• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.1
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• pp.45-59
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• 2019

Since the baseflow, which constitutes most of the river flow in the dry season, plays an important role in the solution of river runoff and drought, it is important to accurately evaluate the characteristics of the baseflow for river management. In this study, land use change was evaluated through time series data of land use, and then baseflow characteristics were analyzed by considering climate change and land use change using climate change scenarios. The results showed that the contribution of baseflow of scenarios considering both climate change and land use change was lower than that of scenarios considering only climate change for yearly and seasonal analysis. This implies that land use changes as well as climate changes affect base runoff. Thus, if we study the watershed in which the land use is occurring rapidly in the future, it is considered that the study should be carried out considering both land use change and climate change. The results of this study can be used as basic data for studying the baseflow characteristics in the Gapcheon watershed considering various land use changes and climate change in the future.

• Journal of Korean Society on Water Environment
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• v.37 no.6
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• pp.520-530
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• 2021

Multivariate statistical analysis and an environmental hydrological model were applied for investigating the causes of water pollution and providing best management practices for water quality improvement in urban and agricultural watersheds. Principal component analysis (PCA) and cluster analysis (CA) for water quality time series data show that chemical oxygen demand (COD), total organic carbon (TOC), suspended solids (SS) and total phosphorus (T-P) are classified as non-point source pollutants that are highly correlated with river discharge. Total nitrogen (T-N), which has no correlation with river discharge and inverse relationship with water temperature, behaves like a point source with slow and consistent release. Biochemical oxygen demand (BOD) shows intermediate characteristics between point and non-point source pollutants. The results of the PCA and CA for the spatial water quality data indicate that the cluster 1 of the watersheds was characterized as upstream watersheds with good water quality and high proportion of forest. The cluster 3 shows however indicates the most polluted watersheds with substantial discharge of BOD and nutrients from urban sewage, agricultural and industrial activities. The cluster 2 shows intermediate characteristics between the clusters 1 and 3. The results of hydrological simulation program-Fortran (HSPF) model simulation indicated that the seasonal patterns of BOD, T-N and T-P are affected substantially by agricultural and livestock farming activities, untreated wastewater, and environmental flow. The spatial analysis on the model results indicates that the highly-populated watersheds are the prior contributors to the water quality degradation of the river.

• Journal of Environmental Impact Assessment
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• v.13 no.6
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• pp.285-294
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• 2004

The purpose of this study is to understand the quantitative change of water resources using RMS(Remote Monitoring System) which takes real time data with high reliability. Also, the characteristic of stormwater runoff was understood by the application of the above system for three streams (Jiam, Yulmun, and Gongji stream) in Chuncheon City. The detailed results of these studies are as follows; RMS(Remote Monitoring System) was constructed by the combination of the automatic water-level meter, which measures water-level of streams at all times, and the wireless communication system sending real-time data from the meter. This system is used to evaluate the stormwater runoff in watersheds and the quantitative changes of streams. It is possible to overcome the limit of field investigations needed, which takes a lot of manpower and time, and it is very efficient to provide the reliable flowrate data. Also, it can be applied to the disaster prevention system for flood because the change of flowrate in stream is monitored at real-time. For 3 streams with different watershed characteristics, correlation equations induced from the relation analysis results. In terms of the relation between water-level and flowrate, flowrate was increased rapidly as the water-level rises in case of small watershed and steep slope. The application results of the proposed system for 3 streams (Jiam, Yulmun, Gongji) in Chuncheon city are as follows; The remote monitoring system was very useful for acquisition of the flow rate in stream that are basic data to understand pollutants runoff in watershed. In case of no-rainy day, the runoff ratio for pollutant loading rate was the highest level in Yulmun stream(BOD:2.3%, TN:20.2%, TP:1.2%). So, it shows the management of pollution source is needed such as rehabilitation of sewer line. Runoff ratio of total phosphorus by rainfall in Gongji watershed was increased about 19 times than no-rainy day, which is estimated as the influence of sewer overflow.

• Water for future
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• v.28 no.4
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• pp.155-169
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• 1995

Three types of methods are used to determine the lag time which is an important parameter in estimating the geomorphological instantaneous unit hydrograph (GIUH) and their results are anlyzed hydrologically in this study. The first method uses only the average velocity and second one uses the combination of the stream length and the average velocity. The third method employs the relationship between watershed area and lag time obtained from the empirical coefficients of Boyd and Singh. To verify the applicabilities of such methods to the actual river basin, the obtained lag times were tested by using the observed data. The results showed that the first method was applicable to small watershed area but not to larger area. The several other hydrologic characteristics beside the watershed area should be considered for the third method because the accuracy of the lag time was not good. Finally, the second method gave the most similar simulation results and the best agreements to the observed runoff data than any other method.

• Journal of Soil and Groundwater Environment
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• v.22 no.6
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• pp.94-103
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• 2017

Surface soil is one of the most important resources that have many functions for human needs such as conservation of water resource, purification of contaminated materials, and productivity of food or energy. However, the surface soil is a limited resource that cannot be recovered readily for a long time once it is lost by erosion. In Korea, the Ministry of Environment enacted the notification on the investigation of surface soil erosion and corresponding countermeasures. As the results, database of soil quality assess criteria (biomass, groundwater recharge, habitat, carbon storage, buffer, and soil loss) was established, and the web-based system that can evaluate surface soil conditions was developed. However, non-experts have difficulties in using the system because the system requires in-depth knowledge about soil qualities. In this study, the Web Geographic Information System (GIS) watershed-based surface soil information system was developed to improve usability of the system and accessibility of soil quaility database. The system provides the current condition of surface soil characteristics and GIS-based soil data at selected locations. The users are able to download soil quality data in different districts, watersheds, and special regions allocated by TauDEM module. The system developed in this study would valuable surface soil information for studies of soil quality and its environmental effects, and thereby contributing to establishing more appropriate and robust soil conservation laws.

• Journal of The Geomorphological Association of Korea
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• v.28 no.1
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• pp.13-33
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• 2021

Successful sediment management at the watershed scale requires an understanding of the erosion, transport and sedimentation processes at the specific site scale. However, studies on the sediment runoff characteristics in a small uppermost watershed, which serves as a sediment supply function, are very rare. Therefore, this study attempted to investigate the fluctuations in major sediment supply areas and sediment runoff in the uppermost mountain small watershed, and for this purpose, ArcSWAT (Soil and Water Assessment Tools with GIS interface) was applied to the Woldong reservoir catchment located in Gosam-myeon, Anseong-si, Gyeonggi-do. The model results were manually calibrated using the monitoring data of the Woldong reservoir sedimentation rate from 2005 to 2007. It was estimated that annual average of 34.4 tons/year of sediment was discharged from the Woldong reservoir basin. This estimate almost coincided with the monitoring data of the Woldong reservoir during the low flow period but tended to be somewhat underestimated during the high flow period. Although the SWAT model does not fully reflect the erosion process of gully and in-channel, this underestimation is probably due to the spatial connectivity of sediment transport and the storage and reactivation of the sediment being transported. Most of the forested hillslopes with a well-developed organic horizon were evaluated as having a low risk of erosion, while the places with the highest risk of erosion were predicted to be distributed in the logged area with some weeds or shrubs (classified as pasture) with relatively steeper slopes, and in the bare land. The results of this study are expected to be useful in developing strategies for sediment control and reservoir management.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.5
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• pp.367-377
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• 2014

Paldang lake which is the most important water resource in Korea is classified as a stream type reservoir and water quality of Paldang lake can be significantly influenced by external pollutant source. So this study was aimed to determine focused control BOD and TP sources of each unit watershed upper Paldang lake through analysis of pollutant source distribution and pollutant runoff characteristics. Generated load, discharge load, delivery load and each load density of 11 unit watersheds upper Paldang lake were calculated using data of water quality and flow rate from pollutant sources and 74 small streams. As a result of generated load, discharge load and delivery load of BOD and TP from pollutant sources, the most BOD generated load was taken by livestock with 66% of total BOD discharge load and domestic had the most BOD discharge load, 42.7%. The ratio of delivery load of livestock and domestic was 36.4% and 34.3%, respectively. Livestock occupied high ratio of TP generated load, discharge load and delivery load with 82.5%, 44.4% and 46.7%, respectively. Gyeongan watershed which had high population density showed the highest BOD delivery load density of $14.6kg/km^2/d$ and the highest TP delivery load density with $1.23kg/km^2/d$ was analyzed in Cheongmi watershed including the biggest number of livestock. From these results, management of domestic sewer and livestock excrement was determined as a focused control pollutant source. And intensive management about domestic sewer in Gyeongan stream and livestock excrement in Cheongmi stream is required for water quality improvement of Paldang lake.

• Journal of Korea Water Resources Association
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• v.53 no.12
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• pp.1143-1157
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• 2020

In this study, a criteria for the SWAT model calibration method in SWAT-CUP which considers multi-site and multi-variable observations was presented. For its application, the SWAT model was simulated using long-term observed flow, soil moisture, and evapotranspiration data in Yongdam study watershed, investigating the hydrological runoff characteristics and water balance in the water cycle analysis. The model was calibrated with different parameter values for each sub-watershed in order to reflect the characteristics of multiple observations through one-by-one calibration, appropriate settings of model simulation run/iteration number (1,000 simulation runs in the first iteration and then 500 simulation runs for the following iterations), and executions of partial and all run in SWAT-CUP. The flow simulation results of watershed outlet point, ENS 0.85, R2 0.87, and PBIAS -7.6%, were compared with the analysis results (ENS 0.52, R2 0.54, and PBIAS -22.4%) applied in the other batch (i.e., non one-by-one) calibration approach and showed better performances of proposed method. From the simulation results of a total of 15 years, it was found that the total runoff (streamflow) and evapotranspiration rates from precipitation are 53 and 39%, and the ratio of surface runoff and baseflow (i.e., sum of lateral and return flow, and recharge deep aquifer) are 35 and 65%, respectively, in Yongdam watershed. In addition, the analytical amount of available water (i.e., water yield), including the total annual streamflow (daily average 21.8 m3/sec) is 6.96 billion m3 per year (about 540 to 900 mm for sub-watersheds).

• Journal of Korea Water Resources Association
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• v.38 no.5 s.154
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• pp.345-354
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• 2005

Time Domain Reflectometry (TDR) with multiplex system has been installed to configure the spatial and temporal characteristics of soil moisture at the Bumreunsa hillslope of Sulmachun Watershed. An intensive surveying was performed to build a refined digital elevation model (DEM) and flow determination algorithms with inverse surveying have been applied to establish an efficient soil moisture monitoring system. Soil moisture data were collected through intensive monitoring during 380 hrs in November of 2003. Soil moisture data shows corresponding variation characteristics of soil moisture on the upper, middle and lower parts of the hillslope which were classified from terrain analysis. Measured soil moisture data have been discussed on the context of physical process of hydrological modeling.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.6
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• pp.119-124
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• 2009

In this study, the characteristics of estimating methodology for RUSLE factors such as soil erodibility factor, slope length-steepness factor, and cover management factor were reviewed and then the relative error according to each methodology was analyzed. RUSLE was applied to experimental watershed for 42 storm events and their results were compared with measured sediment yield to examine the applicability of RUSLE. As a result, this paper found that it should be necessary to consider vegetation effect for forest application of RUSLE as cover management was the most sensitive factor. Also, soil erodbility factor was calculated from data of soil series by National Academy of Agricultural Science caused sediment yield to be overestimated because there were big differences between the soil series and on-site soil texture. The 22.7% of maximum relative error was shown according to selecting the rain energy equation. In addition, it will be necessary to verify the RUSLE factors with more data in order to improve their accuracy.