Hydraulics of Submerged Triangular Weirs and Weirs of Finite-Crest Length with Upstream and Downstream Ramps

Laboratory tests were carried out to investigate the hydraulics of submerged flow over triangular weirs and weirs of finite-crest length with upstream and/or downstream ramp(s). Water surface profiles were recorded as the weir submergence set and for various stages of submergence. Variations in modular limit and discharge reduction factors for the present weirs were studied. It was found that the modular limit varied with the ratio of the free-flow head to the total streamwise length of the weir. Characteristic length scales such as horizontal and vertical distances from the toe of the surface jump and the first wave trough to the downstream crest edge of the weir were measured to generalize different wave patterns. It was found that the toe of the surface jump moved toward the weir as the weir submerged and varied linearly with the submergence level, which is the ratio of tailwater to headwater depths. For weirs of finite-crest length with upstream and downstream ramps (i.e., embankment weirs), the toe of the surface jump moved toward the weir as the submergence level increased up to 0.7. For higher submergence levels, the trough of the surface wave moved toward the downstream and eventually washed away. Efficiency and performance of the present weirs were evaluated with their own free-flow conditions. Empirical formulations were developed to predict the discharge reduction factor with submergence level. The performance of triangular weirs in submerged-flow conditions was found to be better than that of corresponding sharp-crested weirs; weirs became more efficient as the ratio of the free-flow head and the total length of the weir increased.