Lock‐exchange gravity currents with a low volume of release propagating over an array of obstacles

The study discusses, based on high‐resolution 3‐D large eddy simulation results, the evolution of lock‐exchange Boussinesq gravity currents with a low volume of release (LVR) propagating over an array of identical two‐dimensional (2‐D) obstacles (large roughness features in the form of dunes and ribs corresponding to eroded substrates) in a rectangular horizontal channel. The study analyzes the effect of the shape and height of the roughness elements and scale effects between Reynolds numbers at which most laboratory experiments of lock‐exchange currents are conducted and Reynolds numbers closer to field‐scale currents in geophysical applications on the temporal variation of the front velocity, mixing, and flow structure within the gravity current. The temporal evolution of the flow instabilities (e.g., Kelvin‐Helmholtz billows, forward and backward propagating interfacial waves forming as a result of the interaction of the front of the current with the obstacles) and bed friction velocity distributions are analyzed during the different stages of the evolution of the current. The focus is on the later stages of the propagation of LVR currents, after the transition to the self‐similar drag‐dominated regime has started. The differences between the evolution and structure of gravity currents with a low and a high volume of release are highlighted.