Abstract

Post-fire managers throughout the world use predictive models to estimate potential erosion risks to aid in evaluating downstream impacts of increased runoff and erosion, and to target critical areas within a fire for applying mitigation practices. Erosion prediction can be complicated by forest road networks. Using GIS technology and a soil erosion model, this study evaluated the effect of roads on erosion and sediment yield following a wildfire, and whether the predictive models were providing reasonable results. The GeoWEPP model was used to simulate onsite erosion and offsite sediment delivery before and after fire disturbance. A 2-m resolution DEM was used as the terrain layer. Erosion rates in excess of 4 Mg ha-1 yr-1 were predicted mainly from the moderate and high severity burn areas. Roads influenced both flow path and sub-catchment delineations, affecting the spatial distribution of sediment detachment and transport. Through that influence, roads tended to reduce estimated erosion on slopes below the roads, but road fillslopes and steep channels were areas of significant increases in erosion risks. Measured deposition amounts along roads and in sediment basins were similar to predicted amounts. The results confirm that road prisms, culverts and road ditches greatly influence sedimentation processes after wildfire, and they present opportunities to detain eroded sediments before they reach downstream water bodies.