P2.66
Post-Fire Flash Flood Prediction: A Difficult Challenge
John F. Henz, Henz Meteorological Services, Littleton, CO
Recent forest fires in mountainous terrain in Los Alamos, New Mexico; Rattlesnake Gulch of Sabino Canyon, Arizona and the Bobcat and Hi Meadows areas of Colorado's Front Range will present significant challenges to flash flood prediction support. Recent Colorado forest fires, Tiger Gulch in Boulder County in 1989, the Storm King fire of 1994 near Glenwood Springs and the recent Buffalo Creek in Jefferson County in 1996 have under-scored the susceptibility of fire-burn areas to flash flooding and mud slides.
In each of the mentioned Colorado fire-burn areas the fire ravaged areas displayed a hydrophobic nature to the soils and forest areas. The fire-crust seems to act in a much more impervious manner than the natural soil cover increasing runoff from even modest rainfalls. The need for an expert evaluation of fore effects on runoff are crucial to developing an active flood prediciton program. Hydrologists. soil scientists and meteorologists must cooperate in determining criteria for flash flooding.
In 1996, 1997 and 1998 the Buffalo Creek area suffered several flash flooding episodes. HMS conducted radar-rainfall re-constructions which suggest that the fire-burned areas will produce a mud-slide event when rain rates reach 0.50"/15 min to 0.75"/30 minutes and flash flood episodes when rain rates when rain rates reach about an inch per hour. In each case these values are 25-50% less than the rain rates associated with flash flooding in the area prior to the fires.
In the case of Buffalo Creek an automated flood detection network and a valley observer system were established and linked to the National Weather Service and a local flood warning plan. Despite these efforts flash flooding surprised the local population despite the best efforts of everyone. Additional criteris based on the approach of menacing storms, radar reflectivity and the flash flood potential of the atmosphere have eased the situation.
The recent Bobacat and Hi Meadows fores in Colorado are being evaluated for flash flood potential before the arrival of the 2000 monsoon season. Results from these evauations and experiences with both basins will be reported at the conference.
Poster Session 2, Summer Storms (Poster session)
Tuesday, 16 January 2001, 2:30 PM-5:30 PM
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