A neat collection of photos of Japan's futuristic flood prevention system called G-CANS [wiki] in Edogawa:
The G-Cans project (Shutoken Gaikaku Housui Ro, means drain outer Tokyo metropolitan area.) is an underground infrastructure in Tokyo, Japan built for preventing overflow of the city's major waterways and rivers during rain and typhoon seasons.
Work on the project started in 1992; it consists of five concrete containment silos with a height of 65 m and a diameter of 32 m, connected by 6.4 km of tunnels, 50 m beneath the surface, as well as a large water tank with a height of 25.4m, with a length of 177m, with a width of 78m, and with 59 massive pillars connected to a number of 14,000 horsepower (10 MW) turbines that can pump up to 200 tons of water into the Edogawa river per second.
The G-Cans project is also a tourist attraction, and can be visited for free. The main water tank resembles a temple and has been used in some movies and TV programs to create mystic scenes.