Variations in Morphology of Major River Deltas as Functions of Ocean Wave and River Discharge Regimes

Procedures were developed to evaluate the relative contribution of riverine versus marine forces to the construction of river deltas. Seven deltas, the Mississippi (U.S.A.), Danube (Rumania), Ebro (Spain), Niger (Nigeria), Nile (Egypt), Sao Francisco (Brazil), and Senegal (Senegal), were found to represent a spectrum of delta types reflecting process regimes ranging from fluvial-dominated, low-wave-energy, (Mississippi) to wave-dominated, low-fluvial-influence (Senegal). Deltas at the river-dominated end of the spectrum are characterized by highly irregular and protruding shorelines, a sparsity of wave-built features, and low lateral continuity of sands. Wave-dominated deltas exhibit straight shorelines characterized by well-developed barriers and beach ridges with high l teral continuity of sands. The configuration and landform suite characteristic of any given delta depend to a considerable degree on the wave power adjacent to the shore and on river discharge relative to wave forces. Nearshore wave power is not correlative with deep-water wave power but, owing to frictional attenuation, is also a function of the subaqueous slope. River-dominated shoreline configurations result only when the river is able to build flat offshore profiles; where the subaqueous slope is steep, wave-built shoreline landforms dominate the delta.