Water Stewardship Information Sources
| Citation | BGC Engineering. 2011. Run of River Power Corporation, Skookum Creek Hydro Project, Terrain and Geohazard Risk Assessment. Prepated for Run of River Power Corporation. |
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| Organization | BGC Engineering |
| URL | http://squamish.cc/extranet/Planning/Referrals/Skookum%20Clean%20Energy%20Project/EXHIBITS/Ex%20%2015.%20Terrain%20Stability%20-%20Geohzrd%20Risk%20Assess/Terrain%20Stability%20-%20Geohzrd%20Risk%20Assess.pdf |
| Abstract/Description or Keywords | This report provides an assessment of terrain characteristics and geohazard risks to the proposed Skookum Creek project, including the intake, penstock, powerhouse and transmission line. The terrain assessment included characterization of overburden material and bedrock (where exposed) along the trace of the proposed penstock from the intake to the powerhouse. This information is summarized in Table A-1 of Appendix A, and will be used for preliminary design of cut and fill slopes along the alignment, and estimates of material volumes. The geohazard risk assessment provides semi-quantitative rankings of geohazard risks. The objective is to identify sites where further assessment of risk mitigation is appropriate to lower geohazard risk levels to within Run of River Power Corporation’s (RoR’s) level of risk tolerance. Geohazard risk was determined by using BGC’s geohazard risk matrix for large corporate projects (Table 4-1) applied to a proposed base case system design. For the intake, penstock, and powerhouse, the base case was the revision P1 alignment, and assumed the penstock is buried next to the access road near the intake and otherwise laid on a penstock bench. The base case did not assume any pipe bridges or account for any hazard reduction benefit from access road reconstruction, but did assume tributary crossing design based on the Q100 peak flow. For the transmission line, the base case alignment was provided by Andritz Automation Ltd. Twenty six hazard scenarios were identified for the headpond, penstock, powerhouse and transmission line (Figures 1 and 2), with 20 of these relating to the penstock route. Geohazard risk was estimated for each hazard zone based on estimates of the likelihood of a hazard severely damaging the intake or headpond causing an overtopping of the intake, breaching the penstock, damaging the powerhouse, or causing a transmission tower to fail. Economic, reputation and environmental consequences were considered. Since such assessments cannot be done precisely, order-of-magnitude estimates were used and the risk table populated with ranges. The risk assessment for each hazard interval for the intake, penstock and powerhouse is provided in Table B-1 of Appendix B, and for the Transmission line in Table B-2 of Appendix B. No Moderate, High or Very High geohazard risk scenarios were identified for the intake headpond, powerhouse, or transmission line. Seven geohazard risk scenarios, all along the penstock, were assessed as High risk of causing penstock breach for the base case design. The total risk of penstock breach was estimated by adding the probabilities of penstock breach from each hazard zone. This resulted in an assessed return period for a penstock rupture for the unmitigated penstock design base case of 1 to 10 years. Using the base case risk assessment as a guide, preliminary hazard mitigation concepts were applied to the High risk scenarios along the penstock to assist in the development of appropriate mitigation strategies. With the preliminary mitigation plan, estimated residual risks were reduced to Moderate or Low levels and the likelihood of an event occurring somewhere along the penstock causing a penstock rupture was reduced from likely to occur in any given year to an estimated annual probability of occurrence between 0.002 and 0.02 (500 year return period and 50 year return period, respectively). Risk Assessment results are discussed in Section 5, and recommendations discussed in Section 6. At this stage, Run of River Power Inc. should review the consequence ratings and risk estimates, and confirm their tolerable risk threshold. This will then allow further assessment or mitigation design to be completed for sites exceeding tolerable risk levels. |
| Information Type | report |
| Regional Watershed | Howe Sound & Sunshine Coast |
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| Project status | complete |
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