Local Energy Losses for Wave-Type Flows at Abrupt Bottom Changes

Low-head hydraulic structures, like weirs or barrages, are constructed on rivers for irrigation or power-generation purposes. As the upstream water level rises due to these structures, it is necessary to build an energy-dissipation structure such as a stilling basin downstream of the low-head hydraulic structures. The control of hydraulic jumps using abrupt bottom elevation changes at stilling basins may cause wave-type flows. In this study, wave-type flows at abrupt bottom rises and drops were investigated experimentally. For practical reasons, it is important to predict the local energy losses encountered at bottom changes for wave-type flows. Empirical equations for local energy losses and loss coefficients were obtained by evaluating the experimental results for various values of rise or drop heights, discharges, and tailwater depths. The local energy loss in wave-type flows was compared to that of a simple hydraulic jump. It is shown that for some cases local energy losses may become larger than the local energy loss in a simple hydraulic jump. Furthermore, it is difficult to predict the force on a step in the case of wave formation. In this study, a drag coefficient was obtained experimentally to compute the force acting on the step. The variation of this drag coefficient with relative step height is presented.