Experimental Investigation on Discharge Coefficient for Combined Structure of Weir-Gate under Flood Conditions

Combined structure of weir-gate is used in order to measure both flow rate and to prevent accumulation of sediment behind the weir. Combining weir with gate leads to alterations in discharge coefficient. In the current study, five models of combined structure of triangular sharp crested weir-rectangular gate were designed and constructed, and then the effects of hydraulic parameters such as flow depth above the weir crest (h) and geometric parameters such as gate height (d), gate width (b) and the vertical distance between the lower edge of (y) on the discharge coefficient were investigated. The discharge coefficient was found to be inversely proportional to h/d, b/d and h/y.  The results indicated that the combined structures were functionally similar to the gate and a regression equation with R² = 0.97 was developed to predict discharge coefficient. The sensitivity analysis showed that the equation was more sensitive to h/y. The presented equation was compared with those introduced in the literature indicating the accuracy of the developed equation and the shared ranges for using the equations with other studies