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Paleohydrology of the Bella Coola River basin : an assessment of environmental reconstruction 1987

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PALEOHYDROLOGY OF THE BELLA COOLA RIVER BASIN AN ASSESSMENT OF ENVIRONMENTAL RECONSTRUCTION By JOSEPH ROBERT DESLOGES B . E . S . , U n i v e r s i t y of W a t e r l o o , 1980 M . S c , U n i v e r s i t y of W i s c o n s i n - M a d i s o n , 1982 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n THE FACULTY OF GRADUATE STUDIES (Department of Geography) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA OCTOBER 1987 w J o s e p h R o b e r t D e s l o g e s , 1987 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Geography The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date October 10, 1987 DE-6f.Vft-n i i ABSTRACT Recent geomorphic and hydrologic environments of a mid-latitude alpine basin are investigated under the integrative theme of paleohydrology. The aims of t h i s research are: 1) to characterize the response of selected b i o l o g i c a l and geophysical elements to recent c l i m a t i c change; 2) to determine the resolution and length of paleoenvironmental records in the study area; and 3) to ascertain the s i g n i f i c a n c e of observed and inferred environmental change over the L i t t l e Ice Age i n t e r v a l . 2 Bella Coola River drains 5050 km of g l a c i e r i z e d mountains along the central coast of B r i t i s h Columbia. B i o l o g i c a l elements examined on a basin- wide scale included: tree-growth in temperature and moisture-stressed environments, damage to trees in g l a c i a l and f l u v i a l settings, pollen v a r i a t i o n s in a v a r i e t y of sedimentary deposits and s o i l development. Geophysical elements include primarily g l a c i o - l a c u s t r i n e and f l o o d p l a i n sediments, g l a c i e r deposits and r i v e r channel morphology. A retrospective strategy was adopted by testing i n i t i a l l y for the nature of r e l a t i o n s h i p s between synoptic climate, basin hydrology and element response during the period of instrument record (1900 AD to present). Inferences about pre- instrument environments were then made using the proxy data. Events of several types are c h a r a c t e r i s t i c a l l y mixed in a response record. Variations in Douglas and subalpine f i r growth, g l a c i o - l a c u s t r i n e sedimentation rates, g l a c i e r f l u c t u a t i o n s and s h i f t i n g of the B e l l a Coola River r e f l e c t a combination of persistent and e p i s o d i c a l l y extreme behavior. Glaciers appear to respond by advancing or retreating a f t e r departures in winter p r e c i p i t a t i o n persistent for several years. Extreme events, p a r t i c u l a r l y high-magnitude autumn floods, are not e x c l u s i v e l y linked to a p a r t i c u l a r set of mean c l i m a t i c departures. This makes inferences from proxy data such as f l o o d p l a i n deposits and flood-damaged i i i vegetation d i f f i c u l t . Periods of increased flood frequency are supposed to rel a t e to an increase in fl o o d p l a i n sedimentation. Except in very favorable circumstances, paleoenvironmental methods do not have the resolution promised. Climatic information recoverable from tree-ring data and g l a c i o - l a c u s t r i n e sediments is of considerably lower than annual r e s o l u t i o n . S t a t i s t i c a l l y based climate models using proxy data as independent variables produce low levels of explained variance. Proxy data sources in the basin were largely r e s t r i c t e d to the l a s t 300 to kOO years or L i t t l e Ice Age i n t e r v a l . Most g l a c i e r s in the basin reached L i t t l e Ice Age maxima in the middle of the 19th century in response to below average temperatures and above average p r e c i p i t a t i o n between approximately 1800 and 1855 AD. Tree- ring data and equilibrium l i n e a l t i t u d e s on g l a c i e r s indicate that p r e c i p i t a t i o n was on average 25 to 30% greater than the 1951-1980 mean. Inferred below average temperatures in the early l8th century probably signaled the beginning of the L i t t l e Ice Age along the cent r a l coast; however, there was not a major response in g l a c i e r s u n t i l persistent p o s i t i v e departures in p r e c i p i t a t i o n occurred. Recession of g l a c i e r s from L i t t l e Ice Age maxima was slowed by cooler and wetter conditions between I885 and 1900 AD. The persistence of warmer and d r i e r conditions in the f i r s t half of the 20th century was exceptional in comparison with inferred climate of the las t 330 years. Major floods in 1805/06, 1826, 1885 and 1896 correspond to intervals of increased p r e c i p i t a t i o n . i v PALEOHYDROLOGY OF THE BELLA COOLA RIVER BASIN: ASSESSMENT OF ENVIRONMENTAL RECONSTRUCTION Chapter I: INTRODUCTION (1.1) Systems Framework 1 (1.2) Operational Approaches 4 Process models 4 Empirical models 5 Inductive models 7 (1.3) Objectives and Research Strategy 9 (1.4) Data Sources 10 (1.5) Organization 13 Chapter I I: STUDY AREA (2.0) Location 15 (2.1) Physiography 18 (2.2) Bedrock Geology 19 (2.3) Late Quaternary Geology 23 (2.it) Climate Setting 28 (2.5) Hydrology 32 Average Regime 32 Major Floods During the 20th Century 36 (2.6) Sources and Transfer of Clastic Sediment 38 Upland Sediment Sources itO (2.7) Pedologic Setting 46 (2.8) Flora 48 (2.9) Settlement and Logging History 50 Chapter III: HYDROPHYSICAL RECORDS OF ENVIRONMENTAL CHANGE: TESTS WITHIN THE INSTRUMENT PERIOD (3.0) Introduction . 52 (3.1) Post-1945 Synoptic Climatology of the N.E. Pacific Sector 52 Secular Trends in Temperature and Precipitation 55 Comparison With Other Coastal Regions 57 Atmospheric Circulation 60 Frequency and Seasonal Persistence of Synoptic Types 62 (3.2) Response of Hydrologic Variables to Climate Change 69 Regional Winter Snowpack 69 Spr i ng Runoff 73 Spring and Summer Runoff - Bella Coola River 77 Autumn Floods 82 Flood Frequency 87 (3.3) Long-Term, High Resolution Climate Analysis 90 Comparisons With Other Regions 98 (3.4) Conclusions 99 V C h a p t e r IV: GEOMORPHOLOGICAL EVIDENCE OF RESPONSE OF GEOPHYSICAL SYSTEMS TO ENVIRONMENTAL CHANGE: TEST WITHIN THE HISTORICAL RECORD (k.O) I n t r o d u c t i o n 101 (4.1) G l a c i e r F l u c t u a t i o n s and Recent C l i m a t e Change 102 Mass B a l a n c e F l u c t u a t i o n s of G l a c i e r s 103 Mass B a l a n c e and C l i m a t e 107 G l a c i e r Snout F l u c t u a t i o n s 110 (4.2) Recent F l u c t u a t i o n s in Up land Sediment T r a n s f e r s 115 (4.3) Sediment S o u r c e s and P r o c e s s e s of F l o o d p l a i n Development 121 P r o c e s s e s of F l o o d p l a i n Development 121 A l l u v i a l Sed iment S o u r c e s 127 (4.4) E q u i l i b r i u m C o n d i t i o n s and I n f e r e n c e s f rom Channe l Morpho logy 131 V e r t i c a l and L a t e r a l S t a b i l i t y o f B e l l a C o o l a R i v e r 132 I n f e r e n c e s From Channe l Morpho logy ' 137 (4.5) Recent F l o o d p l a i n S e d i m e n t a t i o n 140 (4.6) C o n c l u s i o n s 141 Chapte r V: SEDIMENT0L0GICAL EVIDENCE OF ENVIRONMENTAL CHANGE: TESTS USING LAKE SEDIMENTATION RATES (5.0) I n t r o d u c t i o n 148 (5.1) P a t t e r n s of S e d i m e n t a t i o n in Ape Lake 149 P h y s i c a l S e t t i n g 149 Sediment F a c i e s 15̂ Recent and Long-Term S e d i m e n t a t i o n 156 (5-2) P e r i o d i c i t y o f S e d i m e n t a t i o n in Ape Lake 164 R e s u l t s 166 (5.3) C h r o n o l o g y and C o n t r o l s of S e d i m e n t a t i o n Ra tes 169 Recent S e d i m e n t a t i o n C h r o n o l o g y 170 C o n t r o l s o f G l a c i o - L a c u s t r i n e S e d i m e n t a t i o n Ra tes 172 (5.4) I n f e r e n c e s f rom Long-Term V a r i a t i o n s in G l a c i o - L a c u s t r i n e D e p o s i t i o n 176 Key E v e n t s 178 H y d r o c l imat i c I n f e r e n c e s l8l (5.5) Summary and C o n c l u s i o n s 182 C h a p t e r V I : BIOLOGICAL EVIDENCE OF ENVIRONMENTAL CHANGE: TESTS USING VARIATIONS IN TREE GROWTH (6.0) I n t r o d u c t i o n 184 (6.1) T r e e - G r o w t h and C l i m a t e 184 Methods 187 (6.2) Response C h a r a c t e r i s t i c s 191 (6.3) Growth V a r i a t i o n s and C l i m a t e 194 I n t e r i o r Doug las f i r s 19** S u b a l p i n e f i r 197 (6.4) Development o f T r a n s f e r F u n c t i o n s 200 (6.5) I n f e r e n c e s about 20th C e n t u r y H y d r o l o g y From T r e e - vi Rings 208 Summer Runoff 208 Rainstorm and Snowmelt Flooding 212 (6.6) Summary and Conclusions 215 Chapter VII: INFERENCES ABOUT PRE-INSTRUMENT ENVIRONMENTS IN THE BELLA C00LA RIVER BASIN (7.0) Introduction 217 (7.1) Inferences of Environmental Change From Former G l a c i a l Extent 217 Snowline Fluctuations and Climate Change 218 Estimates of the Contemporary Climatic Snowline 221 Estimates of Former Snowline and Inferences of Hydrologic Change 223 L i t t l e Ice Age G l a c i a l Chronology 227 (7.2) Long-Term, Low and High Resolution Biogeophysical Evidence 230 Fluctuations in Average Temperature and P r e c i p i t a t i o n 231 Inferences from Lake Sedimentation 235 High-Frequency Variations in Tree Growth, Lake Sedimentation Rates and Related Hydroclimatic I nf erences 237 (7.3) Effects on the Bella Coola Valley 240 Floodplain Age 240 Evidence for a Long-Term Flood History 245 Long-Term Floodplain Sedimentation 246 Chapter VIII: SYNTHESIS, CONCLUSIONS AND FUTURE DIRECTIONS (8.1) Methodolgical Implications and Biogeophysical Response Records 252 Recent Hydrocl imat i c Record 253 Tree-Ring Response Record 252 Glac i o-Lacustr i ne Response Record 256 Glacier Response Record 257 A l l u v i a l Response Record 259 General Conclusion 26l (8.2) Recent Environments of the B r i t i s h Columbia Mid-Coast 262 L i t t l e Ice Age Environment 263 (8.3) Future Directions 265 REFERENCES 268 Appendix A: RADIOCARBON DATES OF SELECTED DEPOSITS FROM THE BELLA COOLA BASIN 289 (A.1) Radiocarbon Dating 290 vi i Appendix B: TEXTURAL AND MINERALOGICAL VARIATIONS OF THE BELLA COOLA VALLEY-FILL SEDIMENTS 292 (B.1) Introduction 293 (B.2) Bulk Gravel Samples 293 Results 29̂ (B.3) Mineralogy of the V a l l e y - f i l l 296 Results 297 Appendix C: RECENT PATTERNS OF SEDIMENTATION IN THE BELLA COOLA VALLEY 304 ( C l ) Introduction 305 (C.2) Sampling Design and Methods 305 Rambeau Slough 310 East Hagensborg Slough 310 Walker Island Slough 312 Snootli Slough 313 Mclellan Road Slough 315 Appendix D: APE LAKE SEDIMENTS: SAMPLING, MEASUREMENT AND SUMMARY OF RESULTS 317 (D.l) Introduction 318 (D.2) F i e l d and Laboratory Procedures 318 Compaction and D i s t o r t i o n of Sediments 319 (D.3) P e r i o d i c i t y of Sedimentation at Ape Lake 321 Results 324 Appendix E: TREE-RING SITE CHRONOLOGIES IN AND NEAR BELLA COOLA BASIN 330 (E.1) Introduction 331 (E.2) Tree-Ring Data Ac q u i s i t i o n 331 Tree-Ring Data 334 Appendix F: APPLICATION OF PALE0HYDR0L0GICAL TECHNIQUES FOR RECONSTRUCTING FORMER CONFIGURATIONS OF GLACIERS IN THE BELLA COOLA RIVER BASIN 3̂ 5 (F.l) Accumulation Area Ratios..... 3̂+6 (F.2) Reconstructing Former Climatic Snowlines 3̂ 9 (F.3) Glacier Chronologies for the Be l l a Coola Basin 350 Methods 351 (F.4) Description of Glacier Chronologies at Selected Sites 355 East Nusatsum Valley 355 T s i n i T s i n i and Borealis Glaciers 358 Fyles Glacier 3&0 Deer Lake and Jacobsen Glaciers 3&1 vi i i LIST OF TABLES (2.1) Summary of formations and constituent mineral assemblages of rock types found in the B e l l a Coola basin after Baer (1973) and Tipper (1979) 22 (2.2) Hydrometric data for stations in the B e l l a Coola basin 33 (3-1) Climate Stations in and near the Bella Coola basin 5** (3-2) C l a s s i f i c a t i o n of synoptic c i r c u l a t i o n types from Yarnel (1983) and Barry et al. (1982) 65 (3.3) Winter p r e c i p i t a t i o n and synoptic type frequencies 66 (3.4) Summer temperature and synoptic type frequencies 67 (3>5) Winter snow courses in southwestern B r i t i s h Columbia 70 (3-6) Winter snowpack and synoptic type frequencies 74 (3>7) S i g n i f i c a n t variables and regression c o e f f i c i e n t s for climate-runoff models 80 (3.8) Recognized trends in 20th century conditions in the N.E. P a c i f i c sector 95 (4.1) Empirical response models for g l a c i e r net mass balance and climate in southwestern B r i t i s h Columbia 105 (4.2) Winter mass balance on B.C. south coastal g l a c i e r s and synoptic type frequency 108 (4.3) Summer mass balance on B.C. coastal g l a c i e r s and synoptic type frequency 109 (4.4) Estimates of flood p l a i n sediment volumes for the Be l l a Coola River between Atnarko/Talchako confluence and mouth 126 (4.5) Morphological data for selected reaches of Bella Coola River 136 (5.1) Ape lake morphology 152 (5.2) Pearson's r for varve thickness and hydroclimatic var i ables 173 i x (6.1) Summary of tree ring-width chronologies used in thi s study 190 (6.2) Correlation matrix between PC scores and hydrocl imati c variables 202 (6.3) C o e f f i c i e n t s of transfer functions for winter (Oct.-Apr.) p r e c i p i t a t i o n 203 APPENDIX TABLES (A.l) Summary of radiocarbon derived dates 291 (B.1) C l a s s i f i c a t i o n of basic l i t h o l o g i c a l and mineral c h a r a c t e r i s t i c s of bedrock and a l l u v i a l sediments of major t r i b u t a r i e s to the Bella Coola River 299 (B.2) Constituent minerals of f l o o d p l a i n and channel zone sediments for the Bella Coola v a l l e y 300 (D.l) Cesium-137 results for core 84E2 326 (D.2) Ekman core data and standardized chronology for Ape Lake 327 (D.3) Summer and winter lamina thickness for percussion cores from Ape Lake 328 (D.4) Standardized sedimentation chronology for Ape Lake percussion core 329 (F.l) Accumulation area r a t i o s for selected Canadian g l a c i e r s 3 7̂ (F.2) Summary of c h a r a c t e r i s t i c s of and estimated ages for selected terminal moraines in the Bella Coola basin 356 X LIST OF FIGURES (1.1) A conceptual systems-framework model for environmental reconstruction showing functional r e l a t i o n s h i p s and i n f e r e n t i a l pathways 3 (1.2) Temporal resolution, continuity and sampling i n t e r v a l for biogeophysical and h i s t o r i c a l / i n s t r u m e n t a l data sources 11 (2.1) General location of study area and sampling locations 16 (2.2) B e l l a Coola basin and location of l o c a l hydroclimate stations 17 (2.3) Bedrock geology of the Bella Coola basin and mineral sampling locations 20 (2.4) Observed and inferred v a l l e y - f i l l in the lower reaches of B e l l a Coola River near Snootli Creek 25 (2.5) Hydroclimographs for selected climate stations in the v i c i n i t y of the Bella Coola basin 31 (2.6) B e l l a Coola River annual hydrograph for 1980 35 (2.7) Generalized c l a s t i c sediment routing and primary transport processes in B e l l a Coola basin 39 (2.8) I l l u s t r a t i o n s of primary c l a s t i c sediment sources for the higher-order f l u v i a l network in the Bella Coola basin 44 (2.9) Major sediment transfer routes and storage s i t e s for c l a s t i c sediment in the B e l l a Coola basin 47 (3-1) Seasonal temperature and p r e c i p i t a t i o n departures for coastal and i n t e r i o r regions of west central B r i t i s h Columbia between 1945 and 1983 56 (3.2) Generalized departures of winter p r e c i p i t a t i o n for southern, central and northern coastal areas of B r i t i s h Columbia. General departures in sea surface temperatures for the northeastern P a c i f i c ocean 58 (3-3) 500 mb synoptic scale c i r c u l a t i o n patterns which produce s p e c i f i e d climate departures for coastal B r i t i s h Columbia 61 (3-4) Winter snowpack departures for coastal and i n t e r i o r regions of southwestern B r i t i s h Columbia 72 x i (3-5) Spring runoff departures for three coastal r i v e r s of southwestern B r i t i s h Columbia 76 (3.6) Ten day p r e c i p i t a t i o n time series and associated recurrence intervals for flood generating storms at B e l l a Coola 83 (3.7) Frequency of autumn storm runoff in the Be l l a Coola, Homathko and Squamish Rivers between 19̂ 5 and 1985 86 (3-8) P a r t i a l duration curves of flow frequency for r i v e r s of the Bella Coola basin 89 (3-9) Contoured surfaces of i n t r a - and interannual climate at B e l l a Coola: 1904-1983 91 (3-10) Contoured surfaces of intra and interannual climate at Big Creek:1904-1983 92 (4.1) Relative rates of advance and recession fo selected g l a c i e r s in the Bella Coola basin 112 (4.2) West Saugstad Glacier in lat e July of 1985 showing advances p o s i t i o n 114 (4.3) Indirect evidence for secular changes in sediment deli v e r y to tri b u t a r y channels and a l l u v i a l fans of Bel l a Coola River 118 (4.4) Morphology and channel zone sediments in l a t e r a l l y stable and unstable reaches of Bella Coola River 124 (4.5) A l l u v i a l sediment sources for the Be l l a Coola River f l o o d p l a i n 130 (4.6) Water and bed surface longitudinal p r o f i l e s of Bel l a Coola River between Burnt Bridge Creek and riv e r mouth 134 (4.7) Changes in r i v e r planform and channel widths for a t r a n s i t i o n a l reach of the Be l l a Coola River between 1945 and 1984 138 (4.8) Topographic s e t t i n g of the McCall Flats backwater area of Bella Coola River above Burnt Bridge Creek 142 (4.9) Stratigraphy and pollen concentrations of backwater sediments extracted from the McCall Flats ponds 144 (5-1) Location and bathymetry of Ape Lake, B r i t i s h Columbia 150 xi i (5.2) P h o t o g r a p h s o f the Ape Lake b a s i n a f t e r the O c t o b e r 20 , 1984 g l a c i e r o u t b u r s t f l o o d 153 (5-3) F a c i e s d i s t r i b u t i o n , s e d i m e n t s a m p l i n g ^ l o c a t i o n s and s o u r c e s f o r r u n o f f and s e d i m e n t a t Ape Lake 155 (5.4) P h o t o g r a p h s of Ekman c o r e s and c r o s s - c o r r e l a t i o n of l a m i n a e in s e d i m e n t s f rom the e a s t b a s i n o f Ape Lake 157 (5-5) Laminae t h i c k n e s s v e r s u s d e p t h f o r Ekman c o r e s in t h e e a s t b a s i n o f Ape Lake 159 (5.6) Laminae t h i c k n e s s v e r s u s d e p t h f o r p e r c u s s i o n c o r e s e x t r a c t e d f rom the e a s t b a s i n o f Ape Lake 160 (5.7) Mean g r a i n s i z e v e r s u s s t a n d a r d d e v i a t i o n s in g r a i n s i z e s f o r samples taken f rom c o r e 84C2 163 137 (5.8) C o n c e n t r a t i o n o f Cs in grouped c o u p l e t s f rom c o r e 84E2 compared w i t h a t m o s p h e r i c f l u x r a t e to Lake Mi ch i g a n . 167 (5-9) C o m p o s i t e s e d i m e n t a t i o n c h r o n o l o g y f o r Ekman sampled s e d i m e n t s o f e a s t e r n Ape Lake 171 (5*10) S t a n d a r d i z e d s e d i m e n t a t i o n c h r o n o l o g y f o r p e r c u s s i o n c o r e r sampled s e d i m e n t s o f e a s t e r n Ape Lake 177 (5-11) S e d i m e n t a t i o n a n o m a l i e s and f r e q u e n c y of m i c r o - l a m i n a t i o n s in Ape Lake s e d i m e n t s compare t o r u n o f f a n o m a l i e s in the B e l l a C o o l a R i v e r 180 (6.1) L o c a t i o n of D o u g l a s and s u b a l p i n e f i r s a m p l i n g s i t e s used f o r deve lopment o f t r e e - r i n g c h r o n o l o g i e s 189 (6.2) Response c h a r a c t e r i s t i c s o f growth in Doug las F i r and s u b a l p i n e f i r to v a r i a t i o n s in s e l e c t e d h y d r o c l imat i c v a r i a b l e s . . . 193 (6.3) H igh and low f r e q u e n c y growth s i g n a l s in grouped D o u g l a s f i r c h r o n o l o g i e s f rom the B e l l a C o o l a a r e a 196 (6.4) H igh and low f r e q u e n c y growth s i g n a l s i n grouped s u b a l p i n e f i r c h r o n o l o g i e s f rom the B e l l a C o o l a a r e a 198 (6.5) R e c o n s t r u c t e d v a r i a t i o n s in a n n u a l p r e c i p i t a t i o n f o r e a s t e r n p o r t i o n s o f the B e l l a C o o l a R i v e r b a s i n 205 (6.6) R e c o n s t r u c t e d v a r i a t i o n s in summer t e m p e r a t u r e f o r e a s t e r n p o r t i o n s o f the B e l l a C o o l a R i v e r b a s i n 207 xi i i (6.7) O b s e r v e d , e s t i m a t e d and r e c o n s t r u c t e d summer r u n o f f i n d i c e s f o r B e l l a C o o l a R i v e r above Burn t B r i d g e Creek 210 (6.8) A c o m p a r i s o n of i n t e r - and i n t r a a n n u a l p e r s i s t e n c e of wet w i n t e r s ans warms summers w i t h t r e e growth v a r i a b i l i t y and f l o o d i n g on the B e l l a C o o l a R i v e r 213 (7-1) R e l a t i o n s h i p between r e l a t i v e ELA and c l i m a t e i n d i c e s f o r s e l e c t e d g l a c i e r s in s o u t h w e s t e r n , B r i t i s h C o l u m b i a 220 (7.2) E s t i m a t e s o f c o n t e m p o r a r y and former c l i m a t i c s n o w l i n e f o r e a s t e r n and w e s t e r n p o r t i o n s of the B e l l a C o o l a b a s i n 22k (7.3) G l a c i e r m o r a i n e c h r o n o l o g y f o r the B e l l a C o o l a b a s i n and s e l e c t e d a r e a s in the C a n a d i a n C o r d i l l e r a 229 (7.4) L o n g - t e r m , low f r e q u e n c y v a r i a t i o n s in r e c o n s t r u c t e d a n n u a l p r e c i p i t a t i o n and the f i r s t PC s c o r e o f s u b a l p i n e f i r 232 (7.5) L o n g - t e r m , h i g h f r e q u e n c y v a r i a t i o n s i n the f i r s t PC s c o r e s of Doug las and s u b a l p i n e f i r in the v i c i n i t y o f the B e l l a C o o l a b a s i n 238 (7.6) S p a t i a l d i s t r i b u t i o n of s u r f a c e s of d i f f e r e n t ages on the B e l l a f l o o d p l a i n 243 (7-7) S t r a t i g r a p h y , g r a i n s i z e v a r i a t i o n s , o r g a n i c m a t t e r c o n t e n t and p o l l e n c o n c e n t r a t i o n s in v e r t i c a l a c c r e t i o n s e d i m e n t s of the Brekke s i t e on the B e l l a C o o l a f l o o d p l a i n 248 APPENDIX FIGURES (B.1) Downstream v a r i a t i o n s in g r a i n s i z e f o r s e d i m e n t s o f the B e l l a C o o l a R i v e r and t r i b u t a r y a l l u v i a l f a n s 295 (B.2) V a r i a t i o n s in q u a r t z and l i t h i c f ragment c o n t e n t w i t h g r a i n s i z e in a l l u v i a l sand samples o f B e l l a C o o l a R i v e r 298 (B.3) T e r n a r y d i a g r a m showing d i s c r i m i n a n t f u n c t i o n s d e v e l o p e d t o d i s t i n g u i s h between sed iment s o u r c e s u s i n g m i n e r a l c h a r a c t e r i s t i c s of a l l u v i a l s e d i m e n t s 301 x i v (C.1) Sampling l o c a t i o n s of backchannel and slough depos i t s of the B e l l a Coola v a l l e y 309 (C.2) S t r a t i g r a p h y and p o l l e n concen t ra t ions for r e c e n t l y a c t i v e sloughs of the lower B e l l a Coola R i v e r (Rambeau, East Hagensborg and Walker Is land s i tes) 311 (C.3) S t r a t i g r a p h y and p o l l e n concen t ra t ions for r e c e n t l y a c t i v e backchannels of the lower B e l l a Coola River (Snoot l i and M c l e l l a n Rd. s i t e s ) 31^ (D. l ) Est imates of d i f f e r e n t i a l sediment compaction in Ape Lake sediments us ing bulk d e n s i t y and laminae th i ckness 322 ( F . l ) I l l u s t r a t i o n of a t y p i c a l g l a c i e r in the B e l l a Coola ba s in used to in fe r paleo e q u i l i b r i u m l i n e a l t i t u d e s ik8 (F.2) Loca t ion of moraine sampling s i t e s in the study b a s i n 352 (F.3) (a) Photograph of r e c e s s i o n a l moraines in East Nusatsum v a l l e y and (b) l e f t l a t e r a l moraine of T s i n i T s i n i G l a c i e r 357 (F.4) Photographs of r e c e s s i o n a l moraine f i e l d s for (a) B o r e a l i s and (b) Fy les G l a c i e r s 359 (F.5) Photographs of t e rmina l and r e c e s s i o n a l moraine f i e l d s for (a) Deer Lake and (b) Jacobsen G l a c i e r s 362 XV ACKNOWLEDGEMENTS I would l i k e to thank Dr . Michae l Church who as adv i sor has g iven me tremendous encouragement throughout the course of t h i s r e sea rch . As teacher and s c i e n t i s t , h i s s agac i t y has both i n s p i r e d and mot ivated me to a greater unders tanding of geomorphology and the ear th s c i e n c e s . Th i s p r o j e c t has bene f i t ed s u b s t a n t i a l l y from the exper ience of Dr . Robert G i l b e r t who was ins t rumenta l in a l l phases of f i e l d work at Ape Lake and Dr . June Ryder who provided i n v a l u a b l e guidance in the c o l l e c t i o n and assessment of evidence for g l a c i e r f l u c t u a t i o n s in the study a r ea . Dr . Glenn Rouse k i n d l y made a v a i l a b l e h i s p o l l e n lab and provided d i r e c t i o n and ad ivce in the p repa ra t ion and a n a l y s i s of the p o l l e n da t a . Drs . John Hay, W i l l i a m Mathews and Olav Slaymaker reviewed e a r l y d r a f t s of the t h e s i s and made many v a l u a b l e suggest ions dur ing the execu t ion of t h i s r e sea rch . Able f i e l d a s s i s t a n c e was provided by Mark C a n t w e l l , Lome Davies , Dan Hogan, Tom M i l l a r d and Jane Weninger. I would a l s o l i k e to thank Sandy Hart for h i s a s s i s t a n c e in p r e l i m i n a r y reconnaissance of B e l l a Coola R i v e r . Accommodation and v a l u a b l e i n s i g h t to the B e l l a Coola reg ion was g r a c i o u s l y provided by Tony and L i s Karup. A p p r e c i a t i o n i s extended to my graduate co l l eagues at UBC who were always w i l l i n g to d i s c u s s the research problem at hand. D r a f t i n g of s eve ra l diagrams was k i n d l y provided by Mary Artmont. My g rea tes t thanks and a p p r e c i a t i o n goes to Pamela Moss des Loges who not on ly endured my of ten cantankerous nature but a l s o a s s i s t e d in the f i e l d and i n p repa ra t i on of t h i s d i s s e r t a t i o n . Funding, in the form of a post -graduate s c h o l a r s h i p from the Na tu ra l Sciences and Research C o u n c i l of Canada and a p r e - d o c t o r a l f e l l o w s h i p from the K i l l a m Memorial Fund for Advanced S tud ies i s g r a t e f u l l y acknowledged. 1 Chapter I INTRODUCTION It has long been recognized that c e r t a i n b i o l o g i c a l and geophys ica l components of the environment respond in a p r e d i c t a b l e manner to e x t e r n a l f o r c e s . Remaining evidence of these components a l l ows inferences to be made about the d i s t r i b u t i o n and magnitude of forces in the pas t . Confident i d e n t i f i c a t i o n of past environmental s e t t i n g s r e l i e s upon some knowledge of the a t tendant p h y s i c a l processes , the nature of system responses and how the system might be a f fec ted when c e r t a i n boundary c o n d i t i o n s are a l t e r e d . An in teg ra ted approach towards unders tanding environmental change p r i o r to the pe r iod of instrument records u t i l i z e s evidence from seve ra l b i o g e o p h y s i c a l subsystems in order to assess the cons i s t ency of r e s u l t s and to eva lua te e r r o r s invo lved i n i n t e r p r e t a t i o n s and r e l a t e d in fe rences . The purpose of t h i s t h e s i s i s to assess the u t i l i t y of s eve ra l methodologies in the a n a l y s i s , i n t e r p r e t a t i o n and r e c o n s t r u c t i o n of recent h y d r o l o g i c a l and geomorphological p rocesses . The t e s t f i e l d area i s in a m i d - l a t i t u d e , g l a c i e r i z e d a l p i n e bas in of w e s t - c e n t r a l B r i t i s h Columbia . (1.1) Systems Framework In t h i s work the i n t e r a c t i o n s amongst a tmospheric , h y d r o l o g i c a l , b i o l o g i c a l and ear th surface processes are analyzed around the i n t e g r a t i v e theme of pa leohydro logy . Leopold and M i l l e r (195*0 f i r s t in t roduced t h i s term to desc r ibe "the i n t e r a c t i o n of c l i m a t e , v e g e t a t i o n , stream regimen and runoff obta ined under c l i m a t e s d i f f e r e n t from that of the p resen t" . Schumm (1965) suggested that the term be " r e s t r i c t e d to that p o r t i o n of the h y d r o l o g i c a l c y c l e tha t i nvo lves the movement of water [and sediment] over the sur face of the ear th . . . " . Brown (1982) has proposed that the term be 2 even more narrowly def ined as "the a p p l i c a t i o n s of concepts , methods and models de r i ved from hydrogeomorphological s t ud i e s to f l u v i a l p rocesses , sediments and forms of the pas t " . Th i s l a t t e r d e f i n i t i o n stems from the frequent emphasis on f l u v i a l processes but i s cons idered here as u n n e c e s s a r i l y r e s t r i c t i v e . The common theme in p a l e o h y d r o l o g i c a l s tud ie s i s an attempt to p rov ide a more comprehensive understanding of environmental s e t t i n g s over longer time sca l e s and wi th i nc r ea s ing temporal r e s o l u t i o n . It i s convenient to view the environment as a system comprised of s eve ra l morphogenetic components l i n k e d by a s e r i e s of f u n c t i o n a l r e l a t i o n s and a f f ec t ed by a set of boundary c o n d i t i o n s . F igure 1.1 i l l u s t r a t e s four morphogenetic subsystems of i n t e r e s t in t h i s s tudy: g l a c i a l , g l a c i o l a c u s t r i n e , f l u v i a l and mass w a s t i n g . A set of f u n c t i o n a l r e l a t i o n s between the atmospheric environment and the ear th surface environment can be d e f i n e d . These r e l a t i o n s are formulated on the bas i s of exchanges of energy and mass and are in f luenced by boundary c o n d i t i o n s such as topographic and geo log ic c o n t r o l s , neo tec ton ics and former g l a c i a t i o n . Energy from the atmospheric and h y d r o l o g i c a l components of f i g u r e 1.1 d r i v e s the system r e s u l t i n g in the r e d i s t r i b u t i o n of mass and the format ion of new sedimentary d e p o s i t s . Inferences about former h y d r o l o g i c a l s e t t i n g s , then, are made in the reverse d i r e c t i o n from that of the f u n c t i o n a l r e l a t i ons . The t r ans f e r of in format ion between the h y d r o c l i m a t i c environment and any one of the four morphogenetic subsystems i d e n t i f i e d in f i g u r e 1.1 i s subjec t to a v a r i e t y of temporal and s p a t i a l f i l t e r i n g e f f e c t s . Deposi ts w i t h i n any of the subsystems in t eg ra t e the e f f e c t of shor t - t e rm h y d r o c l i m a t i c processes , or events , hence have a c h a r a c t e r i s t i c low r e s o l u t i o n of the t rue ampli tude and frequency of c l i m a t i c and h y d r o l o g i c v a r i a t i o n s . For example, maximum advances of ice are f r equen t ly marked by 3 : • CLIMATE energy balance water balance c i r c u l a t i o n regime I GLACIER ACTIVITY mass balance moraines. t i l l , outwash * RUNOFF/ STREAMFLOW SEDIMENT TRANSPORT \ \ GLAC10- LACUSTRINE PROCESSES phys ica l 1imnology bathymetry ALLUVIAL ACTIVITY sediments, channel geometry 1aminated lake sediments f l o o d p l a i n and ter race al1uvi um LAND SURFACE weatheri ng vegetat ion/ soi 1 s COLLUVIAL ACTIVITY basin morphometry "X" I _ L _ 1andsl ides/ r o c k s l i d e s earthf lows LAND USE human d e c i s i o n s SEDIMENTARY DEPOSITS • FUNCTIONAL RELATIONSHIP • INFERENTIAL PATHWAY Figure 1.1 F u n c t i o n a l and i n f e r e n t i a l pathways connec t ing four morphogenetic subsystems of i n t e r e s t in t h i s p r o j e c t . Not shown are boundary c o n d i t i o n s which i n c l u d e g e o l o g i c a l and neo t ec ton i c f a c t o r s as w e l l as past g l a c i a l a c t i v i t y (af ter S t a r k e l and Thornes , 1 9 8 l ) . Other subsystems not cons ide red i nc lude e o l i a n , marine and g l a c i o m a r i n e envi ronments . it t e rmina l moraines . However, f l u c t u a t i o n s in the d i r e c t i o n or ra te of ice movement may be a response to a combinat ion of h y d r o c l i m a t i c changes which occur over time sca l e s much shor te r than the i n t e r v a l r equ i r ed for format ion of the d e p o s i t , in c o n t r a s t , l a n d s l i d e s , f l o o d depos i t s or subaqueous s lope f a i l u r e s may represent 'key even t s ' wi thout reference to a p a r t i c u l a r se t of depar tures in long-term mean c o n d i t i o n s of h y d r o c l i m a t e . These two s i t u a t i o n s , which g e n e r a l l y l i m i t the inferences that can be made, are commonly a s soc ia t ed w i t h primary morpholog ica l sources of informat ion and therefore compl ica te the e x e r c i s e . A precursor to succes s fu l a p p l i c a t i o n of the model in f i g u r e 1.1 to past environments i s the i n t e r p r e t a t i o n of va r ious morpho log ica l components such as v e g e t a t i o n , s o i l s , surface forms and sedimentary sequences (Gregory, 1983a). Environmental r e c o n s t r u c t i o n s then, can on ly be made a f t e r abso lu te and r e l a t i v e d a t i n g techniques are a c c u r a t e l y a p p l i e d to sequences of sediment and preserved landforms which have c l e a r l y def ined d e p o s i t i o n a l environments . In t h i s con tex t , a t rue p a l e o h y d r o l o g i c a l model i s r a r e l y ach ieved . (1.2) Operational Approaches Brown (1982) suggested that three types of paleoenvironmental modeling can be undertaken: process , e m p i r i c a l and i n f e r e n t i a l model development. A modi f ied v e r s i o n of t h i s scheme d i scussed here inc ludes three genera l c a t e g o r i e s : (1) process or p h y s i c a l models, (2) e m p i r i c a l models and (3) i n d u c t i v e models . Process Models The most d i f f i c u l t of a l l three ca t ego r i e s i s the process model where the f u n c t i o n a l r e l a t i o n s h i p s between v a r i o u s components of the system are 5 q u a n t i f i e d and grouped to form a general p h y s i c a l model which operates accord ing to p h y s i c a l and geochemical laws. The model i s cons t ruc ted and c a l i b r a t e d under modern c o n d i t i o n s and then a p p l i e d to past environments . The approach i s pu re ly deduc t ive and requ i r e s q u a n t i t a t i v e es t imates of input parameters . General c i r c u l a t i o n models are of t h i s type . C la rke et al. (1984) u t i l i z e a process-model , v e r i f i e d us ing modern ou tburs t f l o o d s , to es t imate former d i scharges of ice-dammed g l a c i a l Lake M i s s o u l a in Washington s t a t e . I ce - f low and heat t r an s f e r r e l a t i o n s are used as governing equat ions to p r e d i c t the s i z e of the s u b g l a c i a l d i scharge t u n n e l . Var ious parameters such as lake volume, water temperature and i c e - th i ckness are requ i red input v a r i a b l e s . Model s i m i l i t u d e and assumptions regard ing ice tunnel geometry and flow r e s i s t a n c e remain p r o b l e m a t i c . Power and Young (1979). among o the r s , have used an in t eg ra t ed watershed model to p r e d i c t fu ture and former runoff from g l a c i e r - c o v e r e d catchments. Th i s type of model i s c a l i b r a t e d aga ins t observed f low v a r i a t i o n s and adjusted accord i n g l y . The major assumptions u n d e r l y i n g process-models a re : (1) a l l dominant processes have been i d e n t i f i e d and c o n t r i b u t i n g f a c t o r s parameter ized , o r , in the case of s i m u l a t i o n s , unknown but important f a c t o r s are c o n t r o l l e d ; (2) governing r e l a t i o n s h i p s are p rope r ly c a l i b r a t e d for the expected range and v a r i a n c e of input da ta ; and (3) the temporal and s p a t i a l r e s o l u t i o n of the input data correspond w i t h the c a l i b r a t i o n d a t a . V i o l a t i o n of the f i r s t or second assumption r e s u l t s in an u n r e l i a b l e model whereas v i o l a t i o n of the t h i r d assumption y i e l d s u n r e l i a b l e r e s u l t s . Empirical Models Though the deduc t ive approach used in bas i s for t h i s second group of models, the process modeling i s u n d e r l y i n g p h y s i c a l a l s o the processes 6 are not q u a n t i f i e d . A p a r t i c u l a r set of processes ( r a i n f a l l , stream f l o w , g l a c i e r flow) is r e l a t e d to responses in b i o l o g i c a l or geophys ica l a t t r i b u t e s of the environment and then r e l a t i o n s h i p s are developed, u s u a l l y us ing s t a t i s t i c a l t echn iques . The r e l a t i o n s are then inver ted to make p r e d i c t i o n s of former process based on response chrono log ies preserved in the environment. These inc lude the q u a n t i t a t i v e a n a l y s i s of vege t a t i on growth pa t t e rn s , v a r i a b i l i t y in g l a c i o l a c u s t r i n e sed imenta t ion , v a l l e y or r i v e r channel morphology, paleochannels and f o s s i l f l u v i a l sediments . Nominal , i n t e r v a l or r a t i o s ca l e data can be used. Mathewes (1973) and Mathewes and Rouse (1975) have attempted q u a l i t a t i v e r e c o n s t r u c t i o n of Holocene pa leoc l ima tes in the lower Fraser V a l l e y of B r i t i s h Columbia us ing p a l e o e c o l o g i c a l evidence preserved in lake c o r e s . Q u a n t i t a t i v e es t imates of temperature and p r e c i p i t a t i o n for the same area and pe r iod were then made us ing c a l i b r a t i o n techniques in which the s p a t i a l d i s t r i b u t i o n of modern vege t a t i on i s c a l i b r a t e d aga ins t contemporary c l ima te s (Mathewes and Heusser, 1981). These r e l a t i o n s are then used to formulate t r ans fe r func t ions in order to es t imate former h y d r o c l i m a t i c c o n d i t i o n s based on the i n f e r r e d pa leoeco logy . Two problems compl ica te the " t r a n s f e r " of these r e l a t i o n s de r ived from s p a t i a l a s s o c i a t i o n s . The f i r s t i s r e l a t e d to the fac t that s p a t i a l v a r i a t i o n s in c l i m a t e can be greater than those exper ienced at a p a r t i c u l a r s i t e through t ime . The second i s that f ac to r s other than the assumed dependent v a r i a b l e ( in t h i s case c l imate) may e x p l a i n a s i g n i f i c a n t p r o p o r t i o n of the temporal v a r i a n c e and are not inc luded in the development of the t r ans fe r f u n c t i o n (Imbrie and Webb, 1983) . The major u n d e r l y i n g assumption in the r e t r o s p e c t i v e a p p l i c a t i o n of e m p i r i c a l models i s that an e q u i l i b r i u m has been achieved between a s p e c i f i c a t t r i b u t e and a dominant process for both the c a l i b r a t i o n and 7 a p p l i c a t i o n i n t e r v a l s . C e r t a i n b i o l o g i c a l or geophys ica l a t t r i b u t e s may adjust very s lowly to imposed change and thus may not r e f l e c t h ighe r - frequency pe r tu rba t ions in the system. In c o n t r a s t , adjustments may be r a p i d but s e n s i t i v e only to forces beyond an exceedence th re sho ld and thus are r e p r e s e n t a t i v e of shor t - t e rm c o n d i t i o n s o n l y . L inear l eas t - squares s t a t i s t i c a l techniques are commonly used in the fo rmu la t i on of e m p i r i c a l models. The a p p l i c a t i o n of these r e l a t i o n s h i p s for environmental r e c o n s t r u c t i o n i s based on the assumption that the exp la ined p o r t i o n of the t o t a l va r i ance r e f l e c t s the primary response c h a r a c t e r i s t i c of the system and that the r e s i d u a l v a r i a n c e i s random " n o i s e " . Th i s c o n s t r a i n t can s e r i o u s l y a f f e c t the s i g n i f i c a n c e of i n t e r p r e t a t i o n s from a l i n e a r model i f the system i s a l s o known to respond s i g n i f i c a n t l y to extreme depar tu res . These l e s s f requent , higher magnitude events become ' k e y ' elements which are l o s t in the assumption of l i n e a r i t y . Inductive Models Thi s category i s based p r i m a r i l y on the i n d u c t i v e approach u t i l i z i n g s i t e - s p e c i f i c evidence for drawing inferences about former environments . Sedimentary sequences (1 i thofacies) and the remains or by-products of b i o l o g i c a l a c t i v i t y are used to r econs t ruc t a s e r i e s of p o s s i b l e environmental c o n d i t i o n s . O r d i n a l and nominal s c a l e data are used f r equen t ly and most ly q u a l i t a t i v e r e s u l t s are ach ieved . Inferences u s u a l l y r e l a t e to a s p e c i f i c set of environmental c o n d i t i o n s such as s p a t i a l and temporal v a r i a t i o n s in runof f , or the chronology and d i s t r i b u t i o n of g l a c i e r i ce movements. S t a r k e l (1984) has used v a r i o u s a l l u v i a l sequences to in fe r the charac te r of c l i m a t e t r a n s i t i o n s over the Holocene Epoch in c e n t r a l Europe. Ryder and Thomson (1986) have used seve ra l sources of evidence from g l a c i a l 8 depos i t s throughout southwestern B r i t i s h Columbia to in fe r the t i m i n g and magnitude of g l a c i a l a c t i v i t y in p o s t - P l e i s t o c e n e t ime. The a p p l i c a t i o n of s eve ra l d a t i n g techniques i s c r u c i a l for e s t a b l i s h i n g c h r o n o s t r a t i g r a p h i c c o n t r o l both l o c a l l y and r e g i o n a l l y . P r e s e r v a t i o n of da tab le m a t e r i a l s and inaccu rac i e s a s s o c i a t e d w i t h radiocarbon da t ing become major l i m i t a t i o n s of the e x e r c i s e . Commonly, p a r t i c u l a r l y for a l l u v i a l sediments, the s t r a t i g r a p h i c record represents extreme or ' k e y ' events on ly ( e .g . f l o o d d e p o s i t s ) . E r o s i o n a l h ia tuses or other unconformi t ies may compl ica te i n t e r p r e t a t i o n s i f a s u b s t a n t i a l p r o p o r t i o n of the i n t e rven ing sequence i s mi s s ing or o therwise d i s t u r b e d . In t h i s way a s u b s t a n t i a l l y d i f f e r e n t record of environmental change may evolve us ing these data sources . R e c o g n i t i o n of these d i f f e r e n c e s i s important for succes s fu l model development. In summary, e m p i r i c a l and i n d u c t i v e approaches, d e s p i t e t h e i r problems, are commonly employed to draw inferences regard ing past h y d r o l o g i c a l and c l i m a t o l o g i c a l c o n d i t i o n s in the reverse d i r e c t i o n from that of the usual f u n c t i o n a l r e l a t i o n s . The process-based approach y i e l d s es t imates of these f u n c t i o n a l r e l a t i o n s and, then the boundary c o n d i t i o n s and i n i t i a l s t a t e are changed to approximate former environments . While i n i t i a l l y more a t t r a c t i v e , t h i s l a t t e r type of model i s the most d i f f i c u l t to develop and s t i l l f r equen t ly su f f e r s from l i n e a r pa ramete r i za t ions which do not e a s i l y accommodate c o n d i t i o n s beyond the c a l i b r a t i o n i n t e r v a l . The three types of models y i e l d d i f f e r e n t c h a r a c t e r i s t i c s of the past environment, and the re fo re should be viewed as complementary approaches to environmental r e c o n s t r u c t i o n s . 9 (1.3) Objectives and Research Strategy The s p e c i f i c study o b j e c t i v e s a re : (1) to i d e n t i f y and r e l a t e the response c h a r a c t e r i s t i c s of s e l e c t e d geophys ica l and b i o l o g i c a l a t t r i b u t e s of the study bas in to recent f l u c t u a t i o n s i n hydroc l ima te ; (2) to determine the r e s o l u t i o n and length of record a v a i l a b l e in these a t t r i b u t e s and eva lua te s eve ra l methodologies for i n f e r r i n g the charac ter of past hydroc l ima tes ; and (3) to assess the w i t h i n - b a s i n and r e g i o n a l (southwestern B r i t i s h Columbia) s i g n i f i c a n c e of measured and i n f e r r e d environmental change in the study a rea . The primary emphasis i s on problems a s soc i a t ed w i th methods used in the r e c o n s t r u c t i o n of past environments . In p a r t i c u l a r , c o n s i d e r a t i o n i s g iven to sources of e r ro r and the s t reng th of inferences drawn from i n d i r e c t and proxy data which may e x i s t in q u a n t i t a t i v e , s e m i - q u a n t i t a t i v e or q u a l i t a t i v e form. E m p i r i c a l and i n d u c t i v e methods only are considered because of d i f f i c u l t i e s in app ly ing and l i n k i n g e x i s t i n g process-based models. The study cons ide r s the u t i l i t y of the model presented in f i g u r e 1.1 as a framework for drawing inferences regard ing recent paleoenvironments in a m i d - l a t i t u d e a l p i n e b a s i n . In order to assess c r i t i c a l l y the r e a l r e s o l u t i o n of responses in the system and to prov ide a bas i s for c a l i b r a t i o n of paleoenvironmental da ta , a r e t r o s p e c t i v e s t r a t egy has been adopted. Th i s i s o p e r a t i o n a l i z e d by c o n s i d e r i n g f i r s t the r e l a t i o n s h i p between hyd ro log i c v a r i a b i l i t y and geophys ica l responses over the pe r iod of recent and d e t a i l e d instrument records (post-19^5)• The r e l a t i o n s h i p s are then tes ted us ing l e s s d e t a i l e d 10 but long- term instrument records as conf i rmatory data (1900-19^5)• Th i s s t r a t egy was adopted as a means of assess ing the s t reng th of inferences from b i o g e o p h y s i c a l data in the pre- ins t rument p e r i o d . Inferences about environmental c o n d i t i o n s p r i o r to 1900 are then made from the evidence of b i o g e o p h y s i c a l a t t r i b u t e s a lone . I n i t i a l l y , i t was a n t i c i p a t e d that t h i s methodology would a l l o w for a r e s o l u t i o n of at l e a s t annual , or perhaps even seasona l , b i o g e o p h y s i c a l responses over the t e s t i n g p e r i o d . However, i n view of p o s s i b l e p e r s i s t e n t t rends in b i o l o g i c a l and geophys ica l a t t r i b u t e s , i t was reasonable to expect a r e s o l u t i o n on ly on the order of years to decades. The pe r iod a f t e r I65O AD def ines the study i n t e r v a l . Th i s was found to be consonant w i t h preserved ev idence . D e t a i l s are g iven in the f o l l o w i n g s e c t i o n s . (l.k) Data Sources B i o l o g i c a l , and geophys ica l data can be grouped and c l a s s i f i e d on the bas i s of temporal c o n t i n u i t y , temporal r e s o l u t i o n and i n t e r v a l of a p p l i c a t i o n (Bradley , 1985)• Some prov ide on ly a d i scon t inuous record of changes and may represent on ly extreme events ( e .g . f l o o d d e p o s i t s ) , w h i l e o thers may appear to g ive a cont inuous record (season-to-season, y e a r - t o - year) of changing c o n d i t i o n s (e .g . t r e e - r i n g s ) . C e r t a i n sources are a p p l i c a b l e to time sca l e s of m i l l e n n i a or longer and o thers may y i e l d data concerning on ly recent (decenn ia l , cen tenn ia l ) p rocesses . The primary data sources for t h i s study can be d i v i d e d i n to four groups of a t t r i b u t e s : b i o l o g i c a l , g e o p h y s i c a l , h i s t o r i c a l and a r c h a e o l o g i c a l , which are based on the most usefu l i n d i c a t o r s of environmental change in m i d - l a t i t u d e , g l a c i e r i z e d a l p i n e bas ins ( f igure 1.2). B i o l o g i c a l sources inc lude t r e e s , f l o w e r i n g vege t a t i on and l i c h e n . Tree r i n g - w i d t h time s e r i e s possess a r e s o l u t i o n of seasonal ( l a t e - 11 10" 00 >-x a. o L U U3 oo i l ta ^ o —i a ea < < h- o Z K d L U a ° 3 OO S ae i—i — *- = y z < 10 3 T O 2 101 10° 10'' I 1 I 1 I——— I H I — 10 10 3 10 2 101 10° 10'1 10 -2 I 1 h 1 Tree-rings »•—^Tree-damage Pollen Lichen Soi l Lake Sediment Glacial Deposits V a l l e y - f i l l Instrumental Written Records Legends Ar t i fac t s 10 - 2 10" Years Figure 1.2 B i o l o g i c a l , g e o p h y s i c a l and h i s t o r i c a l / a r c h a e o l o g i c a l sources used for envi ronmenta l r e c o n s t r u c t i o n in t h i s s tudy . The minimum sampling i n t e r v a l ( a t t r i b u t e r e s o l u t i o n ) in years i s g iven by a s o l i d h o r i z o n t a l l i n e for cont inuous v a r i a b l e s and a dashed l i n e for non-cont inuous v a r i a b l e s . Some a t t r i b u t e s have more than one sampling i n t e r v a l . S o l i d c i r c l e s i n d i c a t e the p e r i o d open for study in y e a r s . R e s o l u t i o n of p o l l e n depends on the cha rac t e r of the host sediments . 12 wood/early-wood) to annual ( t o t a l r i ng -wid th ) growth v a r i a t i o n s and are cont inuous through t ime . Damage to t rees by d i s c r e t e events , such as f l o o d s , or more continuous s t r e s s , l i k e in sec t damage, p rov ide some i n d i c a t i o n of low-frequency, high-magnitude events but g e n e r a l l y these records are d i s c o n t i n u o u s . The o l d e s t t rees a v a i l a b l e for sampling are u s u a l l y l e s s than 10̂  yea r s . P o l l e n and spores are produced s e a s o n a l l y , and i f preserved in sediments a l s o c h a r a c t e r i z e d by a high temporal r e s o l u t i o n , may y i e l d a record of changing p o l l e n c o n t r i b u t i o n s and thus e c o l o g i c a l v a r i a b i l i t y . M o s t l y , p o l l e n i s u se fu l for i d e n t i f y i n g changes over long- term i n t e r v a l s (10 years) w i th a r e s o l u t i o n of 50 to 500 years ( f igure 1.2). L ichen and s o i l development can be used to e s t a b l i s h r e l a t i v e ages for d i f f e r e n t k surfaces as o l d as 10 years u s u a l l y w i th a r e s o l u t i o n of 10 to 500 yea r s . In some instances i t may be p o s s i b l e to produce continuous form/t ime curves w i t h an abso lu te temporal reference but they are d i f f i c u l t to ach ieve , p a r t i c u l a r l y w i th s o i l s . Lake depos i t s form dur ing an i n f l u x of sediment from the surrounding t e r r a i n i n to a near ly c lo sed system and may represent s eve ra l time sca le s and degrees of c o n t i n u i t y depending on sedimenta t ion c o n t r o l s . Low- frequency, high-magnitude depos i t s may be the r e s u l t of i s o l a t e d runoff events which occur over a pe r iod of hours or days . These sediments are d i s t r i b u t e d d i s c o n t i n u o u s l y throughout the sequence. A l t e r n a t i v e l y , autogenous events may occur , such as d e n s i t y underf lows, produced by the bu i ldup of d e l t a i c depos i t s which then exceed s t a b i l i t y l i m i t s . The event i s the consequence of cont inuous sed imenta t ion , but does not mark an e x t r i n s i c event . However, in a long record the changing frequency of f a i l u r e s may be s i g n i f i c a n t . If c e r t a i n runoff regimes p r e v a i l , a cont inuous record of seasonal or annual sedimenta t ion might be preserved 13 (e .g . annua l l y - l amina t ed sediments or v a r v e s ) . In sha l low water away from primary sediment sources , sedimenta t ion ra tes may be low and represent long 2 3 per iods of accumulat ion (10 - 10 y e a r s ) . G l a c i a l sediments are g e n e r a l l y depos i t ed d i s c o n t i n u o u s l y over time sca l e s commensurate w i th the response time of the i ce to changes in accumulat ion and a b l a t i o n (10 -10 y e a r s ) . A record as o l d as 10 -10 years may be present i f sediments are w e l l - p r e s e r v e d . V a l l e y - f i l l sediments, downstream from the headwater source areas , a l s o represent d i scon t inuous sedimenta t ion over longer time sca l e s but may incorpora te sequences depos i ted dur ing s h o r t - d u r a t i o n f l o o d s . In a d d i t i o n to b i o g e o p h y s i c a l sources , in fo rmat ion r e l a t e d to human a c t i v i t y can prov ide i n d i r e c t evidence of environmental change ( f igure 1.2). Data regarding annual or semi-annual changes and extreme shor t d u r a t i o n events are most common. For western Canada w r i t t e n records p r i o r to the middle and l a t e 1800s are r a r e . Indian legends and a r c h a e o l o g i c a l evidence are a l s o u s e f u l , a l though they are l e s s d i r e c t i n d i c a t o r s of environmental s e t t i n g . (1.5) Organization Thi s d i s s e r t a t i o n i s composed of e igh t chap te r s . The o r g a n i z a t i o n i s based on a format for a s sess ing the q u a l i t y of in format ion t r ans fe r from the h y d r o c l i m a t i c environment to the ea r th sur face environment in order to r e f l e c t the main o b j e c t i v e s . Chapter 2 i s a summary of the general p h y s i c a l s e t t i n g of the B e l l a Coola R i v e r ba s in and c h a r a c t e r i z a t i o n of primary sediment sources in the b a s i n . Chapter 3 i s a d i s c u s s i o n of v a r i a t i o n s in s eve ra l h y d r o l o g i c a l a t t r i b u t e s of the recent and long-term instrument pe r iod (1900-1983). Chapter h documents the r e l a t i o n s h i p s between these recent f o r c i n g f a c t o r s and the response of s e l e c t e d geophys ica l components 14 of the landscape. The d i s c u s s i o n i s r e s t r i c t e d to the post-1945 i n t e r v a l for which there are s e v e r a l types of d i r e c t records of environmental change. Chapter 5 i s devoted to the i n t e r p r e t a t i o n and s i g n i f i c a n c e of a h i g h - r e s o l u t i o n record of lake sedimenta t ion ra tes as an independent source of in format ion about environmental change. Chapter 6 i s an i n v e s t i g a t i o n of the response of growth v a r i a t i o n s in t r e e s , and an assessment of t r e e - r ings as a source of h i g h - r e s o l u t i o n data in environmental r e c o n s t r u c t i o n . Chapter 7 i s a d i s c u s s i o n of l o w - r e s o l u t i o n data sources and i n t e r p r e t a t i o n of h y d r o c l i m a t i c v a r i a b i l i t y du r ing the l a t e N e o g l a c i a l i n t e r v a l . The r e g i o n a l s i g n i f i c a n c e of the recons t ruc ted records i s a l s o c o n s i d e r e d . A summary of r e s u l t s and conc lus ions i s g iven in Chapter 8. Data not presented in the main t e x t , p lus a d d i t i o n a l t o p i c s and ana lyses , are g iven in the appendices . 15 Chapter I I STUDY AREA (2.0) Location S t a r k e l and Thornes (198l) suggest that s e l e c t i o n of a drainage bas in for p a l e o h y d r o l o g i c a l a n a l y s i s should be based on the a v a i l a b i l i t y of data regard ing landscape morphology, process mechanics and ear th sur face m a t e r i a l s . In a d d i t i o n , long- term instrument records of recent h y d r o l o g i c change are e s s e n t i a l for q u a n t i t a t i v e r e c o n s t r u c t i o n s . In B r i t i s h Columbia there i s no bas in which f i t s these c r i t e r i a w e l l . B e l l a Coola R ive r b a s i n , a p a r t l y g l a c i e r - c o v e r e d catchment loca ted on the c e n t r a l coas t , approximate ly 500 km northwest of Vancouver ( f igure 2 . 1 ) , was s e l e c t e d because of the a v a i l a b i l i t y of recent h y d r o c l i m a t i c da ta , compara t ive ly e a r l y h i s t o r i c a l records of environmental c o n d i t i o n s and the p o t e n t i a l for p r e s e r v a t i o n of pa leoenvironmenta l evidence in upland source areas and lowland f l o o d p l a i n s . A c c e s s i b i l i t y , ba s in s i z e and the ex i s t ence of s e v e r a l p r e l i m i n a r y s tud i e s concerning p h y s i c a l processes and recent environmental change i n the bas in (Tempest, 197̂ ; Church and R u s s e l l , 1977; Ha r t , 198 la ; Church, 1983) were a d d i t i o n a l f a c t o r s . 2 B e l l a Coola R ive r d r a i n s 5050 km of the g l a c i e r i z e d Coast Mountains of southwestern B r i t i s h Columbia . Two t r i b u t a r i e s j o i n to form B e l l a Coola 2 R i v e r ( f i gu re 2 . 2 ) : the l a rge r Atnarko R ive r (2,430 km ) o r i g i n a t e s i n gen t ly s l o p i n g , u p l i f t e d t e r r a i n to the eas t , and Talchako Rive r d r a i n s 2 1300 km of h e a v i l y g l a c i e r i z e d mountains to the sou th . Severa l smal le r t r i b u t a r i e s enter the 80 km long B e l l a Coola River as i t f lows west to enter North Bent inck Arm ( f igure 2 . 2 ) , an in land ex tens ion of the Burke Channel and Dean Channel f i o r d system. Approximately 1% of the catchment i s covered by c i r q u e , n iche and v a l l e y g l a c i e r s concentra ted in rugged mountainous t e r r a i n in the southwest . Two major v a l l e y g l a c i e r s , Talchako 16 F i g u r e 2.1 General l o c a t i o n of study area and hyd roc l ima te s t a t i o n s used in the a n a l y s i s of c l i m a t e v a r i a t i o n s . A x i s of the Coast Mountains i s an approximate boundary for s t a t i o n s which are r e f e r r e d to in the t ex t as " c o a s t a l " and " i n t e r i o r " . A l s o i nc luded are l o c a t i o n s of g l a c i e r and t r e e - r i n g data used in the s tudy . Figu re 2.2 B e l l a Coola R i v e r bas in i n c l u d i n g major t r i b u t a r i e s and the d i s t r i b u t i o n of upland i c e . A l s o inc luded are the l o c a t i o n s of c l i m a t e and r i v e r gauging s t a t i o n s . 18 and Jacobsen, along with several smaller north-flowing ice masses, emanate 2 from the Monarch I c e f i e l d (total area 350 km ) which straddles the southwest basin perimeter for a distance of kS km. (2.1) Physiography Three d i f f e r e n t physiographic regions as defined by Tipper (1971a) and more generally by Holland (196*0 can be delineated in B e l l a Coola basin. To the south of Be l l a Coola River and west of Talchako River are the rugged, deeply dissected P a c i f i c Ranges of the Coast Mountains, extending from sea le v e l to a l t i t u d e s greater than 3500 m (figure 2 .2 ) . The highest peaks bi s e c t Monarch I c e f i e l d , some of which are v i s i b l e only as nunataks, ranging from 2500 to 3500 m. Local r e l a t i v e r e l i e f is sim i l a r throughout, averaging 1400 to 1600 m. Drainage d i r e c t i o n s are dominantly eastward or northward r e s u l t i n g in slope aspects which exhibit a strong bimodal d i s t r i b u t i o n of north/south or east/west and a comparatively high mean slope angle of 27 degrees.* Mountains of the Kitimat Range to the north of Bella Coola River and west of Noosgulch Creek (figure 2 .2 ) , r a r e l y exceed maximum elevations of 2500 m. Valley bottoms tend to be wider, average r e l a t i v e r e l i e f is lower (1000 m) and the mean slope angle (22^) smaller than those in the P a c i f i c Ranges. Although r e s t r i c t e d to headwater regions, landforms t y p i c a l of the g l a c i a l eroded landscape to the south are also found in the Kitimat Range, including U-shaped v a l l e y s , cirques, horns, aretes, hanging t r i b u t a r y v a l l e y s and several tarns. 1. Mean slope angle was determined as the average of 300 grid-points sampled systematically from 1:50,000 topographic sheets for each physiographic region. A representative slope distance was defined as ±3 100-foot contours measured perpendicular to the slope (except in low- gradient v a l l e y bottoms where ±2 was used). Two sub-samples of 50 g r i d - points each demonstrated that biases due to grid-spacing and o r i e n t a t i o n were not s i g n i f i c a n t . 19 C o n t r a s t i n g w i t h these two regions i s the u p l i f t e d and l e s s rugged Fraser P la teau which dominates t e r r a i n to the east of Talchako Rive r and Burnt Br idge Creek. Gent ly undu la t ing and h i l l y topography (mean s lope angle = 7̂ ) c h a r a c t e r i z e s t h i s reg ion in which the average e l e v a t i o n i s higher (1300 m) than v a l l e y bottom l o c a t i o n s to the west . Average r e l a t i v e r e l i e f i s lower (400 m) than elsewhere in the bas in r e s u l t i n g in the format ion of hundreds of smal l lakes along p r i n c i p a l dra inage l i n e s and on p o o r l y - d r a i n e d , low-grad ien t t e r r a i n . C h a r l o t t e Lake i s the l a r g e s t , 2 cover ing approximately 65 km ( f igure 2.2). Drainage from the p la teau i s concentra ted in only a few major streams (Atnarko R . , Hotnarko R . , Young C r . , Burnt Br idge C r . and Hunlen C r . - see f i g u r e 2.2) which e i t h e r have cut deeply i n to the e a s i l y eroded v o l c a n i c rocks forming p r e c i p i t o u s canyons for tens of k i l ome te r s o r , where rock types are more r e s i s t a n t , formed w a t e r f a l l s w i t h v e r t i c a l drops as l a rge as 250 m. (2.2) Bedrock Geology Physiography and drainage pa t te rns of the B e l l a Coola ba s in are inf luenced by a d i v e r s i t y of rock types and geo log i c s t r u c t u r e s c h a r a c t e r i s t i c of the Coast P l u t o n i c Complex and Intermontane V o l c a n i c B e l t of the western Canadian C o r d i l l e r a . The geo log ic s e t t i n g of the study area desc r ibed below f i t s the general pa t t e rn of the east s lope of the Coast Mountains ( c f . Roddick and Hutch inson , 1972). The geology of the B e l l a Coola area has been mapped in d e t a i l by Baer (1973) and more g e n e r a l l y by Tipper (1979) ( f igu re 2.3)- The o l d e s t rocks are middle T r i a s s i c p lutons of q u a r t z - d i o r i t e and g r a n o d i o r i t e in the southeastern p o r t i o n of the catchment and on the north f lank of B e l l a Coola R ive r near S t u i e . Metamorphism of v a r y i n g i n t e n s i t i e s has generated g n e i s s i c and s c h i s t o s e f o l i a t i o n in some of these rocks , p a r t i c u l a r l y in Figu re 2.3 D i s t r i b u t i o n of bedrock l i t h o l o g i e s in the B e l l a Coola b a s i n (af ter Baer (1973) and Tipper (1979)). T r i a n g l e s are sampling l o c a t i o n s used to c h a r a c t e r i z e l i t h o l o g i c a l and m i n e r a l o g i c a l a t t r i b u t e s of sediments de r ived from t r i b u t a r y b a s i n s . O 21 the headwaters of Atnarko R i v e r . V o l c a n i c , metavolcanic and sedimentary rocks ( T r i a s s i c to lower Cretaceous) c h a r a c t e r i z e the c e n t r a l and southern p o r t i o n s of the catchment compr is ing c h l o r i t e - r i c h greenstone and a n d e s i t e . The v o l c a n i c s e x h i b i t w i d e l y s ca t t e r ed shear zones occupied by s l a t e and argi11 i t e . Eocene quar tz-monzoni tes and g r a n o d i o r i t e s have in t ruded these o lde r v o l c a n i c s and form competent, steepened s lopes where presen t . J o i n t spacing i s wide and f r a c t u r e dens i t y i s low i n these younger p l u t o n i c r o c k s ; thus , the q u a n t i t y of weathered debr i s i s low and the t ex tu re i s u s u a l l y l a rge b locks of angular d e b r i s . Miocene v e s i c u l a r b a s a l t s and r h y o l i t e s are found in the extreme nor theas t marking the boundary between recent p la teau b a s a l t s de r ived from a set of three s h i e l d volcanoes of the i n t e r i o r reg ion to the eas t , and the o lde r v o l c a n i c and p l u t o n i c rocks which dominate the west (Souther, 1986) . Table 2.1 i s a summary of the p r i n c i p a l fo rmat ions , rock types and c o n s t i t u e n t minera l assemblages found in the B e l l a Coola bas i n . Topographic express ion of s t r u c t u r a l fea tures and format ion boundaries i s not w e l l def ined in the r e g i o n . Baer (1973) a t t r i b u t e s t h i s to the s i m i l a r i t y of mechanical p r o p e r t i e s ( e .g . hardness, j o i n t i n g ) for most rock types . O r i e n t a t i o n of i n d i v i d u a l ranges i s not c o n s i s t e n t throughout the area except for the r e g i o n a l northwest t rend of the Coast P l u t o n i c Complex. F a u l t i n g does not appear to be common al though r e l a t i v e displacements in v o l c a n i c rocks are d i f f i c u l t to observe . Baer (1973) mapped two dominant f a u l t d i r e c t i o n s , n o r t h e r l y and n o r t h e a s t e r l y , both of which separate the o lde r c h l o r i t i z e d greenstone and g r a n o d i o r i t e from the younger a n d e s i t e s . U p l i f t has occur red dur ing two orogenic events : a l e s s severe Lower J u r a s s i c event and a s t ronger pe r iod of u p l i f t in the l a t e T e r t i a r y . Baer Table 2.1. Summary o f f o r m a t i o n s and c o n s t i t u e n t m i n e r a l assemblages of rock types found i n the B e l l a C o o l a b a s i n a f t e r Baer (1973) and T i p p e r (1979). E r a P e r i o d L i t h o l o g y M i n e r a l s Lower/ P l i o c e n e r h y o l i t i c l a v a v e r y f i n e - g r a i n e d m a f i c m i n e r a l s o c c a s i o n a l o b s i d i a n Cenozoic Upper/ Miocene Eocene v e s i c u l a r b a s a l t q u a r t z monzonite f i n e - g r a i n e d m a f i c m i n e r a l s s m a l l amygdaloids 20-30% q u a r t z and 35-45% p a g i o c l a s e k-spar as h i g h as 35% b i o t i t e , hornblende and muscovite Eocene/ Paleocene g r a n o d i o r i t e 25-30% q u a r t z and 40-60% p l a g i o c l a s e minor k-spar, b i o t i t e i s the o n l y mafic m i n e r a l Cretaceous/ J u r a s s i c a n d e s i t e f l o w s and agglomerates f i n e - g r a i n e d p l a g i o c l a s e and minor k-spar p l a g i o c l a s e p h e n o c r y s t s , 1-5 mm long minor e p i d o t e and q u a r t z i n f i l l i n g Mesozoic M i d d l e J u r a s s i c Lower J u r a s s i c b l a c k s l a t e / a r g i l l i t e greenstone f i n e - g r a i n e d p h y l l o s i l i c a t e s w i t h o c c a s i o n a l microconglomerate or g r i t w i t h pebbles of q u a r t z monzonite s u b h e d r a l t o a n h e d r a l p l a g i o c l a s e (<0.5 mm) f i n e g r a i n e d m a t r i x o f c h l o r i t e , hornblende, e p i d o t e M i d d l e T r i a s s i c q u a r t z d i o r i t e up t o 35% a n h e d r a l q u a r t z and s m a l l amounts o f k-spar p l a g i o c l a s e , b i o t i t e , hornblende, e p i d o t e and minor c h l o r i t e 23 (1973) and P a r r i s h (1982) have a t t r i b u t e d most of the present geo log ic s t r u c t u r e s to the l a t t e r event . Rock shoulders on the eas tern f l a n k s of the l a rge r massi fs a long Talchako Rive r have been in t e rp re t ed as remnants of a T e r t i a r y e r o s i o n sur face which extends eastward as the Fraser P l a t e a u . U p l i f t , es t imated to be as much as 1800 m (Souther, 1977. 1986), warped the e r o s i o n surface and r e a l i g n e d the drainage such that the Atnarko and Talchako R i v e r s , which were thought to f low eastward from a d i v i d e centered along the a x i s of the Coast Mountains (Tipper , 1971a. 1971b), are supposed to have been captured by knick po in t i n c i s i o n of a r a p i d l y growing, o r o g r a p h i c a l l y - f e d , B e l l a Coola R ive r (Baer, 1973)• (2.3) Late Quaternary Geology The major v a l l e y / f i o r d systems of B r i t i s h Columbia have been deepened by m u l t i p l e g l a c i a t i o n s . The s e v e r i t y of Wisconsinan g l a c i a l a c t i v i t y near the end of the P l e i s t o c e n e has precluded the p r e s e r v a t i o n of i c e - c o n t a c t m a t e r i a l s da t ing from events e a r l i e r in the Quaternary. However, the e n t i r e B . C . coas t probably exper ienced ice-advances e s s e n t i a l l y synchronous w i t h the chronology i d e n t i f i e d for the southern coast (Armstrong, 198l). D e t e r i o r a t i n g c l i m a t e f o l l o w i n g the Olympia n o n - g l a c i a l pe r iod r e s u l t e d in the advance of ice (28,000 - 15,000 years B . P . ; Clague, 198l). Ice f low was from major accumulat ion areas along the a x i s of the Coast Mounta ins . From here i ce spread both east and west, i n i t i a l l y occupying major v a l l e y s and f i o r d s u n t i l i ce th i ckness exceeded the l o c a l r e l i e f , r e s u l t i n g in f low d i r e c t i o n s l e s s dependent on the u n d e r l y i n g topography (Clague, 1981). E r r a t i c s found on the shoulders of e x t i n c t a c t i v e s h i e l d volcanoes (Rainbow, I lgachuz and Itcha Mountains) to the east of B e l l a Coo la , a long wi th i ce -beve led pla t forms on some of the h ighes t peaks in the Monarch I c e f i e l d , i n d i c a t e that i ce th icknesses exceeded 2000 m (Tipper , 2k 1971a)« Ice flow d i r e c t i o n s es t imated by s t r i a e , d r u m l i n s , e ske r s , and f l u t e d t e r r a i n show n o r t h e a s t e r l y f low away from Monarch I c e f i e l d towards C h a r l o t t e Lake and w e s t e r l y down the B e l l a Coola V a l l e y (Baer, 1973; T i p p e r , 1971b). During the maximum advance, about 15,000 years B . P . , i ce from the Coast Mountains probably extended as far west as the c o n t i n e n t a l s h e l f (Clague, 198l) and as far east as W i l l i a m s Lake, there merging w i t h w e s t - f l o w i n g ice from the Cariboo Mountains (Tipper , 1971a). Evidence from the P r ince R u p e r t - K i t i m a t and B e l l a B e l l a areas i n d i c a t e s that d e g l a c i a t i o n along the outer c o a s t a l lowlands was r a p i d w i t h g l a c i e r s r e t r e a t i n g to t h e i r r e s p e c t i v e f i o r d head p o s i t i o n s by 12,500 years B . P . (Clague, 1981; Andrews and Re the r fo rd , 1978). Although no d a t i n g c o n t r o l i s a v a i l a b l e to the east of the d i v i d e , the grea ter e l e v a t i o n and ice th icknesses there may have r e s u l t e d in a l e s s r ap id r e t r e a t . Coas ta l and v a l l e y bottom depos i t s l a i d down by the eastward r e t r e a t i n g i ce were r e l a t e d to the p o s i t i o n of s e a - l e v e l , c o n t r o l l e d by i s o s t a t i c and e u s t a t i c responses of the land and ocean to me l t i ng i c e . R e l a t i v e sea l e v e l s were 150 to 200 m higher u n t i l approximately 9000 years B . P . (Andrews and Re the r fo rd , 1978; Clague et al., 1982), which r e s u l t e d in ice f ron t s t e rmina t ing in the sea, producing c o n d i t i o n s s i m i l a r to those found today in G l a c i e r Bay, A laska (Powel l , 1983). G l a c i g e n i c sediments depos i ted in p r o g l a c i a l f i o r d s comprise a v a r i e t y of m a t e r i a l s i n d i c a t i v e of these changing environmental c o n d i t i o n s . The c h a r a c t e r i s t i c s of the B e l l a Coola v a l l e y - f i l l have been i d e n t i f i e d us ing l o c a l borehole and r e g i o n a l data and sedimentary evidence found in outcrops ( f igure 2.k). O v e r a l l the v a l l e y - f i l l represents f a c i e s produced by g l a c i a l , g l a c i o m a r i n e , marine and a l l u v i a l p rocesses . Thick depos i t s of g l ac iomar ine s i l t y - c l a y were depos i ted dur ing the marine inundat ion phase between 12,500 and 9»000 years B . P . At the same t ime, t r i b u t a r y streams were d e p o s i t i n g 25 c > 0) E +40 gravel-capping f loodplain sequence: silty fine sand and fine gravel channel zone gravels: coarse, cobble-boulder gravel to fine sandy gravel cross-valley prograding alluvial fan: coarsening upward sequence from fine gravelly sand to coarse sandy gravel overlain by coarse cobble-boulder gravel downvalley prograding delta of Bella Coola River: coarsening upward f rom fine sandy gravel to coarse cobble gravel 9580 t 80 yr BP (GSC 3980) : wood laminated fine sandy silt and marine mud marine mud: massive silty clay c o n t i n u a t i o n o f s e q u e n c e i n f e r r e d f r o m r e g i o n a l o b s e r v a t i o n s (Howes, 1983; Powell, 1983; Clague, 1985) glaciomarine mud: massive silty clay, somewhat stony (drop stones?) outwash or subaqueous f lows at ice margin: gravelly sand basal t i l l bedrock F i g u r e 2.h Observed and i n f e r r e d v a l l e y - f i l l i n the lower reaches of B e l l a Coola R i v e r near S n o o t l i Creek. 26 m a t e r i a l i n d e l t a s a long the margin of B e l l a Coola v a l l e y . Continued ice r ece s s ion and p rograda t ion of the main v a l l e y d e l t a produced t h i c k depos i t s of sand and g rave l in a coarsening upwards sequence. Concomi tan t ly , a l l u v i a l fans a long the v a l l e y margin prograded across the v a l l e y d e p o s i t i n g sandy g rave l s and coarser cobble m a t e r i a l . T i l l of v a r y i n g th i ckness mantles most s lopes above the v a l l e y f l o o r . Prominent l a t e - g l a c i a l fea tures such as t e rmina l or r e c e s s i o n a l moraines are rare in t h i s catchment as in many other Coast Mountain v a l l e y s . Ryder (198l) has a t t r i b u t e d t h i s s c a r c i t y of d e g l a c i a t i o n depos i t s to one of two p o s s i b l e mechanisms: (1) r a p i d but o r d e r l y r e t r e a t of ice f ron t s a l l o w i n g for nothing more than b r i e f s t a t i o n a r y per iods and minimal d e p o s i t i o n or (2) in situ a b l a t i o n of main v a l l e y ice which has been cut o f f from the headwater ice source . A hummocky, k e t t l e d r idge extending par t way across the narrow B e l l a Coola v a l l e y above Nusatsum Rive r may be a subdued t e rmina l or medial moraine that was formed dur ing a b r i e f pause in l a t e g l a c i a l ice r e t r e a t . Although morphology i n d i c a t e s that the r idge i s i c e - c o n t a c t in o r i g i n , exposures of s t r a t i g r a p h y along margins of the depos i t are mostly d e l t a i c , and d i p d i r e c t i o n s of fo rese t beds and c o n s t i t u e n t l i t h o l o g i e s suggest that sediment and water were de r i ved most ly from the upper B e l l a Coola v a l l e y , ra ther than from the adjacent Nusatsum R i v e r . In any event , the bedrock- c o n t r o l l e d r e s t r i c t i o n of the main v a l l e y and confluences of the Sal loomt and Nusatsum Rive r s at t h i s p o s i t i o n , appear to have formed a complex d e p o s i t i o n a l environment c h a r a c t e r i z e d by g l a c i a l , marine and a l l u v i a l p rocesses . With the excep t ion of d e l t a i c depos i t s and a high t e r r ace of marine depos i ted c l a y e y - s i l t s , l a t e - g l a c i a l d e p o s i t i o n i s found mostly i n the upper B e l l a Coola v a l l e y compr is ing marine d e l t a s , v a l l e y bottom kames, 27 t i l l benches, l a c u s t r i n e s i l t s , eskers and some e o l i a n t ranspor ted sand d e p o s i t s . However, the number and s i z e of these depos i t s are l i m i t e d . Clague et al. (1982) and Clague (1985) demonstrate that sea l e v e l s were w i t h i n 11 m of present by at l e a s t 9720 years B . P . for the B e l l a B e l l a a r ea . A date of 3,550 ± 80 years (GSC 396**) was determined for wood sampled near the contac t of s u b a r e a l l y exposed marine c l a y and o v e r l y i n g a l l u v i a l d e l t a i c sands near the o u t l e t of Sal loomt R i v e r ( e l eva t i on i s 6l m . s . a . l . ) . The e l e v a t i o n of t h i s contac t i n d i c a t e s that r e l a t i v e sea l e v e l in the B e l l a Coola area was s t i l l higher at that time than at present , a l though marine r eg re s s ion at the s i t e occur red soon a f t e r . Evidence from both nor th and south coas t regions i n d i c a t e s tha t i s o s t a t i c u p l i f t , sea l e v e l adjustments, and ice r e t r e a t were a l l complete by 8,000 years B . P . (Armstrong, 198l ; Clague, 1985). G l a c i e r f l u c t u a t i o n s dur ing the Holocene Epoch have been documented for a number of d i f f e r e n t l o c a t i o n s along the nor theast P a c i f i c r im from Washington to Alaska (Mathews, 1951; M i l l e r , 19&9; Easterbrook and Burke, 1972; Denton and K a r l e n , 1977; Mann and U g o l i n i , 1985; Ryder and Thomson, 1986). E a r l y Holocene advances are recognized on ly i n the A l e u t i a n s (Black , 1981; 1983), Copper R ive r ( S i r k i n et al.,1971) and L i t u y a Bay d i s t r i c t s (Mann and U g o l i n i , I985) of A l a s k a , and even then appear to be asynchronous sugges t ing that they were l o c a l i z e d events , g e n e r a l l y not r e p r e s e n t a t i v e of the warmer and d r i e r c o n d i t i o n s which dominated the nor theast P a c i f i c between 6,000 and 10,000 years B . P . (Clague, 1981). M i l l e r (1969) and Ryder and Thomson (1986) document evidence for an e a r l y N e o g l a c i a l advance ( G a r i b a l d i Stade) approximate ly 5.000 years before p resen t . S i m i l a r evidence has not yet been found in mountain regions to the north of the G a r i b a l d i Park reg ion i n southwestern B r i t i s h Columbia . 28 Severa l i n v e s t i g a t o r s have i n d i c a t e d that an advance of mountain g l a c i e r s occurred between 1800 and 3000 years B . P . , which v a r i e d in i n t e n s i t y , d u r a t i o n and t iming between r eg ions , but is g e n e r a l l y recognized throughout the c o a s t a l r eg ion from Alaska to Oregon. Tiedemann G l a c i e r to the south of B e l l a Coola bas in reached i t s maximum N e o g l a c i a l extent dur ing t h i s p e r i o d , u n l i k e most other g l a c i e r s w i t h i n the reg ion (Ryder and Thomson, 1986). In accord w i th chrono log ies developed for Dome Peak and Mt. R a i n i e r in Washington (Crande l l and M i l l e r , 1964), G a r i b a l d i Park (Mathews, 1951) and southeast Alaska (Mann and U g o l i n i , 1985). Ryder and Thomson (1986) found evidence w i t h i n the P a c i f i c Ranges for i ce advances commencing around 1,000 years B . P . w i th maximum p o s i t i o n s achieved by 300 to 400 years B . P . In most regions t h i s was the most pronounced excu r s ion of a l p i n e g l a c i e r s throughout the e n t i r e Holocene Epoch. A r e g i o n a l l y synchronous response of g l a c i e r s appears to have occurred dur ing r e c e s s i o n from the L i t t l e Ice Age maximum, beginning 100 to 350 years B . P . ( F i e l d , 1975)- Evidence presented in Chapter 1 i n d i c a t e s that a L i t t l e Ice Age chronology, s i m i l a r to that developed by Ryder et a J . (unpublished) for regions to the south of the study a rea , i s a l s o a p p l i c a b l e to the B e l l a Coola b a s i n . (2.4) Climate Setting B e l l a Coola R ive r and the r e s t of the B r i t i s h Columbia coast f a l l w i t h i n the P a c i f i c coast mari t ime c l i m a t e regime, c h a r a c t e r i z e d by the on- shore movement of cyc lones and a n t i c y c l o n e s generated in the moi s t , and u s u a l l y warm, North P a c i f i c r e g i o n . The i n t e n s i t y and frequency of cyc lones vary w i th l a t i t u d e and season, and annual c l i m a t e along the coast i s c o n t r o l l e d by the seasonal pa t t e rn of f ron t s and a i r masses. Kendrew and Kerr (1955) recognized the importance of seve ra l a i r masses and t h e i r 29 as soc i a t ed f r o n t s . During summer a northward s h i f t of the mari t ime a r c t i c f ron t towards southeast Alaska i s accompanied by the i n c r e a s i n g in f luence of m i l d P a c i f i c a i r and the o c c a s i o n a l i n c u r s i o n of mari t ime t r o p i c a l a i r along the c e n t r a l and southern B . C . c o a s t . Warm and dry c o n d i t i o n s p r e v a i l , a l though the pa t t e rn i s not i n v a r i a b l e , p a r t i c u l a r l y i f high pressure r i d g i n g i s poor ly developed, and mois ture bear ing cyc lones migra te southward. The t r a n s i t i o n a l seasons (spring/autumn) are marked by r ap id s h i f t s in mean f r o n t a l p o s i t i o n s and changes in zona l c i r c u l a t i o n i n t e n s i t y . As the w in t e r season progresses , convergence of major a i r streams along the north coast b i s e c t s the reg ion in to a nor thern h a l f , i n f luenced by mari t ime a r c t i c a i r , and a southern h a l f , dominated by warmer and mois ter mar i t ime P a c i f i c a i r (Wendland and Bryson, 1981; Y a r n e l , 1985). Throughout t h i s season the c o n t i n e n t a l a r c t i c f ron t tends to occupy a p o s i t i o n along the a x i s of the Coast Mountains forming a s t rong r i dge of high pressure extending v e r t i c a l l y to mid - t roposphe r i c l e v e l s and h o r i z o n t a l l y as far west as the outer coast (Hare and Hay, 1974). Hence, the eastward movement of c y c l o n i c d i s tu rbances can be impeded. Fronts near ly always occlude and the warm sec tor a l o f t y i e l d s high p r e c i p i t a t i o n along the coas t . Outbreaks of a r c t i c a i r are not uncommon e a r l y in the win te r season (Baudat and Wrigh t , 1969). and i t i s the t iming and d u r a t i o n of these anomalously c o l d and dry per iods which determine snowpack s t a b i l i t y and the p o t e n t i a l for win te r f l o o d i n g and s p r i n g avalanche a c t i v i t y . A success ion of cyclones i n t e r s e c t s the coast du r ing the win te r season and the sepa ra t ion and i n t e n s i t y of these systems are most ly dependent on o r i g i n . Kendrew and Kerr (1955) suggest that three source areas for cyc lone development are important : (1) a southern group which s t a r t as waves on the Polar f ron t in the west P a c i f i c , t r a c k i n g 30 northeastward towards the B . C . coas t ; (2) a nor thern group generated by the e f f ec t s of Po la r a i r unde rcu t t ing Mar i t ime A r c t i c a i r o f f Japan and then t r a c k i n g east in to the Gulf of A l a s k a ; and (3) a t r a n s i t i o n a l group forming between f ron t s in the western and c e n t r a l P a c i f i c . O c c l u s i o n and i n s t a b i l i t y through a cons ide rab l e depth are common to a l l groups of cyclones as they approach the coas t . With decreas ing storm sepa ra t ion there i s an increase in cumula t ive r a i n f a l l l e ad ing to a higher snowpack volume and water content and thus grea ter p o t e n t i a l for high-magnitude win te r and sp r ing runo f f . Compounding the e f f ec t s of s y n o p t i c - s c a l e c i r c u l a t i o n fea tures are l o c a l and r e g i o n a l topographic c o n t r o l s on temperature and p r e c i p i t a t i o n . V a r i a b i l i t y of mean temperature, temperature extremes and t o t a l p r e c i p i t a t i o n , i n c l u d i n g the p ropo r t i ons of snowfa l l and r a i n f a l l , a l l show marked h o r i z o n t a l and v e r t i c a l g r a d i e n t s . For a s e r i e s of three s t a t i o n s forming a wes t - to -eas t t r ansec t from the outer coast to the i n t e r i o r , mean annual temperatures d e c l i n e from 8.1^C to 3-9^C, and t o t a l annual p r e c i p i t a t i o n decreases by an order of magnitude from 4390 mm to 410 mm ( f igure 2.5)- This s t rong in land g rad ien t from a mesothermal, perhumid c l i m a t e to one of c o n t i n e n t a l charac te r occurs over a d i s t a n c e of l e s s than 200 km. Superimposed on the h o r i z o n t a l p r e c i p i t a t i o n g rad ien t are l a r g e , o r o g r a p h i c a l l y induced v a r i a t i o n s in p r e c i p i t a t i o n w i t h e l e v a t i o n . Using May 1 snowpack water e q u i v a l e n t s , recorded 1800 m above the B e l l a Coola c l i m a t e s t a t i o n , as a measure of t o t a l win te r p r e c i p i t a t i o n at t h i s e l e v a t i o n , i t appears tha t , on average, p r e c i p i t a t i o n increases by approximately 100 mm per 100 m of e l e v a t i o n . Approximately 60% of the B e l l a Coola ba s in l i e s in the lee of the Coast Mountains , which i s r e f l e c t e d in the d i s t r i b u t i o n and accumulat ion of snowfa l l du r ing the win te r season. Snow course da ta , c o l l e c t e d for a M A M J J A S O N D MONTH 600 600 I — 400 c o 5 300 o. u t 200 a. 100 BELLA COOLA 52° 22' N 126° 41" W Elev. 18 m TP 1614 TS 191 TR 1424 mean maximum mean temperature mean minimum ,snowfal1 ralnfalI J F M A M J J ASO ND MONTH 30 | 20 S -1 10 * c 0 3 -10 o 600 500 i — 400 e o ™ 300 a. £ 200 o. 100 TATLAYOKO LAKE 61° 40' N 124° 24' M Elev. 8S3 m TP 412 urn TS 142 mm TR 270 mn 30 g 20 f 1 o> lOg O 3 J F M A M J J A S O N D MONTH Figure 2 . 5 Climographs for a west to east t r ansec t through B e l l a Coola b a s i n . S t a t i o n s are loca t ed i n f i g u r e s 2 .1 . and 2 .2 . TP i s t o t a l p r e c i p i t a t i o n , TR i s t o t a l r a i n f a l l and TS t o t a l snowfa l l (Source: Atmospheric Environment S e r v i c e , 1981) . 32 l i m i t e d number of cor responding years from an eas te rn and a western s i t e a t s i m i l a r e l e v a t i o n s w i t h i n the catchment show that l a t e s p r i n g snowpack water equ iva l en t s are 8 to 10 t imes greater in the west (record mean of 1753 mm) than those in the east (record mean of 230 mm). (2.5) Hydrology Average Regime W i t h i n the b a s i n , nine r i v e r gauges have been ope ra t i ve at v a r i o u s times s i n c e 1930, but on ly f i v e p rov ide data for per iods longer than f i v e years a f t e r 1948. The combined data s e r i e s from two s t a t i o n s on the main r i v e r cover the pe r iod 1948-present, w h i l e three of the t r i b u t a r y gauges (Atnarko, Nusatsum, Salloomt) were e s t a b l i s h e d dur ing the summer of 19&5 and have been in ope ra t i on con t i nuous ly s ince then . The main r i v e r gauge, r e loca t ed in 19&5. i s on ly a few k i lome te r s below the conf luence of Talchako and Atnarko R i v e r s , the l a t t e r of which i s gauged j u s t above the conf luence , a l l o w i n g for es t imates of f low in the ungauged Talchako River by s imple s u b t r a c t i o n . Gauge l o c a t i o n s and a summary of hydrometr ic data from each s i t e are g iven in f i g u r e 2.2 and t a b l e 2.2 r e s p e c t i v e l y . V a r i a b i l i t y in bas in -wide runoff i s s t r o n g l y a f fec ted by the d i s t r i b u t i o n of snow. It a l s o i s a f f ec t ed by the l o c a t i o n of shor t and long-term water s torage s i t e s such as lakes and g l a c i e r s . Mean annual runoff from the bas in above Burnt Br idge Creek i s 790 mm w i t h a maximum of 1023 mm recorded in 1976. For p a r t l y g l a c i e r - c o v e r e d t r i b u t a r y catchments s i t u a t e d in the southern and western p o r t i o n s of the bas in ( e .g . Nusatsum River ) mean annual runoff i s s i g n i f i c a n t l y h ighe r , averaging over 2000 mm ( tab le 2.2). Mean annual runoff from the l a rge r Atnarko River d r a i n i n g i c e - free t e r r a i n i s one t h i r d of the d i scharge from Talchako R i v e r , which d r a i n s a 25% g l a c i e r - c o v e r e d a r ea . I n t e r - c o r r e l a t i o n of annual mean and 33 T a b l e 2 . 2 . H y d r o m e t r i c d a t a f o r s t a t i o n s i n t h e B e l l a C o o l a b a s i n . ( S o u r c e : W a t e r S u r v e y o f C a n a d a , 1982) W . S . C . S t a t i o n name ( n u m b e r ) I n t e r v a l o f D r a i n a g e M e a n A n n u a l M e a n A n n u a l M a x i m u m D a i l y D i s c h a r g e X D i f f e r e n c e o f 3 - 1 1 O p e r a t i o n A r e a D i s c h a r g e R u n o f f (mm) (m s ) A u t u m n v s . S p r i n g 2 3 - 1 (# o f y e a r s ) (km ) (m s ) S p r i n g A u t u m n ( d a t e ) ( d a t e ) B e l l a C o o l a R . n e a r H a g e n s b o r g ( 0 8 F B 0 0 2 ) 1 9 4 7 - 6 8 4 , 0 4 0 ( 2 1 ) 668 963 ( 0 6 / 1 1 / 6 4 ) ( 0 1 / 2 4 / 6 8 ) B e l l a C o o l a R . a b o v e B u r n t B r i d g e C r . ( 0 8 F B 0 0 7 ) 1 9 6 5 - p r e s e n t 3 , 7 3 0 ( 2 1 ) 558 703 ( 0 6 / 1 1 / 6 9 ) ( 0 1 / 2 3 / 6 8 ) B e l l a C o o l a R . a t B e l l a C o o l a ( 0 8 F B 0 0 1 ) 1929 ( 1 ) 405 ( 0 7 / 0 9 / 2 9 ) 430 ( 1 6 / 1 0 / 2 9 ) B e l l a C o o l a R . a t H a g e n s b o r g ( 0 8 F B 0 0 8 ) 1 9 3 0 - 3 2 4 , 8 0 0 ( 2 ) 5 6 1 ( 1 0 / 0 6 / 3 0 ) 561 ( 0 9 / 1 7 / 3 0 ) N u s a t s u m R . ( 0 8 F B 0 0 5 ) 1 9 6 5 - p r e s e n t 2 6 9 ( 2 1 ) 83 ( 1 6 / 0 5 / 7 0 ) 190 ( 0 9 / 2 7 / 7 3 ) S a l l o o m t R . ( 0 8 F B 0 0 4 ) 1 9 6 5 - p r e s e n t 161 ( 2 1 ) 9 . 3 1 , 8 2 0 4 3 . 3 ( 1 6 / 0 5 / 7 0 ) 141 ( 1 2 / 1 6 / 8 0 ) A t n a r k o R . ( 0 8 F B 0 0 6 ) 1 9 6 5 - p r e s e n t 2 , 4 3 0 ( 2 1 ) 2 5 8 ( 3 0 / 0 5 / 7 2 ) 289 ( 0 1 / 2 4 / 6 8 ) T a s t s q u a n C r . ( 0 8 F B 0 0 3 ) 1 9 4 6 - 1 9 5 0 ( 4 ) 2 . 2 2 , 3 9 0 2 1 . 6 ( 0 6 / 1 8 / 5 0 ) 3 6 . 5 ( 2 4 / 1 0 / 4 7 ) C l a y t o n F a l l s C r . ( 0 8 F B 0 0 9 ) 1 9 8 0 - p r e s e n t 4 8 1 ( 5 ) 2 1 . 2 ( 0 5 / 2 1 / 8 2 ) 8 5 . 6 ( 0 8 / 0 9 / 8 2 ) T a l c h a k o R . 1 9 6 5 - p r e s e n t 1 , 3 0 0 ( 2 1 ) 6 2 . 7 1 , 5 2 1 407 ( 0 6 / 1 1 / 6 7 ) 552 ( 0 1 / 2 3 / 6 8 ) 1. C a l c u l a t e d a s [ Q ^ / Q ^ ] X 100 w h e r e Q , , i s t h e maximum d a i l y d i s c h a r g e d u e t o s p r i n g s n o w m e l t a n d i s t h e max imum d a i l y d i s c h a r g e d u e t o a n a u t u m n r a i n s t o r m f o r t h e p e r i o d o f r e c o r d . N o t c o m p u t e d f o r s t a t i o n s w i t h a l i m i t e d l e n g t h o f r e c o r d . 2 . F l o w s e s t i m a t e d b y s u b t r a c t i n g A t n a r k o R . d a t a f r o m B e l l a C o o l a R . d a t a a b o v e B u r n t B r i d g e C r e e k . No m a j o r t r i b u t a r i e s j o i n t h e s y s t e m b e t w e e n t h e s e two g a u g i n g s i t e s . F l o w s may b e u n d e r e s t i m a t e d b y 2-3Z. 3** annual maximum discharges i n d i c a t e s that Nusatsum/Talchako R ive r s are h y d r o l o g i c a l l y d i s t i n c t from Sa l loomt /Atna rko R i v e r s , p r i m a r i l y on the bas i s of g l a c i e r melt c o n t r i b u t i o n s to runoff and higher mean e l e v a t i o n s . However, the Atnarko Rive r r e t a i n s a somewhat s i n g u l a r s i g n a l due to the much lower annual p r e c i p i t a t i o n and frequency of l a k e s , which tend to reduce peak d i s c h a r g e s . Severa l seasonal runoff regimes can be i d e n t i f i e d for B e l l a Coola R i v e r , which are t y p i c a l of other r i v e r s a long the B r i t i s h Columbia c o a s t . Beginning in l a t e A p r i l through mid to l a t e June, runoff due to snowmelt is somewhat v a r i a b l e , but s t e a d i l y i n c r e a s i n g d i scharges are e v i d e n t . O c c a s i o n a l l y , runoff i s augmented by r a i n f a l l on the r ipened snowpack. F o l l o w i n g the snowmelt peak in e a r l y to middle June (or l a t e May for some r i v e r s ) , runoff d e c l i n e s u n t i l l a t e J u l y , when d i scharge again increases as g l a c i e r melt begins to c o n t r i b u t e s i g n i f i c a n t volumes of s to red water ( f igure 2.6). Superimposed on s t e a d i l y d e c l i n i n g r i v e r d i scharges from l a t e August onwards are high-magnitude synop t i c runoff events de r i ved from two sources : (1) r a i n f a l l de r ived f loods w i th on ly minor c o n t r i b u t i o n s from m e l t i n g snow or (2) ra in-on-snow events a s soc i a t ed w i th r a p i d l y r i s i n g f r e e z i n g l e v e l s f o l l o w i n g the eastward movement of autumn c y c l o n i c d i s t u r b a n c e s . F i n a l l y , from January to A p r i l win te r low flows dominate the runoff regime. Maximum d a i l y and instantaneous d i scharges almost always occur dur ing the s h o r t - d u r a t i o n autumn f loods ( tab le 2.2), but the h ighes t average runoff i s du r ing the summer snow and g l a c i e r melt pe r iod ( f igure 2.6). Hart (198lb) has shown that the r a t i o of maximum instantaneous to mean d a i l y d i scharge for autumn f loods in the K i t i m a t and P a c i f i c Ranges v a r i e s w i t h dra inage area but i s g e n e r a l l y between 1.5 and 1.9. Maximum d a i l y d i scharges from ra ins torm-genera ted f loods in the gauged catchments are on BELLA COOLA RIVER Annual Hydrograph of Mean Daily Flow, 1980 Water Survey of Canada Gauge 08FB007 Ad = 3,430 km 2 1 = Rainstorm generated f l o o d 2 = Rain-on-snow f l o o d Winter Low Flow Snowmelt G l a c i e r mel t Autumn Rainstorms " j A N I F E B 1 MAR I APR I M A ? I J U N 1 J O T 1 A U G ' S E P ' O C T T N O V " D E C ^ F i g u r e 2.6 The 1980 annual hydrograph for B e l l a Coola R i v e r above Burnt Br idge Creek. 36 average 25~40% greater than s p r i n g snowmelt f l o o d s . However, as g l a c i e r cover and l o c a l r e l i e f increase and bas in s i z e decreases , t h i s d i f f e r e n c e can be as high as 300%. Major Floods During the 20th Century H i s t o r i c a l and instrument records show that there were approximate ly t h i r t e e n major f l o o d events between 1896 and I98O. The pre-1948 record of l e s s extreme f l o o d i n g i s probably incomplete , however; a l l the l a r g e s t f lows were documented. With the excep t ion of a f l o o d in the f a l l of 1950, a l l high-magnitude, autumn and s p r i n g runoff events on the B e l l a Coola R ive r were a s soc ia t ed w i t h win te r seasons (October to A p r i l ) c h a r a c t e r i z e d by p o s i t i v e p r e c i p i t a t i o n anomal ies . Only s i x other seasons in the 88 year record e x h i b i t e d s t r o n g l y p o s i t i v e p r e c i p i t a t i o n anomalies and no evidence of responses in the form of s i g n i f i c a n t f l o o d i n g . Large runoff events were not p reva len t in these years because in a l l s i x cases s p r i n g and summer temperatures were w e l l below normal promoting water s to rage . The most ou ts tanding f l ood events occurred in the middle 1930's and 1960's. The four f loods (1934, 1936, 1965, 1968) are among the s i x l a r g e s t measured or es t imated f lows on the r i v e r . As such they represent 'key even t s ' in the long- term hydrology of the bas in because in each ins t ance , p a r t i c u l a r l y the rain-on-snow events , major channel real ignment or s i g n i f i c a n t overbank sedimenta t ion occu r r ed . For t h i s reason a b r i e f d e s c r i p t i o n of the h y d r o c l i m a t i c c i rcumstances a s soc i a t ed w i t h these two sequences i s g i v e n , and the i m p l i c a t i o n s for e f f e c t s from lower-magnitude events are considered b r i e f l y . The f l o o d of October 10, 193̂  r e s u l t e d from the o c c l u s i o n of f ron t s a s soc i a t ed wi th an i n t e n s i f i e d low pressure system (960 mb) to the west of Vancouver I s l a n d . A b l o c k i n g r i dge of high pressure over the western Uni ted 37 Sta tes l ed to the low s t a l l i n g as i t approached the coas t . High-water appears to have been more l o c a l i z e d because of s i g n i f i c a n t log jams on the r i v e r . Storage of o rgan ic d e b r i s in the channel was probably s i g n i f i c a n t s i nce the l a s t documented f l o o d was ten years be fo re . F lood ing on November 19. 1936 was more severe than the 193** f l o o d for two reasons. F i r s t , a s e r i e s of low pressure systems moving southward from the Gulf of A l a s k a , preceded the l a rge r system y i e l d i n g snowfa l l at middle and at lower l e v e l s in the b a s i n . Second, a w e l l developed warm f ron t swept, through the area r a i s i n g the f r e e z i n g l e v e l s u b s t a n t i a l l y . A m e l t i n g snowpack c o n t r i b u t e d g r e a t l y to the runof f . Synopt ic c o n d i t i o n s for the October 22, 1965 f l o o d were s i m i l a r to those in 193**: northward moving d i s tu rbances produced seven-day t o t a l p r e c i p i t a t i o n of 190 mm p r i o r to the peak d i scha rge ; one of the l a r g e s t f l o o d - r e l a t e d r a i n f a l l p e r i o d s . Ridge development in A l b e r t a was c h a r a c t e r i s t i c of the January 23, 1968 f l o o d . L i k e the 1936 f l o o d , peak d i scharges were much higher due to s u b s t a n t i a l snowmelt as the f r e e z i n g l e v e l increased dur ing a four day pe r iod p r i o r to the f l o o d . Maximum instantaneous flows from t h i s event were probably the l a r g e s t to occur t h i s cen tu ry . With the excep t ion of moderately high s p r i n g runoff in l a t e May of 19**8, there were no f l o o d events of notable between 1936 and 1950. The f l o o d of November h, 1950 was the four th l a r g e s t es t imated f low and appears to have had minimal impact in terms of channel changes. Two f a c t o r s might e x p l a i n t h i s . F i r s t , both the r i s i n g and f a l l i n g l imb of the f l o o d hydrograph were very steep so the peak d i scharge was of shor t d u r a t i o n . Second, runoff i n two of the preceding three sp r ings was s i g n i f i c a n t l y h igh (although not of major f l o o d p ropor t ions ) so that any accumulat ion of organ ic d e b r i s in the channel may have been removed. The i m p l i c a t i o n i s 38 that not a l l l a rge runoff events may have an impact on the r i v e r . There i s some evidence for i n c i p i e n t i n s t a b i l i t y in c e r t a i n reaches of the r i v e r such that moderate f loods may produce s u b s t a n t i a l l o c a l i z e d channel changes. In most cases the i n s t a b i l i t y i s r e l a t e d to the occurrence of log jams which , when removed, modify the d i r e c t i o n of channel f l o w . (2.6) Sources and Transfer of Clastic Sediment An important s tep in de termining the trends of bas in sediment y i e l d and p o s s i b l e a s s o c i a t i o n s w i th changing hydroc l imate i s c o n s i d e r a t i o n of sediment sources and processes of sediment t r a n s f e r . The purpose of t h i s s e c t i o n i s to document the c h a r a c t e r i s t i c s of the sediment cascade and assess the d i s t r i b u t i o n of s e v e r a l primary sediment sources and res idence times in a s soc i a t ed sediment s i n k s . A conceptual model, shown in f i g u r e 2.7, has been adapted from those g iven in Simons et al. (1982) and Roberts and Church (1986) , and i s used here to i l l u s t r a t e the primary sources , t r ans fe r and storage of c l a s t i c sediment in the B e l l a Coola River b a s i n . Three primary sediment sources can be i d e n t i f i e d : (1) in situ weathered bedrock; (2) g l a c i a l depos i t s in p r o g l a c i a l and i ce -marg ina l areas of contemporary g l a c i e r s ; and (3) c l a s t i c m a t e r i a l s , i n c l u d i n g s o i l , which mantle h i l l s l o p e s or i n f i l l e d g u l l i e s , the bulk of which was depos i ted dur ing the l a t e P l e i s t o c e n e and e a r l y Holocene epochs. These m a t e r i a l s are m o b i l i z e d by mass wast ing ( r o c k f a l l / r o c k s l i d e , avalanche, d e b r i s f l o w , g u l l y wash, s o i l creep) and f l u v i a l p rocesses . Storage of r e c e n t l y produced sediment in the upland or headwater areas i s in the form of c o l l u v i a l depos i t s or p a r t l y i n f i l l e d p r o g l a c i a l lakes which were formed dur ing ice r e t r e a t . Residence times w i l l vary as a f u n c t i o n of r e s e r v o i r c a p a c i t y , s lope s t a b i l i t y and sediment t r an s f e r r a t e s . F l u v i a l e r o s i o n and mass was t ing of s lope depos i t s may in t roduce 39 Weathered Bedrock j o i n t s p a c i n g , f r a c t u r e d e n s i t y Fresh Glacial Deposits t e r m i n a l , l a t e r a l and ground moraines r o c k f a l1/ r o c k s l i d e mix ing T i l l and In Situ Soil on Hi 11 slopes I d e b r i s s l i d e d e b r i s f l ow 4 avalanche i f I u v i a l t r a n s p o r t Colluvium, Talus Composite Debris Slopes I f o o t s l o p e e r o s i o n Proglacial Lakes: Lacustrine Deposits f 1 u v i a l t r a n s p o r t Upland Val leys: Channel Storage — . J I 1 channel i e r o s i o n i Tributary A l luv ia l Fans Long-Term Lake Storage T fan u n d e r c u t t i n g , channel e r o s i o n Channel Zone and Floodplain Storage 1 channel m i g r a t i o n bank e r o s i o n ±_ Marine Delta F i g u r e 2-7 G e n e r a l i z e d c l a s t i c sediment r o u t i n g and pr imary t r a n s p o r t processes in B e l l a Coola b a s i n . ko c l a s t i c d e b r i s d i r e c t l y to the channel zone of low-order t r i b u t a r i e s . Gra in s i z e s are u s u a l l y very coarse (bouldery to blocky) and thus t r a n s p o r t - l i m i t e d c o n d i t i o n s p r e v a i l . F l u v i a l t r anspor t moves some of the sediment in to downstream s torage s i t e s such as t r i b u t a r y a l l u v i a l fans , upland v a l l e y t r a i n s , lakes a long p r i n c i p a l dra inage l i n e s or u l t i m a t e l y to the channel and f l o o d p l a i n s of higher order s treams. If s torage c a p a c i t i e s are high and sediment t r ans fe r ra tes low, a t r a n s i t i o n to s u p p l y - l i m i t e d c o n d i t i o n s i s l i k e l y to occur downstream. F i n a l l y , f l u v i a l processes along the main stem of the system w i l l pass sediment through to the b a s i n o u t l e t where sediments are depos i ted in a growing marine d e l t a . I n t e r p r e t a t i o n from a e r i a l photographs o f f e r s the only p r a c t i c a l method of e v a l u a t i n g c l a s t i c sediment sources and d i f f e r e n t i a l movement r a t e s , even though the technique y i e l d s l i m i t e d q u a n t i t a t i v e in format ion on s torage volumes and depos i t s t a b i l i t y . Two sca le s of mapping were undertaken to eva lua te sediment sources : (1) i n t e r p r e t a t i o n of bas in -wide fea tures from medium s c a l e (1:21,000 to 1:40,000) b lack and whi te a i r photography and (2) d e t a i l e d a i r photograph and f i e l d mapping of three 2 2 subcatchments: Sal loomt River (169 km ) , Burnt Br idge Creek (215 km ) , and 2 Nusatsum River (269 km ) ,*which are r e p r e s e n t a t i v e of the s p a t i a l v a r i a t i o n s in h y d r o l o g i c , phys iographic and geo log i c c o n d i t i o n s w i t h i n the bas i n . Upland Sediment Sources Seven types of sediment sources were i d e n t i f i e d : composite deb r i s s l o p e s , t a l u s s lopes (g rav i ty s o r t e d ) , a l l u v i a l fan or t a l l u v i a l d e b r i s cones, r o c k f a l 1 / r o c k s l i d e d e p o s i t s , in situ mountain top d e t r i t u s or fe lsenmeer , l a t e r a l and p r o g l a c i a l t i l l d e p o s i t s , and b lanke t s or veneers of t i l l a long fo res t ed s l o p e s . kl Composite deb r i s s lopes are po lygene t i c landforms produced by any combinat ion of r o c k f a l l , avalanche and d e b r i s f low (c f . Rapp, I960; Chandler , 1973; Church et al., 1979)- H igh ly f r ac tu red and j o i n t e d greenstone rocks in the bas in are an important source for these b locky depos i t s which form below open rock s lopes d i s s e c t e d by numerous avalanche and r o c k f a l l chutes . They are a l s o found on conf ined rock s lopes above the f l anks of a c t i v e c i r q u e g l a c i e r s , where removal of ice by me l t i ng has promoted the f a i l u r e of rock su r f aces . Although wide ly d i s t r i b u t e d and of cons ide rab l e volume throughout the v o l c a n i c t e r r a i n , these s lopes are not o v e r a l l an important source of onward moving c l a s t i c sediment due to the coar se -g ra ined nature of the debr i s and t r anspor t l i m i t e d c o n d i t i o n s which r e s u l t . Ta lus s lopes are g r a v i t y - s o r t e d , r o c k f a l l dominated landforms, forming d i s c r e t e but smal l sheets or m u l t i p l e c o a l e s c i n g cones, p r i m a r i l y above t r e e l i n e , or below steep bedrock c l i f f s at lower e l e v a t i o n s . These depos i t s occur f r equen t ly along the edges of former l ava f lows and below ex tens ion f a u l t s in the p la teau areas of the nor theas te rn catchment, but are poor ly connected to the f l u v i a l network. High magnitude r o c k f a l l s / r o c k s l i d e s are def ined on the bas i s of c r i t e r i a suggested by Mudge (1965) . the most important of which are the slope-base p o s i t i o n of coarse b locky d e b r i s and a v i s i b l e upslope f a i l u r e su r f ace . The l a r g e s t depos i t s occur on t e r r a i n u n d e r l a i n by p l u t o n i c or metamorphic rock types . For example, of the twelve depos i t s i d e n t i f i e d in the Nusatsum b a s i n , e igh t are de r ived from i n t r u s i v e rocks and four from v o l c a n i c / s e d i m e n t a r y sources . Th i s i s s i g n i f i c a n t g iven that the d i s t r i b u t i o n of rock- type i s about the reverse ( f igure 2.3). Most recognized depos i t s are at or above t r e e l i n e and in some cases have impounded smal l l a k e s . Est imates of volume are d i f f i c u l t to make because of unknown depths, but appears to range downward from 10^ m^. The l a r g e s t r o c k s l i d e mapped occur red in approximate ly 1951 in the headwaters of the Atnarko R ive r as a r e s u l t of a f o l i a t i o n plane f a i l u r e in g n e i s s i c rocks g ( J . J . Clague, personal communication, 1986). The volume i s es t imated at 10 3 m . The depos i t r e s u l t e d in minor real ignment of the drainage d i v i d e between the Atnarko and North K l i n a k l i n i R i v e r s . A l l u v i a l fans and t a l l u v i a l deb r i s cones are found below low-grad ien t and steep bas in o u t l e t s , r e s p e c t i v e l y , and u s u a l l y con ta in a pe renn ia l sur face stream along one margin of the d e p o s i t . F l u v i a l p rocesses , snow avalanches and r o c k f a l l s d e l i v e r sediment to the surface of these d e p o s i t s . P e r e n n i a l streamflow on the sur face and a c t i v e toe e r o s i o n by higher order streams i n d i c a t e that these landforms are an important source of sediment. Block f i e l d s are found on e leva ted rock p l a t fo rms , ice eroded benches and c o l s . Sediments are de r ived by in situ mechanical and chemical weather ing of w e l l j o i n t e d bedrock, p a r t i c u l a r l y along non-conformable con tac t s of va r i ous v o l c a n i c rock types . They are perhaps the l e a s t important sediment sources because of l i m i t e d volumes and s t a b l e upland pos i t i ons . L a t e r a l and p r o g l a c i a l t i l l d epos i t s formed by the r eces s ion of v a l l e y , hanging v a l l e y , c i r q u e and niche g l a c i e r s are the most important sources of sediment in g l a c i e r i z e d p o r t i o n s of the catchment, p a r t i c u l a r l y where the depos i t s are on steep t e r r a i n dra ined by avalanche and deb r i s t o r r e n t channels ( f igure 2.8a and b ) . Although the volume of m a t e r i a l d e l i v e r e d to the stream i s low in r e l a t i o n to the amount a v a i l a b l e for t r anspo r t (i.e. low sediment d e l i v e r y r a t i o ) , aggradat ion and channel b r a i d i n g are obvious impacts on the f l u v i a l network immediately downstream from these sources . On a bas in-wide average, l a t e r a l depos i t s are of l e s s o v e r a l l importance. F i g u r e 2.8 I l l u s t r a t i o n s of pr imary c l a s t i c sediment sources for the h i g h e r - o r d e r f l u v i a l network i n B e l l a Coo la b a s i n . (A) Niche g l a c i e r on the western f l ank of the Nusatsum b a s i n s u p p l i e s a s i g n i f i c a n t amount of sediment to channe ls below the g l a c i e r . The d e b r i s t o r r e n t s are w e l l connected to the h i g h - o r d e r f l u v i a l network. (B) Rock g l a c i e r / a b l a t i o n d e b r i s in the south fork of G y l l e n s p e t z Creek i s d i s s e c t e d by numerous avalanche chutes on e a s i l y eroded v o l c a n i c r o c k s . T h i s s i t e i s a s i g n i f i c a n t source of sediment for Ta lchako R i v e r . (C) P r o g l a c i a l lake of Jacobsen G l a c i e r ac t s as an impor tant s to rage s i t e for a b l a t i o n sediments and d e b r i s t r a n s p o r t e d by i c e marg ina l s t reams. (D) Upland p l a i n in the east Nusatsum v a l l e y i s one of s e v e r a l s to rage s i t e s for g l a c i a l d e r i v e d sed iments . 44 M S **5 The f i n a l sources of c l a s t i c m a t e r i a l s are surface wash, s o i l creep and bank e r o s i o n . Roberts and Church (1986) es t imate that sur face wash and s o i l c reep , on average, c o n s t i t u t e l e s s than 10-20% of the t o t a l sediment volume d e l i v e r e d to s m a l l , p a r t l y logged watersheds in the Queen C h a r l o t t e I s l ands . R e l a t i v e d e l i v e r y ra tes in l a r g e , unlogged t r i b u t a r i e s , such as most of those in the B e l l a Coola b a s i n , would be p r o p o r t i o n a l l y lower due to the s t a b i l i z i n g e f f e c t s of the vege t a t i on and a higher frequency of lower -g rad ien t s lope segments. Streambanks are an important source for f l u v i a l entrainment of sediment but , es t imates of c o n t r i b u t i o n to sediment y i e l d in t eg ra ted over an e n t i r e watershed are d i f f i c u l t to make. Four major types of sediment s torage have been i d e n t i f i e d in the B e l l a Coola b a s i n . F i r s t , r e l a t i v e l y deep lakes along p r i n c i p a l dra inage l i n e s , p a r t i c u l a r l y in the Atnarko watershed, e f f e c t i v e l y t rap a l l the c l a s t i c sediment de r i ved from above each lake s i t e . The l a r g e s t , C h a r l o t t e 2 Lake (65 km ) , i s fed by creeks which d r a i n an area of approximate ly 750 2 km , thereby e l i m i n a t i n g any s i g n i f i c a n t c o n t r i b u t i o n from t h i s area of the eas te rn catchment (see f i g u r e 2.2 for l o c a t i o n s ) . Residence times in these s i t e s are comparable in length to the i n t e r v a l of d e g l a c i a t i o n (10 y e a r s ) . Sha l low, p r o g l a c i a l lakes formed dur ing recent g l a c i a l r e t r e a t ( f igure 2.8c) are l e s s e f f i c i e n t s inks but e q u a l l y important over a shor te r time 2 s c a l e (10 years) ( c f . Smith et al., 1982). Second, upland v a l l e y t r a i n s form on l ow-g rad i en t , bedrock- c o n t r o l l e d , v a l l e y f l a t s at higher e l e v a t i o n s in p r o g l a c i a l areas of the southwestern catchment, or on p la teau areas of the eas te rn catchment. 2 G l a c i a l and f l u v i a l sediments de r ived areas as l a rge as 30 km are s to red at these s i t e s ( f igure 2 .8d) . Trap e f f i c i e n c y i s l e s s than that of lakes 3 4 but res idence times are e q u a l l y long (estimated at 10 - 10 y e a r s ) . T h i r d , r o c k s l i d e dams of v a r i o u s magnitudes a l s o form e f f e c t i v e b a r r i e r s to the 46 throughput of c l a s t i c m a t e r i a l s . The i r frequency of occurrence i s much 3 4 lower , but res idence times are a l s o long (10 - 10 y e a r s ) . F i n a l l y , c o l l u v i u m and t i l l , s to red on many of the fo res t ed h i l l s l o p e s , are probably the l a r g e s t sediment s i n k s in the b a s i n . U l t ima te turnover ra tes are most 4 l i k e l y in excess of 10 yea r s . A e r i a l photographs and f i e l d evidence i n d i c a t e that much of the sediment in the upland t r i b u t a r i e s i s de r ived from w e l l - d e f i n e d , uns tab le s lopes and bank e r o s i o n of m a t e r i a l a l ready s tored w i t h i n the v a l l e y f l a t . The d i s t r i b u t i o n and volume of the major sediment sources , along w i t h the l o c a t i o n s of major s torage s i t e s , are p l o t t e d in f i g u r e 2.9- In s e v e r a l t r i b u t a r i e s there are one or two primary sources , such as uns tab le p r o g l a c i a l depos i t s ( e .g . Nusatsum, Nordschow, Thorsen Creeks) or composite deb r i s s lopes (e .g . Burnt B r i d g e , Nordschow, Noosgulch C r e e k s ) . The combined area of the sediment sources in f i g u r e 2.9 c o n s t i t u t e s l e s s than 16% of the e n t i r e watershed. These r e s u l t s suggest that the t r ans fe r of 2 3 sediment to the B e l l a Coola R ive r over a time s c a l e of 10 - 10 years i s a s soc i a t ed w i t h a r e l a t i v e l y smal l number of upland sources and f l u v i a l a c t i v i t y w i t h i n s eve ra l t r i b u t a r y channe ls . (2.7) Pedo log ic S e t t i n g S o i l development in the B e l l a Coola bas in r e f l e c t s the s t rong v a r i a b i l i t y in topography, frequent sediment a d d i t i o n s from r i v e r f l o o d i n g in the v a l l e y and, at higher e l e v a t i o n s , slow decomposi t ion of o rgan ic m a t e r i a l . W i t h i n the conf ines of v a l l e y bottoms most s o i l s vary between poor ly developed o r t h i c regoso ls and e u t r i c b r u n i s o l s ( B r i t i s h Columbia M i n i s t r y of A g r i c u l t u r e , 1973)* Th in Ah hor i zons (3 to 5 cm) over f i n e sand are common on many a l l u v i a l sur faces where, a d d i t i o n s of mine ra l matter may exceed o rgan ic matter accumulat ion s i g n i f i c a n t l y . Under t h i c k con i f e rous Figu re 2 . 9 Major c l a s t i c sediment sources for the h ighe r -o rde r f l u v i a l network and es t imates of res idence time in important s torage s i t e s . Arrows represent the l o c a t i o n of both the sediment sources and primary routes through which sediment is t r a n s f e r r e d (see t e x t for d i s c u s s i o n ) . ^ 48 f o r e s t cove r , d y s t r i c b r u n i s o l s may develop in to o r t h i c humo-fer r ic podzols i f the s i t e has remained s t a b l e for some t ime . Organic s o i l s are r e s t r i c t e d to poor ly dra ined l o c a t i o n s surrounded by both con i fe rous and deciduous v e g e t a t i o n . Typ ic mes i so l s and h y d r i c f i b r i s o l s occupy many of the water - sa tu ra ted a l p i n e meadows. (2.8) Flora The f l o r i s t i c component of the landscape provides an e s s e n t i a l key to geomorphic a c t i v i t y and h y d r o l o g i c change w i t h i n c e r t a i n growth-t ime boundar ies . The c a p a c i t y of many spec ies to wi ths tand environmental extremes yet preserve evidence of s t r e s s f u l p e r i o d s , provides c o r r e l a t i o n s w i t h geomorphic /hydro log ic events , as w e l l as a bas i s for abso lu te and r e l a t i v e d a t i n g . For t h i s purpose some of the dominant vege t a t i on communities are noted. S i x b i o g e o c l i m a t i c zones and seve ra l subzones have been i d e n t i f i e d in the B e l l a Coola b a s i n , each based on the dominance or co-dominance of c l imax t ree spec ies (Robinson and Po ja r , 1981; Leaney and M o r r i s , 198l). Along the l o w e r - e l e v a t i o n western per iphery where m i l d , mo i s t , mar i t ime c o n d i t i o n s p r e v a i l , a t h i c k cover of western red cedar (Thuja plicata Donn) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) i s found. The o l d e s t and t a l l e s t timber grows on compara t ive ly o r g a n i c - r i c h s o i l s of the f l o o d p l a i n and steep c o l l u v i a l s l o p e s . At e l e v a t i o n s below 500 m between B e l l a Coola and F i r v a l e a mix ture of Douglas f i r (Pseudotsuga menziesii (Mirb. ) Franco) and western hemlock o v e r l i e an unders tory of mosses and d e v i l ' s c lub (Oplopanax horridus). Th i s a s s o c i a t i o n grades q u i c k l y i n to a Douglas f i r / r e d cedar/moss ecosystem east of F i r v a l e . The B e l l a Coola R ive r f l o o d p l a i n i s dominated by a f o r e s t cover i n d i c a t i v e of e a r l y s u c c e s s i o n a l phases on r e c e n t l y f looded surfaces or 9̂ areas w i t h high water t a b l e s , and l a t e s u c c e s s i o n a l spec ies on higher and more s t a b l e su r f ace s . Black cottonwood (Populus trichocarpa T o r r . £ G r a y ) , red a lder (Alnus Rubra Bong.) and whi te b i r c h (Betula papyrifera Marsh.) are most ev ident on r e c e n t l y c o l o n i z e d p o r t i o n s of the f l o o d p l a i n w h i l e Western red cedar, S i t k a spruce (P/cea sitchensis (Bong.) C a r r . ) , Douglas f i r and western hemlock dominate o lde r s t a b l e a reas . At middle e l e v a t i o n s throughout most of the bas in (150 to 1000 m) there e x i s t s a c l imax ecosystem comprised of hemlock, a m a b i l i s f i r (Abies amabilis (Dougl.) Forbes) and o c c a s i o n a l l y suba lp ine f i r (Abies lasiocarpa (Hook.) Nut t . ) . Above 1000 m there i s a cont inuous cover of mountain hemlock, amab i l i s f i r and ye l l ow cedar (Chamaecyparis nootkatensis (D. Don) Spach) al though the l a t t e r , which occupies a mesic h a b i t a t , i s present in the east o n l y . A zone of Engelmann spruce (Picea engelmanni i Parry) and subalp ine f i r occurs between the a l p i n e tundra and mountain hemlock zone. Lodgepole pine (Pinus contorta Dougl.) i s a co-dominant spec ies where f i r e s occur f r equen t l y , such as the d r i e r I n t e r i o r P l a t e a u , p r o h i b i t i n g the development of a c l imax s p r u c e - f i r f o r e s t . The e l e v a t i o n of the contemporary t ree l i n e averages 1600 to 1650 m above sea l e v e l , but f l u c t u a t e s s p a t i a l l y w i t h changes in aspec t , s lope s t a b i l i t y and m i c r o c l i m a t e . W i t h i n the tundra are a v a r i e t y of a l p i n e meadow species such as mosses, l i c h e n and heather . 50 (2.9) Settlement and Logging History H i s t o r i c a l obse rva t ions and f a c t o r s i n f l u e n c i n g se t t lement pa t te rns prov ide a p o t e n t i a l l y v a l u a b l e source of both d i r e c t and i n d i r e c t evidence of environmental change. P r i o r to European contac t in the l a t e l8th century the B e l l a Coola v a l l e y was populated by Indians of the S a l i s h n a t i o n , a s p l i n t e r group from t r i b e s of the i n t e r i o r and southern coast regions (Kopas, 1970). Est imates by M c l l w r a i t h (19^8) and more r e c e n t l y by Lepofsky (I985) show that at l e a s t 2,700 people , concentra ted in 27 known v i l l a g e s i t e s , occupied the v a l l e y between S t u i e and B e l l a C o o l a . S ince f i s h i n g was the primary economic resource , v i l l a g e l o c a t i o n s were most ly determined by a c c e s s i b i l i t y to r i v e r h a b i t a t s f avorab le for salmon. F lood ing and channel s h i f t i n g are known to have in f luenced se t t lement l o c a t i o n s and the type of s t r u c t u r e s c o n s t r u c t e d . F i r s t whi te contac t was made in 1793 by a sh ip from the f l e e t of Capta in Vancouver making e x p l o r a t i o n s of Burke Channel and North and South Bent inck Arms. One month a f t e r the f i r s t d i r e c t con tac t , Alexander MacKenzie, t r a v e l l i n g by land from For t Chipewyan on Lake Athabasca, descended i n t o the v a l l e y along the east f l ank of Burnt Br idge Creek, the f i r s t C a u c a s i a n to reach the North American west coast (north of Mexico) by l a n d . No permanent whi te se t t lements were e s t a b l i s h e d u n t i l 1867. four years a f t e r Lieutenant Henry S. Palmer made the f i r s t survey of the route between B e l l a Coola and For t A l e x a n d r i a on the Fraser R i v e r . Severa l of the v i l l a g e s i t e s were s t i l l s ea sona l ly occupied when the l a r g e s t i n f l u x of Europeans, most ly Norwegians, s e t t l e d in the v a l l e y in the autumn of 1896. The p r e l i m i n a r y land survey by Palmer i n 1863* the l e g a l survey of I889-I893 and g e o l o g i c a l mapping by G.M. Dawson (I878) are the f i r s t sys temat ic records of the B e l l a Coola environment. E x p l o r a t i o n and survey notes , j o u r n a l s , l e t t e r s and d i a r i e s from these sources a long w i t h l i m i t e d 51 a r c h a e o l o g i c a l evidence from the p re -con tac t pe r iod p rov ide some data regard ing environmental c o n d i t i o n s over the l a s t s e v e r a l c e n t u r i e s . I n t e r p r e t a t i o n of a e r i a l photographs demonstrates tha t p r i o r to the e a r l y 1950s t imber removal was r e s t r i c t e d to smal l p l o t s on the v a l l e y bottom and was most ly r e l a t e d to land c l e a r a n c e . Between 1946 and 195̂  on ly 2 about 3 km had been commercia l ly logged, a l l of i t below the Nusatsum Rive r conf luence . Up u n t i l 1968 an a d d i t i o n a l 13 km z had been logged most ly a long the steeper s lopes above B e l l a Coola R ive r and in the Sa l loomt , Nusatsum, Noosgulch and Cacooht in t r i b u t a r i e s . From 1968 to 197** another 8 2 km was logged, much of i t on the f l o o d p l a i n above Burnt Br idge Creek and p a r t l y on v a l l e y s lopes of the lower Talchako R i v e r . D e c l i n i n g timber p r i c e s in the l a s t 5 years have r e s u l t e d in renewed a c t i v i t y in the more 2 a c c e s s i b l e t r i b u t a r i e s in the B e l l a Coola b a s i n . Thus over 18 km has been logged s ince 1974, much of i t concent ra ted in the Nusatsum and Noomst 2 Creeks and upper B e l l a Coola R i v e r . The t o t a l of 43 km represents l e s s than 1% of the bas in area but the c o n c e n t r a t i o n of commercial t imber removal on lower s lopes and at t r i b u t a r y j u n c t i o n s in the southwestern catchment would suggest a grea ter p o t e n t i a l for impact on sediment y i e l d . 52 CHAPTER I I I Hydrophysical Records of Environmental Change: Tests Within the Instrument Period (3-0) Introduction V a r i a t i o n s i n r e g i o n a l c l i m a t e are u l t i m a t e l y r e l a t e d to f l u c t u a t i o n s in atmospheric c i r c u l a t i o n . These can occur as p e r s i s t e n t depar tures in c i r c u l a t i o n i n t e n s i t y , s h i f t s in the mean p o s i t i o n of atmospheric f ea tu r e s , or l a r g e - s c a l e changes in c i r c u l a t i o n p a t t e r n . When making inferences about the nature of atmospheric processes and environmental change us ing predominant ly b i o g e o p h y s i c a l ev idence , the f u n c t i o n a l r e l a t i o n s h i p s between v a r i o u s i n d i c a t o r s of c l i m a t e change and c l i m a t e i t s e l f need to be examined for a pe r iod in which both the c l i m a t i c pe r t u rba t i ons and environmental responses are known. It i s the purpose of t h i s chapter to assess the s t r eng th and form of these cause and e f f e c t r e l a t i onsh i ps . (3.1) Post-1945 Synoptic Climatology of the N.E. P a c i f i c Sector P r e c i p i t a t i o n and temperature are commonly a v a i l a b l e measures of c l i m a t e , and p rov ide a means for assess ing the e f f e c t s of changing atmospheric c i r c u l a t i o n . E s t a b l i s h i n g the nature of secu la r v a r i a t i o n s in temperature and p r e c i p i t a t i o n for a g iven reg ion can be d i f f i c u l t for three reasons: (1) i n s u f f i c i e n t sampling dens i t y for an area which e x h i b i t s l a rge s p a t i a l v a r i a t i o n s - t h i s may be due to r e a l d i f f e r e n c e s in l o c a l c l i m a t e , or a l t e r n a t i v e l y , to apparent d i f f e r e n c e s produced by va r ious sampling d e v i c e s ; (2) l ack of temporal homogeneity at a s t a t i o n due to r e l o c a t i o n or changes in data c o l l e c t i o n procedures and equipment; and (3) inadequate methods of a n a l y z i n g and p resen t ing da t a . Keeping in mind these p o t e n t i a l sources of e r r o r , data from s e v e r a l c l i m a t e s t a t i o n s in and around B e l l a Coola were examined in order to i d e n t i f y the r e g i o n a l response. 53 Eight c l i m a t e s t a t i o n s , extending as far west as the outer c o a s t a l p l a i n and as far east as the c e n t r a l C h i l c o t i n River b a s i n , were used to compile seasonal averages of monthly mean p r e c i p i t a t i o n and temperature (see f i g u r e 2.1 for s t a t i o n l o c a t i o n s and t ab l e 3 - l )» Winter i s def ined as the i n t e r v a l October to A p r i l and summer as May to August . September was not inc luded in e i t h e r seasonal average because of the s i g n i f i c a n t nega t ive c o r r e l a t i o n between summer temperature and September temperature (i.e. tends to dampen the s igna l ) and r e l a t i v e l y low t o t a l p r e c i p i t a t i o n du r ing t h i s month. A l l seasonal data s e r i e s were entered in to a f a c t o r a n a l y s i s which y i e l d e d two d i s t i n c t groups based p r i m a r i l y on v a r i a t i o n s in p r e c i p i t a t i o n ( tab le 3-1)• They are r e f e r r e d to here as c o a s t a l and i n t e r i o r regions and are s p l i t between the lower e l e v a t i o n s i t e s to the west and higher e l e v a t i o n s t a t i o n s in the lee of the Coast Mountains . Secular t rends in temperatures were s i m i l a r enough to a l l o w c o n s i d e r a t i o n of a l l s t a t i o n s as one group, but , for c o n s i s t e n c y , temperature t rends are a l s o examined in the two r e g i o n s . To maximize the r e g i o n a l s i g n a l seasonal v a r i a b l e s for a g iven r eg ion are s t anda rd i zed , averaged and then p l o t t e d as adjusted p a r t i a l sums us ing the f o l l o w i n g scheme: P t n ' T t n = E n j = l t= l x t j - X J / n P t ,T = cumula t ive sum of s tandard ized seasonal p r e c i p i t a t i o n (P J t n tn 4. IT \ c 4. 4.- . j _ nt or temperature U ) for n s t a t i o n s and t years X . = observed seasonal va lue for year t and s t a t i o n j X"! = 1951-1980 seasonal mean for s t a t i o n j Adjusted p a r t i a l sums have advantages over s imple moving average t echn iques . These inc lude g i v i n g equal weight to g e n e r a l l y wetter and 54 Table 3.1: Climate Stations in and near the Bella Coola River Basin. Latitude Longitude Elevation Years of Record Variables (ra) number of station moves (year) Rotated Components 1 2 Bella Coola 52 20' 125 38' Bella Coola B.C. Hydro Ocean Fa l l s Bella Bella 52 22' 52°21' 52°10' 126 49' 127°41' 128°09' 1895-Present T,P 1961-Prasent 1924-Present T,P 1 C1959) 0.712 0.431 0 0.599 0.395 0 0.812 0.298 P only 1 (1966) 0.839 0.169 INTERIOR Kleena Kleene 51 59' Tatlayoko Lake 51°40' Tatla Lake 51°54' Big Creek 51°10' 124"56' 847 1928-Present 1973-Present 1904-Present T,P T,P T,P T,P 0 0.313 0.746 1 (1979) 0.453 0.865 0 0.239 0.731 1 (1978) 0.121 0.649 OTHER STATIONS percent total variance 54.9Z 25.IX 52 20' 126 15' T,P Anahim Lake 52 21' 52°28' 125 20' 125°18' 1097 1054 1954-1967 1975-1980 T,P T,P 1. See figure 2.1 for locations. 2. T is temperature. P is precipitation. 3. Rotated component loadings for precipitation stations. Stations are grouped according to the strength of their correlation with each factor. See text for discussion. 55 g e n e r a l l y d r i e r s t a t i o n s w i t h i n a reg ion as w e l l as d i s p l a y i n g both high frequency (year to year) and low frequency (decennial) t rends common to a l l s t a t i o n s . Secular v a r i a t i o n s in seasonal p r e c i p i t a t i o n and temperature between 19̂ 5 and 1984 are shown in f i g u r e 3»1- P o s i t i v e s lope segments i n d i c a t e p e r s i s t e n t l y above average c o n d i t i o n s whereas negat ive s lopes are i n d i c a t i v e of below average c o n d i t i o n s . The i n t e r v a l 1945 to 1984 was s e l e c t e d to f a c i l i t a t e comparisons w i t h other h y d r o c l i m a t i c data which were c o l l e c t e d for t h i s pe r iod o n l y . The 3 n year mean (1951-1980) i s cons idered to be a r e p r e s e n t a t i v e of the pe r iod average and i s a l s o the adopted standard by va r ious atmospheric agenc ies . Secular Trends in Seasonal Temperature and P r e c i p i t a t i o n Winter temperatures show the g rea tes t yea r - to -yea r v a r i a n c e over the common p e r i o d , and long- term trends show a high s p a t i a l coherence between the c o a s t a l and i n t e r i o r regions ( f igure 3 - l a ) . Between 1948 and 1957. c o n s i s t e n t l y below normal temperatures p r e v a i l e d in both r eg ions , whereas from 1958-1965 t h i s t rend reversed i t s e l f w i t h above normal win te r temperatures domina t ing . F l u c t u a t i o n s which fo l l owed were of lower magnitude, m a i n t a i n i n g near average c o n d i t i o n s u n t i l 1975 when win te r temperatures were once again most ly above normal . Summer temperature depar tures ( f igure 3 - lc ) are l e s s pronounced and more p e r s i s t e n t w i t h i n the I n t e r i o r r e g i o n . T o t a l October to A p r i l p r e c i p i t a t i o n t rends a f t e r i960 show a s t rong i n t e r - r e g i o n a l coherence w i t h above normal p r e c i p i t a t i o n from 196l to 1968, average c o n d i t i o n s between I969 and 1976, and below normal a f te r 1977 ( f igure 3 - l b ) . P r i o r to i960 the trends between regions are i n v e r s e l y r e l a t e d , w i t h the excep t ion of a few years c h a r a c t e r i z e d by average p r e c i p i t a t i o n everywhere. Summer p r e c i p i t a t i o n ( f igure 3- ld) has lower 56 1940 1950 1960 1970 1980 1990 +—*—• coastal 1940 1950 1960 1970 1980 1990 Years (AO) F i g u r e 3 - 1 Adjusted p a r t i a l sums of seasonal temperature and p r e c i p i t a t i o n for c o a s t a l and i n t e r i o r reg ions of w e s t - c e n t r a l B r i t i s h Columbia . Departures are from the 1 9 5 1 - 1 9 8 0 s t a t i o n normals and are summed from 1 9 ^ 5 to 1 9 8 3 - P o s i t i v e s lope segments i n d i c a t e p e r s i s t e n t above average depar tures and nega t ive s lopes below average d e p a r t u r e s . 57 yea r - to -yea r v a r i a n c e and the g rea tes t i n t e r - r e g i o n a l d i f f e r e n c e s , which i s most l i k e l y r e l a t e d to d i f f e r e n c e s in p r e c i p i t a t i o n genera t ing mechanisms dur ing the summer. Convect ive thunderstorms occur f r equen t ly in the I n t e r i o r r eg ion whereas summer r a i n f a l l a long the coast i s most ly de r i ved from c y c l o n i c d i s t u r b a n c e s . S ince 1965» summer p r e c i p i t a t i o n along the coast g e n e r a l l y has been above normal and normal to below normal for the I n t e r i o r . Near average c o n d i t i o n s are ev ident in both regions p r i o r to 1965 except for increases in the l a t e 1950s. O v e r a l l , t rends in win te r c l i m a t e are towards w e l l below normal c o a s t a l p r e c i p i t a t i o n and r e g i o n a l temperatures to 1957. above normal p r e c i p i t a t i o n and temperatures to 1964/65, average c o n d i t i o n s everywhere u n t i l 1976 and then below normal p r e c i p i t a t i o n and above average temperatures to 1983- Secular v a r i a t i o n s i n summer c l i m a t e are more v a r i a b l e because of the i nc reas ing importance of l o c a l i z e d atmospheric i n s t a b i 1 i t y . Comparison With Other C o a s t a l Regions o f B r i t i s h Columbia Temperature and p r e c i p i t a t i o n trends for most of the p rov ince have been examined by Crowe (1963). Powel l (1965). Thomas (1975) and Thomson et al. (1984). In each a n a l y s i s , v a r i a b l y - l e n g t h e n e d , unweighted moving averages were used, a method which i s poor ly s u i t e d for d e t a i l e d a n a l y s i s of secu la r v a r i a t i o n s in c l i m a t e when more p r e c i s e de te rmina t ions of c l i m a t e s h i f t s are r equ i r ed ( M i t c h e l l , 1966) . More r e c e n t l y , i n v e s t i g a t i o n s of win te r temperature and p r e c i p i t a t i o n f l u c t u a t i o n s have been undertaken on the Queen C h a r l o t t e Is lands (Karanka, 1986) and va r ious s t a t i o n s a long the B r i t i s h Columbia and Uni ted S ta tes west coast (McGuirk, 1982; Y a r n e l , 1985). A g e n e r a l i z e d summary of win te r p r e c i p i t a t i o n trends for the no r th , c e n t r a l and southern coas ts i s presented in f i g u r e 3 '2 . 58 A North Coast ' 1 ' i • i i i i B Central Coast 1 1 1 ' i i i 1 + o South Coast i • j i ^ i i i i - ~\ SST anomalies N.E. Pacific 1 1 i i i i i i i 1 • r r T - 1 r i 1 r— 1 I + o + o F i g u r e 3 '2 G e n e r a l i z e d depar tures of w i n t e r p r e c i p i t a t i o n from pos t - 1945 normals . Bottom f i g u r e i s g e n e r a l i z e d t rends in sea sur face tempera tures . Areas above and below the zero l i n e de f i ne pe r iods of above and below normal p r e c i p i t a t i o n , r e s p e c t i v e l y . The magnitudes of depar tu re are not i n d i c a t e d . A) nor th coas t t rends from Karanka (1986) (normal p e r i o d 1900-1983) and Y a r n e l (I985) (normal p e r i o d 1948-1980); B) c e n t r a l coast ( t h i s s t u d y ) ; C) south coas t from Powe l l (1965) (normal pe r iod 1900-1960) and Y a r n e l (1985); D) sea sur face temperature anomalies for the nor theas t P a c i f i c (Che l ton , 1984) (normal pe r iod 1947-1984) . 59 The most obvious fea ture of c l i m a t e change along the nor theas t P a c i f i c sec tor i s the synchronous s h i f t in 1976 to above average p r e c i p i t a t i o n along the nor th coast and southeast A l a s k a , and below average p r e c i p i t a t i o n in the c e n t r a l and south coast r e g i o n s . As i n d i c a t e d i n f i g u r e 3-2, these changes were a s soc i a t ed w i t h a s h i f t to above normal sea surface temperatures (SST) in the nor theast P a c i f i c . P r i o r to 1976 p r e c i p i t a t i o n trends along the c e n t r a l coast appear to represent a t r a n s i t i o n a l phase between the almost i n v e r s e l y r e l a t e d trends of the nor thern and southern c o a s t s . For example, above average p r e c i p i t a t i o n along the north coast between 1958 and 1964 p e r s i s t e d u n t i l 1969 a long the c e n t r a l coast and u n t i l 1976 a long the south coas t , sugges t ing a southward s h i f t in mois ture bear ing d i s tu rbances through t h i s pe r iod ( c . f . Namias, 1983; Karanka, 1986) . Between 19̂ 5 and 1957 when win te r p r e c i p i t a t i o n was average to below average for much of c o a s t a l B r i t i s h Columbia, SSTs were average to above average. U n l i k e p r e c i p i t a t i o n , win te r temperature trends show a much grea ter s p a t i a l and temporal coherence s i m i l a r to those in f i g u r e 3 - l a . Above average (1958-1964, 1976-1983) and below average temperatures (1948-1957, 1965-1975) for a l l c o a s t a l areas correspond c l o s e l y to p o s i t i v e and negat ive SST anomal ies , r e s p e c t i v e l y . Secular v a r i a t i o n s in summer temperature and p r e c i p i t a t i o n have not been examined c l o s e l y except for the e a r l i e r i n v e s t i g a t i o n s of Crowe (1963) and Powel l (1965)• There i s some i n d i c a t i o n of r e g i o n a l l y c o n s i s t e n t t rends w i t h above average temperatures p r i o r to 1952 and average to below average temperatures between 1953 and I960. 60 Atmospheric C i r c u l a t i o n U s u a l l y , no one fea ture of the atmospheric c i r c u l a t i o n can e x p l a i n adequately v a r i a t i o n s in surface c l i m a t e s . Sea l e v e l pressure pa t t e rn s , p o s i t i o n i n g of hemispheric semi-permanent pressure systems, i n t e n s i t y and d i r e c t i o n of f low a l o f t , mean p o s i t i o n of seasonal f r o n t s , frequency of storms and o r i e n t a t i o n of storm t r acks are a l l important components. However, there i s i n c r e a s i n g evidence of i n t e r a c t i v e l inkages between atmospheric c i r c u l a t i o n and SST anomal ies . It appears from f i g u r e 3-2 that much of the recent c l i m a t i c v a r i a b i l i t y along the B . C . coast i s a s soc i a t ed w i t h these anomal ies . Horel and Wal lace (1981) demonstrated that above normal SSTs in the eas tern north P a c i f i c r e s u l t in the development of a high pressure r idge over western North America and a trough in the c e n t r a l P a c i f i c . R idg ing a long the coast i s of ten a s soc i a t ed wi th a westward s h i f t in the A l e u t i a n Low (Angel l and Korshover , 1982). If r i d g i n g extends out i n to the P a c i f i c then there are two p o s s i b l e outcomes: c o o l / d r y c o n d i t i o n s as nor thwes te r ly a i r f l o w a l o f t i s advected southward down the t r a i l i n g limb of the r idge ( f igure 3'3a) or warm/dry c o n d i t i o n s i f the r i dge a x i s i s centreed over the coast ( f igure 3-3b) (Ya rne l , 1985)- Wet c o n d i t i o n s w i l l p r e v a i l i f r i d g i n g is poor ly developed, i.e. zona l f low occurs ( f igure 3 ' 3c ) , or i f the r i dge i s d i s p l a c e d eastward by an i n t e n s i f i e d A l e u t i a n Low, in which case the coast i s under the broad, upsweeping, southeas tern quadrant of the low ( f igure 3-3d). Analyses of post-1945 s y n o p t i c - s c a l e c i r c u l a t i o n fea tures by B a l l i n g and Lawson (1982) and McGuirk (1982) i n d i c a t e that f low pa t te rns have been dominantly m e r i d i o n a l , c h a r a c t e r i z e d by a low Rossby wave number l ead ing to p e r s i s t e n t and sometimes extreme c l i m a t i c departures and abrupt s h i f t s i n the charac te r of the c l i m a t e . F i g u r e 3-3 S y n o p t i c - s c a l e pressure pa t t e rns (500 mb) l e ad ing to d i s t i n c t depar tures of temperature and p r e c i p i t a t i o n in southwestern B r i t i s h Columbia (from Y a r n e l , 1985)- (A) High p ressure r i d g i n g extends beyond the coas t to produce c o o l / d r y c o n d i t i o n s . (B) R i d g i n g i s cen t red over the coas t r e s u l t i n g in warm/dry weather . (C) Cooler and wet te r c o n d i t i o n s occur when r i d g i n g i s not dominant producing zones of in tense 500 mb f l o w . (D) R i d g i n g occurs to the eas t of the coas t r e s u l t i n g in warm/wet c o n d i t i o n s . 62 Based on the trends in f i g u r e s 3-1 and 3-2 and the r e s u l t s reviewed above, p o s i t i v e SST anomalies between I958 and 1968, a s soc i a t ed w i th r i d g i n g over the west coas t , promoted above average p r e c i p i t a t i o n along the c e n t r a l and north c o a s t s . Although s t a t i s t i c a l conf i rma t ions cannot be made wi th the a v a i l a b l e storm t rack da ta , t h i s would correspond to a northward displacement of c y c l o n i c t r a j e c t o r i e s . Below average p r e c i p i t a t i o n a f t e r 1976 for the c e n t r a l and southern coasts occur red when the A l e u t i a n Low s h i f t e d westward s i g n i f i c a n t l y fu r the r enhancing the northward displacement of storm t r a c k s . Frequency and Seasonal Persistence of Synoptic Types Per iods of p e r s i s t e n t depar tures in seasonal temperature or p r e c i p i t a t i o n are thought to be c h a r a c t e r i z e d by a set of unique synop t i c c o n d i t i o n s which produce the observed trends (I.e. wet, d ry , c o o l , warm). Each season i s comprised of a l a rge number of synop t i c types . However, i t i s l i k e l y the frequency or w i t h i n - s e a s o n p e r s i s t e n c e of on ly c e r t a i n synop t i c types d r i v e s the mean depar tu re . Th i s hypothes is i s t es ted here us ing an o b j e c t i v e l y def ined set of synop t i c types which are known to y i e l d c e r t a i n c l i m a t i c c h a r a c t e r i s t i c s . Synopt ic c i r c u l a t i o n types for a p a r t i c u l a r season and sequence of years were i d e n t i f i e d us ing a ca ta logue of d a i l y 500 mb and d a i l y sur face pressure pa t te rns developed by Y a r n e l (1983) and Barry et al. (1982) for the nor theas te rn P a c i f i c . Both ca ta logues were cons t ruc ted us ing the o b j e c t i v e c l a s s i f i c a t i o n scheme of K i rchhofe r (1973) in which es t imates of d a i l y atmospheric pressure at predef ined hemispheric g r i d po in t s are subjected to a sequence of s e l e c t i o n and grouping procedures . F u l l d e t a i l s of the ca ta logues and grouping schemes are g iven in Ki rchhofe r (1973) and 63 Yarne l (1984). Only p o t e n t i a l problems wi th the technique are cons idered here . Because of the length of the study pe r iod (>10,000 days in both s tud ies ) a p o r t i o n of the p r e s s u r e / e l e v a t i o n data set i s used to de f ine 'key days ' r e p r e s e n t a t i v e of s p e c i f i c synop t i c groups. The major assumption here i s that the smal le r data set i s r e p r e s e n t a t i v e of the range of synop t i c c o n d i t i o n s over the longer study p e r i o d . Problems w i t h the Ki rchhofe r method i n c l u d e : (1) s e l e c t i o n of a c u t o f f t h re sho ld for grouping types - a low th r e sho ld produces a l a rge r set of synop t i c types and leaves few days u n c l a s s i f i e d , whereas a high th re sho ld produces fewer types but leaves many u n c l a s s i f i e d days (Key and Crane, 1986); (2) g r i d s i z e s e l e c t i o n - s i z e w i l l i n f luence the s p a t i a l r e s o l u t i o n of synop t i c pa t te rns w i th l a rge g r i d s y i e l d i n g poor d e f i n i t i o n of mesoscale c i r c u l a t i o n phenomena; (3) w i t h i n - g r o u p v a r i a b i l i t y - even smal l changes in the i n f l e c t i o n po in t of a trough or r i dge can a l t e r the pa t t e rn of temperature or p r e c i p i t a t i o n over an area w i th no apparent d i f f e r e n c e s in the z o n a l i t y of c i r c u l a t i o n ; and (4) s eve ra l key synop t i c types may not be c l a s s i f i e d by the d a i l y a n a l y s i s du r ing a pe r iod when c i r c u l a t i o n pa t te rns are changing r a p i d l y and when there i s a high frequency of mi s s ing d a t a . Although a l e s s s t r i n g e n t grouping of synop t i c types r e s u l t s from the use of 'key days ' and s p e c i f i c a t i o n of a s u b j e c t i v e l y def ined grouping th re sho ld (Key and Crane, 1986), the same methods were employed in both s t u d i e s , which enhances the c o m p a t i b i l i t y of i n t e r p r e t a t i o n s de r i ved from the ca t a logues . The Ya rne l (1983) c a t a logue , for the pe r iod 19̂ 6-1978, i s based on e igh teen , 500 mb p r e s s u r e - e l e v a t i o n pa t te rns for a 2.5° X 2.5°» 30-point g r i d cover ing the c o a s t a l regions of B r i t i s h Columbia and the far eas te rn P a c i f i c . The Barry et al. (1982) ca ta logue i s based on 31 sur face pressure pa t t e rns for a 35 -point, 5° X 5° diamond-shaped g r i d over western North America and i s for the pe r iod 1899 to 1980. Only 6 g r i d - p o i n t s in the l a t t e r ca ta logue f a l l w i t h i n the c o a s t a l B . C . and Gulf of Alaska r e g i o n . The l a rge r number of synop t i c types in the surface pressure ca ta logue i s due to the greater v a r i a b i l i t y in sur face pressure pa t te rns and the l a rge r s p a t i a l coverage of the g r i d . C h a r a c t e r i s t i c s of synop t i c types in each ca ta logue are summarized in t ab l e 3-2. Di f f e rence of means t e s t s were c a r r i e d out to determine i f there are s i g n i f i c a n t changes in the frequency of surface and 500 mb synop t i c types a s soc i a t ed w i t h win te r p r e c i p i t a t i o n f o r : (1) per iods of above average and below average p r e c i p i t a t i o n i nd i ce s along the c e n t r a l coast and (2) groups of years comprised of the most extreme depar tures i n win te r p r e c i p i t a t i o n i r r e s p e c t i v e of o rde r ing in t ime .* The r e s u l t s presented in t ab l e 3-3a show that the frequency of "wet" surface and 500 mb synop t i c types are not s i g n i f i c a n t l y d i f f e r e n t between the dry pe r iod (1948A9 to 1957/58) and wet per iod (1959/60 to 1968/69). In c o n t r a s t , when groups of years c h a r a c t e r i z e d by the most extreme depar tures are tes ted ( tab le 3-3b), there i s a s i g n i f i c a n t d i f f e r e n c e between wet and dry i n t e r v a l s w i t h an average of ten more days per win te r season dominated by "wet" 500 mb types and f i f t e e n more days per season dominated by mois ture b e a r i n g , surface lows . The same sequence of t e s t s was conducted for coo l and warm summer p e r i o d s , but due to the compara t ive ly weak c i r c u l a t i o n i n t e n s i t i e s du r ing the summer, there i s greater d i f f i c u l t y in i d e n t i f y i n g d i s t i n c t surface pressure pa t te rns a s soc i a t ed w i t h extremes in summer temperature. Thus, on ly the 500 mb pa t te rns are cons idered ( table 3-*0 • S i m i l a r c o n c l u s i o n s can be made for summer temperature regimes as for win te r p r e c i p i t a t i o n in that there i s no s i g n i f i c a n t d i f f e r e n c e in the dominance of a p a r t i c u l a r 1. Extreme years were def ined as those years w i t h c l i m a t i c depar tures i n excess of one standard d e v i a t i o n of the mean. Sample s i z e s were determined by the group w i t h the fewest years f i t t i n g t h i s c r i t e r i o n . 65 Table 3.2. Synoptic Types from Yarnel (1983), Barry et a l . (1982). Group or Type (Yarnel - 500 mb) (Barry - surface) Synoptic Circulation Climate Effect Wet Y-(l,3,4,8,10) B=<3,4,7,11,12, 15,23,31) - southwesterly cyclonic component and advection of moist air due to positive 500mb pressure anomalies over the western USA and central Canada and an intensified Aleutian Low - surface lows are mostly from the west and northwest but also migrate from the south above average precipitation and temperature for the entire B.C. coast (upper air types 1,4) and the central and southern coast (upper air types 3,8,10) Dry Winter Y=(5,9,14,15,17) B=(8,14,18,26,30J north or northwest flow aloft and strong ridging centered on the coast surface lows diverted into Gulf of Alaska or southern US west coast below average temperatures and precipitation for the entire coast (upper air types 5,9) and the southern coast (upper air types 14,15,17) Dry Summer Y-C2.6,11,13,18) B=(5,6,9,13,21) strong zonal flow or ridging centered west of Vancouver Island dry and warm for most of the central and southern coasts (upper air types 2,6) occasional cold lows (11,13,18) Warm Summer Y=(l,4,6,7,15,18) B*»<3,4,6,11,23,25) ridging centered over the coast or inland with advection of warm air aloft from the southwest well above average temperatures for the entire coast (upper air types 1,4) and above average for the central and southern coasts (6,7,15,18) 1. Type numbers refer to the 18 objectively classified daily synoptic-scale patterns (500 mb) of Yarnel (1983) (Y=) and 31 surface pressure types of Barry et a l . (1982) (B=). Table 3.3. Winter Precipitation and Synoptic Type Frequencies. A. Significance test between a dry period and a wet period along the central B.C. coast Mean winter precipitation (mean departure) Wet synoptic type frequency^ Wet synoptic 3 type frequency" dry: 1948/49 to 1957/58 wet: 1959/60 to 1968/69 -0.04 ± 0.03 0.07 ± 0.05 82.2 ± 8.3 86.6 ± 8.8 42.5 ± 10.5 44.4 ± 7.8 One-tailed t-test (a = 0.10, df = 18)' t = 2.73 significant t = 1.11 not significant t = 0.46 not significant B. Significance test between wet years and dry years dry years: 1978,71,70, 56,49 -0.19 ± 0.08 78.8 ± 7.0 33.4 ± 7.23 wet years: 1976,74,68, 64,54 0.27 ± 0.08 89.4 ± 5.8 48.0 ± 8.9 One-tailed t-test t - 8.48 t = 3.38 t = 2.80 (<z = 0.10, df = 8) significant significant significant 1. Calculated as the average departure of winter precipitation (Oct-Apr) for the central coast precipitation index from the 1951-1980 normal. 2. Mean number of days dominated by "wet", 500 mb, synoptic types from October to A p r i l after Yarnel (1983). 3. Mean number of days dominated by "wet" surface synoptic types from October to A p r i l from Barry et a l . (1982). 4. A low significance l e v e l was selected because of the exploratory nature of the analysis. Table 3.4. Summer Temperature and Synoptic Type Frequency. A. Significance test between a cool period and a warm period i n Bella Coola basin Mean Summer temperature (mean departure) Warm Synoptic type frequency^ cool: 1948/49 to 1957/58 -1.7 ± 0.8 warm: 1959/60 to 1971/72 1.9 ± 0.4 20.5 ± 7.0 22.4 ± 8.0 One-tailed t-test (a = 0.10, df - 21) t = 4.62 significant t = 0.56 not significant B. Significance test between cool years and warm years cool years: 1975,57,56, 54,49 -2.3 ± 1.0 warm years: 1972,70,69, 67,61 1.9 ± 0.7 14.5 ± 6.1 26.5 ± 3.9 One-tailed t-test (a = 0.10, df - 8) t = 5.31 significant t - 3.00 significant 1. Warm synoptic types from Yarnel (1983). 68 group of s y n o p t i c types between a warm i n t e r v a l (1959/60 to 1971/72) and coo l pe r iod (1948/49 to 1957/58) ( table 3 . 4 a ) , but for groups of years c h a r a c t e r i z e d by extreme depar tures a s i g n i f i c a n t d i f f e r e n c e i s ev ident ( table 3.*tb) . U n l i k e win te r p r e c i p i t a t i o n , extreme departures in summer temperature tend to f a l l w i t h i n per iods of the same tendency. Th i s would suggest that an i n t e r v a l of p e r s i s t e n t depar tures in summer temperature has a higher p r o b a b i l i t y of extreme occurrences and i t i s these extreme, w i t h i n - p e r i o d , years which are c h a r a c t e r i z e d by s i g n i f i c a n t l y d i f f e r e n t f requencies of synop t i c t ypes . Converse ly , anomalous win te r p r e c i p i t a t i o n does not appear to be r e s t r i c t e d to these longer more p e r s i s t e n t i n t e r v a l s of above or below average depar tu res . One or two e x c e p t i o n a l years may occur dur ing an i n t e r v a l of o therwise average c o n d i t i o n s (e .g . 197*+. 1 9 7 6 ) . in a d d i t i o n to s i g n i f i c a n t changes i n synop t i c type frequency p o s i t i v e anomalies in win te r p r e c i p i t a t i o n can be d i s t i n g u i s h e d by the w i t h i n - s e a s o n p e r s i s t e n c e of synop t i c types . For example, du r ing the very wet win te r season of 1 9 6 3 / 64 , 36 days between mid-October and mid-November (with the excep t ion of one day) were c l a s s i f i e d as "wet" 500 mb synop t i c types - c l e a r l y the most e x c e p t i o n a l s i g n a l in the e n t i r e 33 year r e c o r d . During that same win t e r season and for o thers between i 9 6 0 and 1969 i n t e r v a l s of between 10 and 12 days were not uncommon whereas dur ing wet ter w in t e r s w i t h i n dry per iods these w i t h i n - s e a s o n runs were most ly l e s s than 5 to 8 days . The c o n c l u s i o n drawn here i s that the synop t i c s igna tu re between d r i e r and wet ter i n t e r v a l s i s r e l a t e d to the w i th in - sea son pe r s i s t ence of "wet" synop t i c types whereas anomalously wet years are c h a r a c t e r i z e d by both a higher frequency and grea ter p e r s i s t e n c e of these same types . Extreme depar tures i n p r e c i p i t a t i o n do not appear to be r e s t r i c t e d to a 69 per iod of g iven tendency. Th i s d i s t i n c t i o n i s an important one p a r t i c u l a r l y i f there are w e l l - d e f i n e d response th resho lds in the b i o g e o p h y s i c a l environment below which the impact of changing weather i s not s i g n i f i c a n t . (3.2) Responses of Hydrologic Variables to Climate Fluctuations Large s c a l e motions of the atmosphere are manifested not only in r e g i o n a l p r e c i p i t a t i o n and temperature i n d i c e s , but a l s o in h y d r o l o g i c a l phenomena such as win te r snowpack, r i v e r runoff and g l a c i e r f l u c t u a t i o n s . Linkages between these components of the t e r r e s t r i a l phase of the h y d r o l o g i c a l c y c l e and atmospheric c i r c u l a t i o n can be s p a t i a l l y non- homogeneous and lagged in time (Barry , 198l). Th i s occurs because the atmosphere, a system w i t h low heat and mois ture c a p a c i t i e s , adjus ts r a p i d l y to changing energy l e v e l s (Bradley , 1985)- The high water s torage c a p a c i t y of the t e r r e s t r i a l environment ( e .g . snowcover, g l a c i e r s , l a k e s , groundwater) , s p a t i a l v a r i a b i l i t y in a c t u a l s torage and the e x i s t e n c e of response th resho lds a l l tend to dampen the response to c l i m a t i c change. For t h i s reason i t i s necessary to understand how feedback mechanisms might be important in the system. The s p a t i a l and temporal trends in water s torage and runoff along the southwestern B r i t i s h Columbia coast are examined here . Regional Winter Snowpack Snowpack data have been c o l l e c t e d for a number of s i t e s in southern B r i t i s h Columbia but few have records longer than kO y ea r s . The ma jo r i t y of s o l i d p r e c i p i t a t i o n f a l l s between e a r l y November and l a t e March. Thus A p r i l 1 snow water equ iva l en t s were compiled from a number of s t a t i o n s (see f i g u r e 2.1 for l o c a t i o n s ) and grouped in to homogeneous regions us ing f a c t o r a n a l y s i s ( tab le 3-5)• Two s t a t i s t i c a l l y d i s t i n c t groups e x h i b i t i n g s i m i l a r long term trends but minor in te rannua l d i f f e r e n c e s were i d e n t i f i e d : a Table 3.5. Winter Snow Courses in southwestern B r i t i s h Columbia. Station Latitude Longitude Elevation Years of Record Rotated (m) Components 1 2 COASTAL Bella Coola 52 31* 126°38' 1380 1953-1954 Newcastle Rdg. 50 24' 126°03' 1170 1961-Present 0.746 0.290 Powell (upper) 50 16' 1040 1938-Present 0.753 0.541 Dog Mountain 49 23' 1080 1945-Present 0.823 0.525 INTERIOR Precipice 52 26' 125 38' 1220 1972-1973 1970-1971 Tatlayoko Lake 51°36' 124°20' 1710 1952-Present 0.280 0.848 1300 1952-Present 0.319 0.872 Tenquille Lake 50 32' 122 56' 1680 1953-Present 0.332 0.895 1. See figure 2.1 for locations. 2. Rotated component loadings for snow course stations. Stations are grouped according to factor scores. 71 c o a s t a l zone to the west of the Coast Mountain c r e s t and a zone in the lee of the Coast Mountains towards the d r i e r i n t e r i o r . Secular v a r i a t i o n s in snowpack are p l o t t e d as adjusted p a r t i a l sums in f i g u r e J>.k. A g a i n , p o s i t i v e s lope segments represent above average depar tures and negat ive s lopes below average depar tu res . A grea ter in te rannua l v a r i a b i l i t y i s ev ident for the r e g i o n a l snowpack index r e p r e s e n t a t i v e of the i n t e r i o r but both s e r i e s e x h i b i t three per iods of p e r s i s t e n t depar tures : normal to below normal snowpack between 1957 and 1963f w e l l above normal snowpack between 1964 and 1976, and f i n a l l y s t r o n g l y nega t ive depar tures a f t e r 1976. The occurrence of below normal s p r i n g snowpacks a f t e r 1976 corresponds w e l l w i t h below normal win te r p r e c i p i t a t i o n along the c e n t r a l and southern coast of B . C . coupled w i t h normal to above normal win te r temperatures ( f igure 3-2). Between the mid-1960s and 1975 normal to above normal win te r p r e c i p i t a t i o n along t h i s same c o a s t a l zone i s r e f l e c t e d as p e r s i s t e n t p o s i t i v e depar tures of w in t e r snowpack for both c o a s t a l and i n t e r i o r r e g i o n s . Winter temperatures were on average below normal dur ing t h i s same i n t e r v a l . Below normal win te r p r e c i p i t a t i o n and above normal w in t e r temperatures dominated the southern coast between 1957 and 1964 r e s u l t i n g in below normal snowpacks. The a s s o c i a t i o n between r e g i o n a l snowpack volume and frequency of "wet" win te r c i r c u l a t i o n pa t te rns for per iods and groups of years c h a r a c t e r i z e d by anomalous depar tures i s t e s ted us ing d i f f e r e n c e of means. U n l i k e the s t rong a s s o c i a t i o n between p o s i t i v e snowpack depar tures and above normal p r e c i p i t a t i o n , four of the s i x extreme low snowpack years were not the same years w i t h low win t e r p r e c i p i t a t i o n . For three of these four years win te r temperatures were above average which probably led to grea ter m e l t i n g near the beginning and end of each season. Hence, average p r e c i p i t a t i o n and above normal temperatures r e s u l t e d in low snowpack 72 —I 1 1 1 r 1950 1960 1970 1980 1990 Year (AD) F i g u r e 3-*» Adjusted p a r t i a l sums for A p r i l 1st snowpack (water e q u i v a l e n t ) . Normal p e r i o d i s 1951-1980. Coas t a l w i n t e r p r e c i p i t a t i o n taken from f i g u r e 3-1 i s i nc luded for compar ison . P o s i t i v e s lope segments represent p e r s i s t e n t above average snowpack years whereas nega t ive s lopes represent below average snowpack. 73 volumes. Even w i th these compl i ca t i ons the r e s u l t s in t ab l e 3-6 show that v a r i a t i o n s in s p r i n g snowpack are p o s i t i v e l y l i n k e d to the mean number of days dominated by "wet" synop t i c types for groups of anomalous years and a l s o for the two per iods c h a r a c t e r i z e d by above average (1966-1976) and below average (1977~1980) depar tu res . The l a t t e r r e s u l t i s p a r t l y r e l a t e d to the l i m i t e d number of data du r ing 1977~1980 and the above temperatures which occurred then, but does i n d i c a t e that s easona l ly in t eg ra ted h y d r o l o g i c parameters such as snowpack are s e n s i t i v e to changes in the frequency of s p e c i f i c c i r c u l a t i o n pa t te rns not on ly for extreme years but a l s o for sequences of years in which a tendency for p e r s i s t e n t departures occu r . Spring Runoff Spr ing runoff i s l i k e l y to be greater f o l l o w i n g win t e r s c h a r a c t e r i z e d by anomalously high p r e c i p i t a t i o n and snowpack accumulat ion but s p r i n g and summer temperature c o n d i t i o n s may enhance or depress a c t u a l water y i e l d . Furthermore, sp r ing runoff should be l ess s p a t i a l l y homogeneous than snowpack d i s t r i b u t i o n s because of the la rge s p a t i a l v a r i a b i l i t y in runoff genera t ing mechanisms and s torage c o n d i t i o n s w i t h i n and between b a s i n s . However, as bas in s i z e inc reases , water y i e l d becomes l e s s responsive to i s o l a t e d storms or to snowmelt per iods of shor t d u r a t i o n . Thus, l a rge s c a l e synop t i c t rends may be r e f l e c t e d more d i r e c t l y in temporal runoff v a r i a b i l i t y w i t h i n l a rge r bas ins (Bruce, 197*+). Most hydrometr ic records for streams d r a i n i n g the west s lope of the southern Coast Mountains are shor te r than kO years and the number of medium 2 s i z e d bas ins (3,000 - 6,000 km ) for which d i scharge data e x i s t i s s m a l l . Time s e r i e s of s p r i n g snowmelt runoff for the B e l l a Coo la , Homathko and Squamish R i v e r s , three moderate s i z e catchments d r a i n i n g p a r t l y g l a c i e r i z e d 74 Table 3.6. Winter Snowpack and Synoptic Type Frequency. A. Significance between a high snowpack period and a low snowpack period Mean A p r i l 1st water equivalent (mean departure) Wet synoptic Wet synoptic 2 3 type frequency type frequency high: 1966-1976 low: 1977-1980 One-tailed t-test (a = 0.10, df = 13) 0.69 ± 1.26 -1.01 ± 1.22 t = 2.94 significant catalogues only to 1978 40.3 ± 8.9 32.3 ± 12.1 t = 1.61 sign i f i c a n t B. Significance test between high snowpack years and low snowpack years high snowpack years: 1.32 ± 0.93 91.5 ± 4.13 46.5+8.8 (1976,74,68,67,64,54) low snowpack years: -1.28 ± 0.75 79.2 ± 6.3 29.8 ± 15.2 (1978,77,75,70,62,60) One-tailed t-test (a = 0.10, df = 10) t = 5.22 significant t = 4.01 significant t = 2.32 significant 1. Calculated as the average departure for the three lee side snow courses: Tashta, Tatlayoko and Tenquille. 2. Frequencies of 500 mb patterns after Yarnel (1983). 3. Frequencies of surface pressure patterns after Barry et a l . (1982). 75 mounta ins of s o u t h w e s t e r n B r i t i s h C o l u m b i a , p r o v i d e some e v i d e n c e of s e c u l a r r u n o f f t r e n d s d u r i n g the post-19*t5 p e r i o d (see f i g u r e 2.1 f o r l o c a t i o n s ) . R e s u l t s a r e p l o t t e d as a d j u s t e d p a r t i a l sums in f i g u r e 3«5> The i n t e r v a l May to m i d - J u l y was d e f i n e d as the s p r i n g r u n o f f p e r i o d b e c a u s e h y d r o g r a p h s f rom a l l t h r e e r i v e r s i n d i c a t e t h a t d i s c h a r g e peaks r e l a t e d t o snowmelt o c c u r r e d d u r i n g t h i s t ime (see f i g u r e 2.6). W h i l e t h e r e a r e minor i n t e r a n n u a l d i f f e r e n c e s between each c a t c h m e n t , s i m i l a r l o n g - t e r m s e c u l a r t r e n d s , a r e e v i d e n t . F l u c t u a t i n g , bu t near a v e r a g e d i s c h a r g e s o c c u r r e d between 1947 and 1958 in the B e l l a C o o l a R i v e r . F o l l o w i n g w e l l above a v e r a g e s p r i n g r u n o f f d u r i n g 1958, be low a v e r a g e d i s c h a r g e s in B e l l a C o o l a and Squamish R i v e r s p r e v a i l e d u n t i l 1966. Homathko R i v e r d i s c h a r g e s were more v a r i a b l e t h r o u g h t h i s p e r i o d . A f t e r 1966, d i s c h a r g e s f o r most of the c o a s t were w e l l above a v e r a g e u n t i l 1972 when t h i s t r e n d was s h a r p l y r e v e r s e d f o r the rema inder of the d e c a d e . Post-1980 f l o w s a r e near a v e r a g e . A c o m p a r i s o n o f r u n o f f t r e n d s w i t h snowpack water e q u i v a l e n t s and w i n t e r p r e c i p i t a t i o n ( f i g u r e s 3-1. 3-** and 3-5) r e v e a l s some i m p o r t a n t d i f f e r e n c e s . D u r i n g the i n t e r v a l 1973-1976, when wet w i n t e r c o n d i t i o n s p r e v a i l e d , s p r i n g r u n o f f in a l l t h r e e b a s i n s was below a v e r a g e . T h i s d i v e r g e n c e can be e x p l a i n e d by the o c c u r r e n c e of w e l l below a v e r a g e w i n t e r and summer t e m p e r a t u r e s d u r i n g a l l f o u r of t h e s e y e a r s r e s u l t i n g in lower r u n o f f and i n c r e a s e d water s t o r a g e . S i m i l a r l y , wet but c o o l c o n d i t i o n s between 1963 and 1966 may e x p l a i n the below a v e r a g e s p r i n g r u n o f f , p a r t i c u l a r l y in the Squamish R i v e r . S p r i n g r u n o f f d a t a f rom the n o r t h c o a s t were not examined bu t Royer (1982) has modeled s e c u l a r t r e n d s in a n n u a l f r e s h w a t e r d i s c h a r g e s in s o u t h e a s t A l a s k a . The e s t i m a t e s a r e based on s e a s o n a l t r e n d s in p r e c i p i t a t i o n , t e m p e r a t u r e , and water s t o r a g e and a r e c a l i b r a t e d a g a i n s t v a r i o u s ca tchment r u n o f f d a t a . The a n n u a l t r e n d s appear t o f i t q u i t e w e l l 76 T 1 1 1 1 1 r 1 1 — 1940 1950 1960 1970 1980 Years (AD) F i g u r e 3-5 Adjusted p a r t i a l sums of s p r i n g runoff (May - mid J u l y ) for three c o a s t a l r i v e r s . Normal pe r iods for each s t a t i o n correspond to the length of r e c o r d . P o s i t i v e s lope segments represent p e r s i s t e n t above normal r u n o f f . Note the the r e g i o n a l response of below average runof f a f t e r 1 9 7 2 . 77 the v a r i a t i o n s in win te r p r e c i p i t a t i o n along the north coast ( f igure 3.2a), suggest ing that p r e c i p i t a t i o n i s the dominant f ac to r in de te rmin ing the temporal v a r i a t i o n of runo f f . Above average runoff occurred dur ing the i n t e r v a l 1958 to 19&3 and a f t e r 1976. and below average runoff between 1964 and 1976. Below average runoff and win t e r p r e c i p i t a t i o n p r i o r to 1958 have been documented for P r i n c e of Wales and Revi1 l ag igedo Is lands in the Alaska Panhandle (Karanka, 1986) which con t r a s t w i th the above average annual runoff i d e n t i f i e d by Royer (1982). These d i f f e r e n c e s for the e a r l i e r pe r iod may be due to v a r i a t i o n s in the d e f i n i t i o n of the water year , the much more l i m i t e d area of the l a t t e r study and the s e n s i t i v i t y of the runoff model used by Royer . In gene ra l , the s p a t i a l coherence of win te r p r e c i p i t a t i o n and s p r i n g runoff i s s t r o n g l y ev ident but s p r i n g and e a r l y summer temperatures a l s o c o n t r i b u t e to runoff v a r i a b i l i t y . Spring and Summer Runoff - B e l l a Coola River Fac tors other than win te r p r e c i p i t a t i o n have been incorpora ted i n t o a number of e m p i r i c a l and p h y s i c a l l y based models for e s t i m a t i n g s p r i n g f l o o d d i scharges and high summer water y i e l d s (Ostrem et aj.,1967; Tangborn and Rasmussen, 1976; Power and Young, 1979; C o l l i n s and Young, 198l; Tangborn, 1984; Young 1985)- The most important are the d i s t r i b u t i o n and magnitude of temperature depar tures and the c o n t r i b u t i o n s of g l a c i e r melt to t o t a l runof f . G l a c i e r melt generated runoff can be as high as 50% of the t o t a l water y i e l d even when g l a c i a l cover is r e l a t i v e l y l i m i t e d (Young, 1985). Est imates of g l a c i e r melt c o n t r i b u t i o n s to summer d i scha rge in the Homathko Rive r (21% g l a c i a l covered) range as high as 21% ( B r i t i s h Columbia Hydro, 1984). While accumulat ion season p r e c i p i t a t i o n and a b l a t i o n season temperatures are important model components, these s tud ies of i ce -covered 78 bas ins have shown the importance of more s p a t i a l l y v a r i a b l e parameters such as r e l a t i v e humid i ty , i nc iden t s o l a r r a d i a t i o n and wind in e s t i m a t i n g summer runoff from i n d i v i d u a l g l a c i e r s . D i r e c t measurement, or even i n d i r e c t e s t ima tes , of these a d d i t i o n a l parameters are g e n e r a l l y not p o s s i b l e for p a l e o h y d r o l o g i c a l mode l ing . Models based on primary hydrometeoro log ica l v a r i a b l e s such as temperature and p r e c i p i t a t i o n are l i k e l y to e x p l a i n l e s s of the yea r - to -yea r va r i ance in r u n o f f . An assessment of s imple runoff models for the B e l l a Coola R ive r i s made here in order to document the l e v e l of exp la ined va r i ance us ing primary m e t e o r o l o g i c a l v a r i a b l e s o n l y . A n a l y s i s of a b l a t i o n season runoff i n a l l four gauged t r i b u t a r i e s of the B e l l a Coola R ive r r evea l s some i n t e r e s t i n g d i f f e r e n c e s . Interannual v a r i a b i l i t y of e a r l y season runoff (May-mid-July) i s s i m i l a r throughout the catchment, presumably due to the c o n t r i b u t i o n of water from a bas in -wide m e l t i n g snowpack. As the melt season progresses and icemel t c o n t r i b u t i o n s inc rease , two d i s t i n c t runoff regimes become apparent: (1) a s t r o n g l y d i u r n a l runoff regime for the southern catchment ( e .g . Talchako/Nusatsum Rivers ) and (2) more uni form, but s t e a d i l y d e c l i n i n g f l ows , in the eas te rn and nor thern segments of the catchment ( e . g . Atnarko /Sa l loomt Rivers ) . During high snowpack yea r s , and normal to below-normal snowpack years i n which s p r i n g temperatures ( A p r i l - May) are depressed, high seasonal runoff i s common to a l l t r i b u t a r i e s . It i s low snowpack years coupled w i th high summer temperatures which accentuate the d i f f e r e n c e s in runoff regimes. S ince t h i s l a t t e r s i t u a t i o n occurs r e l a t i v e l y i n f r e q u e n t l y , a summer runoff index was computed for the B e l l a Coola R ive r below Burnt Br idge C r . , which in t eg ra te s d ischarges from both g l a c i e r i z e d and u n g l a c i e r i z e d sources . Although t h i s may reduce the c l i m a t e - r u n o f f r e l a t i o n s h i p by mix ing p o p u l a t i o n s , the index incorpora tes a bas in-wide response to changing 79 hydroc l imates and more p rope r ly es t imates t o t a l summer d i scharge through the lower B e l l a Coola R i v e r . Severa l e m p i r i c a l l y - b a s e d l i n e a r s t a t i s t i c a l models, i n c o r p o r a t i n g s ea sona l ly and r e g i o n a l l y averaged c l i m a t e da ta , were evaluated us ing an i n t e r a c t i v e v e r s i o n of a l l - p o s s i b l e - s u b s e t s r e g r e s s i o n . Indices of seasonal and monthly temperature, p r e c i p i t a t i o n and s p r i n g snowpack for both c o a s t a l and i n t e r i o r regions comprise a group of independent v a r i a b l e s used to es t imate s p r i n g r u n o f f . P r e l i m i n a r y models were cons t ruc ted us ing a 33 year data set (1952-1984), l i m i t e d by the length of s p r i n g snowpack r eco rds . E a r l y season (May to m i d - J u l y ) , l a t e season (mid-July to August) and summer (May to August) runoff i nd i ces were cons idered s e p a r a t e l y . Resu l t s are presented in t ab le 3-7' Sca t t e r p l o t s of b i v a r i a t e r e l a t i o n s h i p s , p r o b a b i l i t y p l o t s of r e s i d u a l s and a t e s t for s e r i a l c o r r e l a t i o n for each model i n d i c a t e that assumptions of the r eg re s s ion technique have not been v i o l a t e d . A l l three p r e l i m i n a r y models r e l a t i n g B e l l a Coola River runoff to 2 c l i m a t e are s i g n i f i c a n t but the s t ronges t i s summer runoff (Ra = O.58) in which win te r p r e c i p i t a t i o n along the coas t , sp r ing snowpack volumes measured in the lee of the Coast Mountains and summer temperature ind ices de r i ved for the i n t e r i o r , enter the equa t ion . Th i s combinat ion of v a r i a b l e s suggests that summer runoff i s c o n t r o l l e d by snowpack c o n d i t i o n s and melt energy in the headwaters of the southern and eas tern catchment. The three p r e l i m i n a r y models were t e s t ed by us ing independent data from the Nusatsum and Sal loomt R i v e r s . Runoff data from these two downstream t r i b u t a r i e s were combined and compared w i t h p r e d i c t e d runoff in B e l l a Coola R i v e r . The use of Nusatsum/Salloomt data was p o s s i b l e because of the high c o r r e l a t i o n between these data and observed d i scharge i n the B e l l a Coola River (r > 0.79)- V e r i f i c a t i o n procedures for r e g r e s s i o n models 80 Table 3.7. Significant variables and regression coefficients for climate-runoff models. Runoff Period Preliminary Models F i n a l Model Climate Indices May to mid-July mid-Jul to Aug Coefficients Summer Summer WP(I) WP(C) SS(I) SS(C) AT(I) AT(C) ST(I) ST(C) Intercept 0.62 0.23 -0.09 1.21 0.11 0.49 0.49 0.01 0.56 0.18 0.78 0.01 0.68 0.78 0.01 Summary S t a t i s t i c s : „2 F SE = 0.52 = 0.45 = 1.50 = 7.15* = 0.45 0.29 0.24 2.22 5.8* 0.12 = 0.62 = 0.58 = 1.51 14.8* = 0.09 = 0.55 = 0.52 = 1.94 17.16* = 0.10 Confirmatory S t a t i s t i c s : r RE 0.74 0.19 0.41 0.05 0.89 0.41 0.84 0.36 WP = winter precipitation (Oct-Ap) SS = A p r i l 1st snowpack (water equivalent) AT = A p r i l temperature ST = summer temperature (May-Aug) (I) = Interior Region (C) = Coastal Region R = coefficient of determination 2 2 R = adjusted R a D = Durbin-Watson d (reject H - no o significant autocorrelation) F = F ratio (* significant; a = 0.025) SE = standard error RE = reduction of error s t a t i s t i c r = correlation coefficient The coefficient of determination (R ) i s adjusted (yielding Ra ) to account for the number of predictor variables in each equation. 81 evaluate how w e l l a model p r e d i c t s a new va lue of the independent v a r i a b l e . Two s t a t i s t i c s repor ted in t ab l e 3-7 (confirmatory s t a t i s t i c s ) are used to t e s t the s i g n i f i c a n c e of the p r e d i c t e d runoff v a l u e s : the c o r r e l a t i o n c o e f f i c i e n t (r) and RE s t a t i s t i c . In a l l three models the c o r r e l a t i o n c o e f f i c i e n t s are s i g n i f i c a n t sugges t ing a reasonable correspondence between a c t u a l and p r e d i c t e d runo f f . The r educ t ion of e r ro r s t a t i s t i c (RE) ( F r i t t s , 1976) has t h e o r e t i c a l l i m i t s of -<» and 1.0 where a p o s i t i v e va lue i n d i c a t e s that the p r e d i c t i o n s made by the model are be t t e r than a p r e d i c t i o n based on the mean of the observed d a t a . Again a l l three models have p o s i t i v e and s i g n i f i c a n t RE va lues suggest ing reasonable p r e d i c t i v e a b i l i t y of the models. The model which incorpora tes s p r i n g snowpack, a v a r i a b l e w i t h the lowest p a r t i a l c o r r e l a t i o n c o e f f i c i e n t , was removed from fu r the r c o n s i d e r a t i o n because snowpack data p r i o r to 1952 are not a v a i l a b l e . The c a l i b r a t i o n pe r iod was extended to 19^8 ( e a r l i e s t a v a i l a b l e runoff) and a l l o u t l i e r s which might have had a s i g n i f i c a n t in f luence on the r e g r e s s i o n c o e f f i c i e n t s were t e s ted us ing Cook's D s t a t i s t i c (Draper and Smi th , 1981) . None were found. The f i n a l model i s used to r econs t ruc t s p r i n g runoff p r i o r to 1948 and these r e s u l t s are d i scussed in chapter 6. A n a l y s i s of s p r i n g runoff hydrographs shows that extreme runoff events in May or June are r e l a t e d to years w i t h p e r s i s t e n t p o s i t i v e depar tures in monthly win te r p r e c i p i t a t i o n and negat ive s p r i n g temperature anomal ies . For t h i s reason, the f i n a l model presented in t a b l e 3-7 may approximate the p o t e n t i a l for high-magnitude s p r i n g runoff but , because there is no s p r i n g temperature index in the f i n a l model, i s apt not to p rov ide a good es t imate of peak s p r i n g d i s c h a r g e . Hence, r e s i d u a l v a r i a n c e in the f i n a l model i s h ighes t dur ing years c h a r a c t e r i z e d by monthly c l i m a t i c anomalies which s i g n i f i c a n t l y in f luence runoff ( e .g . depressed 82 A p r i l temperatures) but are not incorpora ted in to any of the seasonal c l i m a t e i n d i c e s . Autumn Floods As noted in chapter 2 the autumn runoff pe r iod i s h y d r o l o g i c a l l y d i s s i m i l a r to the summer d i scha rge regime. S t e a d i l y d e c l i n i n g f r e e z i n g l e v e l s promote reduced c o n t r i b u t i o n s of g l a c i e r meltwater as the season p rogresses . Superimposed on these d e c l i n i n g f lows are s h o r t - d u r a t i o n , h i g h - magnitude f loods which have two d i s t i n c t sources : (1) runoff due to heavy p r e c i p i t a t i o n only and (2) runoff due to high p r e c i p i t a t i o n combined w i t h r a p i d l y r i s i n g f r e e z i n g l e v e l s and s i g n i f i c a n t snowmelt at middle e l e v a t i o n s . T y p i c a l l y , the former events occur e a r l y i n the autumn (August to October) w h i l e the l a t t e r may occur as l a t e as January f o l l o w i n g accumula t ion of snow throughout much of the b a s i n . A n a l y s i s of d a i l y p r e c i p i t a t i o n records p r i o r to autumn f l o o d events in the B e l l a Coola R ive r suggests that for most high-magnitude f l ows , antecedent p r e c i p i t a t i o n i s important . Flood genera t ing storms are of ten preceded by a sequence of one or two day r a i n f a l l events which sa tu ra te the snowpack or s o i l so that subsequent runoff i s maximized. F igure 3*6 demonstrates a mean sepa ra t ion of k to 5 days between storms, beyond which the p o t e n t i a l for heavy storm runoff i s g r e a t l y reduced. Th i s s epa ra t ion of storm peaks appears to be v a l i d for peak 2h hour p r e c i p i t a t i o n events w i t h recurrence i n t e r v a l s of k years or l e s s ; that i s , f l o o d genera t ing storms w i t h one-day recurrence i n t e r v a l s greater than k years g e n e r a l l y produce enough p r e c i p i t a t i o n to y i e l d s i g n i f i c a n t runoff and are not n e c e s s a r i l y preceded by h y d r o l o g i c a l l y ( c l i m a t o l o g i c a l l y ) d i s t i n c t events ( e .g . autumn f loods of 1950, 1973) . 83 F i g u r e 3-6 Antecedent autumn p r e c i p i t a t i o n for the s i x l a r g e s t p e r i o d - o f - r e c o r d f l oods on B e l l a Coola R i v e r . 24 hour p r e c i p i t a t i o n recur rence i n t e r v a l s are c a l c u l a t e d us ing 80 years of r eco rd at the B e l l a Coola c l i m a t e s t a t i o n . Mean s e p a r a t i o n of storm p r e c i p i t a t i o n peaks i s 4 to 4 . 5 days . 84 A n a l y s i s of synop t i c char t s for ten-day sequences p r i o r to each major f l o o d on the B e l l a Coola River suggests a number of synop t i c c o n d i t i o n s must be met in order to produce s i g n i f i c a n t r u n o f f . The most important i s the r ap id r educ t ion in the v e l o c i t y of eastward moving low pressure systems and in s eve ra l cases a swi tch to a more n o r t h e r l y t r a j e c t o r y i n to the Gulf of A l a s k a . Th i s i s f a c i l i t a t e d by high pressure r i d g i n g over the i n t e r i o r of the p r o v i n c e . Warm and c o l d f ron t s become f u l l y occluded as the cent re of low remains over the c o a s t a l boundary. The warm sec tor a l o f t produces heavy r a i n f a l l and snowmelt at higher e l e v a t i o n s . With the excep t ion of the sma l l e r 1982 f l o o d , cyc logenes i s i s almost always centered south of the A l e u t i a n Low between 155° and 170° W and between 45° and 55° N . Storm p r e c i p i t a t i o n p l o t s in f i g u r e 3-6 a l s o r evea l a major d i f f e r e n c e in synop t i c c l i m a t o l o g y for f loods w i t h i n a sequence of years of above average p r e c i p i t a t i o n ( e .g . 1965. 1968). These events are c h a r a c t e r i z e d by a c l o s e l y spaced sequence of lows i n t e r s e c t i n g the coast under a synop t i c regime which p e r s i s t s for at l e a s t ten days p r i o r to the storm and in some cases l onge r . Floods dur ing other i n t e r v a l s do not have s t rong antecedents and are g e n e r a l l y s i n g u l a r events (e .g . 1950, 1973). The s p a t i a l v a r i a b i l i t y of autumn f loods r equ i r e s c o n s i d e r a t i o n i f inferences regard ing r e g i o n a l hydrology drawn from s i t e s p e c i f i c evidence are to be v a l i d . The i n t e n s i t y or s i z e of c y c l o n i c d i s tu rbances , storm t rack o r i e n t a t i o n and source areas for cyc logenes i s may s i g n i f i c a n t l y a f f e c t one area wi thout any a p p r e c i a b l e e f f e c t in another . Evidence presented e a r l i e r suggests d i f f e r e n t win te r p r e c i p i t a t i o n trends along the north and south coas t s , where the c e n t r a l coast i s a t r a n s i t i o n a l zone a l t e r n a t e l y e x h i b i t i n g c h a r a c t e r i s t i c s of one reg ion or the o t h e r . For t h i s reason the magnitude and t i m i n g of f a l l f l o o d events in the B e l l a Coola ba s in are compared w i t h Homathko and Squamish R i v e r s , 85 catchments of s i m i l a r s i z e and g l a c i e r cover in the c e n t r a l and southern c o a s t a l environments , r e s p e c t i v e l y (see f i g u r e 2.1 for l o c a t i o n s ) . F igure 3.7 i s a p l o t of peak autumn d ischarges above a base d i scharge in each r i v e r for p e r i o d - o f - r e c o r d d a t a . It i s apparent from f i g u r e 3-7 that autumn f l o o d magnitudes for a g iven storm vary s p a t i a l l y . For example, the p e r i o d - o f - r e c o r d maximum f l o o d in October 1957 on Homathko and Squamish R i v e r s was only the s i x t h l a r g e s t on the B e l l a Coola R i v e r . Although magnitudes may v a r y , the s i g n i f i c a n c e of autumn storms can be seen in the coas t -wide response to r a i n f a l l and r a i n - on-snow even t s . The major autumn f l o o d of l a t e October, 19&5 o n B e l l a Coola R ive r corresponds w i t h s i g n i f i c a n t runoff events in the other c o a s t a l r i v e r s , p a r t i c u l a r l y Squamish R i v e r . The l e s s p r e c i s e l y matched record w i th Homathko Rive r may be due to the higher baseflow for that r i v e r and d i f f e r e n c e s in phys iograph ic or g l a c i o l o g i c e f f e c t s . Runoff events in the B e l l a Coola bas in du r ing 1967» 1980 and 1982 were a l s o recorded in these other r i v e r s . Th i s suggests that there i s p o t e n t i a l for us ing h y d r o l o g i c a l records of any one of these r i v e r s as an index of major s y n o p t i c - s c a l e storms for southwestern B r i t i s h Columbia . These s y n o p t i c - s c a l e storms then become ' k e y ' events i n the longer term depar ture of c l i m a t e along the c e n t r a l and southern c o a s t s . Another fea ture common to a l l three r i v e r s i s the increased number of f loods du r ing the pe r iod 1957~1968. Th i s i s c o i n c i d e n t w i t h above average October - A p r i l p r e c i p i t a t i o n along the coast a s soc i a t ed w i t h an increased frequency of r i d g i n g along the P a c i f i c Northwest s p e c i f i c a l l y , and the nor thern Hemisphere i n genera l ( T r e i d l et al., 1981; Knox and Hay, 1985). The evidence i n d i c a t e s that p o s i t i v e SST anomalies for the nor theas t P a c i f i c Ocean and an i n t e n s i f i e d A l e u t i a n Low were major f a c t o r s . 86 O R Qb Qp_ Qb Qp Qb 5.0 - 4.0- 3.0- 2.0- Bella Coola River near Hagensborg Ad=4,040 km2 GC=9% R=3533 m Qb=200 cms | • l I I | I l l I | I I 1 I | "I "1*1 I *| I I I I | F I I I | "I I I >»| 1945 1950 1955 1960 1965 1970 1975 1980 1985 6.0 - 3.0- 2.0- Homathko River at mouth r Ad=5,720 km2 R=3994 m GC=21% 4 Qb=400 cms In I I I I I | I I ' | I I "» "I | "I "l "V* 'I 11 ' 'l '| I I I "I '| "I "l 'l I | 11 | " | i H 1945 1950 1955 1960 1965 1970 1975 1980 1985 5.0 - 4.0 3.0 " 2.0 - Squamish River Bracitendale Ad=2,330 km2 R=2890 GC=16« Qb=350 cms I I I I I l I l l I ' l-l 1»"11 '< H r r M - r - r l - r r - r ' i l I r*i-rJr-r 1945 1950 1955 1960 1965 1970 1975 1980 1985 F i g u r e 3«7 Frequency of autumn (August to January) r a i n s t o r m generated f loods of the B e l l a C o o l a , Homathko and Squamish R i v e r s . Q i s the maximum mean d a i l y f low above a base d i s cha rge Q^. was ' s e l e c t e d as the mean August-September d a i l y d i s cha rge to emphasize f l o o d peaks above the maximum g l a c i e r melt c o n t r i b u t i o n . S t a t i s t i c s i n c l u d e dra inage area ( A , ) , r e l a t i v e r e l i e f (R) and % g l a c i a l cover (%GC) . d 87 In summary, f l o o d i n g on the B e l l a Coola R ive r i s r e l a t e d to s e v e r a l seasona l ly -averaged c l i m a t e c o n d i t i o n s as w e l l as s i n g u l a r anomalies in the general c i r c u l a t i o n . High magnitude s p r i n g runoff i s a f u n c t i o n of accumulated snowfa l l throughout the win te r season and s p r i n g temperatures: a shor t - t e rm response to sea sona l ly in t eg ra ted c l i m a t e . A higher p r o b a b i l i t y of s p r i n g f l o o d i n g occurs du r ing i n t e r v a l s of increased win te r p r e c i p i t a t i o n ( e .g . 1964-1969). Peak autumn f l o o d s , which g e n e r a l l y produce the l a r g e s t instantaneous d i s cha rges , are not r e s t r i c t e d to these same i n t e r v a l s , a l though there i s a higher frequency of f lows above a g iven base d i scharge dur ing years of above average win te r p r e c i p i t a t i o n . The major i m p l i c a t i o n for inferences regard ing seasona l ly -averaged hydroc l imates i s that c e r t a i n f l o o d - r e l a t e d evidence may not be e x c l u s i v e l y a s soc i a t ed w i t h a p a r t i c u l a r runoff regime or i n t e r v a l of p e r s i s t e n t c l i m a t i c depa r tu re s . Flood Frequency F i v e d i f f e r e n t runoff regimes can be i d e n t i f i e d for the B e l l a Coola R i v e r : s p r i n g snowmelt, g l a c i e r me l t , r a ins to rm o n l y , and s p r i n g and autumn ra in -on-snow. Rain-on-snow dur ing the autumn produces the h ighes t d i scharges w h i l e s p r i n g snowmelt and ra ins to rm augmented g l a c i e r melt are probably the next most important in terms of peak d i scharge and sus ta ined high r u n o f f . In h y d r o l o g i c a l terms each cou ld be t r ea ted as a separate popu la t i on w i t h d i s t i n c t d i s t r i b u t i o n s and i n d i v i d u a l s t a t i s t i c a l p r o p e r t i e s (c f . Waylen and Woo, 1983)• In terms of impact on r i v e r morphology, channel and bank e r o s i o n , sediment t r anspor t and r e l a t e d a l l u v i a l processes , d i s t i n g u i s h i n g between these s e v e r a l d i s t r i b u t i o n s i s l e s s important . A l l f lows above the th r e sho ld for s i g n i f i c a n t sediment motion should be cons ide red . Therefore , the p a r t i a l d u r a t i o n s e r i e s i s used here because i t i s based on a l l f lows 88 above a g iven d i scharge regard less of t h e i r o r d e r i n g in t ime . The p a r t i a l d u r a t i o n s e r i e s of a l l four gauged catchments and i n f e r r e d f lows of the Talchako R ive r are shown in f i g u r e 3'8. The curves in f i g u r e 3-8 are ordered on the b a s i s of catchment s i z e w i th the excep t ion of the Talchako River which produces higher-magnitude f loods compared w i t h the l a rge r Atnarko R i v e r . Those bas ins w i th higher percentages of i ce -cover have p r o p o r t i o n a t e l y higher f l o o d magnitudes w i t h i n c r e a s i n g recurrence i n t e r v a l s (; '.e. the r a t i o of Q20/Q2 ' S ^ a r 9 e r * o r t ' i e Talchako , Nusatsum and Sal loomt R i v e r s ) . At recur rence i n t e r v a l s l e s s than 1.5 a l l p l o t s e x h i b i t s i m i l a r c u r v a t u r e . The p a r t i a l d u r a t i o n s e r i e s for B e l l a Coola R. begins to depart from the extreme va lue s e r i e s at f lows near Q_2 which corresponds w i th the mean f l ood c a l c u l a t e d us ing the p a r t i a l d u r a t i o n s e r i e s . Thus, the frequency of f lows w i t h moderate magnitudes on 3 -1 B e l l a Coola R ive r (approximately 400 - 600 m s ) i s no tab ly higher on the p a r t i a l d u r a t i o n s e r i e s . Th i s d i s t i n c t i o n remains an a r b i t r a r y one i f on ly high-magnitude f loods (Q^ or perhaps even as high as Q^Q) produce s i g n i f i c a n t changes in the a l l u v i a l system. However, i f in a d d i t i o n to high-magnitude f loods sequences of moderate f loods have a n o t i c e a b l e impact on the a l l u v i a l system, then an accura te es t imate of t h e i r frequency i s impor tant . Changes in hydroc l ima to logy which favor a higher frequency of f l o o d flows in both autumn and sp r ing seasons are apt to be be t t e r represented by the p a r t i a l d u r a t i o n sequence. P o s s i b l e s h i f t s in the long- term f l o o d frequency curves in response to changes in the h y d r o c l i m a t i c regime are cons idered below and in chapter seven. 89 10* with in „ , , „ , channel f l ows Bella Coola R. Part ial Duration Series overbank f l ows <r> 3 OS < X Sio2 (n=39) alchako R.~ Atnarko R: Nusatsum - R. Salloomt R. (n=21) 10J <2. 1 mean f l o o d ( e vs s e r i e s ) = mean f l o o d ( p a r t i a l d u r a t i o n s e r i e s ) 1.05 1.25 2 5 10 RECURRENCE INTERVAL (YEARS) 20 50 100 F i g u r e 3-8 P a r t i a l d u r a t i o n s e r i e s for runof f from a l l f i v e gauges in the B e l l a Coola R i v e r wate rshed . W i t h i n - c h a n n e l and overbank f lows are de f ined for the s t a b l e reach in which the main gauge i s l o c a t e d ( B e l l a Coola R i v e r above Burnt B r idge C r e e k ) . 90 (3•3) Longer-Term, High-Resolution Climate Analysis The frequency of both extreme and p e r s i s t e n t departures in c l i m a t e dur ing the 20th century can be i n f e r r e d from only a smal l number of c l i m a t e s t a t i o n s in the study a rea . Although inferences of bas in-wide c l i m a t e w i l l be b iased towards these s p a t i a l l y - r e s t r i c t e d r eco rds , comparison w i t h other r e g i o n a l records and notable hemispher ic changes in dominant c i r c u l a t i o n pa t te rns p rov ide a bas i s for a s sess ing the u t i l i t y of the records as sources of r e g i o n a l c l i m a t e i n f o r m a t i o n . Monthly data are examined here for three reasons: 1) to augment and extend the sho r t - t e rm, r e g i o n a l r eco rds ; 2) to p rov ide a bas i s for comparison w i t h b i o l o g i c a l and geophys ica l responses in the b a s i n and; 3) to i d e n t i f y the occurrence of extreme i n t r a - and in te rannua l v a r i a t i o n s in the longer- term c l i m a t e r e c o r d . N e i l s o n (1986) has d i s p l a y e d records of p r e c i p i t a t i o n and temperature as contoured, two-dimensional su r f ace s . Th i s technique has been adopted here for the two longer- te rm s t a t i o n s in the v i c i n i t y of the study a r ea . The B e l l a Coola c l i m a t e s t a t i o n i s assumed to be r e p r e s e n t a t i v e of environmental c o n d i t i o n s towards the west s i d e of the bas in s p e c i f i c a l l y , and c o a s t a l c o n d i t i o n s in g e n e r a l . B i g Creek c l i m a t e data are used to c h a r a c t e r i z e trends in the eas te rn bas in or Fraser P la teau area (refer to f i g u r e 2.1 for l o c a t i o n s and t a b l e 3-1 for f ac to r g roup ings ) . Contour surfaces of t o t a l monthly p r e c i p i t a t i o n and monthly averages of mean d a i l y temperature for the pe r iod 1904 to 1983 are i l l u s t r a t e d in f i g u r e s 3-9 and 3-10. F i f t e e n months of data are presented along the h o r i z o n t a l axes r ep resen t ing the cu r r en t year and the l a s t three months of the prev ious year . The most obvious fea tures of f i g u r e 3-9 are the w in t e r maximum i n p r e c i p i t a t i o n for B e l l a Coola and a t rend towards above average p r e c i p i t a t i o n in the l a t t e r h a l f of the century (with the excep t ion of high October to November p r e c i p i t a t i o n between 193** and 19*t0) . There i s a l s o 91 MONTH F i g u r e 3*9 Contoured su r faces of i n t r a - and i n t e r annua l temperature and p r e c i p i t a t i o n for B e l l a Coola c l imate. s t a t i o n , 1904-1983 (see f i g u r e 2.2 fo r s t a t i o n l o c a t i o n ) . October to December va lues on the l e f t are from the p rev ious yea r . Temperature contour i n t e r v a l i s 5° C and p r e c i p i t a t i o n contour i n t e r v a l i s 40 mm. The shaded areas on the temperature p l o t represen t extreme d e p a r t u r e s . MONTH F i g u r e 3-10 Contoured sur faces of i n t r a - and i n t e r a n n u a l temperature and p r e c i p i t a t i o n for B i g Creek c l i m a t e s t a t i o n , 1904-1983 (see f i g u r e 2.1 for s t a t i o n l o c a t i o n ) . October to December va lues on the l e f t are from the p rev ious yea r . Temperature contour i n t e r v a l i s 5° C and p r e c i p i t a t i o n contour i n t e r v a l i s 20 mm. The shaded areas on the temperature p l o t r epresen t extreme d e p a r t u r e s . 93 evidence for higher and more p e r s i s t e n t October to January p r e c i p i t a t i o n a f t e r 1953- Summer p r e c i p i t a t i o n was lowest between 1924 and approximate ly 1945 and dur ing the i n t e r v a l 1963 to 1976. Mean December to February temperatures were c o n s i s t e n t l y below 0°C u n t i l 1920 a f te r which gradual warming occurred u n t i l at l e a s t 19^5 (note the frequency of c l o s e d contours < -5°C p r i o r to 1920) . Pos t - ig ' tS win te r temperatures, p a r t i c u l a r l y 1948 to 1958 and 1962 to 1976, were more s i m i l a r to those recorded p r i o r to 1920. A tendency towards warmer sp r ings in the l a t t e r h a l f of the century i s a l s o d i s c e r n i b l e (see the s lope of the 5 and 10°C contours near March and A p r i l ) . Cooler summers p r e v a i l e d u n t i l approximate ly 1930 a f t e r which higher temperatures were ev iden t w i t h the excep t ion of 19^5-1957 and 1968-1976 . Some i n t e r e s t i n g d i f f e r e n c e s and s i m i l a r i t i e s are a s soc i a t ed w i t h c l i m a t e trends at B i g Creek ( f igure 3 - 1 0 ) . A summer maximum in p r e c i p i t a t i o n dominates there w i t h lowest summer t o t a l s o c c u r r i n g between 1920 and 1940. Summer and win te r p r e c i p i t a t i o n i s g e n e r a l l y higher a f t e r 1940 compared to the f i r s t h a l f of the cen tu ry . L i k e B e l l a C o o l a , pre-1920 win te r temperatures were amongst the lowest in the century , a l though u n l i k e B e l l a Coola warming was not so ev ident u n t i l a f t e r 1940. The coo le r w in t e r s of 19^8-1955 are most s i m i l a r to the p re -1920 temperature depa r tu res . E a r l y century summer temperatures at B i g Creek were compara t ive ly warm but maximum temperatures were not recorded u n t i l a f t e r 1920, ending around 1930 wi th a c o o l i n g t rend which l a s t e d for the next decade. Summer temperatures a f t e r 1958 are the lowest of the century w i t h the except ions of 1978 and 1979- With the excep t ion of the i n t e r v a l 1930 to 19^0, the pre-1950 pe r iod at B e l l a Coola i s c h a r a c t e r i z e d by years w i th l e s s p e r s i s t e n t depar tures of i n t r a - a n n u a l monthly p r e c i p i t a t i o n when compared w i t h the post-1950 record 9** ( f igure 3-9°). T h i s i s p a r t i c u l a r l y t rue for the win te r months. At B i g Creek, summer and e a r l y autumn months e x h i b i t p e r s i s t e n t p o s i t i v e depar tures in the pre-1920, 1940-1965 and post-1980 r e c o r d s . Extremes in monthly p r e c i p i t a t i o n tend to c l u s t e r w i t h i n these per iods of p o s i t i v e depar ture but are not e x c l u s i v e l y found the re . The contoured surfaces would suggest a non-random o r d e r i n g of c l i m a t e depar tures through the 20th c en tu ry . It has been wide ly recognized that three d i s t i n c t per iods of c h a r a c t e r i s t i c a l l y d i f f e r e n t c i r c u l a t i o n regimes have occurred over the l a s t 80 years r e l a t e d to t r a n s i t i o n s from m e r i d i o n a l f low pa t t e rns (pre-1920 and post-1945) to zona l f low pa t te rns (1920-1945; see t ab l e 3-8). When the energy g rad ien t between the pole and equator i s s teep, a s e r i e s of high ampli tude waves generate s t ronger l o n g i t u d i n a l con t r a s t s in c l i m a t e than would be exper ienced under a zona l f low regime (Makrogannis et al., 1982). P e r s i s t e n t and of ten extreme depar tures occur when the m e r i d i o n a l wave pa t t e rn remains ent renched. Even sma l l l o n g i t u d i n a l s h i f t s in the mean p o s i t i o n of b l o c k i n g r idges and as soc i a t ed troughs can lead to abrupt changes in the d i r e c t i o n of depar tu re . Under a zona l f low regime, yea r - to -yea r va r i ance i s enhanced and the frequency of p e r s i s t e n t departures i s g r e a t l y reduced. B i a s i n g and Lofgren (1980) have analyzed monthly s e a - l e v e l pressure data for the N . E . P a c i f i c sec tor cove r ing the pe r iod 1899 to 1971' Using the map c o r r e l a t i o n method, they were able to c l a s s i f y o b j e c t i v e l y dominant c i r c u l a t i o n types c h a r a c t e r i s t i c of each p e r i o d . During win t e r s of the f i r s t two decades of t h i s century above normal pressures in nor thern Canada r e s u l t e d i n an anomalous f low of c o l d a r c t i c a i r , presumably a s s o c i a t e d w i t h a southward displacement of the a r c t i c f r o n t , r e s u l t i n g i n coo le r and mois ter c o n d i t i o n s along the outer B r i t i s h Columbia c o a s t . A s t rong 95 Table 3.8. Recognized Trends in 20th Century Synoptic Conditions in the N.E. Pacific Sector. 1900 -1920's SYNOPTIC CONDITIONS - meridional flow (some zonal) 1920's -1950's - zonal flow post 1950*5 meridional flow METHODOLOGY cla s s i f i c a t i o n of N. hemisphere surface pressure maps by (1) and eigenvector analysis by (2) SOURCE 41) Dzerdzeevski (1966, 69) (2) Balinicky (1974) 1900 -1920's 1920's - 1950's 1950's -1970 decreased intensity of the January Aleutian Low intermediate conditions increased intensity of the January Aleutian Low and an eastward extension eigenvector analysis of N. hemisphere sea level pressure maps for both January and July Kutzbach (1970) 1899 - 1920's - above normal pressure in high latitudes of the Pacific (cool) map correlation method using 1920's - 1940's - below normal pressure in N. sea level pressure data Biasing and Lofgren (1980) Pacific sector (warm/dry) post 1940'a - more average conditions 1893 - 1920 - cooler/wetter in U.S. West 1920 - 1954 - warmer/drier 1955 - 1977 - cooler/wetter areally averaged monthly mean temperature and precipitation Diaz and Quayle (1960) for the contiguous U.S. 1895 - 1920's 1920's - 1945 increased frequency of cool/wet synoptic types increased frequency of warm/wet synoptic types map correlation method of surface pressure data using Kirchhofar cutoff scores Barry et a l . (1981) post 1945 - more.variable conditions but warm and wet 96 1875 - 1905 - higher precipitation in the Pacific N.W. 1905 - 1945 - reduced v a r i a b i l i t y in and totals of precipitation 1945 - 1975 - higher precipitation and greater v a r i a b i l i t y eigenvector analysis of precipitation records along McQuirk (1982) U.S. west coast 1872-91 - wet periods in northern 1902-11 California associated 1932-41 with a northward s h i f t in eigenvector analysis of 1962-71 the Pacific High precipitation records in the Granger C1979) U.S. West Wahl and Lawson (1971) 1892-1901 - drier periods associated 1912-31 with a southward s h i f t in 1942-61 the Pacific High early 20th C - southward displacement of Aleutian Low and Pacific High - cooler/wetter analysis of Pacific sector pressure data for the 20th Angell and Korshover middle 20th C - northward displacement of century (1974,82) Aleutian Low and Pacific High - greater circulation intensity 1947 - 1966 - higher. 700 mb heights in Gulf of Alaska and Aleutians analysis of 700 mb pressure data and SST anomalies Douglas et a l . (1982) 1966 - 1980 - lower 700 mb heights - increased zonal index 1951-54 - maximum blocking frequency 1966-71 in N. hemisphere analysis of 500 mb pressure Treidl et a l . (1981) anomalies for N. hemisphere Knox and Hay (1985) 1960-65 - minimum blocking frequency 1974-78 i n N. hemisphere 1948 - 1965 - s l i g h t l y higher 500 mb heights for N.E. Pacific upper air pressure data grouped into several synoptic Yarnel (1985) 1965 - 1978 - s l i g h t l y lower 500 mb types heights for N.E. Pacific 97 negat ive pressure anomaly in the A l e u t i a n s led to an increased southwes te r ly flow a l o f t and above normal summer p r e c i p i t a t i o n . Reduced p r e c i p i t a t i o n and higher temperatures a f t e r 1920 fo l lowed a northward displacement of c y c l o n i c a c t i v i t y as p o s i t i v e pressure anomalies dominated the c e n t r a l P a c i f i c , p a r t i c u l a r l y dur ing the summer. C i r c u l a t i o n pa t te rns between 193^ and 1937 best exemplify t h i s pe r iod (B ia s ing and Lofgren , 1980: 717) e s p e c i a l l y i n the sequence of s p r i n g and summer sur face pressure anomalies ; a fea ture which i s most ev ident as warmer summer temperatures recorded at B e l l a Coola ( f igure 3-9) and s i g n i f i c a n t because two of the l a r g e s t autumn f loods on the B e l l a Coola R ive r occurred i n 193** and 1936- Af t e r 1945 a r e tu rn to m e r i d i o n a l f l o w , a l though w i t h higher ampli tudes in the Rossby wave p a t t e r n , was a s soc ia t ed w i th p o s i t i v e pressure anomalies i n the western Uni ted Sta tes (B ias ing and Lofgren , 1980). Monthly and seasonal va r i ance of temperature and p r e c i p i t a t i o n at B e l l a Coola and B i g Creek were eva lua ted for these three per iods (pre- 1920, 1920-19^5. post-1945) a long w i t h an index of year to year v a r i a b i l i t y of monthly v a l u e s . Although some seasonal d i f f e r e n c e s between s t a t i o n s e x i s t , w i t h i n - p e r i o d va r i ances of summer and autumn temperatures were c o n s i s t e n t l y higher (average of 40% greater) in the e a r l i e r and l a t e r p e r i o d s . In a d d i t i o n , v a r i a n c e of summer and win te r temperatures was lowest between 1920 and 19^5• S i m i l a r l y , autumn and s p r i n g p r e c i p i t a t i o n e x h i b i t h ighes t w i t h i n pe r iod va r i ances (average of 65% greater) for the post-1945 p e r i o d . The d i f f e r e n c e s in between-period va r i ances are p a r t l y a f u n c t i o n of the frequency of extreme depar tu res . Maximum 24-hour p r e c i p i t a t i o n events of 80 mm or more at B e l l a Coola have a recurrence p r o b a b i l i t y of l e s s than 20% between 1920 and 1945 compared w i th 25-30% p r o b a b i l i t y du r ing the other two i n t e r v a l s . 98 Mean s e n s i t i v i t y i s used here as an index of year to year 2 f l u c t u a t i o n s w i t h i n each p e r i o d . A high mean s e n s i t i v i t y i n d i c a t e s the p ropens i ty for changes in the s i g n of depar ture between success ive years w i t h i n a g iven i n t e r v a l , and i s thought to represent a lack of p e r s i s t e n c e . Zonal c i r c u l a t i o n regimes c h a r a c t e r i z e these i n t e r v a l s . P r e c i p i t a t i o n at both s t a t i o n s for most months of- the year between 1 9 2 0 and 19̂ 5 e x h i b i t s the g rea te s t yea r - to -yea r f l u c t u a t i o n (15 to 25% more compared w i t h other i n t e r v a l s ) . Autumn and win te r temperatures a l s o e x h i b i t e d higher mean s e n s i t i v i t i e s between 1 9 2 0 and 19^5; however, summer temperature, p a r t i c u l a r l y at B i g Creek, shows a higher mean s e n s i t i v i t y between 1 9 ^ 5 and I 9 8 3 . With the excep t ion of t h i s l a t t e r r e s u l t , mean s e n s i t i v i t y va lues g ive some support to the secu la r v a r i a t i o n s in c i r c u l a t i o n regime shown in f i g u r e s 3 . 9 and 3 - 1 0 . Comparisons With Other Regions Although the number of long- term s t a t i o n s ( > 8 0 years record) in c o a s t a l B r i t i s h Columbia i s l i m i t e d , there are some obvious s i m i l a r i t i e s for the e n t i r e c o a s t a l r e g i o n . Three-year running mean curves presented by Powel l ( 1 9 6 5 ) show a t rend towards average and above average annual p r e c i p i t a t i o n p r i o r to 1 9 2 0 for the outer coast ( e .g . Clayoquot and Q u a t s i n o ) . Th i s t rend i s l e s s pronounced or reversed for the c e n t r a l and southern coas ts sugges t ing that the non-synchronous response in win te r p r e c i p i t a t i o n for c o a s t a l regions p r i o r to 1 9 2 0 was d r i v e n by synop t i c c o n t r o l s s i m i l a r to those i d e n t i f i e d for the p o s t - 1 9 4 5 p e r i o d . Data 2 . Mean s e n s i t i v i t y i s c a l c u l a t e d as f o l l o w s : n-1 M s x = _ U / n - 1 ) E I [ 2 ( x t + 1 - x t ) ] / ( x t + { + x t ) | x = va lue of c l i m a t e v a r i a b l e in year t ; n = number of years 99 presented by both Powel l (19&5) a n c ' Karanka (1986) show a higher mean s e n s i t i v i t y dur ing the i n t e rven ing pe r iod (1920-1940) w i th no obvious or p e r s i s t e n t departures in p r e c i p i t a t i o n . Cooler than normal win te r temperatures between 1904 and 1920 at both B e l l a Coola and B ig Creek are a l s o w e l l documented in Karanka ' s Queen C h a r l o t t e Is lands temperature index and the outer and inner coast c l i m a t e s t a t i o n s analyzed by P o w e l l . Although complete records in B e l l a Coola do not extend beyond 1904, evidence from other c l i m a t e s t a t i o n s ope ra t i ng in the l a t e 19th century (Queen C h a r l o t t e I s l ands , Clayoquot , Steveston) demonstrates that from approximately 1890 to 1904 win te r temperature departures were most ly p o s i t i v e . The tendency for above average win te r temperatures in B e l l a Coola between 1920 and 1945 i s a l s o ev ident for s t a t i o n s a long the North Coast . (3.4) Conclusions Temperature and p r e c i p i t a t i o n v a r i a b i l i t y along the c e n t r a l B r i t i s h Columbia coast e x h i b i t pa t te rns which show some correspondence w i t h noted 20th century changes in c i r c u l a t i o n regime. C l i m a t i c anomalies w i t h i n these per iods are short and not w e l l coord ina ted between temperature and p r e c i p i t a t i o n . The recent record shows that the synop t i c s i gna tu re for anomalously wet w in t e r s i s both a higher frequency and grea ter seasonal p e r s i s t e n c e of s p e c i f i c synop t i c types . C e r t a i n h y d r o l o g i c v a r i a b l e s such as snowpack and s p r i n g f l o o d i n g respond to p e r s i s t e n t c l i m a t i c depa r tu res . Extreme departures in p r e c i p i t a t i o n , which produce key h y d r o l o g i c events , ( e .g . autumn f loods) are more randomly d i s t r i b u t e d across per iods but have a higher p r o b a b i l i t y of occurrence under a m e r i d i o n a l f low regime. There i s a d e f i n a b l e r e g i o n a l s i g n a l of f l o o d anomalies a long the southwestern coast of B r i t i s h Columbia. Sedimentary depos i t s w i t h i n dra inage bas ins of t h i s 100 reg ion are more l i k e l y to r e f l e c t these extreme depar tu res . However, other elements of the b i o p h y s i c a l systems are known to have memory. The f o l l o w i n g chapters w i l l exp lo re the a c t u a l pa t te rns of response. 101 CHAPTER IV Geomorphological Evidence of Response of Geophysical Systems To Environmental ChangerTests Within the H i s t o r i c a l Record (4.0) Introduction In response to h y d r o l o g i c a l changes, c e r t a i n e f f e c t s are apt to occur w i t h i n b i o l o g i c a l and geophys ica l subsystems. The purpose here i s to examine s e v e r a l of these subsystem responses w i t h i n the shor t term, us ing the pe r iod of ins t rumenta l record in the B e l l a Coola b a s i n , and to t e s t the u t i l i t y of b i o g e o p h y s i c a l data for drawing inferences about l o c a l and r e g i o n a l h y d r o l o g i c a l changes. The responses examined i n c l u d e : g l a c i e r f l u c t u a t i o n s , upland sediment t r a n s f e r s , and a l l u v i a l a c t i v i t y of the B e l l a Coola R i v e r . (4.1) Glacier Fluctuations and Recent Climate Change A v a l u a b l e i n d i c a t o r of environmental change i n mid and high l a t i t u d e g l a c i e r i z e d regions i s the f l u c t u a t i o n in water s torage r e f l e c t e d as changes in mass and i c e - f r o n t p o s i t i o n s of g l a c i e r s . P e r s i s t e n c e in the ra te of snow accumulat ion and g l a c i e r a b l a t i o n over s e v e r a l seasons or more, can lead to s u b s t a n t i a l changes in the p o s i t i o n of the i c e - f r o n t and the d e p o s i t i o n of ice-eroded m a t e r i a l s which can then be used to i n fe r the r a te of i c e - f r o n t movements. The purpose here i s to e s t a b l i s h the nature of the r e l a t i o n s h i p between g l a c i e r f l u c t u a t i o n s and p r e v a i l i n g c l i m a t e so as to p rov ide a bas i s for i n t e r p r e t a t i o n of g l a c i e r depos i t s i n d i c a t i v e of former g l a c i e r c o n f i g u r a t i o n s and, u l t i m a t e l y , a s soc i a t ed h y d r o c l i m a t i c cond i t i ons . Seve ra l f a c to r s compl ica te the r e l a t i o n s h i p between g l a c i e r f l u c t u a t i o n and hydroc l ima te . One group of f a c t o r s i s r e l a t e d to annual changes in the water (snow/ice) mass balance of a p a r t i c u l a r g l a c i e r 102 system. A second group i s a s soc i a t ed w i t h g l a c i e r responses, such as f l u c t u a t i o n s in movement in t eg ra ted over the whole ice mass or indexed by changes in g l a c i e r snout p o s i t i o n . In the f i r s t group, c l i m a t i c f a c to r s such as w in t e r p r e c i p i t a t i o n and summer temperature g e n e r a l l y account for much of the va r i ance in the net ice-mass ba lance . However, they remain imperfect i nd i ces because of the importance of other parameters such as the r e d i s t r i b u t i o n of snow by wind and ava lanch ing , i c e - c a l v i n g , and sampling and measurement e r r o r s in de termining a c t u a l mass-balance for a g iven season (Fogarasi and Mokievsky-Zubok, 1978; Mayo and Trabant , 1984). There fore , i t i s u n l i k e l y that s i n g l e or even s eve ra l po in t es t imates of temperature and p r e c i p i t a t i o n can f u l l y account for f l u c t u a t i o n s in net mass balance from year to year . The second group of f a c to r s i s r e l a t e d to changes in i c e - f r o n t p o s i t i o n . Severa l s t ud i e s have demonstrated that snout r e t r e a t may not be synchronous w i th o v e r a l l losses in t o t a l g l a c i e r volume and that g l a c i e r s e n s i t i v i t y to changing c l i m a t e i s r e l a t e d to g l a c i e r s i z e and phys iograph ic boundary c o n d i t i o n s (Ahlmann, 1953; Hoinkes , 1968; Smith and Budd, 198l). The a c t u a l ra te of movement w i l l depend on s i t e - s p e c i f i c f a c t o r s such as s l o p e , degree of confinement, aspec t , t o t a l i ce th ickness and s u b - g l a c i a l drainage f ea tu r e s . Severa l e m p i r i c a l and p h y s i c a l l y based models have been proposed to e x p l a i n the v a r i a t i o n in annual ice mass balance for temperate v a l l e y and c i r q u e g l a c i e r s . Kuhn (1981) has developed a p h y s i c a l model which r e l a t e s changes in mass to pe r tu rba t i ons in parameters such as f ree atmospheric temperature near the g l a c i e r , t o t a l annual accumulat ion (from a l l sources) and the r a d i a t i o n ba lance . A l t e r n a t i v e l y , Tangborn (1980) developed an e m p i r i c a l model which requ i res es t imates of temperature and p r e c i p i t a t i o n measured at nearby s t a t i o n s to es t imate f l u c t u a t i o n s in the annual mass 103 ba lance . Although d e r i v e d from d i f f e r e n t assumptions, the two c l imate -based models of g l a c i e r f l u c t u a t i o n appear to y i e l d s i m i l a r r e s u l t s regard ing changes i n temperature and p r e c i p i t a t i o n corresponding to s p e c i f i c f l u c t u a t i o n s in mass ba lance . In both s tud ies c i t e d above net mass balance appears to be most s e n s i t i v e to changes in win te r p r e c i p i t a t i o n . Th i s i s in con t r a s t w i t h the s i m u l a t i o n model r e s u l t s of Smith and Budd (198l) who found temperature to be the more important v a r i a b l e . T h i s d i f f e r e n c e i s probably r e l a t e d to c l i m a t e v a r i a t i o n s at both the g l o b a l s ca l e ( l a t i t u d e / l o n g i t u d e and mari t ime or c o n t i n e n t a l in f luences) and l o c a l s i t e s c a l e (windward/leeward e f f e c t s ) . Hence, the r e l a t i v e s i g n i f i c a n c e of p r e c i p i t a t i o n and temperature as i nd i ce s of g l a c i e r f l u c t u a t i o n s may not be c o n s i s t e n t between r eg ions . Mass Balance Fluctuations of Glac i e r s in Southwestern B.C. Severa l e m p i r i c a l models are examined in order to assess the r e l a t i o n s h i p between c l i m a t e f l u c t u a t i o n s (temperature and p r e c i p i t a t i o n ) and g l a c i e r response in southwestern B r i t i s h Columbia . G l a c i e r mass balance and e q u i l i b r i u m l i n e a l t i t u d e (ELA) data are a v a i l a b l e for three g l a c i e r s in the Squamish/Li1 looet watersheds beginning in 19&5. and shor te r s e r i e s commencing in 197& fo r three g l a c i e r s in the headwaters of Br idge R i v e r . A l l these s i t e s are loca t ed to the south of the B e l l a Coola R i v e r ba s in (see f i gure 2.1). Monthly and s ea sona l l y averaged c l i m a t e data (temperature and p r e c i p i t a t i o n ) beginning in 1966 were transformed in to two sets of r e g i o n a l c l i m a t e i n d i c e s r ep resen t ing the wet ter south coast (A l t a Lake, G a r i b a l d i , W h i s t l e r roundhouse s t a t i o n s ) and the d r i e r i n t e r i o r (Tatlayoko Lake, T a t l a Lake, Kleena Kleene and B ig C r e e k ) . The l a t t e r set of i nd i ce s i s that used to represent the c e n t r a l coast c l i m a t e s in s e c t i o n 3-1 and was s e l e c t e d 104 because of the p r o x i m i t y of these s t a t i o n s to the Br idge R ive r g l a c i e r s . Although there are other s t a t i o n s c l o s e r to the Br idge River b a s i n , these were s e l e c t e d because of the higher s p a t i a l and temporal coherence of temperature measurements amongst i n t e r i o r c l i m a t e s t a t i o n s and the grea ter r e g i o n a l s i g n i f i c a n c e of any de r i ved r e l a t i o n s h i p s . Independent v a r i a b l e s c o n s i s t e d of win te r p r e c i p i t a t i o n and summer temperature for each of two regions (coas ta l and i n t e r i o r ) and win te r mass balance de te rmina t ions for each g l a c i e r . U n l i k e the Tangborn model, temperature range (an i n d i r e c t measure of c loud cover and r a d i a t i v e f luxes ) was not incorpora ted here s i n c e t h i s v a r i a b l e proved to be of low s i g n i f i c a n c e in h i s model and because such a parameter i s not e a s i l y cons t ruc ted us ing i n d i r e c t or proxy da t a . Table 4.1 i s a summary of m u l t i v a r i a t e e x p l o r a t o r y models for each g l a c i e r . In a l l three cases the s t ronges t response model (model [1]) incorpora tes win te r mass balance and summer temperature, account ing for 73 to 85% of the exp la ined va r i ance in annual net mass ba lance . When win te r mass balance i s excluded (model [2]) the exp la ined va r i ance remains s i g n i f i c a n t for S e n t i n e l and P lace G l a c i e r s but d e c l i n e s to between 52 and 59%. A lower degrees of freedom for Br idge G l a c i e r y i e l d s a n o n - s i g n i f i c a n t model when tes ted under more r e s t r i c t i v e conf idence l e v e l s ( 'a= 0.025). In each model [2] case , win te r p r e c i p i t a t i o n c o n t r i b u t e s more to the exp la ined v a r i a n c e than summer temperature, e s p e c i a l l y for S e n t i n e l and P lace G l a c i e r s which are loca ted in a we t t e r , more mar i t ime , reg ion to the southwest . The reg ion from which c l i m a t e i nd i ce s are de r ived appears to be impor tant . For example, c o a s t a l p r e c i p i t a t i o n i s the more s i g n i f i c a n t v a r i a b l e in e x p l a i n i n g annual mass balance changes on S e n t i n e l G l a c i e r whereas i n t e r i o r p r e c i p i t a t i o n i s of greater s i g n i f i c a n c e for the other two 105 Table 4.1 Empirical response models for glacier net mass balance and climate Glacier Independent Variable (contribution to explained variance) Model Winter Mass Winter Summer d.f. Ra (2) (2) Balance Precipitation Temperature Sentinel [1] [2] 76% 65% (c) 24% ( i ) 35% (i) 18 73% 25.7 18 59% 11.4 Place [1] [2] 88% 79% (i) 12% (i) 21% (i) 18 73% 21.0 18 56% 10.4 Bridge [1] [2] 81% 54% (i) 19% (i) 46% (i) 85% 15. 52% 4.8* 1. Model [1] includes a l l significant variables; model [2] excludes winter net mass balance from the l i s t of independent variables 2. Indices generated using coastal stations are marked (c) and those generated from i n t e r i o r stations are marked ( i ) . 3. * not sig n i f i c a n t at a =• 0.025 106 s i t e s . Th i s was not unexpected s i n c e S e n t i n e l G l a c i e r i s s i t u a t e d in a b e l t of heavy p r e c i p i t a t i o n centered on Mount G a r i b a l d i . Temperature i nd i ce s generated from i n t e r i o r s t a t i o n s are more s i g n i f i c a n t for a l l three g l a c i e r s than are c o a s t a l i n d i c e s . Th i s may be a r e s u l t of the lower o v e r a l l v a r i a n c e in summer temperatures for the coast due to p e r s i s t e n t c loud cove r . While on ly a l i m i t e d number of independent v a r i a b l e s was cons idered here, and the degrees of freedom are g e n e r a l l y low, a s i g n i f i c a n t p o r t i o n of net annual mass balance in c o a s t a l g l a c i e r s can be exp l a ined us ing r e a d i l y de r ived temperature and p r e c i p i t a t i o n i n d i c e s . The three g l a c i e r s examined represent a range in c h a r a c t e r i s t i c s such as s i z e , s l o p e , aspec t , accumulat ion area morphology and l o c a l hydroc l ima to logy and i t i s l i k e l y that these f a c t o r s c o n t r i b u t e to the r e s i d u a l v a r i a n c e . Y e t , r e g i o n a l l y de r i ved c l i m a t e i n d i c e s form a set of s i g n i f i c a n t independent v a r i a b l e s , a l b e i t of v a r y i n g importance between s i t e s . Primary c o n t r o l s of net annual balance are win te r snowpack measured on the g l a c i e r ( r eg iona l snow course data were not s t r o n g l y s i g n i f i c a n t v a r i a b l e s al though they were tested) and summer temperature. S u b s t i t u t i n g r e g i o n a l l y es t imated win te r p r e c i p i t a t i o n , which w i l l u s u a l l y be a v a i l a b l e , reduces the s t r eng th of the r e l a t i o n s h i p but the model remains s i g n i f i c a n t . Data p l o t t e d in f i g u r e s 3-1 through 3-5 i n d i c a t e that the i n t e r v a l 1966 to 1984 was c h a r a c t e r i z e d by some of the g rea tes t depar tures in temperature, p r e c i p i t a t i o n , win te r snowpack and r u n o f f . Although t h i s extreme v a r i a b i l i t y extends the c a l i b r a t i o n range of the S e n t i n e l and P lace G l a c i e r models, a l i m i t a t i o n of l i n e a r models i s that they represent mean responses o n l y . The l e v e l of exp la ined v a r i a n c e in these g l a c i e r - c l i m a t e r e g r e s s i o n models i s as high as that found in the s p r i n g runoff models. The 40 to 50% 107 unexpla ined v a r i a n c e us ing model [2] i s r e l a t e d to at l e a s t three f a c t o r s : the r e l a t i v e importance of temperature and p r e c i p i t a t i o n at each s i t e in de termining net mass ba lance , the s i g n i f i c a n c e of extreme depar tures in c o n t r o l l i n g v a r i a b l e s , and the represen ta t iveness of the r e g i o n a l c l i m a t e i nd i ce s . Mass Balance and Climate Since temperature and p r e c i p i t a t i o n are on ly index c l i m a t o l o g i c a l parameters, the l inkages between g l a c i e r mass balance and synop t i c s c a l e c i r c u l a t i o n pa t te rns were examined. Yarne l (1982) found that a s i g n i f i c a n t p r o p o r t i o n of mass balance v a r i a b i l i t y for two C o r d i l l e r a n g l a c i e r s dur ing the i n t e r v a l 1966 to 197̂  cou ld be exp la ined by the frequency of c e r t a i n synop t i c regimes. The frequency of synop t i c types which produce above or below average win te r p r e c i p i t a t i o n and summer temperature for c o a s t a l B r i t i s h Columbia i s t es ted here aga ins t groups of i n d i v i d u a l years in which win te r and summer mass balances were above or below average. Because of the l i m i t e d length of the data s e r i e s and high in te rannua l v a r i a n c e , per iods of p e r s i s t e n t p o s i t i v e or negat ive mass balance depar tures could not be def ined w i t h conf idence . Resu l t s are presented in t ab les h.2 and 4.3- There a re , on average, 11 more win te r days dominated by "wet" 500 mb synop t i c types and 17 more win te r days c h a r a c t e r i z e d by mois ture producing surface pressure types dur ing s t r o n g l y p o s i t i v e mass balance years compared wi th low mass balance yea r s . In both cases these d i f f e r e n c e s are s i g n i f i c a n t . There i s no s i g n i f i c a n t d i f f e r e n c e in the frequency of "warm/dry" synop t i c c i r c u l a t i o n types between years of high and low summer mass ba lance . Th i s l a t t e r r e s u l t i s r e l a t e d to the d i f f i c u l t i e s in o b j e c t i v e l y i d e n t i f y i n g c i r c u l a t i o n regimes which might produce c l i m a t e depar tures (e .g . warm or dry) du r ing the summer season when the o v e r a l l 108 Table 4.2 Winter Mass Balance on B.C. South Coastal Glaciers and Synoptic Type Frequency Significance test between high winter mass balance years and low winter mass balance years Mass balance years consistent over a l l glaciers Mean winter mass balance Wet synoptic (mean departure) type frequency Wet synoptic 3 type frequency high winter mass balance :(1976, 74, 1971,68,67) 1.48 ± 0.79 90 ± 4.1 46.6 ± 7.4 low winter mass balance :(1978, 77, 1975,70,72) -0.74 ± 0.58 79 ± 5.4 30.4 ± 6.1 One-tailed t-test (a = 0.10, df = 8) t = 4.42 significant t = 3.63 significant t = 3.78 significant 1. Calculated as the mean departure in winter mass balance for two (1966-1975) and fi v e (1976-1984) coastal glaciers. 2. 500 mb synoptic types as defined by Yarnel (1983). 3. Surface pressure types as defined by Barry et a l . (1982). 109 Table 4.3 Summer Mass Balance on B.C. Coastal glaciers and Synoptic Type Frequency. Significance test between high summer mass balance years and low summer mass balance years Mean summer mass balance (mean departure) 500 mb Dry/warm synoptic type frequency high summer mass balance years: (1977,71,70,69,67) 0.18 ± 0.17 23.6 ± 6.5 low summer mass balance years: (1978,76,75,73,72) -0.18 ± 0.07 20.0 ± 5.2 One-tailed t-test t = 4.36 (a = 0.10, df = 8) significant t = 0.97 not significant 110 c i r c u l a t i o n i n t e n s i t y i s low and day to day c i r c u l a t i o n v a r i a b i l i t y i s reduced. I t may a l s o r e f l e c t the lower s i g n i f i c a n c e of summer temperatures in the mass balance models due to the dominance of mari t ime c o n d i t i o n s in the lee of the Coast Mountains . In g e n e r a l , h igh mass balance years are c h a r a c t e r i z e d by an increased frequency of c i r c u l a t i o n s w i t h s t rong c y c l o n i c curva tu re f a v o r i n g the accumulat ion of snow along the south c o a s t . Summer a b l a t i o n does not appear to be s imply r e l a t e d to the frequency of 500 mb synop t i c types which are thought to favor warm/dry c o n d i t i o n s . Hence, g l a c i e r s form on the coast on ly where win te r p r e c i p i t a t i o n i s so high as to dominate the mass ba lance . In land , where summer temperatures may dominate, f l u c t u a t i o n s i n mass balance are l e s s p r e d i c t a b l e . G l a c i e r Snout F l u c t u a t i o n s An a l t e r n a t i v e method for assess ing the response c h a r a c t e r i s t i c s of g l a c i e r s to c l i m a t e change i s to examine the record of f l u c t u a t i o n s i n the mean f r o n t a l , or in some cases l a t e r a l , p o s i t i o n of s e v e r a l g l a c i e r s r e p r e s e n t a t i v e of a p a r t i c u l a r a r ea . Paterson (198l) has o u t l i n e d many of the key v a r i a b l e s c o n t r o l l i n g g l a c i e r snout changes which u l t i m a t e l y respond to pe r tu rba t i ons in mass ba lance . The most important geophys ica l f a c to r s are g l a c i e r s i z e , bed s l o p e , i ce v e l o c i t y , i ce th i ckness and the geometry of accumulat ion and a b l a t i o n a reas . Smith and Budd (1981) have attempted to model the response of both smal l and la rge v a l l e y g l a c i e r s (3 2 to 30 km ) to assumed f u n c t i o n a l changes in accumulat ion and a b l a t i o n . Th i s s tudy, and others l i k e i t , have shown that g l a c i e r response in the form of length changes to some anomalous pe r iod of changing temperature or p r e c i p i t a t i o n , can lag by as much as 150 years depending on the magnitude of the p e r t u r b a t i o n and g l a c i e r geometry. I l l A e r i a l photographs o f f e r the only p r a c t i c a l means for e s t i m a t i n g the temporal v a r i a b i l i t y in g l a c i e r snout changes over l a rge remote a reas . Photographs taken in 1 9 4 7 , 1 9 5 4 , 1964 and 1978/79 are a v a i l a b l e for the B e l l a Coola bas in in a d d i t i o n to f i e l d - b a s e d measurements made between 1 9 8 3 and 1985 • While the coverage i s not annual , the data do a l l o w for at l e a s t a decenn ia l r e s o l u t i o n of changes. From an inventory of ice lower ing and f r o n t a l r e t r e a t of 5 0 g l a c i e r s , s i x were s e l e c t e d as r ep re sen t a t i ve of the s i z e and geometry of g l a c i e r s present in the b a s i n . The s e l e c t i o n was made on the b a s i s of measurements a v a i l a b l e from those g l a c i e r s which were i n v e s t i g a t e d in the f i e l d . R e l a t i v e base l i n e d i s t ances were e s t a b l i s h e d us ing prominent t e r r a i n fea tures near each ice f ron t and were measured us ing s t e r e o p a i r s c o r r e c t l y s ca l ed and o r i e n t e d on an Wi ld A6 s t e reo p l o t t e r . For s imple and very regu la r ice f r o n t s , r e c e s s i o n a l d i s t ances are the average of s e v e r a l measured l i n e segments between two i ce f ron t p o s i t i o n s . Where the i ce margin geometry i s more complex, sur face area changes were computed and d i v i d e d by the length of the i ce margin to y i e l d a mean r a t e of advance or r e t r e a t . The data were then s tandard ized to r e f l e c t the magnitude and d i r e c t i o n of i ce f ron t movements for each g l a c i e r . F igure 4.1 i s a summary of ice f ron t f l u c t u a t i o n s for s i x B e l l a Coola g l a c i e r s du r ing each pe r iod of measurement. The major t rend in the p o s t-1945 pe r iod for a l l s i x g l a c i e r s i s the swi tch from r e g i o n a l l y p e r s i s t e n t r e c e s s i o n p r i o r to 1 9 6 4 , f o l lowed by e i t h e r a r educ t ion in the ra te of r e t r e a t or a c t u a l advances between 1964 and 1 9 7 9 - Examinat ion of the 1964 photography d i d not show evidence for ice advance at that time ( e .g . sediment f ree lobes w i t h s teep, crevassed f ronts) sugges t ing that advances between 1 9 6 4 and 1 9 7 9 commenced sometime a f t e r 1 9 6 4 . For the l a rge r v a l l e y g l a c i e r s such as the F y l e s , Jacobsen and Talchako (the l a t t e r two of which are not shown in f i g u r e 4.1) r e c e s s i o n 112 + o - G l a c i e r A r e a E l e v a t i o n A s p e c t Ape G l a c i e r ( 4 . 6 k m 2 , 1460 m, NE) + o - F y l e s G l a c i e r ( 2 0 . 0 km , 1320 m, NE) ~ \ -H =F w e s t m a r g i n n o r t h m a r g i n o - + o -I N o e i c k G l a c i e r ( 8 . 9 km , 1070 m, NE) n — T T 1 T + B o r e a l i s G l a c i e r ( 2 . 9 k m 2 , 1680 m, NE) " 1 1 1 1 r r , r , , , i , =n 2 West S a u g s t a d G l a c i e r ( 1 . 3 km , 1600 m, NW) ••-•-•-•-•-1 o - A r j u n a G l a c i e r ( 1.5 km , 1200 m, N) 1 T 1 1 1 1 1 1 1 1 [ 1945 1950 1955 1960 1965 1970 1975 1980 1985 Y E A R S (AO) F i g u r e 4 .1 R e l a t i v e r a t e s of advance (+) and r e c e s s i o n (-) of s e l e c t e d g l a c i e r s in the B e l l a Coola b a s i n between 1945 and 1984. 113 was cont inuous but slower a f t e r 1964. Between 1954 and 1964 r e c e s s i o n ra tes were average to above average for many g l a c i e r s , but for the two l a r g e r g l a c i e r s a c t u a l ra tes of r e t r e a t were i nc r ea s ing up to at l e a s t the e a r l y 1960s. Some of the smal le r g l a c i e r s show d e c l i n i n g r eces s ion ra tes throughout the 1947 to 1964 p e r i o d . Between 1979 and 1983-85 the ra tes of advance d e c l i n e d or r ece s s ion once again p r e v a i l e d ( f igure 4.2). Although boundaries sepa ra t ing the per iods of d i f f e r e n t f r o n t a l movement ra tes are a r b i t r a r i l y f i x e d by the dates of a i r photography, some genera l s i m i l a r i t i e s between ice f ron t f l u c t u a t i o n s and p r e v a i l i n g c l i m a t e are e v i d e n t . It appears that for g l a c i e r s in t h i s study area l a rge r than 2 approximate ly 10 km , continuous r eces s ion has occurred throughout the post-19^5 p e r i o d . Th i s i s a c o n t i n u a t i o n of 20th century r eces s ion from L i t t l e Ice Age maxima documented for many par t s of the nor thern hemisphere (Grove, 1979; P o r t e r , 1981) . The d e c l i n e in r e c e s s i o n a l ra tes for these l a rge ice masses and a c t u a l advances of some g l a c i e r s sma l l e r than 2 approximate ly 10 km between 1964 and 1979 appear to be a s soc i a t ed w i t h the p e r s i s t e n t above average win te r p r e c i p i t a t i o n along the coas t , commencing i n 1956 and l a s t i n g u n t i l at l e a s t 1968 ( fol lowed by s e v e r a l i n d i v i d u a l higher snowfa l l years , e.g. 1974, 1976). Winter p r e c i p i t a t i o n was 7 to 10% above the post-1945 average dur ing t h i s i n t e r v a l . Increased r eces s ion ra tes or d e c l i n e s in the ra te of advance between 1979 and 1983-85 are most l i k e l y r e l a t e d to the decreased win te r p r e c i p i t a t i o n and increased summer temperatures a f t e r 1976 for both the c e n t r a l c o a s t a l and c e n t r a l i n t e r i o r regions (see f i g u r e 3 - D - The above evidence i n d i c a t e s that there i s an element of s e n s i t i v i t y in both l a rge and smal l g l a c i e r s r e l a t e d to the magnitude of c l i m a t e changes in the post-1945 p e r i o d . An i n t e r v a l of between 5 and 10 years i s an es t imate of g l a c i e r snout response time to depar tures in r e g i o n a l 114 F i g u r e 4 .2 West Saugstad G l a c i e r in l a t e J u l y of 1985 • Note the lack of a b l a t i o n d e b r i s on the i ce f ron t and the c o m p a r a t i v e l y s teep su r face a long the margin of the snout i n d i c a t i v e of forward i c e - movement . 115 p r e c i p i t a t i o n and temperature which p e r s i s t for at l e a s t 8 to 12 y ea r s . It is d i f f i c u l t to eva lua te what magnitude of c l i m a t e depar ture i s necessary for a g iven i n t e r v a l to ensure a response in the g l a c i a l system but the evidence here seems to i n d i c a t e not more than an average of 7 to 10% in win te r p r e c i p i t a t i o n for a decade. I n t e rp r e t a t i ons of temperature and p r e c i p i t a t i o n records p r i o r to 19*+5 (see chapter 3) do not y i e l d any evidence which would support the con ten t ion that the post-1964 ice f ron t advances are due to c l i m a t i c pe r tu rba t i ons p r i o r to 19̂ 5- Thus, the magnitude and p e r s i s t e n c e of c l i m a t i c depar tures in the post-1945 p e r iod have r e s u l t e d in s i g n i f i c a n t responses in g l a c i e r systems of the B e l l a Coola ba s in and past c l i m a t e changes of s i m i l a r magnitude and d u r a t i o n would have a f fec ted ra tes of ice movement. (4.2) Recent Fluctuations in Upland Sediment Transfers Severa l methods are a v a i l a b l e to assess the magnitude and frequency of c l a s t i c sediment t r ans fe r from upland sources to the higher order f l u v i a l network. The most r e l i a b l e i s repeated surveys of aggradat ion or degradat ion in n a t u r a l h i l l s l o p e g u l l i e s or t r i b u t a r y a l l u v i a l channels ( D i e t r i c h et al., 1982) or in a r t i f i c i a l l y cons t ruc ted sediment t raps or deb r i s bas ins (Leopold and Emmett, 1976; Gardner, 1979). Unfo r tuna t e ly , s eve ra l years or decades of moni to r ing may be requ i red to produce meaningful r e s u l t s because of the lower s e n s i t i v i t y of h i l l s l o p e elements to c l i m a t i c pe r tu rba t ions (Brunsden and Thornes, 1979). A l t e r n a t i v e l y , measurements from a i r photographs taken at s eve ra l d i f f e r e n t times can y i e l d data on the frequency of mass was t ing and, when the a i rpho tos are of a l a rge enough s c a l e and some ground based measurements are a v a i l a b l e , r e l i a b l e es t imates of magnitude a l s o can be made. F i n a l l y , i n d i r e c t 116 evidence in the form of damage to v e g e t a t i o n or d e t a i l e d h i s t o r i c a l records may be u s e f u l . Two methods were adopted to a s c e r t a i n i f there was any s i g n i f i c a n t response of c l a s t i c sediment y i e l d s to changes in recent c l i m a t e and runof f . These inc lude (1) a i rpho to measurements of changes in channel wid th on t r i b u t a r y a l l u v i a l fans and (2) damage or b u r i a l of vege t a t i on on these t r i b u t a r y fans which a l s o prov ide some c h r o n o l o g i c a l da t a . The morpho log ica l a n a l y s i s here i s r e s t r i c t e d to the post-1945 i n t e r v a l because a e r i a l photographs were not a v a i l a b l e u n t i l 1946. A e r i a l photographs taken in 1946, 1948, 1954, 1961, 1974 and 1982 were used to eva lua te the temporal v a r i a b i l i t y in channel widths on major t r i b u t a r y a l l u v i a l f ans . These dates represent the end or beginning of s h i f t s in h y d r o l o g i c a l c o n d i t i o n s in the B e l l a Coola area (see chapter 3)- A c t i v e channel areas on a l l u v i a l fans were computed for e igh t t r i b u t a r i e s of the B e l l a Coola R i v e r . These inc lude Thorsen, S n o o t l i , N o o k l i k o n n i k , Noosgulch, Cacooht in and Burnt Br idge Creeks and Sal loomt and Nusatsum R i v e r s . Thorsen, Nook l ikonn ik and Sal loomt bas ins are c h a r a c t e r i z e d by an absence of long- term s torage s i t e s . Most of the headwater reaches of Burnt Br idge Creek and the east fork of the Nusatsum River are long- term s torage areas , whereas the remaining t r i b u t a r i e s have i s o l a t e d shor t - t e rm s torage s i t e s (see f i g u r e 2.8). Other t r i b u t a r y a l l u v i a l fans , p a r t i c u l a r l y those in headwater sediment-source areas (e .g . Talchako River ) were e i t h e r too conf ined or of l i m i t e d l o n g i t u d i n a l extent to r evea l c o n s i s t e n t t r ends . Each s te reo model was reduced to a common s c a l e us ing a zoom- t r ans fe r s te reoscope . Although not co r r ec t ed for t i l t or swing, base lengths for each model were c a l i b r a t e d aga ins t at l e a s t two d i s t ances measured in the f i e l d which were i d e n t i f i a b l e on each set of a i r photographs. L inea r measurements are accura te to w i t h i n ± 5 m. Channel 117 areas were computed for the reg ion which extends from the apex to the toe of the f an , exc lud ing s t a b l e (vegetated) mid-channel i s l a n d s . These areas are d i v i d e d by channel length along the thalweg to y i e l d an es t imate of mean channel w i d t h . F igure 4.3a i s a p l o t of s t andard ized secu la r changes in mean channel widths between 1948 and 1982 for e igh t t r i b u t a r y fans . Increases in channel width occurred dur ing the i n t e r v a l 1948 to 1954 and I96I to 1974 w h i l e decreases are noted dur ing 1954 to 1961 and 1974 to 1982. Major except ions to t h i s o v e r a l l t rend are S n o o t l i Creek which had c o n t i n u o u s l y decreas ing widths a f t e r 1954 and Sal loomt R ive r where widths cont inued to increase a f t e r 1974. Increas ing widths are a s soc i a t ed w i t h bank e r o s i o n due to increased peak runoff and p e r s i s t e n c e of f l o o d i n g as w e l l as channel b r a i d i n g which i s r e l a t e d to increased sediment accumulat ions w i t h i n the channel zone. Decreasing widths (channel recovery) occur as a s i n g l e thread channel becomes dominant and channel margins are s t a b i l i z e d by v e g e t a t i o n . Channel widening on most t r i b u t a r y fans between 1948 and 1954 appears to be r e l a t e d to the November 1950 f l o o d , t he r e fo r e , channel recovery f o l l o w i n g the f l ood probably began p r i o r to 1954. In four of the e igh t s i t e s channel widths in 1961 were l e s s than those in 1948 sugges t ing a c o n t i n u a t i o n of a longer term trend towards channel s t a b i l i t y . The response of these l a r g e l y unconfined a l l u v i a l channels to high magnitude autumn f loods in 1965, 1968 and 1973 and s p r i n g f loods in 1964 and 1969 i s ev iden t as a t rend towards i nc r ea s ing widths u n t i l 1974. Reduced or l e s s v a r i a b l e widths occur red in most channels by 1982. Par t of the recovery dur ing t h i s l a t t e r i n t e r v a l i s r e l a t e d to t r a i n i n g works (dykes) along the middle and lower reaches of four of the t r i b u t a r i e s . A s i m i l a r t rend can be i d e n t i f i e d us ing damage to v e g e t a t i o n along channel margins as an i n d i r e c t i n d i c a t i o n of f l o o d i n g and sediment 118 F i g u r e 4.3 I n d i r e c t ev idence for s e c u l a r changes in sediment d e l i v e r y to o u t l e t t r i b u t a r y channels of B e l l a Coola R i v e r . A) Mean wid th of a l l u v i a l channels on s e v e r a l t r i b u t a r y f a n s . B) Number of damaged or b u r i e d t r ees sampled a long the the margins of the same t r i b u t a r y channels shown in A. Dates of s p r i n g ( O ) and autumn ( • ) f l oods and major channel t r a i n i n g works are a l s o p l o t t e d . Damage from the I 9 6 8 f l o o d was the most widespread . 119 t r anspor t (Yanosky, 1982,1983). Approximate ly 200 t r ees i n c l u d i n g a l d e r , cottonwood, spruce and f i r were examined for the presence of r e a c t i o n wood i n d i c a t i v e of wood s t r e s s due to bending or s c a r r i n g . A sample of 55 t rees from a l l e i gh t s i t e s showing s i g n i f i c a n t damage i s p l o t t e d in f i g u r e 4.3b. The his togram suggests a higher frequency of damage and b u r i a l a f t e r 1964. There i s some b ias in the data due to p r e s e r v a t i o n problems of t rees p r i o r to the high magnitude f loods of 1965 and 1968 but most of the sampled surfaces were occupied by mature v e g e t a t i o n o lde r than 40 years and g e n e r a l l y at e l e v a t i o n s low enough to have been inundated by most post-1945 peak f l o w s . In a d d i t i o n to channel morphology and t r i b u t a r y fans , the frequency and magnitude of new l a n d s l i d e s throughout the pe r iod were es t imated from photographs for the lower catchment areas of a l l e i gh t t r i b u t a r i e s . While there was a notable increase in the number of smal l s l i d e s ( less than 300 m )̂ in h i l l s l o p e m a t e r i a l s between 1961 and 1982, most seem to have occurred in r e c e n t l y logged areas below access roads, p a r t i c u l a r l y in Noosgulch and Cacooht in Creeks . These smal l s l i d e s may have c o n t r i b u t e d l o c a l l y to sediment t r ans f e r s onto the o u t l e t fans but are not cons idered as major sediment sources . Changes in headwater sediment sources were d i f f i c u l t to eva lua te because bas in -wide a i rpho to coverage was not a v a i l a b l e for each i n t e r v a l and access i s r e s t r i c t e d to only a few s i t e s . A q u a l i t a t i v e assessment of the degree of channel b r a i d i n g downstream from g l a c i a l sources ( e .g . west fork of Nusatsum R i v e r , lower Talchako River ) and below major composite d e b r i s s lopes i n d i c a t e s l e s s temporal v a r i a b i l i t y in channel c o n d i t i o n s because i n many ins tances t r anspor t l i m i t e d c o n d i t i o n s p r e v a i l e d . A d d i t i o n a l c o n t r i b u t i o n s of sediment from p e r s i s t e n t f l o o d i n g would be l e s s 120 n o t i c e a b l e because of the a l ready uns tab le (bra ided , sha l l ow , wide) nature of these reaches . The r e s u l t s presented here p rov ide some i n s i g h t in to the connect ion between runoff v a r i a b i l i t y and sediment y i e l d from major t r i b u t a r i e s of the B e l l a Coola R i v e r over the l a s t 40 yea r s . Evidence presented in s e c t i o n 2.6 demonstrates that a s i g n i f i c a n t amount of m a t e r i a l i s s to red in the f l o o d p l a i n and channel zones of major t r i b u t a r i e s . Therefore , c l a s t i c sediment y i e l d over the shor t - t e rm i s l i n k e d to a v a i l a b l e sediment in h igher -o rde r channel segments of these t r i b u t a r i e s and in f luenced l e s s by the frequency and d i s t r i b u t i o n of headwater sediment sources . A e r i a l photographs support the con ten t ion that increased runoff and frequency of f l o o d i n g r e s u l t e d in the movement of t h i s sediment and d e s t a b i1 i z a t i o n of a l l u v i a l fan channels between the e a r l y 1960s and mid-1970s. Per iods of channel recovery preceded and fo l lowed t h i s i n t e r v a l . The a e r i a l photographs are tempora l ly d i s c r e t e samples and the re fo re these data do not c l e a r l y d i s t i n g u i s h between the p r o p o r t i o n a l impact of s i n g l e f l o o d events versus a pe r iod of increased f l o o d f requency. It i s l i k e l y that the t h r e sho ld for channel recovery (c f . Wolman and Gerson, 1978) i s more c l o s e l y t i e d to the h ighes t magnitude events which in t roduce s u b s t a n t i a l volumes of c l a s t i c m a t e r i a l . In a d d i t i o n , damage and b u r i a l of v e g e t a t i o n i s the consequence of d i s c r e t e events o n l y . However, the d i s t r i b u t i o n i d e n t i f i e d here supports the observed changes in f l o o d frequency over the post-1945 i n t e r v a l . Sampling was r e s t r i c t e d to a smal l number of sur faces a long channel margins some of which may have been inundated p r e f e r e n t i a l l y (i.e. w e l l - d e f i n e d over f low channe l s ) , the re fo re the sample and i n t e r p r e t a t i o n s remain imperfec t . However, the methodologies appear to be v a l i d for making inferences regard ing long-term flow v a r i a b i l i t y in t r i b u t a r y b a s i n s . 121 (4.3) Sediment Sources and Processes of Floodplain Development Inferences about environmental change from geomorphic ev idence , such as channel p a t t e r n , h y d r a u l i c geometry and f l o o d d e p o s i t s , r e q u i r e an understanding of the processes invo lved in the t r a n s p o r t a t i o n and d e p o s i t i o n of a l l u v i a l m a t e r i a l and primary sources of sediment. The purpose of t h i s s e c t i o n i s to document the processes of f l o o d p l a i n development and c h a r a c t e r i z e the a l l u v i a l sediment sources for B e l l a Coola R i v e r . Processes of Floodplain Development The B e l l a Coola River e x h i b i t s an i r r e g u l a r l y sinuous channe l , sometimes s p l i t about channel i s l ands and in some places b r a i d e d : seasonal or pe r enn i a l ' s i d e ' channels - subordinate anabranches of the r i v e r - are common. Th i s r i v e r type has been r e f e r r ed to as a "wandering" g rave l -bed system ( N e i l l , 1973; Church, 1983) . The a l l u v i a l sediments c o n s i s t of 0 to 3 meters of sandy c h a n n e l - f i l l or overbank s i l t y sands depos i ted above s eve ra l meters of channel cobb le - g r a v e l . S i m i l a r sequences have been desc r ibed for sinuous g r ave l channels by Bluck (1971. 1976), Jackson (1978) and Forbes (1983). L a t e r a l a c c r e t i o n is the dominant mode of d e p o s i t i o n . Th i s r i v e r type i s widespread in s t a b l e mountain v a l l e y and fo re l and s e t t i n g s and i s t y p i c a l of s eve ra l r i v e r s d r a i n i n g the west s lope of the southern Coast Mountains of B r i t i s h Columbia . Church (1983) has cons idered recent r i v e r changes in some d e t a i l . D e t a i l s of sediments compr is ing the a l l u v i a l p o r t i o n of the B e l l a Coola R i v e r have been desc r ibed elsewhere (Desloges and Church, 1987) so on ly the most s a l i e n t po in t s are g iven here . Storage of sediment in the contemporary channel zone v a r i e s a long the r i v e r . In s eve ra l reaches, l a rge 122 volumes of r e s iden t g r ave l i n f luence channel pa t t e rn producing m u l t i p l e channels and a s soc i a t ed g r ave l bar development. In te rvening reaches have greater l a t e r a l s t a b i l i t y and occur where the v a l l e y wid th i s r e s t r i c t e d by bedrock or t r i b u t a r y a l l u v i a l f ans . Hence, sediment accumulat ion and r e s u l t i n g f a c i e s a s s o c i a t i o n s w i t h i n the a c t i v e channel zone can be d i v i d e d in to those w i t h i n uns tab le and those w i t h i n s t a b l e reaches . Media l bars and i s l ands dominate the channel w i t h i n uns tab le reaches . Media l bar complexes are composed of s e v e r a l mid-channel bars forming c l u s t e r s upstream from confluences w i th major t r i b u t a r y channels ( f igures 4 . 4 a and b ) . Is lands t y p i c a l l y are wooded and g rave l i s exposed on ly on the upstream s i d e of the i s l a n d . Channel s h i f t i n g occurs by a v u l s i o n . The i s l ands represent o l d f l o o d p l a i n surfaces which have been i s o l a t e d by a v u l s i o n . Approximately 40 percent (22 km) of B e l l a Coola R ive r i s dominated by channel macrofbrms t y p i c a l of l a t e r a l l y uns tab le channels . Bank-at tached l a t e r a l bars or p o i n t - b a r s dominate the more sinuous s t a b l e reaches of the r i v e r ( f igures 4 . 4 c and d ) . A low-f low back channel or chute , a c t i v e only at high f l o w , i s almost always present c o n t a i n i n g a c o b b l e - g r a v e l bed (probably c rude ly s t r a t i f i e d ) and s t r u c t u r e l e s s sand levees on both f l a n k s . These subordinate channels are important s i t e s for the p r e s e r v a t i o n of sediments i n d i c a t i v e of v a r y i n g f low c o n d i t i o n s through t ime . Abandonment and i n f i l l i n g of back channels lead to f l o o d p l a i n development. The o v e r a l l importance of the sandy f a c i e s in terms of contemporary f l o o d p l a i n sediment volumes can be determined by assuming that the depth of scour (thalweg depth) in the a c t i v e channel represents the bottom of the g r a v e l basement or ' ba r p l a t f o r m ' . Th i s assumption can be made because of the apparent v e r t i c a l s t a b i l i t y of the r i v e r (Church, 1 9 8 3 ) . Thicknesses of the sandy f l o o d p l a i n depos i t s range from a few F i g u r e k.k Morphology and channel zone sediments of B e l l a Coo la R i v e r . (A) An uns tab le reach of the r i v e r w i t h med ia l bar d e p o s i t s . M a s s i v e g r a v e l (Gm) or p lanar s t r a t i f i e d sediments (Gp) dominate the channel zone g r a v e l s . (B) Bar topography in uns t ab le reaches i s subdued and f i n e r g r a i n e d sediment wedges cover the g r a v e l s u r f a c e . Note the two year o l d growth of a lde r i n f i n e r sed iments . (C) A sinuous reach of the r i v e r and accumula t i on of o r g a n i c d e b r i s on a po in t bar s u r f a c e . (D) P o i n t bar d e p o s i t s some times e x h i b i t g r a v e l d e l t a s (a) wh ich migra te i n to f i n e r back channel d e p o s i t s (b) . 124 125 cent imeters to over 3 m of coarse g r a v e l l y sand to f i n e sandy s i l t and represent 31 to 36% of the t o t a l ' a c t i v e ' sediment p i l e (see t ab l e k.h). Nowhere does c l a y c o n s t i t u t e more than 15% of any sample: most f r equen t ly i t i s much l e s s . The sedimentary sequences in the a l l u v i u m r e f l e c t the in t eg ra t ed processes of f l o o d p l a i n development over t ime . In uns table reaches of the r i v e r , r ap id channel a v u l s i o n s , the occurrence of m u l t i p l e channels w i t h v a r y i n g c a p a c i t i e s for sediment and water d i s cha rge , and more v a r i a b l e f low c o n d i t i o n s r e s u l t in a d i v e r s i f i e d set of f a c i e s u n i t s w i t h i n the channel and on the the vegetated f l o o d p l a i n su r f ace . With i nc r ea s ing s t a b i l i t y , the s p a t i a l v a r i a t i o n in f low c o n d i t i o n s d e c l i n e s and the p r o b a b i l i t y of t r a n s i t i o n s between f a c i e s u n i t s becomes lower than in l e s s s t a b l e reaches of the r i v e r . P rog res s ive l a t e r a l a c c r e t i o n and the v e r t i c a l s t a b i l i t y of the r i v e r appear to favor the s impler f a c i e s sequence, a l though i n f i l l e d back channels may s t i l l e x h i b i t the wider v a r i e t y of sedimentary s t r u c t u r e s . The greater inc idence of overbank f l o o d i n g in s t a b l e reaches produces v e r t i c a l a c c r e t i o n of the f l o o d p l a i n here and development of the f i n e r - g r a i n e d f a c i e s (Desloges and Church, 1987)' However, l a t e r a l a c c r e t i o n depos i t s dominate the o v e r a l l sequence in j u s t the manner desc r ibed by Wolman and Leopold (1957)• Channel and po in t bar development i s accompanied by the c r o s s - v a l l e y m i g r a t i o n of the channe l , r e s u l t i n g in the format ion of a bar p l a t fo rm and, in a d d i t i o n to the main channel , s eve ra l a c t i v e slough channels or a s i n g l e , poor ly connected back channe l . Sediment volumes (see t ab l e k.k) i n d i c a t e that l a t e r a l a c c r e t i o n of g rave l s accounts fo r approximately 65% of sedimenta t ion dur ing f l o o d p l a i n c o n s t r u c t i o n . As the vege t a t i on deve lops , sands are trapped on bar tops and overbank, so the f l o o d p l a i n r i s e s by v e r t i c a l a c c r e t i o n to i t s f i n a l l e v e l . Table 4.4. Volume estimates of a l l u v i a l - f i l l for the Bella Coola River. 1 (2) (3) Reach Type Valley Length Floodplain Area Overbank (sand) Basement Gravel Proportion of f i l l 2 7 3 7 3 (km) (km ) Volumes X 10 m Volumes X 10 m as overbank sands Unstable 22.1 (39%) 32.6 (42*) 4.2 (60%) 7.6 (59%) 36% Transitional 23.1 (40%) 30.6 (39%) 2.4 (34%) 4.3 (33%) 36% Stable 12.2 (21%) 14.4 (19%) 0.4 ( 6%) 0.9 ( 8%) 31% Total 57.4 (100%) 77.6 (100%) 7.0 (100%) 12.8 (100%) 35% 1. Reach type c l a s s i f i c a t i o n i s based on the frequency of channels and characteristics of floodplain and channel sediments. Unstable reaches are high-gradient sediment storage zones with numerous sloughs, back channels and medial bars. Stable reaches are characterized by more sinuous single-thread channels. Transitional reaches exhibit a combination of morphological features. 2. Volume of fine-grained (sand and s i l t ) v e r t i c a l and l a t e r a l accretion deposits. 3. Volume of coarse-grained (gravels and cobbles) l a t e r a l accretion sediments above maximum thalweg depth. 127 Sands are very mobi le in t h i s h igh-energy , c o b b l e - g r a v e l r i v e r , moving predominant ly in suspens ion . Once r e - e n t r a i n e d , the sand may be f lushed from the system or redeposi ted a s u b s t a n t i a l d i s t a n c e downstream. Much of the sand probably moves through the system in only one or two s tages . The a c t u a l modes of channel m i g r a t i o n in uns tab le reaches are p r o g r e s s i v e e r o s i o n on the cutbank oppos i te a growing channel bar , and r a p i d channel a v u l s i o n , or r educ t ion of f low in the channel around one s ide of a medial bar , l e a v i n g behind a s e r i e s of a c t i v e , " subord ina te" s loughs . Sloughs along the inner margins of po in t bars may remain a c t i v e , sediment t r a n s p o r t i n g channels for per iods in excess of 50 to 80 years f o l l o w i n g s u b o r d i n a t i o n . Complete i n f i l l i n g i s l i k e l y to occur only i f the slough entrance becomes b locked by l a rge o rgan ic d e b r i s . Sedimentat ion would be e p i s o d i c and i n d i c a t i v e of f l o o d events o n l y . In sinuous reaches of lower g r a d i e n t , s loughs become poor ly connected at most f low stages and a back channel develops w i t h d e p o s i t i o n of f i n e sands, s i l t s and organic m a t e r i a l . I n f i l l i n g may never be complete as some of the o lde r sloughs and back channels are p r e f e r e n t i a l l y occupied dur ing high magnitude f l o w s . As a r e s u l t , channel a v u l s i o n s f r equen t ly lead to the occupa t ion of o lde r channels ra ther than the development of new ones. Th i s leads to a r educ t ion in the p o t e n t i a l number of s i t e s w i t h sequences r e p r e s e n t a t i v e of long- term sed imen ta t ion . Although a v u l s i o n produces abrupt real ignment of the channel , p rog re s s ive l a t e r a l a c c r e t i o n and e r o s i o n may be s u b s t a n t i a l l y more s i g n i f i c a n t in the h i s t o r y of f l o o d p l a i n development and sediment exchange. A l l u v i a l Sediment Sources The p r i n c i p a l sources for a l l u v i a l B e l l a Coola v a l l e y are as f o l l o w s : sediments depos i ted w i t h i n the 128 (a) headwater t r i b u t a r i e s i n t r o d u c i n g sediment to the a c t i v e channel ; (b) downstream t r i b u t a r i e s e n t e r i n g along the r i v e r reach c o n t r i b u t i n g sediment d i r e c t l y to the f l o o d p l a i n sur face or to the a c t i v e channel ; (c) bank e r o s i o n and r e - d e p o s i t i o n of p r e v i o u s l y depos i ted a l l u v i a l m a t e r i a l ; and (d) f l u v i a l e r o s i o n of n o n - a l l u v i a l depos i t s r e s iden t w i t h i n the zone of channel a c t i v i t y . Sources (a) and (b) are d i r e c t l y connected w i th the uplands . Sources (c) and (d) represent remobi1 i za t ion of sediment p r e v i o u s l y int roduced in to the v a l l e y . S ince l e s s than 13% of the channel of B e l l a Coola River i s in contac t w i t h n o n - a l l u v i a l d e p o s i t s , the ma jo r i t y of which are e i t h e r w e l l - vege ta ted , s t a b l e c o l l u v i a l s l opes , bedrock or depos i t s of g l ac iomar ine s i l t and c l a y , they are not important sources for the sand and g rave l that dominate the a l l u v i a l v a l l e y - f i l l . Klages and Hsieh (1975). M a z z u l l o (1986) and Sta t t eger et al. (1987) have demonstrated that the mineralogy of a l l u v i a l and l i t t o r a l sand depos i t s may r e f l e c t provenance provided that source areas y i e l d sediments dominated by d i s t i n c t i v e l i t h o l o g i e s , c h a r a c t e r i s t i c p ropor t ions of c e r t a i n m i n e r a l s , or con ta in unique minera l s not found in other source areas ; and that these p r o p e r t i e s are not app rec i ab ly a t tenuated by mixing dur ing t r anspo r t to a p a r t i c u l a r d e p o s i t i o n a l s i t e . To determine which source areas are most important for d e l i v e r y of m a t e r i a l to the B e l l a Coola R i v e r , the compos i t ion of sediments from s e v e r a l major t r i b u t a r i e s was compared w i t h channel zone and f l o o d p l a i n sediments sampled w i t h i n the B e l l a Coola v a l l e y . Samples ex t r ac t ed from the a c t i v e channel zone and f l o o d p l a i n were c l a s s i f i e d on the bas i s of d i s c r i m i n a n t func t ions de r ived for samples taken at the o u t l e t of major 129 t r i b u t a r i e s . The sampling des ign and data a n a l y s i s are d i scussed in Appendix B and the r e s u l t s are p l o