DETAILED TERRAIN ST (TSIL C) HUMMINGBI

MARA CREEK WA

Submitted to

ILITY MAPPING CREEK AND RSHEDS

Riverside Forest P oducts Lumby, B.C

Terratech Consulting Ltd. Salmon Arm, B.C.

Date: 26 March 1999 File: 425-11

F.R. Smith, G.I.T. Project Geologist

C.D. VanBuskirk, P.Eng., P.Geo. Project Review Engineer

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Riverside Forest Products 2 26 March 1999 File: 425-11 Hummingbird Creek and Mara Creek - TSIL C

TABLE OF CONTE~TS Executive Summary ................................................................................................................................... 4

1.0 IN'TRODUCTION ••••.•••.••.•••••••••••••••.••••.•...•.••.••••••.••.•..•.•••••••••••.•..••..••••••••••••..••••••.•••••••..••..•...•••.•••• 6 1.1 Scope ...................................................................... J •..........•••..•..............•..•••.............•.•••..•.••..... 6 1.2 Report Limitations .................................................. J, •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 6

2.0 I PHYSICAL SETTING ••••.••••••.••••.••.•...•..•••.•.•.••••.•••.•...•••.••.•••••••••......•.•.•••••••.•••..•..••.•••.••••.••••.••...... 7 2.1 Topography and Climate ......................................... l ................................................................. 7 2.2 Bedrock Geology ..................................................... ~ ................................................................. 8 2.3 Quaternary Geology ................................................ r ................................................................. 9

3.0 \ SURFICIAL MA. TERI.A.LS .•.•.•••••.•.•..•.•.•.••.•.••••••.•.•..•.••..••••.••.••..••.•••..•••••.•..•..•••...•••••.••..•.•...•....• 11 3.1 Colluvium (C) ......................................................................................................................... 11 3.2 Fluvial Materials (F) .............................................................................................................. 12 3.3 Glaciofluvial Materials (FG

) ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 12 3.4 Glaciolacustrine Materials (L G) ............................................................................................. 13 3.5 Morainal (Till) Materials (M) ................................................................................................ 13 3.6 Organic Materials ................................................................................................................... 14 3.7 Bedrock ................................................................................................................................... 15

4.0 GEOMORPR:OLOGICAL PROCESSES ••••••.•••••••.•.•••.••••••.••••••.••••••.•••..•••••••..••.....••••••••..••.••.• 16 4.1 Rapid Mass Movement (-R) ................................................................................................... 16 4.1.1 Rockfall (-R"b, -Rb) ........................................................................................................... 16 4.1.2 Rockslides (-R" r, -Rr) ......................................................................................................... 16 4.1.3 Debris Slides (-R"s, -Rs) ..................................................................................................... 16 4.1.4 Debris Flows (-R"d, -Rd) .................................................................................................... 17 4.2 Slow Mass Movement (-F) ......................... ; ........................................................................... 18 4.2.1 Slump-Earthflow (-F"x): Upper Mara Creek ...................................................................... 18 4.2.2 Rock Slump (-F"m, -Fm): Upper Mara Creek .................................................................... 19 4.3 Gully Erosion (Gullying) (-V) ................................................................................................ 19

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4.4 Seepage (-L) ............................................................ T ............................................................ 20

METHODS ...•..•••.•.........•••••........••..•••.•.•........••••...•..•.•...• f ............................................................. 20 5.1 Pre-Typing Phase: Terrain and Slope ..................................................................................... 20 5.2 Fieldwork Phase ..................................................................................................................... 21 5.3 Edit Phase ............................................................................................................................... 22 5.4 Soil Drainage .......................................................................................................................... 23 5.5 Slope Stability (Terrain Stability) .......................................................................................... 25 5.6 Erosion Potential .................................................................................................................... 27 5.7 Potential Sediment Delivery to Major Streams ...................................................................... 28 5.8 Mapping Reliability ................................................................................................................ 29

6.0 RESULTS AND MANAGEMENT IMPLICATIONS ............................................................. 30 6.1 Slope Stability ........................................................................................................................ 30 6.2 Erosion Potential ................................................................................................................... 32 6.3 Potential Sediment Delivery to Major Streams ...................................................................... 33

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Riverside Forest Products Hummingbird Creek and Mara Creek - TSIL C

3 26 March 1999 File: 425-11

7.0 0 FF -SITE RISKS ......•......•..........•.............................•.•..•..•.....•..•..........••......•....•........................ 34 7.1 Phase I - B~ckg~oun.d Work ................................. "!" ................................................................ 35 7.2 Phase 2 - Hlstonc Alrphoto Study ......................................................................................... 36 7.3 Phase 3 - Field Assessment of Forested Valley Slopes .......................................................... 37 7.4 Phase 4 - Field Assessment of Creek Channels ..................................................................... 39 7.4.1 Upper Mara Creek ............................................................................................................... 39 7.4.2 Lower Mara Creek .............................................................................................................. 41 7.4.3 Hummingbird Creek ............................................................................................................ 42 7.5 Phase 5 - Review of Climatic Data ....................................................................................... .43 7.6 Phase 6 - Assessment of Water Well Log Data .... ~ ............................................................... .44 7.7 Conclusion .............................................................................................................................. 45

8.0 HARVESTING ROAD CONSTRUCTION AND MAINTENANCE SUGGESTIONS ........ 46

9.0 SUMMARY AND SUGGESTIONS FOR FUTURE WORK .................................................. 47

Figure 1 - Location Plan ................................................................................................................. (following page) ... 6 Figure 2 - Traverse Map ............................................................................................................... (following page) ... 22 Figure 3 - Average Monthly Precipitation ............................................ ~ ....................................... (following page) ... 43 Figure 4 - Hummingbird Creek Watershed .................................................................................. (following page) ... 46

Table 1 - Dates of Fieldwork, Personnel and General Areas Traversed ..................................................................... 22 Table 2 - Soil Drainage Classes and Typical Terrain Units and Soils Associated with Each Class ........................... 24 Table 3 - Slope (Terrain) Stability Classification (after Ministry of Forests, 1995) ................................................... 25 Table 4 - Preliminary Stability Mapping Classification Derived from I1andslide Inventory Data ............................. 26 Table 5 - Final Terrain Stability classification for the Hummingbird Cteek and Mara Creek Study Area ................. 27 Table 6 - Surface Erosion Potential Classes and Typical Terrain AssoJiated with Each Class ................................. 28

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Table 7 - Classification for Surface Erosion Potential Classes ................................................................................... 28 Table 8 - Criteria Used to Assess the Potential for Sediment Delivery to Major Stream Channels ............................ 29 Table 9 - Management Implications Associated with Slope Stability Classes ........................................................... 32 Table 10 - Management Implications Associated with Erosion Potentirtl Classes ...................................................... 33 Table 11 - Management Implications Associated with Potential Sedim~nt Delivery to Major Streams ..................... 34

References .............................................................................................. : .................................................................... 48

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Riverside Forest Products 4 Hummingbird Creek and Mara Creek - TSIL C

EXECUTIVE SUMMARY

26 March 1999 File: 425-11

The Hummingbird Creek terrain stability mapPinJ project was conducted in the summer of 1998 with fmal map and report preparation in the ~nter of 1998/99. The project was undertaken on behalf of Riverside Forest Products (Lumoy Division) with funding provided by Forest Renewal B.C. The maps accompanying this rep6rt provide ratings for slope stability, surface erosion and potential sediment delivery to streams ~hich are intended to be used to assist forest development applications. In addition to terrain m~pping, fieldwork also concentrated on establishing the off-site risk posed by debris slides and flows occurring within the study area. The consideration of off-site risk in association with the tefain stability mapping was included in this study as a result of the 1997 debris flow in Hummingbird Creek. The debris flow, which initiated as a debris slide downslope of Ashton-MarA FSR (Skyline Road) and a previously logged area, damaged a number of homes in the communi~ of Swansea Point.

The Hummingbird Creek and Mara Creek latershedS are located within the Hunters Range south of Sicamous B.C., within the Salmqn Arm Forest District. Both streams flow westward merging near the apex of a large fan just pHor to flowing though the community of Swansea Point and into Mara Lake. The mapping co~prises approximately 3954 hectares, which range from the gently sloping fan of Swansea pOlnt at 348 m elevation to the rugged cirques at the height of the range at Mount Mara at 2194 m The Hunters Range forms part of the Shuswap Highlands' and are characterized by coarse-grain d metamorphic rock, which has been heavily glaciated. Most of the soil types within the study ea are derived from the local bedrock and as such are generally sandy. In addition to the bedroc ,till deposits dominant the study area with glaciofluvial and glaciolacustrine deposits being quite are.

The valley portions of larger streams contain stee bedrock slopes and areas of active rockfall. Larger rockslides are rare however; two large ~ents have been identified within the area. The largest event, below the Skyline Road is infe d to have occurred prior to the last glaciation. Most of the roc~slide debris has been removed however; large blocks were noted in Mara Creek below the scarp zone and some smaller roc ides have occurred in the headscarp area of this slide. The second rockslide was identified id the Mara Creek drainage above the 1300 m elevation. This slide has rotated and slid to the south changing the course of Mara Creek. Smaller areas of active rockfall (steep bluffs and areas of smaller rockslides were noted, however these areas are not expected to affect fores management decisions because of their locations. The till-covered slopes within the pr -glacial rockslide headscarp below Skyline Road appear to be prone to debris slides.

The mapping methods consisted of three ph es: 1) pre-typing of airphotos; 2) fifteen man-days of road and field traversing; and 3) r orting and editing. The work and maps were subjected to several reviews including internal d external reviews, and review by FRBC. The terrain stability mapping polygons were transfe red from 1994, 1: 15,000 airphotos to 1 :5,000 scale maps by Riverside Forest Products using mo o-restitution transfer. The stability class ratings were derived using a system developed by T rratech (1994) and modified for the study area. The surface soil erosion potential classes we e derived based mostly of the soil textures and steepness of the terrain for the given polygon. Potential sediment delivery to major streams is assigned based on the steepness of the terrain in c njunction with the surface sediment

Riverside Forest Products Hummingbird Creek and Mara Creek - TSIL C

5 26 March 1999 File: 425-11

source, topography and proximity to stream channels within the polygon. In total, 115 ground sites were visited resulting in 67% of the mapped polygons being checked in the field. Traverses did· concentrate on the steep terrain below Skyline Road, but also included traverses of most of Mara and Hummingbird Creek channels.

Fieldwork, airphoto mapping and historical airphoto study found natural landslides to be rare within the study area. The most vulnerable area to landsliding, with regards to off-site risks, occurs immediately below Skyline Road. Several other potentially unstable terrain units were identified adjacent to the Hummingbird Creek channel however, most of these areas are steep and difficult to access such that they are not likely to be areas proposed for forest development.

This study was undertaken with the assumption that the area was conducive to regular landsliding and subsequent debris flows activity (EBA, 1998a and Inter-Agency, 1997). However, field survey results and air photo studies were uriable to confirm the presence of other large debris slide sites. In addition, follow-up stream channel surveys of Hummingbird and Mara Creeks indicate that the return period for large debris flows is not likely as short as previously postulated. The evidence for large debris flows within Mara Creek is lacking and

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given the large timber, (estimated to be greater than 300 ~ears old) growing along the channel banks, the return period for debris flows in this area is ekpected to be in excess of 300 years. The 1997 debris flow within Hummingbird Creek resulted in extensive channel scour, which likely removed all signs of previous debris flow actiyity. However, field surveys found no evidence of large landslides having impacted on the stream within the last 120 years (the date of the last major fire within the watershed). Impact scars and other evidence of older debris flows were not found within the Humnlingbird Creek channel. I

Additional evidence, in the form of well log data from drilling performed on the fan, I

suggests that Swansea Point fan may have formed mostly through fluvial processes and not through mass-wasting in the fornl of debris flows. Precipitation values for the area also suggest that the climatic conditions. that lead to the 1997 event w~re unprecedented with high levels of snow melt coupled with a very wet spring and an extreme rainfall event.

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Given all of the data obtained to date for the Swansea Point fan area, it is judged that the debris flow history on the fan and the relative level of risk Ito private property and inhabitants of these properties is uncertain. However, the airphoto studY,1 field surveys and analysis of weather station data, suggest that the likelihood of debris flows occurring within the Hummingbird Creek channel is likely lower than previously reported (EBA, 1998a).

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Presently, there is a lack of evidence for recent debris flow events (other than the 1997 event) having itnpacted on the fan area. As such, it is proposed that future efforts to determine the debris flow history (return-period) concentrate on uncovering evidence of older debris flows on the fan by digging several test pits. Test pits may uncov~r old soil horizons and buried woody debris, buried by past debris flows, that could be dated to, determine the age of historic debris flows. In addition, test pits would hopefully reveal enough I. information about the stratigraphy to determine the origin of the sediments on the fan. I

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Riverside Forest Products Hummingbird Creek and Mara Creek - TSIL C

6 26 March 1999 File: 425-11

1.0 INTRODUCTION I

This report has been prepared as part of a terr.ain stability mapping project of the Hummingbird Creek and Mara Creek watersheds, whi~h lie within the Salmon Arm Forest District. The report is accompanied by four 1:5,000 scale:maps of the Hummingbird-Mara study area. Hummingbird Creek and Mara Creek are located approximately 12 km south of Sicamous, B.C. (Figure 1). Mara Creek enters Hummingbird Creek just above the apex of a large fan deposit. Hummingbird Creek flows across the fan deposit and enters Mara Lake. The community of Swansea Point, a development of s~gle family, seasonal and permanent residences, is located on the fan. The study area as mapped is 3954 ha in size and comprises

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most of TRIM sheet 82L76, 82L86 and 82L87. Detailed (5 m contour interval) topographic maps were prepared for a significant portion of ~I. s area, at a scale of 1 :5,000 by Silvatech Consulting Ltd. in preparation for this study. e study area boundary was placed by aerial photographic interpretation of 1: 15,000 scale photo (1994) with ground checks in critical areas. There is generally good agreement between the warershed boundaries as interpreted from the topographic maps and the airphoto work.

This mapping has been done using standard metho~s of aerial photographic interpretation and field observations. The study area has been divided into a series of polygons with each depicting a relative~y homogeneous area of terrain (surficial materials and geomorphological processes), slope (as classes), soil drainage, slope stability,turface erosion potential and potential sediment delivery to major stream channels.

This report is intended to supplement the infonn~ ion presented on the terrain stability map. The report describes and reviews the geology ~d geomorphology of the study area, the characteristics of surficial materials and geomorpholo$ical processes that are present in the study area, the mapping methodology and map reliallility, and includes a discussion of management implications and debris flow history.

1.1 Scope

This report and maps have been produced as a port on of the Forest Renewal BC Project Contract #TOM98242 101293, entitled, "Hummingbi ara Creek Watershed TSIL C Mapping". This project was undertaken by Terratech onsulting Ltd. for Riverside Forest Products Ltd., Lumby Division.

1.2 Report Limitations

The information presented in this report and on ~ accompanying map is intended for forest development applications only. The slope stability, $rface erosion and potential sediment delivery ratings are not considered appropriate for other lantl use applications. The identification and classification of terrain units and the assignment of ra ings to derivative variables has been done using the standard methods employed by professional terrain mappers in British Columbia. The level of reliability associated with this mapping is onsistent with other Terrain Survey Intensity Level (TSIL) C studies that rely on aerial p otographic interpretation and field observations. The interpretations are largely judgme tal and heavily based on aerial

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