Dynamics of Gravity Currents Flowing up a Slope and Implications for Entrainment

The dynamics of lock-release gravity currents flowing up a sloping bottom are investigated by laboratory experiments. Both full-depth and partial-depth gravity currents are analyzed, and a wide range of bottom slopes are tested. The front evolution is discussed and it is found that the presence of an upslope affects the flow, causing an earlier transition between the different flow regimes. An empirical relation able to predict the length of the slumping phase as a function of the inclination of the sloping bottom and depth ratio of the dense and ambient fluids is proposed. The density fields highlight the presence of a back flow, which, for steep upslopes, is due to the dense current reflected by the upsloping bottom behaving more like an obstacle than as an upsloping bed. In addition, the entrainment of ambient fluid within the dense current is evaluated, and it is observed to decrease as the angle of the upslope increases until it reaches a minimum value, beyond which the density current feels the upslope as an obstacle.