Hydraulics and mixing in controlled exchange flows

[Truncated] Internal hydraulic theory is often used to describe idealised bi-directional exchange flow through a constricted channel. This approach is formally applicable to layered flows in which velocity and density are represented by discontinuous functions that are constant within discrete layers. The layered structure of the hydraulic solution complicates its application to geophysical flows in which strong velocity gradients between layers may produce turbulent mixing which alters the two-layer structure. In this study we investigate mixing in exchange flows through a lateral contraction. The results fall into three distinct parts: a set of numerical simulations used to examine the effect of mixing upon exchange flux, a theoretical analysis of the mechanism of hydraulic control in stratified environments, and a laboratory model which is used to examine the physics of mixing processes in the flow. First, numerical simulations of bi-directional density-driven exchange flows are used to study the effect of turbulent mixing upon these flows. The numerical experiments are designed so that it is possible to specify the intensity of mixing. The simulated flows are compared to two analytical solutions, first, the two-layer hydraulic solution which has no mixing, and second, a solution in which turbulent mixing dominates the flow.