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.
References
[1] CHANSON, H. (2004). "Experimental
Study of Flash Flood Surges Down a Rough Sloping Channel." Water
Res. Res., Vol. 40, No. 3, paper W03301, Ref. 10.1029/2003WR002662,
12 pages (ISSN 0043-1397). {http://eprint.uq.edu.au/archive/00002517/}
[2] CHANSON, H. (2004). "Unsteady
Air-Water Flow Measurements in Sudden Open Channel Flows."
Experiments in Fluids, Vol. 37, No. 6, pp. 899-909 (ISSN 0723-4864).
{http://eprint.uq.edu.au/archive/00002505/}
[3] CHANSON, H. (2005). "Air-Water
and Momentum Exchanges in Unsteady Surging Waters : an Experimental
Study." Experimental Thermal and Fluid Science, Vol. 30, No. 1, pp.
37-47 (ISSN 0894-1777). {http://eprint.uq.edu.au/archive/00002794/}
[4] CHANSON, H., and AOKI, S. (2001).
"Dam Break Wave with Significant Energy Dissipation : Two Case
Studies." Proc. 29th IAHR Congress, Beijing, China, Theme C,
Tsinghua University Press, Beijing, G. LI Ed., pp. 311-318 (ISBN
7-302-04676-X/TV). (CD-ROM, Tsinghua University Press, ISBN
7-900637-10-9.) {http://eprint.uq.edu.au/archive/00000357/}
