An optimum groundwater management which achieved a good balance between conser vation and utilization is required to use the groundwater as sustainable water resources. On the recent groundwater management which uses a numerical simulation, it is important to understand the full breadth of groundwater basin and groundwater storage for evaluation the extent of human impact. However, previous study has not been clarified the full breadth of them throughout Japan, because basic information on the groundwater has not maintained still enough. The present work developed the three dimensional hydrogeological model in Japanese islands using the related database. And the groundwater storage was estimated based on the three dimensional hydrogeological model. As a result, to evaluate the full breadth of groundwater basin became possible from the sharply widerange distribution of stratum. Moreover, we succeeded in providing the useful information such as development potential of unused groundwater resources for groundwater conser vation and development.
Water table provides important information for the evaluation of groundwater resource. Recently, the estimation of water table in wide area is required for effective evaluation of groundwater resources. However, evaluation process is met with dif ficulties due to technical and economic constraints. Regression analysis for the prediction of groundwater levels based on geomorphologic and geologic conditions is considered as a reliable tool for the estimation of water table of wide area. Data of groundwater levels were extracted from the public database of geotechnical information. It was obser ved that changes in groundwater level depend on climate conditions. It was also obser ved and confirmed that there exist variations of groundwater levels according to geomorphologic and geologic conditions. The objective variable of the regression analysis was groundwater level. And the explanatory variables were elevation and the dummy variable consisting of group number. The constructed regression formula was significant according to the determination coefficients and analysis of the variance. Therefore, combining the regression formula and mesh map, the statistical method to estimate the water table based on geomorphologic and geologic condition for the whole country could be established.
The characteristics of seawater / freshwater interface var y locally with groundwater flow in coastal area. A repetition is needed to confirm the updated simulation result with the latest in-situ data. This study is aimed at making a model that can be modified at any point in time for the simulation of groundwater flow and seawater / freshwater interface at the coastal area of Horonobe, where geoscientific data is now being stored for future use. Preliminary simulation results indicated that the seawater / freshwater interface at the test site may be lowered into the Yuchi Formation at the depth of about 1000m. At the future survey, long term information on sea level change will be important for the chemical analysis of groundwater samples with borehole depth. The site at Horonobe is intended for the basic research development for geological disposal waste in coastal area, and the hydrogeological structure will be clarified to the depth of 1000m in several years. The result of this research will be verified at the time.
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