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Heesung Yoon
Korea Institute of Geoscience and Mineral Resources, 124 Gwahak-ro, Yuseong-gu, Daejeon, 34132, Republic of Korea

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Research paper
Published: 29 February 2020 in Groundwater
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This paper describes the impacts of the M5.8(5.1) Gyeongju earthquakes on groundwater levels using data obtained from a unique coastal monitoring well. The monitoring strategy integrates conventional water‐level monitoring with periodic, continuous measurements of temperature and electrical conductivity (EC) within the water column of the well. Another important component of the monitoring system is a new instrument, the InterfacEGG, which is capable of dynamically tracking the freshwater‐saltwater interface. Although the system was set up to monitor seawater intrusion related to over‐pumping, as well as rainfall and tidal effects, it recorded impacts associated with a large earthquake and aftershocks approximately 241 km away. Seismic energies associated with the M5.8(5.1) Gyeongju earthquakes induced groundwater flows to the monitoring well through fractures and joints in the crystalline basement rocks. Temperature and EC logging data showed that the EC vertical profile declined from an average of approximately 5300 μS/cm to 4800 μS/cm following the earthquakes. The temperature profile showed a trend towards lower temperatures as the depth increased, a feature not commonly observed in previous studies. Data from the InterfacEGG suggested that the rise in EC was not due to the saltwater intrusion, but from the tendency for brackish water entering the borehole to induce convective mixing at deeper depths as the seismic waves travel through the well‐aquifer system. The increase in groundwater levels was caused by pulse of colder, less brackish water flowing into the well because of the earthquake. This behavior reflects an enhancement in rock permeability by removing precipitates and colloidal particles from clogged fractures, which improve the hydraulic connection with a nearby unit with a higher hydraulic head. This study suggests there is value added with a more aggressive monitoring strategy. This article is protected by copyright. All rights reserved.

ACS Style

Soo‐Hyoung Lee; Jae Min Lee; Heesung Yoon; Yongcheol Kim; Seho Hwang; Kyoochul Ha; Yongje Kim. Groundwater Impacts from the M5.8 Earthquake in Korea as Determined by Integrated Monitoring Systems. Groundwater 2020, 58, 951 -961.

AMA Style

Soo‐Hyoung Lee, Jae Min Lee, Heesung Yoon, Yongcheol Kim, Seho Hwang, Kyoochul Ha, Yongje Kim. Groundwater Impacts from the M5.8 Earthquake in Korea as Determined by Integrated Monitoring Systems. Groundwater. 2020; 58 (6):951-961.

Chicago/Turabian Style

Soo‐Hyoung Lee; Jae Min Lee; Heesung Yoon; Yongcheol Kim; Seho Hwang; Kyoochul Ha; Yongje Kim. 2020. "Groundwater Impacts from the M5.8 Earthquake in Korea as Determined by Integrated Monitoring Systems." Groundwater 58, no. 6: 951-961.

Journal article
Published: 26 March 2019 in Acque Sotterranee - Italian Journal of Groundwater
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Freshwater-salt water interface (FSI) location is very important information for decision maker in managing coastal aquifer system, however, its temporal change have been hard to get using conventional method such as EC monitoring at one or several fixed depths, geophysical logging or remote sensing techniques. A FSI tracking device, which has density between freshwater and salt water and hence can moves up and down as the freshwater-salt water transition zone moves, is used to get a temporal change data for the interface during several different types of pumping tests, which were performed at coastal monitoring wells in Seocheon, middle west of Korean Peninsula. Four short period pumping tests, three long-period pumping tests, one step-drawdown test, one reverse step-drawdown test were performed at different pumping rate ranging 19.86 to 48.71 m3/d for different pumping period of 60 minutes to 2851 minutes. Time series data shows that the Interface-Egg rises up from -86.0 to -77.6 m amsl after 24-hours pumping and to -40.8 m amsl after 2-days pumping and freshwater lens thickness is getting thinner from 88.1 m to 78.4 m after 24-hours pumping and then 42.3 m after 2-days pumping. These salt water up-coning phenomena are supported by EC profiles which were logged before and after the whole pumping periods. Time series data tell us that salt water upconing in the pumping well happens quickly and recovers at a very slow rate which is about 1.5 cm/d at 3 months after stopping pumping. The time series data of groundwater head and the interface-Egg’s location also shows that there is a tidal influence between pumping periods. The FSI tracker is expected to be practically applied to coastal aquifer management preventing from salt water intrusion, especially at dynamically pumping area for agricultural and/or domestic water supply.

ACS Style

Yongcheol Kim; Heesung Yoon; Soo-Hyung Lee. Freshwater-salt water interface dynamics during pumping tests. Acque Sotterranee - Italian Journal of Groundwater 2019, 1 .

AMA Style

Yongcheol Kim, Heesung Yoon, Soo-Hyung Lee. Freshwater-salt water interface dynamics during pumping tests. Acque Sotterranee - Italian Journal of Groundwater. 2019; ():1.

Chicago/Turabian Style

Yongcheol Kim; Heesung Yoon; Soo-Hyung Lee. 2019. "Freshwater-salt water interface dynamics during pumping tests." Acque Sotterranee - Italian Journal of Groundwater , no. : 1.

Journal article
Published: 23 June 2018 in Water
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This study showed the hydrogeological characteristics of an alluvial aquifer that is composed of sand, silt, and clay layers in a small domain. It can be classified into a lower high-salinity layer and an upper freshwater layer and contains shells and remnant paleo-seawater (average 5000 μS/cm) due to sea level fluctuation. Geological and electrical conductivity logging, a long-term pumping test, and multi-depth water quality measurements were conducted at pumping, injection, and observational wells to evaluate the hydrogeologic properties, identify the optimal recharge rate, and assess artificial recharge. Using a hydraulic test, a large difference in drawdown and salinity appeared at the radially located observational wells because of the difference in hydraulic connectivity between the wells in the small study area. It was concluded that the hydraulic anisotropy and heterogeneity of the alluvial aquifer should be carefully examined when locating an injection well and considering the efficient design of artificial recharge.

ACS Style

Soo-Hyoung Lee; Se-Yeong Hamm; Kyoochul Ha; Yongcheol Kim; Dong-Chan Koh; Heesung Yoon; Sung-Wook Kim. Hydrogeologic and Paleo-Geographic Characteristics of Riverside Alluvium at an Artificial Recharge Site in Korea. Water 2018, 10, 835 .

AMA Style

Soo-Hyoung Lee, Se-Yeong Hamm, Kyoochul Ha, Yongcheol Kim, Dong-Chan Koh, Heesung Yoon, Sung-Wook Kim. Hydrogeologic and Paleo-Geographic Characteristics of Riverside Alluvium at an Artificial Recharge Site in Korea. Water. 2018; 10 (7):835.

Chicago/Turabian Style

Soo-Hyoung Lee; Se-Yeong Hamm; Kyoochul Ha; Yongcheol Kim; Dong-Chan Koh; Heesung Yoon; Sung-Wook Kim. 2018. "Hydrogeologic and Paleo-Geographic Characteristics of Riverside Alluvium at an Artificial Recharge Site in Korea." Water 10, no. 7: 835.

Journal article
Published: 04 May 2017 in Water
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Time series models based on an artificial neural network (ANN) and support vector machine (SVM) were designed to predict the temporal variation of the upper and lower freshwater-saltwater interface level (FSL) at a groundwater observatory on Jeju Island, South Korea. Input variables included past measurement data of tide level (T), rainfall (R), groundwater level (G) and interface level (F). The T-R-G-F type ANN and SVM models were selected as the best performance model for the direct prediction of the upper and lower FSL, respectively. The recursive prediction ability of the T-R-G type SVM model was best for both upper and lower FSL. The average values of the performance criteria and the analysis of error ratio of recursive prediction to direct prediction (RP-DP ratio) show that the SVM-based time series model of the FSL prediction is more accurate and stable than the ANN at the study site.

ACS Style

Heesung Yoon; Yongcheol Kim; Kyoochul Ha; Soo-Hyoung Lee; Gee-Pyo Kim. Comparative Evaluation of ANN- and SVM-Time Series Models for Predicting Freshwater-Saltwater Interface Fluctuations. Water 2017, 9, 323 .

AMA Style

Heesung Yoon, Yongcheol Kim, Kyoochul Ha, Soo-Hyoung Lee, Gee-Pyo Kim. Comparative Evaluation of ANN- and SVM-Time Series Models for Predicting Freshwater-Saltwater Interface Fluctuations. Water. 2017; 9 (5):323.

Chicago/Turabian Style

Heesung Yoon; Yongcheol Kim; Kyoochul Ha; Soo-Hyoung Lee; Gee-Pyo Kim. 2017. "Comparative Evaluation of ANN- and SVM-Time Series Models for Predicting Freshwater-Saltwater Interface Fluctuations." Water 9, no. 5: 323.

Thematic issue
Published: 12 May 2016 in Environmental Earth Sciences
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The monitoring and prediction of temporal change in the location of the freshwater–saltwater interface including the groundwater level (GWL) is the essential information for effective management of coastal aquifer, especially for managing the saltwater intrusion. A simple and novel method for monitoring temporal change in the location of the freshwater–saltwater interface was developed and evaluated by applying to a coastal aquifer in Jeju Island, resulted in obtaining time series data of the freshwater–saltwater interface level (FSL) successfully. And applicability of artificial neural network-based time series models to prediction of the GWL and the FSL is evaluated using the observed data from the site. The prediction result shows that the input configuration including autoregressive components enhances the model performance and the recursive prediction models can be useful for the long-term prediction of the GWL and the FSL in this case study.

ACS Style

Yongcheol Kim; Heesung Yoon; Gee-Pyo Kim. Development of a novel method to monitor the temporal change in the location of the freshwater–saltwater interface and time series models for the prediction of the interface. Environmental Earth Sciences 2016, 75, 882 .

AMA Style

Yongcheol Kim, Heesung Yoon, Gee-Pyo Kim. Development of a novel method to monitor the temporal change in the location of the freshwater–saltwater interface and time series models for the prediction of the interface. Environmental Earth Sciences. 2016; 75 (10):882.

Chicago/Turabian Style

Yongcheol Kim; Heesung Yoon; Gee-Pyo Kim. 2016. "Development of a novel method to monitor the temporal change in the location of the freshwater–saltwater interface and time series models for the prediction of the interface." Environmental Earth Sciences 75, no. 10: 882.

Journal article
Published: 07 April 2016 in Water
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This study investigated changes in stream–aquifer interactions during the period shortly after the construction of the Changnyeong-Haman River barrage (CHRB) on the Nakdong River in South Korea. The hydraulic diffusivity (α) and river resistance (R) values at the semipervious stream–aquifer interface were estimated by using a one-dimensional (1-D) analytical solution with Fourier transform (FT). Prior to the application of the 1-D analytical solution, the noise effects on the groundwater levels were removed by using fast Fourier transform and low-pass filtering techniques. Sinusoidal variation of the river stages was applied to the 1-D analytical solution. For the study period, the R values showed a decreasing trend, while the α values showed an increasing trend, and results showed that the average of the median values of flood duration times (td) and flood amplitudes were reduced to 78% and 59%, respectively. Moreover, the ratio of flood peak time to td demonstrated a decreasing tendency after the construction of the CHRB. Hence, it is concluded that the dredging and increase of river-water storage due to CHRB construction enhanced stream–aquifer interactions during the period shortly after the construction of the CHRB.

ACS Style

Yun-Yeong Oh; Se-Yeong Hamm; Kyoochul Ha; Heesung Yoon; Il-Moon Chung. Characterizing the Impact of River Barrage Construction on Stream-Aquifer Interactions, Korea. Water 2016, 8, 137 .

AMA Style

Yun-Yeong Oh, Se-Yeong Hamm, Kyoochul Ha, Heesung Yoon, Il-Moon Chung. Characterizing the Impact of River Barrage Construction on Stream-Aquifer Interactions, Korea. Water. 2016; 8 (4):137.

Chicago/Turabian Style

Yun-Yeong Oh; Se-Yeong Hamm; Kyoochul Ha; Heesung Yoon; Il-Moon Chung. 2016. "Characterizing the Impact of River Barrage Construction on Stream-Aquifer Interactions, Korea." Water 8, no. 4: 137.

Journal article
Published: 28 December 2014 in Economic and Environmental Geology
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ACS Style

Sang-Ho Moon; Kyoochul Ha; Yongcheol Kim; Dong-Chan Koh; Heesung Yoon. Examination for Efficiency of Groundwater Artificial Recharge in Alluvial Aquifer Near Nakdong River of Changweon Area, Korea. Economic and Environmental Geology 2014, 47, 611 -623.

AMA Style

Sang-Ho Moon, Kyoochul Ha, Yongcheol Kim, Dong-Chan Koh, Heesung Yoon. Examination for Efficiency of Groundwater Artificial Recharge in Alluvial Aquifer Near Nakdong River of Changweon Area, Korea. Economic and Environmental Geology. 2014; 47 (6):611-623.

Chicago/Turabian Style

Sang-Ho Moon; Kyoochul Ha; Yongcheol Kim; Dong-Chan Koh; Heesung Yoon. 2014. "Examination for Efficiency of Groundwater Artificial Recharge in Alluvial Aquifer Near Nakdong River of Changweon Area, Korea." Economic and Environmental Geology 47, no. 6: 611-623.

Journal article
Published: 30 June 2013 in The Journal of Engineering Geology
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ACS Style

Heesung Yoon; Yongcheol Kim; Kyoochul Ha; Gyoo-Bum Kim. Application of groundwater-level prediction models using data-based learning algorithms to National Groundwater Monitoring Network data. The Journal of Engineering Geology 2013, 23, 137 -147.

AMA Style

Heesung Yoon, Yongcheol Kim, Kyoochul Ha, Gyoo-Bum Kim. Application of groundwater-level prediction models using data-based learning algorithms to National Groundwater Monitoring Network data. The Journal of Engineering Geology. 2013; 23 (2):137-147.

Chicago/Turabian Style

Heesung Yoon; Yongcheol Kim; Kyoochul Ha; Gyoo-Bum Kim. 2013. "Application of groundwater-level prediction models using data-based learning algorithms to National Groundwater Monitoring Network data." The Journal of Engineering Geology 23, no. 2: 137-147.