Abstract:The recent population increase and economic development have increased the energy demand in many countries. As global fossil fuel reserves are limited, it is highly likely that the supply of fossil fuels will come under increased pressure and the development of alternative energies throughout the world will become essential. Assuming a Japanese population of 64 million in 2100 with a 20% increase of the power demand per capita from the present level, we studied the electric power supply and demand situation in 2100 by conducting the trial calculation of the maximum development potential of hydroelectric energy, a renewable energy produced in Japan. The findings indicate that the hydroelectric generation capacity can reach approximately 190 billion kWh/year, which is 1.97 times that of 2005 levels. This would be achieved by raising the height of existing dams and flexibly operating dams for power generation in harmony with the flood control and water supply for agricultural and other usage. Presupposing the completion as planned of the nuclear power plants currently under construction and a fivefold increase of the total output of wind power and other alternative power generation sources, it is concluded that a stable power supply will be possible in 2100 without dependence on fossil fuels. KEYWORDS hydroelectric power generation; raising of the dam height; electric power output; fossil fuels.

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Shinya MITSUISHI, Tadahiro TOYODA, Masazumi AMAKATA -8575東京都新宿区西落合2-18-12) Recently, in the wake of drought occurrence, the necessity of promoting comprehensive water resources development not only including river water, also groundwater and reuse of treated domestic wastewater has pointed out. Regarding reuse of treated domestic wastewater, as its water resources is relying on rain water and life sewage water, in case of drought, it has lower safety degree of water use due to scarce rainfall and the implementation of water conservation. This study shows the safety of water utility about the reuse of treated domestic wastewater. We have modeled the status of Fukuoka City water project promoting the use of reclaimed wastewater and the rainwater utilization. We numerically evaluate the effects of reuse of treated domestic wastewater and estimated the available amount of it in the future.Key Words : reuse of treated domestic wastewater, rainwater utilization，reclaimed wastewater， safety of water utility，drought