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A low-cost method to measure the timing of post-fire flash floods and debris flows relative to rainfall

January 1, 2012

Data on the specific timing of post-fire flash floods and debris flows are very limited. We describe a method to measure the response times of small burned watersheds to rainfall using a low-cost pressure transducer, which can be installed quickly after a fire. Although the pressure transducer is not designed for sustained sampling at the fast rates ({less than or equal to}2 sec) used at more advanced debris-flow monitoring sites, comparisons with high-data rate stage data show that measured spikes in pressure sampled at 1-min intervals are sufficient to detect the passage of most debris flows and floods. Post-event site visits are used to measure the peak stage and identify flow type based on deposit characteristics. The basin response timescale (tb) to generate flow at each site was determined from an analysis of the cross correlation between time series of flow pressure and 5-min rainfall intensity. This timescale was found to be less than 30 minutes for 40 post-fire floods and 11 post-fire debris flows recorded in 15 southern California watersheds ({less than or equal to} 1.4 km2). Including data from 24 other debris flows recorded at 5 more instrumentally advanced monitoring stations, we find there is not a substantial difference in the median tb for floods and debris flows (11 and 9 minutes, respectively); however, there are slight, statistically significant differences in the trends of flood and debris-flow tb with basin area, which are presumably related to differences in flow speed between floods and debris flows.

Publication Year 2012
Title A low-cost method to measure the timing of post-fire flash floods and debris flows relative to rainfall
DOI 10.1029/2011WR011460
Authors Jason W. Kean, Dennis M. Staley, Robert J. Leeper, Kevin Michael Schmidt, Joseph E. Gartner
Publication Type Article
Publication Subtype Journal Article
Series Title Water Resources Research
Index ID 70045088
Record Source USGS Publications Warehouse
USGS Organization Geologic Hazards Science Center