Mud and debris flows and associated earth dam failures in the Okanagan region of British Columbia

A review of debris and mud flows occurring over the past 100 years in the Okanagan region of British Columbia, Canada, reveals that most events have been associated with late spring snowmelt, spring rains occurring on the snowpack or intense localized convective rain storms in the summer. A troubling finding is that many of the most destructive debris and mud flows were triggered by failure of earth dams located high above the valley floor. The dam failures were caused by either seepage-related piping or water flowing over the top of the dam. Dam breaches can occur on hot sunny days in the spring, when snowmelt and saturated ground conditions occur in the headwaters of creeks flowing into the Okanagan valley. The record shows that there is a risk not only of property damage, but also of loss of life associated with these events. Comparison is made to similar mud flow events in western USA. [author]