Numerical Assessment of the Influence of Long-Term Topographic Change on Deep Groundwater Flow Conditions

It is important to understand how long-term geological phenomena such as uplift and erosion influence deep hydrogeological and hydrochemical environments, and to predict the influence of such long-term geological phenomena in the future for the geological disposal of nuclear wastes. From the viewpoint of groundwater flow, it is necessary to estimate long-term topographic changes, and to evaluate their influence on deep groundwater flow conditions. In this study, the influence of long-term topographic change on deep groundwater flow conditions was numerically assessed. The general paleotopographic features of a wide area were estimated and groundwater flow simulations were carried out around the Tono area. As a result, the effects of long-term topographic changes and hydraulic features of faults on groundwater flow conditions, such as hydraulic gradient, velocity distribution, flow paths, and lengths, were confirmed. In general, if topographic characteristics such as locations of major mountains and valleys around the site have not changed, the groundwater flow paths will not significantly change. The methodology, which is proposed in this study, used to understand groundwater flow evolutions due to long-term topographic changes is efficient for identifying detailed assessment areas and is recommended based on the results of this study.