りゅういき流域ryuuiki
1.
The geographical area that encompasses all the land where precipitation flows into a particular river, contributing to its water supply.
2.
The region along both sides of a river that is influenced by its waters and ecology, often serving as an important agricultural or ecological zone.
3.
A defined landscape where water from various sources converges to feed into a central river, creating a unique ecosystem dependent on its flow and surrounding environment.
Example:
ダムが切れて流域に大水が押し寄せた。