The large confluence between the Yangtze River and the outflow channel of Poyang Lake is receiving attention due to its importance in flood control and ecological protection in the Yangtze River basin.There is a large floodplain along the outflow channel of Poyang Lake,which is submerged during high flow and dry during low flow.The effects of the submergence of this floodplain on sediment and morphological characteristics at this large confluence have not been known.Hence,a field investigation was done in March 2019(relatively high flow,Survey 3)to complement the previous field studies done in August(high flow,Survey 1)and December 2018(low flow,Survey 2)to identify the temporal variations of sediment and morphological characteristics considering the submergence of this large floodplain.The predominant sediment transport modes were wash load for Poyang Lake and confluence particles and mixed bedload/suspended load for the Yangtze River particles.The sediment transport processes were largely affected by both the secondary flows and the water density contrast between the tributaries with a lock-exchange sediment rich,denser flow moving across the inclined mixing interface in Surveys 1 and 2.The sediment flux across the mixing interface was weakened in Survey 3 when the density contrast was very small.The stagnation zone near the confluence apex had a low sediment concentration and played a role in preventing the sediment flux exchange between the two flows,and its size,and,thus,its importance as a barrier to sediment mixing were related to the submergence of the floodplain.The bed morphology with the local scour holes at the confluence was largely affected by the large-size helical cells,and this kind of effect was weakened as the secondary flows got restricted in Survey 3.The current results expand the database and knowledge on the sediment transport and morphological features of large river confluences.

Kun Li;Hongwu Tang;Saiyu Yuan;Lei Xu;Yang Xiao;Carlo Gualtieri

State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering,Hohai University,Nanjing,China;Yangtze Institute for Conservation and Development,Nanjing,China;Department of Structures for Engineering and Architecture,University of Napoli Federico Ⅱ,Napoli,Italy

国际泥沙研究（英文版）

[1]Kun Li;Hongwu Tang;Saiyu Yuan;Lei Xu;Yang Xiao;Carlo Gualtieri-.Temporal variations of sediment and morphological characteristics at a large confluence accounting for the effects of floodplain submergence)[J].国际泥沙研究（英文版）,2022(05):619-638

bedload,confluences

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