Geohazard Risk Prioritization
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SQUAMISH-LILLOOET REGIONAL DISTRICT Geohazard Risk Prioritization FINAL April 10, 2020 Project No.: 1358007 Prepared by BGC Engineering Inc. for: Squamish-Lillooet Regional District BGC ENGINEERING INC. 500-980 Howe Street, Vancouver, BC Canada V6Z 0C8 Tel: 604.684.5900 Fax: 604.684.5909 BGC ENGINEERING INC. AN APPLIED EARTH SCIENCES COMPANY Suite 500 - 980 Howe Street Vancouver, BC Canada V6Z 0C8 Telephone (604) 684-5900 Fax (604) 684-5909 April 10, 2020 Project No.: 1358007 Sarah Morgan Emergency Program Manager Squamish-Lillooet Regional District Box 219, Pemberton, BC V0N 2L0 Dear Sarah, Re: Geohazard Risk Prioritization – FINAL Please find attached the above referenced report for your review. The web application accompanying this report can be accessed at www.cambiocommunities.ca. Username and password information will be provided in a separate transmission. Should you have any questions, please do not hesitate to contact the undersigned. We appreciate the opportunity to collaborate with you on this challenging and interesting study. Yours sincerely, BGC ENGINEERING INC. per: Kris Holm, M.Sc., P.Geo. Principal Geoscientist Squamish-Lillooet Regional District April 10, 2020 Geohazard Risk Prioritization - FINAL Project No.: 1358007 TABLE OF REVISIONS ISSUE DATE REV REMARKS DRAFT January 31, 2020 Original issue FINAL April 10, 2020 Original issue CREDITS AND ACKNOWLEDGEMENTS BGC Engineering would like to express gratitude to the Squamish-Lillooet Regional District (SLRD, the District) for providing background information, guidance and support throughout this project. Key SLRD staff providing leadership and support included: • Sarah Morgan, Emergency Program Manager • Ana Koterniak, GIS Coordinator. The following BGC personnel were part of the study team: • Kris Holm (Project Manager) • Sarah Kimball (Assistant Project Manager) • Richard Carter • Matthew Buchanan • Beatrice Collier-Pandya • Carie-Ann Lau • Matthieu Sturzenegger • Elisa Scordo • Patrick Grover • Philip LeSueur • Melissa Hairabedian • Alistair Beck. BGC ENGINEERING INC. Page i Squamish-Lillooet Regional District April 10, 2020 Geohazard Risk Prioritization - FINAL Project No.: 1358007 LIMITATIONS BGC Engineering Inc. (BGC) prepared this document for the account of Squamish-Lillooet Regional District. The material in it reflects the judgment of BGC staff in light of the information available to BGC at the time of document preparation. Any use which a third party makes of this document or any reliance on decisions to be based on it is the responsibility of such third parties. BGC accepts no responsibility for damages, if any, suffered by any third party as a result of decisions made or actions based on this document. As a mutual protection to our client, the public, and ourselves, all documents and drawings are submitted for the confidential information of our client for a specific project. Authorization for any use and/or publication of this document or any data, statements, conclusions or abstracts from or regarding our documents and drawings, through any form of print or electronic media, including without limitation, posting or reproduction of same on any website, is reserved pending BGC’s written approval. A record copy of this document is on file at BGC. That copy takes precedence over any other copy or reproduction of this document. BGC ENGINEERING INC. Page ii Squamish-Lillooet Regional District April 10, 2020 Geohazard Risk Prioritization - FINAL Project No.: 1358007 EXECUTIVE SUMMARY The Squamish-Lillooet Regional District (SLRD, the District) retained BGC Engineering Inc. (BGC) to carry out a geohazard risk prioritization study (the regional study) for the District. The primary objective of this study is to characterize and prioritize flood, steep creek (debris flood and debris flow), and non-eruptive volcanic geohazards (lahars) in the SLRD that might impact developed properties. Collectively these processes are referred to as “geohazards” in this document. While the study encompasses both electoral areas and municipalities, BGC was retained to complete prioritization from the perspective of SLRD (not individual municipalities). The goal is to support decisions that prevent or reduce injury or loss of life, environmental damage, and economic loss due to geohazard events. Completion of this risk prioritization study is a step towards this goal. The regional study provides the following outcomes across the SLRD: • Identification and prioritization of geohazard areas based on the principles of risk assessment (i.e., consideration of both hazards and consequences) • Geospatial information management for both geohazard areas and elements at risk • Web communication tool to view prioritized geohazard areas and supporting information • Information gap identification and recommendations for further study. These outcomes support SLRD to: • Continue operating under existing flood-related policies and bylaws, but based on improved geohazard information and information management tools • Review and potentially develop Official Community Plans (OCPs) and related policies, bylaws, and land use and emergency management plans • Undertake flood resiliency planning, which speaks to the ability of an area “to prepare and plan for, [resist], recover from, and more successfully adapt to adverse events” (NRC, 2012) • Develop a framework for geohazard risk management, including detailed hazard mapping, risk assessment, and mitigation planning • Prepare provincial and federal funding applications to undertake additional work related to geohazard risk management within the SLRD. This study provides results in several ways: • This report summarizes methods and results, with additional details in appendices. • Access to the CambioTM web application displaying prioritized geohazard areas and supporting information. This application represents the easiest way to interact with study results. Appendix B provides a guide to navigate Cambio Communities. • Geodatabase with prioritized geohazard areas. • Excel spreadsheet with attributes of prioritized geohazard areas. • Risk Assessment Information Template (RAIT) form as required by the National Disaster Mitigation Program (NDMP). BGC ENGINEERING INC. Page iii Squamish-Lillooet Regional District April 10, 2020 Geohazard Risk Prioritization - FINAL Project No.: 1358007 In total, BGC identified and prioritized 2058 geohazard areas encompassing over 1615 km2 (10%) of the SLRD (Table E-1). Table E-1. Number of prioritized areas in the SLRD, by geohazard type. Priority Level Grand Geohazard Type Very Very High Moderate Low Total High Low Clear-Water Floods 0 143 247 1455 0 1845 (water courses and water bodies) Steep Creeks (Fans) 16 54 57 71 3 201 Volcanic Geohazards 1 11 0 0 0 12 Grand Total (Count) 17 208 304 1526 3 2058 Grand Total (%) < 1% 10% 15% 74% < 1% 100% Table E-2 lists the results worksheets, which are provided in Appendix H. These worksheets can be filtered and sorted according to priority ratings or any other fields in the worksheet. When reviewing results, local authorities may wish to consider other factors outside the scope of this assessment but that also affect risk management decision making. For example, additional factors include the level of risk reduction already achieved by existing structural mitigation (dikes), the level of flood resiliency in different areas, and comparison of the risk reduction benefit to the cost of new or upgraded flood risk reduction measures. Table E-2. Results worksheets provided in Appendix H. Appendix H Contents (Excel Worksheet Name) Study Area Metrics Summary statistics of select elements at risk (count of presence in geohazard areas). Study Area Hazard Summary Summary statistics of elements at risk, according to their presence in geohazard areas. Study Area Hazard Type Summary Summary statistics of geohazard areas, according to the presence of elements at risk. Priority by Jurisdiction Summary statistics of prioritization results by jurisdiction. Steep Creek Hazard Attributes Attributes for all steep creek geohazard areas. Clear-water Flood Hazard Attributes Attributes for all clear-water flood geohazard areas. Volcanic Hazard Attributes Attributes for all volcanic geohazard areas. Gaps identified in this study can be categorized as those limiting the understanding of geohazards: in the characterizing of geohazard exposure and vulnerability (i.e., the built environment); and in the characterization of existing flood protection measures and flood conveyance infrastructure. In no case does this study replace site-specific geohazard risk assessments that aim to identify tolerable or acceptable risk or that support design of mitigative works. BGC also identified opportunities to improve geohazard information management and integrate risk-informed decision making into policy. BGC ENGINEERING INC. Page iv Squamish-Lillooet Regional District April 10, 2020 Geohazard Risk Prioritization - FINAL Project No.: 1358007 Table E-3 lists recommendations for consideration by SLRD and local, regional, and provincial authorities. The rationale for each recommendation is described in more detail in the report. BGC encourages SLRD and stakeholders to review this assessment and web tools from the perspective of supporting long-term geohazard risk and information management within the watershed. This effort would be greatly facilitated by long-term provincial support to take advantage of efficiencies of scale. Table E-3. List of recommendations. Type Description Data Gaps • Develop a plan to resolve