“形成河道”可以翻译为“form a river channel” 或者 “create a river course” 。
例句：
Over time, the flowing water gradually formed a river channel. （随着时间的推移，流动的水逐渐形成了一条河道。）
The continuous erosion by the river finally created a new river course. （河流持续的侵蚀最终形成了一条新的河道。）