Journal of Korea Water Resources Association (한국수자원학회논문집)

Korea Water Resources Association (한국수자원학회)
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Characterizing three-dimensional mixing process in river confluence using acoustical backscatter as surrogate of suspended sediment

부유사 지표로 초음파산란도를 활용한 합류부 3차원 수체혼합 특성 도출

  • Son, Geunsoo (Department of Civil & Environmental Engineering, Dankook University) ;
  • Kim, Dongsu (Department of Civil & Environmental Engineering, Dankook University) ;
  • Kwak, Sunghyun (Water Commission Support Department, Ministry of Environment) ;
  • Kim, Young Do (Department of Civil and Environmental Engineering, Myongji University) ;
  • Lyu, Siwan (Department of Civil Engineering, Changwon National University)
  • 손근수 (단국대학교 토목환경공학과) ;
  • 김동수 (단국대학교 토목환경공학과) ;
  • 곽성현 (환경부 물관리위원회 지원단) ;
  • 김영도 (명지대학교 토목환경공학과) ;
  • 류시완 (창원대학교 토목환경화공융합공학부)
  • Received : 2021.01.05
  • Accepted : 2021.01.26
  • Published : 2021.03.31
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Abstract

In order to characterize the mixing process of confluence for understanding the impacts of a river on the other river, it has been crucial to analyze the spatial mixing patterns for main streams depending on various inflow conditions of tributaries. However, most conventional studies have mostly relied upon hydraulic or water quality numerical models for understanding mixing pattern analysis of confluences, due to the difficulties to acquire a wide spatial range of in-situ data for characterizing mixing process. In this study, backscatters (or SNR) measured from ADCPs were particularly used to track sediment mixing assuming that it could be a surrogate to estimate the suspended sediment concentration. Raw backscatter data were corrected by considering the beam spreading and absorption by water. Also, an optical Laser diffraction instrument (LISST) was used to verify the method of acoustic backscatter and to collect the particle size distribution of main stream and tributary. In addition, image-based spatial distributions of sediment mixture in the confluence were monitored in various flow conditions by using an unmanned aerial vehicle (UAV), which were compared with the spatial distribution of acoustic backscatter. As results, we found that when acoustic backscatter by ADCPs were well processed, they could be proper indicators to identify the spatial patterns of the three-dimensional mixing process between two rivers. For this study, flow and sediment mixing characteristics were investigated in the confluence between Nakdong and Nam river.

하천 합류부는 두 하천이 만나 형성되는 지역으로 합류부 구간의 혼합 매커니즘을 이해하기 위해서는 지류의 다양한 유입조건에 따른 본류와의 수체혼합의 공간적인 패턴을 분석하는 것이 중요하다. 그러나, 대부분의 합류부 연구들은 실측을 통한 현장데이터를 획득하기 어렵기 때문에 수리 및 수질 수치모형을 통한 연구가 주로 수행되어 왔다. 본 연구에서는 지류와 본류의 합류의 혼합 현상을 규명하는 인자로 유속과 수심 등 기본적인 수리학적 인자들 외에 최근 하천 유사측정을 위해 부유사농도의 지표로 연구되고 있는 ADCP의 초음파산란도를 활용하여 합류부에서 상이한 유사특성을 가진 두 수체가 혼합되는 양상을 측정하여 합류부의 혼합 특성을 해석하고자 하였다. 초음파산란도는 부유사와 관련되는 인자로 SonTek ADCP 이동식으로 측정된 초음파산란도(SNR)자료를 빔퍼짐에 대한 보정, 물에 의한 흡수를 고려하여 보정한 후 3차원 혼합거동의 공간적인 분포를 도출하였다. 그리고 측정기간 중 드론(UAV), LISST를 이용하여 합류부의 혼합양상을 모니터링하여 초음파산란도를 이용한 분석결과와 비교하였다. 분석결과, ADCP로부터 제공되는 초음파산란도를 보정한 결과 합류부의 3차원적인 유사 혼합의 공간적 특성을 규명하는 데 적합한 인자라고 할 수 있었고, 상이한 본류와 지류의 유입을 고려하였을 때 다양한 혼합 거동을 분석하는데 지표로 사용이 가능함을 확인할 수 있었다. 따라서 본 연구에서는 남강과 낙동강의 합류부에 대해 초음파산란도를 활용하여 합류부의 혼합 특성을 분석하였다.

Keywords

References

  1. Ashmore, P., and Parker, G. (1983). "Confluence scour in coarse braided streams." Water Resources Research, Vol. 19, No. 2, pp. 392-402. https://doi.org/10.1029/WR019i002p00392
  2. Best, J.L. (1986). "The morphology of river channel confluences." Progress in Physical Geography, Vol. 10, No. 2, pp. 157-174. https://doi.org/10.1177/030913338601000201
  3. Best, J.L. (1987). "Flow dynamics at river channel confluences: Implications for sediment transport and bed morphology." Developments in fluvial sedimentology, Edited by Ethridge, F. G., Flores, R.M., and Harvey, M.D., SEPM Society for Sedimentary Geology: Tulsa, OK, U.S., Vol. 39, pp. 27-35.
  4. Best, J.L. (1988). "Sediment transport and bed morphology at river channel confluences." Sedimentology, Vol. 35, No. 3, pp. 481-498. https://doi.org/10.1111/j.1365-3091.1988.tb00999.x
  5. Best, J.L., and Ashworth, P.J. (1997). "Scour in large braided rivers and the recognition of sequence stratigraphic boundaries." Nature, Vol. 387, No. 6630, pp. 275-277. https://doi.org/10.1038/387275a0
  6. Best, J.L., and Rhoads, B.L. (2008). "Sediment transport, bed morphology and the sedimentology of river channel confluences." River confluences, tributaries and the fluvial network, Edited by Rice, S.P., Roy, A.G., and Rhoads, B.L., John Wiley & Sons, Chichester, UK, pp. 45-72.
  7. Best, J.L., and Roy, A.G. (1991). "Mixing-layer distortion at the confluence of channels of different depth." Nature, Vol. 350, No. 6317, pp. 411-413. https://doi.org/10.1038/350411a0
  8. Biron, P., De Serres, B., Roy, A.G., and Best, J.L. (1993). "Shear layer turbulence at an unequal depth confluence." Turbulence: Perspectives on flow and sediment transport, Edited by Clifford, N.J., French, J.R., and Hardisty, J., Wiley, Chichester, UK, pp. 197-214.
  9. Biron, P., Roy, A., Best, J.L., and Boyer, C.J. (1993). "Bed morphology and sedimentology at the confluence of unequal depth channels." Geomorphology, Vol. 8, No. 2-3, pp. 115-129. https://doi.org/10.1016/0169-555X(93)90032-W
  10. Biron, P.M., Richer, A., Kirkbride, A.D., Roy, A.G., and Han, S. (2002). "Spatial patterns of water surface topography at a river confluence." Earth Surface Processes and Landforms, Vol. 27, No. 9, pp. 913-928. https://doi.org/10.1002/esp.359
  11. Boyer, C., Roy, A.G., and 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, Vol. 111, No. F4, F04007.
  12. Bradbrook, K.F., Lane, S.N., and Richards, K.S. (2000). "Numerical simulation of three dimensional, time averaged flow structure at river channel confluences." Water Resources Research, Vol. 36, No. 9, pp. 2731-2746. https://doi.org/10.1029/2000WR900011
  13. Bradbrook, K.F., Lane, S.N., Richards, K.S., Biron, P.M., and Roy, A.G. (2001). "Role of bed discordance at asymmetrical river confluences." Journal of Hydraulic Engineering, Vol. 127, No. 5, pp. 351-368. https://doi.org/10.1061/(asce)0733-9429(2001)127:5(351)
  14. Dinehart, R.L. (2003). "Spatial analysis of ADCP data in streams." Proceedings of the Federal Interagency Sediment Monitoring Instrument and Analysis Research Workshop, USGS, Denver, CO, U.S., pp. 9-11.
  15. Dinehart, R.L., and Burau, J.R. (2005). "Averaged indicators of secondary flow in repeated acoustic Doppler current profiler crossings of bends." Water Resources Research, Vol. 41, No. 9, W09405. https://doi.org/10.1029/2005WR004050
  16. Gartner, J.W. (2004). "Estimating suspended solids concentrations from backscatter intensity measured by acoustic doppler current profiler in San Francisco Bay, California." Marine Geology, Vol. 211, No. 3-4, pp. 169-187. https://doi.org/10.1016/j.margeo.2004.07.001
  17. Guerrero, M., Rüther, N., Haun, S., and Baranya, S. (2017). "A combined use of acoustic and optical devices to investigate suspended sediment in rivers." Advances in Water Resources, Vol. 102, pp. 1-12. https://doi.org/10.1016/j.advwatres.2017.01.008
  18. Haun, S., Ruther, N., Baranya, S., and Guerrero, M. (2015). "Comparison of real time suspended sediment transport measurements in river environment by LISST instruments in stationary and moving operation mode." Flow Measurement and Instrumentation, Vol. 41, pp. 10-17. https://doi.org/10.1016/j.flowmeasinst.2014.10.009
  19. Hoitink, A.J.F., and Hoekstra, P. (2005). "Observations of suspended sediment from ADCP and OBS measurement s in a mud-dominated environment." Coastal Engineering, Vol. 52, No. 2, pp. 103-118. https://doi.org/10.1016/j.coastaleng.2004.09.005
  20. Kentworthy, S.T., and Rhoads, B.L. (1995). "Hydrologic control of spatial patterns of suspended sediment concentration at a stream confluence." Journal of Hydrology, Vol. 168, No. 1-4, pp. 251-263. https://doi.org/10.1016/0022-1694(94)02644-Q
  21. Landers, M.N. (2011). Fluvial suspended sediment characteristics by high-resolution, surrogate metrics of turbidity, laser-diffraction, acoustic backscatter, and acoustic attenuation Ph. D. dissertation, Georgia Institute of Technology, Atlanta, GA, U.S.
  22. McLelland, S.J., Ashworth, P.J., and Best, J.L. (1996). The origin and downstream development of coherent flow structures at channel junctions. Coherent flow structures in open channels, John Wiley & Sons, Chichester, UK, pp. 459-490.
  23. Mosley, M. (1982). "Scour depths in branch channel confluences, Ohau river, Otago, New Zealand." Transactions of the Institution of Professional Engineers New Zealand: Civil Engineering Section, Vol. 9, No. 1, p. 17.
  24. Mosley, M.P. (1975). An experimental study of channel confluence. Ph. D. dissertation, Colorado State University, Fort Collins, CO, U.S.
  25. Mosley, M.P. (1976). "An experimental study of channel confluences." The Journal of Geology, Vol. 84, No. 5, pp. 535-562. https://doi.org/10.1086/628230
  26. Parsons, D.R., Best, J.L., Lane, S.N., Hardy, R.J., Orfeo, O., and Kostaschuk, R. (2004). "The morphology, 3D flow structure and sediment dynamics of a large river confluence: The Rio Parana and Rio Paraguay, NE Argentina. In GRECO, M.; CARRAVETTA, A.; DELLAMORTE, R. River flow." Proceedings of the Second International Conference on Fluvial Hydraulics, Napoli, Italy, Vol. 1, pp. 43-48.
  27. Parsons, D.R., Best, J.L., Lane, S.N., Orfeo, O., Hardy, R.J., and Kostaschuk, R. (2007). "Form roughness and the absence of secondary flow in a large confluence-diffluence, Rio Parana, Argentina." Earth Surface Processes and Landforms: The Journal of the British Geomorphological Research Group, Vol. 32, No. 1, pp. 155-162. https://doi.org/10.1002/esp.1457
  28. Parsons, D.R., Best, J.L., Orfeo, O., Hardy, R.J., Kostaschuk, R., and Lane, S.N. (2005). "Morphology and flow fields of three dimensional dunes, Rio Parana, Argentina: Results from simultaneous multibeam echo sounding and acoustic Doppler current profiling." Journal of Geophysical Research: Earth Surface, Vol. 110, No. F4, F04S03.
  29. Reichel, G., and Nachtnebel, H.P. (1994). "Suspended sediment monitoring in a fluvial environment: Advantages and limitations applying an acoustic Doppler current profiler." Water Research, Vol. 28, No. 4, pp. 751-761. https://doi.org/10.1016/0043-1354(94)90083-3
  30. Stevaux, J.C., Amancio, A., de Carlos Etchebehere, M.L., and Fujita, R.H. (2009). "Flow structure and dynamics in large tropical River confluence: Example of the Ivai and Parana Rivers, southern Brazil." Geociencias, Vol. 28, No. 2, pp. 5-13.
  31. Szupiany, R.N., Amsler, M.L., Parsons, D.R., and Best, J.L. (2009). "Morphology, flow structure, and suspended bed sediment transport at two large braid bar confluences." Water Resources Research, Vol. 45, No. 5, W05415. https://doi.org/10.1029/2008WR007428
  32. Thevenot, M.M., and Kraus, N.C. (1993). "Comparison of acoustical and optical measurements of suspended material in the Chesapeake Estuary." Journal of Marine Environmental Engineering, Vol. 1, No. 1, pp. 65-79.
  33. Thorne, P.D., and Hardcastle, P.J. (1997). "Acoustic measurements of suspended sediments in turbulent currents and comparison with in-situ samples." The Journal of the Acoustical Society of America, Vol. 101, No. 5, pp. 2603-2614. https://doi.org/10.1121/1.418501
  34. Topping, D.J., Wright, S.A., Melis, T.S., and Rubin, D.M. (2007). "High-resolution measurements of suspended-sediment concentration and grain size in the Colorado River in Grand Canyon using a multi-frequency acoustic system." Proceedings of the 10th International Symposium on River Sedimentation, World Assoc. for Sediment. and Erosion Res., Moscow, Vol. 3, No. 470, p. 19.
  35. Turra, T.M., Marques, V.V., and Stevaux, J.C. (1999). "Confluence bar of the Sao Pedro Brook in the Parana River: Genesis and environmental importance." Boletim Goiano de Geografia, Vol. 19, No. 1, p. 8.
  36. Wall, G.R., Nystrom, E.A., and Litten, S. (2006). Use of an ADCP to compute suspended-sediment discharge in the tidal Hudson River. No. 2006-5055, USGS, NY, U.S.