Simulation of non-uniform sediment transport in a German reservoir with the SSIIM model and sensitivity analysis
Numerical models have been widely used to calculate long-term sediment deposition and erosion in reservoirs. This study investigates the river morphodynamic processes in the Iffezheim reservoir at the Upper Rhine River in Germany with non-uniform bed composition. The computational fluid dynamic model SSIIM is applied to calculate the flow. SSIIM solves the three-dimensional Reynolds averaged Navier-Stokes equations with the k-_ turbulence model on unstructured grids. The suspended load transport is simulated with the convection-diffusion equation, and the equilibrium sediment concentration is calculated by the empirical formula of van Rijn (2007). Nine sediment size fractions are chosen to represent the non-uniform sediment mixture. The purpose of the study is to determine the sensitivity of a set of parameters on the results and investigate whether the bed elevation changes can be accurately simulated. During the simulation of the morphological changes with constant sediment inflow in the Iffezheim reservoir, it has been observed that minor changes in the morphodynamic parameters significantly influence the results concerning the sediment erosion and deposition, e.g. the settling velocity, the thickness of the sediment active layer and the numerical parameters time step and number of iterations for the sediment transport equation. The impact of these parameters on the bed change is investigated in the study and the accordingly chosen parameter values are applied in the ensuing time-dependent simulation. The erosion and deposition predictions have been compared to measured data of regular bed change surveys. The results of the simulations are in reasonably well agreement with the measured data.