• Journal of Environmental Science International
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• v.8 no.4
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• pp.431-441
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• 1999

In this study, the regional frequency analysis is used to determine each subbasin drought frequency with reliable monthly precipitation and the L-Moments method which is almost unbiased and has very nearly a normal distribution is used for the parameter estimation of monthly precipitation time series in Nakdong river basin. As the result of this study, the duration of '93-'94 is most severe drought year than any other water year and the drought frequency is established as compared the regional frequency analysis result of cumulative precipitation of 12th duration months in each subbasin with that of 12th duration months in the major drought duration. The Linear regression equation is induced according to linear regression analysis of drought frequency between Nakdong total basin and each subbasin of the same drought duration. Therefore, as the foundation of this study, it can be applied proposed method and procedure of this study to the water budget analysis considering safety standards for the design of impounding facilities large-scale river basin and for this purpose, above all, it is considered that expansion of reliable preciptation data is needed in watershed rainfall station.

• Journal of Korean Society on Water Environment
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• v.37 no.5
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• pp.369-380
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• 2021

In this work, we analyzed the effects of drought on the water temperature (WT) of Nakdong river basin major river sections using Standardized Precipitation Index (SPI) and WT data. The analysis was carried out on a seasonal basis. After calculating the optimal time scale of the SPI through the correlation between the SPI and WT data, we used the copula theory to model the joint probability distribution between the WT and SPI on the optimal time scale. During spring and fall, the possibility of environmental drought caused by high WT increased in most of the river sections. Notably, in summer, the possibility of environmental drought caused by high WT increased in all river sections. On the other hand, in winter, the possibility of environmental drought caused by low WT increased in most river sections. From the risk map, which quantified the sensitivity of WT to the risk of environmental drought, the river sections Nakbon C, Namgang E, and Nakbon K showed increased stress in the water ecosystem due to high WT when drought occurred in summer. When drought occurred in winter, an increased water ecosystem stress caused by falling WT was observed in the river sections Gilan A, Yongjeon A, Nakbon F, Hwanggang B, Nakbon I, Nakbon J, Nakbon K, Nakbon L, and Nakbon M. The methodology developed in this study will be used in the future to quantify the effects of drought on water quality as well as WT.

• Journal of Environmental Impact Assessment
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• v.11 no.3
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• pp.117-127
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• 2002

This study tested the usefulness of landscape indices for quantifying forest fragmentation due to linear development projects. Research was carried out in the middle-upper Nakdong River watershed, which has been affected by the expressway building, or national road-widening. Landscape indices were calculated from the forest cover maps before and after road-building using FRAGSTATS 3.1. We could successfully demonstrate the forest fragmentation based on landscape indices; (1) patch size decreased, and edge density and patch density increased (2) roads simplified patch shapes, especially in the larger patches, (3) patch core area size decreased, and core area density increased, (4) the distance increased between the focal patch and each of the other patches within the search radius (=1km) as a result of roads. We suggest several important needs for future researches, including continued investigation of scaling issues, development of indices that measure specific components of spatial pattern, and study of the relationships between forest fragmentation and ecological processes.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.507-510
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• 2007

The correlation between groundwater level(GWL) and the moving average of precipitation was analyzed based on the observation data in Nakdong river watershed. The precipitation data was compared and analyzed with the GWL data from adjacent observation point to the precipitation gauge station. The correlation between the moving average of precipitation with several averaging periods and GWL were analyzed and we could choose the averaging period that produces maximum correlation. A severe drawdown was observed from December to April. The maximum correlations between GWL and the moving average of precipitation were occurred from 20-day to 80-day averaging period.

• Journal of Korea Water Resources Association
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• v.43 no.3
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• pp.283-294
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• 2010

The objective of this study is to develop an accurate and stable dynamic water quality model which is capable of reflecting various flows and irregular cross sections and handling numerical oscillations under the low flow conditions. In order to solve the oscillation problem under the low flow conditions, diffusive wave method was applied to the low flow condition in developing a hydraulic model, DyHYD. DyQUAL is also developed as a water quality model to calculate up to 12 water quality variables including autochthonous BOD, water temperature, DO, TN and TP. The developed model is applied to both hypothetical river channels and actual Nakdong river watershed. Additionally, the applicability and reliability of the models are verified by comparing simulation results with observed values. Nash-Sutcliffe coefficients are estimated by comparison between simulation results and observed values. In the calibration and verification process, the coefficients varies from 0.391 to 0.591 and 0.704 to 0.902 for discharge, BOD, TN and TP, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4B
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• pp.405-411
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• 2008

The Nakdong River Estuary Barrage (NREB) was constructed in 1987 to prevent saltwater intrusion and to provide the sustainable water supply in the upstream channel. Sediment dredging has been conducted to eliminate deposited sediments in the approached upstream channel of the NREB. Fluvial changes and sedimentation problems have been continued due to urbanization and development in the watershed as well as construction of the NREB. However, the sufficient field monitoring and researches for sedimentation characteristics and bed changes have not been performed after construction of the NREB. Therefore, bed elevation changes and seasonal sediment concentration distribution were analyzed using the quasi-steady state model with historical field data in this study. The water surface elevation changes with and without sediment dredging operation were calculated using the developed quasi-steady state model and finally the sediment dredging effects were evaluated.

• Journal of Korea Water Resources Association
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• v.31 no.1
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• pp.71-84
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• 1998

The SSARR model adopting IS(integrated snowband) watershed model is applied to the Nakdong River basin for low flow analysis. The IS watershed model is added to new version of the SSARR which has functions of simulating evapotranspiration. infiltration and lower zone routing. It provides annual water budget information as an output file and can be operated by interactive mode. Sensitivity analysis for both cases of high and low flows was carried out, which becomes the knowledge base for model calibration. Model verification was performed using the relative errors of high flows and absolute errors of low flows at the control points. Monthly water budget analysis was done by IS watershed model. and it reveals that runoff coefficient is 52.6%

• Korean Journal of Environment and Ecology
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• v.22 no.1
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• pp.43-58
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• 2008

For this study, which was conducted in the summer from $2004\sim2007$, 10 small and medium sized streams in Korea were selected(Munsan and Gokreung Stream in the Han River watershed, Mi, Ssanggye and Nam Stream in the Nakdong River watershed, Gapeong and Jojong Stream in the Bukhan River watershed, Cheongmi, Yanghwa and Bokha Stream in the Namhan River watershed), and plant surveys were performed using the belt transect method on the most natural 1km sections of each stream in order to clarify the natural environment condition of the plants in each stream. In the results of the plant survey, the total number of plant species recorded was 296. After selecting 121 species of those surveyed plant in order of frequency, an RDA(Redundancy Analysis) and a Pearson Correlation Analysis were performed to determine the correlation between the selected plant species and environmental factors( such as distance from channel, size of bed material, number of bars, altitude, bed slope, width of channel, and measured data of water quality) of the study sites. There was no significant correlation between the 121 plant species and altitude, bed slope, and number of bars at the research sites, but the correlation of plant species with size of bed material, width of channel, electrical conductivity, and phosphate$(PO_4-P)$ concentration was from very high to moderate. Also, the spectrum of these plant species reflects the actual environmental conditions so the method used in the study seems to be correct, but owing to the range of diversity, the results of the study seem to be difficult to extend to other streams. Nevertheless, it is expected that this data can be used as a basic material for researching plants by stream characteristics or in selecting plant species for streams.

• Journal of Korea Water Resources Association
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• v.35 no.4 s.129
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• pp.397-410
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• 2002

In order to quantitatively identify historical drought conditions and to evaluate their variability, drought indices commonly used. The calculation method for the drought index based on the principal hydrological factors, such as precipitation and reservoir storage, can estimate the duration and intensity of a drought. In this study the Palmer-type formula for drought index is derived for the Nakdong River basin by analyzing the monthly rainfall and meteorological data at 21 stations. The Palmer Drought Severity Index(PDSI) is used for dry land sectors to evaluate the meteorological anomaly in terms of an index which permits time and space comparisons of drought severity. The Surface Water Supply Index(SWSI) is devised for the use in conjunction with the Palmer index to provide an objective indicator of water supply conditions in Nakdong River basin. The SWSI was designed to quantify surface water supply capability of a watershed which depends on river and reservoir water The Standardized Precipitation Index(SPI) is evaluated for various time periods of 1 to 12 months in Nakdong River basin. For the purpose of comparison between drought indices correlation coefficient was calculated between indices and appropriate SPI time period was selected as 10 months for Nakdong River basin. A comparative study is made to evaluate the relative severity of the significant droughts occurred in Nakdong River basin since 1976. It turned out that $'94{\sim}'97$ drought was the worst drought in it's severity. It is found that drought indices are very useful tools in quantitatively evaluating the severity of a drought over a river basin.

• Journal of Environmental Science International
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• v.18 no.9
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• pp.983-992
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• 2009

The purpose of the present study is to analyze pollutant runoff characteristics from non-point sources in Joman River basin. The present study contains analyzed results of rainfall and SS, BOD, COD, TN, TP runoff from Joman River basin. This study contains a sensitivity analysis of parameters that affect the simulation results of rainfall and pollutants runoff. Result of the sensitivity analysis shows that proportion of watershed and impervious areas is the most sensitive to peak discharge and total flowrate for rainfall runoff and that WASHPO is the most sensitive parameter for pollutants runoff. For parameter estimation and verification, flowrate and water quality is measured at the Kangdong Bridge in Haeban stream. A single rainfall event is use to perform parameter estimation and verification. Results of the present study show that total pollutant loads of Joman River basin is 11,600 ton of SS, 452 ton of BOD, 1,084 ton of COD, 515 ton of TN, and 49 ton of TP, respectively. In addition, it is found that contribution ratio of non point source and total source is 89% of SS, 63% of BOD, 61% of COD, 21% of TN, and 32% of TP, respectively.