Study On Initiation Characteristics Of Gully-type Desert Mudflow Deposits Based On Catastrophe Theory

Ningxia-Inner Mongolia reach of the upper Yellow River flows through four deserts,and wind erosion and water erosion are serious.In winter and spring,a large amount of desert coarse sand,loess and other materials are transported by strong wind erosion to the mountain torrents channels distributed along the banks of the Yellow River for storage.When the rainy season comes,the sudden rainstorm forms seasonal mountain torrents in the basin,and there are mountain torrents in the mountain torrents along the way,resulting in flood with high sediment concentration and even mud flow disaster flowing into the Yellow River,which has a serious impact on the ecological stability and healthy development of the Yellow River.In this paper,the typical seasonal mo untain torrents gully in Zhongwei reach of Ningxia-Inner Mongolia reach is selected as the research object.Through field scientific research,model test and catastrophe theory,the starting characteristics of gully-type desert mud-flow deposits are analyzed,and the mechanical mechanism of the starting of the deposits trapped in the gully is explored.Through the combination of experiment and catastrophe theory,the starting model of accumulation body is established,the starting criterion is found,and the theoretical model and experiment are compared and verified.The primary research results are as follows:(1)Based on the field investigation and related data investigation,combined with the theory of water and sediment movement,Darcy’s law and limit equilibrium theory,the factors affecting the start-up of gully desert debris flow accumulation are analyzed.The starting model of debris flow accumulation body is established from micro,meso and macro perspectives.The results show that the grain size distribution of the debris flow accumulation,the slope of the channel,the flood intensity and the density of the accumulation are the important factors affecting the start-up of the debris flow accumulation.The starting process of mud-flow accumulation body has sudden jump and lag;The empirical model of pore water pressure and seepage flow in the accumulation body is obtained by fitting the experimental data.(2)Taking the time T as the control variable and the pore water pressure P as the state variable,the starting equilibrium equation of the mudflow accumulation under the folding catastrophe mode is established by fitting the experimental data,and the starting model of the mudflow accumulation under the folding catastrophe mode is deduced;The starting equilibrium criterion of debris flow accumulation body with time t as the control variable is given.The starting criterion is in quantitative agreement with the experimental results.(3)The cusp catastrophe model of debris flow accumulation is establi shed by coordinate transformation and topological transformation,with dimensionless number reflecting topographic factors and accumulation particle groups as control variables and pore water pressure as state variables.By comparing the measured pore water pressure with the calculated pore water pressure of cusp catastrophe model,the calculated results are in good quantitative agreement.According to the obtained model,the starting criterion of debris flow accumulation in cusp catastrophe mode is deduced.The test data show that there is some error between the risk judgment result and the test result,but it is within the allowable range.In this paper,the catastrophe theory is used to study the starting mechanism of gully-type desert mud flow,and the results can provide theoretical basis for disaster prevention and mitigation in Ningxia-Inner Mongolia reach of the Yellow River and reducing sediment flow into the Yellow River.It provides a new idea and method for the prevention,early warning and prediction of desert mud flow disasters,and has practical guiding significance for optimizing the measures for controlling sediment disasters in the region.It has important research value for enriching the theoretical system of soil erosion in arid and semi-arid areas,and has positive significance for enriching the application fields of catastrophe theory.