Sources, sinks and storage of river sediments in the Atlantic drainage of the United States

The history of sediment and its movement in the Atlantic drainage demonstrate some of the difficulties of modeling sediment on a river-basin scale. Soil erosion was accelerated by a factor of at least 10 when European settlers cleared forests and planted crops. Although increasing soil-conservation practice and decreasing crop farming have since reduced the rates of erosion, large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers. The sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come. The reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which, in some places, may be remobilized by large floods. Essentially all the river sediment that reaches the Atlantic coastal zone is trapped in estuaries and coastal marshlands. Probably less than 5% is deposited on the floor of the continental shelf or the deep sea.