Numerical Modeling of the Undertow Structure and Sandbar Migration in the Surfzone |
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| Authors: | XIE Ming-xiao ZHANG Chi YANG Zhi-wen LI Shan LI Xin GUO Wei-jun and ZUO Shu-hua |
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| Institution: | Key Laboratory of Engineering Sediment, Tianjin Research Institute for Water Transport Engineering, M. O. T., Tianjin 300456, China;National Engineering Laboratory for Port Hydraulic Construction Technology, Tianjin Research Institute for Water Transport Engineering, M. O. T., Tianjin 300456, China;State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing Hydraulic Research Institute, Nanjing 210029, China,State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China,National Engineering Laboratory for Port Hydraulic Construction Technology, Tianjin Research Institute for Water Transport Engineering, M. O. T., Tianjin 300456, China,Key Laboratory of Coastal Engineering Hydrodynamics of CCCC, Tianjin Port Engineering Institute, CCCC, Tianjin 300222, China,National Engineering Laboratory for Port Hydraulic Construction Technology, Tianjin Research Institute for Water Transport Engineering, M. O. T., Tianjin 300456, China,College of Environmental Sciences and Engineering, Dalian Maritime University, Dalian 116026, China and National Engineering Laboratory for Port Hydraulic Construction Technology, Tianjin Research Institute for Water Transport Engineering, M. O. T., Tianjin 300456, China |
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| Abstract: | A process-based 3D numerical model for surfzone hydrodynamics and beach evolution was established. Comparisons between the experimental data and model results proved that the model could effectively describe the hydrodynamics, sediment transport feature and sandbar migration process in the surfzone with satisfactory precision. A series of numerical simulations on the wave breaking and shoaling up to a barred beach were carried out based on the model system. Analyzed from the model results, the wave-induced current system in the surfzone consists of two major processes, which are the phase-averaged undertow caused by wave breaking and the net drift caused by both of the nonlinear wave motion and surface roller effect. When storm waves come to the barred beach, the strong offshore undertow along the beach suppresses the onshore net drift, making the initial sandbar migrate to the seaside. Under the condition of calm wave environment, both the undertow and net drift flow to the shoreline at the offshore side of the sandbar, and then push the initial sandbar to the shoreline. The consideration of surface roller has significant impact on the modeling results of the sandbar migration. As the roller transfer rate increases, the sandbar moves onshore especially under the storm wave condition. |
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| Keywords: | process-based numerical model undertow net drift sediment transport sandbar migration |
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