A Planning of Water Environmental Management in Consideration of Population Decreasing in River Basin

The future population is estimated to decrease by the low birthrate in and after 2006 in Japan. We have to consider the problem of the population decreasing and the delay time of the facility development and the natural purification when planning the water environmental management (protection and improvement). In this study, we examined the timing of developing the wastewater treatment facility and analyzed the impact on the water quality, the production and the utility by the population decreasing. We made the sensitive analysis about which the utility is influenced by the population decreasing, the interest rate, the productivity and so on. As the result, we confirmed the necessity for constructing the wastewater treatment facility early and the impact on the water environmental management by the uncertain factors in the future.