Evaluation of Discharge Coefficient in Sharp Crested Side Weirs with Rectangular and Triangular Cross Sections

Side weirs are flow diversion and protection devices that are widely used in irrigation, land drainage and urban sewage systems. This study investigates the discharge coefficient of rectangular and triangular sharp crested side weirs and identifies the effective factors on this parameter by using dimensional analysis and statistical approaches. In addition to calculating the discharge coefficient, equations with 5 percent error for rectangular and 3 percent error for triangular shape have been proposed. For checking the effect of factors on this parameter sensitivity analysis is performed. The results demonstrate that the most important effective factors on discharge coefficient of the rectangular and triangular weirs are Froude number and dimensionless ratio of the main channel wide to the depth of flow in the upstream of the weir, respectively. Error of discharge coefficient (Cd) can be increased up to 7 percent for rectangular weir and 4 percent for triangular side weir with ignoring these factors. Also accurate estimation of discharge coefficient, merely with considering the upstream hydraulic condition, is not correct. The geometry of the cross section should be considered as an effective factor for determination of discharge coefficient, and this approach, decreases error of the calculation up to 3 percent.