• Journal of the Korean Association of Geographic Information Studies
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• v.9 no.4
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• pp.176-192
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• 2006

The need for a systematic drought management has increased since last countrywide drought in 2001. Naturally various studies for establishing drought plan and preventing drought disaster have been conducted. MODIS image provided by Terra satellite has effective spatial and temporal resolutions to observe spatial and temporal characteristics of a region. MODIS data products are easy for preprocessing and correcting geometrically and provide various data set in regular which are applicable for drought monitoring. In this study, Ansung river and the upstream of South Han river basin was chosen for case study to identify and assess spring drought. The multi-period MODIS image and accumulated precipitation were used to detect not only the drought year but also the vegetation change of normal year and the result were compared with various spatial data. The result shows NDVI and LSWI with is more appropriate than LST for assesing spring drought in Korea and two month cumulative precipitation has moderate relationship with drought. It is necessary to use MODIS image which has same period and same space for effective drought analysis because drought is also affected by landover and altitude.

• Korean Journal of Environment and Ecology
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• v.30 no.3
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• pp.328-334
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• 2016

This study identified the habitat use pattern and migration distance of spot-billed ducks during winter that occur for breed and wintering. The study was carried out using GPS-mobile phone based Telemetry (WT-300) to provide the research results as basic data for protection and management of the habitats of water birds in Korea. The tracking devices (WT-300) were attached to a total of twenty spot-billed ducks collected from the rivers and reservoirs in Gyeonggi-do Anseongcheon, Chungcheongnam-do Seocheongun, Jeollabuk-do Mangyunggang, Dongjingang, and Jeollanam-do Haenamgun. It was found that spot-billed ducks used rivers most frequently as their habitats (47.3%), followed by rice fields, ocean, inland wetlands, and tidal flats. While spot-billed ducks used rice fields at night time and ocean, inland wetlands, and tidal flatss at day time, they used rivers regardless of time. Change rate of habitat use pattern was highest between 6:00am and 8:00am and between 16:00pm and 18:00pm. The average daily migration distance was $0.75{\pm}0.27km$/2hours and accumulated migration distance was 8.95km. Spot-billed ducks covered the longest migration distance between 6:00am and 8:00am and between 16:00pm and 18:00pm; the distance they moved during the periods from 6:00am to 8:00am and from 16:00pm to 18:00pm was 2km but during the rest of the time, it was less than 1km for equivalent durations. The time when spot-billed ducks covered the longest migration distance also corresponds to the time when they showed the greatest change rate of habitat use pattern.

• Journal of Korea Water Resources Association
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• v.51 no.2
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• pp.99-107
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• 2018

This study was to evaluate the stream depletion due to groundwater pumping from 17 wells near the Anseongcheon upper stream using the Baalousha's analytical solution (2012) which directly considers stream width and streambed hydraulic conductivity. The input hydraulic values of aquifer and streambed were obtained from the pumping tests and seepage experiments. The estimated streamflow depletion rates divided by pumping rate (dimensionless stream depletion) showed a range from 0.23 to 0.89 for 5 year pumping. In particular, the results revealed that the groundwater pumping has insignificant effects on streamflow when the stream depletion factor (SDF) is higher than 1,000 with values of dimensionless stream depletion lower than 0.4. A more simple Hunt's solution (1999) also applied to the same wells, and the results showed that the difference between the dimensionless stream depletions calculated by using both solutions could be negligible. From the comparison of the Baalousha's solution (2012) with the Hunt's solution (1999) with total 3,000 cases of simulations with combinations of various aquifer and stream properties, the stream-well distance should be more longer than stream width for reducing the discrepancy between both solutions.

• Journal of Korea Water Resources Association
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• v.38 no.4 s.153
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• pp.301-311
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• 2005

The purpose of this study is to assess the quantitative effect of stream discharge due to land use changes. The upstream watershed of Pyeongtaek gauging station of Anseong-cheon ($592.6\;km^2$) was adopted. To accomplish the purpose, firstly, trace land use changes for the selected watershed which have some changes of land use by using Landsat images of 1986 and 1999 of the watershed and secondly, analyse the quantitative effect of stream discharge due to land use changes by applying GIS- based distributed hydrologic model KIMSTORM. The model was calibrated and verified at 2 locations (Pyeongtaek and Gongdo) by comparing observed with simulated discharge results for 7 storm events from 1998 to 2003. Model output was designed to provide information of land use impact on runoff components in the watershed and the sensitivity of impact level of each land use category on storm runoff. Land use impact was evaluated with the land use data sets for 1986 and 1999 for the same rainfall condition (160.5 mm). Area decrease of 4.8 percent of forest and 4.0 percent of paddy field during 13 years (1986 - 1999) within the watershed caused a 30.3 percent increase of peak runoff and a 9.3 percent increase of runoff volume.

• The Journal of Engineering Geology
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• v.27 no.4
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• pp.439-449
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• 2017

The cause of yield reduction in a collector well, which is located in Anseong-cheon watershed in Kyunggi province, is studied by using aquifer sediments' composition and hydraulic conductivity near four horizontal wells, no. 1, no. 4, no. 6, and no. 7 wells. During test-pumping periods, groundwater yield is reduced with a trend of $12.4m^3/d/d$ at no. 1, $2.3m^3/d/d$ at no. 4, $24.4m^3/d/d$ at no. 6, and $187.3m^3/d/d$ at no. 7 and no. 7 well shows the biggest reduction. The sediments along no. 7 horizontal well have low hydraulic conductivity and high coefficient of uniformity ($C_u$), and a deviation of $C_u$ along the well is also large. This characteristics can bring the fine particles' movement and make the openings filled. Additionally, high iron ($Fe^{2+}$) content results in a precipitation of iron hydroxides during pumping or injection and they can produce a clogging in sediments. In the future study, the analysis of physical and hydrochemical changes through a long-term pumping procedure will give a more exact interpretation for the cause of yield reduction.

• Journal of Wetlands Research
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• v.18 no.2
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• pp.121-131
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• 2016

The determination of feasible design flood is the most important to control flood damage in river management. Concentration time and storage constant in the Clark unit hydrograph method mainly affects magnitude of peak flood and shape of hydrograph. Model parameters should be calibrated using observed discharge but due to deficiency of observed data the parameters have been adopted by empirical formula. This study is to suggest concentration time and storage constant based on the observed rainfall-runoff data at GongDo stage station in the Ansung river basin. To do this, five criteria have been suggested to compute root mean square error(RMSE) and residual of oserved value and computed one. Once concentration time and storage constant have been determined from three rainfall-runoff event selected at the station, the five criteria based on observed hydrograph and computed hydrograph by the Clark model have been computed to determine the value of concentration time and storage constant. A criteria has been proposed to determine concentration time and storage constant based on the results of the observed hydrograph and the Clark model. It has also been shown that an exponent value of concentration time-cumulative area curve should be determined based on the shape of watershed.

• Journal of Korea Water Resources Association
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• v.51 no.9
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• pp.803-812
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• 2018

The purpose of this study is to develop Particle Swarm Optimization (PSO) automatic calibration algorithm with multi-objective functions by Python, and to evaluate the applicability by applying the algorithm to the Soil and Water Assessment Tool (SWAT) watershed modeling. The study area is the upstream watershed of Gongdo observation station of Anseongcheon watershed ($364.8km^2$) and the daily observed streamflow data from 2000 to 2015 were used. The PSO automatic algorithm calibrated SWAT streamflow by coefficient of determination ($R^2$), root mean square error (RMSE), Nash-Sutcliffe efficiency ($NSE_Q$), and especially including $NSE_{INQ}$ (Inverse Q) for lateral, base flow calibration. The results between automatic and manual calibration showed $R^2$ of 0.64 and 0.55, RMSE of 0.59 and 0.58, $NSE_Q$ of 0.78 and 0.75, and $NSE_{INQ}$ of 0.45 and 0.09, respectively. The PSO automatic calibration algorithm showed an improvement especially the streamflow recession phase and remedied the limitation of manual calibration by including new parameter (RCHRG_DP) and considering parameters range.

• Journal of Wetlands Research
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• v.12 no.1
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• pp.51-61
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• 2010

Changes in climate have largely increased concentrated heavy rainfall, which in turn is causing enormous damages to humans and properties. Therefore, it is important to understand the spatial-temporal features of rainfall. In this study, RADAR rainfall was used to calculate gridded areal rainfall which reflects the spatial-temporal variability. In addition, Kalman-filter method, a stochastical technique, was used to combine ground rainfall network with RADAR rainfall network to calculate areal rainfall. Thiessen polygon method, Inverse distance weighting method, and Kriging method were used for calculating areal rainfall, and the calculated data was compared with adjusted areal RADAR rainfall measured using the Kalman-filter method. The result showed that RADAR rainfall adjusted with Kalman-filter method well-reproduced the distribution of raw RADAR rainfall which has a similar spatial distribution as the actual rainfall distribution. The adjusted RADAR rainfall also showed a similar rainfall volume as the volume shown in rain gauge data. Anseong-Cheon basin was used as a study area and the RADAR rainfall adjusted with Kalman-filter method was applied in $Vflo^{TM}$ model, a physical-based distributed model, and ModClark model, a semi-distributed model. As a result, $Vflo^{TM}$ model simulated peak time and peak value similar to that of observed hydrograph. ModClark model showed good results for total runoff volume. However, for verifying the parameter, $Vflo^{TM}$ model showed better reproduction of observed hydrograph than ModClark model. These results confirmed that flood runoff simulation is applicable in domestic settings(in South Korea) if highly accurate areal rainfall is calculated by combining gauge rainfall and RADAR rainfall data and the simulation is performed in link to the distributed hydrological model.

• The Journal of Engineering Geology
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• v.29 no.3
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• pp.279-288
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• 2019

The groundwater drawdown at each monitoring well near a radial collector well along Anseong Stream, Korea, was measured and compared with the calculated drawdown using the mirror well concept. The drawdown calculation is performed by treating the collector well as a large vertical well in a homogeneous isotropic aquifer. The measured drawdown at each monitoring well is slightly different from the calculated value due to anisotropy in the hydraulic conductivity and aquifer thickness. The difference between the measured and calculated values at Well OW-7 is large, reaching approximately 48 cm, because a horizontal well is not installed along this direction. Sensitivity analysis of the hydraulic conductivity and aquifer thickness indicates that the hydraulic conductivity is more sensitive to groundwater level changes. Groundwater level changes become a concern when a radial collector well with a large pumping rate capacity is installed, which highlights the need to thoroughly investigate the aquifer characteristics in the surrounding area.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2B
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• pp.159-167
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• 2010

The purpose of this study is to get the adjusted radar rainfalls by ANN(Artificial Neural Network) method. In the case of radar rainfall, it has an advantage of spatial distribution characteristics of rainfall while point rainfall has an advantage at the point. Therefore we adjusted the radar rainfall by ANN method considering the advantages of two rainfalls of radar and point. This study constructed two ANN models of Model I and Model II for radar rainfall adjustment. We collected the three rainfall events and adjusted the radar rainfall for Anseong-cheon basin. The two events were inputted into the Modeland Model to derive the optimum parameters and the rest event was used for validation. The adjusted radar rainfalls by ANN method and the raw radar rainfall were used as the input data of ModClark model which is a semi-distributed model to simulate the runoff. As the results of the simulation, the runoff by raw radar rainfall were overestimated but the peak time and peak runoff from the adjusted rainfall by ANN were well fitted to the observed hydrograph.