l o w r a t e . The e l e v a -t i o n s of the manometer i n t a k e s a r e z-^ and z 2 and the e l e v a -t i o n s of the f l u i d l e v e l s a r e h^ and h 2 w i t h r e s p e c t t o an a r b i t r a r y datum s e t a t z=0. The d i s t a n c e between the manome-t e r i n t a k e s i s M . The d i f f e r e n c e i n f l u i d l e v e l s h - ^ l ^ i s d enoted asAh. L e t us d e f i n e v, the s p e c i f i c d i s c h a r g e t h r o u g h the c y -Figure 3.1 Experimental apparatus for the i l l u s t r a t i o n of Darcy's law (after Freeze and Cherry, 1979) . Figure 3.2 Hydraulic head h, pressure head V, and elevation head z for a laboratory manometer (after Freeze and Cherry, 1979) . 33 U n d e r , as v= | (3.1) where v has the d i m e n s i o n s of [L/T] i f the d i m e n s i o n s of Q a r e [ L 3 / T ] and t h o s e of A a r e [ L 2 ] . The SI u n i t s f o r v would be m/s. A l t h o u g h v has the d i m e n s i o n s of v e l o c i t y i t i s b e t t e r thought of as a f l u x r a t e [ L 3 / T / L 2 ] . Darcy's experiment showed t h a t v i s d i r e c t l y p r o p o r -t i o n a l t o Ah and i n v e r s e l y p r o p o r t i o n a l t o A l . D a r c y's law i n one dimension can then be w r i t t e n a s , v = - K A | ( 3 . 2 ) o r , i n d i f f e r e n t i a l form, V=-K|J (3.3) where K i s a c o n s t a n t of p r o p o r t i o n a l i t y . In e q u a t i o n 3.3, K i s known as the h y d r a u l i c c o n d u c t i v i -t y , h i s c a l l e d the h y d r a u l i c head, and ^ i s the h y d r a u l i c g r a d i e n t . Below i s a d e t a i l e d e x p l a n a t i o n of these parame-t e r s . F r e e z e and C h e r r y (1979), q u o t i n g H u b b e r t ( 1 9 4 0 ) , d e f i n e a p o t e n t i a l as "a p h y s i c a l q u a n t i t y , c a p a b l e of measurement a t e v e r y p o i n t i n a f l o w system, whose p r o p e r t i e s a r e such t h a t f l o w always o c c u r s from r e g i o n s i n which t h e q u a n t i t y has h i g h e r v a l u e s t o t h o s e i n which i t has l o w e r , r e g a r d l e s s of the d i r e c t i o n i n space." They note t h a t a p o t e n t i a l s h o u l d have d i m e n s i o n s of energy per u n i t mass. Through the use of e l e m e n t a r y p h y s i c s , Hubbert i l l u s t r a t e d t h a t the f l u i d 34 p o t e n t i a l $ f o r groundwater f l o w a t any p o i n t i n a porous media i s s i m p l y the h y d r a u l i c head m u l t i p l i e d by the a c c e -l e r a t i o n due t o g r a v i t y $ =gh (3.4) S i n c e g i s near c o n s t a n t , the h y d r a u l i c head h i s j u s t as s u i t a b l e a p o t e n t i a l as $ , and h y d r o g e o l o g i s t s f i n d i t e a s i e r t o work w i t h . In the f i e l d , the h y d r a u l i c head can be measured by i n s t a l l i n g a p i e z o m e t e r which i s s e a l e d a l o n g i t s l e n g t h and a l l o w s water t o e n t e r o n l y a t a s i n g l e p o i n t . The h y d r a u l i c head i s g i v e n by the e l e v a t i o n of the water l e v e l i n the p i e z o m e t e r . I t can be shown the h y d r a u l i c head has two components, the e l e v a t i o n ( g r a v i t y ) term and f l u i d p r e s s u r e term. I f a s a n d - f i l l e d c y l i n d e r were s e t up v e r t i c a l l y , f l u i d would f l o w t h r o u g h i t i n response t o g r a v i t y a l o n e . On the o t h e r hand, i f the c y l i n d e r were h o r i z o n t a l , g r a v i t y would p l a y no r o l e and t o induce f l o w the p r e s s u r e a t one end must be g r e a t e r than the o t h e r ( F i g . 3.2). T h e r e f o r e , h=z+\p (3.5) where z i s the e l e v a t i o n head above an a r b i t r a r y datum and i s the p r e s s u r e head. Both <J> and z have di m e n s i o n s [L] and a r e commonly measured i n meters. The p r e s s u r e head, <r , i s r e l a t e d t o the f l u i d p r e s s u r e p, by p=pg<jj (3.6) where P i s the d e n s i t y of the f l u i d . P i e z o m e t e r measurements can t h e r e f o r e p r o v i d e both h y d r a u l i c heads and f l u i d p r e s -s u r e s . 35 The c o n s t a n t of p r o p o r t i o n a l i t y i n Darcy's law, the hy-d r a u l i c c o n d u c t i v i t y K, i s a f u n c t i o n not o n l y of the porous media but a l s o t h e f l u i d . E x p e r i m e n t a t i o n has found the r e -l a t i o n s h i p t o be K= (3.7) y where k i s the s p e c i f i c or i n t r i n s i c p e r m e a b i l i t y , P i s the d e n s i t y of the f l u i d , g i s the a c c e l e r a t i o n due t o g r a v i t y , and y i s the dynamic v i s c o s i t y of the f l u i d . The permeabi-l i t y k or c a p a c i t y f o r t r a n s m i t t i n g a f l u i d i s a f u n c t i o n of the medium o n l y and has d i m e n s i o n s [ L 2 ] . The d e n s i t y and v i s c o s i t y are p r o p e r t i e s of the f l u i d . The P o r o s i t y R e l a t i o n s h i p w i t h H y d r a u l i c C o n d u c t i v i t y I f the t o t a l u n i t volume V r of a rock or s o i l i s p a r t i -t i o n e d i n t o the volume of the s o l i d s V g, and the volume of the v o i d s V , the p o r o s i t y n i s d e f i n e d as n=V v/V r • (3.8) I t i s u s u a l l y r e p o r t e d as a p e r c e n t a g e or a d e c i m a l f r a c t i o n . The p o r o s i t y can be an i m p o r t a n t c o n t r o l l i n g i n f l u e n c e on the h y d r a u l i c c o n d u c t i v i t y K. In g e n e r a l , an i n c r e a s e i n p o r o s i t y i n c r e a s e s the p e r m e a b i l i t y k. The p e r m e a b i l i t y i n t u r n i n c r e a s e s the h y d r a u l i c c o n d u c t i v i t y , i f f l u i d p r o p e r -t i e s a r e c o n s t a n t . In r o c k , two t y p e s of p o r o s i t y e x i s t , the i n t e r g r a n u l a r p o r o s i t y and the f r a c t u r e p o r o s i t y . The i n t e r g r a n u l a r poro-s i t y r e f e r s t o the p o r o s i t y of the rock m a t r i x . In a g r a n i -36 t i c rock t h i s i s t o a l l i n t e n t s and purposes n e g l i g i b l e . The f r a c t u r e p o r o s i t y r e f e r s t o the p e r c e n t a g e of the t o t a l volume t h a t i s taken up by the f r a c t u r e s i n the r o c k . The f r a c t u r e p o r o s i t y may be as l a r g e as 1 or 2 p e r c e n t or as s m a l l as 10" 3 t o 1 0 " 4 . The i n t e r c o n n e c t i v e s t r u c t u r e of the f r a c t u r e s w i l l i n f l u e n c e the h y d r a u l i c c o n d u c t i v i t y more than the i n t e r g r a n u l a r p o r o s i t y . In the f r a c t u r e d v o l c a n i c r o c k s and basement r o c k s of the Meager Mountain a r e a the f r a c t u r e p o r o s i t y i s the major c o n t r o l l i n g f a c t o r on the h y d r a u l i c c o n d u c t i v i t y . In the g r a n u l a r u n c o n s o l i d a t e d d e p o s i t s i n t e r g r a n u l a r p o r o s i t y i s the c o n t r o l l i n g f a c t o r . Homogeneity and H e t e r o g e n e i t y of H y d r a u l i c C o n d u c t i v i t y I f the h y d r a u l i c c o n d u c t i v i t y K i s independent of p o s i -t i o n w i t h i n a g e o l o g i c f o r m a t i o n , the f o r m a t i o n i s homo-geneous. I f the h y d r a u l i c c o n d u c t i v i t y K i s dependent on p o s i t i o n w i t h i n a g e o l o g i c f o r m a t i o n , the f o r m a t i o n i s he-t e r o g e n e o u s . I f we s e t up an xyz c o o r d i n a t e space, then i n a homogeneous f o r m a t i o n , K(x,y,z)=C, C b e i n g a c o n s t a n t ; whereas i n a heterogeneous f o r m a t i o n K(x,y,z)=C (Freeze and C h e r r y , 1979). A v a r i e t y of e nvironments can cause h e t e r o g e n e i t y . A system may be heterogeneous due t o l a y e r i n g ( F i g . 3.3) such as i n the v o l c a n i c s of Meager M o u n t a i n . An i n d i v i d u a l f l o w or b r e c c i a l a y e r may have a homogeneous h y d r a u l i c c o n d u c t i v i -Figure 3.3 Layered heterogeneity and trending heterogeneity (after Freeze and Cherry, 1979) . Homogeneous, I s o t r o p i c L l — * • (x2, Z 2 ) H e t e r o g e n e o u s , I s o t r o p i c H omogeneous, A n i s o t r o p i c H e t e r o g e n e o u s , A n i s o t r o p i c Figure 3.4 Four possible combinations of heterogeneity and anisotropy (after Freeze and Cherry, 1979). 38 t y but when one l o o k s a t the whole v o l c a n i c p i l e , the system i s h e terogeneous. A d i s c o n t i n u o u s h e t e r o g e n e i t y can be caused by a f a u l t or by a l a r g e - s c a l e s t r a t i g r a p h i c f e a t u r e s such as the overburden-bedrock c o n t a c t . W i t h i n a f o r m a t i o n one can a l s o get t r e n d i n g h e t e r o g e n e i t y ( F i g . 3.3). Trends i n a v o l c a n i c l a y e r i n the Meager Mountain complex c o u l d o c cur i n f l o w s p a r t i a l l y exposed a t s u r f a c e . F r a c t u r e a p e r -t u r e s would be wider a t the s u r f a c e than i n unexposed sec-t i o n s c a u s i n g a d e c r e a s e i n h y d r a u l i c c o n d u c t i v i t y w i t h d e p t h . I s o t r o p y and A n i s o t r o p y of H y d r a u l i c C o n d u c t i v i t y A f o r m a t i o n i s i s o t r o p i c i f i t s h y d r a u l i c c o n d u c t i v i t y K a t any p o i n t i s of the same magnitude i n a l l d i r e c t i o n s . A f o r m a t i o n i s a n i s o t r o p i c i f , on the o t h e r hand, the h y d r a u l i c c o n d u c t i v i t y i s a f f e c t e d by the c h o i c e of d i r e c t i o n of mea-surement a t a p o i n t ( F i g . 3.4) ( D a v i s and De W i e s t , 1966). I f one d e a l s w i t h the t h r e e - d i m e n s i o n a l case t h e r e w i l l be t h r e e p r i n c i p a l d i r e c t i o n s of h y d r a u l i c c o n d u c t i v i t y K , K and K . At any p o i n t i n an i s o t r o p i c f o r m a t i o n K^=K^=K z , whereas i n an a n i s o t r o p i c f o r m a t i o n K =K =K . The basement g r a n o d i o r i t e a t Meager Mountain appears t o be a n i s o t r o p i c . The two prominent j o i n t s e t s have a near v e r t i c a l d i p c a u s i n g the v e r t i c a l h y d r a u l i c c o n d u c t i v i t y K z t o be g r e a t e r than the h o r i z o n t a l h y d r a u l i c c o n d u c t i v i t y K v. 39 The v o l c a n i c r o c k s , on the o t h e r hand, te n d t o be a system of i n t e r b e d d e d h i g h - p e r m e a b i l i t y b r e c c i a s and ash l a y e r s and l o w e r - p e r m e a b i l i t y f l o w s . I t can be shown t h a t t h e r e i s a r e l a t i o n s h i p between such l a y e r e d h e t e r o g e n e i t y and a n i s o t r o p y . F i g u r e 3.5 i s a l a y e r e d f o r m a t i o n where each l a y e r i s homogeneous and i s o t r o p i c w i t h a h y d r a u l i c c o n d u c t i -v i t y K-^  ,1*2 , . . .K^ . I t can be shown t h a t an e q u i v a l e n t v e r t i -c a l h y d r a u l i c c o n d u c t i v i t y K z f o r the system of l a y e r s can be c a l c u l a t e d from the r e l a t i o n K = d £ d i / k i . i - l where n i s the t o t a l number of l a y e r s , d i i s the t o t a l t h i c k -ness of the i t h l a y e r , and K i s the h y d r a u l i c c o n d u c t i v i t y of the i t h l a y e r . S i m i l a r l y , i t can be shown t h a t the e q u i v a l e n t h o r i z o n -t a l h y d r a u l i c c o n d u c t i v i t y K , f o r the l a y e r e d system i s n k.d. i= 1 (3.10) W i t h some m a t h e m a t i c a l m a n i p u l a t i o n of E q u a t i o n 3.9 and 3.10 i t i s p o s s i b l e t o show t h a t K >K f o r a l l p o s s i b l e v a l u e s of K,,K„,...K . In the f i e l d , i t i s not uncommon f o r 1 2 n l a y e r e d h e t e r o g e n e i t y t o l e a d t o r e g i o n a l a n i s o t r o p y v a l u e s on the o r d e r of 100:1 or even g r e a t e r . In the l a y e r e d v o l -c a n i c s a t Meager Mountain the a n i s o t r o p y i s reduced due t o e x t e n s i v e v e r t i c a l and near v e r t i c a l f r a c t u r i n g t h a t i n -40 c r e a s e s the v e r t i c a l h y d r a u l i c c o n d u c t i v i t y K z. Water T a b l e The water t a b l e i s d e f i n e d as the s u r f a c e on which the f l u i d p r e s s u r e p i n the pores of the medium i s e x a c t l y atmos-p h e r i c . In gauge p r e s s u r e , p would be e q u a l t o z e r o , imp-l y i n g from E q u a t i o n 3.6 t h a t ^ = 0 . S i n c e h=i>+z, the h y d r a u l i c head a t any p o i n t on the water t a b l e must be e q u a l t o the e l e v a t i o n z of the water t a b l e a t t h a t p o i n t . A l t e r n a t i v e l y , the water t a b l e can be viewed as an i m a g i n a r y s u r f a c e below which the pore spaces are c o m p l e t e l y s a t u r a t e d w i t h w a t e r . Flow Nets I f h y d r a u l i c head v a l u e s a r e known throughout a t w o - d i -m e n s i o n a l system, c o n t o u r s can be drawn j o i n i n g up p o i n t s of e q u a l p o t e n t i a l . These c o n t o u r s a r e c a l l e d e q u i p o t e n t i a l l i n e s . F l o w l i n e s can be c o n s t r u c t e d p e r p e n d i c u l a r t o the e q u i p o t e n t i a l l i n e s which i s the d i r e c t i o n of the maximum p o t e n t i a l g r a d i e n t . F l o w l i n e s i n d i c a t e the d i r e c t i o n of water movement. The r e s u l t i n g s e t of f l o w l i n e s and e q u i p o -t e n t i a l l i n e s i s known as a f l o w n e t . When c o n s t r u c t i n g a f l o w net f o r a homogeneous, i s o t r o -p i c system w i t h s a t u r a t e d , s t e a d y - s t a t e f l o w , t h r e e t y p e s of b o u n d a r i e s can e x i s t : 1) impermeable b o u n d a r i e s , 2) c o n s t a n t head b o u n d a r i e s and 3) water t a b l e b o u n d a r i e s . Flow i n the v i c i n i t y of an impermeable boundary [ F i g u r e 3.6(a)] must be 41 d, T d 2 K, I *-K, F i g u r e 3.5 R e l a t i o n s h i p between l a y e r e d h e t e r o g e n e i t y and a n i s o t r o p y ( a f t e r F r e e z e and C h e r r y , 1979) . F i g u r e 3.6 Groundwater f l o w i n the v i c i n i t y o f (a) an impermeable boundary, (b) a c o n s t a n t head boundary, and (c) a w a t e r - t a b l e boundary ( a f t e r F r e e z e and C h e r r y , 19 79) . 42 p a r a l l e l t o the boundary because no f l o w can move a c r o s s i t . T h i s demands t h a t f l o w l i n e s a r e p a r a l l e l t o the boundary and e g u i p o t e n t i a l s a re a t r i g h t a n g l e s ( F r e e z e and C h e r r y , 1979). In the case of a c o n s t a n t head boundary, f l o w must meet the border a t r i g h t a n g l e s because the boundary i s a c t u a l l y an e q u i p o t e n t i a l l i n e [ F i g u r e 3 . 6 ( b ) ] . As d i s c u s s e d p r e v i o u s l y , a t the water t a b l e the hydrau-l i c head h i s e q u a l t o the e l e v a t i o n z. The water t a b l e i s c o n s e q u e n t l y n e i t h e r a fl o w l i n e or an e q u i p o t e n t i a l l i n e [ F i g u r e 3 . 6 ( c ) ] , Flow n e t s can be c o n s t r u c t e d f o r any of the systems i l -l u s t r a t e d i n F i g u r e 3.4 and used t o c a l c u l a t e the d i s c h a r g e through the system. For a thorough e x p l a n a t i o n of f l o w net c o n s t r u c t i o n and d i s c h a r g e c a l c u l a t i o n s see Fr e e z e and Cherry (1979) pp. 168-189. Recharge A r e a s , D i s c h a r g e A r e a s , and Groundwater D i v i d e s C o n s i d e r the t w o - d i m e n s i o n a l c r o s s s e c t i o n F i g u r e 3.7 of a s e t of p a r a l l e l r i d g e s and v a l l e y s w i t h an impermeable boundary a t the base. The g e o l o g i c m a t e r i a l s a re homogeneous and i s o t r o p i c . The water t a b l e c o n f i g u r a t i o n i s a subdued r e p l i c a of the topography i n t h e h i l l s and c o i n c i d e n t w i t h the ground s u r f a c e i n the v a l l e y s . T h i s water t a b l e shape i s c h a r a c t e r i s t i c of most topography, a l t h o u g h the a u t h o r i s unaware of any s p e c i f i c s t u d i e s of the water t a b l e c o n f i g u r a -43 t i o n i n mountainous t e r r a i n . The h y d r a u l i c head v a l u e on any one of the dashed e q u i p o t e n t i a l l i n e s i s e q u a l t o the e l e v a -t i o n of the water t a b l e a t i t s p o i n t of i n t e r s e c t i o n w i t h the e q u i p o t e n t i a l 1 i n e ( F r e e z e and C h e r r y , 1S79). From F i g u r e 3.7, i t i s c l e a r t h a t , groundwater f l o w s from the h i g h l a n d s towards the v a l l e y s . The symmetry of the system produces v e r t i c a l b o u n d a r i e s a t AB and CD under the v a l l e y s and r i d g e s , and these b o u n d a r i e s a r e known as ground-water d i v i d e s . I t i s o b v i o u s no f l o w e n t e r s or l e a v e s the a r e a ABCD through the l i n e s AB or CD, t h e r e b y i n d i c a t i n g they a r e " i m a g i n a r y " impermeable b o u n d a r i e s . The r e g i o n ED i n F i g u r e 3.7 i s known as the r e c h a r g e a r e a . In a r e c h a r g e a r e a the net component of s a t u r a t e d groundwater f l o w i s downward, away from the water t a b l e . The r e g i o n AE i n F i g u r e 3.7 i s known as the d i s c h a r g e a r e a . In a d i s c h a r g e a r e a the net component of s a t u r a t e d groundwater f l o w i s upward, towards the water t a b l e . A c r o s s s e c t i o n of the Meager Mountain a r e a , s i m i l a r t o ABCD w i l l be used f o r m a t h e m a t i c a l m o d e l l i n g purposes i n Chapter 7. Steady S t a t e Flow vs T r a n s i e n t Flow S t e a d y - s t a t e f l o w t a k e s p l a c e when at any p o i n t i n a f l o w f i e l d the d i r e c t i o n and magnitude of the f l o w v e l o c i t y a r e c o n s t a n t w i t h t i m e . T r a n s i e n t f l o w , a l s o known as nons-teady or unsteady f l o w , t a k e s p l a c e when at any p o i n t i n a f l o w f i e l d the d i r e c t i o n and magnitude of the f l o w v e l o c i t y F i g u r e 3.7 Groundwater f l o w n e t i n a two-d i m e n s i o n a l v e r t i c a l c r o s s - s e c t i o n t h r o u g h a homogeneous, i s o t r o p i c system bounded on the bottom by an impermeable boundary ( a f t e r Hubbert, 1940) . 0.2 S F i g u r e 3.8 E f f e c t o f topography on r e g i o n a l groundwater f l o w p a t t e r n s ( a f t e r F r e e z e and W i t h e r s p o o n , 1967) . 45 changes w i t h t i m e . Flow n e t s can be drawn f o r b o t h s t e a d y - s t a t e and t r a n -s i e n t f l o w . A flow net f o r a s t e a d y - s t a t e system r e p r e s e n t s the system a t a l l t i m e s . A f l o w net f o r a t r a n s i e n t system o n l y r e p r e s e n t s the system f o r a p a r t i c u l a r i n s t a n t i n t i m e . In r e g i o n a l groundwater f l o w , s t e a d y - s t a t e f l o w can be thought of as r e p r e s e n t i n g the h y p o t h e t i c a l s i t u a t i o n where the water t a b l e m a i n t a i n s the same p o s i t i o n throughout the e n t i r e y e a r . In r e a l i t y , f l u c t u a t i o n s i n the water t a b l e throughout the year i n t r o d u c e t r a n s i e n t e f f e c t s i n t o the f l o w system. However, i f the changes i n the water t a b l e p o s i t i o n are s m a l l compared w i t h the t o t a l t h i c k n e s s of the system, and i f the r e l a t i v e c o n f i g u r a t i o n of the water t a b l e s t a y s the same throughout the f l u c t u a t i o n s , we can r e p l a c e the f l u -c t u a t i n g system w i t h a s t e a d y - s t a t e system w i t h the water t a b l e f i x e d a t i t s mean p o s i t i o n ( F r e e z e and C h e r r y , 1979). In a s t e a d y - s t a t e system, no water i n the system i s g i v e n up from s t o r a g e i n the medium and no water i s taken up i n t o s t o r a g e i n the medium. T h e r e f o r e , the t o t a l r e c h a r g e i n t o the system must e q u a l the t o t a l d i s c h a g e out of the s y s -tem. The r e g i o n a l groundwater f l o w i n Meager Mountain i s assumed t o be s t e a d y - s t a t e f o r the purpose of h y d r o g e o l o g i c i n t e r p r e t a t i o n and m a t h e m a t i c a l m o d e l l i n g . 46 The E f f e c t of the H y d r o g e o l o g i c Environment on the Groundwater Regime The groundwater regime i s c o n t r o l l e d by a number of param e t e r s which c o l l e c t i v e l y c r e a t e the h y d r o g e o l o g i c en-vironment of a g i v e n g e o g r a p h i c r e g i o n . Among the most im-p o r t a n t parameters a r e t o p o g r a p h i c r e l i e f , rock p o r o s i t y and h y d r a u l i c c o n d u c t i v i t y , p r e c i p i t a t i o n and e v a p o t r a n s p i r a t i o n . Minor changes i n topography can va r y the groundwater f l o w a g r e a t d e a l . F i g u r e 3.8 d e p i c t s two c r o s s s e c t i o n s h a v i n g an upland a r e a t o the r i g h t and a v a l l e y t o the f a r l e f t . F i g u r e 3.8(a) shows a f l a t u pland and water t a b l e w h i l e F i g u r e 3.8(b) i l l u s t r a t e s a h i l l y u p l a n d a r e a w i t h a hummocky water t a b l e c o n f i g u r a t i o n . The d i f f e r e n c e between the f l o w systems i s o b v i o u s . A few s m a l l h i l l s change a s i n g l e f l o w p a t t e r n i n t o numerous subsystems w i t h i n a major f l o w system. C l e a r l y , even b a s i n s u n d e r l a i n by homogeneous, i s o t r o p i c g e o l o g i c m a t e r i a l s can have complex systems of groundwater f l o w due t o topography a l o n e ( F r e e z e and C h e r r y , 1979). F i g u r e 3.9 shows the e f f e c t of d i f f e r e n t g e o l o g i c en-v i r o n m e n t s on groundwater f l o w as m a t h e m a t i c a l l y s i m u l a t e d by F r e e z e and Witherspoon (1967). F i g u r e 3.9(a) and 3.9(b) r e -p r e s e n t an a q u i f e r a t depth w i t h a c o n d u c t i v i t y 10 and 100 t i m e s t h a t of the o v e r l y i n g f o r m a t i o n . Water e n t e r s the s y s -tem, f l o w s n e a r l y v e r t i c a l l y downward to the a q u i f e r , t r a v e l s h o r i z o n t a l l y i n the a q u i f e r and f i n a l l y upwards i n the d i s -0.2S 0 0.1 S 0.2S 0.3S 0.4S 0.5S 0.6S 0.7S 0.8S 0.9S S ( e ) Figure 3.9 E f f e c t of geology on regional groundwater flow patterns (after Freeze and Witherspoon, 1967) . 48 charge a r e a . In F i g u r e 3.9(c) the a q u i f e r a t depth a c t s as a t h r o u g h -way f o r f l o w t o pass under the o v e r l y i n g l o c a l systems. An a q u i f e r t h a t p i n c h e s out c r e a t e s a d i s c h a r g e a r e a i n the c e n t r e of the s e c t i o n i n F i g u r e 3.9(d). F i g u r e 3.9(e) i l l u s t r a t e s how the d i f f e r e n c e of o n l y a few meters i n the p o i n t of r e c h a r g e can determine whether water e n t e r s a s m a l l l o c a l f l o w system or l a r g e r e g i o n a l f l o w system. I t i s c l e a r from these s i m p l e examples t h a t the complex geology of the Meager Mountain a r e a can have an enormous e f f e c t on the groundwater f l o w p a t t e r n . Other f a c t o r s a f f e c t i n g the groundwater f l o w such as p r e c i p i t a t i o n , and e v a p o t r a n s p i r a t i o n w i l l d e termine the amount of water a v a i l a b l e t o r e a c h the water t a b l e i n a r e -charge zone. High p r e c i p i t a t i o n w i t h low e v a p o t r a n s p i r a t i o n would a l l o w a l a r g e q u a n t i t y of water t o f l o w t h rough the u n s a t u r a t e d zone t o the water t a b l e , r a i s i n g the water t a b l e c l o s e r t o the s u r f a c e . C o n v e r s e l y , i n an a r e a w i t h low p r e -c i p i t a t i o n and h i g h e v a p o t r a n s p i r a t i o n one would expect the water t a b l e e l e v a t i o n to be lower than i n the f i r s t c a s e . Groundwater f l o w i s an e x t r e m e l y dynamic p r o c e s s v e r y dependent on i t s h y d r o g e o l o g i c environment. T h i s r eview of groundwater fundamentals has been p r e -49 s e n t e d t o enable n o n - h y d r o g e o l o g i s t s t o g a i n a b e t t e r unders-t a n d i n g of the hydrogeology of the Meager Mountain complex as i t i s p r e s e n t e d i n C h a p t e r s 6 and 7. F i r s t l y , however, i t i s n e c e s s a r y t o p l a c e the groundwa-t e r regime i n t o the c o n t e x t of the complete h y d r o l o g i c c y c l e . In the f o l l o w i n g c h a p t e r we w i l l d e v e l o p a water b a l a n c e f o r the L i l l o o e t R i v e r b a s i n . In C a p t e r 7, i t w i l l be shown t h a t t h i s water balance and the h y d r o g e o l o g i c a l model p r o v i d e a c o n s i s t e n t p i c t u r e of the h y d r o l o g y of the a r e a . 50 Chapter 4. PRELIMINARY WATER BALANCE Groundwater i s an important component i n the water budget or water balance of a drainage b a s i n . The simplest water balance equation f o r a watershed for any p e r i o d would take the form 1-0 = §f (4.1) which s t a t e s that i n f l o w I i n t o a basin minus outflow 0 out of the basin must equal the change i n the storage of water d s -5-r- w i t h i n the b a s i n . d t The input and output can be broken down i n t o t h e i r major components. The main input parameter i s p r e c i p i t a t i o n and the important output parameters are e v a p o t r a n s p i r a t i o n and runoff out of the b a s i n . The runoff has two prominent com-ponents, the surface water c o n t r i b u t i o n s and the groundwater c o n t r i b u t i o n s . A water balance f o r the e n t i r e L i l l o o e t drainage basin i s attempted, to estimate the c o n t r i b u t i o n of groundwater dis c h a r g e to the t o t a l r u n o f f . As a s t e a d y - s t a t e s i t u a t i o n i s being assumed, where recharge equals d i s c h a r g e , then the amount of water e n t e r i n g the groundwater system i s a l s o being estimated. T h i s i n f o r m a t i o n i s u s e f u l i n two ways. F i r s t l y , i n Chapter 6, an estimate of groundwater recharge i s c a l c u -l a t e d f o r the Meager Creek sub-basin. The c a l c u l a t i o n s are made in a d i f f e r e n t manner then i n the water balance of t h i s c h a p t e r . I f the two estimates of groundwater recharge give 51 s i m i l a r r e s u l t s then i t can be assumed t h a t they a r e reasona-b l y c o r r e c t . S e c o n d l y , i n Chapter 7, the amount of groundwa-t e r r e c h a r g e i s an i m p o r t a n t v a r i a b l e as an i n p u t parameter i n the m a t h e m a t i c a l model. I f the v a l u e of the groundwater r e c h a r g e i s known w i t h i n a s m a l l range, i t w i l l narrow the p o s s i b l e range of fl o w v a l u e s of the o t h e r v a r i a b l e s t h a t i n f l u e n c e groundwater. To d e v e l o p a water b a l a n c e f o r the L i l l o o e t R i v e r b a s i n the p r e c i p i t a t i o n , t e m p e r a t u r e , e v a p o t r a n s p i r a t i o n , and r u n o f f of the b a s i n w i l l have t o be examined. P r e c i p i t a t i o n and Temperature The f i r s t t e m p e r a t u r e - r a i n f a l l s t a t i o n s i n the study a r e a were i n s t a l l e d i n the summer of 1980, t h e r e f o r e no d a t a of v a l u e i s y e t a v a i l a b l e . The c l o s e s t m e t e o r o l o g i c a l s t a -t i o n s t o Meager Mountain e x i s t a t Pemberton Meadows, 50 km t o the s o u t h e a s t , and B r a l o r n e , 60 km t o the n o r t h e a s t ( F i g . 4.1). The mean d a i l y t e m p e r a t u r e s and mean t o t a l p r e -c i p i t a t i o n f o r these two s i t e s a r e t a b u l a t e d i n Table 4.1. The mean t o t a l p r e c i p i t a t i o n a t Pemberton Meadows i s 1024 mm and a t B r a l o r n e i s 732 mm. The mean d a i l y temperature at Pemberton Meadows i s 7.2 "C and a t B r a l o r n e i s 4.3 "C. The v a l u e s a re averaged from 1941 t o 1970, the c u r r e n t s t a n d a r d 30 year p e r i o d r e c o g n i z e d by the World M e t e o r o l o g i c a l O r g a n i z a t i o n (Environment Canada, 1974). The e l e v a t i o n of the v a l l e y a r e a s around Meager Mountain 52 F i g u r e 4.1 L o c a t i o n o f d a t a g a t h e r i n g s t a t i o n s i n t h e L i l l o o e t R i v e r a r e a r e f e r r e d t o i n t h e t e x t . Table 4.1 Mean t o t a l p r e c i p i t a t i o n and mean d a i l y temperature at Pemberton Meadows and Bralorne 1941-1970 Pemberton Meadows Bralorne ( E l . 300 m) (El . 1300 m) Mean Daily " Mean To t a l Mean D a i l y Mean T o t a l Month Temperature( C) Precipitation(mm) Temperature( C) Precipitation(mm) Jan -6.0 168 -7.8 109 Feb -1.7 85 -3.2 60 Mar 2.6 64 -0.3 48 Apr 8.2 45 4.4 28 May 13.4 31 8.8 27 June 16.0 38 11.7 43 J u l y 18.6 27 14.9 34 Aug 17.1 28 14.2 33 Sept 13.4 64 10.8 42 Oct 7.6 141 5.0 94 Nov 0.8 161 -1.7 98 Dec -3.4 179 -5.7 116 TOTAL 7.2 1024 4.2 732 (From Climate of B r i t i s h Columbia, C l i m a t i c Normals, 1941-1970) 54 l i e a t 760 m, whereas those a t Pemberton Meadows and B r a l o r n e l i e a t 300 m and 1300 m r e s p e c t i v e l y . The Meager Mountain temperature regime i n the v a l l e y s p r o b a b l y l i e s between the temperature regime of the s e two s t a t i o n s . I t has been found t h a t p r e c i p i t a t i o n i s e x t r e m e l y v a r i a b l e i n the c o a s t a l mountains. In g e n e r a l , the amount of p r e c i p i t a t i o n drops o f f d r a m a t i c a l l y from west t o east and from h i g h e l e v a t i o n s t o l o w e r . The wes t - e a s t v a r i a t i o n i s a r e s u l t of m o i s t u r e l a d e n a i r from the P a c i f i c d r o p p i n g the m a j o r i t y of i t s water on the most w e s t e r l y mountains. The mean t o t a l p r e c i p i t a t i o n at Pemberton Meadows i s 1024 mm w h i l e the mean annual r u n o f f i s 1880 mm over the d r a i n a g e b a s i n . T h i s i n d i c a t e s t h a t a g r e a t d e a l more p r e c i p i t a t i o n f a l l s a t h i g h e r e l e v a t i o n s than i n the v a l l e y a r e a s . T h i s p o i n t w i l l be expanded upon i n the r u n o f f s e c t i o n . E v a p o t r a n s p i r a t i o n No d i r e c t measurement of e v a p o t r a n s p i r a t i o n or evap o r a -t i o n a r e a v a i l a b l e f o r the Meager Mountain r e g i o n . Bruce and Weisman (1967) c o l l e c t e d e v a p o r a t i o n pan d a t a , observed s o l a r r a d i a t i o n d ata and e s t i m a t e d s o l a r r a d i a t i o n d a t a from a c r o s s Canada. They s t a t e t h a t p o t e n t i a l e v a p o t r a n s p i r a t i o n i s ap-p r o x i m a t e l y e q u a l t o f r e e - w a t e r e v a p o r a t i o n from s m a l l l a k e s and r e s e r v o i r s , t h e r e f o r e t h e i r a n n u a l e v a p o r a t i o n v a l u e s can be used as e v a p o t r a n s p i r a t i o n v a l u e s . T h e i r maps i n d i c a t e t h a t the Meager Mountain area has a maximum p o t e n t i a l r a t e of 55 e v a p o t r a n s p i r a t i o n of a p p r o x i m a t e l y 500 mm/year. T h i s v a l u e w i l l be used f o r the water b a l a n c e c a l c u l a -t i o n s l a t e r i n t h i s c h a p t e r . Runof f The o n l y l o n g - t e r m measurement of r u n o f f i n the L i l l o o e t R i v e r b a s i n i s a t the L i l l o o e t R i v e r s i t e , 1.5 km n o r t h of Pemberton ( F i g . 4.1) where d a i l y d i s c h a r g e r a t e s have been measured by the Water Survey of Canada s i n c e 1914. F i g u r e 4.2 i l l u s t r a t e s average r u n o f f , temperature and p r e c i p i t a t i o n of the Pemberton V a l l e y . I t i s c l e a r , t h a t r u n o f f c o r r e l a t e s w i t h temperature and not p r e c i p i t a t i o n . T h i s i s due t o the l a r g e amount of r u n o f f which r e s u l t s from m e l t i n g snow and i c e a t h i g h e r e l e v a t i o n s i n the warm summer months. Note, t h a t r u n o f f i s g i v e n i n [ L ] . The volume [ L 3 ] of water d i s -c h a r g i n g out of the b a s i n i s measured and d i v i d e d by the ar e a of the b a s i n [ L 2 ] t o g i v e a r u n o f f v a l u e over the d r a i n a g e b a s i n of dimension [ L ] . As mentioned i n the p r e c i p i t a t i o n s e c t i o n , the mean annual r u n o f f of the L i l l o o e t R i v e r from 1923-1973 was 1880 mm w h i l e the average p r e c i p i t a t i o n a t the Pemberton Meadows s t a t i o n from 1941-1970 was 1024 mm. T h i s i n d i c a t e s t h a t p r e -c i p i t a t i o n a t h i g h e r e l e v a t i o n s i s much g r e a t e r than 1880 mm/year. Mean annual r u n o f f i n the M i l l e r Creek b a s i n , a t r i b u -56 J F M A M J J A S O N D F i g u r e 4.2 H y d r o m e t e o r o g i c a l r e g i m e o f t h e L i l l o o e t R i v e r and v a l l e y b o t t o m ( a t e r T e t i , 1979). T e m p e r a t u r e and p r e c i p i t a t i o n were r e c o r d e d a t Pemberton Meadows (1931-1960). D i s c h a r g e was r e c o r d e d a b o u t 1.5 km n o r t h o f Pemberton (1923-1973). 57 t a r y of the L i l l o o e t j u s t n o r t h of Pemberton i s e s t i m a t e d t o be 2400 mm ± 300 mm. t h i s i s based on summer d i s c h a r g e r e -c o r d s and v i s u a l e s t i m a t e s of d i s c h a r g e d u r i n g w i n t e r low fl o w (Slaymaker, 1973, 1974 and 1975, u n p u b l i s h e d d a t a ) . P r e c i p i t a t i o n i n the Meager Mountain a r e a at h i g h e r e l e v a -t i o n s may be 3000 mm/year or p o s s i b l y h i g h e r . W i t h e s t i m a t e s of p r e c i p i t a t i o n , e v a p o t r a n s p i r a t i o n and r u n o f f a t hand, water b a l a n c e c a l c u l a t i o n s can now be p e r -formed . Water B a l a n c e In the Meager Mountain a r e a , a much more d e t a i l e d water b a l a n c e e q u a t i o n than the p r e v i o u s l y - m e n t i o n e d E q u a t i o n 4.1 i s needed i n o r d e r t o q u a n t i f y a l l the h y d r o l o g i c components. Assuming the s u r f a c e - w a t e r d i v i d e s and groundwater d i v i d e s c o i n c i d e , t h e r e i s no change i n groundwater s t o r a g e , and t h e r e a r e no e x t e r n a l i n f l o w s or o u t f l o w s of groundwater, then a water budget e q u a t i o n would be w r i t t e n f o r an annual p e r i o d as f o l l o w s , P=Q s p+ Q s a - Q s a c + °-sbm+ Qg + E s + Ew <4-2> where P i s the average annu a l p r e c i p i t a t i o n , Q s p i s the s u r -f a c e water component of average a n n u a l r u n o f f due t o p r e c i p i -t a t i o n , Q s a i s the s u r f a c e water component of average annu a l r u n o f f due t o g l a c i a l a b l a t i o n , Q s a c i s the s u r f a c e water component of average r u n o f f due t o g l a c i a l a c c u m u l a t i o n , Qsbm i s the s u r f a c e water component of average annual r u n o f f due 58 to g l a c i a l b a s a l m e l t i n g , Qg i s the groundwater component of average annual r u n o f f , E g i s the e v a p o t r a n s p i r a t i o n from the s o i l - c o v e r e d p o r t i o n of the b a s i n , and E w i s the evap o r a t i o n from the open water p o r t i o n of the b a s i n . Equation 4.2 i n c l u d e s the major components necessary f o r a r i g o u r o u s and acc u r a t e water balance c a l c u l a t i o n i n the Meager.Mountain area. Data i s not a v a i l a b l e f o r a l l the v a r i a b l e s , but a number of s i m p l i f y i n g assumptions can be made to make the problem t r a c t a b l e . In the f i r s t p l a c e , very l i t t l e open water e x i s t s i n the b a s i n , so E can be c o n s i d -ered n e g l i g i b l e . In a d d i t i o n , the component Q sb m r e p r e s e n t s the c o n t i n u a l b a s a l m e l t i n g of g l a c i e r s due to the n a t u r a l geothermal g r a d i e n t of the p o r t i o n of the e a r t h the g l a c i e r c o v e r s . The governing equation i s d z = Ea. dz dt PL U . 3 ) where dt i s the rate of change of t h i c k n e s s of i c e with time, q Q i s the geothermal heat f l u x , P i s the d e n s i t y of i c e and L i s the l a t e n t heat of mel t i n g (personal communication, G. C l a r k , 1981). Lewis and Souther (1978) d i s c o v e r e d , that i n the Meager Creek ba s i n the average geothermal heat f l u x i s approximately 10 times the world average. C a l c u l a t i o n s r e -por t e d i n Appendix II demonstrate that Qgj^  c o n t r i b u t e s a maximum of 3 to 4% of the t o t a l r u n o f f i n the Meager Creek b a s i n . The b a s a l melt c o n t r i b u t i o n f o r the e n t i r e L i l l o o e t b a s i n which has an o v e r a l l heat f l u x c l o s e to the world average i s l e s s than 1%, and i s t h e r e f o r e assumed to be i n s i -g n i f i c a n t . 59 Measurements of g l a c i e r a b l a t i o n or a c c u m u l a t i o n have not been undertaken i n the study a r e a , however i t has been shown by h i s t o r i c a l , b o t a n i c a l and g e o l o g i c a l s t u d i e s t h a t g l a c i e r s i n the Coast Mountains of B r i t i s h Columbia have been r e t r e a t i n g s i n c e the second and t h i r d decades of t h i s c e n t u r y (Mathews, 1951). T h i s r e t r e a t has slowed somewhat s i n c e the n i n e t e e n f i f t i e s . The r a t e of a b l a t i o n of a number of g l a -c i e r s i n s o u t h w e s t e r n B r i t i s h Columbia has been i n v e s t i g a t e d . Mathews (1951) examined a number of g l a c i e r s i n the Mount G a r a b a l d i a r e a 40 to 80 km n o r t h of Vancouver. The most com-p l e t e d a t a e x i s t s f o r the Helm G l a c i e r , which was found t o be l o s s i n g 1.8 t o 2.1 m/y of water e q u i v a l e n t t h i c k n e s s between 1928 and 1947. The g l a c i e r n e a r e s t the study a r e a t h a t has been s t u d i e d i s the P l a c e G l a c i e r 20 km n o r t h e a s t of Pemberton. From 1965 t o 1974 the g l a c i e r l o s t an average of 0.4 m/y (Mokievsky-Zubok and S t a n l e y , 1976). The r u n o f f d a t a a v a i l b l e f o r the L i l l o o e t b a s i n ( F i g u r e 4.3) i s averaged from 1923 t o 1968. This- time p e r i o d c o v e r s the r a p i d a b l a t i o n p e r i o d e a r l y i n the c e n t u r y and the s l o w e r a b l a t i o n p e r i o d i n r e c e n t t i m e . T h e r e f o r e , an average a b l a -t i o n r a t e of 1 m/y has been chosen f o r the g l a c i e r s of the L i l l o o e t b a s i n . G l a c i e r s c o v e r 14% of the s u r f a c e a r e a of the b a s i n . C o n s e q u e n t l y , assuming t h a t a l l the g l a c i e r a b l a -t i o n t a k e s p l a c e as r u n o f f , the g l a c i e r s c o n t r i b u t e 0.14 m/y or 140 mm/y over the e n t i r e d r a i n a g e b a s i n . The above c o n s i d e r a t i o n s a l l o w E q u a t i o n 4.2 t o be r e -60 duced t o p-%>'W % + E s (4.4) The f a c t t h a t E i s the o n l y e v a p o t r a n s p i r a t i o n term a l l o w s E q u a t i o n 4.4 t o s i m p l i f y t o P = Q -Q + Q + E (4.5) sp sac g where E i s the average ann u a l e v a p o t r a n s p i r a t i o n . The average ann u a l r u n o f f , Qsp+Qsac" Qgf over a 50 year p e r i o d was g i v e n e a r l i e r as 1880 mm and the e v a p o t r a n s p i r a -t i o n E was e s t i m a t e d a t 500 mm. Adding the above v a l u e s and s u b t r a c t i n g Q g i v e s an average annual p r e c i p i t a t i o n P, i n the L i l l o o e t b a s i n , of a p p r o x i m a t e l y 2240 mm. ) We would a l s o l i k e t o g a i n some i d e a of the r e l a t i v e v a l u e s of Q s and Q g. D u r i n g the months of January and F e b r u a r y the mean annual temperature i n the L i l l o o e t b a s i n i s below f r e e z i n g ( Table 4.1), so t h a t a l l r u n o f f presumably comes from groundwater d i s c h a r g e i n t o the streams . F i g u r e 4.3 r e p r e s e n t s the mean of the mean d a i l y d i s c h a r g e of the L i l l o o e t R i v e r from 1923 t o 1968. The groundwater component or b a s e f l o w of the r u n o f f can be c a l c u l a t e d from the graph. The s i m p l e s t t e c h n i q u e of b a s e f l o w s e p a r a t i o n i s t o draw a h o r i z o n t a l l i n e t h r o u g h the p o i n t a t which s u r f a c e r u n o f f b e g i n s , p o i n t A (Viessman e t a l . , 1977). T h i s method assumes a s t e a d y - s t a t e groundwater f l o w system. That i s t o say, the groundwater f l o w i s c o n s t a n t throughout the y e a r , t h e r e b y j u s t i f y i n g the h o r i z o n t a l l i n e . The ar e a below the l i n e r e -p r e s e n t s the groundwater component of the average ann u a l 400 1 1 r July Aug Sept Nov Dec F i g u r e 4.3 Mean o f mean d a i l y d i s c h a r g e f o r L i l l o o e t R i v e r (1923-1968) d i v i d e d i n t o s u r f a c e w a t e r component Q S p + Q s a and g r o u n d w a t e r component Q g 62 r u n o f f Qg. The a r e a above the l i n e r e p r e s e n t s the s u r f a c e water component of the average a n n u a l r u n o f f Q Sp +Qsac" T ^ e a r e a below the h o r i z o n t a l l i n e i s 20% of the t o t a l a r ea below the c u r v e , t h e r e f o r e the groundwater component Q g i s 20% of the average a n n u a l r u n o f f of 1880 mm, or 380 mm. In c o n c l u s i o n , the p r e l i m i n a r y s i m p l i f i e d water b a l a n c e e q u a t i o n f o r t h e L i l l o o e t b a s i n i s P - Qsp-Qsac Qg + E < 4 - 5 ) where the average a n n u a l p r e c i p i t a t i o n P e q u a l s 2240 mm and 61% or 1360 mm of t h i s t o t a l i s r e l e a s e d from the b a s i n by the s u r f a c e water component of the average a n n u a l r u n o f f due t o p r e c i p i t a t i o n Q , 17% or 380 mm by the groundwater com-sp ponent of the average annual r u n o f f Q g, and 22% or 500 mm by the e v a p o t r a n s p i r a t i o n E. The s u r f a c e water component of the average a n n u a l r u n o f f due t o g l a c i a l a b l a t i o n Q i s 140 mm/y. The c o n c l u d i n g e q u a t i o n i n d i c a t e s t h a t 17% of the p r e c i -p i t a t i o n f a l l i n g i n the L i l l o o e t R i v e r b a s i n e n t e r s the groundwater system. In Chapter 6, t h i s v a l u e of groundwater r e c h a r g e w i l l be compared w i t h t h e v a l u e c a l c u l a t e d i n t h e Meager Creek s u b - b a s i n by a v e r y d i f f e r e n t method. In Chapter 7, the v a l u e s a r e used as i n p u t parameters i n the m a t h e m a t i c a l model. F i r s t , we w i l l d i s c u s s the f r a c t u r e survey completed a t Meager Mountain i n an attempt t o c a l c u l a t e the h y d r a u l i c con-d u c t i v i t y of the f r a c t u r e d basement r o c k . 63 Chapter 5. HYDRAULIC CONDUCTIVITY OF FRACTURED ROCK The h y d r a u l i c c o n d u c t i v i t y i s a v e r y i m p o r t a n t parameter f o r d e t e r m i n i n g groundwater f l o w p a t t e r n s . As s t a t e d e a r -l i e r , t he h y d r a u l i c c o n d u c t i v i t y i n the Meager Mountain a r e a i s governed m a i n l y by the f r a c t u r e p o r o s i t y of the v o l c a n i c and basement r o c k s . Many r e s e a r c h e r s have developed f o r m u l a s t h a t r e l a t e the f r a c t u r e p o r o s i t y n t o the h y d r a u l i c conduc-t i v i t y K. Snow (1968) i l l u s t r a t e d t h a t a p a r a l l e l a r r a y of p l a n e r j o i n t s of a p e r t u r e b, w i t h N j o i n t s per u n i t d i s t a n c e a c r o s s the rock face has a p o r o s i t y n=Nb and h y d r a u l i c condu-c t i v i t y : . . / .\ where k i s the p e r m e a b i l i t y of the r o c k , P i s the d e n s i t y of the f l u i d , g i s the a c c e l l e r a t i o n due t o g r a v i t y and y i s the dynamic v i s c o s i t y of the f l u i d . T h e r e f o r e , the o n l y f i e l d measurements n e c e s s a r y a r e the a p e r t u r e and s p a c i n g . Note t h a t the h y d r a u l i c c o n d u c t i v i t y v a r i e s as the cube of the a p e r t u r e . I t i s c l e a r , t h a t i n a c c u r a t e measurements of f r a c -t u r e a p e r t u r e s w i l l c r e a t e l a r g e e r r o r s i n the e s t i m a t e d con-d u c t i v i t y . More complex e q u a t i o n s have been d e v e l o p e d f o r two and t h r e e d i m e n s i o n a l a n i s o t r o p i c f l o w i n f r a c t u r e d r o c k . In a d d i t i o n t o a p e r t u r e and s p a c i n g , s t r i k e and d i p measurements (5.1) or (5.2) 64 a r e a l s o needed. The e q u a t i o n s and t h e i r development w i l l not be d i s c u s s e d here but the i n t e r e s t e d reader i s r e f e r r e d t o Snow (1966,1969), B i a n c h i and Snow (1969), Rocha and F r a n c i s s (1977), and S t r e l t s o v a (1976). D u r i n g the summer of 1980 a f r a c t u r e survey was u n d e r t a -ken a t Meager Mountain t o e v a l u a t e the h y d r a u l i c c o n d u c t i v i t y of the basement r o c k . The r e s u l t s of t h i s f r a c t u r e s u r v ey a r e d i s c u s s e d below. To check the v a l i d i t y of t h e s u r v e y , the r e s u l t s a re compared w i t h p u b l i s h e d d ata of the f r a c t u r e p e r m e a b i l i t y of v a r i o u s rock t y p e s . F i r s t l y , however, p r o p e r f i e l d mapping and da t a p r o c e s -s i n g t e c h n i q u e s f o r the h y d r a u l i c c o n d u c t i v i t y d e t e r m i n a t i o n of f r a c t u r e d r o c k s w i l l be d i s c u s s e d . F r a c t u r e Mapping and Data P r o c e s s i n g Methods The f r a c t u r e system i n a rock mass c o n t a i n s d i s c o n t i n u i -t i e s of v a r i o u s s i z e s . The l a r g e s t f r a c t u r e s a re l a r g e - s c a l e s t r u c t u r a l f e a t u r e s such as major f a u l t s and shear zones. These f e a t u r e s a re seldom obs e r v e d i n s u r f a c e bedrock expo-s u r e s but are e a s i l y i d e n t i f i e d by a e r i a l photography. The most common type of f r a c t u r e s a r e j o i n t s which a r e d i s c o n -t i n u o u s d i s c r e t e breaks w i t h i n the rock mass, commonly oc-c u r i n g i n s e t s r e f l e c t i n g the t e c t o n i c h i s t o r y of the rock mass (Raven 1980). T r a n s i t i o n a l between major f a u l t s and j o i n t s a r e f r a c t u r e zones composed of c l o s e l y spaced i n t e r -c o n n e c t i n g b r e a k s . Such zones may have w i d t h s of meters t o 65 t e n s of meters. A number of methods f o r mapping f r a c t u r e systems have been d e v e l o p e d . A method i n common use i s the l i n e s a m p l i n g t e c h n i q u e o r i g i n a l l y employed f o r e x c a v a t i o n s t a b i l i t y analy-s i s by P i t e a u (1971). The method c o n s i s t s of s t r e t c h i n g a measuring tape a l o n g an exposed rock f a c e and r e c o r d i n g the g e o l o g i c a l d i s c o n t i n u i t i e s t h a t i n t e r s e c t the t a p e . The mea-surements and f e a t u r e s t h a t can be r e c o r d e d f o r each d i s c o n -t i n u i t y i n c l u d e : 1 2 3 4 5 6 7 8 9 10 11 12 13 d i s t a n c e from t r a v e r s e s t a t i o n t o s t r u c t u r e rock t y p e s hardness type of s t r u c t u r e s ( f a u l t , j o i n t e t c ) s p a c i n g and f r e q u e n c y of j o i n t s e t s a p e r t u r e s t r i k e d i p l e n g t h of d i s c o n t i n u i t y i n f i l l i n g water roughness waviness P i t e a u and M a r t i n (1977) i n c l u d e g e n e t i c d e s c r i p t i o n s of the above terms t o i n s u r e u n i f o r m r e c o r d i n g by d i f f e r e n t i n -d i v i d u a l s . Mapping a l o n g l e v e l l i n e s on near v e r t i c a l o u t c r o p s neg-66 l e c t s f r a c t u r e s i n the h o r i z o n t a l d i r e c t i o n . F r a c t u r e i n f o r -mation from b o r e h o l e s can be t r e a t e d as l i n e samples t o com-p l e t e the t h r e e - d i m e n s i o n a l assessment of f r a c t u r e o r i e n t a -t i o n . The a p e r t u r e of a d i s c o n t i n u i t y i s one of the most im-p o r t a n t parameters w i t h r e s p e c t t o h y d r a u l i c c o n d u c t i v i t y d e t e r m i n a t i o n , and a l s o the most d i f f i c u l t parameter t o meas-ure i n the f i e l d . Snow (1970) d i s c u s s e s a t e c h n i q u e t h a t i n v o l v e s photography and f l u o r e s c e n t l i q u i d dye. Through the use of dye, s o l v e n t s , and a d e v e l o p e r , f r a c t u r e s can be h i g h -l i g h t e d . C l o s e up photos are taken and measurements of the f r a c t u r e s a r e made w i t h c a l i p e r s on blown up p i c t u r e s p r o -j e c t e d on a s c r e e n . There are a few draw backs t o t h i s method but a p e r t u r e s as s m a l l as 130 microns can be measured w i t h a r e l a t i v e e r r o r of 3 p e r c e n t . The amount of d a t a g a t h e r e d d u r i n g a f r a c t u r e survey can be l a r g e and d i f f i c u l t t o manage. S e v e r a l computer based systems f o r the storage,- r e t r i e v a l , a n a l y s i s and d i s p l a y of s t r u c t u r a l d i s c o n t i n u i t y d a t a have been d e v e l o p e d . Cruden, Ramsden and Herget (1977) d e v e l o p e d a computer based package c a l l e d DISCODAT. I t i s d e s c r i b e d i n a p a r t of the P i t Slope Manual s e r i e s p u b l i s h e d by Energy, Mines and Resources Canada. Both s u r f a c e and b o r e h o l e f r a c t u r e d a t a may be ana-l y z e d w i t h the D i s c o d a t programs. O r i e n t a t i o n diagrams such as s t e r e o n e t s , and h i s t o g r a m s of r e l a t i v e and c u m u l a t i v e f r e q u e n c i e s of the a n g l e of s t r i k e are produced by the 67 D i s c o d a t system, s a v i n g c o u n t l e s s hours of t e d i o u s manual p l o t t i n g . The l i n e s a m p l i n g t e c h n i q u e f o r g a t h e r i n g d a t a and the D i s c o d a t system work w e l l t o g e t h e r t o produce the neces-s a r y d a t a f o r f r a c t u r e d - r o c k - h y d r o l o g y s t u d i e s . Meager Mountain F r a c t u r e Survey D u r i n g the summer of 1980 the author and the employees of N e v i n , S a d l i e r - B r o w n and Goodbrande L t d . performed a j o i n t o r i e n t a t i o n survey on the basement g r a n o d i o r i t e i n the South R e s e r v o i r a r e a . The purpose of the study f o r N e v i n , S a d l i e r -Brown and Goodbrande L t d . was t o g a i n s t r u c t u r a l d ata f o r g e o l o g i c i n t e r p r e t a t i o n and f o r the auth o r t o c o l l e c t d a t a f o r h y d r a u l i c c o n d u c t i v i t y c a l c u l a t i o n s . R e s u l t s T w e n t y - f i v e l o c a t i o n s were examined. Twenty-four s i t e s were i n basement rock and one i n v o l c a n i c r o c k . F i g u r e 5.1 i l l u s t r a t e s the s i t e l o c a t i o n s . The l i n e s a m p l i n g t e c h n i q u e d e s c r i b e d e a r l i e r was not u t i l i z e d i n the survey because the autho r was not aware of the t e c h n i q u e a t the time of the s u r -vey. R a t h e r , t r a v e r s e s were made a l o n g o u t c r o p s and j o i n t s were measured i n a random f a s h i o n . The s p a c i n g between a d j a -cent j o i n t s of the same s e t and the a p e r t u r e of each f r a c t u r e were e s t i m a t e d r a t h e r than measured d i r e c t l y . Lower hemisphere, e q u a l - a r e a , c o n t o u r e d - p o l e p l o t s of the t w e n t y - f i v e s i t e s can be found i n Appendix I I a l o n g w i t h F i g u r e 5.1 L o c a t i o n o f f r a c t u r e s u r v e y s i t e s . 69 the c o o r d i n a t e s and e l e v a t i o n of each s i t e . C l o s e examina-t i o n of the c o n t o u r e d - p o l e p l o t s r e v e a l e d f o u r p e r s i s t a n t j o i n t s e t s t h a t have been h i g h l i g h t e d f o r easy i d e n t i f i c a -t i o n . T a b l e 5.1 e x h i b i t s the v a r i a t i o n i n s t r i k e and d i p of i n d i v i d u a l j o i n t s e t s a t l o c a t i o n s where j o i n t s e t s where e v i d e n t w h i l e Table 5.2 i l l u s t r a t e s the average o r i e n t a t i o n of the j o i n t s e t s at each measured s i t e . Note t h a t j o i n t s e t s 1 and 2 e x i s t a t almost e v e r y s i t e w h i l e j o i n t s e t s 3 and 4 o c c u r o n l y a t a few s i t e s , i n d i c a t i n g t h a t j o i n t s e t s 1 and 2 a r e the dominant s e t s i n the r o c k . I t i s a l s o c l e a r t h a t the j o i n t s e t s a r e a l s o s t e e p l y d i p p i n g . The v a r i a t i o n i n s p a c i n g and a p e r t u r e of j o i n t s e t s can be found i n Table 5.3. and the average v a r i a t i o n s of s p a c i n g and a p e r t u r e of the f o u r j o i n t s e t s are i n T a b l e 5.4. I t i s e v i d e n t t h a t t h e r e i s a wide range of s p a c i n g s from 0.05 to 5.0 m and of a p e r t u r e s from t i g h t t o 20 mm. T h e r e f o r e , the h y d r a u l i c c o n d u c t i v i t y which i s c a l c u l a t e d from these v a l u e s w i l l a l s o have a wide range. The l i s t i s i n c o m p l e t e due to the d i f f i c u l t y of s e e i n g the i n d i v i d u a l j o i n t s e t s on the rock f a c e s a t a number of l o c a t i o n s . C o n s e q u e n t l y , the j o i n t s p a c i n g parameter c o u l d not be e s t i m a t e d . A l s o , the a u t h o r ' s n e g l e c t t o s t r e s s the importance of the s p a c i n g and s e p a r a -t i o n o b s e r v a t i o n s t o o t h e r s t a k i n g measurements, l e d t o mis-s i n g v a l u e s a t a number of s i t e s ' . TABLE 5. 1 O r i e n t a t i o n V a r i a t i o n s of J o i n t Sets S i t e J o i n t Set 1 J o i n t Set 2 J o i n t Set 3 J o i n t Set 4 S t r i k e Dip S t r i k e Dip S t r i k e Dip S t r i k e Dip 1 350-35 65W -88E 106-130 34 -78NE 2 45-75 70N -75S 3 32-68 45NW-75SE 148-170 70W -75E 4 17-45 75SE-85NW 80-94 75S -85N 75-105 35 -65N 5 106-148 40 -60SW 6 4-25 70E -80W 125-144 58 -72SW 55-75 70 -90S 7 105-140 35 75SW 65-80 65 -88S 8 130-170 65SW-80NE 9 22-45 78NW-82SE 154-166 60SW-80NE 68-88 60 -88SE 68-110 20 -45N 10 25-40 68 -90NW 148-170 70NE-80SW 11 150-165 62 -90NE 12 6-24 78SE-84NW 136-162 70NE-80SW 90-116 40 -80NE 13 40-68 40 -80SE 14 38-66 42 -64NW 118-140 60SW-78NE 15 156-180 52 -78E 98-128 75NE-70SW 16 14-35 70SE-80NW 90-122 50 -90NE 17 4-25 72NW-80SE 18 0-36 70NW-68SE 110-158 40 -70SW 19 20-38 76NW-72SE 108-140 44 -75NE 45-72 60 -70NE 20 148-176 70SW-70NE 78-96 40 -60N 21 164-28 70NW-62SE 64-82 68NW-76SE 88-120 56 -80NE 22 145-174 50NE-80SW 23 32-76 64SE-72NW 125-162 45 -72SW 72-118 20 -40N 24 144-170 68NE-80SW 68-96 64 -90S 25 TABLE 5.2 A v e r a g e O r i e n t a t i o n s o f J o i n t S e t s S i t e J o i n t S e t 1 J o i n t S e t 2 J o i n t S e t 3 J o i n t S e t 4 S t r i k e D i p S t r i k e D i p S t r i k e D i p S t r i k e D i p 1 12 82 NW 118 56 NE 2 60 88 NW 3 50 75 NW 159 87 SW 4 31 85 SE 87 85 S 90 50 N 5 127 52 SW 6 15 85 SE 135 65 SW 65 80 S 7 119 55 SW 72 77 S 8 150 82 SW 9 33 88 NW 160 80 SW 78 74 S 89 33 N 10 32 79 NW 159 85 NE 11 158 76 NE 12 15 87 SE 149 85 NE 103 60 NE 13 54 60 SE 14 52 53 NW 129 86 SW 15 113 88 SW 16 24 85 SE 106 70 NE 17 14 86 NW 18 18 89 SE 134 55 SW 19 29 88 SE 124 59 NE 59 65 NW 20 162 90 87 50 N 21 6 86 SE 73 86 NW 104 69 NE 22 159 75 NE 23 54 86 SE 144 59 SW 95 30 N 24 157 84 NE 82 77 S 25 32 80 NW 140 85 SW Table 5.3 Joint Spacing and Aperture Variations Site Joint Set Spacing(m) Aperture(mm) 1 1 0.2-1.0 Tight -3 2 1 0.1-0.5 1-5 3 1 0.5-1.0 Tight -5 3 2 0.1-1.5 5-2 4 1.3 & 4 0.4-2.0 Tight 8 2 1.0-5.0 Tight -5 9 2 0.1-0.5 Tight -10 9 4 0.05-0.25 Tight -5 10 1 0.05-1.0 5-20 10 2 0.05-0.8 Tight -5 11 2 1-1.5 2-20 14 2 0.2-1.0 Tight -5 14 1 0.3-0.5 Tight -3 15-18 1 & 2 0.1-1.0 1-10 Table 5.4 Average Spacing and Aperture Set Spacing(ra) Aperture(mm) 1 0.1 -1.0 Tight -20 2 0.1 -1.0 Tight -20 3 0.4-2.0 Tight 4 0.05-2.0 Tight -5 73 D i s c u s s i o n The methodology used f o r the Meager Mountain f r a c t u r e survey s u p p l i e d inadequate d a t a f o r the c a l c u l a t i o n of the rock mass h y d r a u l i c c o n d u c t i v i t y . The problems w i t h the survey a r e l i s t e d below t o g e t h e r w i t h s u g g e s t i o n s f o r pos-s i b l e f u t u r e remedies. 1) The problem of the m i s s i n g d a t a f o r s p a c i n g and a p e r t u r e measurements c o u l d be r e c t i f i e d by c o o r d i n a t i n g and s t a n -d a r d i z i n g survey p r a c t i c e b e f o r e b e g i n n i n g the work. 2) The s u r v e y s were ta k e n on n e a r - v e r t i c a l o u t c r o p s , conse-q u e n t l y the measured f r a c t u r e s r e p r e s e n t o n l y two dimen-s i o n s . The g a t h e r i n g of j o i n t o r i e n t a t i o n s i n i n c l i n e d bore h o l e s or near h o r i z o n t a l rock f a c e s would c o r r e c t t h i s d e f i c i e n c y . 3) The random measuring of the j o i n t systems can b i a s the r e s u l t s , whereas the l i n e s a m p l i n g t e c h n i q u e e l i m i n a t e s any b i a s . 4) The major problem w i t h the measurements taken a t Meager Mountain l i e s i n the f a c t t h a t the a p e r t u r e s of the f r a c -t u r e s were e s t i m a t e d r a t h e r than measured d i r e c t l y . The c o n d u c t i v i t y of the rock mass v a r i e s as the a p e r t u r e cubed, t h e r e f o r e i n a c c u r a c i e s i n a p e r t u r e measurement a r e m u l t i p l i e d when c a l c u l a t i n g the h y d r a u l i c c o n d u c t i v i t y or f l u x t h rough the r o c k . Simple h y d r a u l i c c o n d u c t i v i t y c a l c u l a t i o n s of the rock mass were attempted u s i n g E q u a t i o n 5.1. However, due t o the 74 v a r i a b i l i t y of a p e r t u r e e s t i m a t e s a t any s i n g l e s i t e , the h y d r a u l i c c o n d u c t i v i t y e s t i m a t e s ( 1 0 + 4 t o 10" 6 m/s) extended over many o r d e r s of magnitude and such e s t i m a t e s are f e l t t o have l i t t l e v a l u e . Even i f more a c c u r a t e a p e r t u r e s had been measured, i t i s q u e s t i o n a b l e whether the measurement of f r a c -t u r e s on s u r f a c e exposures i s adequate f o r computing the con-d u c t i v i t y of rock at d e p t h . A n e a r - s u r f a c e or s u r f a c e f r a c -t u r e i s widened d u r i n g i t s h i s t o r y , by a d e c r e a s e of the s t r e s s f i e l d by e r o s i o n a l u n l o a d i n g and by s u r f a c e p r o c e s s e s such as w e a t h e r i n g and c r e e p ( B i a n c h i and Snow, 1969). Snow (1968) d i s c o v e r e d from t e s t h o l e s i n g r a n i t i c , metamorphic and v o l c a n i c r o c k , t h a t w i t h i n the f i r s t 150 m of depth, the f r a c t u r e d rock p o r o s i t y d e c r e a s e s an o r d e r of magnitude ev e r y 60 m. T h e r e f o r e , s u r f a c e measurements of a p e r t u r e s w i l l g i v e an u n r e a s o n a b l y h i g h c o n d u c t i v i t y f o r the rock mass. How-e v e r , f r a c t u r e d a t a can be used t o i l l u s t r a t e g e n e r a l t r e n d s of the c o n d u c t i v i t y i n a rock mass, such as the d i r e c t i o n of a n i s o t r o p y . A l s o , a r e a s of r e l a t i v e l y h i g h f r a c t u r e d e n s i t y can be d e l i n e a t e d t o p o s s i b l y r e v e a l zones of h i g h e r hydrau-l i c c o n d u c t i v i t y a t d e p t h . In the l a t e r s t a g e s of e x p l o r a t i o n i t may be p o s s i b l e t o measure a p e r t u r e s i n - s i t u i n b o r e h o l e s w i t h a down-hole camera or p e r i s c o p e , and of c o u r s e , once a h o l e i s d r i l l e d , d i r e c t t e s t s f o r h y d r a u l i c c o n d u c t i v i t y such as pump t e s t s and packer t e s t s can be performed. As-, the f r a c t u r e survey at Meager Mountain was unsucces-75 s f u l , l e t us now look a t p u b l i s h e d f r a c t u r e p e r m e a b i l i t i e s of v a r i o u s rock t y p e s , t o o b t a i n a range of h y d r a u l i c c o n d u c t i -v i t y v a l u e s t h a t one might expect i n the study a r e a . P u b l i s h e d F r a c t u r e P e r m e a b i l i t i e s of V a r i o u s Rock Types R e p o r t e d measurements of h y d r a u l i c c o n d u c t i v i t i e s i n f r a c t u r e d rock have been v e r y s c a r c e u n t i l r e c e n t l y , when r e s e a r c h f o r f e a s i b l e n u c l e a r waste r e p o s i t o r i e s was u n d e r t a -ken i n the 1970's. Work performed f o r the Atomic Energy of Canada L i m i t e d (AECL) and the U.S. Department of Energy has p r o v i d e d most of the p u b l i s h e d v a l u e s . Raven and Gale (1977), i n a r e p o r t f o r the G e o l o g i c a l Survey of Canada and AECL, examined the s u r f a c e and s u b s u r -face s t r u c t u r e s and groundwater c o n d i t i o n s a t 25 underground mines, l o c a t e d on the Canadian S h i e l d . I t was found t h a t seepage was r e s t r i c t e d t o the upper 300 m i f no major s t r u c -t u r e s such as f a u l t s or c o n t a c t s were p r e s e n t . They a l s o found t h a t the number and magnitude of these s t r u c t u r a l seep-age zones were g r e a t l y reduced below 300 t o 350 m. S t r u c -t u r e s such as j o i n t s e t s c o n t i n u e d t o depths of up t o 1000 m but the p e r m e a b i l i t i e s of the rock near s u r f a c e d e c r e a s e d l o g a r i t h m i c a l l y w i t h d e p t h . In terms of h y d r a u l i c c o n d u c t i -v i t y , f a u l t s p r o v i d e the h i g h e s t v a l u e s , f o l l o w e d by shear zones, d i k e s , s i l l s and i n t r u s i v e g e o l o g i c c o n t a c t s . Of t h e 25 mine s i t e s examined, the most e x t e n s i v e p r o -gram of down h o l e h y d r a u l i c c o n d u c t i v i t y t e s t i n g was c a r r i e d 76 out a t the G u l l I s l a n d p r o j e c t s i t e i n L a b r a d o r . The h o l e s were d r i l l e d i n f o l i a t e d g r a n o d i o r i t e , hornblende b i o t i t e g n e i s s , and a m p h i b o l i t e . Near s u r f a c e , the h y d r a u l i c conduc-t i v i t y v a r i e d from 10" 5 t o 10" 6 m/s and d e c r e a s e d t o 10"' t o 10" 8 m/s at depths of 60 t o 75 m. From 60 t o 150 m the hy-d r a u l i c c o n d u c t i v i t y showed no s i g n i f i c a n t v a r i a t i o n . . Burgess (1979), i n a n o t h e r AECL r e p o r t , d i s c u s s e s cons-t a n t i n f l o w t e s t s i n 8 b o r e h o l e s completed f o r the Swedish R a d i o a c t i v e Waste Program. The t e s t h o l e s were sunk over 500 m i n t o a g r a n i t i c p l u t o n i n the Precambrian basement. Hy-d r a u l i c c o n d u c t i v i t y v a l u e s i n the upper 100 m v a r i e d from 10" 5 t o 10" 7 m/s, d e c r e a s i n g t o 10"" t o 1 0 " 1 0 m/s from 200 t o 500 m. Raven (1979) c o l l e c t e d h y d r o g e o l o g i c d a t a f o r the N u c l e a r F u e l Waste Management Program at the Chalk R i v e r ( O n t a r i o ) N u c l e a r L a b o r a t o r i e s f i e l d r e s e a r c h s i t e i n 1977 and 1978. V a r i o u s s h u t - i n p r e s s u r e and i n j e c t i o n t e s t s were a c c o m p l i s h e d i n 5 t e s t h o l e s d r i l l e d i n Precambrian monzonite g n e i s s and metagabbro. H y d r a u l i c c o n d u c t i v i t y v a l u e s of 4x10"' t o 4 x 1 0 " 1 1 were o b t a i n e d a t depths between 40 and 72 m. Davison et a l . (1979) r e p o r t e d on v a r i o u s down h o l e t e s t s performed i n a g r a n i t i c p l u t o n a t the W h i t e s h e l l N u c l e a r Research E s t a b l i s h m e n t i n M a n i t o b a . The t e s t s were completed i n two d r i l l h o l e s each 150 m deep. Above 25 m h y d r a u l i c c o n d u c t i v i t y v a l u e s of 5x10" 8 t o 5x10"' m/s were 77 o b t a i n e d . Below 25 m the h y d r a u l i c c o n d u c t i v i t y ranged from 5 x 1 0 ' 1 0 t o 5 x 1 0 " 1 1 m/s. Over the p a s t 10 t o 15 y e a r s , e x t e n s i v e d r i l l i n g and h y d r o g e o l o g i c t e s t i n g has been undertaken a t the H a n f o r d , B a s a l t Waste I s o l a t i o n P r o j e c t i n Washington S t a t e . The geo-l o g y c o n s i s t s b a s i c a l l y of a number of t h i c k b a s a l t i c f l o w s w i t h minor b r e c c i a t e d or weathered h o r i z o n s and s e d i m e n t a r y i n t e r b e d s . The maximum v a r i a t i o n s i n the h y d r a u l i c c o n d u c t i -v i t y a r e from 5x10" 1 m/s i n v e r y sandy weathered l a y e r s t o 5 x 1 0 " 1 3 m/s i n v e r y dense columnar b a s a l t zones. The m a j o r i -t y of the weathered, b r e c c i a t e d zones have h y d r a u l i c conduc-t i v i t y v a l u e s r a n g i n g from 10" 3 t o 10' 5 m/s. Most of the low d e n s i t y b a s a l t s range from 10"' t o 1 0 ' 1 0 m/s and the h i g h d e n s i t y b a s a l t f l o w s v a r y from 10"' t o 1 0 ' 1 0 m/s. D a v i s (1969) r e p o r t e d i n h i s paper on the p o r o s i t y and p e r m e a b i l i t y of v a r i o u s m a t e r i a l s i n c l u d i n g p l u t o n i c , v o l -c a n i c , metamorphic and s e d i m e n t a r y r o c k s and u n c o n s o l i d a t e d d e p o s i t s . H i s f i n d i n g s on the h y d r a u l i c c o n d u c t i v i t y of a number of rock t y p e s are summarized i n T a b l e 5.5 a l o n g w i t h the o t h e r h y d r a u l i c c o n d u c t i v i t i e s d i s c u s s e d above. The p r e c e d i n g v a l u e s i m p l y t h a t the h y d r a u l i c c o n d u c t i -v i t y of most f r a c t u r e d rock l i e s i n the 10' 7 t o 1 0 ' 1 1 m/s range. I t s h o u l d be noted t h a t , the m a j o r i t y of the v a l u e s g i v e n i n the v a r i o u s r e p o r t s were taken i n r e a s o n a b l y u n d i s -t u r b e d r o c k . However, the basement r o c k s of the Meager Mountain area have been h i g h l y d i s t u r b e d . T h e r e f o r e , i t Table 5.5 Summary of Measured Hydraulic C o n d u c t i v i t y Values f o r Various Rock Types Reference Location Rock Type Depth (m) Co n d u c t i v i t y (m/s) Raven and Gale 1977 G u l l Island F o l i a t e d g r a n o d i o r i t e 20 I O - 5 to 1 0 - 6 and b i o t i t e gneiss 60-75 I O - 6 - I O - 8 Burgess 1979 Sweden Granite pluton 0-100 1 0 - 5 - i o - 7 200-500 10" 8 - I O " 1 0 Raven 1979 Chalk River Ontario Monzonite gneiss - -9 -1 1 4x10 - 4x10 Davison, Grisak and Whiteshell Manitoba Granite pluton 25 5 x l 0 ~ 8 - 5 x l 0 ~ 9 Williams 1979 150 5X10" 1 0 - 5X10" 1 1 Rockwell I n t e r n a t i o n a l Hanford Washington Basalt - 4 x l 0 ~ 1 0 - 4 x l 0 " 1 3 1979 Davis 1969 Dense b a s a l t 1 0 " 1 0 pumecious t u f f IO" 7 metasediments 3 x l 0 ~ 7 greywacke 4 x l 0 ~ 7 79 would be e x p e c t e d t h a t the h y d r a u l i c c o n d u c t i v i t y v a l u e s of of the basement r o c k s a r e a t the h i g h end of the range s t a t e d . V a l u e s of 10" 7 t o 10" 8 m/s c o u l d be e x p e c t e d . In the hydrogeology c h a p t e r and m a t h e m a t i c a l m o d e l l i n g c h a p t e r t o f o l l o w , i t w i l l be shown t h a t the h y d r a u l i c condu-c t i v i t y of the basement rock a p p a r e n t l y f a l l s i n t o t h i s 10" 7 t o 1 0 ' 8 m/s range. 80 Chapter 6. HYDROGEOLOGY Hydrogeology can be d e f i n e d as the s c i e n c e t h a t d e a l s w i t h the o c c u r r e n c e , d i s t r i b u t i o n and movement of groundwa-t e r . Three i m p o r t a n t a s p e c t s of the hydrogeology of the Meager Mountain a r e a w i l l be a d d r e s s e d . These a r e the water t a b l e c o n f i g u r a t i o n , the h y d r a u l i c c o n d u c t i v i t y of the v a r i o u s g e o l o g i c a l m a t e r i a l s , and an e s t i m a t e of the amount of groundwater r e c h a r g e . The f o l l o w i n g i n t e r p r e t a t i o n of the hydrogeology i s based on the l o c a l and r e g i o n a l g e o l o g y , the l o c a t i o n and n a t u r e of the hot and c o l d s p r i n g s , p u b l i s h e d h y d r a u l i c c o n d u c t i v i t y v a l u e s of f r a c t u r e d r o c k , the water b a l a n c e c a l c u l a t i o n s , and g e n e r a l f i e l d o b s e r v a t i o n s . F i g u r e 6.1 i s a c r o s s s e c t i o n t h r ough Meager Mountain showing s c h e m a t i c a l l y the g e n e r a l f l o w of groundwater i n the system. L i n e CD r e p r e s e n t s the l o c a t i o n of the groundwater d i v i d e i n the mountain. A l l water e n t e r i n g the groundwater zone south of the l i n e w i l l d i s c h a r g e i n the Meager Creek v a l l e y w h i l e a l l the water e n t e r i n g the system n o r t h of the l i n e w i l l d i s c h a r g e i n t o t he L i l l o o e t R i v e r v a l l e y . The water of the Meager Creek H o t s p r i n g s has a d i f f e r e n t f l o w p a t h than the water of the Pebble Creek H o t s p r i n g s , t h e r e f o r e d i s s i m i l a r water g e o c h e m i s t r i e s found by Hammerstrom and Brown (1977) a re not s u r p r i s i n g . The Meager Creek s i d e of the mountain ( s e c t i o n CDEF) has g r e a t e r d a t a a v a i l a b i l i t y and more geothermal promise than PYLON CAPRICORN PEAK MOUNTAIN Kilometres Flow Lines Water Table F i g u r e 6.1 G e n e r a l g r o u n d w a t e r f l o w i n Meager M o u n t a i n . 82 the L i l l o o e t R i v e r s i d e , so i t w i l l be used f o r f u r t h e r d i s -c u s s i o n i n t h i s c h a p t e r and the f o l l o w i n g c h a p t e r on model-l i n g . Water T a b l e C o n f i g u r a t i o n The water t a b l e c o n f i g u r a t i o n i s imp o r t a n t because i t d e t e r m i n e s the g r a d i e n t or d r i v i n g f o r c e f o r the groundwater f l o w a t Meager Mountain. R e c a l l from Chapter 3 t h a t the g r a -dh d i e n t i n Darcy's Law i s ^ j - where dh i s the change i n head over a change i n d i s t a n c e d l . C o n s i d e r the two w a t e r - t a b l e c o n f i g u r a t i o n s i n F i g u r e 6.2. P o i n t s , A,C,D and F are on the water t a b l e so, by d e f i n i t i o n , the head at these p o i n t s i s e q u a l t o the e l e v a t i o n of the p o i n t s . The head d r o p from A to C i s much g r e a t e r than from D t o F and y e t the change i n 1 i s the same i n both c a s e s . T h e r e f o r e , the g r a d i e n t i s l a r g e r when the water t a b l e i s h i g h e r . A h i g h e r g r a d i e n t causes more water t o move through the system per u n i t t i m e , l e a d i n g t o a l a r g e r volume of water t o d i s c h a r g e i n the v a l l e y a r e a . L i t t l e i s known about the water t a b l e c o n f i g u r a t i o n i n mountainous r e g i o n s . I t i s not known whether i t s i t s h i g h i n most mountains or i s r e l a t i v e l y f l a t . The c o n f i g u r a t i o n de-pends on the h y r a u l i c c o n d u c t i v i t y of the rock and the amount of r e c h a r g e a v a i l a b l e . I n a r e a s of r o l l i n g h i l l s i t has been obser v e d t h a t the water t a b l e t e n d s t o be a subdued r e p l i c a of the topography ( F i g . 4.6). A h i g h l y e l e v a t e d water t a b l e would l e a d t o the d e v e l o p -83 F i g u r e 6.2 Water t a b l e e l e v a t i o n and seepage f a c e development. 84 ment of seepage f a c e s on the s i d e of the mountain [ F i g . 6.2(a)] where the water t a b l e i n t e r s e c t s the s u r f a c e . These zones would be the s i t e of many s p r i n g s . In the f i e l d , v e r y few s p r i n g s were observed and no major seepage a r e a s of l a r g e e x t e n t o c c u r . One i s t h e r e f o r e l e d t o b e l i e v e t h a t the d i s c h a r g e a r e a f o r the groundwater f l o w system i s c o n f i n e d t o the s e c t i o n s of the v a l l e y o v e r l a i n by u n c o n s o l i d a t e d Q u a t e r n a r y d e p o s i t s . I t seems l i k e l y t h a t the water t a b l e i s not s i t u a t e d at a h i g h e l e v a t i o n i n the mountain but r a t h e r o c c u p i e s a more i n t e r m e d i a t e p o s i t i o n [ F i g . 6 . 2 ( b ) ] . The p h y s i c a l l y p o s s i b l e range of water t a b l e c o n f i g u r a t i o n s w i l l be c a l c u l a t e d i n the next c h a p t e r . H y d r a u l i c C o n d u c t i v i t i e s of the G e o l o g i c M a t e r i a l s The o t h e r parameter g o v e r n i n g the groundwater f l o w , be-s i d e s the w a t e r - t a b l e c o n d i g u r a t i o n i s the h y d r a u l i c conduc-t i v i t y K. To e v a l u a t e the g e o l o g i c m a t e r i a l s h y d r o g e o l o g i c a l l y they must be d i v i d e d i n t o groups w i t h s i m i l a r h y d r a u l i c con-d u c t i v i t y c h a r a c t e r i s t i c s . Maxey (1964) d e f i n e s h y d r o s t r a t i -g r a p h i c u n i t s as "bo d i e s of rock w i t h c o n s i d e r a b l e l a t e r a l e x t e n t t h a t compose a g e o l o g i c framework f o r a r e a s o n a b l y d i s t i n c t h y d r o l o g i c system." As mentioned e a r l i e r i n Chapter 2, the f r a c t u r e h y d r a u l i c c o n d u c t i v i t y t h a t o c c u r s a c r o s s a l l the v o l c a n i c l a y e r s has g r e a t e r c o n t r o l over the groundwater flo w than the i n t e r g r a n u l a r h y d r a u l i c c o n d u c t i v i t y d i f -85 f e r e n c e s between l a y e r s . C o n s e q u e n t l y , the e n t i r e v o l c a n i c p i l e can be c o n s i d e r e d as one u n i t w i t h r e s p e c t t o groundwa-t e r f l o w . The basement and the u n c o n s o l i d a t e d d e p o s i t s r e -p r e s e n t two o t h e r u n i t s t h a t would have c h a r a c t e r i s t i c hy-d r a u l i c c o n d u c t i v i t i e s . T h e r e f o r e , the g e o l o g i c a l f o r m a t i o n s i n t he Meager Mountain a r e a can be d i v i d e d i n t o t h r e e h y d r o s -t r a t i g r a p h i c u n i t ; the v o l c a n i c s , the basement, and the un-c o n s o l i d a t e d Quaternary d e p o s i t s . No d i r e c t measurements of h y d r a u l i c c o n d u c t i v i t y have been made but a range can be i n -voked f o r each h y d r o s t r a t i g r a p h i c u n i t . T h e . u n c o n s o l i d a t e d d e p o s i t s e x i s t m a i n l y as v a l l e y f i l l i n t he Meager Creek and L i l l o o e t R i v e r v a l l e y s . D r i l l i n g has r e v e a l e d t h a t the sediments a re m a i n l y sands and b o u l d e r s w i t h t h i n l a y e r s of c l a y . F r e e z e and Cherry (1979) e s t i m a t e t h a t t h e s e d e p o s i t s s h o u l d have h y d r a u l i c c o n d u c t i v i t i e s i n the range 10" 5 t o 10" 2 m/s. The h y d r a u l i c c o n d u c t i v i t y of the g r a n o d i o r i t e and mon-z o n i t e basement i s due t o f r a c t u r e p e r m e a b i l i t y . P u b l i s h e d d a t a d i s c u s s e d p r e v i o u s l y suggest the h i g h l y d i s t u r b e d base-ment would have a c o n d u c t i v i t y from 10" 7 t o I O - 6 m/s. The f r a c t u r e s u r v e y r e v e a l e d t h a t the two dominant f r a c t u r e s e t s have a near v e r t i c a l d i p , c a u s i n g the rock t o have a g r e a t e r c o n d u c t i v i t y i n the v e r t i c a l d i r e c t i o n . I f we denote the h o r i z o n t a l h y d r a u l i c c o n d u c t i v i t y by K x and v e r t i c a l h ydrau-l i c c o n d u c t i v i t y by K z, then the r a t i o of K X:K Z may be as h i g h as 1:5. A c c o r d i n g l y , the v e r t i c a l h y d r a u l i c c o n d u c t i v i -86 t y i n the basement rock p r o b a b l y v a r i e s from 10" 7 t o 10' 8 m/s w h i l e the h o r i z o n t a l h y d r a u l i c c o n d u c t i v i t y p r o b a b l y v a r i e s from 2 x l 0 " 8 t o 2x10"' m/s. The v o l c a n i c r o c k s tend t o be a m u l t i l a y e r e d media of b r e c c i a and ash l a y e r s i n t e r b e d d e d w i t h f l o w l a y e r s . As d i s -c u s s e d i n Chapter 4 the l a y e r i n g g i v e s the v o l c a n i c s an o v e r a l l a n i s o t r o p y w i t h the c o n d u c t i v i t y b e i n g g r e a t e s t i n the h o r i z o n t a l d i r e c t i o n . C o n s i d e r , the t y p i c a l assemblage i n F i g u r e 6.3 of a b a s a l b r e c c i a or t u f f o v e r l a i n by a f l o w w i t h a t h i n weathered h o r i z o n on the top of the f l o w . T y p i -c a l h y d r a u l i c c o n d u c t i v i t y v a l u e s of the d i f f e r e n t l a y e r s , t a k e n from Table 5.5 i n c l u d e 10" 7 m/s f o r the b r e c c i a , 10" 8 m/s f o r the flow and 10" 5 m/s f o r the weathered zone. By i n v o k i n g E q u a t i o n s 3.9 and 3.10, the c a l c u l a t e d e q u i v a l e n t v e r t i c a l h y d r a u l i c c o n d u c t i v i t y K z f o r the assemblage i s 1.9x10" 8 m/s and the c a l c u l a t e d e q u i v a l e n t h o r i z o n t a l hydrau-l i c c o n d u c t i v i t y K x i s 3x10" 7 m/s. The a n i s o t r o p i c r a t i o K X : K Z i s t h e r e f o r e , a p p r o x i m a t e l y 16:1. As s t a t e d e a r l i e r , t h e r e i s e x t e n s i v e v e r t i c a l t o near v e r t i c a l f r a c t u r i n g i n the v o l c a n i c s t h a t w i l l reduce the a n i s o t r o p y p o s s i b l y as low as 1:1 or i s o t r o p i c . A n i s o t r o p i c r a t i o s of g r e a t e r than 5:1 would not be e x p e c t e d . The v e r t i c a l c o n d u c t i v i t y K z of the v o l c a n i c s must be v e r y s i m i l a r t o t h a t of the u n d e r l y i n g basement r o c k . I f i t were n o t , one would e x p e c t e x t e n s i v e s p r i n g l i n e s at. t h e i r c o n t a c t ; i n the f i e l d , v e r y few a r e i n e v i d e n c e . Consequent-87 JL , 1^n W E A T H E R E D K - l O ^ t n / e 1 0 m F L O W K « 1 0 " 8 m / 8 1 0 m B R E C C I A K = 1 0 m/s 1 K 2 = 1.9 x 1 0 " 8 m / s K x = 3 . 0 x 1 0 " 7 m / s F i g u r e 6.3 E q u i v a l e n t h y d r a u l i c c o n d u c t i v i t y i n l a y e r e d v o l c a n i c s . F i g u r e 6.4 C r o s s - s e c t i o n o f Meager C r e e k a t s t a g e l o c a t i o n . 88 l y , the v e r t i c a l h y d r a u l i c c o n d u c t i v i t y i n the v o l c a n i c s p r e -sumably ranges from 10" 7 t o 10"" m/s w h i l e the h o r i z o n t a l h y d r a u l i c c o n d u c t i v i t y i s s i m i l a r or up t o a maximum of 5 times g r e a t e r . E s t i m a t e s of Groundwater Recharge In the Meager Creek b a s i n the o n l y h y d r o l o g i c a l measure-ments a v a i l a b l e i n 1980 were r i v e r s t a g e s r e c o r d e d a t the Meager Creek H o t s p r i n g s b r i d g e i n 1979. These measurements are r e p o r t e d i n Appendix I I I . A r i v e r s tage i s s i m p l y the l e v e l of the stream s u r f a c e . I t can be t u r n e d i n t o a d i s -charge measurement i f the stream bottom c o n f i g u r a t i o n i s known ( t h i s a l l o w s the c a l c u l a t i o n of a c r o s s - s e c t i o n a r e a ) and i f the stream v e l o c i t y i s known. On J u l y 4, 1980 a c r o s s s e c t i o n a t the r i v e r stage s t a -t i o n was taken a l o n g w i t h a r i v e r l e v e l r e a d i n g ( F i g . 6.4). Any stage r e a d i n g taken p r e v i o u s l y can then be c o n v e r t e d t o a c r o s s - s e c t i o n a l a r e a . The v e l o c i t y of the stream, a t any s t a g e , can be c a l c u l a t e d u s i n g the Manning e q u a t i o n . T h i s a l l o w s d i s c h a r g e v a l u e s t o be computed f o r any s t a g e measure-ment. For an e x p l a n a t i o n of the Manning e q u a t i o n see Appendix IV. In Chapter 3 i t was noted t h a t d u r i n g the months of January and F e b r u a r y i t can be e x p e c t e d t h a t the r i v e r d i s -charge w i l l be e n t i r e l y s u p p l i e d by groundwater f l o w . I f the d i s c h a r g e a t the Meager Creek s t a t i o n d u r i n g January and 89 Fe b r u a r y c o u l d be c a l c u l a t e d , then the amount of groundwater d i s c h a r g e and rech a r g e t a k i n g p l a c e i n the b a s i n c o u l d be e s t i m a t e d . R e c a l l from Chapter 3 t h a t , assuming ste a d y s t a t e groundwater f l o w , the recharge t o the system must e q u a l the d i s c h a r g e . Stage r e a d i n g s were not taken i n January or F e b r u a r y but one r e a d i n g taken on December 10, 1979 which c a l c u l a t e s t o a d i s c h a r g e of 3.7 m 3/s. Comparing the d i s c h a r g e a t the L i l l o o e t R i v e r s t a t i o n n o r t h of Pemberton on December 10, 1979 w i t h o t h e r December d i s c h a r g e s over the p a s t 3 y e a r s (Appendix V ) , i t appears to be an average day. We can t h e r e -f o r e assume t h a t the measured d i s c h a r g e a t the Meager s t a t i o n on December 10 i s a l s o a r e a s o n a b l e r e p r e s e n t a t i o n f o r t h a t time of y e a r . Note, t h a t two h o r i z o n t a l l i n e s a re drawn a c r o s s F i g u r e 4.3, the graph of the average d a i l y d i s c h a r g e of the L i l l o o e t R i v e r . The bottom dashed l i n e , d i s c u s s e d e a r l i e r , i s the base f l o w s e p a r a t i o n l i n e or the average J a n u a r y - F e b r u a r y d i s c h a r g e . The upper d a s h e d - d o t t e d l i e r e p r e s e n t s the mean December d i s c h a r g e . I t i s c l e a r , t h a t the J a n u a r y - F e b r u a r y d i s c h a r g e i s a p p r o x i m a t e l y 70% t h a t of December. A l s o r e -c a l l , from Appendix I , t h a t the c a l c u l a t e d b a s a l g l a c i e r melt f l u x i n the Meager Creek b a s i n s u p p l i e s 0.09 m 3/s or 4% of the r u n o f f . The known December d i s c h a r g e r a t e must t h e r e f o r e be reduced by 30% t o r e p r e s e n t J a n u a r y - F e b r u a r y d i s c h a r g e and another 4% t o r e p r e s e n t the groundwater d i s c h a r g e component 90 of the r u n o f f . C o n s e q u e n t l y , the groundwater d i s c h a r g e i s 2.5 m 3/s or 7.9 m 3/y. The measured a r e a of the b a s i n supp-l y i n g the stage s i t e i s 2.18x10 s m2, t h e r e f o r e , the p o r t i o n of the annual p r e c i p i t a t i o n over the d r a i n a g e b a s i n t h a t e n t e r s the groundwater system i s 0.36 m/y or 14.5%; assuming an annual p r e c i p i t a t i o n of 2.5 m/y. T h i s p e r c e n t a g e c o r r e -l a t e s w e l l w i t h the groundwater component of the t o t a l a n n u a l p r e c i p i t a t i o n c a l c u l a t e d from the water b a l a n c e f o r the whole L i l l o o e t R i v e r (16.5%) i n Chapter 4. We can a c c o r d i n g l y assume the v a l u e s of d i s c h a r g e c a l c u l a t e d are r e a s o n a b l y c o r -r e c t . F i g u r e 6.5 s c h e m a t i c a l l y i l l u s t r a t e s the c o n c l u s i o n s on the hydrogeology of the south s i d e of Meager Mountain . I s o -t r o p i c t o h o r i z o n t a l l y a n i s t r o p i c v o l c a n i c s o v e r l i e a v e r t i -c a l l y a n i s t r o p i c g r a n o d i o r i t e basement. The v e r t i c a l h ydrau-l i c c o n d u c t i v i t y of the g r a n o d i o r i t e and the v o l c a n i c s i s s i m i l a r . Very permeable, i s o t r o p i c u n c o n s o l i d a t e d d e p o s i t s f i l l the v a l l e y bottom where a groundwater d i s c h a r g e of 0.36 m/y over the d r a i n a g e b a s i n t a k e s p l a c e . The water t a b l e has an i n t e r m e d i a t e p o s i t i o n i n the mountain complex. These qua-l i t a t i v e i n t e r p r e t a t i o n s of the water t a b l e c o n f i g u r a t i o n , c o n d u c t i v i t y ranges, and f l u x t h r o u g h the system can now be used as i n p u t i n t o a m a t h e m a t i c a l model t o q u a n t i f y our un-d e r s t a n d i n g of the h y d r o g e o l o g y . GRANODIORITE K Area of Outflux into Unconsolidated Valley Fill metres 6 3 4 0 EXPECTED RANGE OF VALUES (m/s) K v z - 10" 7 _ 10" 8 K v x = 1 0 ' 6 . 6 - 10" K 0 2 =10" 7 _ 10" 8 Kgx-10- 7.5 - 1 0 -K u z - 10" 2 _ 10" 6 K u x » 1 0 " 2 _ IO" 6 8.5 Outflux • 0.36 m/y Approximate Water Table Location F i g u r e 6.5 Summary o f t h e h y d r o g e o l o g y on t h e s o u t h o f Meager C r e e k . 92 Chapter 7. GROUNDWATER MODELLING Computer-based n u m e r i c a l methods a re one of t h e major t o o l s used f o r s o l v i n g l a r g e - s c a l e groundwater f o r e c a s t i n g problems (Bear 1979). With the r e c e n t advance of computer t e c h n o l o g y , much e f f o r t has been devoted t o the development of t e c h n i q u e s f o r n u m e r i c a l s o l u t i o n of the p a r t i a l d i f f e r e n -t i a l e q u a t i o n s t h a t govern the f l o w of water i n v a r i o u s geo-l o g i c a l e n v i r o n m e n t s . The end pro d u c t of t h i s r e s e a r c h has been a number of computer programs which i n most c a s e s are r e a d i l y a v a i l a b l e t o any u s e r . With m o d i f i c a t i o n s a hydro-g e o l o g i s t can u s u a l l y make an a v a i l a b l e program a p p l i c a b l e t o her or h i s s p e c i f i c problem. F r e e z e and Ch e r r y (1979) d e s c r i b e m a t h e m a t i c a l m o d e l l i n g as a f o u r - s t a g e p r o c e s s i n v o l v i n g 1) an e x a m i n a t i o n of the p h y s i c a l problem, 2) replacement of the p h y s i c a l problem by an e q u i v a l e n t m a t h e m a t i c a l problem, 3) s o l u t i o n of the mathe-m a t i c a l problem w i t h a c c e p t e d m a t h e m a t i c a l t e c h n i q u e s , and 4) i n t e r p r e t a t i o n of the m a t h e m a t i c a l r e s u l t s i n terms of the p h y s i c a l problem. In t h i s study groundwater f l o w i s s i m u l a t e d u s i n g a de-t e r m i n i s t i c m a t h e m a t i c a l model. I t i s based on p h y s i c a l l a w s , not on s t a t i s t i c a l or e m p i r i c a l r e l a t i o n s h i p s . The e q u a t i o n of f l o w f o r t h i s work i s s o l v e d f o r s t e a d y - s t a t e f l o w . 93 M a t h e m a t i c a l models of groundwater f l o w take the form of boundary v a l u e problems. To f u l l y d e f i n e a boundary v a l u e problem f o r s t e a d y - s t a t e s u b s u r f a c e f l o w , one needs t o know 1) the s i z e and shape of the r e g i o n of f l o w , 2) the e q u a t i o n of f l o w w i t h i n the r e g i o n , 3) the boundary c o n d i t i o n s around the b o u n d a r i e s of the r e g i o n , 4) the s p a t i a l d i s t r i b u t i o n of h y d r a u l i c c o n d u c t i v i t y v a l u e s i n the r e g i o n , and 5) a mathe-m a t i c a l method of s o l u t i o n (Freeze and C h e r r y , 1979). A l l of t h e s e a s p e c t s w i l l be d i s c u s s e d s u b s e q u e n t l y i n the s i m u l a -t i o n s t r a t e g y s e c t i o n . Then, the m a t h e m a t i c a l m o d e l l i n g r e -s u l t s and the s i g n i f i c a n c e of the r e s u l t s w i l l be d i s c u s s e d . F i r s t l y , however, an e x a m i n a t i o n of the computer programs used and t h e i r c a p a b i l i t i e s i s i n o r d e r . The Computer Program The a u t h o r has m o d i f i e d and used two d i f f e r e n t programs f o r the a n a l y s i s of groundwater f l o w i n Meager Mountain . The f i r s t was w r i t t e n by R.A. F reeze and i s known as FEPS; the second was w r i t t e n by S.P. Neuman of the U n i v e r s i t y of A r i z o n a and i s known as FREESURF1. A m o d i f i e d v e r s i o n of FEPS p r e p a r e d by the a u t h o r has been renamed FOPS. The two programs have the f o l l o w i n g s i m i l a r c a p a b i l i -t i e s . 1) The r e g i o n of f l o w i s t w o - d i m e n s i o n a l but can have any s i z e or shape; 2) the h y d r a u l i c c o n d u c t i v i t y d i s t r i b u t i o n can take on any d e s i r e d c o n f i g u r a t i o n or range of v a l u e s ; 3) the h y d r a u l i c c o n d u c t i v i t y can take on any d i r e c t i o n and 94 degree of a n i s o t r o p y ; 4) the b o u n d a r i e s can be g i v e n any one of f i v e p o s s i b l e boundary c o n d i t i o n s . These boundary c o n d i -t i o n s a r e , a) impermeable, b) c o n s t a n t s p e c i f i e d h y d r a u l i c head, c) c o n s t a n t f l u x i n or out of the system, d) f r e e s u r -f a c e (water t a b l e ) on the upper boundary, and e) seepage f a c e on the upper boundary. In a d d i t i o n t o these c h a r a c t e r i s t i c s , FREESURF1 can h a n d l e , 1) t h r e e d i m e n s i o n a l f l o w i f f l o w r a -t a i n s an a x i a l symmetry about the v e r t i c a l c o o r d i n a t e , and 2) i n t e r i o r seepage f a c e s where the f r e e s u r f a c e becomes d i s c o n -t i n u o u s a c r o s s an i n t e r f a c e between two d i f f e r e n t m a t e r i a l s , as i n an e a r t h dam. For background m a t e r i a l and examples of the k i n d s of problems t h a t can be s o l v e d w i t h FREESURF1 the r e a d e r i s d i r e c t e d t o Neuman and Witherspoon (1970). The two most common n u m e r i c a l t e c h n i q u e s used t o s o l v e boundary v a l u e problems i n h y d r o g e o l o g y are the f i n i t e - d i f -f e r e n c e method and the f i n i t e - element method. W h i l e d i f -f e r e n t i n many ways both t e c h n i q u e s o p e r a t e t o s o l v e the groundwater f l o w e q u a t i o n d i r e c t l y . The f i n i t e - e l e m e n t method i s u t i l i z e d by both FOPS and the FREESURF1 programs. The output from the m a t h e m a t i c a l models i s a f i e l d of h y d r a u l i c head v a l u e s a t the n o d a l p o i n t s of a g r i d superim-posed over the f l o w f i e l d . The output can be c o n t o u r e d and used t o c o n s t r u c t f l o w n e t s . By means of Darcy's law, one can c a l c u l a t e the amount of i n f l o w and o u t f l o w a l o n g the b o u n d a r i e s of the f l o w n e t , or the v e l o c i t y of the f l o w a t any i n t e r i o r p o i n t . By means of E q u a t i o n 3.6, one can c a l c u -95 l a t e the f l u i d p r e s s u r e s a t any p o i n t i n the system. The FOPS model was used f o r an i n i t i a l s e n s i t i v i t y a n a l -y s i s . The f r e e s u r f a c e was s e t as a c o n s t a n t head boundary, and the h y d r a u l i c c o n d u c t i v i t y f i e l d , the d e p t h - o f - f l o w f i e l d and the e l e v a t i o n of the water t a b l e were v a r i e d t o observe t h e i r e f f e c t s on the t o t a l d i s c h a r g e l e a v i n g the system. The FREESURF1 model was then u t i l i z e d t o s i m u l a t e v a r i o u s pos-s i b l e h y d r o g e o l o g i c environments a t Meager Mountain and t h e i r e f f e c t on the groundwater regime. The r e c h a r g e r a t e i n t o the system was v a r i e d f o r each h y d r o g e o l o g i c environment t o exam-i n e the water t a b l e c o n f i g u r a t i o n and amount of d i s c h a r g e i t produced. B e f o r e d i s c u s s i n g the r e s u l t s of the m o d e l l i n g , the boundary v a l u e problems we wish t o s o l v e u s i n g the models, must be d e f i n e d . S i m u l a t i o n S t r a t e g y Region of Flow The r e g i o n of f l o w f o r the Meager Mountain groundwater s i m u l a t i o n s i s a t w o - d i m e n s i o n a l v e r t i c a l c r o s s - s e c t i o n as i l l u s t r a t e d i n F i g u r e 7.1. The s e c t i o n was taken a l o n g the l i n e A-B i n F i g u r e 7.2 through d r i l l h o l e s M5-78D and M7-79D. The lower end of the s e c t i o n i s the c e n t r e of Meager Creek w h i l e the upper end i s a t the h i g h e s t p o i n t of C a p r i c o r n M o u n t a i n . The upper boundary i s the ground s u r f a c e and the 96 metres Figure 7.1 Region of flow for mathematical modelling. > 4 f \ L O C * T I O N W*P Figure 7.2 Line of section taken for cross-section in Figure 7.1. 97 lower boundary for the FREESURF1 simulations was chosen a r b i -t r a r i l y at -2000 m elevation. The lower boundary for the FOPS simulations varied from -305 m to -915 m for the sensi-t i v i t y analysis. The cross-section i s considered to have a unit thickness perpendicular to the page. Equation of Flow The equation for saturated, two-dimensional, steady-state flow through heterogeneous, anisotropic material i s : 3 3x K „ (x, z) 5h 3x + 8 z K z ( x , z ) — (7.1) where x and z are the horizontal and v e r t i c a l coordinates, K x and K z are the horizontal and v e r t i c a l components of the ani-sotropic hydraulic conductivity tensor and h i s the hydraulic head. Assigning K=K (X,2) and K =K (X,Z), i d e n t i f i e s the -<*v X z z conductivity d i s t r i b u t i o n as hetergeneous. The solution of Equation 7.1 i s the hydraulic head f i e l d h(x,z) in the cross-section. Boundary Conditions The boundaries BC, CD and meable while AEFB is the water |^ - = 0 on BC and AD 8 x and |^ = 0 on CD d Z DA of Figure 7.1 are inter-table. In mathematical terms (7.2) (7.3) 98 On AE, the h y d r a u l i c head i s e q u a l t o the e l e v a t i o n of Meager Creek because the water t a b l e i s v e r y near the s u r f a c e i n t he v a l l e y f i l l d e p o s i t s , t h e r e f o r e , H=Z r on AE (7.4) where Z r i s the e l e v a t i o n of Meager Creek. The water t a b l e EFB i s t r e a t e d i n two ways. When u s i n g the FOPS program f o r the s e n s i t i v i t y a n a l y s i s the heads a re s p e c i f i e d at a l l p o i n t s on the water t a b l e such t h a t H=z on EFB (7.5) and the problem can be s o l v e d d i r e c t l y . The approach when u s i n g the FREESURF1 program i s t o s p e c i f y the heads on the seepage f a c e , EF: H=z on EF (7.6) where z i s the water t a b l e e l e v a t i o n and the l a n d s u r f a c e e l e v a t i o n . On the f r e e s u r f a c e p o r t i o n of the water t a b l e FB the r a t e of i n f l o w I i s d e f i n e d so t h a t K ( x , z ) U l=I On FB (7.7) d z t h a t i s , the water t a b l e p o s i t i o n i s not s p e c i f i e d but de-pends on t h e amount of p r e c i p i t a t i o n i n f i l t r a t i n g the ground-water system. Under t h e s e c o n d i t i o n s , an i t e r a t i v e s o l u t i o n i s n e c e s s a r y . 99 H y d r a u l i c C o n d u c t i v i t y D i s t r i b u t i o n The v a r i a b l e c o n d u c t i v i t i e s of the i d e a l i z e d g e o l o g i c environment were d i s c u s s e d i n Chapter 6 and d e p i c t e d i n F i g u r e 6.6. Due t o the l a c k of i n f o r m a t i o n on the s u b s u r f a c e g eology i n the Meager a r e a , a number of p o t e n t i a l g e o l o g i c a l c o n f i g u r a t i o n s were m o d e l l e d , b e g i n n i n g w i t h the s i m p l e s t case and w o r k i ng t o the most complex. For the s e n s i t i v i t y a n a l y s i s o n l y the homogeneous i s o -t r o p i c case was used. The main s i m u l a t i o n s performed w i t h the FREESURF1 program u t i l i z e d the f o u r i d e a l i z e d g e o l o g i c a l c o n f i g u r a t i o n s i l l u s t r a t e d i n F i g u r e 7.3. F i g u r e 7.3(a) r e -p r e s e n t s the s i m p l e s t p o s s i b l e g e o l o g y . The e n t i r e c r o s s -s e c t i o n i s assumed to be g r a n o d i o r i t e . F i g u r e 7.3(b) i n -c l u d e s a f a u l t zone t h r o u g h t t o e x i s t below Meager Creek. F i g u r e 7.3(c) i s a two l a y e r system w i t h the v o l c a n i c s o v e r -l y i n g the g r a n o d i o r i t e . F i n a l l y , F i g u r e 7.3(d) the most com-p l e x g e o l o g i c a l c o n f i g u r a t i o n s i m u l a t e d i n c l u d e s a v o l c a n i c l a y e r , g r a n o d i o r i t e and a f a u l t zone. The d e s i g n a t e d imper-meable a r e a i n F i g u r e 7.3(b and d) i s s i m u l a t e d by g i v i n g the a r e a a v e r y low h y d r a u l i c c o n d u c t i v i t y (10" 1 5 m/s). T h e r e f o r e , e q u i p o t e n t i a l l i n e s i n F i g u r e s 7.7 t o 7.11 extend i n t o t h i s zone but i n s i g n i f i c a n t f l o w o c c u r s t h e r e . The c o n d u c t i v i t i e s , a n i s o t r o p i e s , and r e c h a r g e r a t e v a l u e s f o r the system were v a r i e d from run t o run i n an a t -tempt t o d e f i n e the f e a s i b l e range of parameters f o r each h y d r o g e o l o g i c a l environment. F e a s i b i l i t y i s d e f i n e d i n terms o o • p a q . B T n u i T s suoTq.ean6"pguoo xeoxBoioao £'L ajnbTj-i -' 0' r ',' ^ A A A A A A A A A A A A A A A A A A A A A A A A A A A \ A A A A A A A A A A A A A A A A A A A A A A A A A A " L A A A A A A A A A A A A A A A A A A A A A A A A A ^ A A A A A A A A A A A A A A A A A A A A A A A i A A A A A A A A A A A A A A A A A A i A A A A A A A A A A A A A A A l A A A A A A A A A A A A A k A A A * ft A " ft » A A A A t 0 | U t 3 | 0 A •l|JO|pou*JO A A A A A A A A A A A A A A A A A A A A A A A A A A A " A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A ' £_A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A| A A A A A A A 3 jjnseejj L jjnseejj 101 of the f l o w systems t h a t best f i t the c a l u l a t i o n s p r e s e n t e d i n t h i s r e p o r t on the b a s i s of the a v a i l a b l e f i e l d d a t a . The u n c o n s o l i d a t e d Q u a ternary m a t e r i a l was not i n c l u d e d i n the model. The h y d r a u l i c c o n d u c t i v i t y of the v a l l e y f i l l d e p o s i t s i s a number of o r d e r s of magnitude l a r g e r than the h y d r a u l i c c n d u c t i v i t y of the basement or v o l c a n i c s . There-f o r e , t h e • c o n t r o l l i n g f a c t o r f o r the amount of water d i s c h a r -g i n g from the system i n the h y d r a u l i c c o n d u c t i v i t y d i s t r i b u -t i o n i n the r o c k . F u r t h e r m o r e , when water e n t e r s the v a l l e y f i l l from the rock i t t r a v e l s down g r a d i e n t i n the same d i -r e c t i o n as the stream as i l l u s t r a t e d i n F i g u r e 7.4. The ma-t h e m a t i c a l models used are two d i m e n s i o n a l . C o n s e q u e n t l y , the water movement i n the v a l l e y f i l l cannot be m o d e l l e d . F i n i t e Element Method The f i n i t e element method works on the premise t h a t a complex f u n c t i o n can be a p p r o x i m a t e d p i e c e w i s e by a f i n i t e number of s i m p l e r l i n e a r f u n c t i o n s over s m a l l s u b r e g i o n s . The s u b r e g i o n s are c a l l e d elements and the c o r n e r s of the elements a r e c a l l e d nodes. The unknown f u n c t i o n of h y d r a u l i c head w i t h i n an element can be e x p r e s s e d as a l i n e a r f u n c t i o n of the heads at the nodes and can be c a l c u l a t e d m a t h e m a t i c a l -l y . I t i s beyond the scope of t h i s t h e s i s t o d i s c u s s the f i n i t e - e l e m e n t method of s o l u t i o n i n d e t a i l . The i n t e r e s t e d r e a d e r i s r e f e r r e d t o P i n d e r and Gray (1977). For the FOPS and FREESURF1 programs used here a d i f -102 F i g u r e 7.4 Movement o f groundwater i n t h e basement r o c k and v a l l e y f i l l . 103 f e r e n t K x and K z v a l u e can be d e s i g n a t e d f o r each element. Head v a l u e s a r e s p e c i f i e d a t each node on a c o n s t a n t head boundary. Recharge r a t e or t o t a l d i s c h a r g e r a t e s a r e s p e c i -f i e d f o r each element on a f l u x boundary. Impermeable boun-d a r i e s a r e h a n d l e d by the i n t e r n a l o p e r a t i o n s of the program. The f i n i t e element s o l u t i o n o u t p u t i s the h y d r a u l i c head v a l u e at each node. A p l o t t i n g r o u t i n e i n both programs con-t o u r s the v a l u e s i n t o a h y d r a u l i c head p a t t e r n and a f l o w net can be drawn by hand l a t e r , i f n e c e s s a r y . The r e c h a r g e r a t e and t o t a l d i s c h a r g e of water f o r the elements on the upper boundary a r e c a l c u l a t e d a u t o m a t i c a l l y . Input Data For both programs the i n p u t d a t a r e q u i r e d i s , 1) a de-f i n i t i o n of the f i n i t e element mesh i n c l u d i n g n o d a l c o o r -d i n a t e s , n o d a l numbers and element number s p e c i f i c a t i o n s , 2) one of the g e o l o g i c a l c o n f i g u r a t i o n s i n F i g u r e 7.3, and 3) the v e r t i c a l and h o r i z o n t a l h y d r a u l i c c o n d u c t i v i t y v a l u e s f o r each of the f o r m a t i o n s i n the c o n f i g u r a t i o n . In the FOPS program the water t a b l e p o s i t i o n i s d e f i n e d by the programmer and the f l u x e s a c r o s s the water t a b l e are c a l c u l a t e d by the program. The s t e a d y - s t a t e d i s c h a r g e va-l u e s , f o r a g i v e n g e o l o g i c a l c o n f i g u r a t i o n a r e dependent on the water t a b l e p o s i t i o n chosen. C o n v e r s e l y , i n the FREESURF1 program, the f l u x i n t o the system i s d e f i n e d by the programmer and the p o s i t i o n of the water t a b l e i s c a l c u l a t e d 104 by the program. The s t e a d y - s t a t e water t a b l e p o s i t i o n f o r a g i v e n g e o l o g i c c o n f i g u r a t i o n i s dependent on the recha r g e r a t e chosen. W i t h an u n d e r s t a n d i n g of the s i m u l a t i o n s t r a t e g y a t hand, the r e s u l t s of the m a t h e m a t i c a l m o d e l l i n g can now be d i s c u s s e d . S e n s i t i v i t y A n a l y s e s w i t h FOPS In Chapter 6, the amount of groundwater d i s c h a r g e out of the Meager Creek b a s i n was c a l c u l a t e d . The amount of t o t a l d i s c h a r g e depends on the h y d r a u l i c c o n d u c t i v i t y of the ma-t e r i a l , the water t a b l e e l e v a t i o n , and the depth of f l o w . The program FOPS was used t o determine the e f f e c t these p a r a -meters have on the t o t a l d i s c h a r g e . I f i t i s found t h a t a parameter has l i t t l e e f f e c t on the t o t a l d i s c h a r g e i t can be i g n o r e d as a v a r i a b l e i n p u t parameter i n the FREESURF1 simu-l a t i o n s , t h e r e b y r e s u l t i n g i n a na r r o w i n g of the p o s s i b l e range f o r the o t h e r i n p u t p a r a m e t e r s . F i g u r e 7.5 i l l u s t r a t e s the f o u r d i f f e r e n t g e o m e t r i e s used f o r the FOPS s i m u l a t i o n s . FOPS1 r e p r e s e n t s a f l o w f i e l d 5500 m l o n g e x t e n d i n g from -305 m (-1000 f t ) t o 1525 m (5000 f t ) on i t s r i g h t s i d e . The water t a b l e d e c r e a s e s i n h e i g h t towards the l e f t t o a minimum of 425 m. In FOPS2 the f l o w f i e l d was deepened 610 m w h i l e i n FOPS3 and FOPS4 the water t a b l e was r a i s e d above and lowered below the FOPS2 p o s i t i o n . H y d r a u l i c c o n d u c t i v i t y v a l u e s of 1 0 " 7 , 10* 8 and 10'' m/s Summary of Table S e n s i t i v i t y 7.1 Analysis Simulations Geometric Hydraulic T o t a l Discharge Maximum Water Depth of Type Conductivity (m/s) (nl3/s/n\) Table E l e v a t i o n (m) Flow(m) FOP SI l x l O - 7 9.44xl0 - 6 1525 -305 FOP SI l x l O - 8 9.44xl0~ 7 1525 -305 F0PS1 l x l O - 9 9.44xl0 - 8 1525 -305 F0PS2 l x l O - 7 1.15xl0 _ 5 1525 -915 FOPS 2 l x l O " 8 1.15xl0~ 6 1525 -915 FOPS 2 -9 1x10 1.15xl0- 7 1525 -915 FOPS 3 l x l O - 7 1.71xl0" 5 1830 -915 FOP S3 l x l ( f 8 1.71xl0" 6 1830 -915 FOP S3 -9 1x10 1.71xl0~7 1830 -915 F0PS4 l x l O - 7 8.50xl0~ 6 1220 -915 F0PS4 l x l O - 8 8.50xl0~ 7 1220 -915 FOPS 4 -9 1x10 8.50xl0~8 1220 -915 107 where s i m u l a t e d w i t h each geometry. The r e s u l t i n g t o t a l d i s -charge i s summarized i n Ta b l e 7.1. For any g i v e n geometry the o u t f l o w v a r i e s d i r e c t l y w i t h the c o n d u c t i v i t y of the m a t e r i a l . I f one i n c r e a s e s the con-d u c t i v i t y an o r d e r of magnitude, then the amount of t o t a l d i s c h a r g e i n c r e a s e s by an o r d e r of magnitude. For a g i v e n h y d r a u l i c c o n d u c t i v i t y v a l u e , deepening the fl o w f i e l d 610 m as i n ge o m e t r i c type FOPS2 i n c r e a s e s the t o t a l d i s c h a r g e 1.22 t i m e s . T h i s i n d i c a t e s t h a t a v e r y deep f l o w f i e l d would not have a s u b s t a n t i a l l y g r e a t e r t o t a l d i s -charge than a s i m i l a r but s h a l l o w e r system. When the water t a b l e e l e v a t i o n i s i n c r e a s e d 305 m from 1525 t o 1830 m the t o t a l d i s c h a r g e i n c r e a s e s by 1.5 t i m e s . When the water t a b l e e l e v a t i o n i s lowered 305 m from 1525 t o 1220 m the t o t a l d i s c h a r g e d e c r e a s e s by 0.5 t i m e s . There-f o r e , the water t a b l e must be r a i s e d or lowered over l a r g e e l e v a t i o n changes i n o r d e r t o cause a s u b s t a n t i a l change i n the t o t a l d i s c h a r g e from the system. I t i s c l e a r t h e n , t h a t the t o t a l d i s c h a r g e from the f l o w system i s v e r y s e n s i t i v e t o h y d r a u l i c c o n d u c t i v i t y v a l u e s but i s r e a s o n a b l y i n s e n s i t i v e t o water t a b l e v a r i a t i o n s , and e s -p e c i a l l y i n s e n s i t i v e t o the depth of f l o w . A c c o r d i n g l y , i n the f o l l o w i n g FREESURF1 s i m u l a t i o n r e s u l t s , the h y d r a u l i c c o n d u c t i v i t i e s and the water t a b l e p o s i t i o n s w i l l be v a r i e d but the depth of flo w i s chosen a r b i t r a r i l y and remains cons-108 t a n t . FREESURF1 M o d e l l i n g V a r i a b l e Parameters The two parameters i n D a r c y ' s law t h a t d e t e r m i n e th e o u t f l o w Q are the h y d r a u l i c c o n d u c t i v i t y K and the h y d r a u l i c g r a d i e n t . The h y d r a u l i c g r a d i e n t s depend on the hydrau-l i c head f i e l d , and i n the system m o d e l l e d i n t h i s r e p o r t the head f i e l d depends on the p o s i t i o n of the water t a b l e which i n t u r n depends on the amount of i n f l o w I or r e c h a r g e r a t e i n t o the g e o l o g i c system. The c o m b i n a t i o n of the v a r i a b l e s I and K w i l l d e t e r m i n e the f l u x Q out of the system. In Chapter 6 i t was d e t e r m i n e d t h a t the c o n t r i b u t i o n of groundwater f l o w i n the Meager b a s i n above the stage l o c a t i o n i s i n the range 2.5 m 3/s. The Meager Mountain s i d e of the r i v e r c o n s t i t u t e s 45% of the s u r f a c e a r e a of the b a s i n ; t h e r e f o r e we w i l l assume t h a t 45% of the t o t a l groundwater f l o w (1.13 m 3/s) i s c o n t r i b u t e d from t h i s s i d e . I t e n t e r s over the 18,500 m l e n g t h of the v a l l e y . The t w o - d i m e n s i o n a l c r o s s - s e c t i o n model has a t h i c k n e s s of 1 m, c o n s e q u e n t l y i t s c o n t r i b u t i o n t o the t o t a l t o t a l d i s c h a r g e i s 6x10" 5 m3/s/m. We w i l l d e s i g n a t e t h i s f l u x per u n i t l e n g t h as q; i t has u n i t s of m 2/s. The r e c h a r g e r a t e was e s t i m a t e d p r e v i o u s l y a t 0.36 m/y or 1.14x10" 8 m/s. The above e s t i m a t e d v a l u e s of I and q 109 a l l o w f o r the c a l c u l a t i o n of d i f f e r e n t f e a s i b l e h y d r a u l i c c o n d u c t i v i t y d i s t r i b u t i o n s u s i n g FREESURF1. F i n i t e Element Mesh The f i n i t e element mesh used f o r the FREESURF1 s i m u l a -t i o n s i s i l l u s t r a t e d i n F i g u r e 7.6. I t i s superimpoed on a s i m p l i f i e d v e r s i o n of the geology by F a i r b a n k e t a l . (1979). The q u a d r i l a t e r a l elements above 600 m e l e v a t i o n a r e c o l l a s -p i b l e . They can f l e x upwards and downwards t o a l l o w the water t a b l e t o r i s e or lower t o the s t e a d y - s t a t e p o s i t i o n . The i n t e n t i o n of the a u t h o r was t o s i m u l a t e the v o l c a n i c s as i n F i g u r e 7.6, however the program has the l i m i t a t i o n t h a t a l l the elements i n the c o l l a p s i b l e p a r t of the mesh have t o p o s s e s s the same h y d r a u l i c c o n d u c t i v i t y . For t h i s reason the v o l c a n i c l a y e r s i n F i g u r e 7.3(c) and (d) are more e x t e n s i v e than f i e l d mapping and d r i l l h o l e s i n d i c a t e . I t i s f e l t t h a t t h i s w i l l cause o n l y minor i n a c c u r a c i e s i n the s i m u l a t i o n s . The program a l s o has l i m i t a t i o n s s i t u a t i n g the water t a b l e i n i t s e x a c t l o c a t i o n when t h e r e i s an i r r e g u l a r ground s u r f a c e as i n these s i m u l a t i o n s . The s i m u l a t e d p o s i t i o n of the water t a b l e may be s l i g h t l y i n e r r o r a t the d i s c h a r g e end of the system but i t i s f e l t t h a t the p o s s i b l e e r r o r s w i l l have n e g l i g i b l e e f f e c t on the f l o w f i e l d . G d - Granodiorite metres Figure 7.6 F i n i t e element mesh used i n FREESURF1 simulations. i — • o I l l R e s u l t s For the s i m u l a t i o n s the h y d r a u l i c c o n d u c t i v i t y d i s t r i b u -t i o n s were s e l e c t e d as i n T able 7.2. The r e c h a r g e r a t e i n t o the system was v a r i e d u n t i l the maximum and minimum water t a b l e c o n f i g u r a t i o n were found. The r e s u l t i n g c o n t o u r e d hy-d r a u l i c head f i e l d s a r e d e p i c t e d i n F i g u r e s 7.7 t o 7.11. The maximum v a l u e o c c u r s when the water t a b l e i n t e r s e c t s the ground s u r f a c e i n the h i g h l a n d v a l l e y s between mountain peaks as i n F i g u r e 7 . 7 ( a ) . The minimum o c c u r s when the e l e v a t i o n of node 252 becomes l e s s than the e l e v a t i o n of node 271 ( F i g u r e 7.6). Node 252 i s the l a s t node t h a t i s moveable. Node 271 i s set a t a c o n s t a n t head e q u a l t o the e l e v a t i o n of Meager Creek. When node 252 moves lower than 271 i t i n d i -c a t e s the water t a b l e e l e v a t i o n i s too low t o be p h y s i c a l l y r e a l i s t i c . The l i n e s i n F i g u r e s 7.7 t o 7.11 which j o i n p o i n t s of e q u a l h y d r a u l i c head are c a l l e d e q u i p o t e n t i a l l i n e s . For the i s o t r o p i c c a ses f l o w l i n e s can be drawn p e r p e n d i c u l a r t o the e q u i p o t e n t i a l l i n e s t o c o n s t r u c t a flow net as i n F i g u r e 7 . 7 ( b ) . For the a n i s o t r o p i c c a s e s f l o w l i n e s a r e not neces-s a r i l y p e r p e n d i c u l a r t o the e q u i p o t e n t i a l l i n e s . There a r e g r a p h i c methods f o r drawing the f l o w l i n e s but they cannot be drawn on the diagrams d i r e c t l y . The R/D d e s i g n a t i o n s on the diagrams i n d i c a t e the boundary between the r e c h a r g e and d i s -charge a r e a s . The dashed l i n e s show the g e o l o g i c a l boun-d a r i e s as per F i g u r e 7.3. The h y d r a u l i c c o n d u c t i v i t i e s used Table 7.2 Hydraulic Conductivity D i s t r i b u t i o n s G e o l o g i c a l Configuration Simulation Conductivity D i s t r i b u t i o n Dimensionless (as i n F i g . 7.3) Designation (m/s) Ratios FREESURF 1 A Kg=10 K g x = 1 0 _ 7 K g z=10" 8 K g x=10" 8 K g z=10" 7 K g x = 5 x l ( f 9 K g z=5xl0 FREESURF 1 B FREESURF 1 FREESURF 1 C l C2 FREESURF 2 A K g=10 - 8 K f = l ( T 7 K b= FREESURF 2 B K g x = 5 x l 0 _ 9 K g z=5xl0 FREESURF 3 A K v=10 _ 7 K g=10 _ 8 K v = 5 x l 0 _ 8 K g x = 5 x l 0 _ FREESURF 3 B FREESURF 4 A K v=5xl0~ 8 Kf=10 _ 7 K, FREESURF 4 B K v = 5 x l 0 - 8 K f=10 _ 7 K, -8 •15 K g x ~ 1 0 K g z K g z = 1 0 K g x K g z = 1 0 K g x Kf=10K g 8 Kf=10 7 K b = 1 0 _ 1 5 K g z=10K g x & Kf=2K g z K v=10K g 9 K g 2 = 5 x l 0 _ 8 K g z=K v=10K g x g = 1 0 - 8 Kh=10 _ 1 5 Kf=10K g=2K v  g x = 5 x l 0 " ^ K g z = 5 x l 0 _ 8 Kg Z=K v=10K g x & K f=2K g z K g = c o n d u c t i v i t y of the gr a n o d i o r i t e , K g x= c o n d u c t i v i t y of the grano d i o r i t e i n the h o r i z o n t a l d i r e c t i o n . K g z= c o n d u c t i v i t y of the gra n o d i o r i t e i n the v e r t i c a l d i r e c t i o n . K v = c o n d u c t i v i t y of the v o l c a n i c s . Kf = c o n d u c t i v i t y of the f a u l t . K b = c o n d u c t i v i t y of the impermeable area. E q u i p o t e n t i a l p a t t e r n f o r FREESURF IA and FREESURF IB c a s e s . F i g u r e 7.8 E q u i p o t e n t i a l p a t t e r n f o r FREESURF IC c a s e s . 118 f o r each g e o l o g i c u n i t can be g l e a n e d from T a b l e 7.2 w h i l e r e l a t i v e h o r i z o n t a l and v e r t i c a l h y d r a u l i c c o n d u c t i v i t i e s a r e i l l u s t r a t e d on the e q u i p o t e n t i a l diagrams. Case IA i s homogeneous and i s o t r o p i c ; c a s e s IB and IC are homogeneous and a n i s o t r o p i c . A c o m p a r i s i o n of the s e t h r e e c a s e s i l l u s t r a t e s the changes i n the e q u i p o t e n t i a l f i e l d caused by a n i s t r o p y . Note i n the diagrams of FREESURF IB t h a t the f l o w f i e l d becomes d i s t o r t e d due t o a g r e a t e r h o r i z o n t a l a n i s t r o p y . A l a r g e r h o r i z o n t a l h y d r a u l i c conduc-t i v i t y than v e r t i c a l i s u n r e a l i s t i c f o r the basement rock but i s shown here t o d i s p l a y the changes i n the e q u i p o t e n t i a l f i e l d caused by a n i s o t r o p y . In the 1C1 vs 1C2 c a s e s the h y d r a u l i c c o n d u c t i v i t y i s changed but the r a t i o between the h o r i z o n t a l and v e r t i c a l h y d r a u l i c c o n d u c t i v i t y , K X=K Z remains c o n s t a n t a t 1:10. Note i n F i g u r e 7.8 t h a t the h y d r a u l i c head f i e l d i n the two c a s e s i s n e a r l y i d e n t i c a l . T h e r e f o r e , as l o n g as the r a t i o s be-tween the v a r i o u s h y d r a u l i c c o n d u c t i v i t y v a l u e s remains cons-t a n t and the r e c h a r g e r a t e i s i n c r e a s e d or d e c r e a s e d t h e same amount as the c o n d u c t i v i t i e s , the f l o w p a t t e r n w i l l not change. FREESURF 2 d i s p l a y s the e f f e c t of a more permeable f a u l t i n t he system a t shown i n F i g u r e 7.3 ( b ) . The p a r t i a l f l o w net i n F i g u r e 7.9(b) shows how the f a u l t a c t s as a highway t o the s u r f a c e f o r f l u i d s t h a t i n t e r s e c t the zone. I f the hypo-t h e t i c a l f a u l t does e x i s t i t would become t i g h t e r and much 119 l e s s c o n d u c t i v e at d e p t h , analogous t o f a u l t s d i s c u s s e d i n Chapter 5 s t u d i e d by Raven and Gale (1977). Most f a u l t s y s -tems have c l a y seams or s l i c k e n s i d e s t h a t a c t as an imper-meable boundary f o r f l u i d s so the a r e a below the f a u l t i s g i v e n a v e r y low c o n d u c t i v i t y t o s i m u l a t e t h i s impermeable boundary. F i g u r e 7.10(a and b) a r e the FREESURF 3A e q u i p o t e n t i a l p a t t e r n s f o r i s o t r o p i c v o l c a n i c s over i s o t r o p i c basement ro c k . R e c a l l from D a r c y ' s law t h a t the d i s c h a r g e t h r o u g h the rock depends on the h y d r a u l i c c o n d u c t i v i t y K and the hydrau-l i c g r a d i e n t . The h y d r a u l i c g r a d i e n t i n the v o l c a n i c s and basement rock i s s i m i l a r but the h y d r a u l i c c o n d u c t i v i t y i s one o r d e r of magnitude l a r g e r i n t h e v o l c a n i c s than i n the basement r o c k . T h e r e f o r e , most of the f l u x w i l l be t h r ough the v o l c a n i c s . As s t a t e d e a r l i e r t h i s s i t u a t i o n would l e a d t o year round s p r i n g l i n e s a t the b a s a l v o l c a n i c c o n t a c t and few e x i s t a t Meager Mo u n t a i n . F i g u r e 7.10(c and d) r e p r e -s e n t s a more l i k e l y s i t u a t i o n w i t h the v o l c a n i c s and basement rock h a v i n g th e same v e r t i c a l c o n d u c t i v i t y . The e q u i v a l e n t i s o t r o p i c h y d r a u l i c c o n d u c t i v i t y of the basement rock can be c a l c u l a t e d u s i n g the f o r m u l a K =\|KxKz, where K i s the e q u i -v a l e n t i s o t r o p i c h y d r a u l i c c o n d u c t i v i t y , K x i s t h e h o r i z o n t a l h y d r a u l i c c o n d u c t i v i t y , and K z i s the v e r t i c a l h y d r a u l i c con-d u c t i v i t y of the basement r o c k . T h i s v a l u e c a l c u l a t e s t o be 1.58x10" 8 or 3 t i m e s l e s s than t h a t of the v o l c a n i c s . T h i s s m a l l d i f f e r e n c e would not s u b s t a n t i a l l y r e s t r i c t the f l o w from the v o l c a n i c s i n t o the basement. 120 F i g u r e s 7.11 (a and b) r e p r e s e n t the FREESURF 4A e q u i p o -t e n t i a l p a t t e r n s f o r i s o t r o p i c v o l c a n i c s over i s o t r o p i c base-ment w i t h a f a u l t i n the basement rock e x t e n d i n g towards the Meager v a l l e y . The h y d r a u l i c c o n d u c t i v i t y of the v o l c a n i c s i s f i v e times g r e a t e r than the basement and the h y d r a u l i c c o n d u c t i v i t y of the f a u l t i s 10 times t h a t of the basement. A g a i n , t h i s c o n f i g u r a t i o n would cause s p r i n g l i n e s a t the v o l c a n i c - b a s e m e n t c o n t a c t , and few o c c u r . The FREESURF 4B s i m u l a t i o n s are the most r e a l i s t i c , i f a f a u l t e x i s t s . The e q u i p o t e n t i a l p a t t e r n s i n F i g u r e 7.11(c and d) r e p r e s e n t the s i t u a t i o n where i s o t r o p i c v o l c a n i c s o v e r l i e a n i s o t r o p i c basement r o c k s w i t h an i s o t r o p i c p e r -meable f a u l t zone. The v e r t i c a l h y d r a u l i c c o n d u c t i v i t y of the basement g r a n o d i o r i t e and the v o l c a n i c s i s the same. The h o r i z o n t a l c o n d u c t i v i t y of the v o l c a n i c s i s g r e a t e r than t h a t of the g r a n o d i o r i t e and the most permeable zone i s the f a u l t a r e a . The f l u i d p r e s s u r e P i s r e l a t e d t o the p r e s s u r e head as shown i n E q u a t i o n 3.6. T h e r e f o r e , the p r e s s u r e a t any p o i n t i n the e q u i p o t e n t i a l diagrams i n F i g u r e s 7.7 t o 7.11 can be c a l c u l a t e d . F i g u r e 7.12 and 7.13 are p r e s s u r e vs depth graphs f o r the v a r i o u s s i m u l a t i o n s . The v a l u e s where taken v e t i c a l l y downward below the u n c o n s o l i d a t e d - b e d r o c k c o n t a c t as shown by the l i n e A-B i n F i g u r e 7 . 7(d). T h i s p o s i t i o n was chosen because i t i s the a r e a where a number of h o l e s have been d r i l l e d . In the minumum water t a b l e e l e v a t i o n examples, 121 PRESSURE, Pa F i g u r e 7.12 P r e s s u r e v s d e p t h g r a p h o f minimum w a t e r t a b l e e l e v a t i o n e x a m p l e s . 122 PRESSURE, Pa F i g u r e 7.13 P r e s s u r e vs depth graph o f maximum water t a b l e e l e v a t i o n examples. 123 the bottom h o l e p r e s s u r e v a r i e s w i t h i n p l u s or minus 500 Pa of h y d r o s t a t i c p r e s s u r e . I n the maximum water t a b l e e l e v a -t i o n examples, the bottom h o l e p r e s s u r e v a r i e s w i t h i n p l u s or minus 900 Pa of i s o s t a t i c p r e s s u r e . I n o t h e r words, a t 900 m the p r e s s u r e o n l y v a r i e s w i t h i n . 5 t o 10% of i s o s t a t i c p r e s -s u r e i n any of the g e o l o g i c c o n f i g u r a t i o n s m o d e l l e d . The graphs i n F i g u r e s 7.7 t o 7.11 can be c o n s i d e r e d d i -m e n s i o n l e s s i f the r a t i o s of the d i f f e r e n t h y d r a u l i c conduc-t i v i t y d i s t r i b u t i o n s remain c o n s t a n t . The r a t i o s f o r each case s i m u l a t e d are t a b u l a t e d i n T a b l e 7.2. In ot h e r . w o r d s , i f the h y d r a u l i c c o n d u c t i v i t i e s a r e doubled the recha r g e r a t e must be dou b l e d t o a t t a i n the same water t a b l e e l e v a t i o n s and e q u i p o t e n t i a l p a t t e r n . The consequence of t h i s , of c o u r s e , i s t h a t the t o t a l d i s c h a r g e a l s o d o u b l e s . Of the t h r e e v a r i a b l e p a r a m e t e r s , h y d r a u l i c c o n d u c t i v i -t y , r e c h a r g e r a t e , and t o t a l d i s c h a r g e , the t o t a l d i s c h a r g e i s the most a c c u r a t e l y e s t i m a t e d a t a p p r o x i m a t e l y 6x10' 5 m2/s. The t o t a l d i s c h a r g e of the o r i g i n a l s i m u l a t i o n s can be m u l t i p l i e d by a f a c t o r t o produce a t o t a l d i s c h a r g e of 6x10" 5 m 2/s. To keep the same water t a b l e c o n f i g u r a t i o n f o r each graph the c o n d u c t i v i t i e s and r e c h a r g e r a t e must a l s o be mul-t i p l i e d by the same f a c t o r . - The end r e s u l t i s summarized i n T a b l e 7.3. The t a b l e i l l u s t r a t e s t h a t w i t h the s e t t o t a l d i s c h a r g e , the recharge r a t e needed v a r i e s between 1.09x10"" and 1.81x10"'* or 14 and 23% of the t o t a l p r e c i p i t a t i o n . The water b a l a n c e c a l c u l a t i o n s of Chapter 4 and e s t i m a t e s of Table 7.3 Influx and Hydraulic Conductivi ty D i s t r i b u t i o n s with a Set Outflux Type Recharge Rate (m/s) T o t a l Discharge (mVs/m) IA Max Flux 1.77x10 IA Min Flux 1.09x10" 1B Max Flux 1.76xl0~ 1B Min Flux 1.09xl0~ 1C Max Flux 1.76xl0~ 1C Min Flux l . O l x l o " 1C Max Flux 1.81x10" 1C Min Flux 1.10xl0~ 2 Max(iso) 1.78x10" 2 Min(iso) 1.09x10 2 Max(aniso) 1.79x10* 2 Min(aniso) 1.11x10 3 Max(iso,gran) 1.77x10" 3 Min(iso,gran) 1.09xl0~ 3 Max(aniso gran) 1.77x10 3 Min(aniso gran) 1.09x10" 4 Max(iso) 1.76x10" 4 Min(iso) 1.09xl0~ 4 Max(aniso) 1.77x10 4 Min(aniso) 1.10x10 •8 -8 -8 -8 -8 6x10 6x10 6x10 6x10 6xl0~ 6x10" 6x10 6xl0~ 6x10 6x10 6xl0~ 6x10 6x10' 6x10' 6x10' 6x10" 6x10" 6x10" 6x10 •5 •5 -5 -5 -5 -5 -5 -5 -5 •5 -5 •5 •5 -5 6x10 -5 Conductivi ty (m/s) % T o t a l P r e c i p i t a t i o n K =9.12x10 -7 =2.78x10 =4.23x10" K g =l.52x10 K K K K K K K f = 7 . 4 1 x l 0 _ 7 K g = 7 . 4 1 x l 0 _ 8 K f =1.04xl0~ 6 K =1.04xl0~ 7 gx~2. .78x10" gX=4. .23x10" K g z ! gx= 5 ' .94x10" ; g x =6. ;gx=6' ,91x10" ,15x10" K g z 8„ 8 9 2 , g x - 7 . .32x10" K g Z -8 =5.94x10 =6.91x10" =6.15x10 =7.32x10" -7 -8„ K f=9.84x10 K„ =4.92x10 K„,=4.92x10 r g -7 -8 9z K f=9.02x10 K v = 1 . 6 2 x l 0 " 7 K g = 1 . 6 2 x l 0 - 8 K v = 2 . 9 9 x l 0 " 7 K g = 2 . 9 9 x l 0 " 8 K v = 1 . 6 3 x l 0 " 7 K g x = 1 . 6 3 x l 0 " 6 K v = 2 . 7 1 x l 0 " 7 K g x = 2 . 7 1 x l 0 " K g z = 4 . 92x10 ^gz =1.63x10 K g z =2.71x10 K v = l . 3 6 x l 0 " 7 K f = 2 . 7 1 x l 0 " 7 K g = 2 . 7 1 x l 0 ~ K v = 2 . 2 2 x l 0 _ 7 K f = 4 . 4 4 x l 0 _ 7 K g = 4 . 4 4 x l 0 " 8 K v = 1 . 4 2 x l 0 " 7 K f = 2 . 8 3 x l 0 " 7 K g X = 1 . 4 2 x l 0 " 8 K g z =l.42x10 K v =2.24xl0~ 7 Kf=4.48xl0" K g z = 1 . 4 2 x l 0 - 7 K g x =2.24x10 -8 22.3 13.8 22.2 13.8 22.2 12.7 22.8 13.9 22.5 13.8 22.6 14.0 22.3 13.8 22.3 13.8 22.2 13.8 22.3 13.9 Kg = Conductivi ty of the g r a n o d i o r i t e K g x = Conductivi ty of the g r a n o d i o r i t e i n the h o r i z o n t a l d i r e c t i o n KgZ= Conductivity of the g r a n o d i o r i t e i n the v e r t i c a l d i r e c t i o n K v = Conductivi ty of the volcanics Kj = Conductivity of the f a u l t K. = Conductivity of the impermeable boundary 125 groundwater recharge i n Chapter 6 i n d i c a t e d t h a t 13 t o 16% of the t o t a l p r e c i p i t a t i o n became groundwater f l o w . The model v a l u e s a r e thus i n the same range but s l i g h t l y h i g h e r . Note i n F i g u r e s 7.7 t o 7.11 the p o s i t i o n of the d i s -charge and recharge a r e a s . The maximum water t a b l e e l e v a t i o n examples i n d i c a t e t h a t the d i s c h a r g e a r e a i s s i t u a t e d a l o n g way up the mountain s i d e a l t h o u g h no s i g n of the t h i s was observ e d i n the f i e l d . As mentioned i n Chapter 6 the d i s -charge a r e a i s p r o b a b l y r e s t r i c t e d t o the v a l l e y bottom co-v e r e d by u n c o n s o l i d a t e d v a l l e y f i l l d e p o s i t s as i n the m i n i -mum examples. I n t e r m e d i a t e s i m u l a t i o n s between the maximum and minimum extremes show t h a t water t a b l e e l e v a t i o n s as low as the minimum p o s i t i o n or as h i g h as about h a l f w a y between the minimum and maximum p o s i t i o n s have the same a c c e p t a b l e d i s c h a r g e a r e a . T h i s means t h a t the range of f e a s i b l e p e r -centages of the t o t a l p r e c i p i t a t i o n e n t e r i n g the groundwater system drops from 14 t o 22% down t o 14-18% which c o r r e s p o n d s v e r y w e l l w i t h the 13-16% range e s t i m a t e d from the water ba-l a n c e and the e s t i m a t e s of groundwater r e c h a r g e . I n t e r p r e t a t i o n In the f o l l o w i n g d i s c u s s i o n the u n r e a l i s t i c c a s e s I B , 3A and 4A w i l l not be i n c l u d e d . T a b l e 7.3 i l l u s t r a t e s t h a t i n any g e o l o g i c u n i t the h i g h e s t v a l u e of c o n d u c t i v i t y i n the t a b l e i s o n l y one f i f t h t o one o r d e r of magnitude l a r g e r than the l o w e s t v a l u e . When one c o n s i d e r s t h a t c o n d u c t i v i t i e s can 126 v a r y over 10 o r d e r s of magnitude or more, i t i s c l e a r t h a t the m o d e l l i n g has produced a v e r y d e f i n i t i v e s e t of c o n d u c t i -v i t i e s f o r the d i f f e r e n t u n i t s . The h o r i z o n t a l h y d r a u l i c c o n d u c t i v i t y of the basement g r a n o d i o r i t e K x v a r i e s from 1.42x10"" t o 1.52x10" 7 m/s w h i l e i n the v e r t i c a l d i r e c t i o n i t v a r i e s from 7.41x10"' t o 7.32x10" 7 m/s. The h y d r a u l i c condu-c t i v i t y of the v o l c a n i c s K v ranges from 1.42x10" 7 t o 2.71x10" 7 m/s and i n the permeable f a u l t i t ranges from 2 . 8 2 x l 0 " 7 t o 1.04x10"' m/s. I t must be s t r e s s e d , however, t h a t t h e s e answers a r e o n l y f o r the c o n d u c t i v i t y r a t i o s i n T able 7.2. T h e o r e t i c a l l y t h e r e a r e an i n f i n i t e number of p o s s i b l e c o n d u c t i v i t y d i s t r i -b u t i o n s and t h e r e f o r e , an i n f i n i t e c o n d u c t i v i t y range f o r each g e o l o g i c f o r m a t i o n . N e v e r t h e l e s s , the g e o l o g i c e n v i r o n -ments, r e c h a r g e r a t e v a l u e s and t o t a l d i s c h a r g e v a l u e s chosen or c a l c u l a t e d a r e r e a s o n a b l e and the a u t h o r f e e l s t h a t the h y d r a u l i c c o n d u c t i v i t i e s i n T a b l e 7.3 a r e w i t h i n an o r d e r of magnitude of the t r u e v a l u e s . Even though the geology i s not as s i m p l e as d e p i c t e d i n the models, the s i m u l a t i o n s show t h a t the c o n d u c t i v i t y of the g r a n o d i o r i t e v a r i e s o n l y s l i g h t -l y from the s i m p l e s t t o the most complex geology l e a d i n g one t o b e l i e v e t h a t the v a l u e s a r e r e a l i s t i c . In c o n c l u s i o n , from the g e o l o g i c a l c o n f i g u r a t i o n s cho-sen, the m o d e l l i n g i n d i c a t e s t h a t the g r a n o d i o r i t e has a h o r i z o n t a l h y d r a u l i c c o n d u c t i v i t y of a p p r o x i m a t e l y 5x10" 8 m/s and a v e r t i c a l h y d r a u l i c c o n d u c t i v i t y of 1 x10" 7 m/s. The 127 h y d r a u l i c c o n d u c t i v i t y of the v o l c a n i c s i s c l o s e t o l x l O ~ 7 m/s, s i m i l a r t o the v e r t i c a l component i n the g r a n o d i o r i t e and the most permeable zone, the f a u l t , has a h y d r a u l i c con-d u c t i v i t y of r o u g h l y 7 x l 0 ~ 7 m/s. 128 Chapter 8. CONCLUSIONS AND RECOMMENDATIONS In t h i s t h e s i s an attempt has been made t o d e s c r i b e the hydrogeology of the Meager Mountain geothermal a r e a . The main purpose of the t h e s i s was t o d e v e l o p a p r e l i m i n a r y , ma-t h e m a t i c a l model of the r e g i o n a l groundwater f l o w i n the a r e a . A summary of the major f i n d i n g s of t h i s r e s e a r c h i s p r e s e n t e d below. Summary and C o n c l u s i o n Geography 1. The topography i n the Meager Mountain a r e a i s v e r y rugged. The r e l i e f ranges from 425 t o 2700 m over h o r i -z o n t a l d i s t a n c e s of r o u g h l y 5 km. E x t e n s i v e g l a c i e r s y s -tems t e r m i n a t e a t the headwaters of a number of h i g h - g r a -d i e n t , y o u t h f u l streams. The streams produce a r a d i a l p a t t e r n of d r a i n a g e around the mountain. 2. P r e c i p i t a t i o n i n the c o a s t mountains i s v a r i a b l e but a t o t a l a nnual p r e c i p i t a t i o n r a t e of 2.5 m/y i s e x p e c t e d a t Meager Mountain . 3. The mean annual r u n o f f of the L i l l o o e t R i v e r i s 1880 mm/yr w h i l e r u n o f f measurements at M i l l e r Creek which i s at a h i g h e r e l e v a t i o n a r e e s t i m a t e d t o be 2400 ± 300 mm/yr. 4. The p o t e n t i a l e v a p o t r a n s p i r a t i o n i n the Meager Mountain a r e a i s a p p r o x i m a t e l y 500 mm/y. 129 5. The Meager Creek h o t s p r i n g s and Pebble Creek h o t s p r i n g s have a combined d i s c h a r g e r a t e of a p p r o x i m a t e l y 45 1/s. They r e p r e s e n t a minute f r a c t i o n of the r e g i o n a l ground-water d i s c h a r g e . 6. A number of c o l d s p r i n g s e x i s t throughout the Meager Mountain a r e a . Most have d i s c h a r g e s l e s s than 5 1/s. They r e p r e s e n t about 1 t o 2% of the r e g i o n a l groundwater f l o w . Geology 1. Meager Mountain i s p a r t of the G a r i b a l d i b e l t of n o r t h -south t r e n d i n g Q u a t e r n a r y v o l c a n o e s . Meager Mountain i n i t i a l l y e r u p t e d i n the P l i o c e n e and has been dormant f o r a p p r o x i mate the p a s t 2500 y e a r s . The o l d e r p o r t i o n of the mountain c o m p r i s e s m a i n l y w i d e s p r e a d a n d e s i t e and i s b e s t exposed i n the s o u t h . The younger n o r t h h a l f i s composed of d a c i t e f l o w s and l a v a domes o v e r l y i n g the o l d e r a n d e s i t e f l o w s . 2. The v o l c a n i c s e r u p t e d t h rough a basement c o n s i s t i n g of T e r t i a r y and o l d e r g r a n i t i c r o c k s . The e x p l o s i v e n a t u r e of the v o l c a n i c e r u p t i o n s s e v e r e l y may have f r a c t u r e d the basement rock t h e r e b y i n c r e a s i n g i t s f r a c t u r e p e r m e a b i l i -t y . 3. The L i l l o o e t R i v e r and Meager Creek v a l l e y s are f i l l e d w i t h u n c o n s o l i d a t e d d e p o s i t s v a r y i n g from z e r o t o over 250 m i n t h i c k n e s s . The d e p o s i t s c o n s i s t of sand and g r a v e l s w i t h i n t e r b e d d e d t i l l and l a c u s t r i n e c l a y l a y e r s . 130 Hydrogeology 1. The p r e l i m i n a r y water b a l a n c e undertaken f o r the e n t i r e L i l l o o e t b a s i n i n d i c a t e s t h a t 17% of the p r e c i p i t a t i o n e n t e r e s the groundwater system. 2. The Meager Mountain f r a c t u r e survey i n d i c a t e s two dominant, near v e r t i c a l j o i n t s e t s , however, the study d i d not s u p p l y s u f f i c i e n t d a t a f o r the c a l c u l a t i o n of the rock mass h y d r a u l i c c o n d u c t i v i t y . I t i s the a u t h o r ' s o p i n i o n t h a t t h e r e i s no s u i t a b l e method t o make s u r f a c e measurements of f r a c t u r e d r o c k s i n the f i e l d t o a t t a i n a r e p r e s e n t a t i v e e s t i m a t e of h y d r a u l i c c o n d u c t i v i t y f o r the rock mass a t depth. 3. The study of p u b l i s h e d f r a c t u r e p e r m e a b i l i t i e s of v a r i o u s rock t y p e s r e v e a l e d t h a t the h y d r a u l i c c o n d u c t i v i t y of most f r a c t u r e d rock l i e s i n the 10" 7 to 1 0 " 1 1 m/s range. I t i s f e l t t h a t the h y d r a u l i c c o n d u c t i v i t y of the base-ment g r a n o d i o r i t e s i n the study a r e a i s a t the h i g h end of t h i s range, due t o t h e i r h i g h l y f r a c t u r e d n a t u r e . V a l u e s of 10" 7 t o 10" 8 m/s c o u l d be e x p e c t e d . 4. I t can be shown t h a t the most l i k l y p o s i t i o n f o r the water t a b l e i s a t an i n t e r m e d i a t e e l e v a t i o n i n the moun-t a i n system. A p a r t from a v e r y few s p i n g s a t h i g h e r e l e -v a t i o n s , the d i s c h a r g e area i s b e l i e v e d t o be c o n f i n e d t o the s e c t i o n of the v a l l e y o v e r l a i n by u n c o n s o l i d a t e d de-p o s i t s . 5. The f r a c t u r e h y d r a u l i c c o n d u c t i v i t y t h a t o c c u r s a c r o s s a l l the v o l c a n i c l a y e r s has g r e a t e r c o n t r o l over the 131 groundwater f l o w than the i n t e r g r a n u l a r h y d r a u l i c conduc-t i v i t y d i f f e r e n c e s between l a y e r s . I n t h i s s t u d y , the e n t i r e v o l c a n i c p i l e i s c o n s i d e r e d as one h y d r o g e o l o g i c u n i t . The basement rock and the u n c o n s o l i d a t e d v a l l e y f i l l a r e two o t h e r d i s t i n c t h y d r o g e o l o g i c u n i t s i n the study a r e a . The r e p r e s e n t a t i v e h y d r a u l i c c o n d u c t i v i t i e s as determined by p u b l i s h e d d a t a and f i e l d o b s e r v a t i o n s a r e e s t i m a t e t o be 10" 5 t o 10" 2 m/s f o r the u n c o n s o l i d a t e d d e p o s i t s , 10" 7 t o 10"* m/s f o r the basement rock and 10"'-5 t o 10"" m/s f o r the v o l c a n i c s . The h y d r a u l i c c o n d u c t i v i t y of the basement rock i s perhaps as much as 5 tim e s g r e a t e r i n the v e r t i c a l d i r e c t i o n than i n the h o r i z o n t a l d i r e c t i o n due t o the e x t e n s i v e v e r t i c a l f r a c t u r i n g . The h y d r a u l i c c o n d u c t i v i t y of the v o l c a n i c rock i s perhaps as much as 5 time s g r e a t e r i n the h o r i z o n t a l d i r e c t i o n than i n the v e r t i c a l d i r e c t i o n due t o l a y e r i n g . The v e r t i c a l hydrau-l i c c o n d u c t i v i t y i n the basement rock i s s i m i l a r t o t h a t i n the v o l c a n i c r o c k . The groundwater d i s c h a r g e i n the Meager Creek b a s i n c a l -c u l a t e s t o be 14.5% of the t o t a l p r e c i p i t a t i o n , assuming an a n n u a l r a i n f a l l r a t e of 2.5 m/y. T h i s d i s c h a r g e v a l u e range c o r r e l a t e s w e l l w i t h the 17% c a l c u l a t e d f o r the e n t i r e L i l l o o e t b a s i n t h r o u g h the use of a water b a l a n c e . 132 M a t h e m a t i c a l M o d e l l i n g 1. The parameters t h a t must be known t o m a t h e m a t i c a l l y model the groundwater f l o w i n an a r e a i n c l u d e , 1) the r e g i o n of f l o w , 2) the e q u a t i o n of f l o w w i t h i n the r e g i o n , 3) the boundary c o n d i t i o n s around the b o u n d a r i e s of the r e g i o n , 4) the s p a t i a l d i s t r i b u t i o n of h y d r a u l i c c o n d u c t i v i t y v a l u e s i n the r e g i o n . 2. The s e n s i t i v i t y a n a l y s i s u s i n g the program FOPS r e v e a l e s t h a t the amount of d i s c h a r g e v a r i e s d i r e c t l y w i t h the h y d r a u l i c c o n d u c t i v i t y , undergoes moderate changes w i t h water t a b l e e l e v a t i o n v a r i a t i o n s and i s i n s e n s i t i v e t o depth of f l o w v a r i a t i o n s . C o n s e q u e n t l y , i n the main s i -m u l a t i o n s the h y d r a u l i c c o n d u c t i v i t y and water t a b l e e l e -v a t i o n s a r e v a r i e d but the depth of f l o w i s chosen a r b i -t r a r i l y and remains c o n s t a n t . 3. The g eochemical s t u d i e s of the t h e r m a l waters at Meager Mountain completed by Hammerstrom and Brown (1977) and C l a r k (1980) i n d i c a t e t h a t t h e r e i s no e v i d e n c e t h a t the water temperature ever exceeded 140°C. T h i s i n d i c a t e s t h a t t h e f l o w f i e l d f o r t h e t h e r m a l w a t e r s p r o b a b l y i s a s h a l l o w one. The m a t h e m a t i c a l m o d e l l i n g cannot prove t h a t i t i s a s h a l l o w f l o w system, however i t i l l u s t r a t e s t h a t d i s c h a r g e out of the system i s independent of the depth of f l o w . T h e r e f o r e , a s h a l l o w f l o w system i s f e a -s i b l e and the g e o c h e m i c a l s t u d i e s i n d i c a t e i t i s the most l i k e l y s i t u a t i o n . 4. The program FREESURF1 was used f o r the main s i m u l a t i o n s 133 i n t h i s r e p o r t . The most a c c u r a t e l y known v a r i a b l e p a r a -meter i n the Meager Mountain a r e a i s the d i s c h a r g e . In the s i m u l a t i o n s , the d i s c h a r g e v a l u e i s h e l d c o n s t a n t and a p o s s i b l e range of water t a b l e e l e v a t i o n s and h y d r a u l i c c o n d u c t i v i t y d i s t r i b u t i o n s a r e c a l c u l a t e d f o r the 4 geo-l o g i c a l c o n f i g u r a t i o n s c o n s i d e r e d . The s i m u l a t i o n s de-t e r m i n e d t h a t 14-18% of the t o t a l p r e c i p i t a t i o n e n t e r s the groundwater zone which c o r r e l a t e s w e l l w i t h the v a l u e of 17% d etermined i n the water b a l a n c e s t u d i e s , and the v a l u e of 14.5% d e t e r m i n e d i n the Meager Creek b a s e f l o w s t u d i e s . 5. The bottom h o l e f l u i d p r e s s u r e at 900 m i n any of the s i m u l a t i o n s v a r i e s w i t h i n 5 t o 10% of i s o s t a t i c p r e s s u r e . 6. The m a t h e m a t i c a l s i m u l a t i o n s i n d i c a t e d the most l i k e l y v a l u e s f o r the h y d r a u l i c c o n d u c t i v i t y t o be 5x10" 8 m/s i n the h o r i z o n t a l d i r e c t i o n i n the basement r o c k s , 1x10" 7 f o r the v e r t i c a l d i r e c t i o n i n the basement r o c k , 1x10" 7 f o r the v o l c a n i c s and 7x10" 7 f o r the f a u l t zone. W i t h i n one o r d e r of magnitude of the a c t u a l v a l u e s . Recommendat i o n s An a c c u r a t e e s t i m a t e of the amount of groundwater d i s -charge i n the Meager Creek b a s i n w i l l a l l o w a more p r e c i s e o v e r a l l h y d r a u l i c c o n d u c t i v i t y t o be a s s e s s e d f o r the base-ment r o c k . A d e t a i l e d water b a l a n c e i s recommended t o a t t a i n t h i s d i s c h a r g e v a l u e . The water b a l a n c e would have t o be performed over a number of y e a r s and would i n v o l v e the f o l -134 l o w i n g measurements: 1) Measure the volume change of the g l a -c i e r s i n the b a s i n a r e a t o determine t h e i r c o n t r i b u t i o n t o b a s i n d i s c h a r g e . 2) Measure the p r e c i p t a t i o n from the v a l l e y f l o o r t o the h i g h e r e l e v a t i o n s t o a s c e r t a i n the annua l p r e c i -p i t a t i o n and the change of p r e c i p i t a t i o n v a l u e s w i t h e l e v a -t i o n . 3) Measure the d i s c h a r g e y e a r - r o u n d at the stage s i t e s c u r r e n t l y i n use and i n s t a l l a n o t h e r on the L i l l o o e t R i v e r j u s t s o u t h of i t s c o n f l u e n c e w i t h Meager Creek t o c a l c u l a t e the t o t a l d i s c h a r g e out of the a r e a and s u b - b a s i n d i s c h a r g e s . 4) Measure the e v a p o r a t i o n by u s i n g pan d a t a and s o l a r r a d i a -t i o n d a t a t o e s t i m a t e the e v a p o t r a n s p i r a t i o n i n the a r e a . A f r a c t u r e survey i n the v o l c a n i c s would g i v e the g e n e r a l t r e n d s of f r a c t u r i n g . The survey might not be u s e f u l f o r h y d r a u l i c c o n d u c t i v i t y c a l c u l a t i o n s but would determine whether the f r a c t u r e s a re m a i n l y v e r t i c a l as s t a t e d i n the h y d r o g e o l o g i c i n t e r p r e t a t i o n of t h i s r e p o r t and p o s s i b l y r e v e a l zones of r e l a t i v e l y h i g h e r f r a c t u r e d e n s i t y t o p o s s i b -l y r e v e a l zones of h i g h e r h y d r a u l i c c o n d u c t i v i t y a t de p t h . A more r e f i n e d g e o l o g i c a l c o n f i g u r a t i o n and h y d r a u l i c c o n d u c t i v i t y d i s t r i b u t i o n f o r the basement rock w i l l e v o l v e w i t h c o n t i n u e d d r i l l i n g and t e s t i n g . As these two v a r i a b l e parameters become more r e f i n e d , m a t h e m a t i c a l s i m u l a t i o n s of the h y d r o g e o l o g i c environment w i l l a l s o y i e l d more r e f i n e d r e s u l t s . M a t h e m a t i c a l m o d e l l i n g w i l l d e f i n i t e l y be of v a l u e t o t h i s p r o j e c t throughout i t s e x p l o r a t i o n , development and p r o d u c t i o n s t a g e s . 135 The two l i m i t i n g f a c t o r s f o r development of the Meager Mountain geothermal p r o j e c t are the h y d r a u l i c c o n d u c t i v i t y of the basement rock and the temperature of the rock a t d e p t h . Temperature l o g g i n g of the d r i l l h o l e s has r e v e a l e d v e r y p r o m i s i n g geothermal g r a d i e n t s . H y d r a u l i c c o n d u c t i v i t y t e s t s have not been u n d e r t a k e n . I t i s i m p e r a t i v e t h a t down h o l e c o n d u c t i v i t y t e s t s be performed from the top t o the bottom of a l l h o l e s t o r e v e a l the h y d r a u l i c c o n d u c t i v i t y d i s t r i b u t i o n s p a t i a l l y and w i t h depth. Near s u r f a c e , the h y d r a u l i c condu-c t i v i t y may be s u f f i c i e n t l y h i g h f o r p r o d u c t i o n but the tem-p e r a t u r e may be too low. At d e p t h , the temperature may be s u f f i c i e n t l y h i g h f o r p r o d u c t i o n but the h y d r a u l i c c o n d u c t i -v i t y may be too low. The a u t h o r f e e l s t h a t a change of s t r a t e g y i s i n o r d e r f o r the Meager Mountain geothermal p r o j e c t . In the i n i t i a l s t a g e s , e x p l o r a t i o n g e o p h y s i c s and d r i l l i n g a r e n e c e s s a r y t o o u t l i n e the p r o m i s i n g r e g i o n f o r development. Now t h a t t h i s r e g i o n has been d e l i n e a t e d i n the South R e s e r v o i r a r e a a more s o p h i s t i c a t e d t e c h n o l o g y needs t o be employed. Numerous com-p a n i e s e x i s t t h a t p e r f o r m s p e c i a l i z e d down h o l e h y d r o g e o l o g i c t e s t s on f r a c t u r e d r o c k . The employment of these companies i s v e r y e x p e n s i v e , however the i n f o r m a t i o n they can g e n e r a t e i s e s s e n t i a l t o the p r o j e c t at t h i s t i m e . 136 APPENDIX I GLACIAL BASAL MELT FLUX CALCULATIONS IN THE MEAGER CREEK BASIN 137 The g o v e r n i n g e q u a t i o n f o r the r a t e of g l a c i a l b a s a l melt due t o the e a r t h ' s geothermal f l u x i s dz _ q o d t pL dz where ^ i s the r a t e of change of t h i c k n e s s of i c e w i t h t i m e , q Q the geothermal heat f l u x (W/m 2), P the d e n s i t y of i c e (Kg/m 3) and L the l a t e n t heat of m e l t i n g ( J / K g ) . The w o r l d average heat f l u x i s 0.05 W/m2 and the d e n s i t y of i c e and l a t e n t heat of melt have v a l u e s of 900 Kg/m3 and 3 . 3 5 x l 0 " 5 J/Kg r e s p e c t i v e l y . In the Meager Mountain a r e a v a r i e s from 0.1 t o 0.93 W/m3 (Lewis and So u t h e r , 1978) w i t h an average of 0.5 W/m2. T h i s i s ten times the w o r l d average. The r a t e of change of t h i c k n e s s of the g l a c i e r s w i t h time i n the Meager Mountain a r e a i s t h e r e f o r e §^ - 1.66 X 10 m/s d t The a r e a of the g l a c i e r s c o n t r i b u t i n g t o the f l o w i n Meager Creek i s a p p r o x i m a t e l y 51.4 Km2 or 5 . 1 4 x l 0 7 m2. T h i s f i g u r e was c a l c u l a t e d u s i n g a p l a n i m e t e r and topography map. The volume Q of f l u i d r e l e a s e can now be c a l c u l a t e d as Q = g = dz = 0 > Q 9 m 3 / s d t d t The measured groundwater f l o w out of the a r e a i s 2.5 m 3/s; t h e r e f o r e the c o n t r i b u t i o n of b a s a l g l a c i a l melt t o r u n o f f i n the w i n t e r months s h o u l d not exceed 3 t o 4%. APPENDIX II CONTOURED-POLE PLOTS OF FRACTURE DATA III J o i n t set #1 [ ~ j j o i n t set #2 H j o i n t set #3 i ^ J o i n t set #4 GEODfiT - L O U E P HEM I SPHERE EOUOL fiPEP, POLFlP PLOT CONTOUR P L O T FOR: SITE SROI : 5 € 0 2 8 5 0 H 46] OCn' E 1100 t l . OBSERVATIONS: 190 POPULATION: 190 CO CEODAT - LOUER H E M I S P H E R E EQUAL AREA POLAR PLOT CONTOUR P L O T F O R : S I T E S R 0 3 : 3 602 300 N «66 606 E ?ce « 1 O B S E R V A T I O H S : 200 P O P U L A T I O N : 200 CEODAT - LOWEP H E M I S P H E R E EQUAL AREA POLAR P L O T CONTOUR PLOT F O R : S I T E S R 0 4 ! 5 6 0 ) 9 0 6 H 4 6 3 7 0 0 E BSC • O B S E R V A T I O H S : 99 P O P U L A T I O N : 99 CEODAT - LOWER HEMISPHERE EOUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SR05 : 5 €01 375 N 464 300 E 9 4 0 « l . OBSERVATIONS: lee POPULATION: tee CE0DAT - LOWER HEMISPHERE EQUAL APEA POLAR PLOT CONTOUR PLOT FOR: SITE SR06 : 5 602 000 N : 462 900 E : 1000 t i . OBSERVATIONS: 199 POPULATION: 199 CEOHAT - LOUER HEMISPHERE EQUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SR07 : 5 602 066 N : *6l 500 E : 1666 f l . OBSERVATIOHS: 199 POPULATION: 199 CEOIiAT - LOWER HEMISPHERE EQUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SR08 : 5 662 266 N : *67 950 E : 740 «I. OBSERVATIOHS: 258 POPULATION: 230 GEOHAT - LOWER HEM I SPHERE EOUAL UREA POLAP PLOT CONTOUR PLOT FOR: SITE SR9B«9A : 5 661 OOO N • 463 b?: £ OBSERVATIONS: 348 POPULATION: 348 GEOUAT - LOWER HEMISPHERE EOUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SR18 : 5 604 660 N : 466 OBSERVATIONS: 216 POPULATION: 216 CEODAT - LOWER- HEMISPHERE EQUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SR11 : S 6 0 i 325 N : 463 966 E ! 990 f l . OBSERVATIONS: 200 POPULATION: 200 CEODAT - LOUER HEMISPHERE EQUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SRI2 : 5 60S 100 N : 467 700 E : 1220 f l OBSERVATIONS: 201 POPULATION: 201 M C E O D M T - LOWER HEM I S P H E R E E O U A L A R E A P O L A R P L O T C O N T O U R P L O T F O R : S I T E S R I 3 : 5 6 0 3 100 H : 4 6 ; 6 7 5 E : 1600 r l . O B S E R V A T I O N S : 170 P O P U L A T I O N : 170 N CEOBAT - LOWER HEMISPHERE EQUAL AREA POLAR PLOT CONTOUR PLOT FOR: S I T E SR14 : 5 6 0 3 5 0 0 N : 461 2 5 0 E : 1 3 0 0 « 1 . OBSERVATIONS: 149 P O P U L A T I O N : M » CEODAT - LOUER HEMISPHERE EQUAL AREA ROLAR PLOT CONTOUR PLOT FOR: SITE SRI5 : 3 £06 EI30 N | 461 650 E : 760 .1 OBSERVATIONS: 103 POPULATION: 103 H CEODAT - LOUER HEMISPHERE EQUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SRI6 : 3 600 650 N : 461 025 E : 760 «1. OBSERVATIOHS: 101 POPULATION: IOI N I—1 GEGDRT - LOWER HEMISPHERE EQUAL AREA POLRP PLOT CONTOUR PLOT FOR: SITE SRi? : 5 600 858 N : 46i 450 E : 7se #V. OBSERVATIONS: 160 POPULATION: 100 CEODAT - LOWER HEM!SPHERE EOURL AREA POLAR PLOT CONTOUR PLOT F O R : SITE SRI8 : 5 666 850 N : 462 656 E : 748 « 1 . OBSERVATIONS: 116 POPULATION: l i e N ^ . ^ . c V ? ? " M E M I S P H«E EQUAL AREA POLAR PLOT OSATI'ON'SV^  S , T E S"> »' 6 : 6 " ' «< «' • • POPULATION: i e? N CEODAT - LONER HEtllSPHERE EOUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SR26 : 5 660 750 N : 464 756 E I 666 . 1 OBSERVATIONS: 102 ' 6 6 6 POPULATION: 102 CEODAT - LOWER HEMISPHERE EQUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SR21 : 5 sen 900 N : 4£ OBSERVATIONS: 131 POPULATION: 151 CEODAT - LOWEF HEMISPHERE EOUAL AREA POLAR PLOT COttfC'lH PLOT FOR: SITE SR22 I 5 £01 225 N j Ac OBSERVATIONS: 200 POPULATION: 2B8 N CEODAT - LOWER HEMISPHERE EQUAL AREA POLAR PLOT CONTOUR PLOT FOR: SITE SR24 : S 602 450 N : 465 375 E : 1050 l l . OBSERVATIONS: 100 POPULATION: IOO N o r o CEODAT - LOUER HEMISPHERE EOUAL AREA POLAR PLOT COIITOUR PLOT FOR: SITE SRt5 : 5 £94 £75 t< ; 4 £ f E : , 3 & e OBSERVATIONS: 148 POPULATION: MB H APPENDIX I I I RIVER STAGE MEASUREMENTS AT MEAGER CREEK HOTSPRINGS BRIDGE, 19 153 Water Level Observations at Meager Creek, 1979 Water L e v e l (in Feet) Date 1979 Time Observed Crest June 18 1545 19 0930 25 0910 1235 Jul y 3 1525 4 1510 5 1650 6 1700 7 1515 8 1510 9 1910 10 1930 11 1820 12 1930 13 1900 14 2120 15 2100 16 1130 17 2025 18 2045 19 2030 20 0900 21 1825 22 1830 23 1915 24 2030 25 1600 26 1900 27 1605 28 1100 29 1630 30 1535 31 1915 152. 58 152. 58 153. 23 152. 43 153. 23 152. 58 152. 08 154. 0 152. 25 152. 5 152. 65 152. 88 152. 78 153. 18 152. 63 153. 28 153. 8 154. 28 153. 34 154. 18 153. 81 154. 13 153. 23 154. 08 153. ,13 153. 43 152. ,7 153. 0 153. ,08 153. 38 153. ,18 153. 68 152. ,73 153. ,68 153. .88 154. 08 153. .88 154. ,18 152, .88 154. ,18 153. .68 154. ,38 153, .43 153. ,68 153, .48 153. ,58 153, .28 153. .58 153 .28 153. .38 153 .38 153, .58 153 .33 153, .48 152 .83 153, .53 153 .03 153, .48 153 .13 153 .38 153 .33 153 .48 154 Water Level (in Feet) Date 1979 Time Observed Crest August 1 1635 153.28 153.48 2 1530 153.13 153.43 3 1645 153.08 153.33 4 1645 152.98 153.28 5 1615 152.83 153.18 6 1420 152.48 152.98 7 1900 152.86 -8 1630 153.18 -9 1930 153.39 10 1530 153.14 153.68 11 1920 153.45 153.73 12 1810 153.59 153.83 13 1915 153.68 154.18 14 1825 154.25 154.13 15 2030 153.25 153.78 16 1940 153.31 153.73 17 1700 153.25 153.58 18 1900 153.19 153.83 19 1845 153.23 153.58 20 2100 153.55 153.98 21 1845 153.78 -22 1920 153.73 154.43 23 2035 153.57 154.18 24 1900 153.31 153.88 25 1915 153.48 153.88 26 1910 153.58 153.93 27 1130 152.95 -2015 153.34 154.13 28 1050 152.85 -1945 153.51 154.03 29 1200 152.71 1945 153.61 154.03 30 1945 153.28 153.98 31 1845 152.98 153.53 Water Level (in Feet) Date 1979 Time Observed Crest September 1 1945 153.18 153.58 2 1200 153.21 154.58 1945 153.84 154.18 3 1245 153.68 155.98 4 2000 153.08 153.83 5 1000 153.43 153.93 1915 153.25 -6 1945 152.48 -7 1945 152.88 -8 1945 154.05 -9 1845 152.88 154.48 10 - - -11 1300 152.18 -1655 152.48 -12 - - -13 1910 153.03 -14 1845 153.28 153.58 15 1100 152.73 153.53 2155 153.18 153.68 16 1240 152.68 -2030 152.98 -17 0930 152.48 -2030 153.2 153.38 18 1955 153.26 153.48 19 0945 152.68 153.53 November 3 1700 150.71 December 10 1505 150.72 APPENDIX IV DISCHARGE CALCULATION AT THE MEAGER CREEK STAGE SITE, DEC. 10, 1 157 The c r o s s s e c t i o n a l a r e a A of the Meager Creek s t a t i o n on December 10, 1979 was c a l c u l a t e d t o be 2.7 m2. To c a l c u -l a t e the stream v e l o c i t y the Manning e q u a t i o n i s used which s t a t e s t h a t ? / 7 L. JU49 R Z / 3 S 2 n where u i s the v e l o c i t y , R i s the h y d r a u l i c r a d i u s ( r a t i o of c r o s s s e c t i o n a l a r e a t o the w e t t e d p e r i m e t e r ) , S i s the g r a -d i e n t s l o p e and n i s the Manning f r a c t i o n c o e f f i c i e n t . For the Meager Creek s t a t i o n , R=0.76, S=2.63xl0" J and a r e a -s o n a b l e e s t i m a t e of n i s 0.04 t o 0.05. The Manning e q u a t i o n l e a d s t o =1.23 t o 1.53 m/sec. The d i s c h a r g e , Q, o b t a i n e d from Q=uA, i s t h e r e f o r e 3.28 t o 4.10 m 3/s or a p p r o x i m a t e l y 3.7 m V s . 158 APPENDIX V DECEMBER DAILY DISCHARGES OF THE LILLOOET RIVER NEAR PEMBERTON (1977-1979) December D a i l y Discharge of the L i l l o o e t River, Near Pemberton i n m/s (1977-1979) Day 1977 1 32.0 2 31.4 3 32.6 4 30. 3 5 29.2 6 28.3 7 28.0 8 27.5 9 26.9 10 27.5 11 28.3 12 34.0 13 33.1 14 31.1 15 28.3 16 26.9 17 25.5 18 27.8 19 27.2 20 26.9 21 26.6 22 26.3 23 26.1 24 25.8 25 25.5 26 24.9 27 24.6 28 24.4 29 24.1 30 23.8 31 23.8 T o t a l 858.7 MEAN 27.7 MAX 34.0 MIN 23.8 1978 1979 22.7 24.1 22.4 23.8 22.1 23.5 21.8 23.2 21.5 22.9 21.2 22.9 21.0 23.1 20.7 23.2 20.4 24.9 20.1 25.5 19.8 23.8 19.7 22.9 19.5 19.8 19.4 21.5 19.3 20.7 19.1 20.1 19.0 21.0 18.8 24.6 18.7 36.0 18.5 32.6 18.4 29.7 18.3 28.0 18.1 26.6 18.0 25.5 17.8 24.6 17.7 24.4 17.6 23.5 17.4 22.9 17.3 22.4 17.1 22.1 17.0 21.9 600.4 751.7 19.4 24.2 22.7 36.0 17.0 19.8 160 R e f e r e n c e s Anderson, R.G., The geology of the v o l c a n i c s i n the Meager Creek map a r e a , southwestern B r i t i s h Columbia, B.Sc. t h e s i s , Dept. 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