Study On The Evolution Mechanism Of Loitering Channel Bed Under Freezing-thawing Condition

In recent years,with the global climate change,leading to the river runoff and sediment and produce a series of changes in frozen soil boundary,thus affecting the evolution of river morphology and the change of the sediment,external environment and internal factors such as different runoff and sediment evolution trend of the high altitude river has certain influence,so the freezing and thawing condition of river evolution of river channel management is of practical significance and application value.Taking the wandering river in the source area of the Yangtze river as the research object,this paper studies the evolution of the wandering river in freezing-thawing state and the sediment erosion and deposition changes by means of natural model and theory,and reveals the evolution rules of the wandering river in frozen and thawing environment.The formation mechanism of loitering river was sorted out to search for water and sand conditions suitable for loitering river.Natural model test was used to analyze the evolution trend of formed wandering rivers.Of wandering river to simulate the process of freezing and melting process analysis,summed up the changing rule of the two processes,found in the process of the melting of the frozen river border with bank and riverbed gradually melts,at the bottom of the river will gradually appear again wandering type characteristics and wandering river type strength determined by the degree of riverbed melting,and river melt degree on the water with the test of time analyzing and the rise of temperature.And freezing process type wandering channel characteristic gradually disappear,the frozen river and riparian conditions gradually in the process of hardening,limits the incised and to expand on both sides of the speed of river,upstream inflow decreases at the same time,makes the river evolution process gradually slow down,when central river water consolidation,river evolution near standstill.In order to solve the problem such as river sediment movement in the process of freezing and thawing on the influence of river evolution,this article also has carried on the frozen under natural sediment starting test,found frozen silt water flow in the process of starting will speed up the melting of the sediment,and frozen silt sediment particle size when starting a finer more uniform,and the process as a result of the existence of ice,there was a delay starting phenomenon.This phenomenon indicates that the increase of incoming water leads to the accelerated melting rate of Banks and riverbeds,and further indicates that the increase of incoming water in the melting process promotes the activity of wandering rivers in this process.At the end of the paper,the two processes of melting and freezing are summarized respectively,and the characteristics of the wandering river in the two processes of melting and freezing are summarized.