The outer river is a natural river course, whose main function is to drain floods during rainy seasons.

外江是自然河道，其作用是在雨季排泄大量洪水。

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In the lower reaches, where the current slows, the natural accumulation of sediment in the riverbed has caused the river to change course often in the past.

在河流下游，由于流速变缓，泥沙(等沉淀物)自然而然地堆积在河床中，曾经造成黄河经常改道。

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Taking the abandoned delta of Huanghe River as a case, this paper analyzed the natural and artificial driving forces of ecosystem degeneration, with the degeneration course investigated.

本文以废黄河三角洲为例，分析了废黄河三角洲生态系统退化的自然和人为应力以及生态系统的退化过程。

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The aim is to divert the river by a few metres and then allow it to flow on its natural course.

BBC: Ethiopia diverts Blue Nile for controversial dam build