• KCID journal
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• v.13 no.2
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• pp.262-273
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• 2006

The Soil and Water Assessment Tool (SWAT) model has been widely used in hydrology and sediment simulation worldwide. In most cases, the SWAT model is first calibrated with adjustments in model parameters, and then the validation is performed. However, very little study regarding the effects on SWAT estimation of subwatershed delineation was performed. Thus, the SWAT model was applied to the Doam-dam watershed with various threshold values in subwatershed delineation in this study to examine the effects on the number of subwatershed delineated on SWAT estimation. It was found the flow effect of subwatershed delineation is negligible. However there were huge variations in SWAT estimated sediment, T-N, and T-P values with the use of various threshold value in watershed delineation. Sometimes these variations due to watershed delineation are beyond the effects of parameter adjustment in model calibration and validation. The SWAT is a semi-distributed modeling system, thus, the subwatershed characteristics are assumed to be the same for all Hydrologic Response Unit (HRU) within that subwatershed. This assumption leads to variations in the SWAT estimated sediment and nutrient output values. Therefore, it is strongly recommended the SWAT users need to use the HUR specific slope length and slope value in model runs, instead of using the slope and the corresponding slope length of the subawatershed to exclude the effects of the number of subwatershed delineated on the SWAT estimation.

• Journal of Korean Society on Water Environment
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• v.30 no.1
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• pp.16-24
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• 2014

A combined watershed and receiving waterbody model was developed for operational water flow forecasting of the Nakdong river. The Hydrological Simulation Program Fortran (HSPF) was used for simulating the flow rates at major tributaries. To simulate the flow dynamics in the main stream, a three-dimensional hydrodynamic model, EFDC was used with the inputs derived from the HSPF simulation. The combined models were calibrated and verified using the data measured under different hydrometeological and hydraulic conditions. The model results were generally in good agreement with the field measurements in both calibration and verification. The 7-days forecasting performance of water flows in the Nakdong river was satisfying compared with model calibration results. The forecasting results suggested that the water flow forecasting errors were primarily attributed to the uncertainties of the models, numerical weather prediction, and water release at the hydraulic structures such as upstream dams and weirs. From the results, it is concluded that the combined watershed-waterbody model could successfully simulate the water flows in the Nakdong river. Also, it is suggested that integrating real-time data and information of dam/weir operation plans into model simulation would be essential to improve forecasting reliability.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.5
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• pp.21-27
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• 2014

Sediment-laden water is problematic in aquatic ecosystem and for hydraulic structures in a watershed, and agriculture area in a watershed is one of source areas of nonpoint source (NPS), since soil surface typically exposures due to agricultural activities. Especially, severe sediment might flow into stream when agricultural area is located near stream like the Imha-dam watershed. Soil erosion is affected by precipitation, therefore there is a need to consider precipitation characteristics in soil erosion and best management practices (BMPs) simulation. The Web-based Spreadsheet Tool for the Estimation of Pollutant Load (STEPL WEB) allows estimating long-term sediment loads and the impact of best management practices to reduce sediment loads. STEPL WEB and predicted precipitation data by MIROC-ESM model was used to estimate sediment loads and its reduction by filter strip and conversion of agricultural area to forest in the future 30 years. The result indicates that approximately 70 % of agricultural area requires filter strip installation or that approximately 50 % of agricultural area needs to be converted to forest, for 41 % of sediment load reduction.

• Journal of Korea Water Resources Association
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• v.44 no.9
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• pp.741-751
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• 2011

In this study, a methodology was devised to overcome that difficulty for thermal stratification modeling using EFDC. For the increase of reproductability for thermal stratification analysis, the effect of parameter such as distribution of solar radiation, depth of active bed temperature layer, heat transfer coefficients were analyzed. The simulation period was from June to December in 2005 and statistical index is used to analyze the model results. The results showed that distribution of solar radiation is zero and depth of active bed temperature layer is 10 m are suitable for simulation of thermal stratification in Yongdam Dam reservoir. This study results can be used for guideline to analyze the thermal stratification of large dam reservoir in Korea.

• Journal of Korea Water Resources Association
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• v.42 no.1
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• pp.1-8
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• 2009

In this study, based on the major activities which might have affected the ecological system of the Geum River, a conceptual model was proposed to guide scenario development for the eco-hydrological river evaluation. Also, an analysis method employing a set of models consisting, with other supporting programs, of KModSim for watershed network analysis and RAP for ecosystem analysis was developed for eco-hydrological river assessment. Then, hydrological analyses with various scenarios were conducted to examine the flow regime changes expected from the construction and operation of the Youngdam Multipurpose Dam (YMD) and Daecheong Multipurpose Dam (DMD) in the Geum River basin. The results indicated that the "Percentile 10" values for 10% exceeding time were decreased by 20.5% and 8.0% at Sutong downstream of YMD and Gongju downstream of DMD, respectively, while "Percentile 90" values for 90% exceeding time were increased by 56.3% and 340.8% at Sutong and Gongju, respectively, resulting in the reduction of the high flow variability typical for unregulated rivers in Korea. The results of eco-hydrological analyses will be presented in the following papers.

• Journal of the Korean Association of Geographic Information Studies
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• v.2 no.3
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• pp.23-34
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• 1999

This study proposed the possibility of GIS to analyze stream physiographic characteristics of river basin which is important control factor in complex water management. Based on five 1:25,000 topographic maps which cover Yengchon Dam area locates upper area of Kumho River, this study analyzed the characteristics using Arc/Info(UNIX) GIS. Comparing its results and those from the existing method using digital planimeter, it could conclude as follows; First, as the results of the analysis of hypsometric curve of Yeungchon Dam area, it has the topographic characteristics of youth and maturity. And the landform of Yengchon Dam area has developed with regularity when Horton's three laws on the morphology of stream is applied. Second, the possibility of applying GIS to data management and utilization is sufficient even if it requires long time to construct topographic attribute data. Finally, a further research is needed on watershed direction with landform for the purpose of analyzing water source management and topographic property effectively.

• Journal of Korean Society on Water Environment
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• v.21 no.4
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• pp.360-367
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• 2005

We have performed to analyze the trophic state resulting of Lake Yongdam as a result of water quality and nutrient concentration. Lake Yongdam is artifitial multi-purpose Dam resulting from the floods of 2001. The water quality of Lake Yongdam may affect the status of the Geum river basin including the Daecheong reservoir. It is necessary to understand the trophic state to assess water quality until stability after flooding. Water quality was surveyed using depth and hydraulic condition analysis. Further density flow was estimated for stratification and trophic state of Lake Yongdam by chlorophyll ${\alpha}$ concentration (2001~2004). And Environmental factors on chlorophyll ${\alpha}$ concentration were analyzed statistically. Trophic state was evaluated as the oligotrophic state at the main stream of the reservoir and eutrophic state at the upper stream in 2001, but evaluated as eutrophic state in 2002 and 2003 by TSI of Aizaki. From the results of multiple regression analysis using stepwise method, chlorophyll ${\alpha}$ concentration was shown to be very significant when nutrient concentration is high upon initial filling of the Dam. Chlorophyll ${\alpha}$ concentration varied according to sample site, season and year. Concentration were high in the upper stream of Lake Yongdam 4, algae bloom in these watershed were affected by location and high nutrient levels in the summer season which have in turn increased phytoplankton bloom into the reservoir.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.992-1006
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• 2008

The tunnel type spillways is under construction to increasing water reservoir capacity in Dae-am dam. Cutting-slope adjacent to outlet of spillways had been originally designed to be 63 degrees and about 65m in height. Examination is carried out in preceding construction that it is caused to some problems possibility which of machine for slope cutting couldn't approach to the site, blasting for cutting slope might have negative influence on highway and roads nearby, and fine view along the Tae-hwa river would be eliminated. In order to establish stability of tunnel and more friendly natural environment that we are carry out detailed geological surface survey and analysis of slope stability. So, we are design and construct for tunnel excavation with possible method that it is keep up natural slope. The result of survey and analysis that natural slope was divided 3 zone(A, B, C zone). In A and B zone, in first removed floating rock, high tensile tension net is install that it prevent of release and falling of rock, in order to security during under working. In addition to, pre-stressed rock anchor is install purpose of security during tunnel excavation because of fault zone near vertical developed above excavation level. Zone C is relatively good condition of ground, design is only carry out random rock bolt. All zone are designed and constructed drainage hole for groundwater and surface water is easily drain. Desinged slpoe is harmony with near natural environment. Successfully, construction is completed.

• Journal of Korean Society on Water Environment
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• v.34 no.6
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• pp.591-601
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• 2018

Optimized BMP plans for controlling water quality using the Pareto trade-off surface curve in upper basin of Namgang Dam is proposed. The proposed alternatives consist of BMP installation scenarios in which the reduction efficiency of non-point pollutants is maximized in a given budget. The multi-objective optimization process for determining the optimal alternatives was performed without direct implementation of a watershed model such as SWAT analysis, thereby reducing the time taken. The shortening of the calculation time further enhances the applicability of the multi-objective optimization technique in preparing regional water quality management alternatives. In this study, different types of BMP are applied depending on the land use conditions. Fertilizer input control and vegetative filter strip are considered as alternatives to applying BMP to the field but only control of fertilizer input can be applied to rice paddies. Fertilizer input control and vegetative filter strip can be installed separately or simultaneously in a hydrologic response unit. Finally, 175 BMP application alternatives were developed for the water quality management of the upper river basin of Namgang dam. The proposed application alternative can be displayed on the map, which has the advantage of clearly defining the BMP installation location.

• Journal of Korean Society on Water Environment
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• v.27 no.4
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• pp.509-515
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• 2011

For this study the 4 sub-watersheds Okdong A, Hankang B, Jecheon A and Hankang C which are the main streams of the Han River within the mid-level region of Chungju Dam are selected and the analysis of soils has been carried out through the soil basic survey. When it comes to the soil erosion amount the soil nutrient load has been calculated by utilizing the RUSLE erosion equation. In case of the data related to the measurement of water flow and quality the information available from the "Water Information System" one of the websites run by the Ministry of Environment has been used to calculate the water pollution load. The correlation between the soil nutrient load and the water pollutant load has been analyzed through making comparison. According to the results related to the soil nutrient load of each sub-watershed the Hankang C shows the highest values TOC 29,986.92 ton/yr, TN 3,860.33 ton/yr and TP 973.97 ton/yr respectively. Even when it comes to the loads related to water quality the Hankang C shows also comparatively high values TOC 6,625.64 ton/yr, TN 7,335.01 ton/yrand TP 145.49 ton/yr respectively. The soil nutrient loads of the sub-watersheds are shown to increase towards the lower stream meaning the load increases in the order of Hankang CHankang B and Okdong A. When it comes to the water pollutant load the value goes up along down the water system meaning the load gets higher in the order of Hankang C, Hankang B and Okdong A while utilizing the mainstream within the mid-level region of Chungju Dam as the basis. The correlation study showed that the nutrient content of soil is proportional to the pollutant load in water with the strongest positive correlation with TOC.