Technical Note: Integrated Surface-Groundwater Analysis for the Pyoseon Region, Jeju Island in Korea

Abstract

In the Jeju Island (Republic of Korea), surface runoff characteristics are very different from those of the inland. Most streams dry up shortly after rainfall events due to the rapid recharge of deep aquifers through highly permeable volcanic basalt rock. For this reason, accurate estimation of hydrologic components is challenging even with up-to-date watershed models like the Soil and Water Assessment Tool (SWAT). Fortunately, the integrated SWAT-MODFLOW model is capable of simulating complex hydrologic phenomena including stream-aquifer interaction and spatiotemporal groundwater recharge. The integrated SWAT-MODFLOW model was applied for the comprehensive investigation of the hydrologic components of the Pyoseon region in the Jeju Island. The SWAT-MODFLOW model simulated water budget components reasonably well compared with observed data. The pumping module in the SWAT-MODFLOW model, which combines the well package of MODFLOW with SWAT's water transfer options, was used to simulate water pumping from the present 198 wells on the island by increasing pumping amounts up to 20-fold relative to the current pumping amount in order investigate the impact on hydrologic components. When groundwater pumping rate increases by 10- and 20-fold, then the groundwater discharge amount decreases 5.5% and 17%, respectively. Considering topographical characteristics of the island, most of recharged groundwater is shown to be discharged to the sea. Thus, appropriate groundwater extraction in the Jeju Island could reduce the loss of deep aquifer into the sea and subsequently be effective in securing additional water resources.