FACTORS INFLUENCING DEBRIS FLOW ASSESSMENT DURING BURNED AREA EMERGENCY RESPONSE INVESTIGATIONS

Burned Area Emergency Response (BAER) teams addressing the impact of wildfires on Federal land are charged with identifying threats to life and property as well as potential increased water flows, erosion, and sedimentation. Debris flows represent a primary threat to life and property because of their rapid onset, destructive effects, and potential for impact at some distance from the actual wildfire area. Available information on pre-fire conditions influencing debris flow potential is highly variable among wildfire area. BAER assessment should both identify the threats and recommend actions to prevent or mitigate them. While regulations require initial BAER assessment within days of fire control, revisions can be made based on additional investigation. From a practical sense, effective emergency measures must be implemented before the first debris flow-initiating storm event. Hungr and others (1987) noted debris flow mitigation measures can be placed in the source area, along the transport zone or in the deposition zone. Within the source area of a wildfire, the increased erosion and sedimentation leading to debris flows requires restoration of vegetative cover; a long-term rather than emergency measure. Emergency debris flow measures are limited to along the transport zone or in the deposition zone. A variety of techniques exist that attempt to trap, divert, or otherwise limit the destructive impact of debris flows to structures and other infrastructure. Investigators are often charged with helping define suitable locations for applying these techniques and associated design requirements. These mitigation measures also have practical value in reducing the threat to life. Emergency evacuation of people from debris flow-threatened areas is another measure for mitigating the threat to human life. This measure holds great promise, but places an extra burden on investigators identifying potentially impact areas and defining the conditions calling for evacuation.