Journal of Korea Water Resources Association (한국수자원학회논문집)

Korea Water Resources Association (한국수자원학회)
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Numerical analysis of morphological changes by opening gates of Sejong Weir

보 개방에 의한 하도의 지형변화 과정 수치모의 분석(세종보를 중심으로)

  • Jang, Chang-Lae (Department of Civil Engineering, Korea National University of Transportation) ;
  • Baek, Tae Hyo (Department of Civil Engineering, Korea National University of Transportation) ;
  • Kang, Taeun (Department of Civil Engineering, Korea National University of Transportation) ;
  • Ock, Giyoung (Department of Ecosystem Assessment, National Institute of Ecology)
  • 장창래 (한국교통대학교 토목공학과) ;
  • 박태효 (한국교통대학교 토목공학과) ;
  • 강태운 (한국교통대학교 토목공학과) ;
  • 옥기영 (국립생태원 생태평가연구실)
  • Received : 2021.04.26
  • Accepted : 2021.06.15
  • Published : 2021.08.31
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Abstract

In this study, a two-dimensional numerical model (Nays2DH) was applied to analyze the process of morphological changes in the river channel bed depending on the changes in the amount of flooding after fully opening the Sejong weir, which was constructed upstream of the Geum River. For this, numerical simulations were performed by assuming the flow conditions, such as a non-uniform flow (NF), unsteady flows (single flood event, SF), and a continuous flood event (CF). Here, in the cases of the SF and CF, the normalized hydrograph was calculated from real flood events, and then the hydrograph was reconfigured by the peak flow discharge according to the scenario, and then it was employed as the flow discharge at the upstream boundary condition. In this study, to quantitatively evaluate the morphological changes, we analyzed the time changes in the bed deformation the bed relief index (BRI), and we compared the aerial photographs of the study area and the numerical simulation results. As simulation results of the NF, when the steady flow discharge increases, the ratio of lower width to depth decreases and the speed of bar migration increases. The BRI initially increases, but the amount of change decreased with time. In addition, when the steady flow discharge increases, the BRI increased. In the case of SF, the speed of bar migration decreased with the change of the flow discharge. In terms of the morphological response to the peak flood discharge, the time lag also indicated. In other words, in the SF, the change of channel bed indicates a phase lag with respect to the hydraulic condition. In the result of numerical simulation of CF, the speed of bar migration depending on the peak flood discharges decreased exponentially despite the repeated flood occurrences. In addition, as in the result of SF, the phase lag indicated, and the speed of bar migration decreased exponentially. The BRI increased with time changes, but the rate of increase in the BRI was modest despite the continuous peak flooding. Through this study, the morphological changes based on the hydrological characteristics of the river were analyzed numerically, and the methodology suggested that a quantitative prediction for the river bed change according to the flow characteristic can be applied to the field.

본 연구에서는 2차원 수치모형(Nays2DH)을 적용하여 금강에 건설된 세종보를 중심으로 보 개방 후에 홍수량 변화에 의한 하도의 지형변화 과정을 분석하였다. 이를 위해 부등류, 부정류(단일사상), 연속홍수사상을 수문특성을 반영한 흐름조건으로 수치모의를 수행하였다. 부등류 수치모의 조건은 유황에 따른 정상유량으로 상류단 경계조건을 가정하였다. 부정류와 연속홍수사상의 경우에는 실제 홍수사상들로부터 정규 수문곡선 (normalized hydrograph)을 산정 한 후, 시나리오에 따른 첨두유량으로 정규 수문곡선을 재구성하여 상류단 유량으로 가정하였다. 본 연구에서는 지형학적 변화를 정량적으로 평가하기 위해 하상기복지수(BRI)를 산정하여 시간에 따른 하상변동을 분석하였으며, 연구지역의 항공사진과 수치모의 결과를 정성적으로 비교하였다. 부등류 수치모의 결과, 각 유황별 유량이 증가하면 하폭 대 수심의 비는 감소하고, 사주의 이동속도는 증가하였다. 하상기복지수는 초기에는 증가하지만, 시간이 증가함에 따라 변화량이 작아졌다. 또한 유량이 증가하면 하상기 복지수가 증가했다. 부정류 수치모의 결과 사주의 이동속도는 유량의 변화에 따라 감소했다. 또한 첨두홍수에 대한 지형적 반응에서 시간지체(time lag)가 발생했다. 즉, 부정류에서는 하상고의 변화는 수리학적 조건에 대하여 위상지연(Phase lag) 이 나타났다. 연속홍수사상 발생에 의한 부정류 수치모의 결과에서는 각각 첨두홍수 발생에 따른 사주의 이동속도는 홍수발생이 반복됨에도 불구하고 급격하게 감소했다. 또한 부정류 수치모의 결과와 마찬가지로 위상지연이 나타났으며 사주의 이동속도는 지수적으로 감소하는 특성을 보였다. 하상기복지수는 시간경과에 따라 증가하였으나, 첨두홍수가 연속으로 발생하였음에도 불구하고 하상기복지수의 증가율은 완만하였다. 본 연구를 통해 하천의 수문특성을 반영한 지형변화 과정을 수치모의를 수행하여 분석하였으며, 이를 통해 흐름특성에 따른 하상변동의 정량적인 예측모의를 현장에 적용할 수 있는 방법을 제시할 수 있을 것으로 판단된다.

Keywords

Acknowledgement

이 논문은 2021년도 정부(교육부)의 재원으로 한국연구재단의 지원을 받아 수행된 기초연구사업임(2021R1I1A3048276). 항공사진을 제공해 주신K-water의 김호준박사님께감사의 말씀을 드립니다.

References

  1. Ashida, K., and Michiue, M. (1972). "Study on hydraulic resistance and bedload transport raten alluvial streams." Transactions, Japan Society of Civil Engineering, Vol. 206, pp. 59-69. (in Japanese) https://doi.org/10.2208/jscej1969.1972.206_59
  2. Chai, T., and Draxler RR. (2014). "Root mean square error (RMSE) or mean absolute error (MAE)? Arguments against avoiding RMSE in the literature." Geoscientific Model Development, Vol. 7, No . 3, pp. 1247-1250. https://doi.org/10.5194/gmd-7-1247-2014
  3. Colombini, M., Seminara, G., and Tubino, M. (1987). "Finite-amplitude alternate bars." Journal of Fluid Mechanics, Vol. 181, pp. 213-232. doi: 10.1017/S0022112087002064
  4. Crosato, A., and Mosseman, E. (2009). "Simple physics-based predictor for the number of river bars and the transition between meandering and braiding." Water Resources Research, Vol. 45, W03424. doi:10.1029/2008WR007242
  5. East, A.E., Pess, G.R., Bountry, J.A., Magirl, C.S., Ritchie, A.C., Logan, J.B., Randle, T.J., Mastin, M.C., Minear, J.T., Duda, J.J., and Liermann, M.C.(2015). "Large-scale dam removal on the Elwha River." Geomorphology, Vol. 228, pp. 765-786. https://doi.org/10.1016/j.geomorph.2014.08.028
  6. Engelund, F. (1974). "Flow and bed topography in channel beds." Journal of the Hydraulics Division, ASCE, Vol. 100, No. 11, pp. 1631-1648. https://doi.org/10.1061/JYCEAJ.0004109
  7. Garcia, M., and Nino, Y. (1993). "Dynamique des bancs de sediments dans des chenaux droits et a meandres: Essais sur le phenomene de resonance." Journal of Hydraulic Research, Vol. 31, No. 6, pp. 739-761. https://doi.org/10.1080/00221689309498815
  8. Hoey, T.B., and Sutherland, A.J. (1991). "Channel morphology and bedload pulses in braided rivers: A laboratory study." Earth Surface Processes and Landforms, Vol. 16, No. 5, pp. 447-462. https://doi.org/10.1002/esp.3290160506
  9. Im, D., Kang, H., Kim, K.-H., and Choi., S.-U. (2011). "Changes of river morphology and physical fish habitat following weir removal." Ecological Engineering, Vol. 37, pp. 883-892. https://doi.org/10.1016/j.ecoleng.2011.01.005
  10. Jang, C.-L.(2013). "Dynamic characteristics of multiple bars in the channels with erodible banks." Journal of Korea Water Resources Association, Vol. 46, No. 1, pp. 25-34. doi: 10.3741/JKWRA.2013.46.1.25. (in Korean)
  11. Jang, C.-L.(2014). "Numerical experiments of the behavior of bars in the channels with periodic variable width." Journal of Korea Water Resources Association, Vol. 47, No. 1, pp. 37-47. doi:10.3741/JKWRA.2014.47.1.37
  12. Jang, C-L., and Lee, K.S. (2020). "Experimental analysis on the channel adjustment processes by weir removal." Journal of Korea Water Resources Association, Vol. 53, No. 11, pp. 951-960. doi: 10.3741/JKWRA.2020.53.11.951. (in Korean)
  13. Jang, C.-L., and Shimizu, Y. (2005). "Numerical simulations of the behavior of alternate bars with different bank strength." Journal of Hydraulic Research, Vol. 43, No. 6, pp. 595-611. https://doi.org/10.1080/00221680509500379
  14. Jang, C.-L., and Shimizu, Y. (2007). "Vegetation effects on the morphological behavior of alluvial channels." Journal of Hydraulic Research, Vol. 45 No. 6, pp. 763-772. https://doi.org/10.1080/00221686.2007.9521814
  15. Kang, K.-H., Jang, C.-L., Lee, G. H.., and Jung, K. (2016). "Numerical analysis of the morphological changes by sediment supply at the downstream channel of Youngju dam." Journal of Korea Water Resources Association, Vol. 49, No. 8, pp. 693-705. doi: 10.3741/JKWRA.2016.49.8.693 (in Korean)
  16. Korea Institute of Civil Engineering and Building Technology (KICT) (2008). Guideline for small dam removal. (in Korean)
  17. Ministry of Environment (ME) (2019). Monitoring report of weir operation in the 16 weirs of the 4 major rivers. (in Korean)
  18. Ock, G., Choi, M., Kim, J.-C., Park, H.-G., and Han, J.-H. (2020). "Evaluation of habitat diversity changes by weir operation of the Sejongbo Weir in Geum River using high-resolution aerial photographs." Ecology and Resilient Infrastructure, Vol. 7, No. 4, pp. 366-373. doi: 10.17820/eri.2020.7.4.366. (in Korean)
  19. Ritchie, A.C., Warrick, J,A., East, A.E., Magirl, C.S., Stevens, A.W., Bountry, J.A., Randle, T.J., Curran, C.A., Hilldale, R.C., Duda, J.J., Gelfenbaum, G.R., Miller, J.M., Pess, G.R., Foley, M,M., McCoy, R., and Ogston, A.S. (2018). "Morphodynamic evolution following sediment release from the world's largest dam removal." Scientific Reports, Vol. 8, No. 1. doi: 10.1038/s41598-018-30817-8
  20. Seminara, G., and Tubino, M. (1989). "Alternate bars and meandering: Free, forced and mixed interactions." River Meandering, Edited by Ikeda, S., and Parker, G., AGU Water Resources Monograph 12, AGU, Washington, D.C., U.S., pp. 267-320.
  21. Shimizu, Y., Nelson, J., Kattia, A.F., Asahi, K., Giri, S., Inoue, T., Iwasaki, T., Jang, C., Kang, T., Kimura, I., Kyuka, T., Mishra, J., Nabi, M., Patsinghasanee, S., Yamaguchi, S. (2020). "Advances in computational morphodynamics using the International River Interface Cooperative (iRIC) Software." Earth Surface Processes and Landforms, Vol. 45, No. 1, pp. 11-37. doi: 10.1002/esp.4653
  22. Tubino, M., (1991). "Growth of alternate bars in unsteady flow." Water Resources Research, Vol. 27, No. 1, pp. 37-52. https://doi.org/10.1029/90WR01699
  23. Watanabe, A., Fukuoka, S., Yasutake, Y., and Kawaguchi, H. (2001). "Method for arranging vegetation grions at bends for control of bed variation." Collection of Papers on River Engineering, Vol. 7, pp. 285-290.
  24. Wilcox, A.C., O'Connor, J.E., and Major, J.J. (2014). "Rapid reservoir erosion, hyperconcentrated flow, and downstream deposition triggered by breaching of 38-m-tall Condit Dam, White Salmon River, Washington." Journal of Geophysical Research: Earth Surface, Vol. 119, pp. 1376-1394. doi: 10.1002/2013JF003073
  25. World Commission on Dams (WCD) (2000). Dams and development, a new framework for decision-making. The report of the World Commission on Dams, Earthscan, London, UK and Stering, VA, U.S.