Tokyo authorities diverted massive amounts of stormwater into retarding basins to prevent river overflows during the passage of Typhoon 6 [1].
This emergency measure highlights the city's reliance on adaptive infrastructure to manage extreme rainfall that threatens densely populated urban corridors. By using public spaces as temporary reservoirs, the city aimed to reduce the pressure on river systems and prevent catastrophic flooding in residential areas.
The strategy focused heavily on the Nogawa River and its upstream retarding basins, which are designed as large-scale grounds [1]. During the heavy rains, these areas were intentionally flooded to suppress rising water levels. Hidemi Nomoto, the disaster prevention section chief of the Tokyo Metropolitan Government Bureau of Construction, said that 64,000 tons [1] of water flowed into the basins, contributing to the suppression of river levels.
The weather event was characterized by extreme intensity. In some areas, the amount of rain falling in a single day exceeded the average total rainfall for the entire month of June [2]. This surge led to the issuance of multiple "Level 4 Danger Warnings," a high-tier alert indicating that evacuation is necessary to ensure safety [1].
Local municipalities monitored five rivers where the risk of flooding became imminent [1]. The use of the retarding basins allowed the city to manage the surge, though the sight of flooded grounds remained a stark reminder of the storm's power. A reporter on the scene said that water had collected across the entire surface of the grounds [1].
Despite the warnings, officials noted the difficulty some residents face when deciding to evacuate. The gap between receiving a Level 4 alert and taking physical action remains a critical point of concern for disaster managers. Nomoto said that the city continues to emphasize the importance of protecting oneself based on the specific characteristics of their location [1].
“64,000 tons of water flowed into the basins, contributing to the suppression of river levels”
The use of multi-purpose infrastructure, such as sports grounds acting as flood basins, demonstrates Tokyo's strategy of 'integrated water management.' As climate patterns lead to rainfall totals that exceed monthly averages in a single day, the city is shifting from trying to contain all water within pipes to allowing controlled flooding in designated zones to protect critical residential and commercial infrastructure.
