Post-Fire Debris-Flow Hazard Assessments at the U.S. Geological Survey – Recent Advances and Future Directions

Abstract:

Wildfire can have profound effects on the hydrologic response of a watershed, and debris-flow activity is among the most destructive consequences of these effects. The continued high likelihood of catastrophic wildfires in the western U. S. and the encroachment of development into fire-prone areas have created the need to develop tools to identify and quantify the potential hazards posed by debris flows generated from burned watersheds. These tools are critically needed by Federal, State, and local agencies to mitigate the impacts of debris flows on people, their property, infrastructure and natural resources. Applied research at the U.S. Geological Survey (USGS) Landslide Hazards Program is focused on providing timely, science-based assessments of post-fire debris-flow hazard.

Formerly, post-fire debris-flow hazard assessments were disseminated by means of the USGS Open-File Report publication series, which included poster-sized maps that predicted the probability, volume, and combined hazard for given watersheds. Feedback from collaborators suggested that 1) the reports were not sufficiently timely for immediate post-fire use, 2) the static maps were difficult to use for site-specific assessments, and 3) individual assessments were often cost-prohibitive. Beginning in January 2014, the USGS has transitioned to a web-based method for disseminating post-fire debris-flow hazard assessments. This new platform addresses the primary concerns of our stakeholders in three ways. First, the turnaround time has been reduced from 1-2 months for a map and written report, to 3-4 days for a web-based map assessment. This allows response teams to incorporate the assessment results into their reports, which are urgently needed immediately after fires. Second, the new website is interactive and accompanied by downloadable geospatial data of predictions for several storm scenarios. These features permit casual (local residents) and power-users (GIS experts) to evaluate site-specific debris-flow hazards. Finally, the new web-based assessments are completely free and publicly available online. This new method for assessment dissemination permits the Landslide Hazards Program to focus energies on improving existing predictive models of post-fire debris-flow probability, magnitude and timing.