QUANTIFYING THE LONG-TERM SUSPENDED SEDIMENT DISCHARGE AND DELIVERY RATIO OF DRAINAGE BASINS

Understanding and quantifying the long-term suspended sediment discharge of drainage basins is a key goal of geomorphology, with important implications for the study of water quality, agricultural sustainability, and the evolution of landscapes and sedimentary basins over geologic time scales. Previous studies have highlighted the importance of relief/slope, precipitation, temperature, vegetation, and soil texture as controlling variables for suspended sediment discharge in natural/undisturbed landscapes. However, no widely used, globally applicable model for predicting suspended sediment discharge incorporates all of these known controls. In this presentation, I propose a globally applicable model for the long-term suspended sediment discharge from drainage basins that honors the principal controls on suspended sediment discharge previously documented in the geomorphic literature. By incorporating process-based elements to the greatest extent possible, the model is capable of accurately predicting the long-term natural/pre-dam sediment discharges of 128 global rivers using just 2 free parameters. The model uses precisely co-rectified 5-arcminute-resolution input data layers for topography, fractions of clay, silt, sand, and gravel, mean monthly rainfall, and mean monthly Leaf Area Index to predict the suspended sediment flux and sediment delivery ratio of every point on Earth at the resolution of the input raster data. The model explicitly distinguishes the detachment of sediment on hillslopes from the transport of sediment in channels. The model uses slope, soil texture, and mean monthly rainfall and leaf area index as controlling parameters for the detachment component. The transport component is modeled using a Rouse-number-dependent transport criterion than explicitly includes the effects of slope and soil texture. The model can be used to provide baseline estimates of suspended sediment discharges in natural/undisturbed landscapes that can be used to assess the impact of land use changes on suspended sediment discharge.