Study On The Laws Of Sediment Movement About The Bending Braided River Reach

The bending braided river is common in the alluvial plain, which water and sediment movement characteristics are complex. The middle and lower reaches of the Yangtze River is typical bending braided river which have many shoals and the riverbed evolution of these reaches is serious. The conversion between main channel and anastomosing branch result in that the problem of obstraction to navigation is obvious, which become the"bottleneck"of restricting the development of navigation. The water storage of the Three Gorges Project will cause new changes of conditions of channel with many shoals at the middle reaches of the Yangtze and some of which will deteriorate further. Accordingly, the research on the formation reason and evolution mechanism of shoals of the typical bending stretch at the middle reaches of the Yangtze River is significant and has practical value.This paper was carried out from the western communication construction project of the Ministry of Communications and the content of the project is the key technological research on channel rectification on the stretch which shipping condition is seriously bad at the middle reaches of the Yangtze-Jianli stretch. Through the investigation and analysis of planform, hydrologic-sediment property and characteristics of fluvial process of the bending braided stretch of the middle and lower reaches of the Yangtze River. The main factors of the conversion between the main channel and anastomosing branch were studied. Through clear water washout test, at the three diffent period (left-branch based, branch balance,right-branch based), the sediment movement and deformation of the riverbed of bending braided stretch and river island shoalline of four kinds of shoals are systematically simulated. The formation reason and evolution mechanism of shoals of bending braided stretch is given. By comparing the changes of river island head, river island tail, and the body volume of the river island, the stability of four kinds of river islands from top to bottom are as follows:right-branch based, right-branch with side flat based, left-branch based, branch balance. By theoretical analysis and model test, the relation curve of the streamwise variation of silt-carring capacity has been given. Accord to the curve, the conclusion has been drawn that silt-carring capacity was largest at the top of the bend and the below of which, this area is prone to erode and silt-carring capacity is smallest at the diversion area, consequently, this area is prone to siltation. By analysing the property of tubulent, at the bottom of the diversion area, the pulsation kinetic energy is rather dispersed, which is the important reason of the formation of shoals. By comparing the changes of erosion and siltation of stretch prototype with which of generalized physical model, the results are generally reasonable.The research results have been preliminary applied to the practical project and have achieved good economic and social benefits and could be used for other bending braided river channel construction.