Development and verification of a three dimensional density dependent solute transport model for seawater intrusion

Seawater intrusion is identified as a critical issue that needs to be addressed in coastal hydrology, due its irreversible effect on the water quality of coastal freshwater aquifers. Due to the density differences in seawater and freshwater, the density dependent flow phenomenon is dominant seawater intrusion. Three dimensional numerical model is necessary to address the complex hydro-geological formations. Therefore, it is important to develop a three dimensional simulation model to understand the density dependent solute transport process taking place in the seawater intrusion problem. The model developed in this study is based on the transition zone approach which couples the groundwater flow and mass transport equation to solve the density dependent flow. The finite difference method is used as the numerical method to solve the partial difference equations of groundwater flow and solute transport. The method of characteristic is applied to solve the advection term of mass transport equation. Therefore, in this paper, a valued attempt has been taken to simulate the seawater intrusion in the three dimensional point of view under the density dependent flow effect. Motooka area of Fukuoka Prefecture Japan which is a coastal area is selected as an application area for the developed model to emphasize seawater intrusion and justify the model. This area is affected by seawater intrusion and so far numerical study of seawater intrusion under the density dependent flow concept has not performed.