LONGSHORE CURRENT INSTABILITIES: GROWTH TO FINITE AMPLITUDE

Abstract

The growth of shear instabilities in the longshore current to finite amplitude is studied. It is shown, by considering near-critical conditions and the selfinteraction of the fastest growing mode (FGM), that the basic flow is supercritical and that, therefore, the disturbance may be expected to evolve to a finite size, with frequency equal to that predicted by linear stability theory, and final amplitude proportional to the linear growth rate. This is consistent with observation. The mean flow may therefore also be expected to evolve to a new form.