Quantitative estimation of fresh submarine groundwater discharge in Jeju island using geographic information system

Water use in island is mostly dependent on groundwater. Saltwater intrusion has occurred in aquifers in island, and available freshwater is decreasing. Sea level rise due to the climate crisis is increasing the range of saltwater intrusion in coastal aquifers. Saltwater intrusion is driven by complex mechanisms in coastal aquifers, including sea level rise, decrease of fresh submarine groundwater discharge (FSGD) and pumping from coastal aquifers, and geologic properties of coastal aquifers. FSGD from coastal aquifers, coupled with sea level rise, has a significant impact on saltwater intrusion and can reduce the amount of available water resources. Previous FSGD studies have focused on local areas where a large amount of discharge is observed. The existence of FSGD was diagnosed or estimated through various approaches such as field observation, isotope tracking, and water balance analysis. In this study, quantitative analysis of FSGD was performed using the freshwater-saltwater interface estimation formula of coastal aquifers. The location of the freshwater-saltwater interface was calculated using the Ghyben-Herzberg (G-H) equation, and the freshwater above the interface was estimated by FSGD. The geographic information system (GIS) was used to estimate FSGD using observation data over a large area. It was used to interpolate the observation data in a large area in grid units, and the Inverse Distance Weight method was used as the interpolation method. The interpolated data was used to input data for estimating FSGD. The study area was Jeju Island, the largest island in Korea. Quantitative estimation of FSGD can be used as a scientific basis for establishing water resource management plans in island.

Acknowledgement

Research for this paper was carried out under the KICT Research Program (project no.20220275-001, Development of coastal groundwater management solution) funded by the Ministry of Science and ICT.