Featured Project

Validation of Water Budget Analyses and Numerical Modeling of Groundwater Flow, Jeju Island, Korea: Phase II:  Refining the Sustainable Groundwater Yield (In Progress)


Jeju Island is a temperate to subtropical volcanic island located approximately 140 km S of the Korean Peninsula. Though rainfall is abundant of about 1,975 mm/yr, supplying a large quantity of potable water for the ~540,000 inhabitants and agricultural use (i.e., tangerine, banana and citrus cropping, cattle grazing) is difficult given the island’s lack of perennial streams. Although some of the water is withdrawn from springs along the coast, most of the water (~92%) is abstracted as groundwater. As of 2002, the average groundwater withdrawal rate for domestic and agricultural supply was ~1.47 x 106 m3/day. The water budget, defined as the balance between the inflow of water from precipitation and snowmelt and the outflow of water by evapotranspiration, groundwater recharge, and streamflow, has been calculated for Jeju since the late 1960s. Studies estimated island-wide mean annual rainfall (3.39 x 109 m3/yr), evapotranspiration (37.1%), direct runoff (18.8%), and groundwater recharge (44.1%). Using hydrologic data collected from 1993-2002, another water budget analyses estimated mean annual rainfall of ~3.61 x 109 m3/yr with evapotranspiration accounting for 33.7%, direct runoff for 20.5% and groundwater recharge for 45.8% of annual rainfall.

Sustainable groundwater yield is defined as the maximum groundwater amount that can be extracted without significantly reducing the water quality via seawater intrusion. Studies estimated about 1.768 x 106 m3/day as the sustainable groundwater yield for Jeju Island, based on average 1993-2002 rainfall data. Comparison between the average groundwater withdrawal rate and the sustainable groundwater yield shows that 83% of the sustainable yield was already extracted on Jeju in 2002. As an illustration, this is much higher than the 43.5% calculated for the geologically and climatically similar island of Oahu, Hawaii, USA (calculations based on estimates for the time period 2005-2006). This is despite the fact that Jeju’s population is about half that of Oahu. In light of growing domestic and agricultural demand on Jeju, validating the water budget and understanding groundwater flow is critical to managing and regulating potable water resources.


The objective of Phase II is to improve the estimates of sustainable groundwater yield for Jeju Island. Phase II will entail three main tasks:  (1) water budget analyses, (2) groundwater recharge estimation, and (3) groundwater modeling to estimate sustainable yield. Groundwater recharge estimation using a variety of methods will be used to constrain estimates of recharge via the water budget method. Data needed to conduct the analyses will be collected and supplied by the Korea Institute of Geoscience and Mineral Resources (KIGAM). Water budget analysis, recharge estimation, and groundwater modeling work will be done by the Water Resources Research Center (WRRC). Our proposed tasks are largely based on the recommendations made in our Phase I report. Specifically, the following tasks are proposed for Phase II. It should be kept in mind that these tasks will be modified based on discussion with KIGAM more accurately identifying available data.