Consideration to Water Usage and Clarification for Situation of New Water Usage Enabling to the Enterprise of Paddy Fields Inundation on Summer Season

Abstract

Since groundwater is used as the major water supply source in the Kumamoto area, groundwater maintenance is a significant problem. As the water diffusing from the fields of the OOKIKU land improvement district in the middle stream of the Shirakawa basin is an important source for groundwater augmentation, the summer seasonal flooding, which inundates fields in the fallow period, with water permeating into the fields, is performed to intensify groundwater cultivation. It causes a shift from water usage for paddy-rice monocrop agriculture to new uses of water enabled by the summer flooding. However, details of the water usage situation in this area are unclear. Therefore, we investigated the situation by conducting fieldwork and used a numerical computation method. Consequently, we clarified that the fields with high water requirement rates were located over the middle basin in the water usage system and that ample water was needed from June to August. In addition, results of the numerical computation revealed that the level of water intake and discharge in the upper fields of the water usage system was less in comparison with that in lower fields. Thus, it is important to understand the present situation of water usage by utilizing GIS and numerical computation in order to cope with the requirement of water for new uses.