Linear instability mechanisms for sand wave formation

A height- and flow-dependent model for turbulent viscosity is employed to e xplain the generation of sand waves in tidal seas. This new model resolves the problem of excitation of very long waves in sand wave formation, becaus e it leads to damping of the long waves and gives a finite separation betwe en the most excited mode and the zero mode. For parameters within their phy sically realistic ranges, a linear analysis of the resulting system yields a first excited mode whose wavelength is similar to the characteristic wave length of sand waves observed in nature. The physical mechanism of sand wav e formation as predicted by the new model is explained in detail. The dispe rsion relation obtained can be the starting point for a weakly nonlinear an alysis of the system.