The effect of advective processes on the morphodynamic stability of short tidal embayments

Abstract

Abstract An idealised model is used to gain understanding about the formation of channels and shoals in a rectangular basin with fixed sides and a sandy bottom. Forcing is due to a prescribed tidal constituent at the entrance. The basin length is assumed to be small compared to the tidal wavelength. The model consists of the 2D shallow water equations, a suspended load sediment transport formulation and a tidally averaged bottom evolution equation. Channels and shoals can develop as free instabilities in this system. Here the role of nonlinear tides and advective sediment fluxes in the formation process is studied. It is found that advective processes can have both a stabilising and destabilising effect. The tidal residual circulation plays a dominant role in the growth process. Moreover, the destabilising effect of the diffusive sediment transport is reduced by advection. With increasing influence of advective (with respect to diffusive) fluxes the preferred location of the bottom perturbations shifts towards the basin entrance. The model results are consistent with field data and the outcome of complex morphodynamic models.