기후변화에 따른 해수면 상승으로 인하여 해안지역의 지하수계에 해수침투가 가중된다. 지하수의 염분농도가 증가하면 지하수면 상부의 불포화 토양에서도 염분 농도가 증가할 수 있으며, 이는 농경지에서 작물피해를 일으킬 수 있다. 해수면이 상승함에 따라 내륙의 지하수위도 함께 상승한다. 이는 불포화 토양층의 두께를 감소시켜 해안 저지대의 경작에 피해를 끼칠 수 있다. 본 연구에서 지하수 해수침투는 3차원 모델, 토양 염류화 평가는 연직 1차원 모델을 합성 적용하여 해안 농경지에 대한 해수면 상승 피해를 평가하는 방법을 개발하였다. 3차원 해수침투 모델에서 지하수면의 수위 와 농도분포를 계산하고 최상부 절점 중에서 염분 농도가 기준 값 이상인 절점에서 지하수면과 지표면 사이의 토양층에서 연직 1차원 모델링으로 토양층의 염분 농도와 불포화대 두께를 계산하였다. 농경지의 토양 염류화는 작물의 뿌리 심도에서 보통 작물의 생육한계 염분농도를 기준으로 판 단하였다. 개발된 모델링 방법을 가상의 간척농경지에 적용하였다. 해수면 상승자료로 IPCC의 RCP 4.5와 8.5 시나리오를 사용하였다. 평가 결과 는 2050년과 2100년에 대하여 제시하였다. 연구결과 대상지역에서 기후변화 시나리오 RCP 8.5에서 2100년에는 지하수 염류화 피해 면적은 간 척지 육지면적 대비 7.8%, 염류화 토양 면적은 6.0%, 불포화층의 두께가 뿌리심도보다 적은 지역의 면적은 1.6% 증가하는 것으로 분석되었다.

According to the results of the groundwater quality investigation about 230 holes all over the country, the groundwater which was in excess of standard grows larger every year and closed holes increased to 23,457 holes in 1997 from 15,724 holes in 1996. This is the major reasons that water quality contamination, shortage of water quantity, increasing of salinity and so on. There are 7 groundwater salinization sources which are considered as most important on a regional level. And among theses the Cheju Island groundwater salinization sources are (1) halite solution, (2) natural saline groundwater, (3) sea-water intrusion. The method of taking an isotopes is one of research methods of the origin of groundwater salinization and is used in so many studies because it has very high confidence. 18O, 2H, 3H, 14C and so on in an isotopes are frequently used in the method of them. Consequently on this study we analyzed major ions and 3H in groundwater, sea-water and rain of the eastern part of cheju island known as contaminated site from long time ago to examine the origin of groundwater salinization. Relation ratios of the major ions versus chloride ion shows similar tendency to sea-water. This indicates that sea-water entered the groundwater layer. And amount of 3H in holes of the land side is higher than that of the sea side. Relation of chloride ion versus 3H indicates negative character. Therefore we can think that the reason of groundwater salinization of this part is natural saline groundwater and halite solution by relation.

The purpose of this study is to investigate the physicochemical characteristics of salinization of groundwater at the estern area of Cheju island. For this purpose, the major ions of groundwater. spring water are analyzed. The concentration of Cl- and Na-+K- contained in the groundwater at near the coastline are higher than those at inland area away from the coastline. The water quality components of groundwater observed at this area can be classified into 4 types such as Na-Cl, HCO3, Na-Cl-HCO3 and Ca-HCO3. The concentration ratio of SO4- to Cl- is 0.1354(R2=0.972) at this area. This value is very similar with Dittomer's ratio of 0.13. For Na-, K-, and Mg2+ versus Cl-, their ratios also show a significant relationship between sea water and groundwater in this area. From the chloride-bicarbonate ratio, it can be estimated that the intrusion distance of seawater from coastline to inland area is 2.8km at Onpyung-Nansan, Sangdo and Pyungdae areas, and 5.4㎞ at Kosung-Susan area. The mixing ratio between seawater and fresh water by the intrusion of seawater is decreased with the distance toward inland from coastline. This ratio(fresh water : seawater) is 80:20 in spring water adjacent the coastlines, Onpyung area and 99.8:0.2 in the well at No.3 of Susan located at inland away from the coastline. The concentration of Na- observed at field is 25∼45% lower than that theoretically calculated by this mixing ratio. Based on the data of EC, the equipotential line of 500μmhos/㎝ is located at 4∼5㎞ point at Kosung-Susan area and 2.5㎞ point at the other area. The equation of correlation between Cl- concentration and EC values is Cl-=0.1927EC-16.683 for the area lower than 500μmhos/㎝ and Cl-=0.2773EC for the area beyond 500 μmhos/㎝.