Abstract
A combined weir consisting of a sharp-crested rectangular contracted weir and an inverted triangular weir below is a now regulation device used in irrigation works for diverting the flow from a main channel to a secondary channel. The present practice for computing the discharge for classical rectangular and triangular weirs is from curves or equations relating the discharge coefficient and the upstream depth/gate opening ratio parameter including weir geometry, and tailwater depth/gate opening ratio being the fourth parameter which is needed to be updated. The discharge for simultaneous flow still in addition involves few more parameters: the distance between the weirs, the slope of the apron, the opening depth and weir angle. In this paper one generalized equation including all the important variables is obtained from the experimental investigations. This equation is suitable for both horizontal and sloping channel bed under submerged flow and for the free flow, the tailwater depth / weir opening ratio term being neglected. The predictions of the equation agreed well with the experimental data.