Forest Fire Leads to Destructive Debris Flow

A wildfire following a century of sediment accumulating in a steep creek channel created conditions that took only a moderate summer rainfall to trigger a large landslide into Kootenay Lake. The event moved 20,000 to 30,000 m³ of material, including gravel, logs and charcoal, that blocked Highway 3A and destroyed several buildings in southeastern British Columbia.

In 2003 a forest fire spread over most of the Kuskonook Creek catchment including an intense burn on 10% of the upper slopes. The intense burn created hydrophobic soils incapable of absorbing the 5 to 10 mm of rain that fell during the night of August 6 2004, resulting in the debris flow

The next month, another 200 to 1000 m³ of sand, silt and gravel travelled down the mountain creek, enough to close a road and one lane of Highway 3A. The upper watershed is mainly unlogged, and forest harvesting and road building are not associated with either debris flow.

Until vegetation re-establishes in Kuskonook basin and the creek channel stabilizes, debris flows up to 1,500 m³ in volume are expected to occur every 5 to 10 years, triggered by moderate rainfall.