• Journal of Soil and Groundwater Environment
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• v.9 no.3
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• pp.27-32
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• 2004

The oceanic tides have an effect on groundwater levels in coastal fractured rock aquifers. The observed groundwater table fluctuations caused by the effective stress through an aquifer are shown as sine curves similar with tidal fluctuation. To estimate a hydrogeologic parameter, tidal method is utilized with groundwater level fluctuations of two monitoring wells. Cross correlation function is used to calculate time lags between observed groundwater levels and tide, and the deeper well shows longer time lag. The storage coefficients calculated by using tidal efficiency and time lag show large differences. The storage coefficients obtained by using time lags are close to the result of slug test, and that of the deeper well shows closer value by slug test. The tidal efficiency is unsatisfied to apply in the tidal method because of an effect of phreatic aquifer and the vertical flow of groundwater through fractured confining bed. This tidal method can be an economical and effective way to define the parameter by considering the location of observation well and hydrogeologic characteristics of a coastal aquifer.

• 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.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.32-35
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• 2006

The validation of a groundwater source heat pump system installation site is estimated by bydrogeothermic model ing. The hydraulic characteristics of the aquifer system is evaluated from pumping and recovery tests. In addition, the temperature distribution by the pumping and the injection of groundwater, and water level fluctuations are simulated by numerical modeling. The total cooling and heating load for the building is designed as 120RT(refrigeration ton) and the ground water source heat pump system covers 50RT as a subsidiary system The scenario of heat pump operation is organized as pumping and inject ion of groundwater that is performed for 8 hours per day in cooling mode for 90 days during the summer season The heat transfer by the injected warm water is limited near the inject ion wells in the simulated temperature distribution. The reason is that the given operation time is too short to expect broad thermal diffusion in large volume of the aquifer in the simulation time The simulated groundwater level and temperature distribution can be used as important data to develope an energy effective pumping and injection well system. Also it will be very useful to evaluate the hydraulic capacity of a target groundwater reservoir.

• Economic and Environmental Geology
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• v.39 no.5 s.180
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• pp.537-554
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• 2006

Water levels of thermal groundwater ($>30^{\circ}C$) were recorded from March 2002 to June 2006 at several monitoring wells within the Yuseong spa area. Using these data, we elucidated the long-term cyclic fluctuations of thermal groundwater levels with 1 year period. We also observed a noticeable water level variation with periods of 0.5, 1 and 7 days in most monitoring wells, which indicates relatively good hydraulic connectivity within the main hotspring area. By comparing water level variations among several wells, we found out that E-W and N-S trending geological structures should be an important control factor for emplacement and flow of thermal groundwater in the study area. It may be also inferred that geothermal source is highly associated with the hydraulic connectivity of aquifers at the Yuseong spa area.

• Journal of Soil and Groundwater Environment
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• v.28 no.6
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• pp.45-57
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• 2023

To assess land subsidence estimation and preparedness in the Geum River basin, this study applied GIS techniques and identified six key areas. The Geum River basin has experienced an increase in heavy rainfall since late 2010, and four study areas have shown an increase in groundwater levels. Land subsidence primarily occurred from June to September, with higher rainfall years in 2020 and 2023. Approximately 83.6% of land subsidence in Chungcheongbuk-do province occurred in Cheongju-si, mainly attributed to aging sewage pipes. The regions experiencing population growth have likely led to the construction of underground infrastructures and sewer pipes. Thus, it is considered that various factors, including sewage pipe leaks, precipitation, slope gradient, low drainage density, and groundwater level fluctuations, have contributed to land subsidence. Improving land subsidence estimation involves incorporating additional natural factors and human activities.

• Tunnel and Underground Space
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• v.27 no.4
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• pp.205-216
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• 2017

Fluctuations in groundwater level are the major cause of ground subsidence in the abandoned limestone mine. In this study, evaluation of groundwater flow under three different cases of natural condition, aggregate-filling, temporary drainage in groundwater-saturated limestone mine cavities was executed by 3-dimensional analysis. In the case of aggregate-filling, although the water level both in the upper ground of mine cavities and an agricultural watershed was elevated, it was lower than the water level fluctuation of an agricultural water use and rainfall and the flow rate was similar to the flow rate of natural condition. In the case of temporary drainage, as the water level in the upper ground of mine cavities and an agricultural watershed decrease rapidly and the flow rate has increased by 25times, so the risk of ground subsidence increased.

• Journal of Soil and Groundwater Environment
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• v.17 no.4
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• pp.51-62
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• 2012

Effects of climate change on groundwater system requires understanding the groundwater system in temporal and spatial scales through the long-term monitoring. In this study, the spatio-temporal variations of groundwater were analyzed through the continuous observation of water level, electrical conductivity (EC) and water temperature with automatic data-loggers and sampling in a Gwangneung catchment, Korea, for the four years from 2008 to 2011. Groundwater monitoring were performed at the nest-type wells, MW1 and MW2, located in upsteam and downstream of the catchment, respectively. During the survey period, both the total amount of annual precipitation and the frequency of concentrated rainfall have increased resulting in the elevation of runoff. Water level of MW1 showed no significant fluctuations even during the rainy season, indicating the confined groundwater system. In contrast, that of MW2 showed clear seasonal changes, indicating the unconfined system. The lag-time of temperature at both wells ranged from one to three months depending on the screened depths. Results of chemical analyses indicated that major water compositions were maintained constantly, except for the EC decreases due to the dilution effect. Values of the stable-isotope ratios for oxygen and deuterium were higher at MW2 than MW1, implying the confined system at the upstream area could be locally developed.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.438-441
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• 2006

The groundwater level was originally above the surface at the Onyang spa area. However, it is now 98-138m depth below the surface deu to the artificial pumping from boreholes. The fluctuations of the piezometric head were observed in 4 boreholes. Transmissivity estimated from the pumping rate and the drawdown is about $577.51 m^2/day$ The transmissivity of Onyang spa area is much larger than common values of fractured aqui for the drawdown of the piezometric head by artificial pumping is widely spreaded out in that area. The drawdown related to each pumping rate was analyzed and the formula between drawdown and pumping rate was made by a regression analysis. The formula can be applied for the condition of enough groundwater flowing into the Onyang spa area

• The Journal of Engineering Geology
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• v.29 no.3
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• pp.265-277
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• 2019

Changes in the amount, intensity, frequency, and type of precipitation, in conjunction with global warming and climate change, critically impact groundwater recharge and associated groundwater level fluctuations. Monthly gravity levels by the Gravity Recovery and Climate Experiment (GRACE) are acquired to monitor total water storage changes at regional and global scales. However, there are inherent difficulties in quantitatively relating the GRACE observations to groundwater level data due to the difficulties in spatially representing groundwater levels. Here three local interpolation methods (kriging, inverse distance weighted, and natural neighbor) were implemented to estimate the areal distribution of groundwater recharge changes in South Korea during the 2002-2016 period. The interpolated monthly groundwater recharge changes are compared with the GRACE-derived groundwater storage changes. There is a weak decrease in the groundwater recharge changes over time in both the GRACE observations and groundwater measurements, with the rate of groundwater recharge change exhibiting mean and median values of -0.01 and -0.02 cm/month, respectively.

• Journal of Korea Water Resources Association
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• v.54 no.spc1
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• pp.1143-1154
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• 2021

The selection of activation function has a great influence on the groundwater level prediction performance of artificial neural network (ANN) model. In this study, five activation functions were applied to ANN model for two groundwater level observation wells in the middle mountainous area of the Pyoseon watershed in Jeju Island. The results of the prediction of the groundwater level were compared and analyzed, and the optimal activation function was derived. In addition, the results of LSTM model, which is a widely used recurrent neural network model, were compared and analyzed with the results of the ANN models with each activation function. As a result, ELU and Leaky ReLU functions were derived as the optimal activation functions for the prediction of the groundwater level for observation well with relatively large fluctuations in groundwater level and for observation well with relatively small fluctuations, respectively. On the other hand, sigmoid function had the lowest predictive performance among the five activation functions for training period, and produced inappropriate results in peak and lowest groundwater level prediction. The ANN-ELU and ANN-Leaky ReLU models showed groundwater level prediction performance comparable to that of the LSTM model, and thus had sufficient potential for application. The methods and results of this study can be usefully used in other studies.