It has often be suggested that the dynamics of flow through marine straits and level gaps is governed by a rough balance between the along-gap pressure gradient, the along-gap acceleration, and surface friction. The validity of this gap-flow paradigm is explored from several view points, all of which suggest that vertical motions play a fundamental and non-negligible role in strong wind events, even for flow through level gaps.

The basic constraints on inviscid gap flows are derived from a purely theoretical viewpoint using Bernoulli's equation. Results from numerical simulations confirm the Bernoulli function arguments and also allow parallel conclusions to be obtained from analyses of the mass and momentum budgets for control volumes located along the gap. The numerical simulations also allow a quantitative assessment of the role of surface friction. Finally, the basic theoretical and numerical results are shown to be consistent with several observational studies.