@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Science, Faculty of"@en, "Resources, Environment and Sustainability (IRES), Institute for"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Marquis, John Paul"@en ; dcterms:issued "2010-05-20T04:06:04Z"@en, "1985"@en ; vivo:relatedDegree "Master of Science - MSc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description "The storm runoff of small springs and seeps in the West Kootenays was subjected to hydrograph separation using oxygen-18 and conductance methodologies. The results showed that the vast majority of storm discharge was groundwater. Under peak flow conditions, the ratio of prestorm water to storm water was 0.93 for Morley Spring, 0.88 for Anderson Creek, 0.87 for Elliott Creek, 0.84 for Chou Creek and 0.85 for Tank Creek. Further comparison between prestorm discharge and storm water indicated that the groundwater probably originated as spring snow melt. These implications are discussed with regard to the various logging development plans currently being proposed for the study sites."@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/24859?expand=metadata"@en ; skos:note "HYDROGRAPH SEPARATION USING NATURAL ISOTOPE AND CONDUCTANCE METHODS IN THE WEST KOOTENAY AREA OF BRITISH COLUMBIA by JOHN PAUL MARQUIS B . S c , The U n i v e r s i t y o f V i c t o r i a , 1978 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Resource Management Science) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA January 1985 © John Paul Marquis, 1985 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I agree 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 purposes 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 Gft f t f luf iTE S T O D v E S The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 £ 7 fflMBS ABSTRACT The storm r u n o f f of small s p r i n g s and seeps i n the West Kootenays was s u b j e c t e d to hydrograph s e p a r a t i o n u s i n g oxygen-18 and conductance methodologies. The r e s u l t s showed t h a t the v a s t m a j o r i t y of storm d i s c h a r g e was groundwater. Under peak flow c o n d i t i o n s , the r a t i o of prestorm water to storm water was 0.93 f o r Morley S p r i n g , 0.88 f o r Anderson Creek, 0.87 f o r E l l i o t t Creek, 0.84 f o r Chou Creek and 0.85 f o r Tank Creek. F u r t h e r comparison between prestorm d i s c h a r g e and storm water i n d i c a t e d t h a t the groundwater probably o r i g i n a t e d as s p r i n g snow melt. These i m p l i c a t i o n s are d i s c u s s e d with regard t o the v a r i o u s l o g g i n g development plans c u r r e n t l y being proposed f o r the study s i t e s . i ACKNOWLEDGEMENTS I would l i k e to extend my a p p r e c i a t i o n to D.A.A. Toews and D. Gluns of the M i n i s t r y of F o r e s t s i n Nelson f o r t h e i r i n t e r e s t and support i n t h i s study. My thanks to P. Whaite of the Department of Geophysics of the U n i v e r s i t y of B r i t i s h Columbia whose t a l e n t s were r e s p o n s i b l e f o r the maintenance of the mass spectrometer. I a l s o extend my g r a t i t u d e to Dr.. D. L. Golding of the F a c u l t y of F o r e s t r y of the U n i v e r s i t y of B r i t i s h Columbia whose guidance was paramount i n the completion of t h i s t h e s i s . F i n a l l y , a s p e c i a l thanks to my wife Sandra f o r her pa t i e n c e and proof r e a d i n g . i i TABLE OF CONTENTS A b s t r a c t i Acknowledgements i i Table of Contents i i i L i s t of Tables v L i s t of F i g u r e s v i Chapter 1 - I n t r o d u c t i o n Problem 1 O b j e c t i v e s 2 Review 4 Chapter 2 - Methods 22 Chapter 3 - Mountain S t a t i o n Study Area Area D e s c r i p t i o n 26 Study S i t e s and Methods 30 R e s u l t s 31 D i s c u s s i o n of F i n d i n g s 39 Co n c l u s i o n s 43 Chapter 4 - North Shore Study Area Area D e s c r i p t i o n 45 Study S i t e and Methods 46 R e s u l t s 47 D i s c u s s i o n of F i n d i n g s 52 Co n c l u s i o n s 52 i . . Chapter 5 - Slocan V a l l e y Study Area Area D e s c r i p t i o n 54 Study S i t e s and Methods •••• 56 R e s u l t s 58 D i s c u s s i o n of F i n d i n g s 58 C o n c l u s i o n s 65 Chapter 6 - Study C o n c l u s i o n s 67 Appendix A (glossary) 71 References 73 i v LIST OF TABLES Table Page 1. Rainwater data f o r Mountain S t a t i o n study area 32 2. Data obtained f o r the Tank Creek sampling s i t e 33 3. Data obtained f o r the P o s t l e S p r i n g sampling s i t e 35 4. Data obtained f o r the Anderson Creek sampling s i t e .... 37 5. Rainwater data f o r North Shore study area 49 6. Data obtained f o r the Morley S p r i n g sampling s i t e 50 7. Rainwater data f o r Slocan V a l l e y study area 59 8. Data obtained f o r the Chou Creek sampling s i t e 60 9. Data obtained f o r the E l l i o t t Creek sampling s i t e 62 v LIST OF FIGURES F i g u r e s Page 1. Small s c a l e map of study areas 3 2. Geometric hydrograph s e p a r a t i o n 9 3. Barne's method of geometric hydrograph s e p a r a t i o n on l o g a r i t h m i c s c a l e 11 4. Barn's method of geometric hydrograph s e p a r a t i o n on l i n e a r s c a l e . 12 5. Hewlett's constant slope method of hydrograph s e p a r a t i o n 13 6. I s o t o p i c hydrograph s e p a r a t i o n .' 17 7. Topographical map showing the Mountain S t a t i o n and North Shore Study areas 27 8. Sketch Map of the Mountain S t a t i o n study area 28 9. Tank Creek hydrograph 34 10. P o s t l e S p r i n g hydrograph 36 11. Anderson Creek hydrograph 38 12. Sketch map of North Shore study area 48 13. Morley S p r i n g hydrograph 51 14. Top o g r a p h i c a l map showing the Slocan V a l l e y study area 55 15. Sketch map of the Slocan V a l l e y study area 57 16. Chou Creek hydrogrph 61 17. E l l i o t t Creek hydrograph 63 v i CHAPTER 1 - INTRODUCTION Problem Wi t h i n the Nelson F o r e s t Region there are numerous small s p r i n g s and streams t h a t are c u r r e n t l y being used as sources of both domestic and i r r i g a t i o n a l water. Although l i c e n c e d by the M i n i s t r y of Environment, Water Management Branch, these r i p a r i a n p r o p r i e t o r s have no l e g a l recourse should t h i s resource be d i s r u p t e d due to an o f f i c i a l l y s a nctioned, but p o o r l y planned development scheme. The mandate of the Water Management Branch i s simply to i n s u r e t h a t the s p r i n g s are not l i c e n c e d beyond t h e i r s u s t a i n a b l e y i e l d and to e s t a b l i s h a temporal p r i o r i t y f o r water use. I t i s d i f f i c u l t , however to determine the exact y i e l d of these l o c a l water resources as they are very s u s c e p t i b l e to changes i n the weather. The accuracy of p r e d i c t i n g a s u s t a i n a b l e y i e l d i s f u r t h e r complicated by the f a c t t h a t on any given day a l i c e n c e e i s not l i k e l y to use h i s e n t i r e e n t i t l e m e n t and t h e r e f o r e a c o n s i d e r a b l e s u r p l u s may be generated. The mandate of the M i n i s t r y of F o r e s t s , however, i n c l u d e s managing B r i t i s h Columbia's f o r e s t resources f o r the b e n e f i t of a l l p r o v i n c i a l r e s i d e n t s . An apparent c o n f l i c t of i n t e r e s t a r i s e s when l i c e n c e d r i p a r i a n s i n t e r p r e t a proposed l o g g i n g p l a n as a t h r e a t to t h e i r water supply. Residents o f t e n f e e l t h a t the f o r e s t resource i s being managed without due c o n s i d e r a t i o n of l o c a l concerns. Such problems have r e c e n t l y been brought to the f o r e i n p u b l i c meetings convened by the Nelson Region of the M i n i s t r y of F o r e s t s to d i s c u s s proposed developments i n the Slocan V a l l e y and 1 Kootenay Lake areas ( F i g . 1 ) . These areas c o n t a i n many small flow systems. The p h y s i c a l c h a r a c t e r i s t i c s of these systems are not e a s i l y i d e n t i f i e d and as such they may present a management problem f o r f u t u r e development. With the aim of o b t a i n i n g an amicable s o l u t i o n t o these problems, the r e g i o n a l headquarters of the M i n i s t r y of F o r e s t s , i n c o n j u n c t i o n with the concerned d i s t r i c t , have i n t e n s i f i e d t h e i r s t u d i e s of the p h y s i c a l parameters governing the areas i n q u e s t i o n . O b j e c t i v e s The aim of t h i s study was to determine the r e l a t i v e c o n t r i b u t i o n s of prestorm water and storm r u n o f f to t o t a l flow i n s e l e c t e d small s p r i n g s and creeks w i t h i n the Kootenays. This w i l l be accomplished u s i n g both the i s o t o p i c and conductance methods of hydrograph s e p a r a t i o n . The r e s u l t s of t h i s a n a l y s i s w i l l i n d i c a t e the r e l a t i v e c o n t r i b u t i o n s of ove r l a n d flow, i n t e r f l o w and groundwater to t o t a l storm r u n o f f . As a secondary o b j e c t i v e , the r e l a t i v e c o n t r i b u t i o n s of the components to t o t a l storm r u n o f f w i l l be combined with p r e v i o u s l y e s t a b l i s h e d knowledge i n the f i e l d of f o r e s t hydrology to o b t a i n i n s i g h t i n t o the f u n c t i o n i n g of the l o c a l s p r i n g s and creeks i n the Nelson Lake and Slocan V a l l e y areas. T h i s i n f o r m a t i o n w i l l be used to ev a l u a t e how f u t u r e development plans might a f f e c t the q u a l i t y and q u a n t i t y of the water r e s o u r c e . I f adverse impacts are a n t i c i p a t e d recommendations w i l l be made as to how the v a r i o u s development schemes c o u l d be implemented to minimize any d e l e t e r i o u s e f f e c t s . 2 I I 1 1 1 5 10 15 20 25 kilometers (h i g h l i g h t i n g delineates study areas) F i g . 1 West Kootenays 3 Review In a'ddition to the v a r i a b l e s of geology, topography and c l i m a t e , n a t u r a l v e g e t a t i v e cover has a l a r g e i n f l u e n c e on watershed hydrology. I t has been shown t h a t v e g e t a t i v e cover decreases r u n o f f through i n t e r c e p t i o n and subsequent e v a p o r a t i o n (Helvey 19 71). A f o r e s t canopy w i l l reduce the t h r o u g h f a l l of p r e c i p i t a t i o n and thereby l i m i t the amount of water i n f i l t r a t i n g the ground. The magnitude of t h i s e f f e c t depends upon the type and i n t e n s i t y of the p r e c i p i t a t i o n , as w e l l as v a r i a b l e s such as percent crown c l o s u r e , t r e e h e i g h t and t r e e s p e c i e s . V e g e t a t i v e cover a l s o decreases the amount of r u n o f f through t r a n s p i r a t i o n (Hewlett and Nutter 1969). T h i s e f f e c t i s g r e a t e s t d u r i n g the s p r i n g and summer when the m a j o r i t y of p l a n t growth occu r s . The a c t u a l amount of water t r a n s p i r e d w i l l depend upon the type of p l a n t ( i t s s u r f a c e area and r o o t i n g depth) and the a v a i l a b i l i t y of water (as r e f l e c t e d i n the c l i m a t e and the a b i l i t y of the s o i l to r e t a i n a v a i l a b l e m o i s t u r e ) . C r o f t (1948) found t h a t e v a p o t r a n s p i r a t i o n of r i p a r i a n v e g e t a t i o n can account f o r up to 33% of t o t a l flow d u r i n g the l a t e summer. The r o o t i n g system of p l a n t s i s a l s o r e s p o n s i b l e f o r m a i n t a i n i n g a high v o i d r a t i o w i t h i n the s o i l . The v o i d r a t i o , i n t u r n , i n c r e a s e s d e t e n t i o n storage thus d e c r e a s i n g peak flow, p r o l o n g i n g r u n o f f and m a i n t a i n i n g a high p e r c o l a t i o n r a t e . I f the v e g e t a t i o n i s removed the s o i l may become more compacted r e s u l t i n g i n an i n c r e a s e i n the r a t i o of o v e r l a n d flow to subsurface flow (Chamberlin 1972). R e t e n t i o n storage, on the other hand, i s p r i m a r i l y a f u n c t i o n of s o i l p a r t i c l e s i z e . V e g e t a t i v e cover can i n d i r e c t l y a f f e c t the amount o f moisture 4 h e l d by the s o i l through i n p u t s of decomposing l i t t e r . Although f o r e s t h a r v e s t i n g may cause a temporary r e d u c t i o n i n the o r g a n i c m a t e r i a l a v a i l a b l e to the s o i l i t i s u n l i k e l y to have a l a r g e e f f e c t upon the r e t e n t i o n storage as the time r e q u i r e d f o r r e g e n e r a t i o n of v e g e t a t i v e cover i s s h o r t i n comparison to s o i l g e n e s i s . A w e l l developed p l a n t canopy w i l l a l s o reduce ev a p o r a t i o n from the s o i l s u r f a c e by b l o c k i n g i n c i d e n t r a d i a t i o n . T h i s e f f e c t i s f u r t h e r enhanced by v e g e t a t i o n which lowers the vapour pressure g r a d i e n t by s h e l t e r i n g the moist s o i l from s u r f a c e winds. V e g e t a t i v e cover a l s o i n f l u e n c e s the q u a n t i t y and d i s t r i b u t i o n of a snow pack (Golding 1974) . In a dense f o r e s t the o v e r a l l snow pack w i l l be reduced due to i n t e r c e p t i o n . In a more open or patch cut f o r e s t the accumulation may be i n c r e a s e d due to the turbulence caused by the uneven canopy. With very l i t t l e v e g e t a t i v e cover, however, the snow pack may be reduced due to d r i f t and scour. When the d i f f e r e n t e f f e c t s of v e g e t a t i v e cover are t a l l i e d , i t seems q u i t e c l e a r t h a t the t o t a l d i s c h a r g e of a watershed w i l l not be reduced i f the f o r e s t cover i s removed, and i n f a c t , i n most cases i t w i l l i n c r e a s e (Anderson, Hoover and Reinhart 1976). Due to the many d i f f e r e n t f o r c e s exerted by v e g e t a t i v e cover over r u n o f f p a t t e r n s and c o n s i d e r i n g the d i f f i c u l t y of o b t a i n i n g p r e c i s e , r e l i a b l e data, pretreatment q u a n t i f i c a t i o n of t h i s statement i s d i f f i c u l t . These f a c t o r s a l s o make t h i s e m p i r i c a l r e l a t i o n s h i p s i t e - s p e c i f i c and t h e r e f o r e the i n f o r m a t i o n 5 concerning one watershed cannot be t r a n s f e r r e d to another area without a high p r o b a b i l i t y of e r r o r . In some i n s t a n c e s , however, the e f f e c t of v e g e t a t i v e cover on t o t a l y i e l d i s not as important as the time d i s t r i b u t i o n of r u n o f f . Some r e s e a r c h e r s have shown t h a t p l a n t cover can improve s o i l s t r u c t u r e and thereby i n c r e a s e i t s p e r c o l a t i o n r a t e and moisture storage c a p a c i t y . T h i s e f f e c t can i n t u r n lead to an i n c r e a s e i n groundwater flow as opposed to s u r f a c e r u n o f f (Bates 1934, Tennessee V a l l e y A u t h o r i t y 1955). The net r e s u l t of these e f f e c t s i s to more evenly d i s t r i b u t e r u n o f f throughout the year. These r e s u l t s , however, are o n l y l i k e l y to occur i n extreme cases such as the r e v e g e t a t i o n of abused farmland. S t u d i e s have a l s o shown t h a t removal of v e g e t a t i v e cover w i l l i n c r e a s e the t o t a l amount of water a v a i l a b l e f o r r u n o f f which, i n t u r n , w i l l i n c r e a s e flow d u r i n g the summer and f a l l p e r i o d s when the demand f o r water i s g r e a t e s t (Reinhart, Eschner, Trimble 1963). Rbthacher (1970) found t h a t f o r a watershed i n Oregon, 80% of a measured i n c r e a s e i n r u n o f f took p l a c e d u r i n g the winter months. The 20% of the i n c r e a s e d r u n o f f t h a t o c c u r r e d over the summer, however, represented a 150% i n c r e a s e i n the pretreatment low flow measurements, f o r every square k i l o m e t e r c l e a r c u t t h i s 6 r e p r e s e n t s an i n c r e a s e of 1.3 x 10 1 per day. Rothacher (1970) a t t r i b u t e s t h i s i n c r e a s e to reduced e v a p o t r a n s p i r a t i o n , which leads to a g r e a t e r amount of water being h e l d i n both r e t e n t i o n and d e t e n t i o n storage. There s t i l l seems to be c o n s i d e r a b l e c o n t r o v e r s y over the e f f e c t s of f o r e s t h a r v e s t i n g p r a c t i c e s on peak flows. Although Anderson and Hobba (1959) determined t h a t an observed i n c r e a s e i n 6 the s i z e of peak streamflow was a t t r i b u t a b l e to l o g g i n g p r a c t i c e s , H a r r i s (1977) f a i l e d to d e t e c t any s i g n i f i c a n t d i f f e r e n c e i n the s i z e of peak flow a f t e r c l e a r c u t t i n g a watershed i n western Oregon. S t u d i e s conducted by Cheng (1975) and d e V r i e s and Chow (1973) i n B r i t i s h Columbia found a decrease i n the s i z e of peak flows a f t e r c l e a r c u t t i n g as d i d Harr and McCorison (1979) i n Oregon. de V r i e s and Cheng a t t r i b u t e d t h i s r e d u c t i o n to the d i s r u p t i o n of the subsurface channel networks due to l o g g i n g . Other s t u d i e s (Harr, Harper, K r y g i e r , Hsieh 1975, Harr 1976) found an i n c r e a s e i n peak r u n o f f , but a t t r i b u t e d i t t o a high degree of s o i l d i s t u r b a n c e and not to the removal of v e g e t a t i v e cover. The f a c t t h a t f o r e s t s are a renewable resource means t h a t under normal l o g g i n g p r a c t i c e s the system w i l l tend to r e t u r n t o i t s n a t u r a l s t a t e once the treatment i s completed. Again, the exact r a t e of recovery w i l l depend upon many f a c t o r s , but n a t u r a l r e v e g e t a t i o n u s u a l l y reduces the i n i t i a l e f f e c t s on water y i e l d by about 50% a f t e r the f i r s t 10 years (Anderson, Hoover, R e i n h a r t 1976) . The hydrology of a watershed i s not onl y a f f e c t e d by i t s v e g e t a t i v e cover but a l s o by p r a c t i c e s a s s o c i a t e d with f o r e s t h a r v e s t i n g , such as road b u i l d i n g , s k i d d i n g and s l a s h burning (Harr, Harper, K r y g i e r , Hsieh 1975) . These p r a c t i c e s u s u a l l y have the e f f e c t of s o i l compaction and thereby reduce i n f i l t r a t i o n r a t e s and storage c a p a c i t i e s . Under extreme c o n d i t i o n s , such as on the s u r f a c e s of roads, compaction may r e s u l t i n the ge n e r a t i o n of s u r f a c e flow , which can lead t o 7 h i g h e r peak flows d u r i n g storm c o n d i t i o n s and lower flows under d r i e r c o n d i t i o n s . The magnitude of t h i s e f f e c t , however, i s l i k e l y to be small as the area d e d i c a t e d to road c o n s t r u c t i o n u s u a l l y r e p r e s e n t s o n l y a small p r o p o r t i o n of the t o t a l watershed. Zimmer (1981) found t h a t u n l e s s at l e a s t 12% of the watershed was covered by road c o n s t r u c t i o n there was no s i g n i f i c a n t change i n the magnitude of peak flows. The d i v e r s i o n of subsurface flow to s u r f a c e r u n o f f i s f u r t h e r i l l u s t r a t e d i n a study conducted by Megahan (1972) . He found t h a t the cut bank of a haul road i n t e r c e p t e d 28% of a l l subsurface flow with the r e s u l t of d e c r e a s i n g s o i l moisture i n down slope l o c a t i o n s . As p r e v i o u s l y noted, the change i n the hydrology of a watershed a f t e r f o r e s t h a r v e s t i n g may be p a r t i a l l y due to the change i n the r a t i o of d i r e c t r u n o f f to base flow. U n t i l the advent of s t a b l e i s o t o p e methodologies, the s e p a r a t i o n of a hydrograph i n t o i t s component p a r t s of s u r f a c e flow and i n t e r f l o w (storm r u n o f f ) and groundwater flow (prestorm r u n o f f ) was accomplished g e o m e t r i c a l l y (Wilson 1969). One of the most common methods of i s o l a t i n g base flow from the r e s t of the hydrograph i n v o l v e s e x t r a p o l a t i n g the prestorm r e c e s s i o n a l limb to a p o i n t under the peak of the storm hydrograph ( F i g . 2). From here the l i n e i s extended f o r a d i s t a n c e N on the r e c e s s i o n a l limb of the stream hydrograph a c c o r d i n g to the equation: 0.11 N=A (Eq.l) where N i s time i n days from the peak of the hydrograph and A i s the area of the drainage b a s i n i n square k i l o m e t e r s ( L i n s l e y , Kohler, Paulhus 1976) . Anything below t h i s l i n e i s l a b e l e d as 8 Time (days) F i g . 2 Geometric Hydrograph Separation base flow, while the p a r t of the hydrograph above the l i n e i s co n s i d e r e d to be d i r e c t r u n o f f . In the example c i t e d i n F i g . 2, 43% of the peak r u n o f f i s l a b e l e d as o r i g i n a t i n g as prestorm water. Another method of hydrograph s e p a r a t i o n o r i g i n a l l y d e vised by Barnes i n 1939 e n t a i l s p l o t t i n g the di s c h a r g e measurements on a l o g a r i t h m i c s c a l e and time on a l i n e a r s c a l e (Ward 1967). The base flow i s then determined by extending the r e c e s s i o n limb of the hydrograph backwards from i t s p o i n t of i n f l e c t i o n u n t i l i t i n t e r s e c t s a v e r t i c a l l i n e dropped from the p o i n t of maximum d i s c h a r g e . From here the l i n e i s then connected to the i n i t i a l i n f l e c t i o n p o i n t of the hydrograph. Using the same data as c i t e d i n F i g . 2 t h i s second method a l l o c a t e s approximately 52% of the peak r u n o f f to prestorm water ( F i g s . 3 & 4). Hewlett a l s o has an a r b i t r a r y method of i s o l a t i n g the .prestorm component of a hydrograph (Hewlett, Hibbard 1967). His constant slope method extends a tangent from the i n i t i a l i n f l e c t i o n p o i n t on the r i s i n g limb u n t i l i t i n t e r s e c t s the r e c e s s i o n limb. The slope of t h i s l i n e was s e t to 3.66 2 1/s/km /hr . The i l l u s t r a t i o n of t h i s method i n F i g . 5 i n d i c a t e s t h a t approximately 65% of peak flow o r i g i n a t e d as prestorm water. From the hydrographs d e p i c t i n g these methods i t i s ev i d e n t t h a t each a t t r i b u t e s a d i f f e r e n t v alue t o the base flow component. As such they do not r e f l e c t q u a n t i t a t i v e measurements and are onl y v a l i d when used i n a n a l y t i c a l comparisons (e.g., the c l a s s i f i c a t i o n of stream response t o p r e c i p i t a t i o n i n p u t s ) . The advent of q u a n t i t i v e methods of hydrograph s e p a r a t i o n began i n 1967 when LaSala obtained a c l o s e c o r r e l a t i o n between 10 1000 J 100 Flow ( l / s ) 10 -I peak r i s i n g limb >^ recession limb storm water* prestorm water hydrograph separation l i n e T 8 1 2 3 4 5 6 7 Time (days) Fig. 3 Barnes method of hydrograph separation on a logarithmic scale r o 700 600 500 400 Flow (l/s) 200 -I _00 peak rising limb / \\ recession limb - hydrograph separation line J storm water \\ \\ \\ \\ \\ v. \\ prestorm water v ^ \\ I , , 1 4 5 Time (days) Fig. 4 Barnes method of hydrograph separation converted to a linear scale Fig. 5 Hewlett's constant slope method of hydrograph separation the t o t a l d i s s o l v e d s o l i d (TDS) l o a d i n g of stream water samples and the stream's d i s c h a r g e . A few years l a t e r Pinder and Jones (1969) and Newbury, Cherry and Cox (1969) used the r e l a t i v e c o n c e n t r a t i o n s of v a r i o u s ions i n groundwater and stream d i s c h a r g e as a method of hydrograph s e p a r a t i o n . The study conducted by Pinder and Jones (1969) took plac e i n three watersheds i n Nova S c o t i a . Instead of measuring the r e l a t i v e abundance of TDS w i t h i n the water samples they separated groundwater flow from d i r e c t r u n o f f by measuring the r e l a t i v e c o n c e n t r a t i o n s of s p e c i f i c i o n s . When these values were averaged they found t h a t at peak d i s c h a r g e groundwater accounted f o r as much as 42% of t o t a l r u n o f f . During the study, however, Pinder and Jones found t h a t prestorm water taken from the head waters of a stream contained a p p r e c i a b l y fewer ions than water samples taken from the lower reaches of the same water course. They a t t r i b u t e d t h i s f i n d i n g t o the d i f f e r e n c e i n the g e o l o g i c a l composition of the s u b s t r a t e and to the amount of time the water was r e s i d e n t i n the v a r i o u s s t r a t a p r i o r to d i s c h a r g e . The accuracy of t h i s method of hydrograph s e p a r a t i o n i s t h e r e f o r e i n f l u e n c e d by the chemical r e a c t i o n s t a k i n g p l a c e between r u n o f f and the s u b s t r a t e . In the study conducted by Newbury, Cherry and Cox (1969) s p e c i f i c ions were a l s o used as the b a s i s of hydrograph s e p a r a t i o n but they were a l s o a b l e to prove a c l o s e c o r r e l a t i o n between the average c o n c e n t r a t i o n of the sum of the ions and the e l e c t r i c a l c o n d u c t i v i t y of the water sample. In a d d i t i o n to d i f f e r e n t i a t i n g between prestorm water and storm water they were able to separate d i r e c t r u n o f f i n t o o v e r l a n d flow and i n t e r f l o w . By u s i n g a network of piezometers they were able to show t h a t the c o n c e n t r a t i o n of s u l f a t e ions i n i n t e r f l o w was n e g l i g i b l e . W i t h i n the study s i t e the time r e q u i r e d f o r r u n o f f to pickup t r a c e s of s u l f a t e was such t h a t o n l y groundwater d i s p l a y e d any a p p r e c i a b l e c o n c e n t r a t i o n of t h i s i o n . T h i s study showed the groundwater component of t o t a l r u n o f f to be as h i g h as 41%. From these s t u d i e s i t i s obvious t h a t the use of ions as a method of hydrograph s e p a r a t i o n can q u a n t i f y the amount of r u n o f f a t t r i b u t a b l e to groundwater. Although the i n h e r e n t i n a c c u r a c y of t h i s method may be c o n s i d e r a b l e , u n l i k e the g r a p h i c a l methods of hydrograph s e p a r a t i o n i t r e f l e c t s the t r u e dynamics of the r u n o f f system. In the mid 1970's Sk l a s h , Farvolden and F r i t z (1975) began u s i n g the r a t i o of oxygen-18 to oxygen-16 i n water as a means of hydrograph s e p a r a t i o n . T h e i r study was based oh the premise t h a t due to recharge and d i s p e r s i o n processes, groundwater a t t a i n s a uniform i s o t o p i c content t h a t r e f l e c t s the average of the annual p r e c i p i t a t i o n events. T h e r e f o r e the water d e p o s i t e d by a storm t h a t has a d i f f e r e n t r a t i o of oxygen-18 to oxygen-16 would produce a change i n the i s o t o p i c content of the prestorm water. Since oxygen-18 i s a s t a b l e i s o t o p e , i t s r e l a t i v e abundance can o n l y be changed through f r a c t i o n a t i o n or mixing. F r a c t i o n a t i o n i n water i s dependent upon d i f f e r i n g vapor p r e s s u r e s , and under the s a t u r a t e d c o n d i t i o n s of a p r e c i p i t a t i o n event i s u n l i k e l y to r e s u l t i n a p e r c e p t i b l e d i f f e r e n c e i n the i s o t o p i c r a t i o . As a r e s u l t , the i s o t o p i c content of prestorm water can only be a l t e r e d through mixing w i t h storm water. For 15 s h o r t d u r a t i o n p r e c i p i t a t i o n events the change i n the number of oxygen-18 atoms present i n t o t a l r u n o f f w i l l p r o v i d e a means by which prestorm water can be d i s t i n g u i s h e d from the water accumulated by the drainage b a s i n d u r i n g the storm. A more d e t a i l e d e x p l a n a t i o n of the use of n a t u r a l i s o t o p e s i n hydrology can be found i n F r i t z (1981) and Faure (1977). The study areas s e l e c t e d by Sklash, Farvolden and F r i t z (1975) were two l a r g e (700 sq. km) watersheds i n southern O n t a r i o . The s o i l s were p r i m a r i l y g l a c i a l sand and t i l l and were predominantly used as farm land. On 16 May 1974 a storm d e p o s i t e d approximately 2.5 cm of r a i n on the study areas and hydrographs and water samples were c o l l e c t e d . Sklash's i n t e r p r e t a t i o n of the r e s u l t s of i s o t o p i c a n a l y s i s showed t h a t at peak d i s c h a r g e s , up to 70% of the flow was groundwater. The p r o p o r t i o n of groundwater c o n t r i b u t i n g t o the storm d i s c h a r g e was found to be l a r g e r i n downstream areas than i n upstream areas. T h i s t r e n d was a t t r i b u t e d i n p a r t to more e f f i c i e n t groundwater drainage i n downstream areas. F i g . 6 i s an example of the data obtained at one of the sampling s i t e s . I t i s the same hydrograph as t h a t used i n the p r e v i o u s examples but i n t h i s i n s t a n c e the s e p a r a t i o n l i n e q u a n t i t a t i v e l y r e p r e s e n t s the amount of groundwater c o n t r i b u t i n g t o the storm r u n o f f . T h i s method of hydrograph s e p a r a t i o n r e v e a l s t h a t 66% of the peak, r u n o f f can be a t t r i b u t e d t o prestorm water. The prevalance of oxygen-18 i n any g i v e n sample i s always expressed as a r a t i o (r) of the abundance of the h e a v i e r oxygen atoms to those of oxygen-16. 18 16 r(sample)= 0/ 0 (Eq. 2) F i g . 6 Isotopic method of hydrograph separation By convention t h i s v alue i s compared to a standard r a t i o and the d i f f e r e n c e recorded as a d e l (d) value (Jacobs, R u s s e l l , Wilson 1974). 18 d 0 = [ r ( s a m p l e ) - r ( s t a n d a r d ) ] / r ( s t a n d a r d ) (Eq. 3) I f the sample has a higher r a t i o of oxygen-18 atoms than does the standard i t i s s a i d t o be e n r i c h e d and i s denoted by a 18 p o s i t i v e value (e.g., d O=+5.0). I f the r e v e r s e i s t r u e , the sample i s s a i d t o be d e p l e t e d and the numerical v a l u e i s preceded 18 by a n e g a t i v e s i g n (e.g., d O=-5.0). In most s t u d i e s t h i s v alue i s then m u l t i p l i e d by v1000 to g i v e a f i n a l d e t e r m i n a t i o n i n p a r t s per thousand (%«,) or g/1. When determining the oxygen-18 content of water the most wid e l y used r e f e r e n c e i s Standard Mean Ocean Water (SMOW), and by convention t h i s i s taken as having an i s o t o p i c content of par 18 ( i . e , d 0=0.0). Since both oxygen-18 and oxygen-16 are s t a b l e i s o t o p e s (not undergoing r a d i o a c t i v e decay) t h e i r r e l a t i v e abundance i s c o n t r o l l e d through f r a c t i o n a t i o n (c~) . dx/x °«- = (Eq. 4) dy/y Where