River Sediment Delivery to the Coast
Large dams trap a great deal of river sediment. But in many cases this does not result in a significant reduction in sediment delivery by rivers to the coast. This is due largely to the fact that the lower reaches of many coastal plain rivers were sediment bottlenecks long before the dams were built, and did not deliver much sediment to the coast to start with, and to the long under-appreciated importance of sediment sources in the lower coastal plain and within the coastal zone.
This has been known, at least in some case studies, for 30 years. However, these case studies have done little to offset the conventional wisdom that because (A) dams trap sediment (100 percent of bedload and often >90 percent of suspended load), and (B) rivers are an important source of coastal sediments, then (C) sediment delivery to the coast has been reduced to the coastal zone since a proliferation of dam-building in the 1950s and 1960s, leading to problems such as beach erosion and wetland loss.