distributary

A distributary is a branch of a river that flows away from the main stem, rather than into it. It occurs most commonly in deltas and alluvial fans where sediment-laden water spreads out as the river enters a standing body of water, such as a sea, gulf, or lake. Distributaries fork from the main channel and may carry less water, with some channels eventually dying out or rejoining the river further downstream. They are the opposite of tributaries, which feed the main river.

Distributaries form by channel bifurcation or avulsion, often in response to sediment deposition and a decrease in slope. They create a network of channels, frequently braided, that distribute water and sediment across a delta. The rate of sediment supply, sea-level position, tidal action, and human modification influence their pattern and persistence. Distributary channels can shift over time, rework the delta front, or be diverted by canals or flood-control projects.

They deliver sediment to build new land and help distribute floodwaters. In many river deltas, multiple distributaries form a fan of channels, sometimes including major outlets such as the Rosetta and Damietta in the Nile Delta or the Mississippi's outlets toward the Gulf of Mexico, including the Atchafalaya as a notable distributary. In other regions, distributaries support navigation and irrigation networks.