Study On Crossfeed Mechanism Of Sudden Evolution Of Continuous Sharp Meander Channels

Under the action of unsaturated sediment laden flow,the continuous sharp meander channels course is easy to produce large river regime adjustment and cut-off.It is bound to have a far-reaching impact on flood control,shipping,water resource utilization,etc.Therefore,it is of great theoretical and practical significance to study the reconstruction process of the continuous sharp meander channels under the action of unsaturated sediment laden flow.Based on the summary of the existing research results at home and abroad,this paper collects and analyzes the topographic and hydrological data of the river course after the operation of the Three Gorges reservoir,and summarizes the evolution law of the continuous sharp meander channels course under the action of unsaturated sediment laden flow,and establishes the generalized physical model to discuss the cut-off condition and evolution process under the unsaturated sediment laden flow.The main work and achievements of this paper are as follows:(1)Taking the Xiongjiazhou Chenglingji reach as the research object,in this paper,the prototype observation data are used to analyze the regulation of river regime and the change law of riverbed erosion and deposition in different stages of the continuous sharp meander channels after the reservoir operation.After the initial impoundment period,the upstream and downstream band of the continuous sharp meander channels show opposite erosion and deposition properties.This paper studies the critical condition of cut-off of river channel through natural cut-off in history.(2)Based on the generalized model fixed bed test,the variation laws of hydraulic characteristics such as water surface gradient,cross-section velocity distribution and so on are researched.It is found that there are three stepped velocity concentration areas on the convex beach of the first bend of the continuous sharp meander channels under the continuous scour of overbank flow,and the velocity decreases from the neck to the bottom in turn.It is most likely to produce cut-off at the neck of band.(3)In this paper,the erosion and deposition tests and the cut-off tests of thecontinuous sharp meander channels under the action of unsaturated sediment laden flow are carried out.Result shows: The overall performance of the channel under non floodplain flow is that the upstream and downstream bends are respectively from“beach and channel scour” and “channel erosion and beach deposition” to channel scour and beach balanced.Although there is bank collapse at this time,the possibility of cut-off is small.Under the continuous scour of floodplain flow,the continuous sharp meander channels rapidly produces neck cut-off,upstream bend deposition and the convex bank of the downstream bend collapses backward because of the flow impact at the intersection of the breach and the original channel.The river is in the state of deposition before erosion.The new channel tends to be narrow and deep,and the old channel tends to be wide and shallow.