Investigation of the Plan Shape Change Effect and Gate Dimension on Hydraulic Performance of Combined Models of Labyrinth Weir- Gate

Weir and Gate are widely used in control, diversion and measurement of flow in irrigation projects due to their simpler and relatively exact relationship. There are sediment and suspended materials in the direction of channels. The accumulation of sediments and suspended materials in the back side of weir and gate caused change of canal shape and reduction of water measurement accuracy. The combined model of weir- gate have the capability of passing settling down from under the gate and suspended materials over weir simultaneously and prevents from accumulation of sediment and suspended materials in the back side of the weir and helps to the accuracy of water measurement and passing flow. The present research investigated ten combined model of labyrinth weir- gate on the effects of plan shape change and gate height on discharge coefficient in the laboratory. The results showed that the existence of gate and increasing of opening height, increased discharge coefficient in combined model of labyrinth weir- gate. On the other hand, existence of gate in combined model of rectangular labyrinth weir- gate in low total upstream water height to weir height have higher effect on the increasing of discharge coefficient. Whereas in combined model of trapezoidal labyrinth weir- gate, with the same of total upstream water height to weir height, had uniform effect on the increasing of discharge coefficient. The results showed that increasing of upstream water height caused interference of water jets of cycles of labyrinth weir and also interference of water flow passing under the gate and flowing water over the weir. Therefore discharge coefficient was lower in deeper depths. On the other hand, in the same depth, the trapezoidal labyrinth weir had less flow interference with respect to rectangular labyrinth weir, which caused higher increase in discharge coefficient in combined model of trapezoidal labyrinth weir-gate with respect to combined model of rectangular labyrinth weir- gate.