Studies On Gully Development And Regional Difference In Loess Plateau Based On Topographic Feature Elements

Gully is characterized by the frequent material exchange and strong morphological changes in the Loess Plateau.Under the effect of gully erosion,various types of gullies which developed actively-shape distinctive landforms in the Loess Plateau.The development process of the gully profoundly affects the development and evolution of loess landforms.The regional differences of gully development in the Loess Plateau also map the regional differences of landform morphology in the Loess Plateau.A series of studies have been conducted around the gully landform,gully erosion and gully development.However,most of these studies are based on the single point of the gully characteristic point,line or surface,and have not yet constructed a quantitative index system that can comprehensively describe the gully landform and gully development in the Loess Plateau.The loess gully can be considered as a hierarchically geomorphic system composed of the topographic feature point,line and surface.Through the comprehensive analysis of the feature point,line and surface of the gully,the morphological characteristics and development process of the gully can be reflected in a more comprehensive way.Therefore,based on the feature point,line and surface,this paper attempts to construct a comprehensive quantitative index system which can describe the gully development.The corresponding relationship between the quantitative index and the development degree of the gully is constructed by the 9-stage simulated loess watersheds.Based on this,the spatial difference of the gully development in the Loess Plateau is studied.The main contents and conclusions of this paper are as follows:(1)According to the basic principle of index selection,and based on the feature point,line and surface of the gully,a quantitative index system can be constructed to describe the gully development.And the scale effects of the gully characteristic elements and quantitative indexes are analyzed.(2)In order to verify the variability of quantitative indexes in different periods of gully development,the corresponding relationship between the quantitative index and the development degree of the gully is established by the 9-stage simulated loess watersheds.The results show that gully fragmentation,surface cutting depth,gully density,gully fractal,gully average depth and gully head density gradually increase with the enhancement of gully development.Gully average slope gradually increases from the early stage to the active stage of the gully development.When the gully develops into the stable stage,gully average slope is reduced to some extent.Main trench ratio,main channel longitudinal gradient,gully head elevation standard deviation and gully node average confluence accumulation basically show a decreasing trend with the development of the gully.Quantitative indexes can reflect the gully development from different aspects.(3)The variabilities of quantitative indexes are studied in Shenmu,Suide,Yanchuan,Ganquan,Yijun and Chunhua.It is found that there is a strong correlation between the quantitative indexes and the loess landform types.Based on the 156 research samples evenly distributed in the Loess Plateau,a series of spatial dissimilarity maps of quantitative indexes are obtained through GIS spatial interpolation,which reflect the spatial differences in the development degree of the gully in the Loess Plateau.The results show that different quantitative indexes reflect the spatial differentiation of the gully development in the Loess Plateau from different aspects.Although different quantitative indexes have different explanations for the gully development in the Loess Plateau,they also have some similarities.Finally,the division of the gully development in the Loess Plateau is realized,and the accuracy of the division results is verified.The results show that the zoning of the gully development can more accurately reflect the development degree of the gully in the Loess Plateau.