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.