Conclusions
Through a GIS-based soil erosion model and high resolution LiDAR terrain data, this study provided a spatial analysis of road-related flow path delineation and soil loss in post-fire forest conditions. Fire greatly increased the soil erosion risk with estimated levels greater than 4 Mg ha-1 yr-1 for nearly 80% of the burned area. Our model predictions conformed well with reported sediment depositions immediately following the fire. The modelling showed that even though roads are generally thought to exacerbate erosion problems, in the post-fire environment they had complex and variable effects on runoff and sediment transport. Overall the roads and downstream system of detention basins created opportunities to catch a considerable amount of sediment. In some cases, the roads diverted upland runoff and sediment to the adjacent subwatershed. The road fillslopes were predicted to be at risk for high onsite soil loss risk as were channels downstream of roads. The modeling and onsite observations suggest that a properly designed road drain system including well-spaced culverts with energy dissipating outlets can reduce the likelihood of water and sediment flooding over the road surface and minimize the risk of downstream channel erosion or gullying.