Energy Loss Below Rectangular Sharp-crested Weirs for Free Flows

This study considers the flow over a rectangular sharp-crested weir and the associated energy loss occurring just below the weir for free flows. Previous studies described the surface flow regime as the weir gets submerged with the increase of tailwater. For relatively smaller tailwater depths compared to the weir height, the flow regime, and energy loss downstream of the weir have not been studied in detail. Laboratory experiments were performed with a sharp-crested rectangular weir placed inside a horizontal rectangular flume to observe the flow regime for tailwater depths up to the weir height. It was seen from these preliminary experiments that for small tailwater depths, the main energy loss occurs due to the turbulent mixing with the pool behind the nappe. As the tailwater depth increases, a hydraulic jump forms on the falling nappe and the energy dissipation appears to occur mostly due to the mixing inside the jump. Empirical equations were developed for the relative energy loss and the theory of hydraulic jump in the sloping channel was used to predict the energy loss in the jump below the weir.