HR: 14:40h
AN: H43G-05 [Abstracts]
TI: An Approach for Assessing Post-Wildfire Debris-Flow Hazards Applied to Basins Burned by the 2003 Old
and Grand Prix Wildfires in Southern California
AU: * Cannon, S H
EM: cannon@usgs.gov
AF: U.S. Geological Survey, Box 25046 DFC MS 966, Denver, CO 80225
AU: Gartner, J E
EM: jgartner@usgs.gov
AF: U.S. Geological Survey, Box 25046 DFC MS 966, Denver, CO 80225
AU: Rupert, M G
EM: mrupert@usgs.gov
AF: U.S. Geological Survey, Box 25046 DFC MS 966, Denver, CO 80225
AU: Michael, J A
EM: jamichael@usgs.gov
AF: U.S. Geological Survey, Box 25046 DFC MS 966, Denver, CO 80225
AB:
The increased incidence of catastrophic wildfires in the western United States and the encroachment of development into
fire-prone ecosystems have created a critical need for methods to quantify potential hazards posed by debris flows produced
from burned watersheds. Debris flows are one of the most hazardous consequences of rainfall on recently burned hillslopes.
Statistical models developed to estimate the probability and magnitude of post-wildfire debris-flow activity were used to
generate debris-flow hazard maps for basins burned by the Grand Prix and Old fires in October 2003 in southern California.
The probability maps are based on the application of a logistic multiple-regression model that describes the percent chance
of debris-flow production from an individual basin as a function of areal burned extent, soil properties, basin gradients,
and storm rainfall. The peak discharge maps are based on application of a multiple-regression model that estimates
debris-flow peak discharge at a basin outlet as a function of basin gradient, areal burn extent, and storm rainfall. In
response to 25-year, 10-year, and 2-year recurrence rainstorms, conditional probabilities of debris-flow occurrence ranged
between 0 and 99%, and estimated peak discharges ranged between 10 and 190 m3/s. These maps identify those basins that are
most prone to large debris-flow events and provide information for mitigation and evacuation planning. Evaluation of the
response of the December 25, 2003, rainstorm that triggered debris flows and flooding from the recently burned basins allows
for an assessment of the effectiveness of the mapping approach and provides guidance for refinement of the models.
DE: 1815 Erosion and sedimentation
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting