Hydraulic design for the two-stage stilling basin

The two-stage stilling basin is a design sometimes used for high head energy dissipating structures. The distinguishing feature of the design is that essentially two hydraulic jumps occur in series in the same structure. The tailwater depth for the first jump is created by a fixed weir. Tailwater for the second jump is due to the natural tailwater available in the downstream channel. Since most of the energy of flow is dissipated in the first jump, the required tailwater depth to produce a jump in the second basin is considerably decreased, with the result that the entire stilling basin floor may be placed at a higher elevation than for a single basin. This can be advantageous in certain situations.In this paper the results of hydraulic model tests for a two-stage stilling basin are reported. The characteristics of the basin first were studied two-dimensionally using a parallel sided flume. A design criterion was established and this was subsequently verified on a three-dimensional model.