Impact On Erosion And Deposition In Main Stream By Flow And Sediment Diversion At Three Outlets Along The Jingjiang River

The Yangtze River Basin,especially the middle and lower reaches is an important area for the development of China's agriculture and industry,with a significant position in China's economic development.At the same time,known as the "Golden Channel",the freight volume of the Yangtze River ranks first in the world,and it keeps an important strategic position in the pattern of regional development.Three outlets along the Jingjiang River are the links between the Yangtze River and the Dongting Lake,diverting flow and sediment of the Yangtze River into the Dongting Lake,adjusting the water and sediment distribution of Jingjiang River,and affecting the erosion and deposition evolution trend of the main stream.At present,the.study about the influence of the flow and sediment diversion at three outlets to the erosion and deposition of the main stream is sketchy and dispersed,so it's particularly critical to understand the influence in a systematic and in-depth way,and it can provide a scientific basis for the flood control and river management of the lower reaches of the Yangtze River.Based on the systematic summary of diversion characteristics of Jingjiang three outlets,the influence of the flow and sediment diversion at three outlets to the flow and sediment of the main stream is discussed,and the mechanism of flow and sediment diversion on erosion and deposition in main stream is discussed and analyzed quantitatively,and the influence of the flow and sediment diversion at three outlets to the main-flow swing and bottomland morphology near the distributary gate is analyzed,and the characteristics of water flow and erosion and deposition of the riverbed near the distributary gate are simulated.The main contents of this paper were as follows:(1)The influence of the flow and sediment diversion at three outlets to the flow and sediment of the main stream.Data analysis showed that,before the impoundment of Three Gorges Reservoir,the runoff and sediment discharge of Jingjiang especially the lower reach increased significantly because of the decrease of the flow and sediment diversion at three outlets,after the cut-off of the lower Jingjiang,the runoff and sediment discharge of Jingjiang were increased about 5×1010m3 and 0.75×108t,the peak flow increased 9300m3/s.After the impoundment of Three Gorges Reservoir,the influence is less.(2)The influence of flow and sediment diversion at three outlets to the erosion and deposition in main stream.The decrease of runoff and sediment diversion at three outlets promotes the erosion of Jingjiang River,and the cumulative contribution to Jingjiang River is 0.95×108t caused by the decreasing of sediment deposition,accounted for 5.23%of the total erosion of Jingjiang River during 1957?2010,and the promoting effect is becoming weakened with the time.(3)The influence of flow and sediment diversion at three outlets to the channel morphology of main stream.The boundary conditions and the characteristics of diversion are different,and the effect of distributary to the erosion and deposition of main stream is different.The decrease of diversion in Songzikuo is beneficial to the erosion of the shoal in the Lujiahe channel.But the influence of diversion in Taipingkou to the the riverbed morphology is weak.The decrease of the diversion in Ouchikou causes the main-flow swing deviate from distributary gate in the upper reach and straighten the main-flow swing in the lower reach,it's beneficial to stabilization of the bottomland in the upper one,but not to the lower one.After the impoundment of Three Gorges Reservoir,the influence is less.(4)Numerical simulation of flow and sediment diversion.Choosing the Songzikou as the research object,the characteristics of the erosion and deposition in main stream under different diversion ratios are analyzed:The influence is less in the upper reach with different diversion ratios of Songzikou,but near the distributary gate reach,the greater the diversion ratio,the closer to the gate of the main-flow swing,and the stronger erosion of the left side and deposition of the right side.Although the main-flow swing in the lower reach changes little,the flow velocity decreases and the erosion of the riverbed is weakened.