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.