• Korean Journal of Ecology and Environment
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• v.48 no.1
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• pp.12-25
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• 2015

The tributaries of Daechung Lake play an important role in controlling eutrophication in the lake, which is used for agricultural purposes and as potable water. However, water quality properties were not extensively studied in the tributaries of Daechung Lake. The objectives of this study are to investigate spatial and temporal properties of water quality and to characterize streams which could threaten water quality of Daechung Lake. For this study, water samples were weekly or monthly collected from February 2014 to October 2014 in 9 streams. Water quality parameters analyzed in this study include biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen and phosphorus (TN and TP), suspended solids (SS), and chlorophyll a. Based on temporal distribution and principal component analysis, BOD, COD, TOC, SS, and TP were controlled by not only river discharge that increased during summer due to heavy rain fall, but also due to anthropogenic input (e.g., bridge construction and/or agricultural activity). Dilution is also one of the factors explaining TN and conductivity, both of which decreased with increased discharge. Generally, concentrations of contaminants (BOD, COD, TOC, TN and TP) in the tributaries were higher than those of Daechung Lake. However, pollution load indicated that only the main channel of Geum River and Sook Stream may largely influence lake waters, attributed mostly to their large volumes. This implies that the main channel and Sook Stream are the major influences on the water quality of Daechung Lake.

• Journal of Korea Water Resources Association
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• v.52 no.2
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• pp.97-105
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• 2019

In this study, the baseflow indices in Nakdong river watershed and the whole country's river were calculated by using SWAT model and PART method. The annual averaged baseflow in the Nakdong river watershed was estimated at 40% - 44% of the total discharge rate, and it is found to be higher than 90% during the winter months of December and January. An analysis of the baseflow index from 317 gauge stations across the country revealed that the contribution of baseflow to the nation's stream flow rate stood at an annual average of 40%, ranging from less than 20% to over 80% by region. Also, the impact of the decreasing baseflow due to land use changes in 1975 and 2000 was analyzed in Keumhogang river watershed under the same weather conditions. The results revealed that the number of days under the standard instream flow increased by 19-24 days as a result of the increase in the urbanization rate.

• Membrane and Water Treatment
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• v.10 no.5
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• pp.339-352
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• 2019

Long term water quality change was analyzed to evaluate the effect of the Total Maximum Daily Load (TMDL) policy. A trend analysis was performed for biochemical oxygen demand (BOD) and total phosphorus (TP) concentrations data monitored at the outlets of the total 41 TMDL unit watersheds of the Nakdong River in the Republic of Korea. Because water quality data do not usually follow a normal distribution, a nonparametric statistical trend analysis method was used. The monthly mean values of BOD and TP for the period between 2004 and 2015 were analyzed by the seasonal Mann-Kendall test and the locally weighted scatterplot smoother (LOWESS). The TMDL policy effect on the water quality change of each unit watershed was analyzed together with the results of the trend analysis. From the seasonal Mann-Kendall test results, it was found that for BOD, 7.8 % of the 41 points showed downward trends, 26.8 % and the rest 65.9% showed upward and no trends. For TP, 51.2% showed no trends and the rest 48.8% showed downward trends. From the LOWESS analysis results, TP began to decrease in most of the unit watersheds from mid-2010s when intensive chemical treatment processes were introduced to existing wastewater treatment plants. Overall, for BOD, relatively more points were improved in the main stream compared to the points of the tributaries although overall trends were mostly no trend or upward. For TP, about half of the points were improved and the rest showed no trends.

• Journal of Korean Society on Water Environment
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• v.27 no.4
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• pp.542-550
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• 2011

Changes of suspended sediment concentration in the Seomjin river estuary located in south sea of the Korea peninsula were investigated during the spring tide in autumn (i.e. 25 hours in October) 2000 and winter (i.e. 25 hours in February) 2001. The changes of temperature and salinity during the spring tide in October 2000 showed larger variations than the those in February 2001. During the spring tide in October 2000, currents at bottom layer were observed to be stronger than during the spring tide in February 2001, showing that both of the two periods had ebb currents-predominant tide asymmetries. The suspended sediment concentrations in October 2000 were larger than the those in February 2001. At the time of the maximum of tide currents or after about one hour of the maximum during the autumn months, the suspended sediment turbidity was observed to be maximum. Another observation station at Hadong upstream from the Seomjin river estuary showed about one hour delay in tide phase, Thereby, the suspended sediment concentration showed high turbidity after two hours at bottom and three hours at surface layer, in particular, in October 2000. This results can be explained by the facts that river discharge increased significantly after the summer rainy season, causing also increase of erosion processes by strong current velocity at bottom layer.

• Journal of Environmental Impact Assessment
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• v.20 no.1
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• pp.89-96
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• 2011

This study was carried out to assess the variations of water quality caused by the dam construction on the river. Six dams-Yongdam, Miryang, Hoengseong, Boryeong, Jangheung and Buan- constructed recently in Korea were selected for the study. Chemical oxygen demand(COD) was increased in the initial stage of water storage at dams compared to the lotic(river) environment, but after 3 years it was maintained lower and stabilized concentrations. Five dams except for Jangheung Dam were maintained Ia~Ib grade conditions under the water quality criteria of Korea. The concentrations of total nitrogen(T-N) were decreased under the lentic(reservoir) environment compared to the river status. Total phosphorus(T-P) was decreased 13~63% at the reservoir condition. We concluded that increase of COD concentration was due to the debris organic materials of the land, but temporary phenomenon. T-N and T-P concentrations were decreased at the lentic condition compared to the lotic.

• Journal of Environmental Science International
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• v.20 no.12
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• pp.1533-1540
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• 2011

This study was conducted to identify the sedimentation quantity and settling velocity, sediment fundamental data that an important position of water quality management of Seston, POC, PP and PN in Nakdong river basin using a sediment traps to collect suspended material pollutants. Nakdong river basin is that average sedimentation quantity of seston, POC, PP and PN were 124~1,125 g/$m^2$/d, 2,963~25,072, 26~347, 445~2,184 mg/$m^2$/d, respectively. Settling velocity of Seston, POC, PP and PN were 17.0, 35.5, 8.7, 2.4 m/d. It was appeared that various results according to the river flow, weather and other environmental factors. There was no significant correlation, each suspended material pollutants. Sedimentation rates are likely to be overestimated because the flow is not considered to resuspended materials. Therefore diversification through continued monitoring is needed to be analyzed.

• Environmental Engineering Research
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• v.11 no.4
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• pp.181-193
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• 2006

The hydrophilic or hydrophobic characteristics of dissolved organic matter (DOM) from different origins in lake and river waters were investigated using spectrometric and chromatographic analyses of water samples. DOM in a deep, mesotrophic lake (Lake Unmun) was fractionated using three types of ion exchange resins and classified into aquatic humic substances (AHS), hydrophobic neutrals (HoN), hydrophilic acids (HiA), hydrophilic neutrals (HiN), and bases (BaS). The DOM fractionation provided insight into the understanding of the nature of heterogeneous DOM molecules present in different water sources. The UV/DOC ratios were determined for samples from the influent river and lake waters during DOM fractionation and incubation. AHS prevailed over DOM in the lake and river waters. After biodegradation, the relative contribution of AHS in the total DOM became more significant. It indicates that the AHS fraction would increase while water stay long time in the lake.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.3
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• pp.185-189
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• 2011

To predict the deposition characteristic in the Nakdong river estuary, the material budget of Suspended Solid(SS) was investigated with the amount of Nakdong river discharge being set as dry season and flood season. The results of material budged of SS in dry season and flood season were 60,708 kg/day(inflow) and 306,892 kg/day(outflow), respectively.

• Journal of Korean Society on Water Environment
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• v.35 no.1
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• pp.55-63
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• 2019

The Four Major Rivers Restoration Project started in 2009 and completed in early 2013 is a large-scale inter-ministry SOC project investing ₩22.2 $10^{12}$ and one of the Project's objectives was to enhance the water-quality grade through recovering the river eco-system and environment. The average concentration and probability distribution of water-quality constituents at given and selected sampling sites are very significant elements for analyzing and controlling the water-quality of rivers or reservoirs effectively. Average concentration can be estimated by point estimator, distribution function of water-quality constituents or Bootstrap method, in which the distribution function estimated with more data in case of insufficient dataset, is applied. Ipo and Gangcheon water-quality monitoring stations in South Han River were selected to compare and analyze the variation of concentration before and after Ipo and Gangcheon Weirs construction, using the whole 4-year's data, from 2005 to 2008 and from 2014 to 2017. Water-quality constituents such as BOD and COD relating to oxygen demanding wastes and TP and Chlorophyll-a relating to the process of nutrient enrichment called eutrophication were also selected. The guidelines for water-quality control and management after weir construction including evaluation of water-quality constituents' variations can be presented by this paper.

• Journal of Korean Society on Water Environment
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• v.27 no.5
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• pp.719-728
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• 2011

The results of investigation on the water quality of the unit watersheds in the Yeongsang/Seomjin River indicate that $BOD_5$, SS, T-P decrease in most of the unit watersheds. However, $COD_{Mn}$ and T-N increase since the Total Maximum Daily Loads (TMDLs). It is thought that $COD_{Mn}$, which is included non-biodegradable matters, is difficult to decrease only using by conventional biological treatment facilities and T-N is affected by non-point source, etc. The results of assessment on 3 years $BOD_5$ indicate that most of the unit watersheds were being improved except Yeongbon A, Seombon C and Yocheon B. In addition, it was found that T-P were also being improved except Yocheon B and Hwangryeong A. Consequently, water qualities of the unit watersheds have been improved in many cases since the TMDLs.