On the Mechanisms Generating the Nearshore Bars on a Sandy Coastal Slope

Abstract

The study is aimed at investigation of the problem in what conditions the morphodynamic self-organizational mechanism controlling the growth of small perturbations arisen on bed could be responsible for the nearshore bars development. A simplified sediment transport model is used in which the sediment discharge is turned out directly proportional to the local bed slope. This model allows reducing the problem to an analytical solving of the diffusion equation which gives the base to predict the evolution of perturbation arisen on bed. The conclusion is argued that the favorable preconditions for the nearshore bar formation can exist in the case of onshore sediment transport associated with the dominating contribution of wave asymmetry in transport process. However under conditions of steep stormy waves the undertow is developed providing offshore sediment flux from the beach. In this case, the breaker bar is formed by two mechanisms–self-organization and convergence of opposite sediment fluxes. The results obtained are in agreement with available data and also assist to explain some properties of multiple-bar systems found out from observations.