Flow Rate Capacity Improvement of Triangular Plan Form Sharp Crested Weirs

Hydraulic engineers are always seeking solutions to increase the flow rate capacity of weirs in order to overpass and regulate large flow rates with low upstream afflux, preventing the submergence of valuable lands and private properties. The current study intends to improve the flow rate capacity of sharp-crested triangle weirs using upstream slopes or guiding vanes. The laboratory work involved building and testing twenty-one weir models. Six weir models were left unmodified, while six were modified with upstream slopes changing the angle of vertex θ = 45°, 60°, and 75°, and the height of the weir P_w = 20 and 25 cm. Nine weir models were modified with guiding vanes, with vane heights of 20, 15, and 10 cm. Laboratory results showed that the flow rate coefficient C_dt value decreases as the ratio of upstream head H_cr to height of weir P_w increases, and weirs with a small angle of vertex and a low height of weir allow high flow rates to overpass. In all situations investigated, modified weir models produced greater values of C_dt than unmodified ones. Two empirical power equations were given for estimating C_dt in terms of H_cr/P_w and angle of vertex θ. One for weir models modified with upstream slopes and the other for weir models modified with guiding vanes. The flow rate magnification decreased significantly as H_cr/P_w increased, and models with a small angle of vertex and low weir height provided high flow rate magnification values. A weir model with θ = 45°, P_w = 20 cm, and P_v = 10 cm, modified with guiding vanes, showed the biggest percentage increase in flow rate, ranging from 110 to 220%.