A model study of the influence of submerged tidal barriers on estuarine mixing and exchange processes

Model studies have been undertaken to study the spatial and temporal development of a brackish pool within an impoundment supplied by a freshwater inflow and bounded by an impermeable barrier that is overtopped periodically by a tidally generated saline water inflow. The results demonstrate the relative influence of the freshwater inflow and downstream tidal conditions in controlling the temporal development of this pool. In particular, the experimental data illustrate that the dimensions of the brackish pool reach equilibrium after a specific number of tidal cycles, with the normalized thickness of the pool being dependent primarily on the strength of the freshwater inflow. The density structure of the water within the impoundment is interpreted in terms of two contributory processes, namely, (1) turbulent entrainment of fresh receiving water into the saline intrusion; and (2) shear-induced interfacial erosion of the brackish water by the overriding fresh water during receding tidal conditions. A scaling analysis shows that the temporal growth of the brackish pool thickness can be parameterized successfully in terms of a volume ratio representing the dilution capacity of the freshwater stored in the impoundment during the saline intrusion phase.