Effect of weir flow on gate discharge in combined cylindrical weir- gate

Problems related to sedimentation and depositions can be minimized by using a system where weirs and gate are combined in open canals while the floated materials run over and sediments run under the structure. Because of effect of overflow on underflow، the variation rate of discharge coefficient with geometric and hydraulic parameters is different with their use each other separately. It is important for cylindrical weir-gate because the flow nape will sit on the weir completely the current work describes the results of experimental investigation on effect of weir flow on gate discharge coefficient for cylindrical weir-gate. In this way the gate discharge is measured against upstream water depth in two condition of weir flow and without weir flow. The experiments are carried out in a laboratory flume 10 m length، 60 cm wide and 70 cm height. Results indicate that increasing dimensionless parameters of Hw/a and Hw/D cause decreasing the discharge coefficient for weir flow and it rises about 1-25% without weir flow. For a constant values of the Hw/a increasing the gate height، the effect of weir on gate discharge coefficient decreases for the cylindrical weir-gate.