HYDROLOGIC CONDITIONS AND TERRESTRIAL LASER SCANNING OF POST-FIREDEBRIS FLOWS IN THE SAN GABRIEL MOUNTAINS, CA, U.S.A — IJEGE
 
 
You are here: Focus and scope Issues from 2005 to 2018 5th International Conference on Debris-Flow Hazards "Mitigation, Mechanics, Prediction and Assessment" Topic 6 - Debris-flow Monitoring and Alert Systems HYDROLOGIC CONDITIONS AND TERRESTRIAL LASER SCANNING OF POST-FIREDEBRIS FLOWS IN THE SAN GABRIEL MOUNTAINS, CA, U.S.A
Document Actions

HYDROLOGIC CONDITIONS AND TERRESTRIAL LASER SCANNING OF POST-FIREDEBRIS FLOWS IN THE SAN GABRIEL MOUNTAINS, CA, U.S.A



Abstract:
To investigate rainfall-runoff conditions that generate post-wildfire debris flows, we instrumented and surveyed steep, small watersheds along the tectonically active front of the San Gabriel Mountains, California. Fortuitously, we recorded runoff-generated debris-flows triggered by one spatially restricted convective event with 28 mm of rainfall falling over 62 minutes. Our rain gages, nested hillslope overland- flow sensors and soil-moisture probes, as well as a time series of terrestrial laser scanning (TLS) revealed the effects of the storm. Hillslope overlandflow response, along two ~10-m long flow lines perpendicular to and originating from a drainage divide, displayed only a 10 to 20 minute delay from the onset of rainfall with accumulated totals of merely 5-10 mm. Depth-stratified soil-moisture probes displayed a greater time delay, roughly 20- 30 minutes, indicating that initial overland flow was Hortonian. Furthermore, a downstream channel-monitoring array recorded a pronounced discharge peak generated by the passage of a debris flow after 18 minutes of rainfall. At this time, only four of the eleven hillslope overlandflow sensors confirmed the presence of surface-water flow. Repeat TLS and detailed field mapping using GPS document how patterns of rainsplash, overland-flow scour, and rilling contributed to the generation of meter- scale debris flows. In response to a single small storm, the debris flows deposited irregular levees and lobate terminal snouts on hillslopes and caused widespread erosion of the valley axis with ground surface lowering exceeding 1.5 m.

Authors:
Kevin M. Schmidt - U. S. Geological Survey, 345 Middlefield Rd., MS-973, Menlo Park, CA, 94025, U.S.A
Maiana N. Hanshaw - U. S. Geological Survey, 345 Middlefield Rd., MS-973, Menlo Park, CA, 94025, U.S.A
James F. Howle - U. S. Geological Survey, P.O. Box 1360, Carnelian Bay, CA, 96140, U.S.A.
Jason W. Kean - U. S. Geological Survey, P.O. Box 25046, MS-966, Denver, CO, 80225, U.S.A
Dennis M. Staley - U. S. Geological Survey, P.O. Box 25046, MS-966, Denver, CO, 80225, U.S.A
Jonathan D. Stock - U. S. Geological Survey, 345 Middlefield Rd., MS-973, Menlo Park, CA, 94025, U.S.A
Gerald W. Bawdeng - U. S. Geological Survey, 3020 State University Dr. E., Sacramento, CA 95819, U.S.A.
Keywords
Rainfall-runoff, debris flow, rainfall threshold, terrestrial laser scanning, lidar, wildfire, warning system
Statistics