出典:Wikipedia
出典:『Wikipedia』 (2011/08/01 18:45 UTC 版)
A tributary or affluent is a stream or river that flows into a main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the mainstem river serve to drain the surrounding drainage basin of its surface water and groundwater by leading the water out into an ocean or sea.