Abstract
Jeju Island is the largest island in South Korea. Recently, extensive groundwater abstraction has been reported from the shallow aquifer in the northeast region of the island. This study simulated the freshwater resources of the aquifer to estimate the sustainability of groundwater use on Jeju Island in terms of its vulnerability to seawater intrusion. Three-dimensional finite-difference numerical groundwater models were simulated using the MODFLOW-family code SEAWAT. Precise and recent groundwater level and multi-depth salinity data obtained from the study site were used for model calibration; the simulated results showed good agreement with the observed data. SEAWAT was used to delineate the current seawater-freshwater interface to quantitatively estimate the coastal fresh groundwater resources. Future stress scenarios were also simulated in response to increased pumping and various changes in the recharge. The results showed that current groundwater use in the coastal aquifer did not induce seawater intrusion in the coastal aquifer, but seawater intrusion will occur if the dry season continues for the next ten years. The vulnerability assessment based on the predicted groundwater levels and ion concentrations using numerical simulations suggests future vulnerability in the aquifer; therefore, continuous assessment and visualization of the aquifer sustainability is vital. Future projections by the integrated SEAWAT simulation and GALDIT assessment showed that an increase in groundwater pumping may escalate the vulnerability status of coastal groundwater resources from moderate to high in some areas of the study site, by inducing lateral seawater intrusion in deeper areas of the unconfined aquifer.
Highlights
Coastal areas are often characterized by urbanization, population growth, and environmental degradation
Coastal groundwater resources in island regions are more vulnerable to saltwater intrusion (SWI) than mainland coastal aquifers because they exhibit geological and topographic characteristics that complicate the use of surface water resources (Praveena et al 2010; Rozell and Wong 2010; Sulzbacher et al 2012; Oki 2005)
The sustainable development of groundwater resources is challenging under conditions of rapid economic growth, in island areas that are susceptible to SWI
Summary
Coastal areas are often characterized by urbanization, population growth, and environmental degradation These factors can lead to saltwater intrusion (SWI). Numerical models are commonly used to estimate the spatial and temporal heterogeneity of coastal groundwater resources and predict aquifer environments (Chang et al 2011; Feseker 2007; Masterson and Garabedian 2007; Oude Essink et al 2010; Praveena et al 2010). The impacts of groundwater pumping and recharge were modeled for Manukan Island in eastern Malaysia (Praveena and Aris 2010), and it was determined that groundwater pumping should be reduced to 75% of the current volume. This would ensure sustainable groundwater use in the region with the implementation of artificial groundwater recharge. Chang et al (2016) simulated a simplified numerical model of a barrier island in the United States to confirm whether the water from the groundwater pumping site conformed to drinking water standards for chloride, and estimated the water resources for future scenarios in which coastal water resources and anthropogenic activities had decreased due to climate change
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