EVALUATION OF HYDROLOGIC SYSTEMS IN TAKAMATSU AREA AND THE EFFECTS OF WATER TRANSFER THROUGH KAGAWA TRANS-BOUNDARY CHANNEL

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The present study aimed to understand the hydrologic systems in Takamatsu and the effects of Kagawa trans-boundary water channel with emphasis on groundwater. Main results can be classified and summarized as follows.1. The database was created about ground elevation, land use, geology, water use, meteorology and digitalized using a GIS software, ArcGIS. In particular, the digital geological information database of Takamatsu was established based on existing boring data at more than two thousands stations.2. Unconfined groundwater has been monitored at 65 stations and confined groundwater at 7 stations quarterly to clarify the temporal and spatial variations of the groundwater level and quality. It was confirmed that the unconfined groundwater level shows the highest in late summer and the lowest in winter and spring with annual change of 1-2 m and that the contour lines mostly run parallel to those of ground level. Concerning the water quality, Stiff diagrams and the cluster analysis d … More emonstrated that groundwater quality has shown little change with a few stations where the effects of fertilization and sea water intrusion were detected. Tritium analysis of confined groundwater indicated that unconfined groundwater has penetrated into the confined aquifer.3. Water balance analysis was made to quantify hydrologic systems at present and before the construction of Kagawa water channel. It suggested that the water channel and the land use change have led to considerable changes, i.e., the increase of surface runoff by 30mm, river low flow by 190mm and effluent from sewage system by 270mm and the decrease of evapo-transpiration by 60mm, infiltration into ground by 150mm and the groundwater uptake by 170mm.4. Numerical simulation of confined groundwater flow was performed on 500m x 500m mesh with estimated hydro-geological parameters, groundwater exploitation, initial and boundary conditions. Although the calculations show reasonably well results against recorded water levels at four stations, further improvement is necessary the reliable estimation of allowable groundwater uptake. More detailed information on hydro-geological parameters and groundwater exploitation rates is highly necessary. Less