• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.04a
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• pp.81-84
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• 2002

제주도 동부지역 구좌읍 한동리-송당리를 연결하는 직선상의 4개 지점에서 착정한 심부관측정에 대한 시추코어 지질검층과 심도별 수온ㆍ전기전도도 검층 결과, 제주도를 형성시킨 화산활동과 관련된 화산분출물(용암류 및 쇄설물)은 해수면하 136~170m 범위까지만 분포하고 있고, 그 하부에는 미교결의 U층(U Formation)이 분포하고 있는 것으로 밝혀졌다. 구좌읍 한동리에 소재한 둔지봉(해발 280m)을 경계로 해안지역의 U층 상부에는 용암이 바다속으로 흘러갈 때 생겨나는 베개용암(Pillow Lava)이 분포하고 있음이 최초로 확인되었으며, 이 베개용암층을 통해 고염분지하수가 내륙쪽으로 확산되는 것으로 밝혀졌다. 담수지하수체 하부에 존재하는 고염분 지하수체는 해안에서 내륙쪽으로 오면서 점진적으로 감소하고 기저지하수체(담ㆍ염수 혼합대를 형성하는 지하수체)는 해안으로부터 약 6~6km(해발 120~130m)지역까지 분포하고 있으며, 담수지하수 렌즈체의 두께는 이론적인 G-H비 보다 훨씬 얇은 것으로 나타났다.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.9
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• pp.995-1005
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• 2005

The study with laboratory sandbox model has been carried out to address potential use of reclaimed water, as a countermeasure artificially recharging the coastal aquifer, to effectively prevent from seawater intrusion due to overexploitation. It also investigated plausibility for either preserving or recovering the freshwater interface facing with seawater intrusion. To do this, we assessed hydraulic properties in artificial aquifer seawater/freshwater interface) depending upon the variation of extraction, storage and injection of reclaimed water. The variation of interface between freshwater and seawater were visualized by Surfer 8(Golden Software, USA) according to given experimental conditions. The interface between seawater and freshwater has been sensitively influenced by the change of extraction rate, where seawater zone migrated much faster into freshwater zone even though extraction rate became decreased. However, decreasing recharge rate could slow down moving of saline water zone toward freshwater zone. When the recharge was solely introduced into the sand box model, saline water intrusion was retarded than those of recharge and extraction working together. And also, the level of salinity of saline water was diluted by artificial recharge. It finally revealed that the artificial recharge would hydraulically avoid seawater intrusion while the freshwater sources could be conservatively utilized.

• Journal of Korea Water Resources Association
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• v.46 no.7
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• pp.783-794
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• 2013

Saline groundwater, in addition to fresh groundwater, is actively developed for inland aqua culture in Jeju Island where groundwater is practically the only source of freshwater. In this work we analyzed impacts of saline and fresh groundwater development on groundwater systems in Sungsan subwatershed in Jeju. A sharp-interface model was used to simulate fresh and saline groundwater flows. Withdrawal of freshwater imparted adverse impacts by lowering groundwater level and inducing saltwater encroachment. Withdrawal of saline water imparted mixed results: on one hand it lowered groundwater level, on the other hand it reduced saltwater encroachments. However, freshwater development lowered groundwater level much more than salinewater development did. Modified Ghyben-Herzberg ratio was developed for a transition zone with finite width. Comparison against observed data resulted in fair agreement.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.116-116
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• 2017

지하수 인공함양은 수자원확보 및 비상시 용수를 목적으로 세계적으로 연구 및 프로젝트가 진행되고 있다. 인공함양의 방법에는 여러 가지의 방식이 있지만 본 연구는 관정을 통해 주입하는 ASTR(Aquifer Storage Transfer and Recovery)방법을 이용하여 연구하였다. ASTR이란 지표수를 인공적인 방법으로 대수층에 주입시키고, 일정기간 저장시키거나 유하시킨 후 양수하는 방법이다. 염수로 포화된 피압대수층에 담수를 주입하여 염수를 치환할 수 있는 주입-양수 시스템을 연구하였다. 염수로 포화된 대수층에서 인공함양기술을 성공시키기 위해서는 양수정으로 유입되는 염수비율이 0%을 만족하며, 주입으로 인한 수위상승량은 지반변형을 일으키지 않는 최소한의 값을 가지는 것이다. 본 연구는 앞서 언급한 인공함양기술을 성공시키기 위해 지하수 흐름모델과 최적화 모델을 결합한 최적전산모델을 이용하여 모의하였다. 지하수 흐름모델은 경계면모델을, 최적화 기법은 GA(Genetic Algorithm)을 이용하였다. 구축된 목적함수로는 양수정의 담수비율 최대화, 주입정에서의 수위상승량 최소화 그리고 양수개시시간 최소화로 구성하였다. 제약조건으로는 총 주입량 및 양수량 그리고 주입 및 양수정 개수이다. 서술한 목적함수와 제약조건을 만족하는 주입/양수정의 위치 및 유량을 최적전산모델로부터 얻을 수 있다. 기존 지하수 인공함양 및 개발은 사례별 연구 또는 전문가의 주관적 판단에 의존하는 경향이 있었다. 본 연구는 최적화 기법을 통해 복수의 관정에서 정량적인 산정이 가능하다. 현재 모델링에 의존한 연구로써 한계가 있지만, 추후 실제현장에 적용하여 모델 검정을 통해 신뢰도를 높이며 지하수 인공함양 개발에 많은 공헌을 할 수 있을 것으로 예상한다.

• The Journal of Engineering Geology
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• v.19 no.1
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• pp.9-14
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• 2009

In this work applicability of a sharp-interface model to well-scale problems is examined. In coastal areas one of the main concerns in groundwater development is saltwater intrusion. To determine the saltwater intrusion at a well one needs to evaluate the saltwater content from a pumping well. We conducted laboratory sand-tank experiments to determine if a sharp-interface model can simulate the saltwater content of a pumping well. Lateral saltwater intrusion experiments and freshwater lens experiments are conducted. A partially penetrating well and a fully penetrating well are used. Comparison between numerical results and observation results indicates that the sharp-interface model can determine saltwater contents reasonably well. We conclude that a sharp-interface model can be applied to well-scale groundwater flow problems in coastal areas.

• Journal of Korea Water Resources Association
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• v.48 no.12
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• pp.1023-1035
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• 2015

This study applies 3-D N-S solver based on PBM (Porous Body Model), LED-WASS-3D ver 2.0 to directly analyze non-linear interaction of seawater-freshwater-coastal aquifer in order to simulate the seawater infiltration into coastal aquifer. This numerical simulation is the first trial in Korea, as well as unusual and new numerical analysis abroad. Firstly, to validate the applied numerical model, the validity and effectiveness was verified for the numerical model by comparing and considering it with the result of laboratory experiment for seawater-freshwater interface in coastal aquifer. And then it simulated the seawater infiltration into coastal aquifer considering the changed levels of seawater and groundwater in order to analyze the distribution characteristics of flow field and seawater-freshwater interface of coastal aquifer as the level difference between seawater and groundwater and rate of seawater level (${\Delta}h/h$) increased. In addition, the characteristics of seawater infiltration were analyzed from the vertical salinity in the coastal aquifer by ${\Delta}h/h$, which cannot be obtained from existing non-diffusion numerical models. Finally, it analyzed the effect of ${\Delta}h/h$ on the seawater infiltration distance in coastal aquifer, which was indexed.

• Tunnel and Underground Space
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• v.14 no.3
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• pp.229-240
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• 2004

Coastal aquifers may serve as major sources fur freshwater. In many coastal aquifers, intrusion of seawater has become one of the major constraints imposed on groundwater utilization. The management of groundwater in coastal acquifers means making decision as to the pumping rate and the spatial distribution of wells. Several numerical techniques for flow and solute transport simulation can provide the means to achieve this goal. As a basic study to predict the intrusion of seawater in coastal phreatic aquifers, the coupled flow and solute transport analysis was conducted by use of the 3-D finite element code, SWICHA. In order to understand how the location and the shape of freshwater-seawater transition zone were affected by the boundary conditions and hydrogeologic variables, parametric study was carried out.

• The Journal of Engineering Geology
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• v.33 no.1
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• pp.105-119
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• 2023

Water supply is decreasing due to climate change, and coastal and island regions are highly dependent on groundwater, reducing the amount of available water. For sustainable water supply in coastal and island regions, it is necessary to accurately diagnose the current condition and efficiently distribute and manage water. For a precise analysis of the groundwater flow in the coastal island region, submarine fresh groundwater discharge was calculated for the Seongsan basin in the eastern part of Jeju Island. Two methods were used to estimate the thickness of the fresh groundwater. One method employed vertical interpolation of measured electrical conductivity in a multi depth monitoring well; the other used theoretical Ghyben-Herzberg ratio. The value using the Ghyben-Herzberg ratio makes it impossible to accurately estimate the changing salt-saltwater interface, and the value analyzed by electrical conductivity can represent the current state of the freshwater-saltwater interface. Observed parameter was distributed on a virtual grid. The average of submarine fresh groundwater discharge fluxes for the virtual grid was determined as the watershed's representative flux. The submarine fresh groundwater discharge and flux distribution by year were also calculated at the basin scale. The method using electrical conductivity estimated the submarine fresh groundwater discharge from 2018 to 2020 to be 6.27 × 10⁶ m³/year; the method using the Ghyben-Herzberg ratio estimated a discharge of 10.87 × 10⁶ m³/year. The results presented in this study can be used as basis data for policies that determine sustainable water supply by using precise water budget analysis in coastal and island areas.

• The Journal of Engineering Geology
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• v.32 no.2
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• pp.257-270
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• 2022

This study evaluated the hydraulic factors contributing to the decreasing groundwater levels across Jeju island. Time-series data for groundwater level, precipitation, and groundwater usage and information on land use were acquired, and the correlations among them were analyzed to evaluate the causes of the decreasing groundwater. The effects of precipitation and groundwater usage on the fluctuations of groundwater level were quantified using response surface analysis and sensitivity analysis, and methods for groundwater quantity management by region were proposed. The results showed that the rate of groundwater decrease in the western region was larger than that in the eastern region. For the eastern region, the influence of precipitation was large and the rate of decrease in the groundwater level was relatively small. The geological formation of this part of the island and continuous seawater intrusion suggest that although the absolute amount of groundwater extracted for use was large, the decrease in the groundwater level was not seen to be great due to an increase in pressure by seawater intrusion. Overall, precipitation and groundwater usage had the greatest effect on the amount of groundwater in the western region, and thus their data would be most useful for informing groundwater management, whereas other factors (e.g., sea level and the location of the freshwater-seawater transition zone) must be considered when understanding Jeju's eastern region. As the characteristics of groundwater level fluctuations in the eastern and western regions are distinct, an optimal management plan for each region should be proposed to ensure the efficient management of groundwater quantity.