• Journal of Korean Society on Water Environment
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• v.25 no.3
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• pp.441-451
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• 2009

To evaluate the soil erosion best management practices, many computer models has been utilized over the years. Among those, the USLE and SWAT models have been widely used. These models estimate the soil erosion from the field using empirically-based USLE/MULSE in it. However, these models are not good enough to estimate soil erosion from highland agricultural watershed where severe storm events are causing soil erosion and muddy water issues at the receiving watersheds. Thus, physically-based WEPP watershed version was applied to a watershed, located at Jawoon-ri, Gangwon with very detailed rainfall data, rather than daily rainfall data. Then it was validated with measured sediment data collected at the sediment settling ponds and through overland flow. In this study, very detailed rainfall data, crop management data, soil data reflecting soil reconditioned for higher crop production were used in the WEPP runs. The $R^2$ and the EI for runoff comparisons were 0.88 and 0.91, respectively. For sediment comparisons, the $R^2$ and the EI values were 0.95 and 0.91. Since the WEPP provides higher accuracies in predicting runoff and sediment yield from the study watershed, various slope scenarios (2%, 3%, 5.5%, 8%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%) were made and simulated sediment yield values were analyzed to develop appropriate soil erosion management practices. It was found that soil erosion increase linearly with increase in slope of the field in the watershed. However, the soil erosion increases dramatically with the slope of 20% or greater. Therefore special care should be taken for the agricultural field with slope greater than 20%. As shown in this study, the WEPP watershed version is suitable model to predict soil erosion where torrential rainfall events are causing significant amount of soil loss from the field and it can also be used to develop site-specific best management practices.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.138-138
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• 2021

Flash floods are one of the types of natural hazards which has severe consequences. Flash floods cause high mortality, about 5,000 deaths a year worldwide. Flash floods usually occur in mountainous areas in conditions where the soil is highly saturated and also when heavy rainfall happens in a short period of time. The magnitude of a flash flood depends on several natural and human factors, including: rainfall duration and intensity, antecedent soil moisture conditions, land cover, soil type, watershed characteristics, land use. Among these rainfall intensity and antecedent soil moisture, play the most important roles, respectively. Flash Flood Guidance is the amount of rainfall of a given duration over a small stream basin needed to create minor flooding (bank-full) conditions at the outlet of the stream basin. In this study, the Sejong University Rainfall-Runoff model (SURR model) was used to calculate soil moisture along with FFG in order to identify flash flood events for the Geum basin. The division of Geum river basin led to 177 head-water catchments, with an average of 38 km². the soil moisture of head-water catchments is considered the same as sub-basin. The study has measured the threshold of flash flood generation by GIUH method. Finally, the flash flood events were used for verification of FFG. The results of the validation of seven past independent events of flash flood events are very satisfying.

• Journal of Wetlands Research
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• v.24 no.4
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• pp.256-267
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• 2022

This study analyzed the current status and trend of water quality using long-term water quality monitoring data measured over the past 5 years in the Seohwacheon Basin, located upstream of Daecheong Lake. In the Seohwacheon Basin, a project is underway to reduce the occurrence of algal blooms in the Daecheong Lake and to improve water quality, and continuous management is required for water quality management. The current water quality evaluation aims to identify the water quality management point, and the good water grade and the integrated water quality index (WQI) were used. For trend evaluation, the effect of the water quality improvement project was evaluated using the Mann-Kendall test and Sen's Slope. As a result of the evaluation, the current water quality index was used to identify the watersheds and when to manage water quality, and the effect of the improvement project was confirmed through trend analysis. Through this study, it is possible to review the water quality status and improvement effect using long-term water quality monitoring data, so it is expected to be applicable to similar types of watersheds in the future.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.3B
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• pp.185-192
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• 2012

Drought vulnerability index was developed by selecting drought-related indicators with trend test. Study areas were determined by considering the weir locations from the four major rivers restoration project in Nakdong and Geum river watersheds. Ten indicators were selected and they were categorized into three groups, water resources, precipitation pattern, and social aspects. Annual average surface water level, annual minimum surface water level, annual average groundwater level, and annual minimum groundwater level data sets were collected for water resources aspects. The number of non-rainy days, rainfall concentration ratio, and rainfall deviation were considered for precipitation pattern category. The amount of water available per capita, financial soundness for water resources, and water usage equity were related to social aspects. Mann-Kendall, Hotelling-Pabst, and Sen trend tests were performed for the ten indicator data sets and the results were scored for the drought vulnerability index. The results shows Gumi, Sangjoo, and Hapcheon weirs are relatively vulnerable to drought. The indices were relatively low for the regions in Geum river watershed compared to those in Nakdong river watershed.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.1 s.24
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• pp.57-66
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• 2007

The purpose of this study is both the variation of hydrologic topographical informations extracted by using WMS and the quantitative effect of rainfalll-runoff simulation due to dividing watershed. Miho stream basin in Geum river was selected by this study. Watershed dividing method are determined by area, channel slope and channel length. Hydrological response of divided watershed using Clark method, SCS method and Snyder method was compared with actual measured flood hydrograph. As a results, area-based watershed dividing method are particularly suitable the hydrologic applications using SCS method. This study can be used as basic data for the phase of the runoff variation in Miho stream basin.

• Journal of Korean Society on Water Environment
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• v.33 no.5
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• pp.525-530
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• 2017

The attainment ratios of the water quality goals of the 114 mid-watershed representative stations, examined during the period2011 to 2015, were evaluated in the study. Of the four major river basins, the attainment ratio on water quality goal of the Geum River basin turned out to be the lowest. As a result of formal evaluation of the attainment ratios of BOD, COD and TOC, it was found that the attainment ratio of COD was much lower than that of BOD and TOC (I a circumstance thought to be caused by the higher COD/BOD and COD/TOC ratios of the water quality of the river than those of the environmental water quality standard). As well, higher COD/BOD and COD/TOC of wastewater discharged from point and non-point sources (other than those of the environmental water quality standards) might possibly represent one of the reasons. We also compared attainment ratio between the main stream and tributaries, which indicated that the higher attainment ratio was present in the main stream. The attainment ratio is also documented as more significant in the winter season than the summer season, possibly due to the contribution of non-point pollutants swept in by rain during the summer season during documented periods of high precipitation. Thus, water quality management in summer season and improvement of water quality of the tributaries might be important as a means of increasing attainment ratio on water quality goal.

• KCID journal
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• v.9 no.2
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• pp.59-67
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• 2002

Considering complexity of industry and environmental surroundings of Geum river basin, factors of environmental pollution are very complicated and multi-changed. It is very needed to survey the discharge, water quality change and pollutant loading from up

• Journal of Ecology and Environment
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• v.38 no.4
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• pp.619-627
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• 2015

Cyanobacteria were sampled at five sites in the Han River, Nakdong River, and Geum River watershed from June 2014 to May 2015 and then cultivated. Two genera and five species of the cyanobacteria were newly recorded in Korea. The newly recorded species were Limnothrix redekei, Pseudanabaena galeata, Pseudanabaena amphigranulata, Sphaerospermopsis aphanizomenoides, and Calothrix parietina. As a result, the Korean flora of the cyanobacteria now include four orders, 22 families with 73 genera, 143 species, and two varieties, giving a total of 146 taxa.

• Magazine of the Korean Society of Agricultural Engineers
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• v.20 no.3
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• pp.4739-4749
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• 1978

This studies were conducted to derive synthetic unitgraphs and triangular unitgraphs correlated with watershed characteristics which can be used to the estimation and control of flood for the rational development of Agricultural water resources. Derived Synthetic unitgraphs and Triangular unitgraphs can be applied to the ungaged watersheds were compared with average unitgraphs by observed data. Seven small watersheds were selected as studying basins Han, Geum, Nakdong, Yeongsan and Inchon river system. The results summarized for these studies are as follows: 1. Average unitgraphs by observed data and dimensionless unitgraphs for synthesis were derived for all river systems. 2. Peak discharge per unit area of the unitgraph, qp, was derived as qp=10-0.389-0.0424Lg with a high significance. 3. Formulas for the base width of unitgraph of 50 and 75 percent for peak flow for each water systems was adopted as Table 5. 4. The base length of the unitgraph, Tb, in hours in connection with time to peak, Tp, in hours was expressed as Tb =4.3Tp. 5. Peak discharge, Qp, were obtained as Table 6 by the Triangular form to all subwatersheds. 6. Relative errors in the peak discharge of the synthetic unitgraphs showed to be 7.3 percent to the peak of observed average unitgraphs except errors of peak discharge for Yeongsan river system. This indicates that Synthetic unitgraphs for the small watersheds of Han, Geum, Nakdong and Inchon river systems can be applied to the ungaged watersheds. On the other hand, It was confirmed that the accuracy of Instantaneous Unit Hydrograph with only 1.6 percent as relative errors was approaching more closely to the observed average unitgraph than that of synthetic unitgraph with relative errors. 23.9 percent for Yeongsan river system. 7. Errors in the peak discharge of the triangular unitgraph to the observed average unitgraph showed to be 0.6 percent to 7.5 percent which can be regarded as a high precision within the range of 200 to 500$\textrm{km}^2$ in area. On the contrary, application of triangular unitgraph within the range of 200$\textrm{km}^2$ in area has defined as a unsuitable method because of high relative errors, 26.4 percent to 61.6 percent.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.4
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• pp.268-275
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• 2013

To evaluate the effects of submerged aerators installed at Chudong and Muneui areas in Daechung Reservoir on improvement of water quality and reduction of algal bloom, the water quality was monitored at the effected and control areas at the time of operation. The water temperature and concentrations of dissolved oxygen, total phosphorus, and total nitrogen in depth at the effected and control areas were not different each other, indicating the submerged aerators at these areas are not effective for circulation of water body and reduction of nutrients. In warmer season, the concentrations of total phosphorus in deep water, which was probably released from contaminated sediment or inflowed from watershed, was high. To decide the operation of aerators in this season, the concentration of total phosphorus in water should be considered because the dispersed phosphorus by operation of aerators can enhance the algal growth.