长江河口北槽近期盐淡水混合与悬沙输运研究

基于2013年枯季大潮期间在长江口北槽河道现场定点观测数据(包括潮流、悬沙浓度、盐度),通过对盐水入侵影响水流结构及泥沙运动过程的分析,对北槽河道盐淡水混合与悬沙输运进行了研究。结果表明:观测期间,北槽河道纵向及垂向受不同程度的盐度梯度影响,涨落潮过程中垂线流速不再保持无潮河流的分布规律,河口水流结构发生改变,促使出现上层水流向海、下层水流向陆的河口环流。在多重因素作用下,特别是环流阻碍了河流泥沙的正常下泄,并有利于底层泥沙上溯,出现上层输沙向海、下层输沙向陆的现象。各段河道中,垂向净环流项均向陆输沙,但向海的平流输沙及潮泵输沙作用更强,所以观测期间悬沙表现均为向海净输移。

Study on salt-fresh water mixing and suspended-sediment transportation at North passage of Yangtze River estuary

Based on the data (including tidal current, suspended sediment concentration, and salinity) obtained from fixed-point observation at Yangtze River estuary during the dry season and tide period in 2013; and through the analysis on impacts of the salt water intrusion on flow structure and sediment movement, a study was conducted on the salt-fresh water mixing and suspended sediment transportation in North passage of the Yangtze River estuary. The results show that during the observation period, north passage was under the influence of salinity gradient both horizontally and vertically in some degrees; during the ebb and flow, vertical velocity no longer follows the distribution patterns of tideless river. The flow structure in estuary changed, creating an estuarine water circulation in that the upper water flowing out to the sea whereas the bottom water flowing back to the upstream. Under influences of multiple factors, especially the obstruction to the sediment discharge due to estuarine water circulation that it is favorable to the bottom sediment movement to upstream, so the circulation results in the phenomenon of upper sediment flowing out to the sea and bottom sediment moving back to the upstream. In different river sections, vertical net circulation transports sediment back to the upstream, but much more sediment is transported to the sea under the influence of advection and tidal pumping action, as a result, in the observation periods, net transport volume of the suspended-sediment is to the sea.