Evaluation of longitudinal / transverse dispersion coefficients and prediction of concentration at river confluence in two-dimensional solute transport analysis

Kyong Oh Baek; Dong Yeol Lee; Il Won Seo

doi:10.3741/JKWRA.2021.54.4.255

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2021 Vol.54, Issue 4 Preview Page Next Page

Research Article

Evaluation of longitudinal / transverse dispersion coefficients and prediction of concentration at river confluence in two-dimensional solute transport analysis 2차원 혼합 해석시 합류부에서 종/횡분산계수 산정 및 농도예측 기여도 평가

30 April 2021. pp. 255-264

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Abstract

Mixing characteristics of the longitudinal/transverse directions is inevitably different in rivers with a large aspect ratio. Particularly complex mixing behavior occurs in the area of the confluence where tributaries and main streams of different concentrations meet, and it is necessary to accurately implement such mixing characteristics by assigning appropriate values of longitudinal and transverse dispersion coefficients. In this study, the mixing behavior according to the different values in the longitudinal/transverse dispersion coefficient was analyzed by using the two-dimensional model (RAMS) at the confluence where three rivers (the Nakdong River, the Geumho River, and the Jincheon Creek) meet. Firstly the longitudinal and transverse dispersion coefficients were calibrated and validated based on the electrical conductivity (EC) acquired from field measurements. Through the calibration and validation, it was shown that the longitudinal dispersion coefficient was about 25 times larger than the transverse dispersion coefficient in this area. Then assuming that a hazardous substance (phenol) was introduced into the upper boundaries of the Geumho River and the Jincheon Creek due to an accidental spill, the concentration of phenol arrived at the water intake facilities was calculated by using the calibrated numerical model. As a result, characteristics such as time and peak concentration of hazardous substances reaching the water intake facilities were very different according to the ratio of the longitudinal/transverse dispersion coefficient values. In fact, this is an example that the selection of the dispersion coefficients can affect decision-making such as stopping water intake during an appropriate time at the facilities, when if phenol is introduced into a river. In the end, when using a two-dimensional mixing model in a river, it was confirmed that the provision of an appropriate value of the longitudinal/transverse dispersion coefficient was an important factor.

Keywords

Two-dimensional solute transport

Confluence

Longitudinal and transverse dispersion coefficients

Accidental spill

평면 2차원 혼합 해석시 연안이나 호소의 경우 수평방향 분산이 균일하다고 볼 수 있지만, 종/횡의 비율이 세장(細長)한 하천의 경우 종/횡 방향의 혼합 특성은 상이할 수 밖에 없다. 특히 농도가 서로 다른 지류와 본류가 만나는 합류부 일대는 복잡한 혼합 양상이 발생하므로, 수치모형을 활용할 경우 종분산과 횡분산계수를 분리하여 각각 적절한 값을 부여함으로써 재현성을 높일 수 있다. 본 연구에서는 기저농도가 서로 다른 세 하천(낙동강, 금호강, 진천천)이 만나는 낙동강 강정고령보 ~ 달성보 일대를 대상 구간으로 삼아, 2차원 하천해석 소프트웨어인 RAMS를 활용하여 종/횡분산계수 값의 차이에 따른 2차원적 혼합특성을 분석해 보았다. 이를 위해 먼저 실측을 통해 취득한 전기전도도(EC) 자료를 기반으로 종분산 및 횡분산계수를 각각 검/보정하였다. 검보정 결과 이 구간에서는 종분산계수가 횡분산계수에 비해 약 25배 크다는 것을 확인하였다. 다음으로 금호강 및 진천천 상류단에 수질사고로 유해물질(페놀)이 유입되었을 경우를 가정하여 매개변수(분산계수)가 검/보정된 모형(종/횡분산계수를 25배 비율로 부여)으로 하류 양수장(우암/월성 양수장)에 도달하는 유해물질의 농도를 예측해 보았다. 또한 분산계수가 검보정되지 않은 모형(종/횡분산계수를 동일한 값으로 부여)으로 유해물질의 양수장 도달 농도를 계산하였다. 그 결과 종/횡분산계수값의 비율에 따라 유해물질이 양수장에 도달하는 시간, 도달된 물질의 첨두농도 등이 매우 다르게 나타났다. 이는 실제로 페놀이 유입된다면 취/양수장 등에서 적정시간 취수중단 등의 조치를 취해야 하는데, 해석모형의 분산계수가 의사결정에 큰 영향을 미칠 수 있음을 보여준 사례라 할 수 있다. 향후 수질사고 예측/대응 시스템을 구축하는 경우, 계산엔진으로 활용되는 모형의 분산계수 결정에 유의해야 함을 환기시킨다.

키워드

2차원 혼합

합류부

종/횡 분산계수

수질사고

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Information

Publisher :KOREA WATER RESOURECES ASSOCIATION
Publisher(Ko) :한국수자원학회
Journal Title :Journal of Korea Water Resources Association
Journal Title(Ko) :한국수자원학회 논문집
Volume : 54
No :4
Pages :255-264
Received Date : 2020-12-29
Revised Date : 2021-03-05
Accepted Date : 2021-03-05
DOI :https://doi.org/10.3741/JKWRA.2021.54.4.255

Journal of Korea Water Resources Association ISSN:2799-8746(Print) 2799-8754(Online) 한국수자원학회 논문집

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