Natural Hazard Risk Assessments
Natural Hazard Risk Assessment Study AreasThis map shows the extent of natural hazard risk assessments completed by the CVRD. It is not a map of all natural hazards in the region; instead it shows those areas where the risks from a specific hazard have been studied. You can zoom in and click on an area to see what hazard or hazards have been assessed. GIS data for these studies can be downloaded here.
Geohazard Risk Assessment - North Slope of Cowichan Lake
Ebbwater Consulting and Palmer Environmental Consulting Group carried out an assessment of the risks associated with various types of landslides (debris flows, debris floods) on the steep slopes above Youbou and Lake Cowichan. The work included a geohazard assessment of the slopes to identify the likelihood of geohazards throughout the study area. An impact analysis looked at the consequences of a landslide, including impacts on people and infrastructure, along with economic, environmental, and cultural impacts. The greatest risks are of loss of life and impacts from disrupted infrastructure such as blocked roads. These risks are predicted to increase with climate change as the projected increased intensity of rainstorms will cross a critical threshold for triggering landslides.
Risk Assessment of Floodplains
Northwest Hydraulic Consultants conducted a risk assessment of the floodplains around Cowichan Lake, Shawnigan Lake and the Riverbottom Road area of the Cowichan River. Provincial floodplain mapping for these areas is out of date and does not encompass the entire floodplains. Modelling of flood levels was carried out for four scenarios, including a present day (baseline) scenario and increases in precipitation of 10, 20 and 40 percent to represent the range of climate projections. Flood construction reference plane isolines and depth grids were developed for each scenario and elements exposed to flooding were identified. For the Cowichan Lake floodplain, wave run-ups were calculated for each one kilometre reach of shoreline for both an easterly and westerly ten year wind event. Risk assessments were prepared to consider: people and societal impacts; environmental impacts; local economic impacts; local infrastructure impacts; and, public sensitivity impacts. Impacted elements were broken down by jurisdiction and reported using tables and maps.
Coastal Sea Level Rise Risk Assessment
Northwest Hydraulic Consultants conducted a risk assessment for coastal sea level rise along the east coast of the region, including the gulf islands. Provincial policy directs local governments to plan for 0.5m sea level rise by 2050 and 1.0m by 2100; however, recent sea level rise projections have suggested that the rate of change will likely be greater than these projections. Modelling of sea level rise including high tides and storm surges was conducted for four scenarios, including a present day (baseline) scenario and sea level increases of 1.0m, 1.5m and 2.5m. Flood construction reference plane isolines and depth grids were developed for each scenario and elements exposed to flooding were identified. Wave run-ups were calculated for each 500 m reach of coastline for both an easterly and westerly ten year wind event Risk assessments were prepared to consider: people and societal impacts; environmental impacts; local economic impacts; local infrastructure impacts; and, public sensitivity impacts. Impacted elements were broken down by jurisdiction and reported using tables and maps.
Regional Dam Safety Reviews and Risk Assessments
Ecora Engineering & Resource Group undertook a comprehensive dam safety review and risk assessment of the four dams owned by the CVRD: Ashburnham Creek Dam, Shawnigan Lake Weir, Stocking Lake Dam and Youbou Creek Dam. The reviews included geotechnical, structural and hydrotechnical analyses of the dams, along with an assessment of operating procedures and emergency plans, resulting in a series of prioritized recommendations for each dam. The reviews recommend that the consequence classification be increased from Significant to High for the Stocking Lake Dam and Shawnigan Lake Weir due to the potential for loss of life within the dam breach flood inundation areas. In addition, a number of recommendations were made for each dam, including high priority recommendations for significant repairs or replacements to some of the dams.
Sh-hwuykwselu (Busy Place) Creek Stormwater Management and Mitigation Plan
CVRD staff in partnership with Cowichan Tribes and the Ministry of Transportation and Infrastructure have established a Stormwater Management and Mitigation Plan (the Plan) for the Sh-hwuykwselu (Busy Place) Creek Watershed in the Cowichan/Koksilah floodplain in the CVRD. The Plan will guide prioritized stormwater infrastructure improvements to mitigate flooding and erosion risk from high rain water flows, to enhance watershed health, to improve the quality of rain water runoff and protect the quality of groundwater aquifers. The Plan was prepared for the CVRD by Kerr Wood Leidal Associates.
As part of the development of the Plan, slope stability issues were identified along the slope above Allenby Road between Indian Road and Koksilah Road. McQuarrie Geotechnical Consultants conducted an overview assessment of the slope stability hazards and concluded that “…considering the slope angles, geologic conditions, and past evidence of landslides, the entire slope should be considered unstable or potentially unstable, creating a landslide hazard to any developments along the crest and toe."