Deriving a spatially-explicit hillslope sediment delivery ratio model based on the travel time of water across a hillslope

To derive a sediment budget at the catchment scale, sediment transport models such as SedNet typically require an estimate to be made of the input of sediment to each stream link for each defined sub-catchment. This requires an estimate of both the erosion and delivery of sediment from every pixel within each sub-catchment. The total erosion within each pixel is calculated using the Universal Soil Loss Equation (USLE), while the delivery of sediment from that pixel to the nearest stream is based on a hillslope delivery ratio (HSDR). At large scales (250 m), a constant HSDR is typically used, however at the 5 m scale used in this study, a spatially-explicit HSDR was required. To derive this, a physics-based hillslope erosion model, LISEM, was applied and calibrated to a representative, monitored hillslope in the Weany Creek catchment. The results of this modelling approach were then generalised to derive a relationship between travel time and HSDR which was then applied to the whole of the Weany Creek catchment.