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UBC Theses and Dissertations

Clastic sediment sources and suspended sediment yield in a Coast Mountain watershed, British Columbia Hart, Jackson Sanford 1979

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CLASTIC SEDIMENT SOURCES AND SUSPENDED SEDIMENT YIELD IN A COAST MOUNTAIN WATERSHED, BRITISH COLUMBIA JACKSON SANFORD HART B.Sc, Trent University, 197b A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in THE FACULTY.OF GRADUATE- STUDIES (The Department of Geography) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1979 © Jackson Sanford Hart, 1979 In presenting this thesis in partial fulfillment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. September, 1979. Department of Geography The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Abstract This dissertation investigates the clastic sediment sources and suspended sediment yields of clear-cut and undisturbed areas of a glacially-2 -modified, 33 km watershed in the southern Coast Mountains of British Columbia. S u r f i c i a l materials were mapped and the character of sediment movement interpreted by morphologic evidence. Basin sediment yields through snowmelt, summer low flow and f a l l storm periods were related to . the magnitude of precipitation inputs, storage changes of snow and the availability of clastic sediment to the. channel system. In the undisturbed area sediment activated along steep tributary streams of the till-mantled valley walls below treeline was considered most important to basin scale yield. In the alpine zone mass wastage activity is widespread yet effects mainly a redistribution of materials on slopes; sediment supply to the fluvial' system is limited by the extensive presence of coarse materials and the lower drainage density. Snowmelt period sediment export exceeded that during summer low flow and October storm periods; however, approximately 60 percent of the total sediment yi e l d observed took place during a November rain-on-snow event of an estimated 10 year recurrence interval. During the October storm period, when sediment yields from the forested and clear-cut slopes could be isolated, sediment removal from the clear-cut slope was greater by approximately eight times and this accelerated erosion was attributed almost entirely to road effects. i i i Contents ^ Page Abstract i i Contents i i i List of Tables v List of Figures v i List of Photographs v i i Acknowledgements v i i i 1. Introduction 1 1.1. Lillooet River watershed studies 1 1.2. Wasp Creek watershed study.... 3 1.3. Related studies +^ 2. Description of the study area 7 2 . 1 . Location and area T 2.2 . Physiographic setting 7 2 . 2 . 1 . Bedrock geology 7 2 . 2 . 2 . Glaciation and glacierization. 7 2 . 2 . 3 . Watershed form... 9 2 .3 . Climate 9 2. U. Vegetation... 10 2 .5 . Land use 11 3. Methods 12 3 .1 . Introduction.... 12 3.2. Precipitation 12 3.3. Stage and discharge '- 12 3 . 3 . 1 . Measurement 12 3 . 3 . 2 . Discharge record length and synthesis 13 3.3.3. Hydrograph separation 13 3.3.U. Flood frequency analysis 13 3.U. Sediment source mapping 13 3.U.I. Undisturbed area. 13 3.U.2 . Clear-cut area 1^ 3.5. Sediment yield 1^ 3 . 5 . 1 . Network...: 1^ 3 . 5 . 2 . Sample collection 1^ 3 - 5 - 3 . Sample analysis. 15 3 .5 -^ - Sediment yie l d computation 15 a) Interpolation method 15 b) Sediment rating curve method 16 c) Mean sediment concentration-discharge, method 19 d) Upper Wasp Creek yield estimate for the November storm.. 19 e) Yield from the clear-cut area 19 k. Hydrometeorologic observations • 21 k.l. Introduction 21 h.2. Precipitation 21 h.2.1. Gauge relations 21 k.2.2. Seasonal variation? 21 h.3- Stage and discharge 2U 1+.3.1. Stage-discharge relations 2*+ k.3.2. Seasonal discharge variation 28 k.3.3. Flood frequency analysis 30 U.3.J+. Hydrologic response 30 k.k. Conclusion 33 iv 5. Sediment sources and availability 35 5.1 . Introduction.. 35 5.2. Sediment sources 35 5.3. Sediment transfers - undisturbed area 39 5 . 3 . 1 . Glacial processes 39 5.3 .2 . Slope processes 39 a) Large scale mass movements 39 b) Rockf alls 39 c) Debris avalanches 39 d) Debris flows *+0 e) Snow avalanches b2 f) Slow mass movements b2 5 . 3 . 3 . Fluvial processes ^3 5.*+. Sediment transfers - clear-cut area bb 5.^+.l. Slope processes bb a) Debris avalanches U5 b) Mass movements along roads U5 5-4.2. Fluvial processes U6 5.5. Sediment sinks - undisturbed area hi 5.6. Sediment sinks - clear-cut area bl 5. T- Sediment availability - undisturbed area ^7 5.8. Sediment availability - clear-cut area bQ 6. Sediment yie l d 51 6 .1 . Introduction 51 6.2 . Sediment yie l d results 51 6 . 2 . 1 . Snowmelt period - May to July 51 6 . 2 . 2 . Summer period - August and September 51 6 . 2 . 3 . F a l l storm period - October and early November 53 6 .3 . Sediment discharge regimen 53 6 . 3 . 1 . Upper Wasp Creek 5b 6 . 3 . 2 . Lower Wasp Creek 55 6 . 3 . 3 . Wasp Creek tributary streams 57 G.b. Conclusion 57 7- Discussion and conclusions.... 58 7.1 . Vertical zonation of geomorphic processes 58 7.2. Seasonal analysis 58 7.3 . Effects of terrain disturbance 59 l.b. Conclusions •: 6 l 7.5 . Further work 62 Bibliography 63 Photographs 66 Appendices • 71 A. Wasp Creek seasonal hydrographs. 72 B. Sample analysis procedure 73 C. Suspended sediment data 7^ List of Tables Page Table 1. Wasp Creek watershed hydrometeorologic data summary 25 Table 2. Sediment sources of Wasp Creek basin 36 Table 3. Surface conditions of clear-cut area 36 Table B.l. Sample analysis procedure 73 Table C.l. Suspended sediment yield data summary 7k Table C.2.' Sediment concentration data for Wasp Creek tributary streams. 75 v i List of Figures Page Frontispiece: Oblique aerial view to southwest over the Wasp Creek watershed, August 2, 19^7- B.C. Government photograph BC 399= 67 ix Figure 1. Lillooet River drainage system above Lillooet Lake.. 2 Figure 2. Wasp Creek watershed bedrock geology 8 Figure 3. Precipitation and temperature data for Pemberton Meadows, B.C., 19U1-1966 1 0 Figure k. Discharge-sediment concentration relationships for the three largest storm runoff events at lower Wasp Creek 17 Figure 5- Rainfall, discharge and sediment concentration graphs for the October 17 storm, lower Wasp Creek 18 Figure 6. Regression relation of Ryan River and Wasp Creek rain gauge catches ^2 Figure 7- Tenquille Lake snow course data, 1,700 m 23 Figure 8. Pemberton Meadows precipitation data, 230 m 23 Figure 9- Lower Wasp Creek discharge rating curve 26 Figure 10. Upper Wasp Creek discharge rating curve. 27 Figure 11. a) Generalized mean of mean daily discharge for Lillooet River ( 1928 -1968 ) ; b) mean daily discharge for Lillooet River in 1975--. • 2 9 Figure 12.. Frequency of maximum daily discharge intensities for rivers of the Lillooet River drainage system 31 Figure 13. Wasp Creek hydrologic response to storm events 32 Figure lk. Hypsometric analysis of Wasp Creek basin 33 Figure 15. Idealized cross-section of Wasp Creek valley wall and s t r a t i -graphic column . . 35 Figure 16. Wasp Creek watershed s u r f i c i a l geology 37 Figure 17- Wasp Creek clear-cut 38 Figure 18. Colour infrared aerial photograph of study.area with overlay showing drainage network ^1 Figure 19- Longitudinal profile of Wasp Creek ^ Figure 20. Vertical zonation of sediment sources in upper Wasp Creek watershed ^9 Figure 21. Wasp Creek watershed clastic sediment transfer model 50 Figure 22. Upper Wasp Creek sediment rating curves 52 Figure 23. Upper Wasp Creek flow and sediment discharge duration curves for June 21 to July 31 , 1975 5^ Figure 2h. Lower Wasp Creek sediment yi e l d response to storm runoff events 56 Figure A . l . Wasp Creek seasonal hydrographs 72 v i i List of Photographs Page Photograph 1. View up Basin C showing extensive colluvium 67 Photograph 2. Debris avalanche scar along drainage line on steep, till-mantled valley wall of Wasp Creek 67 Photograph 3. Small debris flow tracks on colluvial slope near treeline. 68 Photograph h. View up Wasp Creek showing coarse colluvium on right and all u v i a l cone on l e f t 68 Photograph 5. Debris flow deposit along Ryan River 69 Photograph 6. View up Wasp Creek above the upper Wasp gauging station. . 69 Photograph 7- Road cut-slope in clear-cut area exposing glacial t i l l . .. 70 Photograph 8. Gullying of road surface during snowmelt period 70 v i i i Acknowledgements I would l i k e t o acknowledge with g r a t i t u d e the considerable a s s i s t a n c e provided by my supervisor Dr. Olav Slaymaker w i t h a l l aspects of t h i s pro-j e c t . The advice of Dr. Robert W i l l i n g t o n at the design stage proved most valu a b l e . Dr. Michael Church's comments at the design stage and h i s c r i t i -cisms of the f i n a l d r a f t were appreciated by adoption. The f i e l d work could not have been conducted without the e f f o r t s of my f i e l d a s s i s t a n t s , Dr. Ian Laidlaw and Mr. E r i c Leonard, under sometimes t r y i n g c o n d i t i o n s . F i n a n c i a l a s s i s t a n c e was provided by a grant from the Department of Employment and Immigration and a N a t i o n a l Research C o u n c i l grant t o Dr. Slaymaker. The i n f r a - r e d imaging of the study area was conducted and s u b s i d i z e d by the Canada Centre f o r Remote Sensing. I am g r a t e f u l t o Mr. Denis B f i e r e of the F a c u l t y of F o r e s t r y f o r h i s a s s i s t a n c e w i t h the pre-p a r a t i o n f o r t h i s photo run. The B r i t i s h Columbia Forest S e r v i c e k i n d l y s u p p l i e d h e l i c o p t e r time and Mr. Jack M c C l e l l a n of t h i s agency c o n t r i b u t e d l o g i s t i c a l support which g r e a t l y aided the f i e l d e f f o r t s . The co-operation of L & K Logging L t d . and Mr. Lawrence V a l l e a u of V a l l e a u Logging L t d . was e s s e n t i a l t o work i n the Ryan R i v e r b a s i n and i s much appreciated. F i n a l l y , I extend my g r a t i t u d e t o Ms. C h r i s t i n a M a y a l l f o r f i e l d a s s i s t a n c e , f o r proof reading the f i n a l d r a f t and f o r her forebearance during a somewhat p r o t r a c t e d process. Frontispiece: Oblique aerial view to southwest over the Wasp Creek watershed, August 2, 19U7. B.C. Government photograph BC 399: 67. 1 1. Introduction The steep mountain slopes of the Canadian Cordillera are overlain by a mantle of glacial t i l l , a legacy of.Pleistocene glaciation. Relative to work in non-glaciated areas this terrain has received scant attention with respect to problems of erosion and sedimentation and so research to better understand the behaviour of the natural system and consideration of related management problems are clearly required. Research is underway in the Lillooet River watershed and the present study was developed to provide com-plementary information for the partially clear-cut slopes of a tributary basin. 1.1. Lillooet River watershed studies 2 The Lillooet River system above Lillooet Lake drains a 3,800 km area of the southern Coast Mountains of British Columbia (Figure l ) . The main 2 valley bottom, occupying an area of 110 km , is flanked by steep, forested slopes rising to alpine areas above the 1,500 m to 2,000 m elevation. The basin r e l i e f ranges from 19k m at Lillooet Lake to the 2,936 m summit of Bridge Peak. Areas of perennial snow and ice, predominantly in the western region of the basin, occupy about 7 percent of the total area (Gilbert, 1973) . The valley bottom is occupied by glacio-fluvial and f l u v i a l deposits and the valley walls are mantled by Pleistocene and Holocene glacial t i l l , colluvium and minor alluvium. The Coast Mountain plutonic complex, com-prised principally of quartz diorite and granodiorite, .underiiesrthe^lar-r-gest fraction of the basin. Other intrusive rocks are present of Jurassic and older (?) to Tertiary age, Cretaceous metasedimentary and metavolcanic rocks and Tertiary and Quaternary volcanics (Woodsworth, 1977) . A variety of hydrologic and geomorphic studies has - been carried out within the Lillooet River watershed. In 1969 studies were initiated in . alpine and subalpine areas of the Miller Creek basin which addressed water, solute and sediment yields from glacierized and non-glacierized areas (Woo and Slaymaker, 1975; Zeman and Slaymaker, 1975; Slaymaker, 1977) - Hydro-logic and geochemical research is on-going in the basin (Braun, in prep.; Slaymaker and Gallie, 1979; Teti, in prep.). Studies along the larger watercourses include Ponton's (1972 a&b) investigation of the sectional and downstream hydraulic geometry of the Green and Birkenhead Rivers and Teversham's (1973) (see also Teversham and Slaymaker, 1976) investigationc of vegetation response to f l u v i a l activity on the Lillooet River valley bottom.. Between 1970 and 1972 Gilbert (1973) examined the sedimentary en-vironment of the Lillooet Lake delta. This work provided measures of total 2 3 clastic sediment yield based on long-term sedimentation rates in Lillooet Lake. Gilbert calculated mean rates of delta front advance between 1858 and 1969 and identified a t r i p l i n g of rate in the post-19^8 period. The ac^ -celerated sedimentation coincides with river training works on the valley bottom between 19^ +6 and 1951, a 2.5 m lowering of Lillooet Lake in 1952, and the increased land use of logging of the forested slopes, agriculture on the valley bottom and associated road construction. The river training and lake lowering operations, which resulted in an increased channel gradient along a 50 km reach above the lake from 0.0008 to 0 .0010 , are of singular importance, yet only partially account for the yield increases (Slaymaker and Gilbert, 1972) . Over the period I9U6- I969 the logged area was increased 2 2 from less than h km (0 .1$) to 8 l km (2.1%) and agricultural land use from 2 2 k km to U8.5 km. ( 1 . 3 $ ) . The magnitude of these changes suggests that they may also be significant at the watershed scale. Gilbert's work described a relatively long-term sedimentary record which integrated the contributions from the differing sediment source areas. The need for investigation of these contributing areas was thus indicated. The complex physiographic setting coupled with the effects of human distur-bance of the terrain render this a task requiring comprehensive and long--term investigation. The present study addresses one aspect of this problem. 1.2. Wasp Creek watershed study A study of the Wasp Creek watershed, tributary to the Ryan River (Figure l ) , was developed to provide preliminary, clastic, sediment source and sus-pended sediment y i e l d information for the mountain slopes of the Lillooet watershed. The study area was selected for i t s physiographic similarity to extensive areas/ of the Lillooet watershed and because the logging of a lower slope had been carried out in a manner consistent with normal practice in the region. Both partially clear-cut and undisturbed areas were monitored through a range of hydrologic conditions from May to November, 1975- Since these areas were not entirely isolated for hydrologic measurements and differ in size and physical character the approach taken is descriptive ra-ther than a paired experimental watershed study. The spatial scale of the study integrates the response of a diversity of sediment sources both above arid below treeline. These sources were exa-mined in an effort to evaluate their relative importance to sediment pro-duction at the watershed scale. An intermediate-sized watershed was thought appropriate to this enquiry. At a larger scale the contributions from the k mountain slopes and the effects of terrain disturbance are masked by sedi-ment yields from other areas while with decreasing scale the representa-tiveness of the basin is reduced. The six month study period permits only qualitative observations of the kinds and relative importance of the sediment sources in the undis-turbed area. Without longer term information the unit source area and watershed scales of activity cannot be wholly reconciled. However, the recency of logging activity permits more definitive evaluation of i t s effects to date. The central objectives of the study may be summarized as follows: 1. to define kind and magnitude of observable sediment sources; 2. to differentiate sediment sources and suspended sediment yields of undisturbed and clear-cut areas; and 3. to relate observed sediment yield to environmental determinants in a series of independent hydrologic events. 1.3. Related studies The sediment sources and yields of the forested and logged slopes of the British Columbia Coast Mountains have to date received l i t t l e attention. Reference may be made to evidence from adjacent areas of the northern Pacific Mountain System - the Coast and Cascade Ranges of Washington and Oregon, the Olympic Mountains of Washington and the Coast Mountains of southeastern Alaska. These are the areas of closest physiographic and climatic similarity to'"the'.study^region. Research in Alaska has been in both glaciated and non-glaciated areas underlain by granitic and metamorphic bedrock. In Oregon and Washington research has been conducted on soils de-rived from a variety of underlying bedrock types of non-glaciated areas. Both regions have annual precipitation receipts of about 2,500 mm; recorded intensities are high in coastal Alaska and the Cascade Range and somewhat lower along the more subdued Oregon Coast Range. Several investigations of the undisturbed, forested slopes have been carried out throughout•these areas (e.g. Wooldridge, 196^; Rothacher et a l , I96T; Swanston, 1967; Williams, 1967; Brown and Krygier, 1971; Fredriksen, 1970; Swanson and Swanston, 1977 ) . The significant sediment transfer pro-cesses are s o i l creep, debris*"slides and flows, surface erosion, and chan-nel bed and bank erosion. Factors controlling their rates of operation are numerous and produce widely disparate results. However, two important generalizations emerge. F i r s t l y , work in Alaska indicates that mantles of glacial t i l l are less erodible than bedrock- or colluvially-derived soils 5 (Swanston, 1969) - Secondly, considerable va r i a b i l i t y of sediment yield -may occur both between basins during a single storm (Williams, 196k) and from year to year for the same basin (Rothacher et a l , 1967; Brown and Krygier, 1971) - An assessment of the effects of terrain disturbance must be approached with caution against an expected background of high natural variability observable even within the short term of most studies. For a short study period order of magnitude differences of y i e l d coupled with site observations are required to ascribe causal factors. Most writers have recognized substantial acceleration of erosion with logging and road construction. Clear-cutting alone (without slash burning) has not been found to significantly increase surface erosion (Fredriksen, 1970; Brown and Krygier, 1 9 7 1 ) ; however, on unstable slopes root decay lessens shear strength and may cause U-5 times as many shallow debris slides (Bishop and Stevens, I 96U) . The more significant increases of y i e l d are attributed to the steepening of slopes, deflection of flow and exposure of s o i l which accompanies road construction (Dyrness, 1967; Fredriksen, 1970; Swanson and Dyrness, 1975) . Anderson ( 1970 ) , in review of results from Oregon and Northern California, cites yield increases from clear-cut areas up to a factor of k and relates 80 percent of these to surface: erosion and mass movements associated with roads. Jeffrey (1968) has observed that logging effects have created problems in British Columbia comparable to those elsewhere. The roads rather than the clear-cut slopes are identified as the principal causes of accelerated erosion.. In the southern Coast Mountains O'Loughlin (1972) found shallow debris slides and avalanches on'forested and logged slopes to be most simi-lar in kind to those operating on the glacial t i l l slopes of southeastern Alaska. Although the slopes were relatively stable the incidence of failure increased by a factor similar to that reported in other logged areas. The relative effects of logging appear to transcend physiographic controls. 2 O'Loughlin estimated that 95 t/km /yr might represent the amount of sediment activated by debris slides and avalanches in the Coast Mountains. Slaymaker and McPherson (1977) point out that much of this redistributed material may be retained in temporary storage and not readily removed by f l u v i a l action. As well, the generally low availability of material in the stream-banks of intermediate-sized watersheds may lead to lower yields than are expected. These observations underscore the need to relate i n -dividual" .''processes to watershed scale yields - for assessments of the effects of human disturbance of the terrain this is particularly important. As for the slopes below treeline, the alpine zone of the Coast Mountains has received l i t t l e attention with respect to clastic sediment movement. A :'f ew studies of individual processes have been conducted (e.g. Mackay and Mathews, 197^ a&b; Patton, 1976) and some preliminary sediment yield data are available from both glacierized and non-glacierized areas (Mokievsky-Zubok, pers. comm.; Slaymaker, 1977) . However, to explain transfer processes in the study area reference is made to observations made elsewhere both in the Canadian Cordillera (see review by Slaymaker, 197^) and in other mountainous regions (see review by Caine, 197^) . 2. Description of the study area 2 . 1 . Location and area 2 The study area is a 33 km watershed m the southern Coast Mountains of British Columbia about 130 km north of Vancouver. Figure 1 shows the northward drainage of Wasp Creek into the Ryan River and thence to the Lillooet River. 2.2 . Physiographic setting A brief description of the basin physiography is given here. In section 5 the s u r f i c i a l geology and geomorphic processes are discussed in greater detail. 2 . 2 . 1 . Bedrock geology Woodsworth (1977) mapped the Wasp basin as principally granodiorite and quartz diorite of the Mesozoic plutonic complex (Figure 2 ) . A fault zone traverses the basin from northwest to southeast to form one boundary of a narrow zone of lower Cretaceous metasedimentary and metavolcanic rock of the Gambier Group underlying less than 20 percent of the basin. The constituent materials of this unit are mapped as andesitic to dacitic tuff, breccia, agglomerate, andesite, a r g i l l i t e , conglomerate, lesser marble, greenstone, and phyllite; however their relative occurrence in the basin is not known. Figure 2 is taken from Woodsworth's 1:250,000:-scale''map and should be interpreted accordingly. 2 . 2 . 2 . Glaciation and glacierization The southern Coast Mountains were affected by several major glaciations during the Pleistocene Epoch. It is known that ice of the Vashon Stade of the Fraser Glaciation over-rode most peaks of this region (Ryder, 1972) and there is some evidence to suggest that at least one preceding glaciation was thicker and more extensive than this most recent one (Tipper, 1971 ) . The maximum Fraser ice sheet elevation over the Wasp Creek area has not been conclusively established. Mathews (pers. comm.) report's an erratic at the top of Mt. Meager (2,6^5 m) hO km to the northwest and a probable ice surface elevation of 2,250 m in the Garibaldi Lake area (Mathews, 1950) 50 km to the south. Since the main ice stream sloped to the south along the Lillooet River valley the 2 , ^ 0 m maximum elevation of the Wasp basin was most li k e l y over-ridden. The rounded form of the basin summits would sup-port this conclusion. Since retreat of Pleistocene ice, alpine glaciers have occupied, per-haps discontinuously, the upper north-facing slopes of the study area. Mathews' (1950) work indicates that these Holocene alpine glaciers achieved 8 Figure 2. WASP C R E E K WATERSHED BEDROCK G E O L O G Y :::::::::::::::::::: clear-cut — — — — divide — treeline road — 1 0 0 0 — index contour contour interval 100m granodiorite ;'ri~i~rrfl quartz diorite •••Iv.'.'.M metasedimentary and metavolcanic (Gambier Group) assumed fault line (after Woodsworth, 1977) 1 2 Kilometres _i i — l 9 stages of maximum advance during the early eighteenth and middle nineteenth centuries in the Garibaldi Park area. In the Wasp basin fresh morainic deposits above the 1,1+00 m elevation attest to glaciation within the last century of about 20 percent of the total study area. Aerial photo analysis provides some - inconclusive evidence at two sites of earlier, more extensive advances which may correlate with the eighteenth century maxima of the "L i t t l e Ice Age" inferred by Mathews for some glaciers in his study area. Retreat of the ice in this century has l e f t remnants of these glaciers occupying 6 percent of the basin. 2 . 2 . 3 . Watershed form The r e l i e f range of the Wasp basin is from-575 m to 2,hk0 m. The steep-sided, trough-shaped main valley (see frontispiece) reflects modifi-cation by the Fraser and preceding glaciations. The slopes, constructed largely of resistant granodiorite and quartz diorite, maintain an average gradient of 3^° ^" with the steeper slopes predominating below treeline. The more subdued upper elevations are broken by cirque forms, serrate ridges and steep headwalls, products of locally intense alpine glaciation. 2 .3 . Climate There is a transition across the Lillooet watershed from maritime influences along the southwestern margins to a more continental climate to-wards the northeast (Slaymaker and Zeman, 1975 ) . The local and regional var i a b i l i t y is poorly represented by the network of climate stations. Long--term records are available only for the relatively low elevation sites at Alta Lake (670 m) to the southwest and Pemberton Meadows (230 m) 26 km above Lillooet Lake along the Lillooet River. In addition, a snow course is maintained at Tenquille Lake on the eastern side of the Lillooet River at 1,700 m. elevation (B.C. Ministry of the Environment). Although the recorded amounts are unrepresentative of the region the distribution of precipitation through the year is illustrated by the Pemberton Meadows station. Figure 3 shows the winter wet and summer dry conditions which prevail. In the study area the occurrence and storage of precipitation as snow varies with elevation from November through April at lower -elevations.\to*October "through July at higher elevations. Mean snow accumulation' in the basin, where 50 percent of the area is above 1,775 ni, is expected to be at least as great as that recorded at Tenquille Lake. 1. This value is based on a randomly selected set of measurements made on a 1:50,000 scale (100 foot contour interval) topographic map. 2. This record was discontinued in 1966 and the station moved to Pemberton. 180 160 140 T 120 J. | 00 g 80 60 40 ao 0 tomberton Meadows, 230 | | snow water equivalent 20 15 10 (J 5 s o. 0 P -5 10 Jan Feb Mar Apr May |un Jul Aug Sep Oct Nov Dec Figure 3- Precipitation and temperature data for Pemberton Meadows, B.C., 19^1-1966 The normal environmental lapse rate of 6.U°C/l,000 m may be applied to the seasonal temperature data of Figure 3 to give a f i r s t indication of tempera-ture change with elevation. The hydrometeorologic observations made during the study period are presented in section k. 2.k. Vegetation The vegetation composition in the Wasp basin shows a continuous gra-dation in species through the range of elevation represented. The tree species and major shrub species are identified for three generalized zones to describe this gradient only, and not to suggest the occurrence of par-ticular communities. The slopes below 1,200 m elevation are forested by Pseudotsuga menziesii (Douglas F i r ) , Tsuga heteroTphytla (Western Hemlock) and Thuja p l i a a t a (Western Red Cedar). Stands of Pinus aontorta latifolia (Lodgepole Pine) are present in a 1930 burn area on the northeast slopes. The major shrub species are Salix spp. , Oplopanax horridum, Rubus parviflorus and Vaaoinium spp. In a zone of 1,200 m to 1,500 m tree species present are Abies lasiocarpa (Alpine F i r ) , Tsuga heterophylla, Tsuga mevtensiana (Mountain Hemlock), Abies amabilis (Amabilis Fir) and Chamaeoyparis nootkatensis (Yellow Cypress). The major shrub species are Vaaoinium spp., Salix spp. and Paahistima myrsinites. Above the 1,500 m elevation to tree-line at 1,600 m to 1,900 m the tree species are Abies lasiocarpa, Pinus albioaulis (Whitebark Pine) and Tsuga mevtensiana. The major shrub species are Rhododendron albiflorum, Vaaoinium spp., and Paahistima myrsinites. Alnus sinuata (Sitka Alder), the resilient' tree cover of the snow avalanche tracks, is found through the entire elevation range cited above. Above treeline the vegetation cover, where present, is principally herbaceous (forbs and grasses) with Cassiope mertensiana and Phyllodoae empetriformis the common shrubs. 2.5- Land use Clear-cutting of a lower, west-facing slope of the Wasp basin commenced in 1973 and continued in 197^ and 1975 with annual removal of Uo, 33 and U2 hectares respectively. The clear-cut extends over an elevation range of 7^5 m to 1,235 m and occupies 3-5 percent of the total basin area. The area was not burned after timber removal and had been replanted at the time of writing. A high-lead system was used over most'of the area with some timber removal by skidder (a large-wheeled, articulated vehicle) in areas of rela-tively low gradient slopes. High lead operations involve an overhead cable system which "yards" logs to a central landing for loading. Of the systems used locally this one minimizes the extent of road coverage. Surface dis-turbance results from logs being dragged along the yarding track, ancillary vehicle operation and the requisite road construction. 12 3. Methods 3.1. Introduction Throughout the six month study precipitation inputs and streamflows were monitored to - characterize the hydrometeorologic variations within and between snowmelt, summer low flow and f a l l storm periods. These variations were related to suspended sediment flux at the stream gauging stations. Mapping of sediment, sources was conducted and the important sediment trans-fers and sinks described to infer their relative importance to the water-shed scale sediment yields during the observed events. Congruent with the scale of the study a largely descriptive approach was taken to differentiate responses of the source areas. 3.2. Precipitation In the Wasp Creek basin rain gauges were established to provide an index of storm magnitude. Canadian Atmospheric Environment Service standard rain gauges were maintained at the 790 m and 1,220 m elevation on the clear--cut slope and at the lower site a tipping bucket recording gauge was opera-ted during the f a l l storm period. Information from these gauges was aug-mented by standard gauge data measured 7 km. to the. cant .along the.Ryan River at the 275 m elevation. Standard gauge catches were measured following i n -dividual r a i n f a l l events and the timing of the events was given by the t i p -ping bucket gauge record. To test the null hypothesis of a higher catch at the 1,220 m gauge than at the 790 m gauge a Student's t test was performed for the eleven paired observations. The test revealed the two sets of data to be equal at the 95 percent significance level. The mean of the catches at each gauge was used as the index of storm magnitude unt i l the onset of snow in October. After mid-October, with snow accumulating at low elevations of the Wasp basin, the Ryan River station data were used to estimate precipitation in the study area. Gauge catches at this station were regressed against the mean catches in the study area for nine storm events to define a predictive relation. 3.3 . Stage and discharge 3 . 3 . 1 . Measurement Manual staff gauges were established in three Wasp Creek tributary channels draining the clear-cut area and periodic measurements of stage were taken. At two stations along Wasp Creek (designated upper and lower) stage was measured continuously by Ott XX float type water level recorders. Discharge of Wasp Creek was measured by dilution gauging (Church and Kellerhals, 1970) through a range of stages spanning those observed during the study period. These data were regressed in simple arithmetic and logarithmic form and the strongest relationship for each station was selected. 3 - 3 . 2 . Discharge record length and synthesis By application of the stage-discharge relations the stage records were converted to discharge hydrographs. At the lower Wasp Creek station the discharge record is then continuous from May 8 to November 15 . At the upper Wasp station a continuous record is available from July 1 to October 21 . This record was extended for the periods June 21 to July 1 and October 21 to November 2 by interpolation from point observations. For synthesis of the November storm event reference was made l) to the observed lag times between the stations of the hydrograph peaks, 2) to the timing of the flood rise at the lower station, and 3) to the single discharge measurement made about two hours before the estimated peak flow. The discharge record for both stations is shown in Figure A . l . 3 . 3 . 3 . Hydrograph separation A common but arbitrary method of separation of direct storm runoff from baseflow was used. The trend of the pre-storm flow was extrapolated to the time of the peak flow and from that point a line was drawn to a point on the hydrograph a prescribed number of days (N) after the peak. Linsley et a l (1975) cite a "rule of thumb" that was used as follows: N = 0.8A 0' 2 (1) 2 where: A = drainage basin area (km ). 3 . 3 A . Flood frequency analysis Long-term discharge gauging stations have not been maintained on either Wasp-Creek or Ryan River. The frequency of occurrence of the observed peak flows cannot therefore be determined directly. Reference was made to the hydrologic records of six other rivers of the Lillooet River system (Water Survey, of Canada, 1977) . These records span differing periods, are of varying length, and, at the time of study, had been'discontinued except for that of the Lillooet River. Nonetheless, the flood frequency analyses are indicative of the characteristic hydrologic response of each river. For comparative purposes the annual maximum daily flows were divided by basin area to give recurrence intervals for the maximum daily discharge inten-s i t i e s . 3'h. Sediment source mapping 3.1+.1. Undisturbed area The f i r s t reconnaissance of the Wasp watershed was conducted "by helicopter. Mapping of the s u r f i c i a l materials and channel network was then done at the 1:25,000 scale "by interpretation of aerial photos with sub-sequent f i e l d checking carried out on foot. This map has been reduced to 1:50,000 for inclusion in this report. During.the f i e l d season the most recent aerial photos were 1:1^,500 scale"'" black and white photos taken in 1973. In September, 1975 an aerial photo run was conducted by the'Canada Centre.for Remote.Sensing to provide colour infra-red photography at the 1:1^,500. and 1:37 5 500" scales 1; these photos were available for analysis subsequent to the f i e l d programme. The metric 1:50,000.. scale topographic, map appearing herein was re-drafted from the N.T.S. 1:.50,000 scale (100 foot contour interval) map. A 1:37»500 colour infra-red photograph is presented with an overlay showing the channel network. Site references are to quadrats defined by the grid established, on the overlay. 3.k.2. Clear-cut area Road access to the clear-cut area.permitted more detailed observations to be made of sediment sources than were possible for the undisturbed area. Mapping of sediment sources was carried out primarily by ground reconnais-sance with reference to the available maps and aerial photos. Slope failure and channel forms were surveyed by theodolite and resurveyed in the event of significant change. A Brunton compass was used for surveys over d i f f i c u l t terrain. A l : 1 5 , 8 U O scale (100 foot contour interval) topographic map, sup-plied by the B.C. Forest Service, covered the entire clear-cut area. This map was redrafted to metric contours and enlarged to a 1:10,000 scale. Site references for the clear-cut area are to the grid established on this map. 3.5- Sediment yield 3 . 5 - 1 . Network Suspended sediment samples were collected at the three manual staff gauge sites within the clear-cut area and at the continuous stage recording stations along Wasp Creek above and below the clear-cut area. 3 -5 .2 . Sample collection Since the channel sections at the Wasp gauging stations could not be waded sediment samples were taken at a single point within the cross-section 1. Approximate scales at the mean watershed elevation of 1,775 m. of flow. This method does not integrate variations in the vertical and horizontal. It was assumed that the highly active turbulent exchange of the steep, tumbling flow regime stream reaches would afford satisfactory dispersion of suspended sediment through the cross-section. Samples were taken either by hand or by a probe connected to an Instrumentation Specialties Co. model 1391 automatic water sampler. 3 . 5 - 3 . Sample analysis The method of sample analysis entailed: settling of samples; decan-tation of a dissolved sediment fraction; and evaporation of each fraction in porcelain dishes. Table B.l. sets out the steps of the procedure. The method has the advantage of simplicity and of yielding measures of the dis solved, clastic and volatile fractions of the sample. However, i t intro-duces significant error for very low sediment concentrations. Weighing error and weight changes of the porcelain dish during treatments were the significant problems. The magnitude of these error sources was evaluated by determination of the weight changes of four dishes subject to a series of treatments designed to replicate the range of conditions during sample analysis. These tests indicated that 95 percent of the observations w i l l f a l l within ±3 mg/l of the true value for 100 ml samples. Of the 260 samples analysed 16 registered concentrations less than 3 mg/l and of thes data two were between - 3 and 0 mg/l and one was -U.5 mg/l. Indirect evi-dence for the accuracy of the method i s given by the consistent trends of the serial data and'by' the:-.'strength of the sediment rating curves. 3.5-1+. Sediment yield computation . Sample analysis gives a measure of the concentration of suspended inorganic sediments passing the gauging station at the time of sampling. The product of concentration and discharge gives an estimate of the sedi-ment transport rate or sediment load which is expressed as a mass passing the gauging station during a specified'; time (tonnes per hour for this study). The several methods used to determine sediment yi e l d during a given period are described below. a) Interpolation method The most direct and dependable method is to define a sediment dischar graph by interpolation from the calculated rates of sediment transport. The area beneath this line represents the total sediment discharge during the period. The frequency of sampling was adequate to employ this method for a l l but one of the storm runoff events at the lower Wasp station and for the single summer storm runoff event only at the upper Wasp station. b) Sediment rating curve method This method involves the regression of the calculated rates of sediment transport against stream discharge to produce a sediment rating curve for the reference period. The rating curve is used to predict a sediment tran-sport rate at each of the observed flow levels. These rates are multiplied by the total time occupied by the corresponding flow level (as shown by a flow duration curve) and the products summed to give total sediment yield. While this method i s widely used there are several problems inherent to its application in this study. Rating curves may misrepresent sediment yields in situations where sediment concentrations are not satisfactorily explained by runoff variations alone. Such is the case in Wasp Creek where slugs'of sediment may: be'discharge! caused by episodic activity such as :<;•-."" s'16pe."fai-Iure;..'oroby-vehicle operation within streams during high flow, non--storm periods. A second problem is that a systematic change of watershed conditions through the period, such as. s o i l moisture or snow cover varia-tion, might effect a concomitant shift in sediment concentration at a given flow. The sediment concentration-discharge plot for the three largest runoff events, at the lower Wasp station (Figure k)xillustrates a considerable between storm variability of concentration at a given discharge. Rating curves for individual storms may also be unsatisfactory. During each storm runoff event monitored at the lower Wasp station the peak sediment concen-tration preceded the stream discharge peak. The graph of the October 17 storm response exemplifies this behaviour (Figure 5 ) . The proximity of the gauging station to the clear-cut area,, the principal, source of sediment, causes the peak sediment concentration to precede the peak flow by several hours. In this case the lags between the hyetograph centroid and the peaks of concentration and discharge were 8.5 and 12.5 hours respectively. Since sediment concentration is normally found to increase directly with discharge the sediment transport rate (T) increases more rapidly than discharge (Q). Sediment rating curves are therefore frequently defined as simple functions of the form: logT = alogQ - b (2) where a and b are numerical constants (Leopold'and Maddock, 1953 ) . A li m i -tation here is that Q, being used to derive T, appears on both sides of the equation thereby giving spurious strength to the relation. A sediment con-centration-discharge relation would be required to describe.the true co-variation of the measured flow and sediment data. The rating curve is used in this form for predictive purposes only, not to describe the physical 10 ; f 102 c o ro k-C CD O c o o c CD E CO • • • • 4 1 101 IfjO • T Storm date: August 27 • October 17 «J November 17 • • J I I I I 111 J I I I I 111 10 L 10 1 Discharge (m^/s) 10' Figure h. Discharge-sediment concentration relationships for the three largest storm runoff events at lower Wasp Creek. 18 Figure 5. Rainfall, discharge and sediment concentration graphs for the October IT storm, lower Wasp Creek. relationship underlying the data. The rating curve method must clearly be applied with caution. It is used for the computation of sediment yields during the snowmelt and storm periods on the upper Wasp. During these periods the direct covariation of flow and sediment transport rate appear, reasonably consistent. The 95 percent confidence limits on the mean have been defined to express the i n -herent accuracy of the relations. c) Mean sediment concentration-discharge method During periods when, sediment data showed no consistent variation with, discharge or were inadequate in number to allow construction of sediment discharge graphs a.third approach was taken to estimate sediment yield. The mean daily flow was multiplied by the mean sediment concentration and thence by time to give an approximate sediment yi e l d for the period. This method introduces a bias to the results which may be substantial where flow and sediment concentration variations are large (Church, 1978 ) . The method was used for the lower Wasp non-storm data and for the upper Wasp data during the baseflow period of the summer. During the summer period while flows were relatively steady and concentrations very low this bias is not significant. However, for the lower Wasp Creek snowmelt period measurements significant inaccuracies could be present hence estimates- of sediment delivery based on slope observations were necessitated. d) Upper Wasp Creek yield estimate for the November storm The sediment transport rate at the upper Wasp station was obtained at only one point for the November storm. This datum is thought to be close to the peak sediment concentration. A sediment discharge hydrograph was de-rived from the synthesized flood hydrograph using the f a l l storm rating v : . -curve. e) Yield from the clear-cut area An estimate of the yield from the clear-cut area alone is made by f i r s t assuming that the sediment production rates for the undisturbed area of the lower Wasp basin may be approximated by the measured rates of the upper Wasp basin and that the residual represents the yie l d from the clear--cut area. Since Stream C, the major Wasp Creek tributary between the up-per and lower stations was found to have very low sediment concentrations this assumption is deemed conservative. If the sediment yield at the upper station is subtracted from that at the lower station i t must also be assumed that the sediment is maintained in suspension between the two sta-tions. This second assumption is thought to be valid within the limits of accuracy of the calculation. 21 k. Hydrometeorologic observations k.l. Introduction This section details the precipitation, stream stage and discharge observations pertinent to the study. The seasonal variation, magnitude and frequency of events and effects of watershed condition are discussed. k.2. Precipitation k.2.1. Gauge relations The regression of the catches at the Ryan River and Wasp Creek gauges produced the following predictive relation: M = 1.59R - 5.65 (3) where: M = mean catch of clear-cut gauges (mm) R = Ryan River gauge catch (mm) R2= 0.983 standard error = 6 .69 . This equation shows consistently higher inputs at the Wasp gauges however, as Figure 6 illustrates, no data were available for a large range of storm sizes. The regression relationeis produced in large part by the bivariate mean of the lower data and the single outlier hence the true relation'through this interval cannot be estimated with a high degree of confidence. In Figure 6 a regression relation f i t to the lower data alone is shown for comparison. Since the predictions of individual amounts required are be-yond the range of this latter relation equation 3 has been selected and the confidence limits on the observation defined. k.2.2. Seasonal variation Measurements taken at the Tenquille Lake snowcourse, about 15 km to the northeast of the Wasp basin, are used to indicate the timing of snow accumulation and ablation in the study area. Figure 7 shows the water equivalent of the snowcover from March 1 to June 1, 1975 to be below the median amount through the 22"-yearcrecord and that on June 1 the exceedance probability of the snow water equivalent was about 67 percent. Since r temperatures were near normal for the winter period at Pemberton (B.C. Department of Agriculture) the below average snowpack is attributed primarily to low winter snowfall. The snowpack recession in the study area and resultant flows are discussed in section k.3.2. A 50 year precipitation record was available from the Pemberton Meadows station about 10 km east of the study area at an elevation of 230 m. ' This station was closed in 1966, however, daily measurements were taken throughout the study period at a standard gauge nearby. Although these data are not perfectly comparable they suitably i l l u s t r a t e the general seasonal Figure 6. Regression relation of Ryan River and Wasp Creek rain gauge catches. 2.00 r 1.75 h ~ 1.50 c 2" 1.25 $ 1.00 o 0.75 r-0.50 exceedance probability: * 5% .A A - N ^ A 50% > \ 9 5 % J L Feb Mar Apr May Jun Figure 8. Pemberton Meadows precipitation data, 230 m 1916 - 1965 1975 M Missing data exceedance probability: 5% -50% 95% M Figure 7- Tenquille Lake snow course data, 1,700 m A • 1953-1974 A A 1975 M Nil . J L 280 240 200 160^| c o u 1 2 0 £ ^ 80 -I 40 May |un Jul Aug Sep Oct Nov 2k "variation relative to the long-term record (Figure 8 ) . Precipitation in 1975 was below normal in May, July and September and well above normal in October and November. Estimates based on the Ryan River data suggest pre-cipitation below normal in June and above normal in August. The rainstorm amounts measured during the study period are summarized in Table 1. The f i r s t major storm occurred at the end of August and delivered about 75 mm of r a i n f a l l . During September no rain f e l l in the study area. October precipitation was relatively heavy; to October 20, five discrete storms supplied a total of 271 mm of rain to the Wasp gauges. This precipitation occurred as rain at the gauges and snow at high eleva-tions. In the f i n a l 10 days of the month precipitation occurred primarily as snow throughout the basin. By November the snowline was at the 750 m elevation and at 1,000 m on the clear-cut slope snow had accumulated to a depth of about 0.5 m. The water equivalent of this cover was not e s t i -mated, however, the precipitation amount predicted by solution of equation 3 is kk mm at the clear-cut site. Between November 2 and 5 rain f e l l at a l l elevations; the estimated amount for the clear-cut area given by equation 3 is 180 mm. U.3. Stage and discharge I4.3.I. St age-discharge relations The stage-discharge relations for the Wasp Creek stations are defined below and illustrated in Figures 9 and 10. For the lower Wasp station the relation i s the logarithmic form: logQ = 1.3UlogS - l.kk (k)" where: = discharge at lower Wasp (m^/s) S^ = stage at lower Wasp (cm) i 2 = 0.956 1 standard error (for log units) = O.O85. For the upper Wasp station the relation is the semilogarithmic form: logQ = 0.013S -0.604 (5) 3 where: Q = discharge at upper Wasp (m /s) S^ = stage at upper Wasp tern) i 2 = 0.975 standard error (for log units) = 0.031. A problem of serial correlation of the residuals of equation 5 may be present, however, the data were considered insufficient to define a higher order relation. 1. For"transformed data the correlation index (i ) (Ezekiel and Fox, 1959) is used to show the strength with which the function explains the observed values. 25 Table 1. Wasp Creek Watershed Hydrometeorologic Data Summary Storm date Aug. 27 Oct. 3 . Oct. 9 Oct. 14 Oct. 17 Oct. 31 Nov. 4 Precipitation (mm) 76 U8 7.U' 22 163 113 180 Storm runoff (mm) lower Wasp Creek (LWC) 16.5 4.3 0.34 1.33 13.2 2.9 39 upper Wasp Creek (UWC) 13.1* 3.1 N/A 0.40 3.0 U/K 34 LWC - UWC 22.1 6.5 N/A 3.1 32 U/K 49 Storm runoff LWC Storm runoff UWC 1.2 1.4 N/A 3.3 4.5 U/K 1.2 Storm runoff LWC - UWC Storm runoff UWC 1.6 2.1 N/A 7.8 10.9 U/K 1.5 Storm runoff lower Wasp Creek 0.22 0 .09 0.05 0.06 0.08 0.03 0.22 Precipitation upper Wasp Creek 0.18 0.06 N/A 0.02 0.02 U/K 0.27 Basin area: lower Wasp Creek - 33.0 km ; upper Wasp Creek - 21.5 km N/A: not applicable; no detectable.change in discharge. U/K: unknown; recorder inoperative 50 r Stage (cm) Figure 9. Lower Wasp Creek discharge rating curve. Figure 10. Upper Wasp Creek discharge rating curve. U.3.2. Seasonal discharge variation Figure 11 presents the long-term mean of the mean daily discharge"and the 1975 mean daily discharge for the Lillooet River gauging station (Water Survey of Canada). Congruent with the accumulated snowpack measured at Tenquille Lake in 1975 the snowmelt runoff in the Lillooet River was some-what below the mean to the end of June. The long-term record shows a second peak in July related to glacier and high elevation snowpack melt; in July, 1975 above normal temperatures caused a relatively high runoff. Flows then remained generally below normal unt i l the early November rain--on-snow event which generated a flood that was the third largest of the 57 year record. The discharge record in the Wasp basin commenced May 8 (Figure A.'l.) at which time the snowline was at about the 750 m elevation. From May 8 to May 27 the snowline receded to about the 1,200 m level and flows at the lower Wasp station were relatively low at a median 1.8 m /s. Between May 27 and the end of July discharge was derived increasingly from the higher and areally more extensive levels of the basin. Flows in the lower Wasp Creek had a median of k.k m /s and during periods of high radiant energy exhibited the distinctive, nivally-controlled daily rhythm of peaks and troughs 'ranging over about 1 m /s. Discharge during this period peaked in July with contributions from the small glaciers and the high elevation 3 snowpack. Peak discharges were 7-5 and 10.2 m /s for the upper and lower Wasp stations respectively. A summer low flow period i s distinguished for the months of August and September. The median flows in upper and lower Wasp Creeks were 2.3 3 and 2.9 ' m /s respectively. The single major storm which occurred during 3 this period caused instantaneous peak flows of h.l and 5-9 m /s at the upper and lower stations respectively. Throughout the October storm period baseflow was lower than during both the snowmelt and summer periods. The median flow in lower Wasp Creek 3 1 for the 20 days of low flow was 1.7 m /s. Instantaneous storm peaks 3 ranged to 2.8 and 3.7 m /s at the upper and lower stations respectively. These flows are significantly lower than the preceding snowmelt peaks. The November rain-on-snow flood was the only one to exceed the snow-3 melt peaks. An instantaneous peak flow of 19.9 m /s was recorded at the 3 lower Wasp station. The estimated peak flow for the upper Wasp was 11 m /s. 1. The October record for upper Wasp Creek is incomplete. 4 .3 -3. Flood frequency analysis The maximum daily discharge intensity observed on the Ryan River was 3 2 1 2 estimated at 0.4 m /s/km on November 4. Figure 12 shows the peak flood oh the Lillooet River brie day later to be the third largest on record with 3 2 a discharge intensity of O.36 m /s/km and a recurrence interval (with this datum included in the analysis) of about 20 years. The.relative similarity of these discharge intensities is a f i r s t indication that the Ryan River may respond more as the Lillooet, Green and Birkenhead Rivers than as the Soo River or Rutherford Creek. The recurrence interval for the observed 3 Ryan River flood might then be approximated at 10 to 20 years. There is insufficient evidence to assign a recurrence interval for the Wasp Creek peak because of the scale contrast; however, the flood frequency curve for this smaller basin would probably have a higher intercept and slope. 4.3.4. Hydrologic response The hydrologic response of Wasp Creek to storm inputs is shown in Figure 13 and the data summarized in Table 1 for both the upper and lower gauging stations. The r a i n f a l l -.arid- .runoff -.events are distributed over three orders of magnitude and are therefore displayed on logarithmic paper. Runoff-rainfall ratios are lowest for the October storms and highest for the larger summer storm and the November rain-on-snow event. The statis-t i c a l relations underlying each set of data have not been defined for the observations are few and encompass widely varying environmental conditions. The relative positioning of the data is best explained qualitatively. Two factors have an over-riding influence upon the variability of the data of Figure 13 - storage changes of snow and land use effects. The single major summer storm in late August gives an indication of basin hydrologic response with the snow cover at a minimum extent. The higher runoff at the lower station is considered an effect of the surface disturbance by logging activity. This storm produced about 65 percent more runoff in the lower basin alone than the upper basin. 1. Based on a stage-discharge rating curve established for the gauging station at the 275 m elevation. 2. The flood frequency analyses of Figure 12 are constructed to il l u s t r a t e the array of annual peaks and thus include storm runoff, glaciermelt and snowmelt peaks. The data are presented in this form for descriptive pur-poses and should not be used for prediction (U.S. Water Resources Council, 1977) . 3. This estimate is corroborated by one local resident's recollections of Ryan.,River'stage, .fluctuations during the past 60 years (G. Ross, pers. comm. Years of River Basin 9 record area (kmz) 22 • Birkenhead River at Mount Currie (08MG008) 595 N.B. 1. The flood records span differing periods 38 • Green River near Pemberton (08MG003) 854 and all but the Lillooet River gauging station 26 • Green River near Rainbow (08MG004) 195 had been closed by 1975. 57 O Lillooet River near Pemberton (08MG005) 2,170 2. Snowmelt, glaciermelt and storm 25 V Rutherford Creek near Pemberton (08MG006) 161 runoff peaks are included in the analyses. 24 • Soo River near Pemberton (08MG007) 238 1 V V v v 7 ? • • O A O fi • o O O Nov. 5, 1975 _L » I I L J L JL J I L _L JL _L ' ' ' J 1.01 e 12. 1.1 1.3 1.5 2 2.33 3 4 5 7 10 20 30 40 60 80 100 Recurrence interval (yr) Frequency of maximum daily discharge intensities for rivers of the Lillooet River drainage syst 32 102 Storm conditions: 1. August 27 - summer storm 2. October 3 - snow above 1,400 m $. October 9 - snow above 1,100 m (no stormflow at upper Wasp station) 4. October 14 - snow above 1,100 m 5. October 17 - snow above 1.100 m 6. October 31 - snow above 900 m 7. November 4 - rain-on-snow at all aievations • 1 • 1 • 5 10' • 2 • 2 6 • 10' ,0 _ lower Wasp Creek • upper Wasp Creek • • 10" J I I I I I I I I I i 10u 101 Rainfall (mm) 10' Figure 13. Wasp Creek hydrologic response to storm events. Throughout the October storm period the singular effect of the clear--cut area becomes less distinct. As the annotations on Figure 13 indicate snow was f a l l i n g at upper elevations during this period. A portion of the precipitation input then was stored as snow and not immediately released as runoff. The hypsometric curves of Figure 14 suggest that this zone of storm runoff production represented less than 25 percent of the lower basin alone and less than 5 percent of the upper basin. The factors by which runoff production from the lower basin exceeded that from the upper basin ranged from 2.1 to 10 .9 through this period (Table l ) . The large November storm supplied at least 180 mm of r a i n f a l l during a two day period at a l l elevations to a snowcover exceeding 0.5 m above the 1,000 m elevation. Flows generated in the lower Wasp area exceeded those from the upper basin by about 50 percent. 2,600 r Proportional area (%) Figure 14. Hypsometric analysis of Wasp Creek-basin. 4. 4. Conclusion The foregoing observations record a wide range of flows through three periods of snowmelt, summer low flow and f a l l storms. Given the range of watershed conditions and the scale and time period of the study a s t a t i s t i c a l modelling of the system's responses has not been undertaken. This section has provided a description of the conditions encountered as background to the analysisoof •hasin sediment yield. In this context the three important controls.of hydrologic response at the watershed scale have been identified as storm magnitude, the variable distribution of snow, and the presence of the clear-cut area. 5. Sediment sources and availability 5.1 . Introduction The purposes of this section are to describe the sources of clastic sediment distributed throughout the Wasp Creek watershed, to assess their relative availability to the channel network and thence their contribution to basin sediment yield. The s u r f i c i a l materials are mapped and described and morphologic evidence i s used to assess the character and distribution of sediment transfer processes and sediment sinks within the basin. 5.2. Sediment sources Figure 15 is an idealized cross-section of a Wasp Creek valley wall showing the characteristic zonation and stratigraphic sequence of the s u r f i c i a l materials. The upper elevations of the basin are dominantly exposed bedrock overlain in places, by felsenmeer, colluvium, loess, and Holocene or Pleistocene t i l l . Small glacierized areas are present on up-per north-facing slopes. At lower elevations deposits of Pleistocene t i l l are extensive, broken by coarse colluvium, alluvium and frequent bedrock outcrops. The distribution of the s u r f i c i a l materials is shown in Figure 16 and their texture, characteristic landforms and degree of vegetation cover described in Table 2. The clear-cut area is displayed in Figure 17 and i t s surface condi-tions described in Table 3. The characteristics of the tributary basins draining the clear-cut are also tabulated. Figure 15. Idealized cross-section of Wasp Creek valley wall and s t r a t i -graphic column. 36 Table 2 Sediment Sources of Wasp Creek Basin S u r f i c i a l % of Texture C h a r a c t e r i s t i c Degree of Material Basin Landforms Vegetation Area Cover bedrock 29 consolidated steep headvalls; low sparse gradient exposures g l a c i a l i c e 6 not applicable not applicable none felsenmeer 0.1 angular cobbles and boul- l e v e l to gently sloping sparse ders accumulations colluvium 2h angular cobbles and boul- talus sheets and cones sparse ders ; minor f i n e sediment Pleistocene 31 poorly sorted, v e i l - i n - generally t h i n mantle on well t i l l durated; pebbles to boul- v a l l e y walls; decreasing vegetated ders with f i n e matrix depth with elevation Holocene 8 poorly sorted; fines to lodgement, l a t e r a l and sparse t i l l boulders terminal moraine alluvium 1 .8 poorly sorted, fines to cones of steep t r i b u t a r y w ell boulders (cones); s i l t creeks; narrow, fragmen- vegetated and sand over gravel tary v a l l e y f l a t s along (valley f l a t s ) main channel loess U / K s i l t weathered veneer through- well out basin in association vegetated with Pleistocene t i l l (not d i f f e r e n t i a t e d ) Table 3 Surface Conditions of Clear-cut area Surface condition Total Clear-cut Basin A Basin B Basin C S u r f i c i a l Material t i l l ; minor bed- t i l l ; minor bed- t i l l ; minor bed- t i l l ; minor 1 rock, colluvium rock and i DOI IU- rock and c o l l u - rock, colluv: and alluvium vium vium and alluvium % of Area Clear-cut 100 31* 100 1.9 Area (km^) 1.15 1 . 1 6 0.01k 0.123 Elevation range (m) 71*5-1,235 7 1*5-1,800 71*5-880 925-2,1*1*0 % Surface Exposure B.8 15 16 3.5 Road Length (km) 11.07 6.5 0.35 0 . 6 0 Road Gradient (degrees) 0 - 15 0-12 0-10 <3 F i l l - s l o p e Angle (degrees) 3l*-l*2 3h-k0 36-1)2 3I4-I4O Cut-slope angles (degrees) k0-60 kO-6o generally 1*0-60; 1*0-60 up to 9 0 Cut-slope heights (m) generally 1-2; 1-2 up to 6 1-2 up to 6 37 Figure 16. WASP C R E E K WATERSHED SURFICIAL GEOLOGY — 1 0 0 0 — clear-cut divide treeline road index contour contour interval 100m B G F C P H bedrock glacial ice felsenmeer colluvium Pleistocene till Holocene till 38 Figure IT. WASP CREEK CLEAR-CUT. 39 5.3. Sediment transfers - undisturbed area In this section the most significant processes of sediment transfer are discussed. These are grouped as gla c i a l , slope and f l u v i a l processes. The discussion is based largely on an evaluation of the morphologic evidence for sediment movement. The mechanics of the individual processes are only con-sidered for purposes of definition and basic description. 5 . 3 . 1 . Glacial processes The two most important controls of glacial erosion are generally recog-nized as being ice thickness and velocity (Embleton and King, 1968) . In the Wasp basin the extensive presence of recent t i l l deposits suggests that relatively active glacial erosion has taken place. However, the glaciers have retreated considerably from their maximum Holocene advances and at pre-sent are thin, low r e l i e f forms which do not generally meet the ice thickness and velocity c r i t e r i a for effective erosion. The controls and net contribu-tions of the glaciers to sediment yield are evaluated in section 6 .3 . 5 .3 .2 . Slope processes Of the processes operating on slopes there is a continuum from the s t r i c t l y colluvial (or mass wastage) mode through to a f l u v i a l mode. Some writers,?• (e.g. Rapp, i 9 6 0 ) have grouped the "transitional" processes such as debris flows and debris avalanches as f l u v i a l processes. In this report a l l mass movements of sediment are grouped as slope processes. a) Large scale mass movements Examination of the erosional and depositional landforms has revealed no evidence for large scale mass movements such as deep-seated debris or rock slides and slumps. b) Rockfalls From bedrock slopes fragments released by frost shattering are delivered downslope by rockfalls with further size reduction caused by impacts during transport. In alpine areas the widespread distribution and scale of the col-l u v i a l slopes attest to the importance of the process (Photo; l ) . Below treeline the process is active where steep bedrock exposures remain. c) Debris avalanches Debris avalanches involve planar failure and rapid downslope movement of clastic and organic debris (Swanston, 1969) . With increases in water con-tent downslope a debris avalanche may generate a debris flow along a drainage line. In the Wasp basin i t is the shallow.j weathered t i l l horizons of the steep valley walls below the 1,600 m elevation that are most subject to this process. The characteristic forms are spoon-shaped scars in the i n i t i a t i o n zone funnelled into linear tracks along drainage lines or stream channels (Photo.2). Failure of the oversteepened walls of the tributary creeks also occurs (e.g. site 112, Figure 18 ) . Smaller scale debris avalanches without a significant downslope flow component are common on slopes of 3 5 ° to 4 5 ° . Debris avalanching is less evident in the alpine zone congruent with the generally lower slope gradients. The process is nonetheless active where steep t i l l slopes are present (e.g. site Gl6). On collu v i a l slopes failure of small masses may cause debris flowage downslope. d) Debris flows Debris flows are rapid movements of material of high water content and 20 to 80 percent particles coarser than sand (Bloom, 1978 ) . They are dis-tinguished from mudflows by their coarser texture. On alpine colluvial slopes in the Wasp basin debris flow channels are present flanked by levees and terminating in small, lobate cones at the change of slope to the valley floor (site J 1 5 ; Photo. 3 ) . A pre-condition for debris flowage is the avai-l a b i l i t y of fine-grained material; on the slope illustrated this material derives principally from underlying Pleistocene t i l l . Slopes constructed of Holocene t i l l appear to be less susceptible to transfer of material by this mode. This is attributed more to the relatively small upslope area available for collection of the mass of water and sediment than to inherent s t a b i l i t y . Below treeline the slopes along the main valley transmit debris flows which originate on steep glacial t i l l slopes, form leveed channels in transit and debris accumulations at the slope base. The process may be primarily res-ponsible for the construction of the a l l u v i a l cones along the lower valley walls (Photo, 4 ) . Large debris flows were not observed in operation in the study area, however, one such event was witnessed along the Ryan River during the November rain-on-snow event. Planar failure of an undercut t i l l slope at 1,200 m elevation contributed material to a steep tributary channel. Along the channel material was both deposited in coarse-textured levees and en-trained by the dense, rapidly flowing slurry. At the slope base, at 275 m, 3 successive lobes bearing boulders as large as 10 m in a matrix of finer sediment were carried into the Ryan River over a period of several hours. Some of these were sufficiently large to momentarily block the flow of the river which had a flow width of 16 m, a mean depth of 4 . 5 m and an estimated mean velocity exceeding 2 m/s.1 Numerous run-out channels, levees and small 1. It might be noted here that the erosional consequences to the downstream channel of the Ryan River, which was i t s e l f in flood, were enormous. Approximate scale at mean basin elevation: 1:37,500 Date of photography September 5, 1975 watershed divide intermittent stream channel channel flowing during September low flow period Figure 18. Colour infrared aerial photograph of study area with overlay showing drainage network. lobes remained (Photo. 5). e) Snow avalanches In the Wasp basin snowfalls are heavy and in late winter and spring rapid temperature increases and high intensity r a i n f a l l may occur. These conditions are ideal for the release, ofcwet' snowsavalanches-. Slopes, above and below treeline were inspected at the time of spring melt during a three year, period. Winter avalanche deposits were, relatively free of sedi-ment and the late winter and spring deposits contained only small amounts of both fine and coarse material. At the times of inspection the alpine slopes were largely protected by snow hence sediment movement was limited. As the snowcover diminishes transfer of debris by snow avalanching may be more significant. These slopes display many of the characteristic features re-sulting from avalanching including exposed fine sediments on upper slope surfaces, downslope size sorting, basal concavity and the absencei?cin:i.most cases, of channelization. Below treeline minor deposits of debris were ob-served which had been removed from the surfaces of the run-out slopes. These slopes are maintained largely free of a l l trees but Alnus sinuata, however, this cover offers considerable protection from erosion. Experience in the Rocky Mountains has shown the geomorphic role of avalanches to be .. negligible on vegetated slopes.(Luckman;- 1978). Unvegetated "avalanche cones""^ " are not present below treeline in the Wasp area. f) Slow mass movements Slow mass movement processes are identified which may be relatively im-portant to landscape evolution yet, by virtue of their less visible effects, their significance is more d i f f i c u l t to determine than that of the more rapid mass movements discussed above. Reference is made here to the most effective processes observed in temperate mountain environments - s o i l creep, solifluction and frost creep. Inr'.the: Waspibas.in:*t.he>,ubiquit'6us recurved^.treeltrunks •.•andvibver-hangihg soilvmantles at convex breaks in slope provide ample evidence of s o i l creep on the steeper slopes. The t i l l slopes appear to be subject to the most rapid.-.creep", although the process may be active as well on the lower angle colluvial slopes; however, as Gardner (1973) comments, the "true creep" of the talus mantle is d i f f i c u l t to discern given the variety of formative processes. Above treeline solifluction is the dominant creep process (Carson and 1. Luckman recommends reservation of this term for the deposits of this form and genesis which develop below treeline. Kirkby, 1972) . In the Wasp Creek alpine zone the characteristic forms such as lobes and terraces (Washburn, 1973) are developed to only a minor extent on slopes underlain by s i l t y soils derived from Pleistocene t i l l and loess. The coarse-grained colluvium is less frost-susceptible (Williams, 1957 ) , more rapidly drained and therefore less subject to solifluction. Uplifting of particles by needle ice growth at the s o i l surface or s o i l heave by deeper-seated frost penetration may cause frost creep of material v.o Needle ice growth occurs at lower elevations in spring and throughout the basin in late summer and f a l l . Since this period of ac-t i v i t y coincides with the periods of snowmelt'and storm runoff i t may be important to the loosening of fine materials for f l u v i a l transport. Frost penetration in this area of heavy snow cover is confined to a shallow depth (Mackay and Mathews, 1974b) thus transfer by deep-seated frost heave is l i k e l y of limited significance. 5 . 3 . 3 . Fluvial processes The network of channels detectable on the 1:14,500 scale photographs is shown as an overlay in Figure 18. The channels known to be flowing during the September, 1975 low flow period are distinguished from the remaining scoured lengths visible on the photographs7 The non-scoured, linear drainage depressions (discussed below) are not included in the analysis; the result is a conservative measure of drainage density. In alpine areas the network is less developed due to the extensive pre-sence of bedrock and coarse colluvium. The 64 percent of the upper Wasp basin which lie s above treeline has a mapped drainage density of only 0.10 2 km/km . The effectiveness of surface erosion on'the exposed alpine slopes has not been determined. Inspection of the t i l l slopes reveals that r i l l i n g occurs where fine-grained sediments are present. The channels tributary to Wasp Creek below treeline are confined to the more erodible glacial t i l l and a l l u v i a l materials. On the forested slopes 2 of the upper Wasp basin a higher drainage density of 0.25 km/km has formed to transmit the supply of water and sediment. Material is conveyed in a range of modes from mass movements to the s t r i c t l y f l u v i a l mode. Non-channelized, linear drainage depressions are also developed in the t i l l slopes below treeline. Examples are visible in Figure 18 in the clear--cut area. These features may have formed by channelization during the im-mediate post-glacial period, however, contemporary enlargement is more lik e l y by mass movement and solution. They have been observed to transmit surface flow only when their weathered s o i l mantles are saturated. Wasp Creek flows mainly over glacial t i l l which i t has selectively eroded to leave a coarse lag boulder deposit resistant to degradation (cf. Ponton, 1972b) . Over the greater length of channel lateral activity is restricted by strongly vegetated, confining valley walls of colluvium, glacial t i l l , a l l u v i a l cone material or bedrock; Because of these controls the longitudinal profile is one imposed by the glacially-conditioned val-ley slope (Figure 19 ) . The resultant flow regime., described as "tumbling flow" by Peterson and Mohanty ( i 9 6 0 ) , has roughness elements of the scale of the mean channel depth and a conconmitant high energy dissipation (Photo. 6 ) . - Along short lengths of channel local base-level controls have caused upstream aggradation allowing channel formation in i t s own alluvium. Bed material loads along such reaches and in pools along tumbling flow reaches are sand to cobble size. 2,000 r 6 5 4 3 Disuncc to confluence with Ryan River (km) Figure 19 . Longitudinal profile of Wasp Creek. 5.1+. Sediment transfers - clear-cut area The focus in this section w i l l be upon the way in which the sediment transfer processes are altered by logging ac t i v i t i e s . The observations of slope processes during the snowmelt period have particular significance be-cause the suspended sediment sampling programme i s unlikely to detect iso-lated slugs of sediment moved in the manner described. For the f a l l storm period the sediment y i e l d data give a more certain measure of the export of sediment from the clear-cut area. 5.1+.1. Slope processes 1 a) Debris avalanches As elsewhere in the Wasp basin drainage depressions and channels on the oversteepened t i l l slopes of the clear-cut area are most subject to debris avalanching. The steepest slopes are in the area that was logged during 1975; during the study two debris avalanches were recorded in this area. On May 16 a debris avalanche was initiated at an elevation of 1,010 m on the slope below the road at site F20 (Figure 17 ) . Failure occurred at a mean depth of 20 cm (measured normal to the failure plane) on a 42° gradient. 150 m^  of weathered t i l l materials were carried down-slope by a combination avalanche-flow mode and deposited on the snow and ice overlying Wasp Creek. The depression within which failure occurred had a high sodtwater content imparted by the on-going snowmelt at the site and by the deflection of snowmelt runoff from the road onto the slope. A second debris avalanche was initiated at 1^050 m elevation above the road (site G19) . The failure took place at shallow depth in a depression at an angle of 40° and caused 125 of debris to move downslope principally by flowage to a lower gradient slope at the 925 m elevation. This failure occurred during the early November rain-on-snow event and was not related to road drainage. Similarly steep slopes are found between the main logging road and Wasp Creek at sites E9 and E10. This area may have sustained debri avalanching prior to 1975, however, the material would have been delivered directly to Wasp Creek and the erosional evidence obscured by later road work. The remaining area of the clear-cut, standing at a mean angle of 2 8 ° , is relatively stable. b) Mass movements along roads During the snowmelt period considerable slumpage of cut-slopes was observed along a 500 m section of road paralleling Wasp Creek above 950 m 3 elevation. The slump block volumes were generally less than 10 m with the 3 largest being 35 m • These failures most frequently took place where there was a concentration of surface or subsurface snowmelt drainage. During road maintenance the slumped? material'-and further- cutr-slope and road surface material was pushed over the f i l l - s l o p e . In one case this initiated a debri flow which ran out into Wasp Creek. Below the 950 m level the road paral?-.:: lel i n g the creek had been cleared by the time of study. Cut-slopes are high along this segment (Photo. 7) hence at least similar volumes might be ex-pected to have been moved. During the f a l l rains cut-slope slumpage was an order of magnitude less than that during snowmelt and subsequent road main-tenance was not immediately required. 5.4.2. Fluvial processes The pre-logging channel network is shown in Figure IT. Road construc-tion effectively extends this network by surface compaction and, in many cases, removal of the weathered s o i l materials. To limit road surface ero-sion runoff is diverted onto non-channelized surfaces downslope causing i n f i l t r a t i o n of the water and deposition of the sediment. This diversion is effected by various types of cross-ditches, road-side ditches, road obstructions and, on roads following contours, by inclination of the road width downslope: (or "oixtsloping" the road). Direct storm runoff was con-fined largely to the road surfaces (including cut- and fill- s l o p e s ) and the established channels. However, in some cases runoff volumes were suf-ficient to maintain flow along the non-channelized drainage lines. Inspec-tion of these drainage lines revealed flow and sediment transport in cases where runoff was derived from road surfaces. Where drainage was not from roads flow was observed during only the largest storm. In neither case was significant erosion of the drainage lines themselves observed. The net effect of road construction for the entire clear-cut area was to extend the continuous drainage network by a factor of 2.5- For the par-t i a l l y clear-cut Basin A'.the::drainage-.densityrwas. dbubledr-from. 1.T''to 3.5 2 km/km.. Basin B, non-channelized before road construction, gained a 2 drainage density of 25 km/km . The drainage, density of Basin C was not significantly changed by road construction. These measures of the linear extension of the drainage system only partially express the modification of the f l u v i a l system. It is estimated that the extended network directly drained 5 to 6 hectares of exposed mineral s o i l by surface and channel erosion. This represents 4 to 5 percent of the clear-cut area. A further 4 to 5 percent of the area is similarly disturbed but was not connected to the continuous channel network. For a given length and design of road surface, erosion increases with increasing road gradient, sediment availability and runoff. The most severe road surface erosion observed was along the steep (10° to 15°) segments of the recently constructed road at sites FIT to"F21. During the snowmelt 3 period gullying of this road caused removal of approximately 40 m of sedi-ment (Photo. 8). "Less readily measureable contributions from sheet erosion and r i l l i n g would be added to this total. Sediment entrained along this road was carried into either Wasp Creek or Stream C. During the snowmelt period then, for this one 500 m segment of road, a conservative figure 3 would be an export of 50 m of sediment by f l u v i a l activity alone. 5.5. Sediment sinks - undisturbed area There is substantial storage of unconsolidated sediment in the Wasp basin. The products of recent glacial and subaerial erosion are added to an extensive mantle of Pleistocene t i l l . Storage of colluvial and glacial sediments has been at a time scale of millenia. Transfers from one sink to another may occur without making the material available to the channel network. Deposits which experience shorter terms of storage are those which are connected to, or may be transported to the channel network and are sufficiently fine-grained for f l u v i a l transport. In the areas affected by surface runoff, particularly in the alpine zone, coarse materials which resist transport occur extensively. Sediment entrained by f l u v i a l action may in turn be deposited for long periods. The total alpine area that is lake-drained represents 27 percent of the basin. The two largest of these lakes, draining 20 percent of the basin, are effective sinks for a l l but. the finest wash-load fraction This is particularly significant for these lakes drain the apparently most active glaciers. The al l u v i a l cones along the main Wasp valley also con-stitute effective sediment sinks although for potentially shorter periods. Although the material in these cones may be re-entrained by f l u v i a l action, as for other deposits a fraction is too coarse for transport along the main channel. Along Wasp Creek a l l u v i a l sediment is stored along lower gradient reaches in both bed and banks which may be moved during the larger floods. 5.6. Sediment sinks - clear-cut area As elsewhere in the basin the storage time of glacial deposits is long where they are removed from f l u v i a l action and relatively short along the drainage network. Along the altered network sediment sinks are present wherever the energy for transport is dissipitated. Along roads such dis-sipation occurs at gradient changes and irregularities on road and f i l l --slope surfaces. Flow diversion onto non-channelized areas w i l l cause sedi ment to be deposited if. the distance to the next road or channel is s u f f i -ciently long. Along channels sediment i s deposited along lower gradient reaches, in pools and by obstructions such as log debris. The sinks within the drainage network are, in most cases, relatively short term; successive storms transport material further downslope. With time the effective sinks are f i l l e d and, assuming a constant sediment supply, shorter term sediment storage and higher sediment yi e l d result* 5.7- Sediment availability - undisturbed area An examination of the s u r f i c i a l deposits in the undisturbed area reveals that the character of sediment sources and transfers above and below treeline can be differentiated. In Figure 20 the distribution of s u r f i c i a l materials and the characteristic landforms are shown for the undisturbed area of the Wasp for which sediment yield data have been collected. Only 25 percent of the alpine zone i s overlain by glacial t i l l materials containing significant proportions, of fine-grained sediment; the remaining area is bed-rock, glacial ice and the generally coarse-grained colluvium and felsenmeer. This limited extent of fine-grained materials and the low drainage density 2 of 0.10 km/km indicates a dominance of mass wastage over f l u v i a l transfer processes. Much of the sediment moved is returned to storage without con-tributing material to the drainage network. Below treeline glacial t i l l overlies 65 percent of the area, slopes are steeper, and a higher drainage density of 0.25, km/km has developed. The most effective transfers occur along the steep tributary creeks which incise the t i l l . A l l u v i a l cones are constructed of material, thus transported and these cones in turn provide a source of sediment available for removal from the basin. Along Wasp Creek the t i l l deposits, are eroded along some reaches, however, the colluvial deposits are generally':too coarse. Alluvium deposited by Wasp Creek is available for transport but has only a minor presence. A conceptual model has been constructed to summarize the system of clastic sediment transfer and to illu s t r a t e the most important processes (Figure 2 l ) . It is concluded that, by virtue of i t s texture and availability to the f l u v i a l system, glacial t i l l sources are most important and that at the watershed scale Pleistocene t i l l sources below treeline dominate. 5.8. Sediment availability - clear-cut area The transfers adjudged to be relatively important for the undisturbed area (shown on Figure 21) are the same for the clear-cut area. The change has been of the relative magnitude, frequency and extent of operation of the processes. To a drainage network which has been more than doubled in extent are connected exposed s o i l surfaces representing k to 5 percent of the c l clear-cut area. As well, terrain disturbance has increased, the susceptibir-.i l i t y of slopes to mass failure. The limited sediment storage within the altered f l u v i a l system, and the particular juxtaposition of roads, channels and steep slopes have rendered the activated sediments readily available for delivery to Wasp Creek. Figure 20. Vertical zonation of sediment sources in upper Wasp Creek watershed. Figure 21. Wasp Creek watershed clastic sediment transfer model. primary weathering BEDROCK glacial erosion ^ loess ^ •(> -•o Pleistocene till mass wastage and/or fluvial transport mass wastage t ~ r Jluvial _ J -transport r <HoioceneorV Pleistocene y till X glaciai erosion felsenmeer Holocene till i glacial eriosion mass wastage fluvial transport alluvium lacustrine lake drainage YIELD mass wastage and/or fluvial transport fluvial transport | | sediment source, sink <^ y extra-watershed origin O decision - • transfer mmm^ important transfer <^^^ output 6. Sediment y i e l d 6.1. I n t r o d u c t i o n The study p e r i o d was l i m i t e d t o s i x months hence the data are i n t e r -preted to d i s t i n g u i s h the e f f e c t s of the p r e v a i l i n g h y d r o l o g i c c o n d i t i o n s and the d i f f e r i n g a v a i l a b i l i t y of sediment but not t o e l u c i d a t e longer term geomorphic changes. 6.2. Sediment y i e l d r e s u l t s 6.2.1. Snowmelt p e r i o d - May t o J u l y During the snowmelt p e r i o d of May t o the end of J u l y no c o n s i s t e n t v a r i a t i o n of sediment concentration w i t h discharge was i d e n t i f i e d f o r the lower Wasp Creek s t a t i o n . The v a r i a b i l i t y of the data was caused p r i n c i -p a l l y by the e f f e c t of the on-going l o g g i n g o p e r a t i o n s , i n p a r t i c u l a r the road maintenance and v e h i c l e t r a f f i c . The mean concentration of the IT samples was nevertheless r e l a t i v e l y low at 21 mg/l ( s t d . dev.: 21 mg/l). 2 The estimated sediment y i e l d i s 600 t ( l 8 t/km ) f o r the p e r i o d (Table C.I.). For the upper Wasp Creek s t a t i o n the continuous discharge r e c o r d commenced June 21. The mean concentration of the twelve samples taken was very low at 6 mg/l ( s t d . dev.: 7.h mg/l). For these --samples--sediment concentration and th e r e f o r e sediment t r a n s p o r t r a t e v a r i e d d i r e c t l y w i t h discharge a l l o w i n g d e f i n i t i o n of the sediment r a t i n g curve i n Figure 22. The strongest simple r e l a t i o n t e s t e d describes a l o g a r i t h m i c f u n c t i o n of the form: l o g T s = 3.591ogQu - 3.30 (6) where: T = snowmelt p e r i o d sediment t r a n s p o r t r a t e 5 (t/h) = discharge at upper Wasp (m /s) i 2 = 0.97 standard e r r o r ( f o r l o g u n i t s ) = 0.352. 2 Applying t h i s r e l a t i o n a y i e l d of 65 t (3 t/km ) i s estimated f o r the per i o d . The corresponding estimate f o r the lower Wasp i s 230 t (about 7 t/km 2). 6.2.2. Summer p e r i o d - August and September Throughout the summer p e r i o d Wasp Creek sediment concentrations were g e n e r a l l y very low. With the exception of the s i n g l e storm event, con-c e n t r a t i o n s exceeding 5 mg/l were not detected and the sample means at both s t a t i o n s were i n the range of 2 t o 3 mg/l. Since the data are scant and l i e g e n e r a l l y w i t h i n the d e t e c t i o n l i m i t s of the a n a l y s i s no s i g n i f i -cant d i f f e r e n c e i n the means can be assigned. For the upper and lower 52 53 2 2 stations the yields are estimated at 3*+ t (1.6 t/km ) and h3 t (1.3 t/km ) respectively. The specific yield is somewhat higher for the upper "basin; this difference i s an artifact of the higher discharge intensity and is not known to be significant. The sediment yield estimates for the single summer storm are h.h and 9-5 t (0.2 and 0.3 t/km ) for the upper and lower stations respectively. 6.2.3. F a l l storm period - October and early November At the upper Wasp station, with the exception of the November rain-on-r -snow event, sediment concentrations during the f a l l storm period were very low. The five samples taken near the peak flows of the October storms had concentrations less than 10 mg/l through a flow range of about 1.5 to 2.5 m /s. The single sample taken during the November storm had a concentration of 715 mg/l. Taken together with the summer storm data 21 observations were available, to define a sediment rating curve for storm runoff events (Figure 22). The strongest simple relation was the logarithmic form: . log T r = U.091ogQu - 2.82 (7) where: T = storm period sediment transport rate r (t/h) i 2 = 0.999 standard error (for log units) = 0.191. The 95 percent confidence interval on the slope of this relation is ±0.55 thus i t is not significantly different from the slope of equation 6. Con-siderable strength is imparted to equation 7 "by the four order of magni-tude range of the data. The confidence limits show the band within which the line would l i e at the 95 percent level. Howevermore data could en-large these limits or show that such a simple "'form does not apply over the entire range. Applying this relation the yield for the October period of 2 baseflow and stormflow together was estimated at"10 t (0.5 t/km ). The 2 estimate of the November storm yi e l d is approximately 300 t (lh t/km ). At the lower Wasp station sediment concentrations during the f a l l storm events ranged to a maximum of 1,610 mg/l recorded during the November storm. The total sediment yield from October 1 to November 6 was 955 t 2 2 (29 t/km ) of which an estimated QkO t (25 t/km ) or 88 percent was pro-duced during the November storm. 6.3. Sediment discharge regimen In this section the regimen of sediment discharge at each gauging station is discussed with respect to the control exerted by the variable hydrologic conditions and sediment availability through the study period. 6.3-1. Upper Wasp Creek Throughout both snowmelt and storm periods the higher flows were most s i g n i f i c a n t i n terms of t o t a l work done. For the snowmelt p e r i o d the s e d i -ment dur a t i o n curve (Straub, 1935) together with the flow d u r a t i o n curve ( F o s t e r , 1934) show th a t 50 percent of t o t a l y i e l d was discharged during flows, t h a t occur l e s s than 7 percent of the time (Figure 23). For the storm p e r i o d the higher flows and dependent sediment t r a n s p o r t r a t e s are not known w i t h s u f f i c i e n t accuracy t o i n d i c a t e more than t h a t the November storm s u p p l i e d about 95 percent of the period's y i e l d . Storm r u n o f f was a more e f f e c t i v e agent of e r o s i o n than snowmelt r u n o f f at a given discharge (Figure 22); however, the sediment produced during the snowmelt p e r i o d of l a t e June and J u l y exceeded t h a t of the October storm p e r i o d . By v i r t u e of a greater frequency of high flows and a longer p e r i o d of a c t i v i t y snowmelt r u n o f f may do the most work through the longer term. For the snowmelt p e r i o d , given the r e l a t i v e l y low sediment concentra-t i o n s and t h e i r systematic v a r i a t i o n w i t h discharge, f l u v i a l e r o s i o n of g l a c i a l t i l l and i t s r e d i s t r i b u t e d products along the steep t r i b u t a r y creeks i s considered most important. During storm events sediment y i e l d was con-t r o l l e d by the v a r i a b l e occurrence of p r e c i p i t a t i o n as snow throughout the b a s i n . Snow accumulated during October above the 1,100 m t o 1,400 m e l e v a t i o n s ; hypsometric a n a l y s i s shows t h a t sediment and r u n o f f production would thus be r e s t r i c t e d t o the lower 5 percent of the b a s i n area. The character of sediment movement i n t h i s zone and the very low sediment F i gure 23. Upper Wasp Creek flow and sediment discharge d u r a t i o n curves f o r June 21 t o J u l y 31, 1975-y i e l d suggest only minor f l u v i a l erosion of the available material and l i t t l e mass movement activity. For the summer storm and the rain-on-snow event the contributing area of sediment and runoff extended to a l l eleva-tions and yields were correspondingly higher. The high suspended sediment concentration of the rain-on-snow event may reflect the increasing im-portance of mass movement contributions to the channel network as storm size, watershed saturation and contributing area increase. The summer low flow observations at the upper Wasp station are of interest with respect to glacial sediment supply. Sediment production from glaciers would be high during this period of high rates of ablation and glacial erosion. The very low sediment concentrations measured pro-vide no evidence of significant glacial sediment yield. 6.3.2. Lower Wasp Creek Comparison of the upper and lower Wasp Creek records provides an in-dication of the amount of sediment removed from the clear-cut area. For the snowmelt period, however, the effects of terrain disturbance are better illustrated by the measurements made within the clear-cut area i t -self. The estimated yi e l d at the lower Wasp station is higher (the con-tributions from the upper Wasp being included) and of the same order as that of the mass of sediment observed to have been delivered from the clear--cut area. Although in agreement with the slope observations the':yield data lack the resolution to further characterize the regimen of sediment discharge. It is estimated that the specific yield at the lower station exceeded that at the upper station by a factor of two to three during snow-melt (Table C.l.). For the five storms for which adequate data are available the sediment yields are plotted against storm runoff and r a i n f a l l (Figure 2k). A regres-sion relation i s not defined yet the trend suggests*-an exponential rate of increase of yield over a two order of magnitude range of r a i n f a l l and runoff. In general, for progressively larger storms the f l u v i a l processes at a site become more effective and sediment availability increases with the expanding drainage network. Additionally, slopes are increasingly susceptible to failure as s o i l moisture contents increase. For the summer storm the low sediment production rate relative to storm size for the clear-cut area is attributed to the low antecedent moisi_: ture conditions and therefore both the less extensive drainage network and the lower susceptibility to slope failure. The specific y i e l d at the lower station was greater than that at the upper station by a factor of 1.5; in Rainfall (mm) 10 2 10 3 1 1 I I I I I 1 1 1 1 I I I I < S B • 5 Storm date: 1. August 27 2. October 3 3. October 14 4. October 17 5. November 4 4 « • 4 2 • 1 rainfall-sediment yield datum • 3 « • 3 runoff-sediment yield datum • 1 00 l I I I I 1 I I I 1 I I I I I I I I I 10° 101 10 2 Storm runoff (mm) Figure 24. Lower Wasp Creek sediment yi e l d response to storm runoff events. this case the relative effects of terrain disturbance are masked by sediment and runoff production from higher elevations of the basin. During October the snowline remained below the treeline allowing com-parison of specific yields from clear-cut and forested slopes. The rates 2 . 2 were 9-3 t/km for the forested area and at least 80 t/km for the clear-cut area assuming that only the portion below 1,250 m was producing runoff and sediment. During the November storm, although yields from the clear-cut area were very high, the relative effects of terrain disturbance at the watershed scale were less than during the smaller October storms. As noted for the summer storm the contributions from the lower, forested slopes could not be discerned against the background of sediment delivery from a l l elevations of the basin. The lower Wasp specific yields exceeded those of the upper Wasp by about two times. For the six month study period the sediment production rate on the 2 clear-cut slope was about 750 t/km . The rate for the undisturbed basin, 2 without adjustment for the variable contributing area, was 23 t/km . 6.3.3. Wasp Creek tributary streams Sediment samples were taken during storm periods in Streams A, B and C draining the clear-cut slope (Table C.2.). The sediment concentration data confirm the singular importance of roads upon accelerated erosion. Basins A and B, which experienced substantial drainage network extension and mineral s o i l exposure as a result of road construction, had sediment con-centrations two to four orders of magnitude higher than those for Basin C which had virtually no drainage network alteration. In addition, the data show Basin C to have had concentrations lower than those at the upper Wasp station; the lake above the clear-cut apparently acts as a sink for sediment delivered from the undisturbed slopes of the basin allowing the effects of the clear-cut area to be isolated. No increased sedimentation related to clear-cutting and timber removal independent of road effects was observed. 6.4. Conclusion In this section the observed sediment yields have been related to the physical characteristics of the basin and to the variable hydrologic con-ditions. Rates of sediment production during snowmelt and storm runoff periods are shown to be significantly higher on clear-cut than forested slopes. 7. Discussion and conclusions 7 . 1 . Vertical zonation of geomorphic processes A differentiation of sediment sources and transfers in the study area suggests that the area below treeline is of dominant importance to basin sediment yield. In this zone slopes are steeper, glacial t i l l is extensive and a higher drainage density has developed to convey material by f l u v i a l action and mass movement to the main channel. In the alpine zone mass movement activity is widespread yet much of the material is returned to storage without contributing sediment to the channel system. Evidence for the relative importance of f l u v i a l processes in this- zone is less conclusive surface erosion of the exposed s o i l surfaces may make f l u v i a l activity more significant than is suggested by the limited extent of the channel network. 7.2. Seasonal analysis The sediment yield data show that whereas the absolute quantities of sediment passing each gauging station differed markedly the proportions in passage during each season were relatively similar. As much as UO percent of the six month total sediment'yield, may have been discharged during the three month snowmelt period; yields of the two month summer period repre-sented less than 10 percent of the tota l ; and the October to early November storm period accounted for the remaining proportion of at least 50 percent. Of this latter amount more than 85 percent (95 percent for the upper Wasp basin) was removed during the large rain-on-snow event. Throughout most of the study period, for both clear-cut and undisturbed areas, sediment activated by f l u v i a l processes was quantitatively most sig-nificant. At the watershed scale the variable distribution of snow was an important control upon the contributing area of runoff and sediment. During the snowmelt period sediment concentrations were low and varied d i -rectly with melt runoff. Higher concentrations at a given discharge were caused by storm runoff. Sediment yields from the area below the snowline exhibited a direct variation with storm magnitude. Sediment activated by glacial processes was not detected at either the Wasp Creek or Stream C gauging stations. The fine sediment deriving from this source is both lost to lacustrine and minor a l l u v i a l sinks and diluted by runoff from the 9^ percent of the basin area which is presently ungla^ cierized. Slope processes at the watershed scale become increasingly important as s o i l moisture content and storm.magnitude increase.. Increasing s o i l moisture supplies the requisite external stress for slope failure and an expanded drainage network renders these sediments more available to basin sediment yield. Swanston (1970) and O'Loughlin (1972) report that a 24--hour r a i n f a l l of 150 mm w i l l saturate the weathered t i l l horizons in steep drainage depressions. Assuming a similar response in the study area saturation of these sites was achieved during the November storm and pos-sibly during one additional storm as a result of high antecedent moisture contents. The slope failure observed in the clear-cut attests to the instability of these slopes under such conditions. Sediment movement through a watershed to eventual yield is typically viewed as a continuum of slope to f l u v i a l transfers. The presence of glacial t i l l in the study area modifies this concept somewhat; glacial sediments are available to the f l u v i a l system without the necessity of slope mass movements. Slope processes nevertheless supply material yet channels incise the mantle of t i l l to contribute sediment directly to basin yield. For the periods for which f l u v i a l processes are adjudged to be dominant the observed yields may have derived either from redistributed sediments or directly from glacial t i l l which has been'substantially stable since deposition. The data base does not permit a more definite determination. The assessments made of the relative importance of slope and f l u v i a l processes to the activation of sediment are applicable only at the watershed scale for the sequence of events observed.. A further q u a l i f i -cation is that geompr.phic' processes take place in response to progressive change in the system hence not a l l physiographically similar sites respond at the same time to a given external stress (Schumm, 1973) . It is clear that evaluations of the geomorphic evolution of a system must be based on a long-term. study. The data reported here are suitable only to the assess-ment of clear-cut effects and of the undisturbed basin's response over the observation period. 7.3 . Effects of terrain disturbance Specific sediment yields at the lower Wasp station exceeded those at the station above the clear-cut by a factor greater than two during the six month study period. If the excess specific yield is assigned to the 1.15 • 2 km clear-cut then rates of sediment delivery from this area exceeded those of the undisturbed area by more than 30 times. This difference was con-trolled in large measure by the variable sources of runoff at the watershed scale. During the October storm period, when sediment delivery was from lower elevations only, rates of erosion in the clear-cut area were about eight times those of the forested slopes. This magnitude of accelerated erosion is more representative of the effects of disturbance upon the forested slopes than the observations made while a l l levels of the basin were producing sediment and is within the range observed elsewhere in the Pacific Mountain System (cf. Anderson, 1970; Fredriksen, 1970) . In Oregon and northern California Anderson found the effects of roads to generally account for 80 percent of the increased yields. In the study area, however, due in large part'to the absence of slash burn effects, the accelerated erosion was caused almost entirely by roads. Road construc-tion extends the surface.drainage network, under-cuts and steepens slopes, and brings about higher concentrations of runoff downslope; together these changes cause higher rates of sediment transfer by cut-slope slumping and debris avalaiching below roads and by accelerated removal of exposed material by f l u v i a l action. The pattern of roads caused the continuous drainage net-work to be extended by 2.5 times and to effici e n t l y drain exposed surfaces covering k to 5 percent of the clear-cut area. An additional, equivalent proportion was exposed by road construction but was not connected directly to the channel system, thereby allowing activated sediments to be returned to storage on the slopes. The lower road traversing the area clear-cut during 1975 experienced the most severe mass movement and surface erosion. This road had been recently constructed and, as noted elsewhere (Fredriksen, 1 9 6 5 ) , this causes an i n i -t i a l l y high production of sediment. Continued maintenance of the road also resulted in increased erosion. Additionally, in this area of the clear-cut t i l l slopes are naturally oversteepened and susceptible to failure when moisture contents are high. One shallow debris avalanche during the snow-melt period occurred below the road on a slope of 3 9 ° ; a second occurred during the rain-on-snow event on a k0° slope independent of road effects. Observations in other areas show the greatest frequency of failure of weathered t i l l materials to be in the range 3 6 ° to ^ 0 ° (Bishop and Stevens, 196h; Swanston, 1969; O'Loughlin, 1972) . Above the h0° gradient soils are increasingly thin and less subject to significant mass movement activity. It has been demonstrated that the effect of roads in the clear-cut area has been to reduce the storm size required to exceed the resistance to both slope failure and surface erosion. The higher frequency storms are thereby rendered more important than in undisturbed areas. This study, however, has addressed only the short-term effects related to a limited range of hydrologic conditions. Over the longer term i t may be expected that road surfe.ce erosion would supply decreasing quantities of sediment and that, the slopes would adjust by failure to the oversteepened condition and disrupted drainage. (Gradual root decay, which may provide additional stress (Bishop and Stevens, I96U; Swanston, 1 9 7 0 ) , has not been investigated here.) The duration and character of this recovery would be dependent upon the particular combination of hydrologic conditions experienced and the management practices adopted. 7.4. Conclusions The central conclusions of this, study may be summarized as follows: 1) Colluvial deposits are extensive in the study area yet, particu-larly in alpine areas, mass wastage appears- to effect mainly a redistribu-tion of materials on slopes with limited supply of sediment to the channel system. Pleistocene and Holocene t i l l and minor a l l u v i a l cone sediments are more available for export and this is achieved most effectively by snow and debris avalanches, debris flows and f l u v i a l processes which transmit sedi-ment along the steep tributary channels below treeline to the main channel. Relatively l i t t l e a l l u v i a l material is stored in the banks of Wasp Creek i t s e l f . 2) During the snowmelt and the October storm periods the activation of sediment by f l u v i a l processes is thought to have been most important at the watershed scale. Storm runoff was a more effective agent of erosion than snowmelt runoff at a given discharge, however the greater duration of high flows during the snowmelt period caused rates of sediment transport to be 2-3 times greater than during the October storm period. 3) The estimated 10-year recurrence interval rain-on-snow event in November supplied 52 and 60 percent of the six month total yield from the lower and upper basins respectively. The high sediment transport rates during this event suggested that delivery of sediment to the channel net-work by slope mass movements was signifcant. 4) The low sediment transport rates of the summer period indicate that sediment produced in the 6 percent glacierized area has l i t t l e im-portance at the watershed scale.. 5) Road construction caused the continuous drainage network to be ex-tended by a factor of 2.5 and to drain directly exposed mineral s o i l covering 4-5 percent of the clear-cut area. Under-cutting of slopes and deflection of sediment and water over f i l l - s l o p e s accelerated sediment delivery to Wasp Creek by both f l u v i a l and mass movement activity. Debris avalanches were initiated at gradients of 39° and 40° within the clear-cut area. 6) For the six month study period sediment yields from the clear-cut area were at least 30 times greater than yields from the undisturbed area of the watershed. This can be attributed partially to the curtailment of erosion by a snow cover at. elevations above the clear-cut. During the October storm period sediment yields from the slopes below treeline could be isolated and rates of sediment production were about 8 times greater on the clear-cut than the forested slopes. This accelerated yield was caused almost entirely by road effects. 7 • 5 • Further work This study provides a description of sediment sources and their rela-tive contributions to basin yield which differentiates clear-cut and undis-turbed areas. To describe adequately the response of the undisturbed mountain watershed more detail i s required at the site and basin scales and, as for any satisfactory hydrologic record, a longer term of monitoring is indicated. It is f e l t that further work within a basin of more manageable size would be valuable. The study area should be of a scale and character that would allow: a thorough description of the s u r f i c i a l materials; detailed monitoring of the precipitation inputs and; inspection of the important sediment source areas during the course of an individual hydro-logic event of perhaps a 2^-hour duration. Accompanying studies of the importance of bed load sediment transport are also required. Bibliography Anderson, H.W. , 1970. Relative contributions of sediment from source areas and transport processes. In: Eroc. Symp. on Forest Land Use and Stream Environment, Oregon State Univ., Corvallis, p. 55-6.3. B.C. Department of Agriculture, no date. Climate of British Columbia: Tables of Temperature, Precipitation and Sunshine: Report for 1975 B.C. Ministry of the Environment, seasonal. Snow survey bulletins, Water Investigations Branch Bishop, D.N. and M.E. Stevens, 1964. Landslides on logged areas in south-east Alaska. 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Stream gauging techniques for remote areas.using portable equipment. Inland Waters Branch, Dept. of Energy Mines and Resources, Tech. Bull. No. 25 , 89 p. Dyrness, C.T., 1967. Erodibility and erosion potential of forest watersheds. In: Int. Symp. on Forest Hydrology, H.W.E. Sopper and H.W. L u l l (eds.), Pergamon Press, New York, p. 599-609 Embleton., C. and C.A.M. King, 1968. Glacial and Periglacial Geomorphology. Edward Arnold (Publishers) Ltd., London, 608 p. Ezekiel, M. and K.A. Fox, 1959- Methods of Correlation and Regression Analysis. John Wiley and Sons, Inc., London, 5^8 p. Foster, H.A., 1934. Duration curves. Am. Soc. C i v i l Engs. Trans. 99= 1213-1267 Fredriksen, R.L., 1965. Sedimentation after logging road construction in a small western Oregon watershed. In: Proc. Fed. Inter-Agency Sedimenta-tion Conf., 1963, U:S. Dept. of Agric. Res. Serv., Misc. Pub. No. 970, Washington, D.C., p. 56-59 Fredriksen, R.L., 1970. 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In: Mountain Geomorphology, H.O. Slaymaker and H.J. McPherson (eds.), Tantalus Research Ltd., Vancouver, p. 151-160 Ponton, J.R., 1972b. Hydraulic geometry of Green and Birkenhead Rivers: southwestern Coast Mountains, British Columbia. Unpub. M.A. dissertation, Univ. of B.C. , 77 p. Rapp, A., i 9 6 0 . . Recent development of mountain slopes in Karkevagge and surroundings, Northern Scandinavia. Geog. Ann. 1+2(2-3): 71-200 Rothacher, J., CT. Dyrness and R.L. Fredriksen, I967. Hydrologic and 'related.characteristics of three small watersheds in the Oregon Cascades. Pacific Northwest For. and Rg. Exp. Stn. , U.S. Dept. of A g r i c , Portland, 5h p. Ryder, J.M. ,.1972.. Pleistocene chronology and glacial geomorphology: studies in southwestern British Columbia. In: Mountain Geomorphology, H.O. Slaymaker and H.J. McPherson (eds.), Tantalus Research Ltd., Vancouver, p. 63-72 Schumm, S.A., 1973. Geomorphic thresholds and the complex response of drainage . systems. In: Fluvial Geomorphology, M.. Morisawa (ed.), \ n ' ~ " ' Publics, in Geomorphology, State Univ. of New York, Binghamton, p. 299 -310 Slaymaker, H.O., 197^. Rates of operation of geomorphological processes in the Canadian Cordillera. In: Geomorphologische Prozesse und Prozesskombinationen in der Gegenwart, H. Poser (ed.), p. 319-332 Slaymaker, H.O., 1977- Estimation of sediment yi e l d in temperate alpine environments. In: Erosion and Solid Matter Transport in Inland Waters, proc, of the Paris symp., I.A.S.H. -AVI.S.H. Pub. No. 122 Slaymaker, H.O. and T. Gallie, 1979- Mountain watershed solute sources: implications for nivation. Canadian Assoc. of Geographers Abstracts, Annual Meeting 79 , C.N. Forward (ed.), Univ. of Victoria Slaymaker, H.O. and R.E. Gilbert, 1972. Geomorphic process and land use changes in the Coast Mountains of B.C.: a case study. Symp. Int. de Geomorphologie, Liege, France, p. 269-279 Slaymaker, H.O. and H.J. McPherson, 1977. 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Ph.D. dissertation, Michigan State Univ. 206 p. Swanston, D.N., 1969. Mass wasting in coastal Alaska. U.S. Dept. of Agric. Forest Service, Research Paper PNW -83, 15 p. Swanston, D.N., 1970. Mechanics of debris avalanching in shallow t i l l soils of southeast Alaska. U.S. Dept. of A g r i c , Forest Service, Research Paper PNW-103, 17 p. Teti, P., in preparation. The va r i a b i l i t y of stream chemistry in a Coast Mountain watershed, British Columbia. Unpub. M.Sc. dissertation, Univ. of B.C., 185 p. Teversham, J.M., 1973. Vegetation response to f l u v i a l activity in the Lillooet River floodplain. Unpub.. M.A. dissertation, Univ. of B.C. Teversham, J.M. and 0. Slaymaker, 1976. Vegetation composition in relation to flood frequency in Lillooet River valley, British Columbia. Catena 3(2): 191-202 Tipper, H.W., 1971- Glacial geomorphology and Pleistocene history of central British Columbia. Geological Survey of Canada Bulletin 196, 89 p. & maps U.S. Water Resources Council, 1977- Guidelines for determining flood flow frequency. Hydrology Committee, Bulletin 17A, Washington, D.C. Washburn, A.L., 1973. Periglacial Processes and Environments. Edward Arnold (Publishers) Ltd., London, 320 p. Water Survey of Canada, annual. Surface Water Data British Columbia, Fisheries and Environment Canada, Ottawa Water Survey of Canada, 1977. Historical Streamflow Summary British Columbia to 1976. Fisheries and Environment Canada, Ottawa Williams, P.J., 1957- Some investigations into solifluction features in Norway. Geogr. Journal ,123: 42-55 Williams, R.C., 1964. Sedimentation in three small forested drainage basins in.the Alsea River basin, Oregon. U.S.G.S. Circular 490, 16 p. Woo, M. and H.0. Slaymaker,.1975• Alpine streamflow response to variable snowpack thickness and extent. Geog. Ann. 3-4(57A: 201-212 Woodsworth, G.J., 1977. Geology Pemberton map-area (sheet 92J). Geological Survey of Canada, O.F. 482 Wooldridge, D.D., 196H. Effects of parent material and vegetation on properties related to - s o i l erosion in central Washington. Soil Science Soc. Amer. Proc. 28(3): 430-432 Zeman, L.J. and H.0. Slaymaker, 1975- Hydrochemical analysis to discrimi-nate variable runoff source areas in an alpine basin. Arctic and Alpine Research 7(H): 3H1-351 66 P H O T O G R A P H S 67 68 Photograph k. View up Wasp Creek showing coarse colluvium on right and a l l u v i a l cone on l e f t . Photograph 6. View up Wasp Creek above the upper Wasp gauging station. Photograph 7. Road cut-slope in clear-cut area exposing glacial t i l l . Photograph 8. Gullying of road surface during snowmelt period. 71 A P P E N D I C E S Figure A.l. Wasp Creek seasonal hydrographs. Appendix B. Sample Analysis Procedure Table B,l.' Steps: 1. store the 275 ml samples in dark for 30 days before analysis; 2. draw off the top 100 ml into a tared evaporation dish and weigh; 3. withdraw a second 100 ml and dispose; k. agitate remaining fraction of sample containing settled suspended load sediment and then draw off into a second tared evaporation dish and weigh; 5. dry samples in oven at 90°C u n t i l a l l water has evaporated; 6. reweigh both dishes to determine weight of organic and dissolved and suspended mineral sediment; 7- burn off organic matter at 1+00°C for 1+5 minutes; and 8. reweigh both dishes to calculate weight of dissolved and suspended load mineral sediment. Appendix C. Suspended Sediment Data Table C.l. Suspended Sediment Yield Data Summary Period Yield Specific Yield (t/km2) upper Wasp lower Wasp upper Wasp lower Wasp lower. Wasp tonnes study perioo. tonnes study perioo. upper. Wasp . Snowmelt - May 8 to July 31 l 6 5 a 33 6oo. 37 7-7 18 2.3 Snowmelt - June 21 July 31 65 13 230 lit 3.0 7.0 2.3 Summer low flows -Aug. 1 to Sept. 30 3h 6.8 h3 2.7 1.6 1.3 0.8 Summer storm -Aug. 27 k.k 0.9 9-5 0.6 0.2 0 .3 1.5 October baseflow and stormflow .10 2.0 115 7.2 0.5 3.5 7.0 October 3 storm — 8 -5 . 0.5 0.3 October Ik storm — 2.6 0.2 0.1 October 17 storm 68 k.2 • 2.1 October 31 storm — 6.0b O.k 0.2 November k storm 300 6o 3k0 52 Ik 26 1.9 Total study period order - 500 100 1,608 100 23 kg 2.1 a. Estimate made to compare stations - flow record not continuous, "b- Estimate based on Figure 2k. Table C.2. Sediment Concentration Data for Wasp Creek Tributary Streams Stream Date Time Stage (cm) Sediment ••^ Concen-tration (mg/l) 11/5 22 27/8 0920 500 3/10 1020 71.'0 31 3/10 2020 68.5 235 5/10 0915 67.5 16 5/10 1115 68.0 -14 5/10 1515 66.5 260 5/10 1715 67.5 25 5/10 1835 68.0 64 9/10 1305 68.0 123 14/10 1830 68.0 338 16/10 1130 66.0 93 16/10 1315 66.0 256 16/10 2250 63.5 600 27/8 0920 200 27/8 1515 22,300 15/9 1105 63.0 694 3/10 1020 61.0 5,730 3/10 2020 58.O 14,200 5/10 0915 59.0 1,820 5/10 1115 59-5 855 5/10 1515 57.0 9,470 5/10 1715 58.0 2,640 5/10 1835 58.O 1,860 9/10 1305 59-0 717 14/10 1830 57-5 6,770 16/10 1130 58.5 4,790 16/10 1315 58.5 7,960 16/10 2250 59.0 14,100 27/8 1200 <1 27/8 1430 6 15/9 1305 2 3/10 1030 78.0 <i 5/10 1615 60.0 <l 9/10 1405 67.O <i 16/10 1250 62.0 <i 16/10 2310 63.0 2 17/10 1435 <1 4/11 1200 6 

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