Maintenance water - Ijyousui

Japanese: 維持用水 - いじようすい

The flow rate of Japanese rivers fluctuates greatly, and during droughts the amount of water flowing through them is extremely low. During such droughts, once water has been withdrawn for various uses, such as for power generation, agriculture, industry, and urban water, there are often no flowing water remaining in the river. Maintenance water is the minimum amount of water that should be secured in a river during droughts, even after water has been withdrawn for various uses. It is determined by setting up planning reference points at several points on the river and taking into consideration a drought that occurs once every 10 years and taking into account a comprehensive range of factors, including shipping, fishing, scenery, prevention of salt damage, prevention of estuary blockage, protection of river management facilities, maintenance of groundwater levels, preservation of flora and fauna, and keeping the flowing water clean.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

日本の河川は流量変動が激しく，渇水時には流水量が非常に少なくなる。こうした渇水時に，発電用水，農業用水，工業用水，都市用水などの各種利水が取水してしまうと，河川に流水が残されない場合がしばしば出現する。維持用水は，各種利水が取水したあとでも，渇水時に河川に最低確保されるべきであるとして定められた流水量である。その決定方法は，河川の数ヵ所に計画基準点を設け，10年に1度発生する程度の渇水を対象に，舟運，漁業，景観，塩害の防止，河口閉塞の防止，河川管理施設の保護，地下水位の維持，動植物の保存，流水の清潔の保持などを総合的に考慮して定められる。

出典　株式会社平凡社世界大百科事典第２版について　情報

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