Journal of Fluid Mechanics

The initial stages of dam-break flow 1

P. K. STANSBY a1, A. CHEGINI a1 and T. C. D. BARNES a2
a1 Hydrodynamics Research Group, School of Engineering, The University, Manchester M13 9PL, UK
a2 School of Mathematics, University of Bristol, Bristol BS8 1TW, UK


Experiments have been undertaken to investigate dam-break flows where a thin plate separating water at different levels is withdrawn impulsively in a vertically upwards direction. Depth ratios of 0, 0.1 and 0.45 were investigated for two larger depth values of 10 cm and 36 cm. The resulting sequence of surface profiles is shown to satisfy approximately Froude scaling. For the dry-bed case a horizontal jet forms at small times and for the other cases a vertical, mushroom-like jet occurs, none of which have been observed previously. We analyse the initial-release problem in which the plate is instantaneously removed or dissolved. Although this shows singular behaviour, jet-like formations are predicted. Artificially smoothing out the singularity enables a fully nonlinear, potential-flow computation to follow the jet formation for small times. There is qualitative agreement between theory and experiment.

In the experiments, after a bore has developed downstream as a result of highly complex flow interactions, the surface profiles agree remarkably well with exact solutions of the shallow-water equations which assume hydrostatic pressure and uniform velocity over depth.

(Received March 10 1997)
(Revised January 21 1998)


1 This article first appeared in volume 370, pp. 203-220 but without p. 213. This reprinting replaces that version and it will be the one that is referenced.