Modelling Sediment Delivery Ratio Based on Physical Principles

Sediment delivery ratio (SDR) is traditionally defined as the fraction of upland gross erosion that is transported out of a defined area, e.g., a plot or catchment. It is, effectively, an index of sediment transport efficiency. Previously, it is treated as an empirically-lumped parameter used as a mechanism for compensating for sediment deposition within a catchment area. In this paper, we propose a simple sediment transport model based on the concept of linear reservoir cascades. It links SDR to catchment hydrological response and the dominant sediment deposition processes. The new SDR formulas thus derived are used to explain the spatio-temporal heterogeneity of sediment transport processes and their interactions with rainfall and catchment characteristics. Further, implications for spatially-distributed sediment transport modelling over large spatial extents are explored. Using this model we demonstrate, for the first time, that ambiguity in the previous definition of SDR could be one major source of confusion in the controversial debate about sediment transport in large catchments.