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

在特大城市中，与水有关的问题有三个：(1)防洪；(2)水资源利用；(3)水环境。本研究以北京市区和大阪沿海城区为研究对象，发现了一些共同的问题，也发现了一些独特的问题。对于(1)，由于降水较少，北京中心地区几乎没有问题，而大阪地区的商业和居民区则需要采取许多策略来避免暴雨带来的淹没。涅雅河流域是城市化速度较快的低地，特别要求建设多种类型的蓄水池等防洪设施。在未来的愿景中，我们必须重新利用这种强水作为城市水的二次使用。北京市区正在开发大量的城镇用水和工业用水。维持和恢复地下水环境是一种有利的处理方法，但需要新的排水系统和水处理厂。我们担心用水和水环境之间的需求不平衡。大阪等发达国家的大城市在21世纪中叶将出现人口减少、高龄化社会、出生率下降等现象。为了在城市地区创造良好的水文过程，我们必须考虑到这些未来的问题。

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.