特大洪水期间长江口浑浊带分粒级输沙特征

Multi-fraction sediment transport in the turbidity maximum of the Yangtze Estuary during the extreme flood

中文关键词:  长江口  浑浊带  特大洪水  分粒级输沙  泥沙来源  流域减沙

英文关键词:Yangtze Estuary  turbidity maximum  extreme flood  multi-fraction sediment transport  sediment source  reduced fluvial sediment supply

中文摘要:

      基于2020年7月特大洪水期间长江口浑浊带南槽、北槽和北港多站位同步实测水沙动力数据，研究了河口浑浊带分粒级输沙时空特征及其对泥沙来源响应的指示意义，结果表明：1）北港和北槽是流域泥沙净向口外输移的主要输沙通道，南槽是海域泥沙净向口内输移的主要输沙通道，主槽内粉砂是主要输沙组分，占比63.2%，口外粉砂和黏土是主要输沙组分，分别占43.2%、40.9%；2）大潮粉砂输运占比高于小潮，黏土输运占比低于小潮，口外测站砂组分在大小潮期间在横沙浅滩和九段沙间沿岸输移，横沙浅滩附近大、小潮离岸输沙分别是北港口外的1.7倍和8倍，不利于横沙浅滩淤涨；3）当前流域减沙高达70%，此次特大洪水期间黏土、粉砂和砂三组分近底净向口内输移为减沙背景下的口外供沙提供了有力的佐证。

英文摘要:

      The multi-fraction sediment transport in the turbidity maximum of the Yangtze Estuary was studied based on the data collected under the extreme flood in July 2020. It aims to exhibit the spatial and temporal changes in the multi-fraction sediment transport over a spring-neap tide and identify the effect of the changes in sediment supply. The results show that: 1) the North Channel and North Passage are the main channels for net seaward sediment transport delivering fluvial sediment whereas the South Passage is the main channel for net-transporting offshore sediment. The main channel transports 63.2% silt fraction whereas offshore sediment transport indicates 43.2% and 40.9% of the fractions silt and clay, respectively. 2) Silt fraction transport is higher at spring tide than that at neap tide whereas clay fraction transport is lower at spring tide than that at neap tide. The location of sand accumulation moves between seaward of Hengsha flat and Jiuduan shoal over a spring-neap tidal cycle. Moreover, offshore sediment transport is 1.7 and 8 times larger than alongshore sediment transport at spring and neap tides, respectively at Hengsha flat which suppress the accretion of the tidal flat. 3) As fluvial sediment supply has reduced by 70%, the net landward sediment transport in the South Passage implies that offshore sediment supply plays an important role, which needs to be considered in the future study.