• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.1361-1365
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• 2004

오염물질의 유입 유형은 일정한 농도를 가진 오염물질이 일정한 비율로 연속적으로 유입되는 경우와 순간적으로 특정한 농도를 가진 오염물질이 하천으로 유입되는 경우로 나눌 수 있다. 본 연구에서는 오염물질에 대해 댐 방류량을 일시적으로 증가시켜서 희석 및 세척시키는 플러싱(flushing) 효과에 관하여 연구하였다. 실측한 수리인자를 이용하여 적용성이 크다고 발표된 경험식에 의하여 확산계수를 결정하였다. 플러싱에 의한 오염물질의 희석정도 및 확산특성을 파악하기 위해서 RMA-4 모형을 잠실수중보$\~$신곡수중보 구간에 적용하였다. 정체되어있는 경우와 순간적으로 유입되는 경우, 성산대교 부근에서 농도가 1ppm이하로 감소하는 시간을 각 유량별로 분석하였다. 댐 방류량에 의한 플러싱을 시도한 경우에 본류의 오염물질이 지류로 역류하는 범위를 파악할 수 있었다.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.10
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• pp.563-572
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• 2015

The purpose of this study was to model the effect of flushing discharge on algae removal by multi-purpose weir operation in Yeongsan River (Seungchon Weir) using a 3-dimensional (3D) model. The chlorophyceae Eudorina sp. formed bloom in May 2013. Flushing discharge was conducted in two different ways for algal bloom reduction. To elucidate the spatial variability, a high-resolution 3D model, ELCOM-CAEDYM, was used to simulate the spatial variations of water quality and chl-a over a month. The results showed that ELCOM-CAEDYM could reproduce highly spatially resolved field data at low cost, and showed very good performance in simulating the pattern of algal bloom occurrence. The effect of each flushing discharge operation was analyzed with the results of modeling. The results of case 1, flushing discharge using an open movable weir, showed that the algal bloom between the Seochang Bridge and the Hwangryong River junction is rapidly flushed after operating the movable weir, but the residual algae remained in the weir pool as the discharge decreased. However, the results of case 2, fixed weir overflow with a small hydropower stop, showed that most of the algae was removed after flushing discharge and the effect of algae removal was much bigger than that in case 1, as per modeling results and observed data.

• Journal of Korea Water Resources Association
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• v.37 no.10
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• pp.857-868
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• 2004

Since the self-purification capacity of rivers in Korea is significantly controlled by environmental maintenance flow supplied by upstream reservoirs during drought season, it is obviously important to operate the river and reservoir systems considering not only water quantity aspect but also conservation of downstream water quality and ecosystem. In this study, an unsteady river water quality model KORIVl- WIN was developed as a tool for evaluating the impact. of reservoir operations on the downstream water quality. The model parameters were calibrated and verified using field data obtained in Geum River on September and October of 2002, respectively. Intensive data sampling was performed on November 22, 2003 to investigate the effect of a short-term flushing discharge of Daecheong Reservoir, which increased outflow from 30 $m^3$/s to 200 $m^3$/s for 6 hours, on downstream water quality. The model performance was evaluated by comparing simulated results with observed data including hydraulics, biochemical oxygen demand(BOD$_{5}$), nitrogen and phosphorus species during the flushing event. It showed very good performance in predicting the travel time of flushing flow and water quality variations of dissolved forms of nitrogen and phosphorus species, while revealed large deviations for BOD$_{5}$ possibly due to missing the effect of organic matters resuspension from river bottom sediment during the wave front passage.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.3 s.14
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• pp.43-50
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• 2004

This study had been performed to analyze flushing effects for instantaneous contaminants input with changing dam discharge in River. RMA-2 and RMA-4 models were applied to the downstream part of the Han River(from Jamsil submerged weir to Singok submerged one) The longitudinal dispersion coefficient of $50m^2/s$ was used. The four cases of dam discharges were selected as $500m^3/s,\;1000m^3/s,\;1500m^3/s$ and $2000m^3/s$, respectively, for 1 hour. The drought flow was fixed $200m^3/s$ in the Han River. The arrival time and the concentration of contaminant, the area of dispersion were estimated with RMA-4 model in the downstream part of the Han River. The arrival time which the concentration of contaminants become under 1ppm was analyzed with the stagnant and the instantaneous inflow contaminant at the section of Sungsan Bridge. The more increasing a dam discharge, the more short a dilution time of contaminant. The relation between the dam discharge and dilution time shows linearity. The instantaneous contaminant input was sensitively affected by the dam discharge than the stagnant contaminant one in the river. If it is tried to flush with a temporally increased dam discharge, it should be understood the range of overflowed contaminant dispersion from main channel to tributary channel.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1317-1321
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• 2007

대표적인 하천수질모형으로는 정상상태 모형인 QUAL2E와 비정상상태 모형인 CE-QUAL-RIV1이 있다. 정상 및 비정상상태 수질모형의 용도는 QUAL2E가 월별 및 순별 장기수질예측에 매우 활용도가 높다고 하면 CE-QUAL-RIV1는 갑작스런 수질사고와 같은 단기수질모의 즉, 댐방류 플러싱효과를 분석하는 효과에 매우 최적화된 모형이라 할 수 있다. 대부분의 하천 수질 예측모델이 비정상상태 흐름이 아닌 정상상태 흐름만을 고려하여 개발되었기 때문에 댐이나 수문에 의해 차단된 조절하천에서 부정류 흐름상태를 고려한 수질예측 모델이 필요하다. 본 연구의 대상 유역인 서낙동강은 상류에는 대저수문, 하류에는 녹산수문이 위치하고 있으며, 이와 같은 수문들에 의하여 하천의 유량이 조절되는 호소형 하천으로 자연적인 하천흐름이 원활하지 않은 정체수역이다. 따라서 장기간 오염물질이 퇴적되고 있으며, 이로 말미암아 수질오염이 매우 심한 곳이기도 하다. 서낙동강은 대저수문 유입량과 녹산수문 방류량에 따른 하천수질의 영향이 크며, 개발욕구가 강한 경상남도 김해시와 부산광역시 강서구가 위치한 수계로서 현재 발생부하량 뿐만 아니라 장래에 예상되는 발생부하량도 매우 큰 하천이다. 이와 같은 문제를 해결하기 위한 가장 근원적인 방안은 적절한 수문운영을 통하여 수역 내의 유속을 적절히 조절하고, 이를 통하여 수질개선 효과를 확보하는 것이다. 본 연구에서는 정체수역인 서낙동강의 대저수문 유입량과 녹산수문 방류량을 수문운영에 따라 하천유량을 통하여 실측하고, 이로 인한 수질 변화를 체계적으로 조사함으로써 다수의 수문운영 조건에 따른 비정상상태에서의 서낙동강 본류의 수질을 실측하여, 수질이 좋은 낙동강 본류 원수의 유입에 따른 수질개선 효과와 녹산수문 방류에 의한 플러싱 효과를 정량적으로 평가해보고자 하였다. 본 연구에서 실측된 수문 유입량 및 방류량 증가에 따른 하천수질변화 결과를 비정상 하천수질모형을 통해 검증하고, 이를 활용하여 서낙동강의 수질 개선을 위한 적절한 유량 및 운영방안을 구축할 수 있을 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.478-478
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• 2016

4대강 다기능 보 건설 이후 보 내에서 발생하는 녹조를 효과적으로 저감시키기 위해 다양한 방법들이 시도되고 있으며, 댐-보 및 보-보간 연계운영 기법은 수량을 이용하여 대규모 구간에 걸쳐 효과적으로 조류를 저감시킬 수 있어 최근 주목을 받고 있다. 본 연구에서는 영산강 수계 승촌보와 죽산보를 대상으로 조류저감을 위한 다기능보 연계 운영 시나리오에 대해 2차원 모델링을 이용하여 효과를 분석하고 향후 조류저감을 위한 가동보 운영방안 수립에 적용하고자 수행되었다. 시뮬레이션 기간은 2014년 7월 1일부터 7월 15일까지 남조류가 다량으로 발생하였던 시기를 모의기간으로 하였다. 분석시나리오는 최근 낙동강에서 적용된 바 있는 pulse형 방류를 실시하여 수체내에 유속과 난류를 증가시키되 승촌보와 죽산보를 연계하여 순차적인 방류와 담수를 반복하는 형태를 가정하였다. 또한 방류 규모에 따라 수위 저하범위를 0.3~2 m로 차등 적용하여 조류저감 효과를 예측하였다. 예측결과 소수력 발전방류를 이용한 pulse형 방류 연계운영 CASE에서는 최대 승촌보 3.8% 죽산보 8.4%의 저감 효과가 예측되었다. 반면 소수력과 수문방류를 동시에 이용하여 수위 저하범위를 크게 적용하는 CASE에서는 승촌보에서 최대 12.5%, 죽산보 4.7%의 저감율로 방류규모 증가에도 불구하고 죽산보의 저감율은 증가하지 않는 결과를 나타내었다. 이는 상대적으로 저수량이 큰 죽산보에서 큰 폭으로 수위를 저하시킬 경우 수위회복 기간이 길어지고 이 시기에 조류가 성장할 수 있는 조건을 제공하기 때문인 것으로 판단된다. 따라서 조류의 발생 규모와 공간적 분포, 보별 유입지류 유입특성과 저수량 등 조류발생에 관련된 다양한 인자를 복합적으로 고려하여 효율적인 운영방안이 수립되어야 할 것으로 판단된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.42 no.2
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• pp.171-179
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• 2022

In this study, the characteristics of algae mitigation according to dam operation were quantitatively analyzed for Uiam Lake, where the Chuncheon Dam is located upstream of the main stream, Uiam Dam is located downstream, and Soyang Dam is located in the tributary stream. Nine dam operation scenarios were applied to the event of the summer of 2018 (at that time an algae alert occurred) using the EFDC model, which is capable of calculating three-dimensional hydrodynamics and water quality levels such as those associated with chlorophyll-a. The dam operation scenarios were set to generate a flushing effect via discharges in the form of pulse waves from the upstream dams and by lowering the water level at the downstream dam. At Uiam Lake, the flushing effect was different depending on the operation of the dam, and the amount of algae reduction at each point was different owing to topographic characteristics and the different base water temperatures from BukHan River and Soyang River. With regard to a point located on the left bank, it was predicted that the peak level of chlorophyll-a would be reduced by approximately 50 % or more upon pulsed discharge at 50 m³/s for three days at Soyang Dam. However, for the right bank, the amount of discharge from Soyang Dam had little effect on algae mitigation. Therefore, an appropriate dam operation could be effective for algae mitigation at specific points in the water body where large dams exist upstream and downstream, such as at Uiam Lake, in an emergency situation in which algal blooms rapidly.

• Journal of Korean Society on Water Environment
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• v.21 no.6
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• pp.609-616
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• 2005

A high ammonia nitrogen ($NH_3-N$) concentration has been recursively observed every winter season in Geum River, which hindered chemical treatment processes at a water treatment plant. A flushing discharge from Daecheong Dam was often considered to dilute $NH_3-N$, but information on the quantitative effect of flushing on the downstream water quality was limited. In this study, the impact of a short-term reservoir flushing on the downstream water quality was investigated through field experiments and unsteady water quality modeling. On November 22, 2003, the reservoir discharge was increased from $30m^3/sec$ to $200m^3/sec$ within 6 hours for the purpose of the experiment. The results showed that flushing flow tends to reduce downstream $NH_3-N$ concentrations considerably, but the effectiveness was limited by flushing amount and time. An unsteady river water quality model was applied to simulate the changes of nitrogen concentrations in response to reservoir flushing. The model showed very good performance in predicting the travel time of flushing flow and the effect of flushing discharge on the reduction of downstream $NH_3-N$ concentrations at Maepo and Geumnam site, but a significant discrepancy was observed at Gongju site.

• Journal of Korean Society on Water Environment
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• v.25 no.1
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• pp.48-57
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• 2009

A two-dimensional (2D), laterally-averaged hydrodynamic and water quality model, CE-QUAL-W2 was applied to evaluate the performance on simulating the effect of flushing from Daecheong Reservoir on the downstream water quality variations during the flushing events held on November, 2003 and March, 2008. The hydraulic and water quality simulation results were compared with field measurement data, as well as a one-dimensional (1D), unsteady model (KORIV1) that revealed limited capability in the previous study due to missing the resuspension process of river bottom sediments. The results showed that although the 2D model made satisfactory performance in reproducing the temporal variations of dissolved matters including phosphate, ammonia and nitrate, it revealed poor performance in simulating the increase of biological oxygen demand and suspended sediment (SS) concentrations during the passage of the flushing flow. The reason of the error was that the resuspension process of the 2D model is only the function of shear stress induced by wind. In reality, however, as shown by significant correlation between bottom shear stress ($\tau$) and observed SS concentration, the resuspension process can be significantly influenced by current velocity in the riverine system, especially during flushing event. The results indicate that the resuspension of river bottom materials should be incorporated into the water quality modeling processes if $\tau$ is greater than a critical shear stress (${\tau}_c$) for better simulation of flushing effect.