Figure 6 | (a) Contaminant concentration distribution (gr/L) at 13 cm distance from channel bed; (b) contaminant concentration distribution (gr/L) at 17 cm distance from the channel bed.

이 소개 자료는 “Water Supply Vol 22 No 10″에 게재된 “Numerical simulation of pollution transport and hydrodynamic characteristics throughthe river confluence using FLOW 3D” 논문을 기반으로 작성되었습니다.

Figure 6 | (a) Contaminant concentration distribution (gr/L) at 13 cm distance from channel bed; (b) contaminant concentration distribution (gr/L) at 17 cm distance from the channel bed.
Figure 6 | (a) Contaminant concentration distribution (gr/L) at 13 cm distance from channel bed; (b) contaminant concentration distribution (gr/L) at 17 cm distance from the channel bed.

1. 연구 목적

주요 연구 질문:

  • 본 연구는 하천망의 지류를 통해 유입되는 오염 물질의 농도와 본류와 지류 간의 수위 차이가 오염 물질 혼합에 미치는 영향을 조사하는 것을 목표로 한다.
  • 특히, 90도 각도로 합류하는 지류와 본류를 대상으로 오염 물질의 혼합과 확산, 그리고 그에 따른 수리학적 현상을 분석하고자 한다.

기존 연구의 한계:

  • 기존의 합류점에서의 침식 및 퇴적 과정에 대한 연구는 많았으나, 오염 물질의 혼합 및 분포와 관련된 효과적인 매개 변수에 대한 정보는 여전히 부족하다.
  • 따라서 본 연구는 오염 물질 혼합 및 분포에 대한 이해를 높이고, 오염 영향을 줄이기 위한 수위 조절 구조의 필요성을 강조하고자 한다.

2. 연구 방법

수치 모델링:

  • 본 연구에서는 FLOW 3D 수치 모델을 사용하여 하천 합류점에서의 오염 물질 수송 및 수리학적 특성을 시뮬레이션하였다.
  • 모델은 주류 7m, 폭 1m, 지류 길이 1.8m, 폭 1m, 높이 1m의 3차원 형상으로 설계되었으며, 합류점 부근에는 정확도를 높이기 위해 중첩 격자(nested mesh)를 사용하였다.

경계 조건:

  • 주류와 지류의 상류에는 일정한 수압 조건(constant pressure)을 적용하였고, 주류 하류에는 자유 유출 조건(free outlet)을 설정하였다.
  • 중첩 격자에는 다양한 방향으로부터의 경계 조건 유입을 고려하여 대칭 조건(symmetry boundary condition)을 적용하였다.

3. 주요 결과

수위 차이와 혼합:

  • 지류와 본류 간의 수위 차이가 증가할수록 횡방향 혼합이 더 빠르게 일어나는 것을 확인하였다.
  • 수위 차이가 없는 경우에는 혼합 곡선 추출 방법을 통해 횡방향 혼합이 완료되는 하천 길이를 파악하였다.

재순환 영역의 특징:

  • 합류점의 재순환 영역에서 가장 높은 오염 물질 농도와 유속 벡터가 관찰되었으며, 2차 흐름이 발생하여 오염 물질을 일시적으로 가두는 현상을 확인하였다.
  • 이 영역은 높은 전단 속도, 난류 에너지, 난류 강도를 가지며, 때로는 음의 회전 흐름으로 인해 낮은 종방향 유속을 나타냈다.

4. 결론

수위 조절의 중요성:

  • 수위 차이는 지류에서 본류로 오염 물질이 유입되는 데 가장 중요한 요인이며, 본류의 오염 영향을 줄이기 위해 합류점에 수위 조절 구조를 설치하는 것이 필요하다.
  • 본 연구에서 관찰된 합류점에서의 흐름 패턴과 영역들은 기존 연구와 일치했으며, 각 영역이 오염 물질 확산에 미치는 영향을 논의하였다.

향후 연구 방향:

  • 재순환 영역에서 생성되는 와류는 오염 물질을 일시적으로 포획하고 농도를 증가시키는 데 효과적인 매개 변수이다.
  • 지류에서 홍수 흐름이 발생하여 지류의 수위가 본류보다 높아지는 경우에만 합류점 상류에서 오염 농도 증가가 관찰되었다.
Figure 1 | Conceptual model of different flow pattern zones through the river confluence.
Figure 1 | Conceptual model of different flow pattern zones through the river confluence.
Figure 6 | (a) Contaminant concentration distribution (gr/L) at 13 cm distance from channel bed; (b) contaminant concentration distribution (gr/L) at 17 cm distance from the channel bed.
Figure 6 | (a) Contaminant concentration distribution (gr/L) at 13 cm distance from channel bed; (b) contaminant concentration distribution (gr/L) at 17 cm distance from the channel bed.

Reference

  • Alizadeh, L. & Fernandes, J. 2021 Turbulent flow structure in a confluence: influence of tributaries width and discharge ratios. Water 13 (4), 465.
  • Ashmore, P. E. 1991 How do gravel-bed rivers braid? Canadian Journal of Earth Sciences 28 (3), 326-341.
  • Ashmore, P. & Gardner, J. 2008 Unconfined confluences in braided rivers. In Rice, S. P., Roy, A. G. & Rhoads, B. L. (eds) River Confluences, Tributaries and the Fluvial network John Wiley & Sons, Chichester, UK, pp. 119–147.
  • Benda, L., Poff, N. L., Miller, D., Dunne, T., Reeves, G., Pess, G. & Pollock, M. 2004 The network dynamics hypothesis: how channel networks structure riverine habitats. BioScience 54 (5), 413–427.
  • Best, J. L. 1986 The morphology of river channel confluences. Progress in Physical Geography 10 (2), 157–174.
  • Best, J. L. 1987 Flow Dynamics at River Channel Confluences: Implications for Sediment Transport and Bed Morphology. SEPM Special Publication, Tulsa, OK, USA.
  • Best, J. L. 1988 Sediment transport and bed morphology at river channel confluences. Sedimentology 35 (3), 481–498.
  • Best, J. L. & Ashworth, P. J. 1997 Scour in large braided rivers and the recognition of sequence stratigraphic boundaries. Nature 387 (6630), 275–277.
  • Best, J. L. & Reid, I. 1984 Separation zone at open-channel junctions. Journal of Hydraulic Engineering 110 (11), 1588–1594.
  • Best, J. L. & Rhoads, B. L. 2008 Sediment transport, bed morphology and the sedimentology of river channel confluences. In Rice, S. P., Roy, A. G. & Rhoads, B. L. (eds) River Confluences, Tributaries and the Fluvial Network John Wiley & Son, Chichester, UK, pp. 45–72.
  • Best, J. L. & Roy, A. G. 1991 Mixing-layer distortion at the confluence of channels of different depth. Nature 350 (6317), 411–413.
  • Biron, P. M. & Lane, S. N. 2008 Modelling hydraulics and sediment transport at river confluences. In Rice, S. P., Roy, A. G. & Rhoads, B. L. (eds) River Confluences, Tributaries and the Fluvial Network John Wiley & Sons, Chichester, UK, pp. 17–43.
  • Biron, P., Best, J. L. & Roy, A. G. 1996a Effects of bed discordance on flow dynamics at open channel confluences. Journal of Hydraulic Engineering 122 (12), 676–682.
  • Biron, P., Roy, A. & Best, J. 1996b Turbulent flow structure at concordant and discordant open-channel confluences. Experiments in Fluids 21 (6), 437–446.
  • Biron, P. M., Ramamurthy, A. S. & Han, S. 2004 Three-dimensional numerical modeling of mixing at river confluences. Journal of Hydraulic Engineering 130 (3), 243–253.
  • Biron, P. M., Buffin-Bélanger, T. & Martel, N. 2018 Mixing processes at an ice-covered river confluence. In E3S Web of Conferences.
  • Boyer, C., Roy, A. G. & Best, J. L. 2006 Dynamics of a river channel confluence with discordant beds: flow turbulence, bed load sediment transport, and bed morphology. Journal of Geophysical Research: Earth Surface 111 (F4), 1–22.
  • Bridge, J. S. 1993 The interaction between channel geometry, water flow, sediment transport and deposition in braided rivers. Geological Society, London, Special Publications 75 (1), 13–71.
  • Chabokpour, J. & Samadi, A. 2020 Analytical solution of reactive hybrid cells in series (HCIS) model for pollution transport through the rivers. Hydrological Sciences Journal 65 (14), 2499–2507.
  • Chabokpour, J., Azamathulla, H. M., Azhdan, Y. & Ziaei, M. 2020a Study of pollution transport through the river confluences by derivation of an analytical model. Water Science and Technology 82 (10), 2062–2075.
  • Chabokpour, J., Chaplot, B., Dasineh, M., Ghaderi, A. & Azamathulla, H. M. 2020b Functioning of the multilinear lag-cascade flood routing model as a means of transporting pollutants in the river. Water Supply 20 (7), 2845–2857.
  • Ettema, R. 2008 Management of confluences. In Rice, S. P., Roy, A. G. & Rhoads, B. L. (eds) River Confluences, Tributaries and the Fluvial Network John Wiley & Sons, Chichester, UK, pp. 93–118.
  • Fielding, C. R. & Gupta, A. 2008 Sedimentology and stratigraphy of large river deposits: recognition in the ancient record, and distinction from ‘incised valley fills’. In Gupta, A. (ed.) Large Rivers: Geomorphology and Management John Wiley & Sons, Chichester, UK, pp. 97–113.
  • Gaudet, J. M. & Roy, A. G. 1995 Effect of bed morphology on flow mixing length at river confluences. Nature 373 (6510), 138–139.
  • Ghostine, R., Vazquez, J., Terfous, A., Rivière, N., Ghenaim, A. & Mosé, R. 2013 A comparative study of 1D and 2D approaches for simulating flows at right angled dividing junctions. Applied Mathematics and Computation 219 (10), 5070–5082.
  • Holbrook, J. M. & Bhattacharya, J. P. 2012 Reappraisal of the sequence boundary in time and space: case and considerations for an SU (subaerial unconformity) that is not a sediment bypass surface, a time barrier, or an unconformity. Earth-Science Reviews 113 (3–4), 271–302.
  • Ikinciogullari, E., Emiroglu, M. E. & Aydin, M. C. 2022 Comparison of scour properties of classical and Trapezoidal Labyrinth Weirs. Arabian Journal for Science and Engineering 47, 4023–4040.
  • Konsoer, K. M. & Rhoads, B. L. 2014 Spatial–temporal structure of mixing interface turbulence at two large river confluences. Environmental Fluid Mechanics 14 (5), 1043–1070.
  • Lane, S. N., Parsons, D. R., Best, J. L., Orfeo, O., Kostaschuk, R. & Hardy, R. J. 2008 Causes of rapid mixing at a junction of two large rivers: Río Paraná and Río Paraguay, Argentina. Journal of Geophysical Research: Earth Surface 113 (F2), 1–16.
  • Liu, X., Li, L., Hua, Z., Tu, Q., Yang, T. & Zhang, Y. 2019 Flow dynamics and contaminant transport in Y-shaped river channel confluences. International Journal of Environmental Research and Public Health 16 (4), 572.
  • Lyubimova, T. P., Lepikhin, A. P., Parshakova, Y. N., Kolchanov, V. Y., Gualtieri, C., Roux, B. & Lane, S. N. 2020 A numerical study of the influence of channel-scale secondary circulation on mixing processes downstream of river junctions. Water 12 (11), 2969.
  • Mackay, J. R. 1970 Lateral mixing of the Liard and Mackenzie rivers downstream from their confluence. Canadian Journal of Earth Sciences 7 (1), 111–124.
  • Mosley, M. P. 1976 An experimental study of channel confluences. The Journal of Geology 84 (5), 535–562.
  • Parsons, D. R., Best, J. L., Lane, S. N., Orfeo, O., Hardy, R. J. & Kostaschuk, R. 2007 Form roughness and the absence of secondary flow in a large confluence–diffluence, Rio Paraná, Argentina. Earth Surface Processes and Landforms: The Journal of the British Geomorphological Research Group 32 (1), 155–162.
  • Ramamurthy, A. S., Carballada, L. B. & Tran, D. M. 1988 Combining open channel flow at right angled junctions. Journal of Hydraulic Engineering 114 (12), 1449–1460.
  • Ramón, C. L., Hoyer, A. B., Armengol, J., Dolz, J. & Rueda, F. J. 2013 Mixing and circulation at the confluence of two rivers entering a meandering reservoir. Water Resources Research 49 (3), 1429–1445.
  • Rhoads, B. L. & Kenworthy, S. T. 1998 Time-averaged flow structure in the central region of a stream confluence. Earth Surface Processes and Landforms: The Journal of the British Geomorphological Group 23 (2), 171–191.
  • Rhoads, B. L. & Sukhodolov, A. N. 2001 Field investigation of three-dimensional flow structure at stream confluences: 1. Thermal mixing and time-averaged velocities. Water Resources Research 37 (9), 2393–2410.
  • Rhoads, B. L. & Sukhodolov, A. N. 2008 Lateral momentum flux and the spatial evolution of flow within a confluence mixing interface. Water Resources Research 44 (8), 1–17.
  • Richards, K. 1980 A note on changes in channel geometry at tributary junctions. Water Resources Research 16 (1), 241–244.
  • Riley, J. 2013 The Fluvial Dynamics of Confluent Meander Bends. University of Illinois at Urbana, Champaign, IL, USA.
  • Sambrook Smith, G. H., Ashworth, P. J., Best, J. L., Woodward, J. & Simpson, C. J. 2005 The morphology and facies of sandy braided rivers: some considerations of scale invariance. Fluvial Sedimentology VII, 145–158.
  • Schindfessel, L., Creëlle, S. & De Mulder, T. 2015 Flow patterns in an open channel confluence with increasingly dominant tributary inflow. Water 7 (9), 4724–4751.
  • Shit, P. K. & Maiti, R. 2013 Confluence dynamics in an ephemeral gully basin (A case study at Rangamati, Paschim Medinipur, West Bengal, India). Research Journal of Applied Sciences, Engineering and Technology 15 (5), 3895–3911.
  • Shin, J., Lee, S. & Park, I. 2021 Analysis of storage effects in the recirculation zone based on the junction angle of channel confluence. Applied Sciences 11 (24), 11607.
  • Song, C. G., Seo, I. W. & Do Kim, Y. 2012 Analysis of secondary current effect in the modeling of shallow flow in open channels. Advances in Water Resources 41, 29–48.
  • Tang, H., Zhang, H. & Yuan, S. 2018 Hydrodynamics and contaminant transport on a degraded bed at a 90-degree channel confluence. Environmental Fluid Mechanics 18 (2), 443–463.
  • Van Rooijen, E., Mosselman, E., Sloff, K. & Uijttewaal, W. 2020 The effect of small density differences at river confluences. Water 12 (11), 3084.
  • Webber, N. B. & Greated, C. 1966 An investigation of flow behavior at the junction of rectangular channels. Proceedings of the Institution of Civil Engineers 34 (3), 321–334.
  • Xiao, Y., Xia, Y., Yuan, S. & Tang, H. 2019 Distribution of phosphorus in bed sediment at confluences responding to hydrodynamics. Proceedings of the Institution of Civil Engineers-Water Management, 149–162.
  • Yu, Q., Yuan, S. & Rennie, C. D. 2020 Experiments on the morphodynamics of open channel confluences: implications for the accumulation of contaminated sediments. Journal of Geophysical Research: Earth Surface 125 (9), 1–25. e2019JF005438.
  • Yuan, S., Tang, H., Xiao, Y., Qiu, X., Zhang, H. & Yu, D. 2016 Turbulent flow structure at a 90-degree open channel confluence: accounting for the distortion of the shear layer. Journal of Hydro-Environment Research 12, 130–147.
  • Yuan, S., Tang, H., Xiao, Y., Chen, X., Xia, Y. & Jiang, Z. 2018 Spatial variability of phosphorus adsorption in surface sediment at channel confluences: field and laboratory experimental evidence. Journal of Hydro-Environment Research 18, 25–36.
  • Yuan, S., Tang, H., Li, K., Xu, L., Xiao, Y., Gualtieri, C., Rennie, C. & Melville, B. 2021 Hydrodynamics, sediment transport and morphological features at the confluence between the Yangtze River and the Poyang Lake. Water Resources Research 57 (3), 1–21. e2020WR028284.
  • Zhang, T., Feng, M., Chen, K. & Cai, Y. 2020 Spatiotemporal distributions and mixing dynamics of characteristic contaminants at a large asymmetric confluence in northern China. Journal of Hydrology 591, 125583.