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drainage basin; catchment basin; river basin; watershed; valley
この川の流域には多くの町がある。
There are many towns in the basin of this river.
大雨で流域一帯が洪水の被害を受けた。
The entire basin area suffered flood damage from heavy rain.
流域の環境保全に取り組んでいる。
We are working on environmental conservation in the river basin.