田中調節池, Retention basin between Kashiwa and Abiko, Japan

The Tanaka Retention Basin is a water storage facility located between Kashiwa and Abiko that collects excess water during heavy rainfall. This large-scale structure holds massive volumes of water to prevent flooding in the surrounding communities and protects the river system downstream.

Planning for this retention basin began in 1926 as part of efforts to improve river systems in the region, and construction was completed in the 1960s. This development marked a shift toward modern flood management techniques designed to protect growing urban areas.

Local schools use this basin in their environmental lessons, helping students understand water management and flood control. It serves as a living classroom where visitors can see how communities work with nature to stay safe.

The basin is accessible from various points around its perimeter, offering viewing areas where visitors can observe the water storage in action. The best time to visit is during or after heavy rainfall, when the basin's flood-prevention role becomes most visible.

During the 2019 typhoon, this basin and two others together managed a record amount of water equivalent to the volume of 72 Tokyo Domes. This extraordinary performance demonstrated how critical such infrastructure is for protecting millions of people from disaster.