小尺度湍流过程对河口物质输运与能量交换至关重要.受传统观测方法的限制,河口浅水区域的剖面观测资料至今较为匮乏,进而限制了湍流过程的研究.为此,采用新型5波束声学多普勒流速剖面仪(Nortek Signature 1 000kHzAD2CP)在长江口开展湍流剖面观测,获取高频、低噪的高质量湍流剖面数据,并与声学多普勒点式流速仪(acoustic doppler velocimeters,ADV)同步观测的数据进行对比.结果表明,通过AD2CP与ADV获得的近底部边界层摩阻流速u*、拖曳系数Cd、雷诺应力SR等特征参数基本一致,底摩擦与波浪能量为河口区域湍动能的主要输入源.湍流垂向结构存在显著的非局地平衡,即温盐等斜压作用引起的浮力通量、对流项以及强波浪作用影响的脉动压力做功、黏性输运等因素可能为长江口湍流非局地平衡的主因.

废黄河三角洲是南黄海内陆架的重要物源.为深入探索废黄河口海域沉积物输运机制,利用2015～2016年夏季与冬季在废黄河口外海域10个站位获取的现场沉积动力数据,计算潮不对称参数、余流、悬沙输运量等.分析结果表明,废黄河口海域沉积物输运模式存在显著的空间差异,大部分海域悬沙沿等深线向南输运,仅在近岸侧局部悬沙向岸或向北输运、离岸最远处站位向北输运但输运率较小;近岸浅水海域以平流输沙为主,其他离岸区域以再悬浮作用为主.由于流速和悬沙浓度之间的相位差,导致余流(净水输运)方向与净悬沙输运方向存在差异.研究沉降速度与悬沙输运涨落潮不对称的关系,发现沉降速度越大,悬沙输运的不对称性就越显著;沉降速度是造成近底部流速与悬沙浓度相位差的主要原因,导致废黄河口外净悬沙输运存在显著的垂向差异.

Driven by global changes and human activities, the sediment source/transport, and riverbed erosion and deposition pattern of the Yangtze River Basin are undergoing continuous adjustments, which influence both magnitude and property of fluvial sediment to the estuary. In order to explore sediment transport and correlated topographic changes of the Yangtze River Estuary within 40 years in response to variations of fluvial sediment discharge from the upstream basin, this study uses sediment grain size trend models and multi-year zonal analysis methods to predict temporal and spatial variations of morphological changes within the Yangtze Estuary, based on grain size data and topographic data from 1980 to 2020. The results show that sediments converge toward the center of the channel within the northern branch, and a deposition center forms close to the south and north channel diversion area within the southern branch, consistent with the morphological changes between 2012 to 2020 calculated from sea maps, validating the effectiveness of the grain size trend model in predicting morphological changes within the Yangtze River Estuary. The results of the multi-year zonal analysis show that: 1980—2003 was characterized by a high volume of fluvial sediment discharge, and the entire estuary area was dominated by deposition with slightly finer sediment. Fluvial sediment discharge experienced a rapid decrease from 2003 to 2012, while the estuary area was still dominated by deposition before 2009 with similar grain size. 2009—2012, however, was a transitional period when erosion and sediment coarsening started to appear out of the estuary, although limited to small areas. From 2012 to 2020, large-scale erosion and grain size coarsening occurred widely in the estuary, and a significant correlation was found between the particle size and the magnitude of erosion. Our study shows that high-resolution zonal analysis can effectively catch the local morphological change signals in the Yangtze River Estuary. In the past 40 years, the Yangtze River Estuary has changed from deposition-dominant mode to partially erosion mode, and it may face continuous coastal erosion in the future.