EMERGENCY ASSESSMENT OF POST FIRE DEBRIS FLOW AND FLOODING HAZARDS, 2015 VALLEY AND BUTTE FIRES, CALIFORNIA

State Post Fire Watershed Emergency Response Teams were deployed to the Valley Fire and Butte Fire burn areas after receiving Presidential disaster declarations. The teams were tasked to perform rapid assessments that evaluated potential risk from post-fire flooding and debris flows. The multi-agency teams were composed of individuals with expertise in geology, hydrology, forestry, engineering, GIS, and water quality, including engineering geologists from the California Geological Survey. Emergency response teams identified on-site and downstream threats to public health or safety from post-fire flooding and debris flows and developed preliminary emergency protective measures. Teams utilized a variety of data including Burn Area Reflectivity Classification (BARC) maps developed by the US Forest Service and CalFire, GeoWEPP (Geographical interface for the Water Erosion Prediction Project) maps that estimate the quantity of erosion during a design storm event, and USGS post-fire debris flow hazard modeling that estimates the probability and volume of debris flows for selected basins in response to a design storm.

A sequence of logical steps required field validation of one set of data that enabled the use of that data in empirical models which were used in the field to identify possible hazards. Emergency response teams identified areas of concern based on USGS debris flow modeling data, FEMA 1% annual chance floodplain mapping, and BARC data. Helicopter reconnaissance and aerial imagery (Google Earth) were used to augment on-the-ground observations. Site-specific observations were compiled using a “Burn Site Evaluation Summary” form that noted the at-risk feature, address, GPS location, hazard, likelihood of occurrence, and risk to life and/or property. In addition the responsible agency and possible emergency protection measures were noted. The information was reported and presented to FEMA, CalOES and local public safety officials. Reported data is intended to serve as a preliminary tool to assist emergency responding agencies in development of post fire emergency response plans and to notify affected residents and land owners. Additionally, members of the emergency response team provided assistance to the public safety agencies in interpretation of the detailed scientific data and information.