• Journal of Korea Water Resources Association
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• v.54 no.11
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• pp.891-901
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• 2021

In this study, a hydrological cycle soundness evaluation method was developed using monthly meteorological observation data. The Gyeongan stream watershed was divided into five sub-basins and eight criteria were established for hydrological cycle evaluation: the number of non-rainfall day, the number of non-rainfall day fluctuation, over 30 mm per day, over 30 mm per day fluctuation, average river level, average river level fluctuation, average groundwater level and average groundwater level fluctuation. Observation data were normalized and weights for evaluation by each sub-basin were calculated using the entropy method. The hydrological cycle soundness evaluation indices were calculated using TOPSIS applying the calculated weight value. As a result of the study, it was found that the hydrological cycle soundness was unstable in the Gyeongan-upstream from November to January, the Gyeongan-suwipyo from February to April, Gonjiam stream from April to May, and the Gyeongan-downstream from November to February. In this study, the developed technique is expected to serve as a quantitative basis for policy decision to recover hydrological cycle soundness.

• Journal of Korean Society on Water Environment
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• v.20 no.6
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• pp.698-702
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• 2004

At five stations in Gyeongan River, a tributary of Lake Paldang, physicochemical and biological environmental factors of water, particulate matters, and sediments were investigated biweekly from April 11 to December 22 in 2001. The studied area was characterized as a stream-lake system. The system is primarily referred to a place where the environmental factors had considerably changed depending on the amount of precipitation. As a result, the river turned out to be strongly eutrophicated. Also, some characteristics of the water and the particulate matters at midstream such as average concentrations of conductivity, nutrients, and chlorophyll $\alpha$ were higher than the characteristics of up and down-stream. However, the concentrations of organic matters and ratio of clay and silt of the midstream were determined to be higher than up and down-stream sediments. As the result of the factor analysis, 4 major different patterns for environmental factors are found from samples of water, particulate matters, and sediments.

• Journal of Wetlands Research
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• v.14 no.4
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• pp.561-569
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• 2012

This study estimates landscape indices of the Gyeongan-stream watershed from 1975 to 2000 by classifying the land cover into impervious cover and pervious cover depending on its state using a landscape analysis program. For the indicator of biodiversity this study uses Total Core Area(TCA) among landscape indices. The estimated TCA is then used along with an Impervious Cover Model(ICM) to compare the number of fish species that appear in the Gyeongan-stream watershed. In the relations between TCA and the impervious cover ratio, it has been found that as the impervious cover ratio increases, TCA decreases accordingly. It shows that as the ratio of impervious cover in the landscape increases due to urbanization and development, the critical area that individual species need for isolation from outside has decreased. Also, the monitoring of the number of fish species that appear in the Gyeongan-stream watershed shows that in the areas with low impervious cover ratio there are more fish species appearing that inhabit in clean, uncontaminated water. It has been identified that the Gyeongan-stream watershed falls into the category of Impacted Stream and that its state is worsening, and since the watershed in this area responds to the impervious cover ratio very sensitively, its fish diversity it is required to improve the state of the basin through its proper and careful management.

• Economic and Environmental Geology
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• v.56 no.2
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• pp.139-153
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• 2023

This study aimed to understand the spatiotemporal variations in nitrogen content in the Gyeongan stream along the main stream and at the discharge points of the sub-basins, and to identify the origin of the nitrogen. Field surveys and laboratory analyses, including chemical compositions and isotope ratios of nitrate and boron, were performed from November 2021 to November 2022. Based on the flow duration curve (FDC) derived for the Gyeongan stream, the dry season (mid-December 2021 to mid-June 2022) and wet season (mid-June to early November 2022) were established. In the dry season, most samples had the highest total nitrogen(T-N) concentrations, specifically in January and February, and the concentrations continued to decrease until May and June. However, after the flood season from July to September, the uppermost subbasin points (Group 1: MS-0, OS-0, GS-0) where T-N concentrations continually decreased were separated from the main stream and lower sub-basin points (Group 2: MS-1~8, OS-1, GS-1) where concentrations increased. Along the main stream, the T-N concentration showed an increasing trend from the upper to the lower reaches. However, it was affected by those of the Osan-cheon and Gonjiamcheon, the tributaries that flow into the main stream, resulting in respective increases or decreases in T-N concentration in the main stream. The nitrate and boron isotope ratios indicated that the nitrogen in all samples originated from manure. Mechanisms for nitrogen inflow from manure-related sources to the stream were suggested, including (1) manure from livestock wastes and rainfall runoff, (2) inflow through the discharge of wastewater treatment plants, and (3) inflow through the groundwater discharge (baseflow) of accumulated nitrogen during agricultural activities. Ultimately, water quality management of the Gyeongan stream basin requires pollution source management at the sub-basin level, including its tributaries, from a regional context. To manage the pollution load effectively, it is necessary to separate the hydrological components of the stream discharge and establish a monitoring system to track the flow and water quality of each component.

• Korean Journal of Ecology and Environment
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• v.39 no.2 s.116
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• pp.236-244
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• 2006

Water quality fluctuation of Gyeongan water area in Paldang reservoir, which measured from the downstream sampling point of Gyeongan stream (G1) to dam sampling point (P), was examined in the light of seasonal rainfall and regional difference in the year of 2002. Annual COD, T-P and T-N concentration dropped conspicuously at the point P (in front of dam) although concentration of Gl point was high. Concentration variation of COD, T-P and T-N from Gl to P point in Gyeongan area was small in August and September. And at G l point showed relatively low concentration. Chlorophyll-a concentration varies less during the autumn season (October to December) than spring season (March to June). Water temperature of Bughangang (north Han-river) area was relatively lower in August and higher in November compared with that of other areas. COD and SS concentration showed big regional difference except in November when the concentrations of which were relatively low. The high Chlorophyll-a concentration of April fell conspicuously in rainy season. Gyeongan area, where the water depth is relatively shallow, indicated steep temperature gradient in April compared with that in August or November. High 55 concentration in April at P point characterized surface layer while the opposite was recorded in August. Mixing of upper and lower layers had taken place causing dilution of COD, T-N and T-P concentration in August. This condition was maintained throughout November. Therefore, spring-summer seasons needed more attention for water management countermeasure than summer-autumn seasons.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.566-569
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• 2004

This study is to trace the change of stream shape using the past series of aerial photographs, and to compare the land use changes of riparian area along the stream. For the Gyeongan national stream, aerial photographs of 1966, 1981 and 2000 were selected and ortho photographs were made with interior orientation and exterior orientation, respectively. As apparent changes of the stream, the consolidated reaches of stream with levee construction were straightened and their stream widths were widened. Especially the stream width of inlet part of Paldang lake was widened almost twice because of the rise of water level by dam construction in 1974. The land use maps (1966, 1981,2000) of riparian areas were also made, respectively and classified into 6 categories (water, forest, agricultural land, urban area, road, sandbar) by digitizing. The area of forest and agricultural land decreased and urban area increased as the stream maintenance was performed.

• Journal of The Korean Society of Agricultural Engineers
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• v.47 no.2
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• pp.15-21
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• 2005

This study is to trace the change of stream shape using the past series of aerial photographs, and to compare the land use changes of riparian area along the stream. For the Gyeongan national stream, aerial photographs of 1966, 1981 and 2000 were selected and ortho-photographs were made with interior orientation and exterior orientation, respectively. Apparent changes of the stream were found that the consolidated reaches of stream by levee construction became straight together with widening of their stream widths. Especially the stream width of inlet part of Paldang lake widened almost twice because of the rise of water level by dam construction in 1974. The land use of riparian areas of three selected years were classified into six categories (water, forest, agricultural land, urban area, road, sandbar) by digitizing method. The forest and agricultural lands decreased and urban area increased as the stream maintenance had been performed.

• Journal of Korea Water Resources Association
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• v.38 no.5 s.154
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• pp.379-390
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• 2005

This study is to trace the change of stream shape using the past series of aortal photographs and topographic maps, and to compare the land use changes of inland along the stream. For the Gyeongan first & second class of local stream, aerial photographs of 1966, 1981 and 2000 were selected and ortho photographs were made with interior orientation and exterior orientation, respectively. In addition, topographic maps of 1914 - 1915 were used to compare with stream of 1966, 1981 and 2000. As apparent changes of the stream, the consolidated reaches of stream with levee construction were straightened and their stream width widened. Especially the stream width of inlet part of Paldang lake was widened almost twice because of the rise of water level by dam construction in 1974. The land use maps (1966, 1981, 2000) of riparian areas were also made, respectively and classified into 6 categories (water, forest, agricultural land, urban area, road, sandbar) by digitizing, The main changes of land use were agricultural land, urban area, road and sandbar.

• Journal of Korea Water Resources Association
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• v.40 no.6 s.179
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• pp.459-468
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• 2007

To estimate the groundwater recharge, the fully distributed parameter based model, MIKE SHE was applied to the Gyeongan-cheon watershed which is one of the tributaries of Han River Basin, and covers approximately $260km^2$ with about 49 km main stream length. To set up the model, spatial data such as topography, land use, soil, and meteorological data were compiled, and grid size of 200m was applied considering computer ability and reliability of the results. The model was calibrated and validated using a split sample procedure against 4-year daily stream flows at the outlet of the watershed. Statistical criteria for the calibration and validation results indicated a good agreement between the simulated and observed stream flows. The annual recharges calculated from the model were compared with the values from the conventional groundwater recession curve method, and the simulated groundwater levels were compared with the observed values. As a result, it was concluded that the model could reasonably simulate the groundwater level and recharge, and could be a useful tool for estimating spatially/temporally the groundwater recharges, and enhancing the analysis of the watershed water cycle.

• Korean Journal of Environmental Biology
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• v.31 no.4
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• pp.478-485
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• 2013

Fish field survey, especially fish distribution and their ecological characteristics, was performed in the downstream region of Gyeongan stream during the period of before (June) and after (October) the summer monsoon in 2010. Depending on the characteristics of each site, fyke net or casting net was used for fish sampling. Feeding classification was determined by the analysis of stomach contents. Total number of family and species sampled were 5 and 17, respectively. The dominant family was Cyprinidae (12 species), and relative abundance (RA) of the most dominant species, Lepomis macrochirus and Zacco platypus, was 38% and 24%, respectively. Exotic species and Korean endemic species observed were 3 (423 individuals, RA 44%) and 4 (98 individuals, RA 10%), respectively. Tolerance guild analysis as characteristics of ecological indicators revealed an undoubtedly high percentage (97%), compared to others as reflected by the identification of just one sensitive species. Analysis of trophic guilds showed that L. macrochirus dominated among insectivores (44% RA). The food of L. macrochirus composed of, aquatic insects, benthic invertebrates, zooplankton, Chironomidae, and waterweed. Thus, we determined that L. macrochirus could be classified as insectivores (partially carnivores) in this study. Conversely, Z. platypus consumed Cladocera exclusively, greater than 90% of their feed. We presume that stable isotope analysis would identify the exact position of these species in the food web.