Irrigation water use and groundwater in alluvial plains in Ehime Prefecture

Abstract

Two alluvial plains, Saijyo plain and Shuso plain, are located at a coastal area of Seto Inland Sea in Saijyo city, Ehime prefecture. In the area, a lot of groundwater was used with wells from long ago because of a little surface water resource, and the conservation and management of groundwater is a most important policy of the city. In this paper, water use, water balance and water quality in the two plains were compiled based on our previous research. As the result, it was indicated that the dependency of irrigation water on groundwater was relatively high and over-pumping has been often a matter on severe lowering of groundwater level and seawater intrusion in the Saijyo plain. It was also analyzed that the seepage from paddy fields played an important role on groundwater recharge in both of plains. Furthermore, it was shown that high concentration of nitrate nitrogen in groundwater was a problem in Shuso plain due to the use of fertilizer in orchards.