STAND, a dynamic model for sediment transport and water quality

We introduce a new model–STAND (Sediment-Transport-Associated Nutrient Dynamics)–for simulating stream flow, sediment transport, and the interactions of sediment with other attributes of water quality. In contrast to other models, STAND employs a fully dynamic basis for quantifying sediment transport, thus distinguishing it from the well-known HEC-6 model. This latter, in particular, computes a steady-state form of sediment transport based on an approximation of transient flow regimes by a sequence of steady-state hydraulic conditions. STAND has a three-level structure. The first level accounts for the hydraulics of open-channel flow, using the conventional St Venant equations. The second level computes sediment transport potential and actual transport rates based on the information provided by the first level. In the third level (not discussed herein), changes of nutrient concentrations along the studied river can be computed as a function of nutrient transport, adsorption/desorption of nutrients to suspended sediment, and releases from bed-sediment pore water. Having introduced STAND and compared and contrasted its structure with HEC-6, STANDʹs performance is evaluated against a comprehensive data set obtained from a section of the Weihe River, a major tributary of the Yellow River, in China, and compared to results from HEC-6. From both visual evaluation and the statistics of the residual time series, it can be concluded that STAND provides the better simulation, notably under conditions of strongly transient stream behavior.