THE REMARKABLE OCCURRENCE OF LARGE RAINFALL-INDUCED DEBRIS FLOWS AT TWO DIFFERENT LOCATIONS IN THE SOUTHERN SIERRA NEVADA, CA ON JULY 12, 2008
At about the same time, the southern cell was largely centered over Erskine Creek, a main tributary of the west-flowing Kern River. Debris flows issued from the headwater channels of Erskine, Thompson and Clear creeks. Estimated velocities along one headwater channel of Erskine Creek were between 8.5 and 10.5 mph. In Erskine Creek, the largest of the three drainages, tributary debris flows coalesced into a single flow that passed down the main channel, through the town of Lake Isabella, CA and into the Kern River. A helicopter observed it reaching Lake Isabella about 5:30 PM. Extensive rilling was observed in the upper watershed burned over by the Piute wildfire during the previous 14 days. While some damage occurred along the channel through Lake Isabella, the more significant impacts were the trapping of engines and fire crews within the Erskine Creek Canyon through the night and adverse effects to the water supply system for Bakersfield, CA.
In addition to their similar triggering mechanism and time of occurrence, the July 12th debris flows at both locations: 1)involved widespread upland rilling, 2) eroded and incorporated significant material from within channels, 3) were very fluid, and 4) had a long runout distance from their source areas.