distributary

n. side stream of a river that leads water away from the main one

A distributary, or a distributary channel, is a stream that branches off and flows away from a main stream channel. They are a common feature of river deltas. The phenomenon is known as river bifurcation. The opposite of a distributary is a tributary. Distributaries usually occur as a stream nears a lake or the ocean, but they can occur inland as well, such as in an endorheic basin, or when a tributary stream bifurcates as it nears its confluence with a larger stream. In some cases, a minor distributary can "steal" so much water from the main channel that it can become the main route.
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Noun
1. a branch of a river that flows away from the main stream and does not rejoin it
(antonym) feeder, tributary, affluent
(hypernym) branch

(a.)
Tending to distribute or be distributed; that distributes; distributive.
  

A branch of a river that flows away from the main stream and does not return to it. (TNDOT1)