RECENT ADVANCES IN POST-FIRE DEBRIS-FLOW HAZARD ASSESSMENT AT THE U.S. GEOLOGICAL SURVEY

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, 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. Each assessment included a written report and several poster-sized maps illustrating the predicted probability, volume, and combined debris-flow hazard for given watersheds. Feedback from Burned Area Emergency Response [BAER] teams, the National Weather Service, the U.S. Forest Service, and other stakeholders 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 for stakeholders.

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 BAER 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 (i.e. local residents) and power-users (i.e. GIS experts) to evaluate site-specific debris-flow hazards. Finally, the new web-based assessments are completely free and publicly available online.