Author(s): Sameh Kantoush; Erik Bollaert; Anton Schleiss
Keywords: Sedimentation of shallow reservoirs; Suspended load; Sediments retention basin; Rectangular reservoir geometry; Flow patterns; Trap efficiency; Sediments release
Abstract: The deposition behaviour of fine suspended sediments in shallow reservoirs is a phenomenon which is not yet fully understood. Sediments trap efficiency plays a key role in the effective operational life of reservoirs. This paper presents the influence of the width of rectangular shallow reservoir on the trap efficiency of sediments. The experimental study focuses on the sedimentation of shallow reservoirs mainly by suspended sediments. The water surface elevation in the reservoir was similar for all experiments. Neither the water nor sediments discharge conditions were changed during the experimental runs. Real time measurements of suspended sediments concentrations were carried out to monitor the inflow and the outflow condition. This allows to understand the complex relation between flow patterns, sediments exchange and sediments transport. In spite of the symmetric setup, an asymmetric flow and sediments pattern developed. For all tested geometries, the influence of suspended sediments on both flow patterns and bed forms was found very similar. At the beginning of the tests, the highest sediments depositions and concentrations were found along the main jet flow, where the velocity is highest. The flow pattern was stable, with smooth or relatively low roughness over the entire bed. However, after some time, ripples developed underneath the main jet, with thicknesses of about 0. 15 times the flow depth. These were able to change the flow pattern. The higher the shape factor of the reservoir, the more uniform were the depositions over the entire surface. Furthermore, the time evolution of deposition patterns with different reservoir geometries could be assessed. Sediments Trap Efficiency (TE) in the reservoirs was calculated by using two different approaches. The results show different correlations for trapping efficiency with variable rectangular widths.