RISK ASSESSMENT OF FUEL MANAGEMENT PRACTICES ON HILLSLOPE EROSION PROCESSES Peter R. Robichaud and William J. Elliot Frederick B. Pierson Peter M. Wohlgemuth Research Engineer Project Leader Research Hydrologist Hydrologist USDA-Forest Service USDA-Agric. Res. Service USDA-Forest Service Rocky Mt. Res. Sta. Northwest Watershed Res. Center Pacific Southwest Res. Sta. 1221 South Main St. 800 Park Blvd, Plaza 4, Suite 105 4955 Canyon Crest Dr. Moscow, ID 83843 Boise, ID 83712 Riverside, CA 92507 208-882-3557 208-422-0720 909-680-1501 probi/rmrs_moscow@fs.fed.us fpierson@nwrc.ars.pn.usbr.gov pwohlgemuth/psw_rfl@fs.fed.us welliot/rmrs_moscow@fs.fed.us ABSTRACT Fuel and land management activities in the past century have placed wildland values such as soil and water quality at greater risk due to increased soil erosion. Eroded sediment can lead to decreased long-term soil productivity and adversely impact aquatic ecosystems. Higher runoff rates from severely burned landscapes can lead to flooding and increased risk to human life and property. Over the past ten years, we have completed studies on eight sites in the Northwest and Southeast U.S. measuring erosion impacts associated with prescribed burning. We are now carrying out field and laboratory studies addressing knowledge gaps in our understanding of fuel management practices on soil erosion, and developing a user-friendly computer interface to be able to evaluate the risk and consequences of erosion hazards following wildfires, mitigation treatments, and prescribed burns. Specific tasks that we are addressing include: determining hillslope characteristics that govern dry ravel processes such as slope steepness, vegetation density, soil texture and disturbance impacts; determining the spatial and temporal variability in infiltration and erosion parameters needed to predict overland flow and soil detachment after wildfire; quantifying effectiveness of three mitigation practices in reducing sediment production for specified design storms following wildfires; and evaluating measured erosion rates and estimates of sediment production after wildfires at the upland watershed/catchment scale. Data collection has begun from a burned over catchment and preliminary results will be presented. Additional discussion will address methodologies and approaches to evaluate and model erosion risk and hazard. Keywords: erosion, fire severity, risk assessment, modeling INTRODUCTION Fire is a natural and important part of the disturbance regime of many ecosystems. However, fuel management practices have altered fire size and intensity in the past century, which have in turn affected the runoff response and pushed erosion rates beyond natural levels. Fire suppression efforts have increased fuel loading over historical amounts, and altered wildland species composition. The larger fuel loads and thicker ground cover material contribute to higher severity fires. Such fires remove more of the ground cover material protecting the mineral soil, which leads to downstream flooding and sedimentation. This sediment adversely affects spawning and rearing sites for anadromous fish species, mobilizes in-stream sediment, destroys aquatic habitat, may adversely affect downstream water supply systems and lead to a decrease in soil productivity of sensitive forest soils. Additionally, higher runoff rates from severely burned landscapes can lead to flooding and increased risk to human life and property. For a given watershed if several low severity fires occur over a century as opposed to a single or few high severity fires on much of the area, the damage from erosion, debris flows, mass wasting and floods following fires will likely be lower. Background