Gold Creek / Rock Creek Inspections Monitoring, Road Deactivation and Environmental Road Maintenance Planning Risk Analysis

Transcription

1 2006 FIA Gold Creek / Rock Creek Inspections Monitoring, Road Deactivation and Environmental Road Maintenance Planning Risk Analysis Prepared for: Prepared by: Forsite Consultants Ltd. #330 42nd St SW Salmon Arm, BC V1E 4R1 Tel: (250) Fax: (250) October 31 st, 2006

2 Table of Contents TABLE OF CONTENTS...II 1.0 INTRODUCTION SCOPE OF ASSESSMENT CONVENTIONS FOLLOWED OFFICE AND FIELD REVIEW TERRAIN CHARACTERISTICS AND GEOMORPHOLOGICAL PROCESSES RISK ANALYSIS PROCEDURE OBSERVATIONS ANALYSIS AND RECOMMENDATIONS GOLD CREEK SITE A (REACH 0139) GOLD CREEK SITE B (REACH 2902) GOLD CREEK REACH GOLD CREEK REACH 0134 / GOLD CREEK REACH GOLD CREEK REACH GOLD CREEK REACH 4700 / GOLD CREEK REACH GOLD CREEK REACH 6207 / GOLD CREEK REACH GOLD CREEK REACH GOLD CREEK REACH GOLD CREEK REACH GOLD CREEK SITE GOLD CREEK SITE GOLD CREEK SITE GOLD CREEK SITE 9 / ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE ROCK CREEK SITE X ROCK CREEK SITE MOSQUITO CREEK (SITE 1) HONEYMOON BAY (SITE 2) MOMICH LAKE SITE MOMICH LAKE SITE CLOSURE...78 ii

3 LIST OF FIGURES Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Location Key Map..6 Gold Creek Sites..... attached Rock Creek Sites..... attached Site 0139 detail Site R-9, Branch D Road detail...55 Site R-11, Branch C Road detail Mosquito Creek Site 1 detail...70 iii

4 1.0 Introduction Forsite Consultants Ltd. (Forsite) was retained to carry out post work inspections, monitoring and prescriptions for sites in the Rock Creek, Gold Creek, Mosquito Creek, Marjory Creek and Momich Watersheds. (see figure 1 for a key map).these sites have had previous work and/or inspections completed. The objective of this report is to address remaining concerns and to establish closure on these sites. 1.1 Scope of Assessment The purpose of this report is: To describe conditions at specific assessment sites and where such conditions may have a specific impact. To provide a Risk Analysis of the potential environmental impacts of the assessment sites To recommend site-specific actions to reduce the likelihood of further environmental impacts. 1.2 Conventions Followed Soil classifications and landform descriptions use terminology defined in the publication Terrain Classification System for British Columbia B.C. Ministry of Environment Slope gradient classification follows the convention defined in the publication Terrain Classification System for British Columbia B.C. Ministry of Environment Gentle 5-27% Moderate 28-49% Moderately Steep 50-70% Steep > 70% Page 4

5 2.0 Office and Field Review Prior to and following the field assessment the following materials were reviewed: Stereo air photo coverage of the study area (~1:20,000 scale) 1:20,000 digital design file maps Geologic Survey of Canada Bedrock Geology Mapping located on Ministry of Energy and Mines MapPlace webpage Gold Creek Level 2 Fish Habitat Assessment (Silvatech 1995) Level 2 Road Condition Assessment 9silvatech 1996) Detailed Proposal Zone 1 and 2 Works Phase (Silvatech 1996) Level 2 Stream Channel Assessment (Silvatech 1998) Bioengineering as-builts (Silvatech 1998) Watershed Restoration Plan (Silvatech 2001) Road Assessment 9Silvatech 2004) Fieldwork was completed by Peter Weisinger M.Sc. GIT of Forsite on August 14, 15 th and 18th-19 th See Figure 2 for a map of the study area and location of the assessment sites. A helicopter over-flight of the Gold Creek sites was completed on August 11 th Attending were Peter Weisinger M.Sc. GIT and Rod Williams P.Geo of Forsite. The helicopter overflight focussed primarily on previously identified sites, but observations of general watershed condition and sediment sources and other potential problem areas were noted. Rock Creek Environmental Maintenance Project Plan (Summit 2003) Road Assessment (2004) Environmental Maintenance Projects (Mosquito, Honeymoon, Marjory) Fieldwork was completed by Peter Weisinger M.Sc. GIT of Forsite on August 1-4 th, See Figure 3 for a map of the study area and location of the assessment sites. Additional field review of the Rock Creek site R11 was conducted on October 20, Page 5

6 Birch Island Vavenby Rock Creek Sites (Figure 3) Mosquito Creek Rock Creek Honeymoon Bay Momich Lake Seymour Arm Blucher Hall Gold Creek Sites (Figure 2) St. Ives Gold Creek Magna Bay Anglemont Adams Lake Celista Eagle Bay Sun Peaks Squilax Scotch Creek Lee Creek Blind Bay Sorrento Notch Hill Balmoral Solsqua Sicamous Figure 1 Key Map Annis Page 6

7 3.0 Terrain Characteristics and Geomorphological Processes 3.1 Rock Creek / North Adams Lake Sites The sites in the Rock Creek area are generally located either in the valley bottoms, or on mid slopes. Soils encountered were generally either sandy tills or sandy glaciofluvial and fluvial materials. These soils wee found to have low cohesion and were easily eroded. The upper portion of Rock Creek is on a wet rolling plateau, with the creek becoming incised in its lower reaches. Instability in this area was generally limited to sediment production due to drainage diversions as a result of road construction. In the incised lower draw, drainage diversions leading to gentle over step types of landslides were found to be of concern. 3.1 Gold Creek Watershed The sites in Gold Creek are located primarily on the Adams Plateau. Soils encountered ranged from sandy glaciofluvial materials in draws and in the Gold Creek Draw, to weathered colluvial rubble and tills on the flat upland areas. The sides of the Gold Creek watershed are steep, with significant relief. Gentle-over-steep types of failures are associated with a number of these sites, and pose the highest hazard. Concerns were primarily drainage diversions which had led to instability downslope, or were directly related to minor sediment production adjacent to streams. 4.0 Risk Analysis Procedure This report provides a qualitative evaluation of hazards associated with sites previously identified in the study area, a description of the potential consequences, and recommendations to reduce the hazards and associated risks. Acceptance of the qualitative consequence values and the subsequent risk analysis is the responsibility of the licensee or the regulatory authority, as is the determination of acceptable risk and the decision to proceed with any action based on that risk analysis. Consequence ratings have been estimated based on standard practice and identification of downslope resources in the area. The main streams in the study area (Gold Creek and Rock Creek) are fish bearing. Sediment delivery to a fish stream is considered a moderate to high consequence dependent on the magnitude of the hazard and location of the identified site in relation to the stream. Page 7

8 5.0 Observations, Analysis and Recommendations 5.1 Gold Creek Site A (Reach 0139) Location: Gold Creek Reach 1039, Map Reference: G-0139 Previously identified issues: The old road location was constructed across a slide with sediment from road surface and fillslope eroding, depositing material in the stream. (Silvatech 1998) Restoration undertaken: The road has been relocated and the original road deactivated. The portion of road adjacent the slide area has been recontoured and grass seeded as per Option A in the Silvatech (1998) Report. The remainder of the road has been deactivated through cross ditching. Observations: The road section located directly downslope of the slide area is experiencing some streambank erosion (see photo plates and ) Although grass seeding has been successful on the open slopes reducing surface erosion, lateral erosion of the streambank is continuing, with sediment mobilising events likely occurring during periods of peak flow. The channel appears to be migrating laterally towards the former road location, being confined by bedrock on the opposite (right) side. Severity of erosion has decreased since remediation measures have been implemented. Risk Analysis: There is judged to be a high likelihood of sloughing of road fill materials and ongoing delivery (with peak / seasonal flows) of sediment to Gold Creek at this site, on the order of 1-2m 3 annually. This is considered a moderate consequence. The risk is therefore high. Prescription: Place large diameter Rip Rap along ravelling cut bank to slow lateral stream erosion Revegetate with deciduous species adjacent to stream. Plant coniferous species on rehabilitated road surface and on old slide area Page 8

9 Photo Aerial view of Reach 0139 Photo Eroding streambank Reach 0139 Page 9

10 Figure 4 Site 0139 detail Page 10

11 5.2 Gold Creek Site B (Reach 2902) Location: Gold Creek, Reach 2902, Map Reference: G-2902 Previously identified issues Fillslope failure and unstable cutslopes in fine grained soils contributing sediment to stream (Silvatech 1998). Restoration undertaken Road has been relocated, old road pulled back and hydroseeded / bio-engineered. Observations The road has been bypassed, and the site has been fully recontoured. Grass seeding was partially successful, having taken on the recontoured road, though not on the upper portion of old cutslopes (Photo plate 5.2.1). Bio-remediation attempts were unsuccessful (Photo 5.2.3) and the site has not yet revegetated. The former bridge (log box?) at the stream crossing has been removed, though cribbing was left in place. The stream appears to be stable. Only minor amounts of sediment from the old road location appears currently to be entering the stream at high streamflows, where some material may be entrained at the crossing. Risk Analysis There is judged to be a moderate likelihood of sediment producing events (small surficial slides, rilling) at this site. This would result in a small amount (< 5m 3 ) of material mobilised at the stream crossing during a peak flow event and from small erosional events on the unvegetated upper cutslope. This would be considered a low consequence. The risk is therefore low. Prescription Bioengineering of slopes recommended to further stabilise the area as per (Silvatech 1998) Report. Consider planting area with coniferous species Hand grass seed the remaining open slopes Page 11

12 Photo Deactivated road at reach 2902 Photo Wooden cribbing left in place, minor sloughing of old road fill. Page 12

13 Photo Evidence of unsuccessful bio-remediation. Page 13

14 5.3 Gold Creek Reach 0106 Location: Gold Creek, Reach 0106 Map Reference: G-0106 Previously identified issues Severely aggraded active channel, deposition area/ sediment wedge above bedrock constriction. Restoration undertaken None reported. Previous prescriptions suggest monitoring and controlling sediment input from upstream. Observations The stream is heavily aggrading, with multiple channels and significant lateral movement where the channel is not confined by bedrock. Numerous log jams were noted along this reach. There is no sign of direct connectivity to the road system. Problems in this area are symptomatic of overall hydrologic conditions in the watershed. Risk Analysis No risk analysis was performed at this site. A risk analysis for this reach would be a function of hydrology of entire watershed, which is beyond the scope of this study. Prescription Continue to monitor drainage issues in the watershed / control sediment sources in previously developed areas. Photo Aerial view of reach 0106 showing severe aggradation. Page 14

15 5.4 Gold Creek Reach 0134 / 7902 Location: Road [~2.5 km] Map Reference: G-0134 Field Identification: Previously identified issues A spur road has diverted flows from upslope leading to slope failures below (Silvatech 1998). Restoration undertaken Natural drainage patterns have been restored, spur and branch roads deactivated. Observations The upper spur road has been thoroughly deactivated with numerous cross drains. The natural flow of the main drainage path has been restored. Large cross ditches effectively prevent further diversion on the upper spur road. Some intercepted small flows on the upper spur have been diverted to cross drain culverts on the 100 Road. The crossing at the upper road is well armoured, with some very minor sediment input from ravelling road fills. Some drainage intercepted by lower road and 600CMP at 218. There is evidence of previously large flows in the ditchline on the lower road. The lower stream crossing at 220 is eroding some fill material. Aerial observations the slide has partially naturally revegetated. The site is likely still a significant sediment source as it is adjacent to Gold Creek. Bio-engineering and seeding should be carried out as per the prescription in Silvatech (1998) report. Risk Analysis As the natural drainage patterns have been restored, there is judged to be a low likelihood of initiating another large landslide which could impact Gold Creek at this site. Such a slide would result from drainage diversion and concentration in a gentle over steep type of scenario as happened with the previous slide. This would result in significant input of sediment to Gold Creek, and result in long-term sediment source production. This is considered a high consequence. The risk is therefore moderate There is a moderate to high likelihood of further sediment mobilisation on the old slide path, with sediment delivery of <25m 3 to Gold Creek. This would result in input of a small to moderate (to 25m 3 ) amount of sediment to Gold Creek, which would be considered a moderate to high consequence. The risk is therefore moderate to high. Prescription If the 100 Road is to continue to remain operational, monitor exiting culverts and restoration efforts on the road to ensure continued functioning. If no future use of the road is anticipated, permanent deactivation should be considered (i.e. pull all culverts) Revegetate slide as per Silvatech (1998) bioremediation prescription. Page 15

16 Photo Stream crossing Page 16

17 Photo Lower portion of slide entering Gold Creek Page 17

18 5.5 Gold Creek Reach 1901 Location: Tributary 250m upslope of Reach 1901 of Gold Creek Map Reference: G-1901 Previously identified issues Collapsed bridge on old road has diverted flows south along road, through forested area and into Gold Creek. Deposition of materials in forested area. Restoration undertaken Collapsed culvert has been removed, berm constructed and planted with dogwood. Observations Observation from helicopter overflight revealed no further disturbance of tributary channel. Risk Analysis There is judged to be a low likelihood of a future breach of the stream channel as a result of the old road location, which could result in minor sediment deposition into gold Creek. This is considered a moderate consequence. The risk is therefore low. Prescription None required Page 18

19 5.6 Gold Creek Reach 3801 Location: Gold Creek Reach 3801, Map Reference: G-3801 Field Identification: 203 Previously identified issues Large log jam/pile at bottom of slide, perched fills at deactivated road crossing ( 203). Restoration undertaken Road crossing has been deactivated. Upper road at initiation point of failure has been deactivated. Observations Crossing at lower road still has some minor perched fills present, though the crossing has been sloped back and rehabilitated. Current flow is crossing over old road surface in a self-armoured channel no sign of recent disturbance. Road surface is revegetating (grass seeding effective). Some perched fills are still present but most material appears to have been pulled back in critical areas. Sediment mobilisation is not likely to be a catastrophic failure but rather a progressive erosion of fill materials. Risk Analysis There is judged to be a moderate likelihood of a mobilisation of road fill materials, resulting in transport of fine sediment (<5m 3 ) to the tributary of Gold Creek. This is considered a low consequence. The risk is therefore low. Prescription No further work required / continue to monitor Page 19

20 Photo Stream crossing old road. Page 20

21 5.7 Gold Creek Reach 4700 / 4601 Location: Road upslope of Reach 4700, and bridge crossing of Reach 4601 Map Reference: G-4700 / G-4601 Field Identification: 122 Previously identified issues Creek diverted by old skid trail and mainline. Failure 300m below mainline and channelized debris flow into Gold Creek. Restoration undertaken Natural drainage was restored on mainline, 500mm culvert installed. Failure was grass seeded. Observations The slide headwall and main portion of the slide is revegatating and appears to be stabilising some sidewall failures are taking place on the channelized portion of the slide. Some coniferous vegetation is starting to reestablish. Material had been scoured to bedrock in track of the slide, and remobilisation is unlikely. On the eastern side of the headwall, there is significant flow emanating at the base, with soil materials perched upslope. There remains the possibility that further headward erosion will continue. The area upslope of the slide ( 121) and to the south of the main slide have a number of old revegetated slide scarps present. At 122, the road cuts through a rock outcrop, and as a result the ditchline is very shallow and prone to overflowing onto the road. Evidence of water flow downslope suggests that this may be a point at which some water had previously been diverted to the slide. The drainage diversions identified in the Silvatech 1998 report have been restored. Risk Analysis Drainage diversions upslope have been repaired, however natural drainage is seeping from the headwall of the scarp. There is judged to be a low to moderate likelihood of further sliding of material at the landslide site, resulting in delivery of <25m 3 of material to the reach and a moderate likelihood of delivery to Gold Creek. This is considered a moderate consequence. The risk is therefore low to moderate. Prescription Monitor and maintain ditchline on road / Improve ditchline through 117 Allow slide area to revegetate naturally. Page 21

22 Photo View up headwall of slide Photo View down slide path Page 22

23 5.8 Gold Creek Reach 6402 Location: Spur in Block 81-1 Map Reference: G-6204 Field Identification: Previously identified issues Stream diverted by skid trail. Restoration undertaken Stream restored to original channel. Roads and trails deactivated. Observations The point of diversion by the old skid trail has been restored and the stream is now flowing in what appears to be the original channel. The diversion has been blocked by a vegetated berm, however water is seeping through this berm and still flowing down the skid trail. There is a low to moderate likelihood that a large streamflow could ovetop the structure and again be diverted by the skid trail. In some areas the skid trail is at a lower elevation than the natural stream draw. 128 is a low point on the trail. Some seepage is emanating on the road at 124. This appears to be an area where some of the stream flow is diverted, primarily as subsurface flows, to the road. There is no cross drain structure here, and water flows down the ditch to pond on the high side of the road at the junction of the deactivated road downslope, resulting in wet road conditions. There is a 400mm CMP which takes the flow at 126 across the mainline. Risk Analysis There is judged to be a low to moderate likelihood of a stream avulsion at the previous point of diversion, resulting in flows being diverted down the skid trail, entrainment of fine materials at the road crossing and subsequent delivery to the stream system to the north. This would also result in the loss of a small amount of productive area. This is considered a low to moderate consequence. The risk is therefore low to moderate. Prescription Upgrade berm by hand, increasing height by ~0.3m, and width by about 1m, with locally available rock. Monitor berm on skid trail for future avulsions. Improve ditchline to 126 (400mm CMP), clean sump. Page 23

24 Diverted stream flow along skid trail and ditchline Natural stream channel Photo Aerial view of site Photo seepage onto road Page 24

25 Photo There is still some minor drainage along the old skid trail (left). (photo taken from top of berm.) Page 25

26 5.9 Gold Creek Reach 6207 / 6208 Location: Block 81-1 Map Reference: G-6207 / G-6208 Field Identification: 126 Previously identified issues: (6207) Stream diverted by skid trail, no riparian buffer maintained through block. (6208)Stream diverted by skid trail causing twin channels. Poorly defined channel at mainline crossing, some flows follow ditch south. Restoration undertaken (6207) Stream restored to original channel, roads and trails deactivated. (6208) Culvert entrance and ditch grading improved, channel definition improved near culvert Observations Streams have been restored to original flows. Skid trail that had been an issue on 6207 is revegetating. Culvert functioning well. Risk Analysis There is judged to be a low to negligible likelihood of further diversions at these two sites. Prescription No further works required Photo Culvert 6208 Page 26

27 Photo Reach 6208 Page 27

28 5.10 Gold Creek Reach 7001 Location: Reach 7001 Map Reference: G-7001 Field Identification: Previously identified issues Creek was temporarily diverted by skid trail, deposition at culvert inlet. Restoration undertaken Creek restored to natural channel, inlet cleaned. Observations The point of diversion was repaired, the stream appears to currently be taking about 90% of the flow. There is still some minor diversion taking place along the old skid trail. Diverted flow returns to channel downstream. Risk Analysis There is judged to be a low likelihood of recurrence of a stream avulsion at this site. This would resulting in streamflow being diverted by the skid trail with some minor sediment entrainment. Sediment is not likely to reach a fish bearing stream. This is considered a low consequence. The risk is therefore low. Prescription Potential disturbance by machine likely to be more disruptive than leaving the site undisturbed. Restoration (cross-ditching) could be conducted by hand, however the majority of the flow is likely to stay in the natural channel. Cross drain flow on trail back to stream draw by hand. Install wide shallow swale (culvert backup) at stream crossing 130. Page 28

29 Photo Stream looking towards road. Direction of diversion along old skid trail indicated. Page 29

30 5.11 Gold Creek Reach 7203 Location: Road in Block Map Reference: G-7203 Field Identification: 204 Previously identified issues Streams had been diverted by skid trails in the block, culverts washed out, deposition downstream. Restoration undertaken Diversions have been restored by hand, road deactivated. Observations Streams at road crossing have stabilised, and are well incised. Swales at stream crossing are revegetating. There is some minor lateral erosion of road fill materials at crossings, but this is expected to decrease as riparian vegetation re-establishes. Risk Analysis There is judged to be a low to negligible likelihood of mobilising sufficient sediment to impact a fish bearing reach of the Gold Creek from this site. Prescription No works required Photo Stream crossing reach 7203 Page 30

31 5.12 Gold Creek Reach 7205 Location: Reach 7205 at road crossing Map Reference: G-7205 Previously identified issues Creek diverted by skid trails, hazard of diversion along mainline. Restoration undertaken Channel restored, culvert improved. Observations Deflector berm and culvert have been upgraded no issues at crossing. Risk Analysis There is judged to be a low to negligible likelihood of mobilising sufficient sediment to impact a fish bearing stream from this site. Prescription No further works required. Photo Reach 7205 at road crossing Page 31

32 5.13 Gold Creek Reach 7604 Location: Reach 604 in Block Map Reference: G-7604 Field Identification: 134 Previously identified issues No riparian buffer in block, slash in streams, blocked and damaged culvert. Restoration undertaken None Observations 600mm CMP in place, functioning. There is evidence of significant flows in this draw. Riparian area well vegetated and regrowing. Soils in this area are rocky and free draining. No immediate concerns as long as culvert remains functional. Risk Analysis Given the past history of plugging, and evidence of significant seasonal flows in this stream, there is a moderate likelihood that this culvert will become plugged or fail, leading to a washout of the road and subsequent sediment delivery to the stream system. There is a moderate likelihood of material being delivered downstream to Gold Creek. This would be considered a moderate consequence. The risk is therefore moderate. Prescription Pull culvert / construct broad armoured swale with planned road deactivation, or install failsafe cross ditch as per Silvatech (1998) prescription. Photo Crossing at Reach 7604 Page 32

33 Photo mm CMP at Reach 7604 crossing Page 33

34 5.14 Gold Creek Site 1 Location: Road in Block Map Reference: G-1 Field Identification: 115 Previously identified issues Damaged and blocked 300mm culvert, road requires deactivation. (Silvatech 2004) Restoration undertaken None Observations Crushed and mangled culvert still in place. There is evidence of significant ditch flow in the past (foreground in photo). The culvert is at a low point in the road, with ponding water on the high side. Risk Analysis This site is on flat to gently sloping plateau. There is judged to be a low to negligible likelihood that significant drainage diversion could take place at this site. Prescription Remove culvert and install cross ditch. This can be done with deactivation on the remainder of the road. Photo Crushed culvert. Page 34

35 5.15 Gold Creek Site 7 Location: Road in Block Map Reference: G-7 Field Identification: 201 Previously identified issues Deck material rotting, but crib wall and stringers look in good shape. (Silvatech 2004) Restoration undertaken None Observations Deck on the bridge is rotting out. There has been a small slide to the northwest of the bridge in the road cut (see photo ). No significant amount of debris has entered the stream as a result, however several trees have been uprooted and are threatening to fall onto the bridge deck / upstream of the bridge which may result in a temporary blockage. The cribbing on the downstream side of the town side approach is beginning to erode. The stream gradient downslope is 80% for about 7m immediately after the crossing. A blockage / collapse of the structure may lead to alteration of flow and/or significant erosion of the stream bed and / or mobilisation of debris downslope. The bridge could likely be left in place for some time before significant problems arise, however a high flow event or mass movement event in the channel may accelerate deterioration and lead to significant sediment input. Note: Reach 4700 is located upslope of this bridge. There is no evidence of the debris flow reaching this location. Risk Analysis There is judged to be a low likelihood of a structural failure on this bride (cribbing collapse / creek blockage) within the next 20 years that could result in significant sediment delivery to Gold Creek. This is considered a high consequence. The risk is therefore moderate. Prescription Bridge superstructure and cribbing should be removed, and approaches sloped back and revegetated. Pull back all materials adjacent the creek to create a broad swale, and armour stream crossing with coarse rock Remove material slumping into creek at road cut Supervision of deactivation works by a qualified registered professional is recommended. Page 35

36 Photo Log Bridge, 201 (Silvatech 1998 Site 7 ) Photo Log Bridge, 201 (Silvatech 1998 Site 7 ) SE corner of Cribbing starting to collapse. Page 36

37 5.16 Gold Creek Site 8 Location: Bridge at crossing between blocks and Map Reference: G-8 Field Identification: 202 Previously identified issues Bridge, Site 8. No significant issues identified guardrails were beginning to rot. Silvatech (1998) Restoration undertaken None Observations Bridge is showing significant rot, but no sign of imminent collapse. Bridge will likely remain intact for a number of years, but continued degradation will compromise load bearing capacity. Risk Analysis There is judged to be a low likelihood of a structural failure on this bridge that would result in delivery of a small to moderate amount of sediment to the stream, considered a low to moderate consequence. The risk is therefore low. Note: This bridge will continue to deteriorate, holes have formed in the deck and the structure may become unsafe to use in the next 20 years. The bridge may not be safe for vehicular traffic. If this bridge is to remain, a load rating should be performed. Prescription This bridge will not support machinery. Works planned for site 7 require removal of this bridge for access. Bridge superstructure and cribbing should be removed. Pull back all materials adjacent the creek to create a broad swale, and armour stream crossing with coarse rock Supervision of deactivation works by a qualified registered professional is recommended. Page 37

38 Photo Bridge at 202, ( Site 8 in Silvatech 1998 report) Page 38

39 5.17 Gold Creek Site 9 / 10 Location: Block Road Map Reference: G-9, G-10 Field Identification: 113, 114 Previously identified issues (9) Failed 400mm CMP, water running along road surface, then back into natural channel. (10) Infilled ditch is causing creek to flow down the road. Restoration undertaken None Observations A number of diversions of natural drainage paths along the road system were observed. This road system should be deactivated and have natural drainage patterns restored. These sites are not part of the Gold Creek watershed and drain to the watershed to the west. This road system has not been deactivated, and though no significant issues were identified at the specific sites addressed in this report, ( 9 and 10) the entire road system accessing Blocks should be assessed in detail and deactivated. These roads and blocks are located on the plateau, with drainage to the west into a deeply incised creek draw. The draw is mapped as terrain class IV and V (potentially unstable and unstable). Risk Analysis There is judged to be a moderate likelihood that improper drainage management in this entire road system (including sites 9 and 10) could lead to drainage diversions which would result in landslides in the class IV and V terrain in the watershed downslope (to the east). This could result in significant disturbances in the watershed and subsequent downstream effects on Adams Lake. This is considered a high consequence. The risk is therefore high. Prescription At stations 113, 114 and 115 (corresponding to the area of Silvatech (2004) sites 9 and 10), culverts should be removed and cross ditched. This entire road system associated with Blocks 502 (1-6) should have a deactivation prescription prepared as it presents a possible gentle-over-steep hazard. (note: Preparation of deactivation prescriptions for this area are planned for Summer of 2007) Page 39

40 Photo Blocked culvert causing ponding in ditchline with seasonal runoff over road. Photo Damaged culvert at Site 9 ( 114) Page 40

41 5.18 Rock Creek Site 1 Location: Forest Service Rec. Site ( Silviculture Camp ) at Tsikwustum (Rock) Creek. Map Reference: R-1 Field Identification: 52, 53 Previously identified issues Considerable bank erosion along right bank adjacent to rec site. Potential to loose rec. site land, sediment delivery to creek and lake. Restoration undertaken Unstable bank material was excavated back, and separated boulders placed as armour at the toe of the bank and the area was grass seeded. Observations The forest recreation site is located on the right bank of Tsikwustum (Rock) Creek, at the mouth of the river on Adams Lake. This recreation site is built on an active fan, and as such is subject to large debris flood events, and large annual high flow events. There is a 1-4m high bank along the edge of the site (see composite photo ) that had been sloped back and armoured in The bank is being eroded and there is undercut portion of this bank adjacent to the recreation site. Toe protection on the bank appears inadequate, as further erosion has taken place (compared to 2004 photos). Erosion is being accelerated by human activities; there is evidence in this area of disturbance by campers (walking access, digging). A large open grassy area (grass seeded in 2004) is located adjacent to the bank, as well as an access route to one of the lower camp sites. Note: A large flood event could significantly impact the camp site. This assessment addresses only on the possibility of sediment delivery to the creek as a function of normal (annual) high flows at the site indicated in the Silvatech (2004) report. No evaluation of risk to the site infrastructure or human life is made with respect to large, low return period flood events. Such an assessment is likely warranted, and should be carried out separately. Risk Analysis There is judged to be a moderate to high likelihood of further erosion along this slope, resulting in delivery of sandy material to Rock Creek. This is likely to occur during flood / high water events, and would be significantly diluted. This is therefore considered a low to moderate consequence. The risk is therefore moderate to high Prescription Slope back steep section (blue arrows in photo ) where overhang and exposed roots threaten to collapse. Place large rip rap (~2m diameter) at the base of the section 52 to 53, slope back top of the bank and grass seed. Restrict vehicle access at the top of the bank by placing a row of large boulders ~ 5m back from the top of the break in slope Consider restricting access with a fence along the top bank leaving a well marked path to the river to limit bank disturbance. Continue to monitor site, inspect after high flow events. Page 41

42 52 53 Photo Photo composite Eroding bank of Rock Creek adjacent to Silviculture Camp Forest Rec. Site. Photo Detail of eroding bank. Page 42

43 5.19 Rock Creek Site 2 Location: Tributary to Rock Creek Map Reference: R-2 Field Identification: 51 Previously identified issues 1800 mm CMP plugged with woody debris. Cutslope to the east (bush side of crossing) is delivering fine sediment Restoration undertaken Culvert has been cleared Observations Culvert log jam has been cleared, and is now unobstructed. Given the size of this creek, there is a moderate to high likelihood that future jams will take place. The recommendations in the Silvatech (2003) report to inspect the culvert frequently (twice per year); this should be done prior to and following freshet. A large jam could cause a significant blockage and subsequent debris flow at this site that would impact the S3 reach of Rock Creek downstream. The large cutslope to the east of the site continues to ravel and has infilled the ditchline, causing ditch flows to flow across the road and onto the fillslopes on the bush side of the crossing (see photo ; blue arrow indicates flow). This is leading to erosion of the fillslope and deposition of sediment into the stream. If this condition persists, it could lead to more significant erosion and / or fillslope failures. Risk Analysis There is judged to be a moderate likelihood of a significant washout of the road, resulting in significant sediment delivery and possibly a debris flow in the creek. This is considered a high consequence. The risk is therefore high Prescription. Inspect culvert regularly (twice per year; prior to and following freshet) Clean and widen ditchline, carry flow to crossing (red arrow in Figure ) Grass seed ditch and cutslope by hand or optionally hydroseed slope if feasible as per Silvatech (2003) Page 43

44 Photo Rock Creek tributary (Site 2 Silvatech 2003) 51 in field Photo Rock Creek tributary culvert inlet Page 44

45 5.20 Rock Creek Site 3 Location: Slide S-19 downslope of Rock Creek road near bridge crossing Map Reference: R-3 Field Identification: 50 Previously identified issues Surface soils in slide susceptible to surface erosion, sediment delivery potential to creek is high. Restoration undertaken Has been hand grass seeded several times. Observations The slide location is at a low point on the road, there is a long ditch run to this point, and water likely had saturated the road prism / run over the edge at the slide site. Perched fill materials are still present and are prone to ravelling. The slide is partially revegetating, some grass seeding has taken on the lower portions, but the steep upper portion is likely to continue to be a sediment source. Rock Creek (S2) is located directly downslope. Risk Analysis The site is a permanent sediment source because slopes at the top are too steep to revegetate. There is judged to be a moderate likelihood of a small slide initiating on oversteepened materials at the headscarp of the slide with resulting minor sediment delivery (<5m 3 ) to the S-2 creek downslope. This is considered a moderate consequence. The risk is therefore moderate. Prescription Carefully pull back top of slide area to 1.5V:1H (66%) maximum slope for the top portion of the slide. Hand-grass seed the slope. Upgrade ditchline along road this site. Page 45

46 Photo , slide S-19 looking down at exposed soils. Page 46

47 5.21 Rock Creek Site 4 Location: Non-status road near reach break 5/6 Map Reference: R-4 Field Identification: 4 Previously identified issues Erosion along 9m length of left bank of road poses a risk to the road and is a minor sediment source to the creek. Restoration undertaken Done as per Silvatech (2003) report Observations This is a broad low gradient reach, with significant coarse woody debris in creek. Comparison of pictures of previous site suggests low debris movement. Stream is classed as S2. Site has been restored, and remaining ravelling is expected to be very minor. Site is revegetating, road surface erosion has ceased. Risk Analysis There is judged to be a low to negligible likelihood of delivery of significant sediment to Rock Creek at this site. Prescription None / continue to monitor site. Page 47

48 5.22 Rock Creek Site 5 Location: Non status road (Tsikwustum Lake Road) near junction with Branch C Block C-206. Map Reference: R-5 Field Identification: 44 Previously identified issues Erosion of road surface near 450mm CMP due to plugged inlet 50% function only. Restoration undertaken None (Pre work indicated done) Observations The ditch block at the 450mm culvert has failed, and flow has eroded ditchline. Drainage flows through 1000mm CMP downstream. There is significant flow coming down the ditchline that has eroded the ditchblocks of the culverts upstream, and has resulted in significant sediment mobilisation (photo ) in the ditch and subsequent deposition (photo ) in the ditch at lower gradient areas. Sediment is being transported downstream, with significant aggradation in the channel and fines washing into Rock Creek. Restoration at this site should be done in conjunction with remainder of the road to the east (Sites 6 and 7). The culvert is experiencing severe piping because of excessive flows at this site, and material is eroding at the outlet. Risk Analysis There is judged to be a high likelihood that the culvert at this site will continue to fail and erode sediment form the outlet and road surface. This will result in significant fine sediment transport downstream to Rock Creek. This is considered a high consequence. The risk is therefore high Prescription Repair (re-install) culvert (600mm CMP minimum) and armour sump. Ensure drainage measures in ditch upstream are addressed. Repair in conjunction with Site 11 (R-11) deactivation. Page 48

49 Photo Erosion of ditchline Photo Significant deposition at low point before culvert. Page 49

50 5.23 Rock Creek Site 6 Location: Non status road (Tsikwustum Lake Road) Map Reference: R-6 Field Identification: 42 Previously identified issues Non functioning culvert is filly suspended above ditch, which has downcut ~0.4m in sandy materials. Restoration undertaken None (Pre work indicated done, but comparison to Silvatech report photos reveals site has not been repaired) Observations Culvert is still fully suspended and ditchblock has not been repaired. This is resulting in severe ditch runs downstream, scouring ditchline and transporting sediment to Site 5, and subsequently to Rock Creek. Risk Analysis There is judged to be a high likelihood that the non-functioing of this culvert will will result in significant runoff and subsequent fine sediment transport downstream to Site 5 and then Rock Creek. This is considered a high consequence. The risk is therefore high Prescription Install large ditch block, constructed out of large rock. Install broad failsafe cross ditch to prevent further breaches of the ditch block. Repair in conjunction with Site 11 (R-11) deactivation. Page 50

51 Photo Eroded ditchblock at 42 (R6) Photo Perched Culvert at 42 (R6) Page 51

52 5.24 Rock Creek Site 7 Location: Non status road (Tsikwustum Lake Road) Map Reference: R-7 Field Identification: 40 Previously identified issues Piping of fine-textured soils at a 1400mm culvert has caused slumping of road surface. Restoration undertaken Road repaired Observations The culvert at this site is functional and in good condition. The ditch block and sump may have been overtopped, at some point in the past resulting in increased flow down the ditch line. Risk Analysis There is judged to be a low likelihood that the ditch block will be overtopped and eroded and result in further significant runoff and subsequent fine sediment transport downstream to Sites 5 and 6 and subsequently to Rock Creek downstream. This is considered a high consequence. The risk is therefore moderate. Prescription Improve ditch block with large rip-rap Repair in conjunction with Site 11 (R-11) deactivation. Photo culvert inlet and ditchblock Page 52

53 5.25 Rock Creek Site 8 Location: Non status road (Tsikwustum Lake Road) Map Reference: R-8 Field Identification: 39 Previously identified issues Inlet slumping, piping of fine textured materials. Restoration undertaken Repaired road and armoured inlet. Observations 1000mm CMP. Site has been repaired using coarse materials. No recent significant sediment production was noted. Note that this stream is connected to the streams diverted at site 11. this site should be monitored after restoration, to ensure flow capacities and sediment mobilisation changes are noted. Risk Analysis There is judged to be a low likelihood of significant sediment production at this site. Further deterioration and piping of fines would transport sediment to a fish bearing portion of the reach immediately downslope, with a high to moderate likelihood of deposition of materials into Tsikwustum Lake. This is considered a high consequence. The risk is therefore moderate. Prescription Continue to monitor site Ensure site 11 restoration (R-11) does not divert excessive flows to this stream Page 53

54 5.26 Rock Creek Site 9 Location: Branch D Map Reference: R-9 Field Identification: 14 ( 9-16) Previously identified issues Waterbars and cross-ditches between Tsikwustum Lake Road and the first junction off branch road D are filling with sand and losing functionality. Restoration undertaken Reported as done as per Silvatech (2003) Observations Waterbars have been improved but problems of road surface erosion still present. Sandy soils highly prone to erosion. Additionally, ditchlines experiencing significant erosion. Culvert ditch block at 9 could fail, diverting significant drainage to lower ditch. Waterbar at 13 infilling. This road system is intercepting and diverting significant flows. Full deactivation should likely be considered for the future. Risk Analysis There is judged to be a moderate to high likelihood of road surface degradation and sediment production on this road section, however there is no direct connectivity to Rock Creek. Road surface degradation is considered a low consequence. The risk is therefore low. Prescription 9 Improve failsafe cross ditch. Riprap ditchblock. 10 Improve waterbar 12 Install failsafe cross ditch 13 Clean / improve backup cross ditch Page 54

55 Rock Creek Main Branch D Figure 5 (Site R-9), Branch D Road Photo existing 600mm CMP Page 55

56 5.27 Rock Creek Site 10 Location: Branch D crossing on Tributary #1 Map Reference: R-10 Field Identification: 6, 7 Previously identified issues A section of approximately 500m of road is at risk of erosion by tributary #1 had breached a ditch block at a 1400mm CMP resulting in streamflows being routed along the ditch, and had washed out a block of a 600mm ditch block downslope. Restoration undertaken Work done by Interfor as per instructions provided by Silvatech in September 2002 Observations Large ditchblocks put in place at 1400mm culvert and at 600mm downslope. Ditchblocks functioning. 1400mm ditch block is adequate, but contains a high proportion of fines and rock of smaller diameter and may be washed out in the event of an extreme flow. Ditchblock construction at 600mm culvert is very good. There are no failsafe cross ditches in place. Risk Analysis There is judged to be a moderate likelihood of the ditchblock at the 1400mm pipe to be breached, resulting in another stream avulsion and subsequent ditch erosion and sediment production. The area downstream of the two culverts is flat and marshy, and any sediment entrained is likely to settle out before entering Rock Creek. This is considered a low consequence. The risk is therefore low. Prescription Improve ditch block at 1400mm culvert with large diameter rock Install broad failsafe cross ditches at both culvert locations Page 56

57 Photo mm culvert with ditchblock Photo Ditch block at 600mm Culvert Page 57

58 5.28 Rock Creek Site 11 Location: Branch C Map Reference: R-11 Field Identification: 19-40, Previously identified issues Severe ditch erosion along 75m of road has resulted in a deep ditch in sandy tills. Sediment delivery to stream network moderate. Site R11 was examined as part of the current study. It was determined from this initial investigation that additional issues with drainage diversions in the road network upslope of the site were contributing to the problems identified at site R11. It was decided that a second, more detailed investigation should be carried out. This separate investigation was done on October by the author, and has been included in this final revision of the report. Restoration undertaken None evident. Observations The original study and the follow-up detailed study focused on the two road systems, Branch C and the associated spur to the south (See Figure 6). Soils in this area consist of a veneer to blanket of sandy tills and bouldery glacio-fluvial materials over relatively impermeable gneissic bedrock. There is significant shallow groundwater flow which has been intercepted by road construction and exacerbated by harvesting in this area. As a result, ditch flows are significant, and diversions have led to washouts in culverts downslope, notably at assessment Sites 5, 6 and 7. At site R11, the ditch and road surface have been severely eroded and a significant amount of sediment has been mobilised in the ditchline and where the ditch flow has washed out the road. The ditchline had eroded to a significant depth, and original crossdrains / culverts have been perched The upper portion of Branch C has been deactivated from 1 to 18. This portion of the road is not contributing to the drainage issues identified in the previous studies, and only minor remediation, if any, is required It appears that interception of subsurface groundwater and subsequent diversion by roads and trails in the area of the branch to the south of (Waypoints ) have contributed to the excessive ditch flows on Branch C. The spur road has been deactivated, with frequent cross ditches dispersing drainage, and natural stream channels have been restored to satisfaction at waypoints 100 and 131. The road surface in this area is revegetating, and sediment production is minimal in this area. The lower portion of the spur, from 131 to the POC with Branch C has also been deactivated, however the deactivation has been in large part unsuccessful, and significant water is intercepted and channelled along the road surface and ditch to Branch C. Waterbars in this area need to be extended as cross ditches from stations Risk Analysis Due to drainage interception/diversion and concentration, there is judged to be a high likelihood of further Page 58

59 sediment production at these sites, with a moderate likelihood of sediment delivery to the stream system (S5 stream through R7 and the S6 stream through R6) and subsequently to Rock Creek (S2). This is considered a high consequence. The risk is therefore high Prescription The following prescription is meant to disperse ground water flows as much as possible where such flows have been intercepted and concentrated as ditch flows, as well as to restore stream flows to natural channels where these may have been diverted by road construction. Note: all cross ditches on this road section should be deep enough to intercept all ditch drainage, and should be broad, with gentle approaches. Armour all cross ditches with large rock. Install ditch blocks constructed with coarse rock and boulders. Branch C Road 1 existing cross drain - no action required 2 existing 500 CMP at low point in road with functioning failsafe cross ditch - no action required CMP, perched inlet. Low risk - no action required 500 CMP, good ditchblock in place Low risk - no action required Stations 6, 7, 9, 10, 11, 13, 14, 16, 17 are all existing cross ditches, functioning well, low risk. - no further action required 17B 18 block 20 POC of several spurs upslope, start of deepened ditchline - no action required 500CMP, ponding upslope - Pull culvert and install broad armoured cross ditch. and ditch Existing waterbar install broad armoured cross ditch and ditch block 20A Install broad armoured cross ditch and ditch block. Extend cross ditch south to ribbon, to intercept surface flows on old trail on south side of ditch. 21 S5 Stream, ditch block has been overtopped leading to significant diversion. - Install broad armoured cross ditch and ditch block. 21A Existing culvert, significant seepage from old spur upslope. - Pull culvert and install broad armoured cross ditch. and ditch block 22 Existing culvert - Pull culvert and install broad armoured cross ditch 23 Existing culvert - Pull culvert and install broad armoured cross ditch, install ditch block on bush side Page 59

60 25 Install broad armoured cross ditch and ditch block CMP with good ditch block - Pull culvert and install broad armoured cross ditch. and ditch block Install broad armoured cross ditch and ditch block Install broad armoured cross ditch and ditch block 29 S6 channel - Install broad armoured cross ditch and ditch block, restore natural stream channel Construct a large armoured cross ditch from station 30 to 31 across the POC of the spur road to the south, and across Branch C. The intent of this ditch is to channel runoff from the spur to the S6 which crosses at 29. Ditch should have a gradient of 2-3%. Install a large ditch block in the existing ditch Exisiting cross ditch is perched. - Install broad armoured cross ditch and ditch block Install broad armoured cross ditch and ditch block Exisitng 500 CMP Pull culvert Install broad armoured cross ditch and ditch block Install broad armoured cross ditch and ditch block Install broad armoured cross ditch and ditch block 39 Low gradient portion of road. - Install broad armoured cross ditch and ditch block angle ditch across as indicated by ribbons. Spur Road 131, 132, 133 Existing waterbars do not intercept the ditchline, leading to significant ditch flows. cross ditch waterbars to ditch line (drain ditch flow across road to disperse drainage) Page 60

61 Photo severe ditch erosion. Page 61

62 Figure 6 (Site R-11), Branch C Road detail Page 62

63 5.29 Rock Creek Site 12 Location: Non-Status Road (Tsikwustum Lake Road) north end of Tsikwustum Lake Map Reference: R-12 Field Identification: 45 Previously identified issues 400mm culvert draining a small pond plugged with woody debris. Evidence of flooding on road surface. Restoration undertaken None evident Observations Culvert inlet obscured by woody debris, but pond has drained. Inlet of culvert completely blocked by coarse woody debris. Road shows signs of being overtopped by seasonal flows resulting in road surface erosion. Culvert is located in large road fill, removal would likely result in road being impassable. Creek is classed as S3, but fish passage is not possible upstream of this location. A fish passage assessment should be performed at this site. Risk Analysis There is judged to be a moderate likelihood of a road washout in this location, resulting in delivery of sediment to the S3 class stream and subsequently to Tsikwustum Lake, and loss of use of the road. This is considered a moderate consequence. The risk is therefore moderate. Prescription Depending on management objectives: Pull culvert and pull back fill material and armour crossing with rock OR Install failsafe cross ditch and continue to monitor site and clean out as necessary. A fish passage assessment should be performed at this site. Page 63

64 Photo Site 12 Ponding upstream of culvert. Page 64

65 5.30 Rock Creek Site 13 Location: Permitted Road (Tsikwustum Lake Road) Near Branch E Junction Map Reference: R-13 Field Identification: 48 Previously identified issues Surface erosion at a 600mm CMP possibly due to undersized culvert. Restoration undertaken Replaced with 1000mm CMP Observations 1000mm CMP on S4 class creek, functioning normally. Minor sediment production on cutslopes. Risk Analysis There is judged to be a low to negligible likelihood of further sediment production at this site. Prescription No further work required Photo mm CMP 48, Site 12 Page 65

66 5.31 Rock Creek Site 14 Location: Tsikwustum Lake Road (North Rock Creek Road) Map Reference: R-14 Previously identified issues Road fill erosion and slumping at 400mm CMP. Sediment source with a high potential to enter stream network. Restoration undertaken Culvert replaced, works completed as per Silvatech (2003) report. Observations Culvert replaced with 800 mm CMP functioning. No apparent issues since replacement. Connectivity to S2 immediately downstream. Risk Analysis There is judged to be a low to negligible likelihood of further sediment production at this site. Prescription No further work required Page 66

67 5.32 Mosquito Creek (Site 1) Location: Mosquito Creek Map Reference: M-1 Field Identification: Previously identified issues Stream diversions Restoration undertaken Works as prescribed by Silvatech (2004) report completed by October 29, Observations Works completed as described in Silvatech (2004) report were reviewed. This report recommended grass seeding, which appears to have been completed to satisfaction. Cross drain structures and culverts have been put in place. Flow appears to have been redirected back to the original stream locations satisfactorily. There is some evidence of minor road surface runoff taking place the road has been rutted by vehicle traffic, and minor runoff is eroding the road surface. This road surface flow is intercepted by waterbars and cross ditches, and is only a minor concern. The road is still accessible by truck; consider limiting vehicle access to ATVs only. Concerns on the upper rehabbed portion of road are generally with shallow cross drain structures which could fail and divert drainage down the road, and lack of failsafe cross ditches at culvert locations, where a blockage would send water down ditchlines, altering natural drainage patterns a portion of the cross drained flow runs down the ditch and partly down the road surface. Although it is intercepted by the cross ditch at station 56. At 58 creek crossing cross ditch is not sufficiently deep, large flows could run down the road. The ditchline from 62 back is taking substantial flows. Base mapping provided indicates that this flow comes from a stream which has been diverted along the ditch line, and had been ditched across the new road at the switchback ( 66). There is an armoured cross ditch at 63, which puts this stream back into what appears to be a the natural channel again. This stream then joins the S5 stream, crossing the road at 67 in a 1200mm culvert. The 600mm culvert at 66 (previous diverted flow path) is now experiencing only minimal flows. There is a failing box culvert at 69, which is only about 30% effective and will soon fail. Risk Analysis There is judged to be a moderate likelihood of ditch flows and cross drained flows running over or down the road surface due to shallow / non-existent waterbars / failsafe cross ditching. This would result in road surface erosion and drainage diversions on the access road and sediment delivery to S-6 and S5 classed streams. This is considered a moderate consequence. The risk is therefore moderate. Prescription Install waterbars to remove road surface diversions 58 Deepen cross ditch. 61 Install failsafe cross ditch 67 Install broad shallow failsafe cross ditch large flow potential, and overflow could run down Page 67

68 road Significant sediment production in ditchline, seepage all along this ditch. Grass seed. 69 Replace failing box culvert with 800mm CMP CMP Install broad backup cross ditch CPP Install broad backup cross ditch. Consider restricting the deactivated portion of the road to ATV traffic only to minimise sediment production from rutting. Note: The road back of 71 to the road junction is cut into poorly consolidated weathered schistose bedrock and tills. Ditchlines are slumping and infilling. This road will require inspection and significant maintenance measures (beyond the scope of this assessment) Photo Road surface drainage being intercepted by Cross Ditch, grass seeding effective. Page 68

69 Photo , Failing wood culvert Page 69

70 Figure 7 Mosquito Creek Site 1 Detail Page 70

71 5.33 Honeymoon Bay (Site 2) Location: Honeymoon Bay recreation site. Map Reference: H-2 Previously identified issues Grass seeding may be required in areas of previous restoration works. Restoration undertaken Ditch line cleanout Half-waterbars allowing trailer access to rec. site. Construction of rock weirs in ditching and settlement ponds at the lower end adjacent to the lake Minor grading of road surface CMP cleanout, armour ditch in areas of past erosion / concentrated flows Observations Works as described in Silvatech (2004) report have been completed. Ditchline clean and functioning, some grass and shrub vegetation establishing naturally. Road cut materials exposed and some ravelling into ditchline taking place. Shallow waterbars are located on the upper portion of the road, and are effectively draining road surface runoff into the ditchline. These are starting to wear / infill due to traffic with some washboarding taking place. The sumps for the two 300 mm pipes appear to have been very recently cleaned out (Spring 2006?) The material removed has been piled directly adjacent to the sumps and is slumping back in. Drainage laden with fine sediment is discharging into the lake directly below (See photos a c). Culverts are undersized and have a high likelihood of becoming plugged. Risk Analysis There is judged to be a high likelihood of continuous delivery of a small amount of fine sediment via the ditchline and inadequate sumps at the culvert inlets to Adams Lake. This is considered a low consequence. The risk is therefore moderate. Prescription Remove slumping material adjacent to culvert sumps, establish broad shallow armoured sumps and grass seed. Grass seed ditchline and cut slopes as prescribed in Silvatech (2004). Monitor and maintain waterbars on upper portion of access road. Page 71

72 Photo a Honeymoon Bay 300mm pipe at end of ditch above lake. Photo b Honeymoon Bay. Sump at end of road, appears recently cleaned out. Page 72

73 Photo c Honeymoon Bay. Culvert discharge directly into lake. Photo Berm deflecting creek drainage down ditchline. Page 73

74 Photo Improved ditchline on Honeymoon Bay recreation site road. Page 74

75 5.34 Momich Lake Site 3 Location: South of Momich Lake Map Reference: M-3 Previously identified issues Old log box culvert holes have developed in the road, with water passing beneath the road. Road has existing deactivation.(silvatech 2004) Restoration undertaken This site is located near the end of a road which has been deactivated (primarily cross ditched) and is revegetating. Observations The road has been deactivated with frequent cross ditches and is revegetating with alder and immature coniferous species. The site in question is an old log box culvert which is conveying water under the road surface. Holes have formed in several places. Immediately downslope of this site, the outlet of this cross drainage is armoured with very large boulders (>1.5m diameter). The site is in a broad shallow draw. Slopes below are planar at about 40-45%. There is a failsafe cross ditch in place. The road prism is unlikely to fail catastrophically, and blockage of the current flow would be conveyed across the road surface in the failsafe back into the natural channel. Risk Analysis Because of the existence of a backup cross ditch and heavy armouring of the outlet, There is judged to be a low to negligible likelihood that this failing log box will significantly in a slope failure. Prescription Removal of this structure will not result in a significant reduction in risk, and bringing equipment up this already deactivated road is likely to result in excessive disturbance. No further work required Page 75

76 Photo Site 3 Momich Lake area. Page 76

77 5.35 Momich Lake Site 5 Location: South of Gannet Lake Map Reference: M-5 Field Identification: 5 Previously identified issues Ravelling has blocked a culvert. Restoration undertaken None Observations Culvert inlet almost entirely blocked by boulders but still partially functioning. Cross drain culvert taking about 5% of the flow. Significant stream upslope could lead to large washout if not repaired. Risk Analysis There is judged to be a high likelihood of the culvert completely failing and causing a washout resulting in sediment delivery to the S5 stream downslope, with a moderate likelihood of sediment delivery to the S3 reach of the same stream. This is considered a moderate consequence. The risk is therefore high. Prescription Clean out or replace culvert OR Pull culvert and re-establish natural stream course. Photo Site 5 Gannet Lake area. Page 77

78 6.0 Closure This assessment focussed primarily on previously identified sites, but observations of general watershed condition and sediment sources and other potential problem areas were noted. Several natural sediment producing sites were noted during the Gold Creek helicopter overflight, but no additional areas with significant issues related to forest harvesting or road construction, other than those identified in this report, were observed. This risk analysis has been carried out in accordance with generally accepted engineering and geoscientific practice for the area. Conclusions and recommendations presented herein are based on air photo interpretation and visual site inspections of selected areas in each watershed. Further, assessments of soils and slope stability are based on interpretation of surface features and limited sub-surface investigation; actual ground conditions may vary from those inferred. This report provides a qualitative evaluation of hazards associated with sites previously identified in the study area, a description of the potential consequences, and recommendations to reduce the hazards and associated risks. Acceptance of the qualitative consequence values and the subsequent risk analysis is the responsibility of the licensee or the regulatory authority, as is the determination of acceptable risk and the decision to proceed with any action based on that risk analysis. We trust that this report satisfies your present requirements. Should you have any questions or comments, please contact our office at your convenience. Sincerely, Forsite Consultants Ltd. Prepared by: Reviewed By: Peter Weisinger, M.Sc. G.I.T. Project Geoscientist Rod Williams, P.Geo Project Geoscientist Page 78