The Urban Development Corporation (UDC) is one of the biggest implementation bodies for urban development in Japan. UDC has developed rainwater infiltration technology since 1975. This technology has effectively reduced runoff to a river and sewer system in the new town project areas. Recently, UDC has developed a new system which is defined as a “Rainwater Recycle Sewer System”, which is supported by “Rainwater Storage and Infiltration Technology (RSIT)” applicable to new town creation and urban renewal. The new system consists of two elements: RSIT components based on Public-Private Partnership (PPP) and a stormwater drainage system. Herein, the private sector is responsible for the main part of RSIT, and the public sector is responsible for the stormwater drainage from the development area. As a result, the capacity of public facilities, such as rainwater sewers and stormwater reservoirs, can be reduced effectively. In parallel, the initial/running cost of public facilities is expected to be reduced. In conclusion, the authors would stress the importance of a co-maintenance system also based on PPP, which will be required especially in order to properly operate the whole system for the long term.

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