A Method to Measure the Temporal Variation of Freshwater-Saltwater Interface and Applications to Coastal Aquifers in Korea

Management of coastal aquifers is becoming increasingly important with the growing population near the coast and prospects of global climate change. Therefore, many countries have installed monitoring wells along coastlines and monitor the groundwater level and electric conductivity at fixed depths. To prevent the salt water intrusion, however, it is necessary to observe the temporal variation of the freshwater-saltwater interface. In the present study, we developed a monitoring device to monitor the temporal variation of the freshwater-saltwater interface directly based on the concept of the neutral buoyancy. The devices were installed at monitoring well of the Yellow sea coast and eastern coast of Jeju island in Korea, and time series data of the freshwater-saltwater interface were obtained as well as the groundwater level. The groundwater level and freshwater-salter interface data are highly correlated with the tide level of which the lag times were 80 and 195 minute, respectively. To predict the temporal change of groundwater level and freshwater-saltwater interface, time series models based on an artificial neural network were developed. The result of the prediction shows that correlation coefficients between observed and predicted values are over 0.9 and 0.78 for groundwater level and freshwater-saltwater interface, respectively.