The depth of low permeable layer in Jeju Island was analyzed using the geologic columnar section data. The highest low permeable layer was found in center of Mt. Halla and the deepest area was in eastern part of Jeju Island. The study area, Seongsan watershed, is located in the eastern part of Jeju where the low permeable layer showing deep in a northward direction.
Based on this analysis, the MODFLOW modeling was performed for groundwater flow of Seongsan watershed. The boundary of Seongsan watershed was set up as a no-flow and the modeling result showed the difference -0.26~0.62 m compared to the observed groundwater level. Meanwhile, MODFLOW model results considering low permeable layer showed -0.26~0.36 m differences compared to groundwater level and indicated more accurate than no-flow method result. Therefore, to interpret the groundwater flow over Seongsan watershed, comprehensive consideration including the low permeable layer distribution below the basalt layer is needed.

Abstract
 1. 서 론
 2. 연구방법
  2.1. 제주도 저투수층
  2.2. 연구대상유역
  2.3. 지하수 해석모형 구축
 3. 결과 및 고찰
  3.1. 제주도 저투수층 구조
  3.2. 지하수 흐름분석
  3.3. 성산유역의 표고와 지하수위 비교
  3.4. 보정후의 지하수 흐름해석
 4. 결론
 REFERENCE

• 김민철(제주대학교 토목공학과) | Min-Chul Kim (Department of Civil Engineering, Jeju National University)
• 양성기(제주대학교 토목공학과) | Sung-Kee Yang (Department of Civil Engineering, Jeju National University) Corresponding author
• 오승태(제주대학교 토목공학과) | Seung-Tea Oh (Department of Civil Engineering, Jeju National University)