Nearly all analytical models of lock-exchange flow are based on the shallow-water approximation. Since the latter approximation fails at the leading edges of the mutually intruding fluids of lock-exchange flow, solutions to the shallow-water equations can be obtained only through the specification of front conditions. In the present paper analytic solutions to the shallow-water equations for non-Boussinesq lock-exchange flow are given for front conditions deriving from free-boundary arguments.

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... nalytic solutions are also derived for other proposed front conditions-conditions which appear to the shallowwater system as forced boundary conditions. Both sets of solutions to the shallow-water equations are compared with their counterparts from the Navier-Stokes equations and a mixture of successes and failures is recorded. The apparent success of some aspects of the forced solutions of the shallow-water equations, together with the fact that in a real fluid the density interface is a free boundary, shows the need for an improved theory of lock-exchange flow taking into account nonhydrostatic effects for density interfaces intersecting rigid boundaries.