Dam Break Waves on stepped bottom

Propagation of dam-break induced waves is a challenging topic, studied since many years, for its important practical impact. This paper presents some laboratory experiments of dam break waves propagating on a stepped fixed bottom, with the bed discontinuity placed upward or downward of the gate. It is observed that on sharp edges of the rigid boundaries the flow is smooth. Such behaviour seems to be imputable to the formation of a system of concentrated vortices, which ensures the smoothness of streamlines of the main flow. The experimental data are compared against numerical solutions of the first order shallow water equations solved using an exact Riemann solver. The comparison shows that the numerical solutions, with a sharp front, are not able to correctly reproduce the observed behaviour. These results suggest that, while significant progresses have been made, a serious problem still remains in using the shallow water equations in case of non-uniform bottom geometry.