Hydrogeological characterization of seawater intrusion in tidally-forced coastal fractured bedrock aquifer

SummaryHydrogeological investigation was carried out to characterize seawater intrusion in a tidally-forced coastal fractured bedrock aquifer in the west coast of Korea peninsular, which was also subject to heavy groundwater extraction. Times series analysis, using the data of electrical conductivity (EC), groundwater level and tidal oscillation, showed that intensive groundwater extraction from the wells near the shore caused a severe seawater intrusion. The geophysical loggings and hydraulic tests indicated that the tidally-forced coastal fractured aquifer in the study area was characterized by the shallow fresh groundwater, transition zone, and deep high saline water zone. The extent of seawater intrusion highly depended on conductive fractures and their hydraulic connectivity. In the deep saline water layer, progressive seawater intrusion took place mainly by persistent intensive pumping and in part by tidal activity. The conductive fractures acted as a pathway for saline water flow from the deep saline water zone to the transition zone, when groundwater was extracted. The extent of transition zone depended on the change of groundwater level by groundwater pumping or recharge. This study indicated that a persistent intensive extraction of groundwater would intensify seawater intrusion in tidally-forced coastal fractured aquifer and proper measures would be required to prevent it.

► This study investigates how tide and pumping affects seawater intrusion dynamically.
► Seawater intrusion took place by intensive pumping and partly by tidal activity.
► Fractures become pathway for saline water from deep saline zone to overlying aquifer.