Factors controlling variations in river sediment loads

Sediment transfer from continents to oceans via rivers is one of the important processes regulating river-bank stabilization, soil formation, biogeochemical cycling of elements, crust evolution and many other earth-related processes. Due to changes in continental positions during the geologic past, water flow and sediment loads in rivers have also shown variations during different time periods. Recent estimations budget sediment flux from rivers to oceans of about 18 x 10(9) tons annually. However, it is estimated that the present-day sediment load in rivers has been greatly altered due to large-scale human perturbations. Factors such as relief, channel slope, basin size, seasonality of rains and tectonic activities control sediment loads in rivers. Human interventions in the form of reservoirs for water storage have impounded and trapped huge sediment loads on the continental parts. Similarly, land use patterns also had their effects on sediment flux to the oceans. Rivers flowing over the Pacific islands have large sediment yield as also the Himalayan rivers, Ganga and Brahmaputra, due to high relief and tectonic disturbances, whereas rivers in North America, China and Africa show decrease in sediment flux due to trapping of sediments in the reservoirs.