Flushing sediment through reservoirs



About 1% of the total storage capacity in the world’s reservoirs is lost annually due to sedimentation. Sediments can also block intakes in reservoirs and damage tunnels or turbines. One of the most effective techniques to remove these sediments is flushing, whereby water level is lowered sufficiently to re-erode deposits and flush them through the intakes. Outflow sediment discharge may well be related to the parameters such as the sediment characteristics in the reservoir, during flushing and geometry of flushing channel.
In this study, laboratory experiments were performed on a 1-D reservoir model in a flume in the hydraulics laboratory of Shiraz University to investigate the flushing operation processes by using polymer particles. The polymer particles were lightweight and non-cohesive with an average grain size of about 2.40 mm and density of 1065.3 (kg/m3). The model was installed in a flume; 30 m long, 1 m wide and 0.75 m height. The length of the test section was 11.5 m, and sediments were placed at a length of 4.8 m long upstream from the dam position. Experimental runs have been performed for two flow conditions; 0.0004678 m3/s and 0.000628 m3/s. The very low inflow discharge helped for better monitoring and measuring of the effective parameters. A sluice gate was placed at the central bottom of the dam (as the bottom outlet) and was opened at a constant rate to make the complete drawdown. Results showed that the rate of sediment flushing is strongly associated with outflow rate, water surface gradient with the dam section and the width of the flushing channel. The results from this study were in agreement with that in the literature. It is considered that the low density of the particles causes them to behave as very fine and non-cohesive sediment particles, like loess sediments.