2022 Post-Wildfire Debris-Flow Hazard Assessments

Wildfire can substantially alter the hydrologic response of watersheds to rainfall, and debris-flow activity is among the most destructive consequences of these events. To assist federal, state, and local agencies in planning for postfire hazards, the U.S. Geological Survey (USGS) conducts debris-flow hazard assessments for recent wildfires. This page holds all postfire debris-flow hazard assessments produced by the USGS during 2022. Each hazard assessment is provided as an attached zip archive. The zip archives follow the naming convention <fire>_<start date>_<id>.zip, where <fire> is the name of the fire event, <start date> is the date the fire started, and <id> is the fire ID used by legacy distribution tools. Each assessment maps the modeled likelihood, potential volume, and combined hazard of debris flows across the burn area for a series of design rainstorms. Each assessment also include estimates of the rainfall rates required to trigger debris flows. These results are generally representative of the conditions immediately after the fire. Assessment results are provided as Shapefiles, and each assessment includes one or more README files documenting the provided Shapefiles and relevant data fields. All assessments include a README named "PostFireDFEstimates_README.pdf", which describes fields that report hazard modeling results for various design storms. Some assessments also include a README named "PostFireDFThresholdEstimates_README.pdf", which describes fields that report the rainfall thresholds needed to trigger debris flows for various design probability levels. Each assessment also includes a pdf image named "image.pdf" that maps the combined hazard results for a selected design rainstorm. Although the README files are mostly accurate, they have several known issues. First, many assessment datasets include files and/or data fields not described in their associated READMEs. These extra fields are processing artifacts of the hazard modeling algorithm, so do not represent relevant results. Second, all fields described by the READMEs have been truncated to 10 characters in the data tables. Third, all README fields that begin with "M1_X" instead begin with "L_X" in the data tables. Fourth, the field named "M1_R" in the READMEs is named "R" in the data tables. Assessments were produced by USGS personnel running legacy codebases designed to implement: * The "M1" debris-flow likelihood model of Staley and others (2017) * The "emergency" potential sediment volume model of Gartner and others (2014) * The debris-flow combined hazard classification scheme of Cannon and others (2010) Operational personnel may have modified stream network delineation and modeling parameters in order to ensure quality. References: Cannon, S.H., Gartner, J.E., Rupert, M.G., Michael, J.A., Rea, A.H., and Parrett, C., 2010, Predicting the probability and volume of postwildfire debris flows in the intermountain western United States: Geological Society of America Bulletin, v. 122, no. 1-2, p. 127-144, https://doi.org/10.1130/B26459.1. Gartner, J.E., Cannon, S.H., and Santi, P.M., 2014, Empirical models for predicting volumes of sediment deposited by debris flows and sediment-laden floods in the transverse ranges of southern California: Engineering Geology, v. 176, p. 45-56, https://doi.org/10.1016/j.enggeo.2014.04.008. Staley, D.M., Negri, J.A., Kean, J.W., Laber, J.L., Tillery, A.C., and Youberg, A.M., 2017, Prediction of spatially explicit rainfall intensity–duration thresholds for post-fire debris-flow generation in the western United States: Geomorphology, v. 278, p. 149-162, https://doi.org/10.1016/j.geomorph.2016.10.019.

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