Morphology of a delta prograding by bulk sediment transport

Abstract

A theoretical geomorphic model is developed for the progradation of a river delta in which the patterns of deposition and movement of sediment on the delta front slope are dominated by bulk-transport processes, such as creep and landsliding. The model predicts an exponential delta front profile, in which the maximum slope is controlled by the sediment supply to the delta, the rate of sediment transport on the delta front slope, and the depth of the receiving basin. Applications of the model to the Fraser and Mississippi River Deltas and to the Rhine River Delta in Lake Constance give good agreement with the progradation and morphology of these deltas. A difference in transport coefficient between the Mississippi River and the other deltas is attributed to differences in sediment composition and/or rate of sediment supply between this and the other deltas. The derived sediment-transport coefficients are found to be much higher than those for subaerial hillslopes. Our results suggest that deltas prograding by the processes considered in this paper will adjust quickly to changes in sediment supply.