长江口北支上口江心沙近期演变及其对北支上段的影响

The recent morphological evolution in the upper mouth sandbar of the North Branch and the impacts on its upper reach in the Changjiang Estuary

针对近年来长江口南北支分汊口近北支一侧水域发育的新生沙体,采用该区域2010—2020年的实测地形资料,分析了江心沙近10年的演变特征,并采用水动力数学模型结合经验公式分析沙体进一步淤涨或对其采取疏浚措施后对周边水动力和地形冲淤变化的影响。结果表明,近10年间,江心沙面积增加了近5倍,滩顶高程从<1 m逐步发育至>3 m,近期沙体已不再“长大”,但仍在逐渐“长高”,并有从低滩向高滩逐渐转化的趋势;若江心沙进一步淤涨,北支分流比将进一步减小,海门港至日新河段主槽流速减小并产生淤积,不利于北支的入流,同时跃进港近岸流速增加,深槽将进一步冲刷逼岸,不利于沿线海塘安全;若对江心沙采取疏浚措施,北支分流比将增加,有利于缓解其上段“S”型河势,海门港至日新河段流速增加,深槽冲刷,有利于北支入流以及分流比的增加,同时,跃进港近岸流速减小,出现淤积,有利于该岸段海塘安全。

Due to the new-born sandbank found in the upper river mouth of the North Branch in Changjiang Estuary,the bathymetry data during 2010—2020 was used to investigate its evolution and trends in the last decade.Additionally,a hydrodynamic numerical model combined with an empirical formula was used to further explore the effects on the hydrodynamics and bathymetry after the sandbank was further silted up or dredged.Results indicate that,in the past 10 years,the area of the sandbank has increased by nearly 5 times,and its elevation has gradually developed from less than 1 m to more than 3 m.In the recent years,the sandbank has stopped growing larger,but still gradually grown taller,and exhibited a trend of transformation from the lower tidal flat to the higher one.If the sandbank further silts up,the water diversion ratio of the North Branch will be further reduced.At the same time,the velocity of the main channel from Haimen Port to Rixin River will decrease,which may lead to siltation and the restrict of inflow in the North Branch.The nearshore water speed around Yuejin Port will increase,and may enhance the erosion there,which may threaten the safety of sea dikes.If the sandbank is dredged off,the water diversion ratio of the North Branch will increase,which takes advantageous to alleviate the S-shaped river regime in the upper North Branch.At the same time,the velocity from Haimen Port to Rixin River will increase,the main channel will be deepened,which will promote the water diversion ratio in the North Branch,decrease the nearshore water speed around Yuejin Port,induce the local siltation,and finally benefit the safety of sea dikes.