- 15 Mar 2018
- 09:00 - 10:00
- PennState University, 362 Willard Building, Pennsylvania, USA
Mário Franca, Professor of Hydraulic Engineering and River Basin, will give a seminar at the Fluid Dynamics Research Consortium of the PennState University on Sediment Entrainment, Distal Transport and Deposition by Saline Gravity Currents.
The propagation of bottom gravity currents in lakes, reservoirs, seas, and oceans strongly depends on the interaction with the floor. This interaction is determinant for flow resistance, pressure induced movements of the bed and exchange of dissolved and undissolved species across the benthic layer. Furthermore, it governs processes of entrainment, distal transport and deposition of sediment, with consequences for reservoir sedimentation, submarine cable and pipelines destruction, resuspension of contaminated deposits, and carbon degassing from sediment deposits. Sedimentary basins caused by turbidity currents form some of the world’s most important hydrocarbon reservoirs and the topography of ocean and sea floors is shaped by large-scale gravity currents.
In this presentation we address simultaneously the feedback between the hydrodynamics of a gravity current and the geomorphic changes of a mobile bed. Laboratory experiments of saline gravity currents, produced by lock-exchange, flowing over a mobile bed channel reach, are presented. Different initial conditions of the current were tested together with three different grain sizes of the erodible sediment. Results from velocity measurements are combined with the visualization of the sediment movement in the mobile reach and with post-test topographic and photo surveys of the geomorphology modifications of the channel bed. We show that the mean vertical component of the velocity and bed shear stress are highly correlated with the first instants of sediment entrainment.
Vertical turbulent velocity is similarly related to entrainment, although with lower correlation values, contributing as well to the sediment movement. Bed shear stress and Reynolds shear stress measured near the bed are correlated with sediment entrainment for longer periods, indicating that these quantities are associated to distal transport as well. Geomorphological changes in the mobile bed are strongly related to the work done by the bed shear stress. On the other hand, we show that the nature of the grain of the mobile bed reach influences the hydrodynamics of the current which means that a feedback mechanisms between both occurs during the passage of the unsteady gravity current.
The signature of this geomorphological work, which is visible in the form of longitudinal streaks of accumulated sediment downstream the mobile bed, is related to the flow initial buoyancy and to the size of the mobile bed sediment.
For more information, click here https://www.fdrc.psu.edu/seminars