The Effect of Water Level on The Effectiveness of Sediment Flushing
This research is focused on determining the effective flushing water level in pressure flushing activity at storage sedimen based on the hydraulic physical model test in the laboratory. The effective water level is the elevation of water level in sediment flushing which result in the highest concentration of sediment scours. Effective flushing water level is the elevation of water level near the top layer of sediment deposit which can trigger the erosion of the top layer of sediment so that it creates a maximum scours. That elevation is known as Effective Flushing Water Level (EFWL). This research was conducted in the laboratory using Wonogiri Reservoir prototype, with scale model of 1:66.67. The model operated without inflow, started from control water level (CWL) .and lowered gradually by operating the flushing gates. The gates were operated of a = 2.50 cm. The flushing implementation was repeated with variation of sediment thickness Hs=1.50; 3.00; 3.75 and 4.50 cm. The water level, sediment concentration, flushing discharge, and the flow velocity in the upstream of the gates were observed every 1.50 cm lowered of water level. Coal dust was used in this research to substitute sediment material. The result of this research is expected to be used as an initial consideration of effective sediment flushing in Wonogiri reservoir protoype in order to reduce the capacity loss of the reservoir due to sedimentation , or in other words to extend the life time plan of reservoir.