• Korean Journal of Soil Science and Fertilizer
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• v.42 no.1
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• pp.37-45
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• 2009

Susceptibility assessment of groundwater contamination is a useful tool for many aspects of regional and local groundwater resources planning and management. It can be used to direct regulatory, monitoring, educational, and policy-making efforts to highly vulnerable areas. In this study, a semi process-based was proposed to evaluate relative susceptibilities to groundwater contamination by nitrate on a regional scale. Numerical simulation based on data from each soil series was done to model water flow within soil profiles that were related to groundwater contamination by nitrate. Relative vulnerability indices for each soil series were produced by manipulation of amount of leaching flux, amount of average water storage in a soil profile, and amount of average water storage change. These indices were designed to convey the trend of leaching flux and to maximize spatial resolution. The resulting vulnerability distribution map was used to locate highly vulnerable sites easily with an appropriate grouping the indices, and was then compared with those from groundwater nitrate concentrations monitored. An excellent agreement was obtained across nitrate concentrations from the highly vulnerable regions and those from the low to stable regions.

• Journal of Korean Society on Water Environment
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• v.27 no.1
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• pp.61-72
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• 2011

In order to assess hydrologic and nonpoint source pollutant behaviors in a watershed with Soil and Water Assessment Tool (SWAT) model, the accuracy evaluation of SWAT model should be conducted prior to the application of it to a watershed. When calibrating and validating hydrological components of SWAT model, the Nash-Sutcliffe efficiency coefficient (EI) has been widely used. However, the EI value has been known as it is affected sensitively by big numbers among the range of numbers. In this study, a Web-based flow clustering EI estimation system using K-means clustering algorithm was developed and used for SWAT hydrology evaluation. Even though the EI of total streamflow was high, the EI values of hydrologic components (i.e., direct runoff and baseflow) were not high. Also when the EI values of flow group I and II (i.e., low and high value group) clustered from direct runoff and baseflow were computed, respectively, the EI values of them were much lower with negative EI values for some flow group comparison. The SWAT auto-calibration tool estimated values also showed negative EI values for most flow group I and II of direct runoff and baseflow although EI value of total streamflow was high. The result obtained in this study indicates that the SWAT hydrology component should be calibrated until all four positive EI values for each flow group of direct runoff and baseflow are obtained for better accuracy both in direct runoff and baseflow.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.412-412
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• 2022

지속가능한 물관리를 위해서는 강우, 수문학적 반응의 동적 순환과 생공업 및 농업 기반시설과 같은 관리 조치에 사용되는 물을 포함한 가용수(Available Water)의 시공간적 영향을 파악할 수 있어야 한다. 가용수의 구성요소를 파악하기 위해 블루워터와 그린워터의 개념이 제안되었다. 블루워터는 강수로 인해 형성된 지표수, 지하수 및 호수·저수지의 저류량을 포함하며, 그린워터는 강수로부터 불포화 토양층에 저장된 토양수분과 수역, 초목에서 대기 중으로 방출되는 증발산을 말한다. 블루워터와 그린워터를 산정하기 위해서는 동적 수자원과 인적 요소에 의존되는 수자원을 정확하게 구별해야 하며 물 가용성 평가를 용이하게 하는 통합 기반 개념의 수문학적 모델이 필요하다. 따라서 본 연구에서는 5대강을 대상으로 각 유역의 가용수량의 변화를 파악하기 위해 각 유역별 블루워터와 그린워터를 평가하고자 하였다. 5대강 유역의 장기간 변화와 광범위한 분석을 위해 SWAT(Soil and Water Assessment Tool) 모형의 수문모델링 결과를 활용하였다. SWAT 모형의 신뢰성 있는 수문 검보정을 위해 전체 기간(2005~2020) 중 모형의 보정(2005~2009) 및 검증(2010~2017)기간을 설정하였으며, 각 유역의 다목적댐과 다기능 보의 실측방류량을 이용하여 댐 운영모의를 고려하였다. 검보정된 SWAT 결과를 활용하여 블루워터와 그린워터를 분류하였으며 가용수량을 평가하는 방법을 제시하였다.

• Journal of Environmental Science International
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• v.23 no.4
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• pp.605-613
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• 2014

In this work, the delay time for groundwater recharge was estimated by comparing simulated recharges by means of SWAT(Soil and Water Assessment Tool) model and WTF(Water Table Fluctuation) method. The delay time for groundwater recharge means that the time when the water from rainfall travelled through vadose zone just after getting out of soil zone bottom. As measuring this delay time is almost impossible, we used to compare the estimated values from modeling(SWAT) and analytic method(WTF). The test site is Hancheon watershed which has 8 groundwater measurement stations. The results show that the altitude has a linear relationship with the estimated delay time values. To validate these results, we conducted corelation analysis between transformed groundwater levels and observed ones. The results showed that computed groundwater levels have good corelation($R^2$=0.97, 0.87, respectively). The estimated delay time would be used for the groundwater behaviour characteristics in vadose zone. As recharge rates vary according to the height, the delay time is thought to be an import variable for the proper groundwater recharge estimation.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.7
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• pp.544-551
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• 2011

The objective of this study was to analyze VIRULO model, a probabilistic quantitative model, which had been developed by US Environmental Protection Agency. The model could assess the viral attenuation capacity of soil as hydrogeologic barrier using Monte Carlo simulation. The governing equations used in the model were composed of unsaturated flow equations and viral transport equations. Among the model parameters, those related to water flow for 11 soil types were from UNDODA data, and those related to 5 virus species were from the literatures. The model compared the attenuation factor with threshold of attenuation to determine the probability of failure and presented the exceedances and Monte Carlo runs as output. The analysis indicated that among 11 USDA soil types, the viral attenuation capacity of loamy sand and sand were far lower than those of clay and silt soils. Also, there were differences in the attenuation in soil among 5 viruses with poliovirus showing the highest attenuation. The viral attenuation capacity of soil decreased sharply with increasing soil water content and increased nonlinearly with increasing soil barrier length. This study indicates that VIRULO model could be considered as a useful screening tool for viral risk assessment in subsurface environment.

• Journal of Korean Society on Water Environment
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• v.26 no.3
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• pp.387-398
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• 2010

SWAT model would be applied to evaluate the pollutant removal capacity with various best management practices (BMPs) in Kyongan stream watershed which plays an important role in water quality conservation and improvement of Paldang reservoir. The methods for the representation of various BMPs scenarios with SWAT is developed and evaluated. Riparian buffer strip, agricultural conservation practices to reduce fertilizer, sediment, and nutrients occurring from farm field (Grassed swale, Contour farming/Parallel terrace, Field border, Farm retention pond, Grade stabilization structure), and washland such as wetland and pond to extend detention and improve water quality are represented in SWAT. And to represent the expansion of existing Waste Water Treatment Plants (WWTPs) in Soil and Water Assessment Tool (SWAT), reduction effect for point source pollutants was simulated. As the result of simulation, the removal rates of SS, TN, TP from scenarios of Kyongan stream watershed are the average annual SS yield by 5.2% to 69.2%, the average annual TN yield by 0.5% to 26.3%, and the average annual TP yield by 1.3% to 32.5%, respectively. This study has demonstrated that the SWAT is a very reliable and useful water quality and quantity assessment tool, and the BMPs representation in SWAT for watershed management is able to effectively simulate in Kyongan Stream watershed.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.287-287
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• 2023

Surface water-groundwater interaction (SWGI) is an important hydrological process that influences both the quantity and quality of water resources. However, regional scale SWGI model calibration and uncertainty analysis have been a challenge because integrated models inherently carry a vast number of parameters, modeling assumptions, and inputs, potentially leaving little time and budget to explore questions related to model performance and forecasting. In this study, we have proposed the application of iterative ensemble smoother (IES) for uncertainty analysis and calibration of the widely used integrated surface-subsurface model, SWAT-MODFLOW. SWAT-MODFLOW integrates Soil and Water Assessment Tool (SWAT) and a three-dimensional finite difference model (MODFLOW). The model was calibrated using a parameter estimation tool (PEST). The major advantage of the employed IES is that the number of model runs required for the calibration of an ensemble is independent of the number of adjustable parameters. The pilot point approach was followed to calibrate the aquifer parameters, namely hydraulic conductivity, specific storage, and specific yield. The parameter estimation process for the SWAT model focused primarily on surface-related parameters. The uncertainties both in the streamflow and groundwater level were assessed. The work presented provides valuable insights for future endeavors in coupled surface-subsurface modeling, data collection, model development, and informed decision-making.

• Journal of Korean Society on Water Environment
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• v.36 no.6
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• pp.592-610
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• 2020

In South Korea, the concept of water environment was expanded to include aquatic ecosystems with the Integrated Water Management implementation. Watershed-scale modeling is typically performed for hydrologic component analysis, however, there is a need to expand to include ecosystem variability such that the modeling corresponds to the social and political issues around the water environment. For this to be viable, the modeling must account for several distinct features in South Korean watersheds. The modeling must provide reasonable estimations for peak flow rate and apply to paddy areas as they represent 11% of land use area and greatly influence groundwater levels during irrigation. These facts indicate that the modeling time intervals should be sub-daily and the hydrologic model must have sufficient power to process surface flow, subsurface flow, and baseflow. Thus, the features required for watershed-scale modeling are suggested in this study by way of review of frequently used hydrologic models including: Agricultural Policy/Environmental eXtender(APEX), Catchment hydrologic cycle analysis tool(CAT), Hydrological Simulation Program-FORTRAN(HSPF), Spatio-Temporal River-basin Ecohydrology Analysis Model(STREAM), and Soil and Water Assessment Tool(SWAT).

• Journal of Korean Society on Water Environment
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• v.26 no.4
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• pp.637-647
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• 2010

The Universal Soil Loss Equation (USLE)-based modeling systems have been widely used to simulate soil erosion studies. However the GIS-based USLE modeling systems have limitation in gully erosion evaluation which is one of the most important factor in soil erosion estimation. In this study, the integrated soil erosion evaluation system using with Sediment Assessment Tool for Effective Erosion Control (SATEEC) system, nLS and Unit Stream Power-based Erosion/Deposition (USPED) model was developed to simulate gully erosion. Gully head location using nLS model, USPED for gully erosion, and the SATEEC estimated sheet and rill erosion were evaluated and combined together with the integrated soil erosion evaluation system. This system was applied to the Haean-myeon watershed, annual average sediment-yield considering sheet, rill and gully erosion was simulated as 101,933 ton/year at the study watershed. if the integrated soil erosion evaluation system is calibrated and validated with the measured data, this system could be efficiently used in developing site-specific soil erosion best management system to reduce soil erosion and muddy water inflow into the receiving waterbody.

• Journal of Korean Society on Water Environment
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• v.23 no.4
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• pp.467-473
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• 2007

Although the dominant land use at the Imha-dam watershed is forest areas, soil erosion has been increasing because of intensive agricultural activities performed at the fields located along the stream for easy-access to water supply and relatively favorable topography. In addition, steep topography at the Imha-dam watershed is also contributing increased soil erosion and sediment loads. At the Imha-dam watershed, outflow has increased sharply by the typhoons Rusa and Maemi in 2002, 2003 respectively. In this study, the Soil and Water Assessment Tool (SWAT) model was evaluated for simulation of flow and sediment behaviors with long-term temporal and spatial conditions. The precipitation data from eight precipitation observatories, located at Ilwol, Subi and etc., were used. There was no significant difference in monthly rainfall for 8 locations. However, there was slight differences in rainfall amounts and patterns in 2003 and 2004. The topographical map at 1:5000 scale from the National Geographic Information Institute was used to define watershed boundaries, the detailed soil map at 1:25,000 scale from the National Institute of Highland Agriculture and the land cover data from the Korea Institute of Water and Environment were used to simulate the hydrologic response and soil erosion and sediment behaviors. To evaluate hydrologic component of the SWAT model, calibration was performed for the period from Jan. 2002 to Dec. 2003, and validation for Jan. 2004 to Apr. 2005. The $R^2$ value and El value were 0.93 and 0.90 respectively for calibration period, and the $R^2$ value and El value for validation were 0.73 and 0.68 respectively. The $R^2$ value and El value of sediment yield data with the calibrated parameters was 0.89 and 0.84 respectively. The comparisons with the measured data showed that the SWAT model is applicable to simulate hydrology and sediment behaviors at Imha dam watershed. With proper representation of the Best Management Practices (BM Ps) in the SWAT model, the SWAT can be used for pre-evaluation of the cost-effective and sustainable soil erosion BMPs to solve sediment issues at the Imha-dam watershed. In Korea, the Universal Soil Loss Equation (USLE) has been used to estimate the soil loss for over 30 years. However, there are limitations in the field scale mdel, USLE when applied for watershed. Also, the soil loss changes temporarily and spatially, for example, the Imha-dam watershed. Thus, the SW AT model, capable of simulating hydrologic and soil erosion/sediment behaviors temporarily and spatially at watershed scale, should be used to solve the muddy water issues at the Imha-dam watershed to establish more effective muddy water reduction countermeasure.