Predicting road erosion rates in selectively logged tropical rain forests

The main sediment sources created by selective harvesting of tropical rain forests come from building access roads and log haulage tracks that often extend the drainage network and deliver large quantities of sediment to channels. When unchecked, these tracks develop into gullies that continue to erode long after logging. Several years after harvesting, hollow log culverts beneath access roads can fail during exceptional storms sending surges of sediment into the drainage system. Predicting the erosion so caused involves calculating rates of erosion per unit length and width of road, estimating total road length within the catchment area, making allowances for road gradient and substrate, and calculating the potential sediment yield. Remote sensing of roads and tracks under a regenerating forest canopy requires considerable ground-truthing. Estimates derived for disturbed catchments compare favourably with measured rates in small catchments. However, episodic large sediment fluxes caused by road collapse are difficult to predict.