River Delta

A river delta is a typically triangular landform built up where a river deposits its sediment on reaching an ocean, sea, estuary, lake, reservoir or a slower river that cannot carry away the incoming sediment. As the river's flow spreads out and slows in the standing water, it loses the energy to keep its sediment suspended, and the sediment settles out as alluvium, building the delta outward over time; the name comes from the Greek letter delta, because the shape of the Nile Delta resembles the triangular capital letter. River deltas are major centers of agriculture and population, protect the coastline behind them, shape the freshwater supply of the surrounding region and, because different species depend on different parts of the delta, support significant biodiversity while acting as long term stores of carbon. Damming, water diversion and other land use changes upstream are significant threats to delta ecosystems, since a delta's size depends on the balance between the sediment its watershed supplies and the sediment that is removed or redistributed.