Numerical Simulation of Saltwater Intrusion Caused by Land-Use Change and Groundwater Pumping in a Salinity-Affected Coastal Aquifer, Japan

Lowering of groundwater level may cause saltwater intrusion in coastal aquifers. Since decrease in groundwater recharge rate and overpumping lower groundwater level, recharge rate and pumping rate are main factors of saltwater intrusion In the study area, the land-use has been changing since a university campus was newly constructed. Therefore, there is concern that this rapid land-use change will increase the extent of saltwater intrusion in this area. The main aim of this thesis is to evaluate the effects of land-use change which decreases recharge rate, and groundwater pumping on saltwater intrusion. The simulations are conducted in different cases to compare those effects. The two models, groundwater recharge model and three dimensional density dependent solute transport model are applied to calculate salinity concentrations. The simulation results show that higher groundwater pumping rate enhances more saltwater intrusion than the land-use change. This is because the recharged water in the surrounding area prevents drastic lowering of groundwater level. Furthermore, the decrease in recharge rate due to the land-use change lowers groundwater level uniformly in the whole area, which maintains the seaward hydraulic gradient and velocities. This thesis can be used to prevent saltwater intrusion in this study area in the future.The study investigated effects of pumping and urbanization on groundwater levelk and risk for saltwater intrusion in south of Japan. The results show that effects of presesnt urbanization are negligible