Mosquito Creek Debris Flood Hazard and Risk Assessment

CLIENT: District of North Vancouver

LOCATION: North Vancouver, British Columbia, Canada

Mosquito Creek drains a 15.5 km2 watershed on the North Shore Mountains north of Vancouver and flows through the densely urbanized District and City of North Vancouver.  Previous studies determined that the creek is subject to debris floods.  The National Research Council of Canada (NRCan) is applying multi-hazard risk assessment procedures for various regions in BC and chose Mosquito Creek as one of its target areas. As part of its natural hazard management plan, the District of North Vancouver (DNV) requested an assessment of debris flood hazards and associated risk to life.  Using a combination of empirical methods, dendrochronology and expertise, BGC assessed debris flood hazard extent, velocity and depth for estimated 100, 200, 500 and 2500-year debris-flow return periods.

Based on results from the hazard assessment, risk for individuals and groups living within the hazard area, including residential homes and a fire hall was estimated.  Compared to risk tolerance criteria adopted by the DNV, we estimated that societal risk exceeds tolerable standards and that individual risk exceeds tolerable standards for 10 homes.  The results from the risk to loss of life study have prompted DNV to implement a series of risk reduction measures.