Sustainable use of integration of ground and surface waters

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The recent economic growth and the expansion of urban areas have caused the rapid increase in water demand, and it resulted in damages of the hydrological environment such as water pollution and land subsidence. Thus, the water issues are to construct the balanced water supply-demand system and to conserve the hydrological environment. This study discusses the water management in the specific area based on the field survey, which is conducted in the Ryukyu islands, the Kumamoto area, and the Sanuki plain. The Ryukyu islands consist of limestone with high permeability, and groundwater is a major water source. Miyako island is flat hill without rivers, and groundwater is used for irrigation by constructing the underground dam. At the same time, the management system is established for groundwater development and conservation. In the Kumamoto area located at the foot of Mt. Aso, groundwater is highly developed for municipal supply. In the Sanuki plain the measures to increase the water supply are performed as follows: construction of multi-purpose reservoirs, water transfer within the basin, and inter-basin water transfers. Although the large scale system of water supply has been built, it is still difficult to supply adequate water during the period of little rainfall. Keeping the balance of supply and demand throughout the year, it requires the conjunctive use of surface and ground water, the conservation of hydrological environment, and the wise management of land use.