Water flowing under the tiled roofs - Hamamatsucho Kouro and the urban floods - (1999 - 2000)

Water flowing under the tiled roofs - Hamamatsucho Kouro and the urban floods - (1999 - 2000)

From the late 1990s to the early 2000s, Japanese cities were enveloped in a wave of rapid high-rise development and redevelopment. In particular, the Hamamatsucho area in Minato Ward, Tokyo, strengthened its character as a transportation hub where the JR, Tokyo Monorail, and Oedo lines intersect, and the surrounding area became lined with office buildings and luxury hotels with more than 40 floors.

The towering skyscrapers that tore through the sky were a symbol of the economy, but at the same time, they also posed a threat to the water that lurked deep beneath the city's surface. Covered with asphalt, the city no longer allows rainwater to soak into the ground, and every drop of rain flows into the drainage canals. This structure was the source of a new disaster, the "inland flood," which would overflow from the bottom of the city once the sky broke.

This crisis became a reality on August 5, 1999, when a torrential downpour hit Suginami. This localized torrential downpour dumped 120 mm of rain per hour on Suginami Ward, Tokyo, flooding some 7,500 houses. Lives were lost in underground parking lots, and the muddy water flowing back up through manholes exposed the limits of the city's drainage capacity. This catastrophe caused the concrete-paved city to reconsider the "pathways of water.

Against this backdrop, an innovative wastewater treatment technology was attempted in a high-rise building in Hamamatsucho, a 40-story building with 10,000 employees, where a treatment system with the following characteristics was implemented:

- Zero excess sludge generation: minimized by-products of the treatment process and reduced maintenance costs.
- No use of chemicals: No chemicals such as Pit regulators or coagulants are used, reducing environmental impact and operational burden.
- Capable of treating wastewater with high BOD: The purification capacity can even handle wastewater equivalent to that of food factories and livestock farms.

As a result of these achievements, treatment costs were reduced by more than 20 million yen per year in FY1999. Furthermore, in terms of reducing the burden on public sewage, the project was recognized as an architectural attempt that contributes to reducing flood risk in the city as a whole.

The following year, in September 2000. This time, the city of Nagoya was submerged in deep water. The Tokai Torrential Rain brought torrential rains of over 500mm to Aichi and Gifu, damaging over 100,000 houses. The underground shopping center in front of Nagoya Station was submerged in a muddy stream, the subway system was paralyzed, and people died in parking lots. This disaster exposed the invisible weakness of the city's "underground.

Through these two water disasters, the administration came up with a new policy:

- Obligation to install rainwater runoff control facilities (Tokyo Metropolitan Government Bureau of Sewerage)
- Suginami rainwater trunk line construction plan
- Obligation for building owners to install storage facilities
- Start of consideration of the "Urban Flooding Countermeasures Law" led by the Ministry of Land, Infrastructure, Transport and Tourism

The wastewater treatment technology installed in the Hamamatsucho high-rise building was a "private-sector initiated urban disaster prevention" that was born ahead of these developments, and like water quietly flowing under an tiled roof, it has become a force that quietly supports the future of the city.

In this way, in the short but intense period of time from 1999 to 2012, the city faced water and technology evolved in response to disaster. In other words, it was the dawn of an era that sought a new equilibrium between the city and nature.