Analyzing the Engineering of the Kasukabe Reservoir in Japan

In Kasukabe, Japan lies the world’s biggest underground floodwater facility. Large artificial concrete caverns that compose the Metropolitan Area Outer Underground Discharge Channel, also called the G-Cans project, sprawl under the city’s surface-level infrastructure.

The large subterranean drainage system was developed to prevent devastating flooding of the waterways that surround the city. Because of surges in rainy and typhoon seasons, the regional geography is stricken by significant flooding events yearly.

The city itself lies on the outskirts of Tokyo in the Saitama prefecture; however, above the ground, there is little that indicates just what exists below.

Engineering the reservoir

Building on the project began in 1992 and extended approximately a decade and a half, with the project totally finished in 2006. While on paper, the project has only five containment silos, the importance of their size will offer any observer pause. Each silo is 213 ft (65 mt) high and 104 ft (32 mt) in diameter.

These bigger silos are then attached by 4 mi (6.3 km) of massive tunnels, all at a deepness of 165 ft (50 mt) beneath the surface. Columns weighing 500 tons each support the central reservoir, a concrete tank measuring 580 ft (177 mt) long by 83 ft (25.4 mt) high. Inside this tank sit 78 10 MW pumps capable of transferring roughly 200 tons of water into the nearby Edo River every second.

Staff at the facility are constantly alert, especially during Japan’s rainy and typhoon seasons from June to late October. The reservoir has assisted reduce the number of homes affected by water damage in close-by areas by around 90%.

During dry periods, the surge tank is currently used as a tourist attraction. Visitants can visit the site for roughly 3000 Japanese Yen, or approximately 30 USD. While any jet-hopping civil engineer may be bursting to take a trip and see this underground wonder, it should be noted that the trips are only carried out in Japanese.

At this moment, though, it is natural to wonder what the city did before they built the Kasukabe Storage tank. How did a bustling town survive devastating seasonal flooding?

First, the infrastructure was sparse enough that the floods were not considered a significant issue. Nevertheless, from the 1960s to the 1980s, much of the region’s farmland had been replaced with housing and industrial centers, significantly lowering the chance for rainfall and snowmelt to infiltrate underground.

The first problem

When the suburbs of Tokyo were originally being developed, the sprawl occurred so fast that little thought was provided to flood control. Nevertheless, the city soon learnt its lesson as it experienced countless disastrous floods, rendering several areas unbuildable.

As the populace expanded and much more ground was covered with non-porous concrete, engineers knew that something had to be realized to treat the situation.

After years of dealing with the floods, 1992 noted the start of the fightback against devastating flooding in the area due to the construction of the external underground discharge channel tunnels.

This enormous system works through a system of switches that engineers might control during high rain or flooding events. Because of the series of tunnels that run throughout the city, connected to the underground reservoir, engineers can direct almost all drainage from the city into the five big silo storage tanks.

What the system performs

The system’s end goal is not merely to hold water, though, in flooding occurrences that have a fast beginning, the first job of alleviating the flooding danger is managing the surge. The underground reservoirs are built enormously to manage large volumes of water that rapidly flow into the city during surges. The water that stays in the storage tanks can then be discharged more slowly into the Edogawa River, carrying it through natural channels into Tokyo Bay.

Other engineers often view the system as a fascinating remedy to huge flooding events prompted by fast population growth. Several civil engineers consider the Kasukabe Reservoir as an effective solution to the trouble of flooding.

An identical flood center is being built in Osaka Prefecture, scheduled for completion in 2044. Moreover, even more may be needed as global warming raises the occurrence and regularity of severe storms. According to Japan’s Meteorological Agency, the number of typhoons that intimidate Tokyo annually has jumped 1.5 times in the last forty years.

But, back to the reservoir being a tourist attraction. Why would tourists want to see enormous underground concrete caverns? Well, the design of the undersea tanks gave them a type of cathedral-esque look. Due to the immense support pillars scattered throughout, the empty tanks present as stylish serene pieces of engineering sitting beneath the dynamic city above.

Watch the video below for an animated presentation of how the system functions.

Read the original article on Interesting Engineering.