Author(s): Claudia Adduce
Linked Author(s): Claudia Adduce
Keywords: Gravity currents; Image analysis technique; Bottom obstacle; Density fields;
Abstract: Gravity currents are flows produced by a density difference between two fluids. These flows can form during flooding events, when sediments are entrained from the river bed and transported toward a lake or a reservoir. To avoid the reduction of the reservoir storage capability, bottom mounted barriers/obstacles are often used. In this study, several laboratory experiments were performed with and without a triangular bottom obstacle, in order to investigate the processes occurring between a dense current and an ambient fluid, due to the presence of the obstacle. The relevant parameter varied during the tests is the obstacle ratio between the height of the obstacle and the initial water depth. An image analysis technique has been used to evaluate the instantaneous density fields of the gravity current.
The analysis performed shows that the gravity current’s dynamics is strongly affected by the obstacle. When a gravity current interacts with an obstacle, a portion of the fluid overflows while the rest of it is reflected back. Experiments with higher obstacle ratio are more affected by the presence of the obstacle, because the amount of fluid flowing over the obstacle is small. Consequently, the mass loss causes a large reduction of the gravity current velocity. In addition, the bulk entrainment parameter has been evaluated. Despite the formation of a macro vortex, when the gravity current flows over the obstacle, the bulk entrainment parameter at the end of the experiment is not affected by the presence of the obstacle.