Journal of Environmental Impact Assessment (환경영향평가)

Korean Society of Environmental Impact Assessment (한국환경영향평가학회)
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Evaluation of Eutrophication and Control Alternatives in Sejong Weir using EFDC Model

EFDC 모델에 의한 세종보의 부영양화 및 제어대책 평가

  • Yun, Yeojeong (Department of Environmental Engineering, Chungbuk National University) ;
  • Jang, Eunji (Department of Environmental Engineering, Chungbuk National University) ;
  • Park, Hyung-Seok (Department of Environmental Engineering, Chungbuk National University) ;
  • Chung, Se-Woong (Department of Environmental Engineering, Chungbuk National University)
  • Received : 2018.08.31
  • Accepted : 2018.10.19
  • Published : 2018.12.31
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Abstract

The objectives of this study were to construct a three-dimensional (3D) hydrodynamic and water quality model (EFDC) for the river reach between the Daecheong dam and the Sejong weir, which are directly affected by Gap and Miho streams located in the middle of the Geum River, and to evaluate the trophic status and water quality improvement effect according to the flow control and pollutant load reduction scenarios. The EFDC model was calibrated with the field data including waterlevel, temperature and water quality collected from September, 2012 to April, 2013. The model showed a good agreement with the field data and adequately replicated the spatial and temporal variations of water surface elevation, temperature and water quality. Especially, it was confirmed that spatial distributions of nutrients and algae biomass have wide variation of transverse direction. Also, from the analysis of algal growth limiting factor, it was found that phosphorous loadings from Gap and Miho streams to Sejong weir induce eutrophication and algal bloom. The scenario of pollutant load reduction from Gap and Miho streams showed a significant effect on the improvement of water quality; 4.7~18.2% for Chl-a, 5.4~21.9% for TP at Cheongwon-1 site, and 4.2~ 17.3% for Chl-a and 4.7~19.4% for TP at Yeongi site. In addition, the eutrophication index value, identifying the tropic status of the river, was improved. Meanwhile, flow control of Daecheong Dam and Sejong weir showed little effect on the improvement of water quality; 1.5~2.4% for Chl-a, 2.5~ 3.8% for TP at Cheongwon-1 site, and 1.2~2.1% for Chl-a and 0.9~1.5% for TP at Yeongi site. Therefore, improvement of the water quality in Gap and Miho streams is essential and a prerequirement to meet the target water quality level of the study area.

본 연구의 목적은 금강의 중류에 위치한 갑천과 미호천의 직접적 영향을 받는 대청댐과 세종보 구간에 대해 3차원 수리-수질 해석 모델인 EFDC를 구축하고 모델을 보정한 후, 대청댐의 유량조절과 갑천 및 미호천의 부하량 삭감 시나리오에 따른 세종보 구간의 영양상태와 수질개선 효과를 평가하는데 있다. EFDC 모델은 2012년 9월부터 2013년 4월까지 측정된 수위, 수온 및 수질 변수를 사용하여 보정하였으며, 모델은 실측 수위의 변화와 수온 및 수질의 공간적, 시간적 변화를 재현했다. 연구결과, 연구대상 하천구간에서 영양염류와 조류 생체량의 공간 분포는 횡단 방향의 변화가 크다는 것을 확인 하였다. 또한 조류 성장 제한 요인 분석 결과, 갑천과 미호천에서 세종보에 이르는 인 부하가 부영양화와 녹조발생을 일으키는 요인으로 나타났다. 시나리오 모의결과, 갑천과 미호천의 오염 부하량 감축은 청원-1지점의 경우 Chl-a 4.7~18.2%, TP 5.4~21.9%, 연기지점은 Chl-a 4.2~17.3%, T-P 4.7~19.4% 저감하여 대상 하천의 수질 개선과 부영양 지수 개선에 큰 영향을 미치는 것으로 확인되었다. 한편, 대청댐 및 세종보의 유량을 조절하는 시나리오는 청원-1지점의 경우 Chl-a 1.5~2.4%, T-P 2.5~3.8%, 연기지점은 Chl-a 1.2~2.1%, T-P 0.9~1.5% 저감되어 수질 개선에 거의 영향을 미치지 않았다. 따라서 세종보의 녹조저감과 수질개선 목표를 달성하기 위해서는 갑천과 미호천의 수질 개선이 필수적이며 가장 중요한 선결 조건이라 판단된다.

Keywords

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Figure 1. Locations of the study area

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Figure 2. Numerical grid of (a) the main channel and the flood plain, (b) the orthogonality deviation

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Figure 3. Comparison of observed and simulated water temperature at (a) Geumbon-G and (b) Geumbon-H

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Figure 4. Comparisons of observed and simulated water quality variables at Yeongi

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Figure 5. The spatial distribution of (a) Total P, (b) Total N, (c) Chlorophyll a, (d) Algae

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Figure 6. Simulated water quality variations with the scenarios for pollutant load control from Gap Stream and Miho Stream

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Figure 7. Comparisons of Calson TSI for the pollutant load control scenarios at Cheongwon-1(a), Yeongi(b)

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Figure 8. Comparisons of the water quality variations under the scenarios of flow control from Daecheong Regulating Dam and Sejong Weir

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Figure 9. Comparisons of Calson TSI for the flow control scenarios at Cheongwon-1(a), Yeongi(b)

Table 1. The correlation equations between discharge and water temperature used for inflow water temperature estimation

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Table 2. Simulation scenarios of water quality control in the study site

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Table 3. Error statistics in the simulations of water surface elevation for one-layered and three-layered EFDC models

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Table 4. Error statistics in the simulations of water temperature for one-layered and three-layered EFDC models

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Table 5. Comparisons of errors in the water quality simulations between one-layered and three-layered EFDC models at Hyundo, Cheongwon-1, Yeongi

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Table 6. Reduced average water quality concentration compared to RUN0 for each scenario at Cheongwon-1 and Yeongi sites.

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Table 7. Comparisons of water residence time for the different flow control scenarios

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