Published online by Cambridge University Press: 28 March 2006
The solitary wave is a well-known example of a flow of permanent type which can be studied by shallow-water theory. A scheme due to K. O. Friedrichs (see Friedrichs & Hyers 1954) can give both an approximation to the exact wave form and a framework for a proof of its existence. It is used here to approximate the solution of a related problem, that of a steady flow near the critical speed over a small obstacle in the bed of a stream. The flow can be considered as a perturbation of a solitary wave since it will approach a solitary wave as the obstacle shrinks in height.