Computer Models of Delta Growth due to Sediment Input from Rivers and Longshore Transport

Abstract

Computer-simulation models are developed to investigate the growth and equilibrium shape of a river delta in which wave action is the dominant force in redistributing sands deposited at the river mouth. Common values of sediment supply by rivers are used, and known relations for sand transport along beaches are applied. Although of a preliminary nature, the models appear to yield reasonable comparisons with real beaches and delta shapes. The models indicate that the deltas quickly reach an equilibrium configuration in which the wave energy flux is just capable of transporting and redistributing along the shore all the sand supplied by the river. The wave breaker angle decreases systematically along the delta away from the river mouth due to a progressive decrease in the quantity of river sand remaining to be transported (with increasing distance from the river mouth an increasing proportion of the river sand has already been deposited). When the wave energy flux is low or the river sediment supply too high for the existing waves nearly all the sand remains near the river mouth, producing one distributary which, if duplicated, would form a bird-foot delta. Oblique wave approaches produced asymmetric deltas but the asymmetry was not as pronounced as anticipated. The application of such simulation models to real case studies of shoreline alteration, natural or man-made, is also discussed.