Extended Engelund–Hansen type sediment transport relation for mixtures based on the sand-silt-bed Lower Yellow River, China

While the grain-sorting morphodynamics of gravel- and sand-bed rivers has been intensively studied, sand-silt bed rivers such as the Lower Yellow River (LYR), China and the Pilcomayo River, Paraguay/Argentina have received much less attention. As a first step, we use a database from the LYR in the 1980s to develop a grain size specific extended Engelund–Hansen total bed material load relation. We then use this relation in two morphodynamic calculations. First, we “spin-up” the calculation from an arbitrary bed slope over 600 years to reproduce the downstream fining observed before the closing of Xiaolangdi Dam in 2000. We then cut off the sediment supply, and reproduce the observed pattern of bed coarsening as the bed armours in response to degradation. We argue that our model is likely not site-specific, but applies to other sand-silt bed rivers, basic data for which is as yet lacking.