A drainage basin or watershed; the geographic area where water collects and drains into a river and its tributaries.
森林伐採は流域の土壌侵食を促進する可能性がある。
Deforestation can accelerate soil erosion in a watershed.
このダムは上流の流域面積が広い場所に建設された。
This dam was built in an area where the upstream watershed area is large.
流域ごとの水資源管理が重要だ。
Water resource management by watershed is important.