Research On The Effects Of Diversion Engineering And Bathymetric Change Of Ruifeng Shoal On The Ebb Flow Diversion Ratio Of The North And South Passage,Changjiang Estuary

The ebb flow diversion ratio of the North Passage in the Changjiang Estuary experienced a drastic decline after.the Deep Waterway Project.For estuaries under tide,the ebb flow diversion ratio is the key index to maintain the stability of the branchs.Therefore,the research on the reason why it declined has attracted many scholars' attention.In this paper,the influence of Deep Waterway Project and terrain change of Ruifeng Shoal on the ebb flow diversion ratio of the South and North Passage is examined by combining the field observation with the numerical model.The result shows that:The summer survey of 2015 shows that the water flux in the South Passage is larger than that in the North Passage,and with the larger water flow rate the difference becomes larger;the spring ebb flow diversion ratio of North Passage was 41.9%and increased slightly to 43.1%during neap.The existing of submerged dike has played a positive role in stabilizing the river regime and Jiangyanan Shoal,but the submerged dike has little effect on the ebb flow diversion ratio of the North Passage;however if the direction of submerged dike changed,The ebb flow diversion ratio will change dramatically,its influence gets larger while deflecting southwards.When the angle of submerged dike is changed,the ebb flow diversion ratio of the upper sections changes more obviously than the lower ones,which is due to the balance effect of the Hengsha Channel.In the recent 20 years,the terrain of Ruifeng Shoal has undergone dramatic changes under the influence of man-made dredging and other factors,the channel evolved from "W" shape to "U" shape,leading to the increase of cross-section area;thalweg in the channel upstream the diversion of the North and South Passage moved northward.Dredging of Ruifeng Shoal and adjusting of the reach in the lower part of South Channel are beneficial to the runoff flowing into the upper North Passage which increases the ebb flow diversion ratio of the North Passage,but owing to the regulation of the Hengsha Channel,there is little effect on the lower section.