Numerical simulations of bidirectional density-driven exchange flows are used to study the effects of turbulent mixing in these flows. The numerical experiments are designed so that it is possible to specify the intensity of mixing, which allows the investigation of a wide range of flows that are difficult to model in the laboratory. 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. We are able to model exchange flows similar to either of these limits by modifying the turbulent mixing, as well as simulating behavior between these two extremes. The simulations demonstrate that the two analytical solutions form the limits of a wide class of problems and that the flow regime in between the limiting solutions can be described by a single nondimensional parameter GrTA2. ¿ 2001 American Geophysical Union