Environmental Balance of Water System in Megalopolis -- In Cases of Beijing and Osaka Bay Areas--

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Among the problems in megalopolis there are three ones related to water : (1) flood control, (2) water use, (3) water environment. The target model cities in this study were set as Beijing Urban Area and Osaka Coastal Urban Zone, and we found some common problems as well as unique ones.With respect to (1), there is almost no problem in the central area of Beijing because the precipitation is small, while many serategies are essential to avoid the inundation from the heavy storm in business and residential zone in Osaka areas. The Neya River Basin, the low land urbanized rapidly, is specially demanded to build many flood control facilities such as various typed water storage reservoir or tank. In future vision we have to reuse such strong water as a secondary usage of water in the city.In Beijing Urban Area, they are developing large amount of town water and industry water. It is a favorable treatment to keep and recover the groundwater environment, but they need a new sewer systems and water treatment plants. We are afraid of the unbalance of demand between water use and water environment.It is said in large cities in developed countries such as Osaka Urban Area that the population decrease, the high age society, and the decrease of birth rate will appear in the middle of the 21Century. For the creation of sound hydrological process in the urban area, we have to take those future problems in mind.