Gravity currents shoaling on a slope

Laboratory experiments are performed to examine gravity currents propagating into an ambient of uniformly decreasing depth. Predominantly, the study is of a surface gravity current shoaling over a bottom slope as it approaches a corner between the horizontal surface and the sloping topography. For sufficiently high Reynolds number currents, they are found to propagate at a constant speed over the slope until the depth of the ambient below the nose is comparable to the depth of the current in the lee of the gravity current nose. It then decelerates at a constant rate set by the product of the reduced gravity, g′, and the magnitude of the topographic slope, s. The shape of the head evolves to form a front parallel to the slope itself and the ambient ahead of the current accelerates downslope with significant turbulence between the ambient and current head. The dependency of the deceleration upon g′s is anticipated from WKB-like extensions of steady-state gravity current theory that include the effect of the ambient depth in one case varying slowly in space as the current first passes over the slope and in another case varying slowly in time as the nose approaches the corner. However, the measured deceleration magnitude of 0.31( ± 0.01)g′s is found to be larger than these heuristic predictions. C © 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4818440]