Study On Evolution Simulation Of Loess Gully Based On DEM

The Loess Plateau is one of the unique geographic regions with the value of geoscientific research value in the world.After 2.6 million years of loess accumulation and transportation,unique geomorphological landform of gully has been formed,which are vertical and horizontal,fragmented and uneven.The main reason caused this kind of geomorphology is gully erosion.The gully development process is that surface runoff gathers in the gully.And then downward erosion,side erosion and head-cut erosion occurs simultaneously.The rill formed after surface runoff eroding slope surface.With the continuation of rainfall and the collection of runoff,the slope surface gradually developed from rill,shallow gully and gully.Geographic Cellular Automata(GeographicaI Cellular Automate,GeoCA)was used to achieve transformation rules of gully development through GIS spatial analysis technology and the process of gully erosion,hydrological runoff generation and confluence,the theory of erosion and sediment yield,as well as gully development which is considering the characteristics of head-cut erosion was combined.Finally,the simulation model of loess gully development has been established.The paper consists of three parts as following:1 the Formulation of Rules for Loess Gully Development in GeoCAThe vertical and transverse gullies constituted the loess landform.The three types of erosion,downward erosion,side erosion and head-cut erosion,promotes the gully development.The development of gully also reflected the evolution process of loess landform.Head-cut erosion was one of the important ways to afFect the development of gully.It affected the gully shapes in the process of erosion,especially the development and evolution on gully head.The mechanism of head-cut erosion and its influence on the development of loess gullies were explored,and then the mechanism and physical process of gully development were followed,the morphology and erosion characteristics of gully head are expanded and studied in the gully development following.Finally,transformation rules are made for gully development taking into account the characteristics of head-cut erosion.2 the construction of model of loess gully development?Implementation of Model StructureBased on the characteristics of head-cut erosion,the theory of erosion,sediment yield and runoff yield in the process of gully development,the research parameters are optimized iteratively.Besides,according to the geographic theory and the coupling and spatiality of Geographic Cellular Automata,the study designed the transformation rules of geographic cells for gully development and constructed the model structure considering the characteristics of head-cut erosion.? Implementation of Model FunctionCombining with the technology of Geographic Cellular Automata,this study gave each cell with relevant geographic meanings and expressed the change of gully development process using elevation as the dominant state value at each time node.The model is eventually established by designing transformation rules and integrating relevant programming software platform according to the characteristics of spatial coupling of Geographic Cellular Automata.3 The Analysis and Verification of Gully Development ModelThe construction of model aimed to get the correct and meaningful conclusion,and the correct conclusion cannot be separated from the reasonable model validation.In this stxidy,the validation of the simulation model was implemented by inputting the measured data of the digital elevation model of the small watershed called Madigou catchment.Adjusted the model structure and related parameters,the simulated and measured results are compared from three aspects:gully morphology,gully development degree and erosion changes to verify and evaluate the precision of the model.In conclusion,this research makes the transformation rules of gully development,and realizes the construction,evaluation and analysis of the model under the support of relevant programming platform based on the theory of gully development considering the characteristics of head-cut erosion,combining with the technology of Geographic Cellular Automata.