寒潮大风对废黄河水下三角洲水动力与悬沙输运的影响

The influences of cold front winds on hydrodynamics and suspended sediment transport in the abandoned Yellow River subaqueous delta

中文关键词:  寒潮大风  水体层化  悬沙浓度  沉积物输运  废黄河三角洲

英文关键词:Cold front winds  Water column stratification  Suspended sediment concentration  Sediment transport  Abandoned Yellow River Delta

中文摘要:

      水下三角洲是重要的海岸地貌单元，寒潮大风事件是影响其稳定性的主要动力过程之一。为探究寒潮大风对水下三角洲水动力与悬沙输运过程的影响，于2021年12月在南黄海废黄河水下三角洲近岸浅水区（约9 m）和离岸海底平台深水区（约19 m）开展现场观测。以寒潮前、中、后3个全潮周期为典型时段开展对比研究，计算底部切应力，分析流速剪切和悬沙浓度引起的层化效应，探讨其对悬沙输运的影响。结果表明：寒潮前的流速剪切和悬沙浓度引起的层化导致高悬沙被限制在水体中下层，表层悬沙浓度低；寒潮后的水体层化弱于寒潮前，表明寒潮大风的影响可以持续数天。与寒潮前和寒潮后相比，寒潮中两个站位水体垂向混合充分，悬沙浓度和输运率显著升高，近岸站位的瞬时输运率显著增大，尤其在近岸浅水区域更为显著，其沿岸输运率可达6.88 kg/（ms），分别是寒潮前和寒潮后的2.49和2.27倍；离岸输运率达7.84 kg/（ms），是寒潮前和寒潮后的2.49和4.51倍。寒潮大风也显著改变了沉积物输运的主控因素和净输运率方向，表现在寒潮前受潮流控制的南向输运，寒潮中为波浪主控的向岸或向海输运。本研究量化了一次完整的寒潮大风对废黄河水下三角洲的水动力和沉积物输运的作用，为研究冬季风暴对海岸地区的影响提供了第一手观测资料和直接的观测证据。

英文摘要:

      The subaqueous delta is an important coastal morphological unit, and the cold front wind is one of the major factors affecting its stability. To explore the impact of cold front winds on coastal hydrodynamics and suspended sediment transport processes in subaqueous deltas, field observations at two stations were carried out in December 2021 in the abandoned Yellow River subaqueous delta of the south Yellow Sea. One station was located in the steep-sloped nearshore area (about9 m), and the other was in the offshore submarine platform (about19 m). To compare results among three full-tide cycles before, after, and during a cold front, the bottom shear stress is calculated, the stratification effect caused by velocity shear and suspended sediment concentration is analyzed, and the influence on suspended sediment transport is discussed. The results show that, before the cold front, the high suspended sediment concentration is limited to the middle and lower layers of the water column, and surface suspended sediment concentration is low. The stratification after the cold front is weaker than before the cold front, indicating that the influence of the cold front can last for several days. Compared with before and after the cold front periods, the water column was well mixed and vertical stratification was weak, and the suspended sediment concentration and transport rate increased significantly during the cold front. The instantaneous transport rate of the nearshore stations was higher than that before and after the cold front. The influence of the cold front on sediment transport was more significant in the nearshore shallow water area, where sediment transport rate could reach 6.88 kg/（ms） and was 2.49 and 2.27 times higher than before and after the cold front. The offshore transport rate was 7.84 kg/（ms）, 2.49 and 4.51 times higher than before and after the cold front. It was also found that the cold front altered net sediment transport direction, being southward and tidal-current-dominated before the cold front, whereas onshore-offshore and wave-dominated during the cold front. This study quantitatively evaluated the effects of one cold front event on hydrodynamics and sediment transport in the Abandoned Yellow River Delta. It provided first-hand observation datasets and direct evidence of the impacts of winter storms on coastal regions.