Sediment Transport and Sedimentation along Lowland Rivers

Thomas Dunne
Department of Geological Sciences, University of California Santa Barbara
tdunne@bren.ucsb.edu

The geomorphology of large, lowland rivers involves features not encountered in upland rivers. Their small gradients are significantly perturbed by tectonic deformation of resistant materials beneath or along valleys, causing changes to sediment transport capacities and channel migration. Effects of Quaternary sea-level changes propagated far inland, leaving an imprint on the modern budget of sediment transport and resulting alluvial landforms. Changes of land and sea level continue to affect the sediment balance and form of some river mouths. The scale of channel and floodplain changes involves large sediment fluxes, and therefore evidence of changes in boundary conditions, such as sea level and sediment supply, persists for long periods. Overbank flow persists for months, and this regime, combined with the fine sediment load of lowland rivers, causes large amounts of overbank sedimentation. The combination of intense overbank sedimentation with high channel-shifting rates along many large rivers focuses attention on the interaction of channel and floodplain to explain the sediment budget of valley floors.