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Dam break wave down a flat stepped storm waterway


Flood waves resulting from flash floods and natural dam overtopping have been responsible for numerous losses. In the present study, surging waters down a flat stepped waterway (Slope = 3.4 degrees) were investigated in a 24 m long chute. Wave front propagation data were successfully compared with HUNT's (1982,1984) theory. Visual observations highlighted strong aeration of the leading edge. Instantaneous distributions of void fractions showed a marked change in shape for (t-ts)*g/do ~ 1.3, which may be caused by some major differences between the wave leading edge and the flow behind, including non-hydrostatic pressure distributions, plug-slug flow regime and different boundary friction regime. Practically, the results quantified the large amount of entrained air (i.e. 'white waters') at the wave front, which in turn reduces buoyancy and could affect sediment motion at the leading edge because the sediment relative density is inversely proportional to the entrained air content. The video shows several wave propagation runs for a 0.0713 m step height (step length: 1.2 m. Some sequence is shown again at a lower speed to illustrate the three-dimensional nature of the front. Some Red-and-white stripes are visible on some steps. The distance between successive stripes is 5 cm everywhere. The channel width is 0.5 m.


York-wee TAN, Jerry LIM, Hubert CHANSON


Hubert Chanson