As an environmental public health major, I am highly interested in water quality and how water impacts health. Exploring the underground regulating reservoir in Tokyo was highly interesting and introduced me to new ideas about floodwater management. Tokyo Metropolitan Government implemented the Kanda River/ Loop Road No. 7 Underground Regulating Reservoir to protect against flood waters that the Kanda River and Zenpukuji Rivers cannot handle during flooding events.
Allowing flood waters to collect in an underground reservoir like this reduces damage to downstream basins. Water is collected via the intake facilities which receive the water and guide it to the underground tunnel. Connecting ducts, discharge pumps, and shafts lead the water underground to be held in the reservoir tunnel. The total storage volume of both stages of the regulating reservoir project is 540,000 m^3. The 4.5 km tunnel has three intake facilities located at the Kanda, Zenpukuji, and Myoshoji Rivers.
While we explored the underground tunnel it was impressive to see the massive diameter. The inner diameter of the tunnel was 12.5 meters. It was mind-blowing to realize we were 57 meters below ground in a massive tunnel. The tunnel needed to be placed so deep within the Earth to avoid subway lines and plumbing, while also being deep enough to sit below the flow of the rivers.
During our tour of the regulating reservoir, we got to visit the control room where the control boards and monitors are located. This control center operates and monitors water inflow from the rivers and handles discharge pumping. The control facility can raise and lower the gates of intake spots to control when and how much water flows into the tunnel.
The intake facilities are equipped to handle the mass flow of water in a way that redirects the water and reduces noise. If water is allowed to freely flow into the reservoir, there are loud noises, vibrations, and other disturbances. By forcing the water to instead spiral down the drop shaft, it gets quieter and flows faster.
Walking around the facility and seeing the control room with the models of the reservoir was very impressive but it still didn’t prepare me for seeing the real thing. After going down 11 flights of stairs, I was amazed at the size of the tunnel. I can’t even begin to comprehend the amount of water that would fill a tunnel that big. I think reservoir tunnels such as this one are a great way to protect the community from massive amounts of rainfall that can cause flooding.