On the Equivalence of Top and Bottom Gravity Currents in a Linearly Stratified Channel: A Review and Extension of Data Processing and Prediction Theory

The analysis of gravity currents in a stratified ambient (relevant to geophysical and environmental applications) is complicated by the relatively large number of physical input parameters that allow for various scalings of the data; this is exacerbated for particle-driven flows where additional parameters are involved. This creates a lack of consistency, or even confusion, concerning the interpretation and prediction power of the available knowledge. We discuss the propagation of lock-release (Boussinesq, inertial–buoyancy) gravity currents at the bottom, top, and middle (intrusion) of a linearly stratified ambient tank. We focus attention on the evaluation of the constant speed of propagation in the initial phase (or stage) called "slumping." Two major methods have been used in previous studies: (a) empirical or data-processing analysis (EDP) and (b) shallow-water (SW) theory analysis. The methods use different definitions of the stratification parameter and different scalings of the variables (including the speed of propagation). We show that the SW method, with a small extension, is physically and mathematically more convenient; results of experiments, simulations, and approximate models can be consistently unified for both top and bottom gravity currents, with and without particles. This generalization improves the insights and the prediction power concerning these phenomena.