Environmental Damage from Urban Flooding (1990s-2020s)-May 1996

Environmental Damage from Urban Flooding (1990s-2020s)-May 1996

1990s:
Urban flooding caused by torrential rains became a frequent occurrence in the 1990s and an issue throughout Japan. 1994 saw severe water shortages in the summer, and rainwater reuse began to attract attention. In Tokyo, the Sumida Ward Office installed a 1,000 cubic meter underground rainwater storage tank and reused more than 30,000 tons of water annually. In addition, the Tokyo Dome (designed by Takenaka Corporation) collected rainwater from its 36,000 square meter roof and used 600 cubic meters per day as toilet flushing water.

In Fukuoka City, the Fukuoka Dome installed a 2,900 cubic meter rainwater storage tank and used approximately 55,000 cubic meters of rainwater per year for sprinkling plants and flushing toilets. These efforts were implemented with the aim of both preventing urban flooding and making effective use of resources, but collaboration among local residents and businesses remained an issue.

2000s:
In 2001, the Tokyo Metropolitan Government completed the "Metropolitan Area Outer Discharge Channel" (underground temple), which consists of a 6.3 km long tunnel and a huge pressure regulating tank that can drain more than 500,000 m3 of rainwater annually. This facility was a great success, preventing the flooding of approximately 20,000 households during the heavy rains of 2008.

In 2004, Osaka City formulated a "Basic Plan for Countermeasures against Heavy Sewerage Rainfall" and built drainage capacity to handle 70mm of rainfall per hour. 2009 saw the construction of additional rainwater storage facilities in the Yodo River basin, expanding the total storage capacity to 50,000 cubic meters. Furthermore, in collaboration with companies and research institutes, flood forecasting technology has evolved, contributing to disaster risk reduction.

2010s:
Amid frequent extreme weather events due to climate change, the Tokyo Metropolitan Government promoted the "Tama River Flooding Prevention Project," which minimized damage to the Arakawa River basin during Typhoon No. 15 in 2011 by strengthening drainage pumps. In addition, during the 2014 guerrilla downpour, Sumida Ward's underground regulating reservoirs came into operation and treated approximately 12,000 cubic meters of rainwater.

In Osaka City, the Osaka Mega Rainwater Storage System, designed by Takenaka Corporation, began operating in 2015. With a storage capacity of approximately 100,000 cubic meters, the system has improved the efficiency of drainage into Osaka Bay. In Fukuoka City, the storage capacity of the Sanno Regulating Pond doubled in 2018, reusing 70,000 cubic meters of rainwater per year. This significantly reduced damage during Typhoon No. 21.

2020s:
After 2020, the Tokyo Metropolitan Government is expanding the Metropolitan Area Outer Discharge Channel, and in 2023, a new type of drainage pump was introduced. This pump can drain 45 tons of rainwater per minute, further reducing the risk of flooding in residential areas along the Arakawa River.

Osaka City is promoting the "Osaka Mega Flood Countermeasures" in 2022, increasing the total capacity of storage tanks to 100 million cubic meters. Furthermore, in cooperation with Daikin Industries, a new type of rainwater filtration system was introduced. The rainwater purified by this system is used for urban greening projects.

In 2023, Fukuoka City introduced a "smart rainwater harvesting system" developed in cooperation with Daikin, which has increased the amount of rainwater that can be reused to 120,000 cubic meters per year. This has significantly reduced flood damage during typhoons and lowered disaster risk.