Modelling Sediment Delivery Ratio Based on Physical Principles

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