A study on formation of saltwater-freshwater interface and upconing in coastal aquifers based on experiments with hydraulic models

This study was to evaluate saltwater interface and upconing caused by the intrusion of saltwater into coastal aquifers. There are many coastal areas in the around the world where the issue of seawater intrusionis troublesome.This was an experimental study using a hydraulic model to observe characteristics of the interface between freshwater and saltwater caused by the difference in density, as well as to research the formation of upconing, a seawater wedge occurred when drain in a well. Results of the experiment showed that the boundary between saltwater and freshwater in a coastal aquifer isproportional to the hydraulic gradient in dynamic state and inversely proportional to the density of fluid, so it is formed at a position lower than the sea level. It was confirmed that the upconing caused by excessive pumping was related to the depth to the saltwater-freshwater boundaryin the bottom of a pumping well. It was also con- firmed that the time duration required for the saltwater-freshwater boundary to restore its original state was more than twice the duration of upconing. By using the hydraulic model, it was possible to observe the formation of saltwater-freshwater boundary and upconing phenomenon in coastal aquifers distributed around islands or coastal areas. The purpose of this study was to obtain basic information such as the position of wells and pumping capacity to obtain groundwater more securely, which is not contaminated owing to seawater intrusion which may occur when pumping in coastal aquifer.