Numerical Simulation Of Formation And Evolution Of River Channel Downstream Of The Hoh-Xil Region

Due to the increasing trend of climate warming and humidification in Qinghai Tibet Plateau,a large number of internal lakes overflowed in Kekexili area,resulting in the formation of new river channels in the downstream area.The formation of the new river not only causes serious damage to the original topography of the area,but also poses a serious threat to the ecological environment,transportation and the safety of peopled lives and property.Therefore,it is urgent to predict the evolution process of the new river channel in this area,and through the analysis of the research results of the river channel evolution,further put forward the effective measures to slow down the overflow flow on the riverbed erosion.In this paper,the new channel in the lower reaches of Salt Lake is taken as an example to study the evolution trend of channel erosion and deposition.The research process and conclusions have important theoretical value,and also provide reference value for the practical engineering of solving the problem of inner flow Lake overflow in the region.Firstly,on the basis of the existing mathematical model of water and sediment dynamics,a one-dimensional water and sediment dynamics model suitable for the calculation of channel scour evolution in the lower reaches of Salt Lake is constructed through modification and improvement.The model is verified by the measured data,and the results show that the calculated values are in good agreement with the measured values.Then,taking Tuotuohe hydrological station as the reference station,using hydrological analogy method and large water surface evaporation formula,considering the two factors of "incoming water" and "evaporation",the discharge process of Salt Lake is interpolated and extended.Finally,the development process of erosion and deposition of the New River under the condition of natural overflow and the process of erosion and deposition after the construction of artificial channel are predicted and calculated.Through the analysis and comparison of different calculation results,it is found that the overflow of Salt Lake will cause serious damage to the downstream area without human intervention,Therefore,in order to alleviate the increasingly serious problem of riverbed erosion in the area,it is necessary to build artificial channel in the downstream of the Salt Lake to drain the overflow water.The main contents and conclusions of this paper are summarized as follows:(1)A one-dimensional dynamic model of water and sediment for the calculation of channel scour evolution in the lower reaches of the Salt Lake is established.The model fully considers the unique climatic and geological conditions in Kekexili area.Then it is verified by the measured data.The model is the first time to simulate the evolution process of erosion and deposition of the new river,which is the main means to determine the necessity and rationality of the emergency project construction of Salt Lake drainage and dredging.(2)From 2009 to 2018,the average annual discharge of Salt Lake is 342.2 million m3,and the discharge of Salt Lake is intermittent.The discharge of Salt Lake is mainly concentrated in July to October,accounting for 84.3%of the average annual discharge.(3)In this paper,the long-term prediction and calculation of the erosion evolution process of the lower reaches of the Salt Lake under the condition of natural overflow and the construction of artificial channel are carried out.Compared with the calculation results under different conditions,the accumulated scouring amount under the construction of the channel is 1.78 million m3 less than that under the natural overflow condition;The erosion depth of the reach from manyiyakou to sonandajie protection station can be reduced by 1.46m?3.12m;The reach from sonandajie protection station to Qinghai Tibet highway can reduce the scour depth by about 0.86m;The scour depth can be reduced by 0.58m?0.65m near the Qinghai Tibet highway and railway.(4)In order to minimize the harm caused by the overflow of the Salt Lake to the downstream area,the artificial channel is built in the downstream of the Salt Lake to drain the overflow water.The calculation results of the channel evolution under this scheme are as follows:the accumulated scouring amount of the overflow lake water in the 10th year is about 3.27 million m3,of which the maximum scouring of the riverbed is located at the overflow pass(0+OOOm)of the Salt Lake,and the scouring depth is about 2.44m;The maximum deposition of the riverbed is located at the protection station of sonandajie(8+875m),and the bed elevation is about 0.46m;The scour depth near the infrastruture is about 0.40m~1.30m.