SALMON RIVER TRI~UT ARIES

Transcription

1 SALMON RVER TR~UT ARES TERRAN STABLTY REPORT {T.5.1. LEVEL 'C'}; to accompany : Terrain and Terrain Stability Maps 82L.053, 82L.054, 82L.063, 82L.06~t and 82L.073 Prepared for Riverside Forest Products Limited Armstrong Divisionl Armstrong, BC and Forest Renewal British cdlumbia Kamloops Forest Re~ion Kamloops, BC! Prepared by i QU~ TERRA Environmental C9nsulting Ltd.. Comox, British Columbia and Terence Lewis Consulting in SOilr and Land Use Courtenay, BC March,1998 \..

2 TABLE OF CONTENTS NTRODUCTON... 3 OBJECTiVES... 3 PHySiOGRAPHy... 3 Bedrock Geology... 5 Climate... 6 METHODOLOGy... 6 Pretyping... 6 Fieldwork... 0 Map Production Mapping Constraints and Reliability... 8 SURFCAL MATERALS... 9 TERRAN STABLTY Stability Criteria Management mplications of Stability Classes... 0 LANDSLDE NDUCED STREAM SEDMENTATON CLASSES SURFACE EROSON POTENTAL CLASSES POTENTAL FOR SEDMENT DELVERY FROM SEDMENT EROSON SOURCES CLASSFCATON SUMMARY AND CONCLUSiONS REFERENCES APPENDX 1 : DETALED SECTON DESCRPTONS

3 l NTRODUCTON The Salmon River Tributaries project area consists of three distinct tributary drainages of the Salmon River, British Columbia. The Gordon, Silver and Hobson Creek watersheds flow into the lower Salmon River within 20 kilometers of Salmon Arm. BC i1and are designated 'Community Watersheds' for the local residents. Terrain and terrain stability conditions within the Gordon, Silver and Hobson Creek areas were assessed and mappedi at a scale of 1 :20,000 and are presented on the five TRM map sheets that accompany this report. The maps and report, together, provide background information to be used as an aid for planning and development purposes and are intended to guide future development actijity in the Salmon River drainage area. n particular, this report and the associated maps are i~tended to highlight areas in which more detailed on-site terrain stability assessments are warranted prior to road construction and/or logging activity. OBJECTVES The overall objective of this project was to collect, collate, and present data on: the surficial geology, geomorphology, terrain stability. landslide-induced ~tream sedimentation, surface soil erosion potential, sediment delivery potential and sediment drainage in the Silver, Hobson and Gordon Creek Community Watersheds. Specifically. a TerrJin Survey ntensity Level"C" Terrain and Terrain Stability report was to be produced and supportjd by both digital and hard copy terrain and terrain stability maps. These maps were to be Pfduced at a 1 :20,000 scale on provincial TRM bases (82L.053, 054,063,064, and 073). l PHYSOGRAPHY Located within the Salmon Arm Forest District of the Kamloops Forest Region, the project area consists of three tributaries draining British Columbia's nterior Plateau. Two of the drainages, Gordon Creek and Silver Creek, flow east some 7 kilometers before entering the Salmon River; while the Hobson Creek drainage. located on the eastern side of the Salmon River valley, flows some 5 kilometers to the northwest before feeding the Salmpn River near its mouth. These three drainages cover a total area of 7,800 hectares (figure 1). Morphologically the Silver and Gordon Creek drainages are :quite similar. They both initiate in the Spa Hills upland plateau of the Thompson Plateau physiographic subdivision (Roed, 1996; Fulton. 1974); are draped by materials from the last glacial and inte~glacial cycle and have been' 3

4 N i i o Skm,.. ", "" Helicopter Routes Q Study Boundaries Figure 1: Salmon River Tributaries ;7'- --- Creeks Location and Field Reliability Map Roads,-...", Truck and Foot Traverses 4

5 incised and oversteepened by numerous glacial outwash chtnnels. The Hobson Creek drainage. on the other hand, initiates in the Shuswap Highlands physiographic subdivision (Fulton, 1974) and incises nto a thick sequence of glacial till and glaciofluval outwash before entering the Salmon River Valley. Exposures of bedrock are rare in all of the drainages, however, where they i exist (Le. in the incised outwash channels of Silver and Gor~on Creek or in the upper reaches of the Hobson drainage) they tend to be moderately steep and provide relatively rapid runoff. The study area was shaped by numerous glacial and interglacial events, however, it was the latest glacial period, the Fraser Glaciation, which produced most or the thick upland tills, glaciolacustrine deposits and low valley, glaciofluvial sediments evident today. Ranging in elevation from approximately 360 meters above sea level (a.s.l.) in the 10wJr Salmon River valley to upper plateau and ridge elevations of approximately meters a.s.1. in the upper Silver Creek drainage, the local relief is over 1300 meters. Bedrock Geology The Silver Creek drainage is underlain entirely by Silver crerk Formation schists, quartzites and lesser limestones, marbles and amphibolites. The Gordon 9reek drainage is primarily underlain by intrusive granodiorite, granite; quartz monzonite, minor diorite, quartz diorite and gabbro; and to a lesser extent by Silver Creek Formation rocks in the northj The Hobson Creek drainage, on the! other hand, is a complex of Kamloops Group andesite, basalt flows, breccias and tuffs at its upper elevations. These rock types overlie Kamloops Group conglomerates. sandstones and shales evident in the mid-slopes of the drainage, while along the northern and western flanks of the drainage there is a dominance of intrusive granodiorite. grd1ile and quartz monzonite (Owsiacki, 1995). : : The local dioritic, gneissic and schistic lithologies are found fhroughout the tills of the Gordon and Silver Creeks drainages (Appendix 1) and it is this country rick which is largely responsible for the predominantly coarse texture of the material. The silty texture of the Hobson Creek tills are likely a function of the fine textured basaltic and sedimentary sou~ce rock found in the upper Hobson i drainage. However, large sub-angular granodioritic clasts (likely from the northern exposure of granodiorite) and a north to south trending Fraser ice flow (ffulton et a., 1974), suggest that the Hobson Creek fine textured tills may also be the result of rer' orked glaciolacustrine sediments from the ancestral Shuswap Lake. 5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30