Cavities behind a spillway with a wide sill

The paper reports experimental results on flow regimes with and without cavities behind a rectangular sill in an open channel. Photographs illustrating the shapes of the free ends of the cavities are given. It is shown that the domains of existence of various flow regimes overlap in the phase space of problem parameters, which leads to nonuniqueness of various functions of the parameters. Quantitative information is obtained for free surface profiles, the discharge coefficient, and the pressure on the flow bottom.