THREE-DIMENSIONAL NUMERICAL MODELLING OF RESERVOIR FLUSHING TO OBTAIN LONG-TERM SEDIMENT EQUILIBRIUM

Abstract

Within this study, the technical feasibility of reservoir flushing is assessed in order to restore the storage capacity of the Schwarzenbach pumped storage reservoir. For this purpose, a fully three-dimensional numerical model is used to investigate the efficiency of different flushing scenarios. The applied numerical program SSIIM 2 solves the Reynolds-averaged Navier-Stokes equations accordingly to the finite volume method and with a k-ε turbulence closure for an adaptive, unstructured and non-orthogonal grid. The suspended sediment transport is calculated by solving the transient convection-diffusion equations for multiple grain sizes. The model is set up based on bathymetric data, sediment characteristics from bed samples, the initial thickness of the deposited sediments and the in- and outflow discharge rates. In order to investigate the success of reservoir flushing, three scenarios with different water levels are simulated. The simulated bed level changes, as well as the calculated amount of flushed out sediments, are presented in this study. The results reflect the dependency on the success of the flushing on the lowering target.