2015 Volume 71 Issue 5 Pages I_33-I_40
In Japan, recent low birthrate and aging population have progressively led to a crisis for infrastructure. In particular, the quantity of waste water from homes and factories is remarkably decreasing, along with the decline of economic activity resulting from the overseas move of Japanese companies. As a result, a condition of overcapacity of sewage systems has arisen. On the other hand, the risks of natural disaster, such as damage from local flooding by heavy rain, are rapidly increasing. But the capacity of rainwater drainage systems remains chronically short. We suggest that underground space is not being used effectively in urban sewage systems.
In our study, which focused on the rainwater drainage systems and sewage systems of enormous social capital infrastructure, we commented on the conditions and problems of two systems. To improve the spatial conditions of the two systems, we suggested that space reallocation is required. As such, we proposed a framework of hybrid sewerage systems and showed its various benefits in terms of environmental issues and disaster prevention of inland flooding.
Targeting a specific district in Japan, we estimated that the capacity of rainwater drainage systems would improve from 61.6mm/hr. to 65.0 mm/hr. by introducing hybrid usage of sewerage systems. As a result, the possibility of inland flooding damage in this district could be reduced up to 20.7%.
Finally, Realizing hybrid sewerage systems would contribute greatly to appropriate reallocation policy for rainwater drainage systems and sewage systems in terms of cost, construction period, and feasibility, compared with the river reforming works and the rainwater drainage pipes' constructions.
