Hydrologic conditions and terrestrial laser scanning of post-firedebris flows in the San Gabriel Mountains, CA, U.S.A
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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 overland-flow 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 overland flow 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 metter-scale debris flows. In response to a single small storm, the debris flows deposited irregular levees and lobate terminal snouts on hillslopes and caused wide- spread erosion of the valley axis with ground surface lowering exceeding 1.5 m.
Study Area
Publication type | Article |
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Publication Subtype | Journal Article |
Title | Hydrologic conditions and terrestrial laser scanning of post-firedebris flows in the San Gabriel Mountains, CA, U.S.A |
Series title | Italian Journal of Engineering Geology and Environment |
DOI | 10.4408/IJEGE.2011-03.B-064 |
Year Published | 2011 |
Language | English |
Publisher | Sapienza Università di Roma |
Contributing office(s) | Geologic Hazards Science Center, Geology, Minerals, Energy, and Geophysics Science Center |
Description | 11 p. |
First page | 583 |
Last page | 593 |
Conference Title | 5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment |
Conference Location | Padua, Italy |
Conference Date | June 14-17, 2011 |
Country | United States |
State | California |
Other Geospatial | San Gabriel Mountains |
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