Restricted Exchange and Saline Blockage over a Submerged Sill

Results are presented from a series of large-scale experiments investigating the internal dynamics of bi-directional exchange flows generated across a submerged, trapezoidal, sill obstruction, with net-barotropic flow components in the upper fresh or lower saline water layers. High-resolution velocity fields and density profiles were obtained using particle image velocimetry and micro-conductivity probes, respectively, in the vicinity of the obstruction to measure
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). These measurements provided qualitative and quantitative interpretation of mixing and entrainment processes generated by the bi-directional exchange flows, as well as defining the parametric conditions under which the lower saline intrusion layer became blocked across the sill. An analytical two-layer hydraulic exchange flow model was developed to include frictional and entrainment effects, both of which were needed to account for turbulent stresses and saline entrainment into the upper freshwater layer, resulting in mass exchange between the counter-flowing fresh and saline layers across the sill.