Analysis of seawater intrusion into a Ryukyu limestone coastal aquifer using an immiscible approach: -- development and conservation of groundwater resources on a small island (I) --

摘要

In order to study proposals for meeting increasing water demands on a small island where the source of freshwater is coastal groundwater, it is important to be able to analyse the movement of the freshwater-saltwater interface where seawater intrudes into the coastal aquifer. This paper describes a numerical analysis that can reproduce measured freshwater-saltwater interface levels in a Ryukyu limestone coastal aquifer. Numerical analysis of quasi 3D groundwater density flow using the finite difference method can model the movement of the tip of the saltwater intrusion and the distribution of basement rock. This method was adopted for the reverse operation of the permeability coefficient and porosity based on the groundwater level. The numerical solutions show good agreement with the measured values for movement of the freshwater-saltwater interface It is concluded that this is a practical method for analysing the movement of the freshwater-saltwater interface where seawater intrudes into a large coastal aquifer, because the measured value is affected by hydrogeological characteristics.