For those weary of floods, grown tired of or bored with floods over the years and decades of flooding in the metropolis, you may find some comfort here by Mark Horstman, a science journalist/reporter for ABC- Catalyst. Mark talks about the worlds largest underground flood water diversion facility, in Saitama,Tokyo. It is a flood prevention giant system which took 13 years to build at a cost of $3 billion, that drains water from flooded residential areas into underground 70 meters tall x 30 meters diameter silos (5 of these shafts) below ground, store it and eventually discharges it into rivers. The connecting tunnel 50 meters below ground measures about 10 meters in diameter. The tunnel stretches for 6.3 km, including a sharp curved line with a minimum radius of 250 meters. Before being discharged into rivers, the drained water is stored in a huge pressure-controlled tank. The tank is designed to perform multiple functions, including abating the force of running water and adjusting water pressure that could change sharply if a water pump breaks down. Measuring 177 meters long and 78 meters wide, and lying about 22 meters below ground, the water tank is larger than a soccer pitch. The ceiling of the water tank is supported by 59 pillars which are 18 meters tall and weigh 500 tons each. An inside look at the tank structure conjures up the image of a “temple” below ground. Flood water stored in the channel can be discharged into rivers at a maximum rate of 200 cubic meters per second. In other words, a 25-meter swimming pool full of water is drained in a second. Under this mechanism, each drainage pump has a high-speed impeller that gives flowing energy to water, discharging it rapidly. The impeller is powered by a gas turbine engine, a modified version of the high-performance engine used in jetliners. Hot, strong wind generated by burning fuel revolves the impeller, which in turn makes the water flow. The impeller is compact and generates less vibration and noise, saving much needed space below ground. (Source: Trends in Japan website.) abc.net.au/catalyst/stories/4112766.htm
Posted on: Sun, 26 Oct 2014 14:27:45 +0000
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