Developing a Risk Analysis Procedure for Post-Wildfire Mass Movement and Flooding in British Columbia

Abstract: Many communities in British Columbia are situated on alluvial fans fed by steep mountain creeks, which are subject to debris flow or flooding hazards. Development on most of these fans has taken place without planning for debris flow hazard. Several severe wildfires in 2003 were followed by incidents of debris flows and flooding, that affected inhabited private property and infrastructure. In the past, the increased hazard of flooding, erosion, and mass movement caused by wildfire has not been fully appreciated in British Columbia. A process is now underway to develop a systematic procedure for risk analysis following wildfires in British Columbia, and recently there have been some government initiatives to address the risk associated with natural hazards. Some semi-quantitative examples illustrating risk assessment on fans are presented. Some related aspects of planning for risks on alluvial fans, and the challenges of conducting risk analyses over large areas with low population density, are discussed