Study of the effect of sloping-broad crested weir on the uniformity of flow into bilateral intakes in a channel bend

Construction of weirs in river bends results in the non-uniformity of water flow across the channel bend and the poor performance of intake structures on both sides of the river. The main hypothesis for enhancing the uniformity is the change of the weir-crest profile from horizontal to sloping crest. The aim of the present study was to test the performance of horizontal and sloping broad-crested weirs in a channel bend under clear flow conditions, using both experimental and numerical models. The FLOW-3D model was calibrated and verified with the use of the experimental data. The numerical model was then applied for the simulation of different scenarios to test the effects of such parameters as the location of the weir at the bend; slope of the weir’s crest; geometries of bilateral intakes including alignment, width and sills; and upstream flow conditions. The results indicate that the sloping crest weir provides an enhance performance by reducing transverse gradients of water surface at upstream control section, and thereby increasing the flow rates towards the two bilateral intakes. It is concluded that a weir with sloping crest (in the range of 2º to 5º toward the outer bank of the bend), at the position of 30 to 60 degrees along the bend, with the intake angle in the range of zero and 60 degrees (respect to the main channel flow), the ratio of intake to main channel width of (1:10), and with the use of entrance sill satisfies the requirements for a better performance. The intake angle of zero is the best choice. In the case of normal intakes, the weir is recommended to be placed at 30 degrees downstream of the bend entrance.