• Journal of Korean Society on Water Environment
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• v.23 no.6
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• pp.889-896
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• 2007

From the direct outflow of Chungju Dam to the junction of water body and watershed in Paldang lake is the scope of this research. This study performed to investigate the main cause of water quality deterioration and the influenced region in the middle field range of the Namhan river Basin with the onsite measurement of water quality and flow rate simultaneously during spring dry season. The purpose of this study is to find out the time-spatial variation characteristics of water quality and flow rate. Following the flow direction $BOD_5$ and $COD_{Mn}$ concentration increased to the highest value of 3.7 mg/L, 5.9 mg/L at Wolgesa respectively. Chl.a concentration increased to $50mg/m^3$ or so at Kangsang, after that it decreased to $37mg/m^3$ at the junction of Paldang lake. Organic matter concentration variation trend showed similar than that of Chl.a. Also $BOD_5$ concentration tendency was similar to Chl.a in every measuring sites except Paldang lake mixing zone. The major factors of water quality deterioration in Namhan river and Paldang lake during dry season were algal bloom and followed internal production. High phosphorus load from Dalcheon and Seom river caused dry season algal bloom and internal production in transitional zone which was stagnant area in downstream of Namhan river.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.2
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• pp.25-39
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• 2019

The water pollution Accident in the South Han River is increasing due to increase of pollutants inflow from small streams from rural areas and reduced flow rate. This study predicted the change of water quality in the main stream of the South Han River due to climate change through the linkage of watershed and water quality models. Also, This study analyzed the effect of water quality improvement on Seomgang and the South Han River by securing the flow during the dry season. According to the scenarios for securing the river flow during drought season, the river flow in the Seomgang is increased up to 2.19 times, and the water quality during the drought season was improved up to $BOD_5$ 20.5%, T-N 40.8%, T-P 53.4%. Also, the water quality of the main stream of the South Han River improved to 5.22% of $BOD_5$, 5.42% of T-N and 7.69% of T-P as the river flow was secured from the Seomgang. The result of this study confirms that securing the baseflow in the Seomgang according to the scenarios for securing the river flow during the dry season has a positive effect on the improvement of the water quality of the rivers in the main river of the Seomgang and South Han River. The results of this study will contribute to the establishment of reasonable management to improve the water quality of the main stream of the Seomgang and South Han River.

• Ecology and Resilient Infrastructure
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• v.9 no.1
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• pp.1-14
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• 2022

The total maximum daily load (TMDL) implemented in Korea mainly manages the mainstream considering a single common pollutant and river discharge, and the river system is divided into unit watersheds. Changes in the water quality of managed rivers owing to the water quality management in tributaries and unit watersheds are not considered when implementing the TMDL. In addition, it is difficult to consider the difference in the load of pollutants generated in the tributary depending on the conditions of the water quality change in each unit watershed, even if the target water quality was maintained in the managed water system. Therefore, it is necessary to introduce the total maximum load management at tributaries to manage the pollution load of tributaries with a high degree of pollution. In this study, the HSPF model, a watershed runoff model, was applied to the target areas consisting of 53 sub-watersheds to analyze the effect of water quality changes the in tributaries on the mainstream. Sub-watersheds were selected from the three major areas of the Paldang water system, including the drainage basins of the downstream of the South Han-River, Gyeongan stream, and North Han-River. As a result, BOD ranged from 0.17 mg/L to 4.30 mg/L, and was generally high in tributaries and decreased in the downstream watershed. TP ranged from 0.02 mg/L - 0.22 mg/L, and the watersheds that had a large impact on urbanization and livestock industry were high, and the North Han-River basin was generally low. In addition, a pollution source reduction scenario was selected to analyze the change in water quality by the amount of pollution load discharged at each unit watershed. The reduction rate of BOD and TP according to the scenario changes was simulated higher in the watershed of the downstream of the North Han-River and downstream and midstream of the Gyeongan stream. It was found that the benefits of water quality reduction from each sub-watershed efforts to improve water quality are greatest in the middle and downstream of each main stream, and it is judged that it can be served as basic data for the management of total tributaries.

• Journal of Environmental Impact Assessment
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• v.23 no.3
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• pp.187-196
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• 2014

The objective of this study is to evaluate and analyze Osu stream watershed water environment system. The data were collected from January 2009 to December 2011 including water temperature, pH, DO, EC, BOD, COD, TOC, SS, T-N, T-P and discharge. The data were used for principle component analysis and factor analysis. The results are as followes. The primary factors obtained from both the principal component analysis and the factor analysis were BOD, COD, TOC, SS and T-P. Once principal component analysis and factor analysis have been performed with the collected data and then the results will be applied to both simple regression model and multiple regression model. The regression model was developed into case 1 using concentrations of water quality parameters and case 2 using delivery loads. The value of the coefficient of determination on case 1 fell between 0.629 and 0.866; this was lower than case 2 value which fell between 0.946 and 0.998. Therefore, case 2 model would be a reliable choice.The coefficient of determination between the estimated figure using data which was developed to the regression model in 2012 and the actual measurement value was over 0.6, overall. It can be safely deduced that the correlation value between the two findings was high. The same model can be applied to get TOC concentrations in future.

• Journal of Korean Society on Water Environment
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• v.27 no.5
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• pp.587-596
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• 2011

The interest in hydrological modeling has increased significantly recently due to the necessity of watershed management, specifically in regards to lumped models, which are being prosperously utilized because of their relatively uncomplicated algorithms which require less simulation time. However, lumped models require empirical coefficients for hydrological analyses, which do not take into consideration the heterogeneity of site-specific characteristics. To overcome such obstacles, a distributed model was offered as an alternative and the number of researches related to watershed management and distributed models has been steadily increasing in the recent years. Thus, in this study, the feasibility of a grid-based rainfall-runoff model was reviewed using the flood runoff process in the Han River basin, including the ChungjuDam, HoengseongDam and SoyangDam watersheds. Hydrological parameters based on GIS/RS were extracted from basic GIS data such as DEM, land cover, soil map and rainfall depth. The accuracy of the runoff analysis for the model application was evaluated using EFF, NRMSE and QER. The calculation results showed that there was a good agreement with the observed data. Besides the ungauged spatial characteristics in the SoyangDam watershed, EFF showed a good result of 0.859.

• Journal of Korean Society on Water Environment
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• v.27 no.3
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• pp.314-321
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• 2011

The potential effects of increased water temperature on fish assemblages and their habitats were studied in the streams of the Han River watershed when the water temperature was supposed to increase by $1^{\circ}C$, $2^{\circ}C$, and $3^{\circ}C$ in each sampling site. The percent changes in suitable habitats for each species and in species number within a site were determined, based on the estimated maximum thermal tolerances of 51 fish species whose habitats were classified into four reaches: upstream, up-/midstream, midstream, and mid-/downstream. The maximum thermal tolerance ranged between $25.0^{\circ}C$ and $31.0^{\circ}C$ and significantly increased as the habitat reaches move from upstream to mid-/downstream. With the increases in water temperature, the average suitable habitats for all 51 species were decreased by 31% ($+1^{\circ}C$), 46% ($+2^{\circ}C$), and 60% ($+3^{\circ}C$). The increased water temperature, however, did not induce significant differences in the changes in suitable habitats among four reaches within each level of temperature increase. The relative frequencies of the sampling sites classified into six levels according to the percent change in the number of species in each site were significantly different among three levels of water temperature increase, with relatively greater changes in the sites where 0~20% and 61~100% of species were affected.

• Proceedings of the Korean Society of Environment and Ecology Conference
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• 2008.10a
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• pp.31-32
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• 2008

• Proceedings of the Korean Society of Environment and Ecology Conference
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• 2010.04a
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• pp.81-83
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• 2010

• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.6
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• pp.23-29
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• 2011

This study was conducted to identify the effect of lapse rate application according to elevation on the estimation of large scale watershed rainfall. For the Han river basin (26,018 $km^2$), the 11 years (2000-2010) daily rainfall data from 108 AWS (Automatic Weather Station) were collected. Especially, the 11 heavy rain and typhoon events from 2004 to 2009 were selected for trend analysis. The elevation effect by IDW (Inverse Distance Weights) interpolation showed the change up to +62.7 % for 1,200~1,600m elevation band. The effect based on 19 subbasins of WAMIS (Water Resources Management Information System) water resources unit map, the changes of IDW and Thiessen were -8.0 % (Downstream of Han river)~ +19.7 % (Upstream of Namhan river) and -5.7 %~+15.9 % respectively. It showed the increase trend as the elevation increases. For the 11 years rainfall data analysis, the lapse rate effect of IDW and Thiessen showed increase of 9.7 %~15.5 % and 6.6 %~9.6 % respectively.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.1
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• pp.111-120
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• 2018

The purpose of this study was to develop a ridge regression (RR) model to estimate BOD and TP load using runoff weighted value. The concept of runoff weighted value, based on distributed curve-number (CN), was introduced to reflect the impact of land covers on runoff. The estimated runoff depths by distributed CN were closer to the observed values than those by area weighted mean CN. The RR is a technique used when the data suffers from multicollinearity. The RR model was developed for five flow duration intervals with the independent variables of daily runoff discharge of seven land covers and dependent variables of daily pollutant load. The RR model was applied to Heuk river watershed, a subwatershed of the Han river watershed. The variance inflation factors of the RR model decreased to the value less than 10. The RR model showed a good performance with Nash-Sutcliffe efficiency (NSE) of 0.73 and 0.87, and Pearson correlation coefficient of 0.88 and 0.93 for BOD and TP, respectively. The results suggest that the methods used in the study can be applied to estimate pollutant load of different land cover watersheds using limited data.