Influence of the Gate and Weir Interaction on Discharge Characteristics of the Weir - Gate Combined Flow Structure

Theoretical equations were resulted for calculating the combined discharge and discharge coefficient on weir- gate combined flow structure under free flow condition, by applying the energy equation between two points along the passing streamline from lip of the gate. One of the points was considered at the upstream of the weir-gate combined flow structure and the other one at the vena contracta. The gate relative discharge (the ratio of the gate discharge to the weir- gate combined flow structure discharge) was considered as an interaction factor. Influence of the gate relative discharge on combined discharge coefficient and stagnation point level at upstream of the structure was characterized using the proposed equations. The results of this research showed that the combined discharge coefficient under free flow condition decreased with an increase in the gate relative discharge. Stagnation point was near to the weir crest when overflow started from the weir, and it would travel below (near to the gate lip) when overflow from the weir was increased. Influence of the gate relative discharge on combined discharge coefficient was negligible, but its effect on weir discharge coefficient (due to the stagnation point level changes) was considerable.