Journal of Soil and Groundwater Environment (한국지하수토양환경학회지:지하수토양환경)

Korean Society of Soil and Groundwater Environment (한국지하수토양환경학회)
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Change of Seawater Intrusion Range by the Difference of Longitudinal Dispersivity in Hydrodynamic Modeling

수리동역학적 모델링에서 분산지수에 따른 해수침투 범위의 변화

  • Published : 2002.12.01
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Abstract

As a parameter for hydrodynamic modeling to define the range of seawater intrusion, dispersivities are frequently determined from pre-experiments or theoretical studies because field experiments need a lot of time and expenses. If the dispersivities are inadequate for an aquifer, the numerical results may have some errors. We examined the validity of longitudinal dispersivities by comparing the ranges of seawater intrusion with numerical modeling, field data and apparent resistivity sections. In the numerical modeling the TDS distributions simulated by the Xu's longitudinal dispersivity are more similar to the values of TDS measured at monitoring wet]s and boreholes than those by the Neuman's longitudinal dispersivity. The ranges of seawater intrusion by numerical simulations using Xu's longitudinal dispersivity show that the contour line of 1000 ㎎/L. as TDS is located at 480 m from the coast in May, while at 390 m in July. The difference is originated from the shift of the interface between seawater and fresh water. It moved toward the coast in July because of the seasonal increase of hydraulic gradient according to rainfall. A contour line of 15 ohm-m was used to define the range of seawater intrusion in apparent resistivity sections. From this criterion on the interface between seawater and fresh water, the range of seawater intrusion is located at 450 m from the coast. This result is similar to the range of seawater intrusion simulated by the numerical modeling using Xu's dispersivity. Therefore the range of seawater intrusion shows the difference due to the dispersivities used for the hydrodynamic modeling and the dispersivity generated by the Xu's equation is considered more effective to decide the range of seawater intrusion in this study area.

분산지수는 해수침투 범위를 파악하기 위한 수리동역학적 모델링을 실행하는데 필요한 매개변수이며. 이를 현장실험으로 구하기 위해서는 많은 시간과 비용을 필요로 하기 때문에 종종 기존의 실험과 이론적 연구에서 제시된 것을 이용한다. 그러나 그 분산지수가 실제 대수층의 특성을 나타내지 못할 경우, 모델링 결과에 많은 오차가 발생할 가능성이 크다 본 연구에서는 수치모델링에서 모사된 해수침투 범위와 현장측정치 및 겉보기비저항 단면도를 비교하여 이용된 분산지수의 타당성을 검증하였다. 수치모델링 결과, Neuman의 종분산지수보다 Xu의 종분산지수를 적용한 TDS분포가 연구지역내 관측공과 모니터링 우물에서의 현장측정치와 비교하였을 때 더 유사한 값을 나타내었다. Xu의 분산지수를 이용한 수치모델링에서 해수침투 범위는 건기인 5월에는 TDS 1000mg/L 등치선이 해안에서 약 480m 지점에 위치하며, 7월에는 해안에서 약 390m 지점에 위치한다. 이 차이는 강우에 의한 수리경사의 계절적인 변화에 의해서 해수와 담수의 경계면이 7월에 약 90m 정도 해안쪽으로 더 이동하였기 때문에 나타났다. 겉보기비저항 단면도에서는 해수와 담수의 경계로서 15 ohm-m 등치선을 이용하여 해수침투 범위를 설정하였으며, 그 결과 해수침투 범위가 해안으로부터 약 450m 지점에 위치하였다. 이것은 Xu의 분산지수를 이용한 수치모델링에서 모사된 해수침투 범위와 유사한 결과이다. 따라서 수리동역학적 모델링에서 분산지수에 따라 해수침투 범위가 차이를 보이는데, 본 연구지역에서는 Xu의 공식을 이용하여 산출된 분산지수가 해수침투의 범위를 결정하는데 더 유효하였다.

Keywords

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