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。

youdao

Later it declined due to the change of a river course.

后来因为河水改道，才逐渐衰落下来。

youdao

The course changes frequently, and the area is so flat that a small change in the level of the river may inundate a considerable area.

河道变化多端，下游地区却很平坦，水位少许上涨河流就会淹没一大片土地。

youdao

It takes a huge effort, backed by a lot of money, to change the course of the mighty river that is the federal government.

FORBES: There's Much Too Little Money In Politics