Titre/Title : Experimental and Model Studies of Restricted Exchange Flows in estuaries
Contact : Joel Sommeria (équipe MEIGE)
Résumé/Abstract : Results will be presented from a series of large-scale experiments (Hydralab 2014, Grenoble) investigating the dynamics of exchange flows with a net-barotropic component across a submerged, trapezoidal, sill obstruction. High-resolution velocity and density profiles are obtained in the vicinity of the obstruction to observe internal-flow dynamics under a range of parametric forcing conditions (i.e. variable saline and fresh water volume fluxes ; density differences ; sill obstruction submergence depths). Detailed synoptic velocity fields are measured across the sill crest using 2D particle image velocimetry, while the density structure of the stratified exchange flows is measured using micro-conductivity probes at several sill locations. These measurements are designed to aid qualitative and quantitative interpretation of the internal-flow processes associated with the lower saline intrusion layer blockage conditions, and indicate that the primary mechanism for this blockage is mass transfer from the saline intrusion layer due to significant interfacial mixing and entrainment under dominant, net-barotropic, flow conditions in the upper freshwater layer. An analytical two-layer exchange flow model has also been developed to include frictional and entrainment effects, both of which are needed to account for turbulent stresses and saline entrainment into the upper freshwater layer. The experimental results are used to validate two key model parameters : (i) the volume flux ratio between the counter-flowing upper fresh and lower saline layers ; and (ii) the mass loss from the lower saline layer due to entrainment into the upper fresh layer. The seminar will finish with a summary of what we plan to do in our upcoming Hydralab+ project in Spring/Summer 2018.