遊水池

1. Origins, structure, and basic meaning

• Structure: 遊水池 (ゆうすいち) is a basin temporarily storing floodwater. It appears through its surroundings and as a mapped facility.
• Basic usage: Its perimeter is inspected before heavy rain; a riverside basin is marked blue on a map.

2. Common pitfalls and similar expressions

• Flood-control perimeter inspected and retention facility mapped
  • The first direct object is 周囲; the second subject is the basin itself. It is flood infrastructure, not a recreational pond.