State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China; Department of Earth and Environment, Boston University, Boston 02215, MA, USA.
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China; Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, Shandong, China.
Sci Total Environ. 2022 Feb 25;809:152076. doi: 10.1016/j.scitotenv.2021.152076. Epub 2021 Dec 2.
Maintaining accretion and progradation in a mega delta is crucial to its geomorphic stability and ecology. Extreme riverine floods can disturb hydro-sediment dynamics with great damage to the deltaic landscape, as for instance deltaic erosion. Nowadays, most mega deltas suffer from sediment starvation. Understanding the impact of extreme floods is a priority to determine the long-term fate of deltaic systems. Herein, we used the Delft 3D model and field data to study the hydraulics and morphodynamics of the 2016 extreme riverine floods in the South Passage (SP) of the Yangtze Delta. Results reveal that extreme floods can increase water levels, velocities, and bed shear stresses in an inner estuarine channel and mouth bar, while the flood has a weak effect in offshore areas. High-energy floods trigger strong tidal asymmetry and Euler residual currents, which intensifies downstream suspended sediment transport and bottom riverbed erosion. In comparison with those during extreme floods in 2016, net erosion after floods passed away was generated with seaward weakened magnitudes, the corresponding mean bathymetric erosion thickness was 19.97 cm, 12.71 cm and 4.62 cm in inner estuarine channel, mouth bar and offshore area, respectively. Even though the seaward deposition patches were due to lower scouring effect and converged sediment. Hydrodynamic increments in deeper channels were more significant, while shoals and deeper areas were strongly eroded with the lowest erosion between -5 m to -6 m isobath. These results further clarified the bathymetric patterns with highlights of extreme riverine floods that can amplify the sediment-insufficient risks in such mega fluvial-tidal delta.
维持大河三角洲的进积和加积对于其地貌稳定性和生态至关重要。极端河流洪水会对三角洲景观造成巨大破坏，从而扰乱水沙动力，例如三角洲侵蚀。如今，大多数大河三角洲都面临着泥沙供应不足的问题。了解极端洪水的影响是确定三角洲系统长期命运的首要任务。在此，我们使用 Delft 3D 模型和野外数据研究了长江三角洲南槽（SP）2016 年极端河流洪水的水力学和形态动力学。结果表明，极端洪水会增加河口内部航道和河口坝的水位、流速和床面剪切应力，而洪水对近海地区的影响较弱。高能洪水引发强烈的潮汐非对称和欧拉余流，从而加剧下游悬浮泥沙输运和河床底部侵蚀。与 2016 年极端洪水相比，洪水过后的净侵蚀是在向海减弱的情况下产生的，相应的平均海底侵蚀厚度在河口内部航道、河口坝和近海区域分别为 19.97cm、12.71cm 和 4.62cm。尽管向海方向的沉积斑块是由于冲刷效果降低和汇聚的沉积物造成的。较深航道的水动力增量更为显著，而浅滩和深水区则受到强烈侵蚀，最低侵蚀深度在-5m 到-6m 等深线之间。这些结果进一步阐明了极端河流洪水的海底形态模式，突出了这种大河陆架三角洲泥沙不足的风险。
