Wildfires and Debris Flows
The Southern California wildfires of 2007 stripped ground cover from millions of acres, including many steep canyons. Now that the fires are over the homes of thousands of Californians in and near such canyons are at risk from dangerous debris flows. USGS, in partnership with NOAA, FEMA and state and local agencies, is working to provide the scientific information emergency agencies need to predict debris flows and protect lives and homes.
The USGS Multi-Hazards Demonstration Project coordinated the USGS response to the 2007 southern California firestorms. The effort was unprecedented in its scope, efficiency, deployment, and results. Upon the onset of the fires the USGS funded airborne remote sensing data, helped to staff the debris flow mapping project, and coordinating the fire response internally, with the Joint Field Office in Pasadena, and later with OES and FEMA officials at the Multi-Agency State and Federal State and Federal task force (MAS-G) in Colton, CA.
Just in time for the first round of post-fire rains, the USGS and FEMA were able to complete and release a series of flood inundation and debris flow maps showing the areas within the eleven burned areas that may be impacted by flooding and debris flows. These maps illustrated to federal, state, and local emergency responders the volume of debris flows that can be expected from specific areas, and identified the areas prone to impact by floods and debris flows. The maps were provided to forecasters with valuable information as part of the joint NOAA-USGS flash flood and debris flow warning system for recently burned areas in southern California.
USGS scientists were also able release an “ash advisory” before the rains based on preliminary results of ash samples taken immediately from burn sites in suburban and wildland areas. Several ash samples analyzed to date produce elevated pH levels, suggesting the ash may generate “caustic alkalinity upon contact with rainwater or water-based body fluids such as perspiration or fluids lining the respiratory tract.” Residential ash samples preliminarily showed elevated levels of some metals or metalloids such as arsenic, lead, copper, and/or zinc.
The USGS conducted assessments of some critically endangered species within the fire footprints. Several aquatic species were in extreme peril of extirpation from flooding, debris flows, and dry ravel. For example, half of the remaining populations of the endangered tidewater goby south of Los Angeles County downstream from the Ammo Fire were taken into captivity by USGS to ensure their persistence through the winter. Several populations of genetically pure southern California steelhead may have become extirpated from the continuous dry ravel filling the few remaining pools it occupies.
Department of the Interior Secretary, Dirk Kempthorne visited the multi-hazard multi-discipline effort in January hiking with USGS scientists at the site of the Canyon fire in Malibu, CA where science, partnerships and newly installed USGS instruments and streamgages are helping to keep emergency responders and the public informed and alert. As of this writing, winter’s rains are in the forecast for southern California. These winter rains have the potential to wash the denuded hillsides into neighbor-hoods in devastating debris flows (also called mudflows) and floods into neighborhoods and contaminated ash from the fires into the regions water supplies.
