A 3D numerical model was developed to simulate seawater intrusion and aquifer recovery in Niijima Island under the future Nankai earthquake and tsunami scenario. The FEFLOW code was used to solve density-dependent groundwater flow and mass transport in unsaturated-saturated porous media. The simulations indicated that the maximum amount of seawater intrusion during the tsunami was controlled by the total unsaturated void space of the soil beneath the inundation area. After the tsunami, directions of seawater movement and flushing time depended on the pre-tsunami groundwater flow conditions and bedrock structures. Some groundwater was found to be survived from salinization, and showed the potential to provide water supply in an equivalent amount of the pre-tsunami level without worsening the recovery process. The simulated attempt to remove the intruded seawater from a polluted well could accelerate aquifer recovery but might not be practical due to the cost of maintaining intensive pumping over years.
We developed a numerical method (ASG method) for simulating a coupled atmospheric gas–surface water system, simulated by Navier–Stokes equations, and groundwater system, simulated by water saturation equations. Here, we derived dimensionless formulas for ASG method to avoid the influence of a dimension of analytical domain, in this study. Further we used the ASG method to simulate the configuration and movement of the infiltration front in an embankment composed of sand and obtained results similar to those obtained by a water tank experiment in another study. In addition, in a practice problem using non-dimensional values, we simulated the movement of gas and water when surface water flowed over an embankment expressed in dimensionless form.
Consequently the ASG method could simulate the movement of water and gas across the interface between a surface system and a porous medium including the practice embankment.
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