Analysis Of Morphological Characteristics Of Loess Gully Based On Cross Section

Along with the development of loess gully,the variation of its cross section is the most significant,with distinct regional and phased differences.Gully cross-sectional morphology is the result of long-term effects such as gully erosion.Gully morphology affects gully erosion,gravity erosion,etc.,which affects the direction of gully development in turn.Researches of gully morphology is currently one of the hotspots in the Loess Plateau related research.However,there is still a lack of quantitative analysis of cross-sectional morphology and slope morphology intersected with the cross section from different stages.In this thesis,6 typical watersheds of loess landforms and 9-phase simulated watersheds were taken as sample areas.Combined with the theory and method of digital terrain analysis(DTA),the morphological characteristics of the cross section and its slope were comprehensively analyzed,in order to further explore the internal mechanisms and laws of the evolution of gully landforms.The main contents and conclusions are as follows:1.Analysis of morphological characteristics of loess gully cross sectionTaking 6 small watersheds and 9-phase simulated watersheds as the study sample areas,the cross sections of the gullies were extracted.Quantitative indicators were selected from three aspects of statistical characteristics,profile characteristics and erosion characteristics.The cross-sectional morphology of the gully was analyzed from different spatial locations,development stages and levels of gullies.The statistical characteristics,profile characteristics and erosion characteristics of the gully decrease from the main gully to the first-level and the second-level stream.All indicators of the gully have a linear relationship with the distance from the gully mouth.The closer to the gully,the severer the erosion activity,the larger the value of each index,the more stable the development of the gully.According to the overall changes in the width,depth and cross-sectional area of the 4 branches in the simulated watershed,the development can be divided into three stages: initial stage,active stage,and stable stage.2.Analysis of morphological characteristics of slope intersected with gully cross sectionSlope segmentation and classification were conducted with 6 small watersheds and 9-phase simulated watersheds to extract slope units where the cross section of the gully lies.Quantitative indicators were selected from two aspects of morphological and topographical characteristics.From the second-level,the first-level branch to the main gully,the average gradient of the slope is continuously decreasing.The plan curvature is rising from a negative value to a positive value,indicating that the slope is from concave to convex horizontally.The profile curvature of all slope is positive,and the slope units are concave along the direction of maximum gradient.The average gradient of the slope is decreasing from gull head to its mouth.From initial to stable stage,slope units are transformed from a concave slope to a convex slope in the horizontal direction;most of the slope units are concave slopes along the gradient direction.3.Analysis of the evolution model of the loess gully cross sectionThe variation of width and depth of the gullies were analyzed,and the transformation law of the form of the slope where lies the cross-section was studied.Multivariate regression was used to simulate the evolution of the gully width and average depth.Meanwhile,the Markov chain was employed to establish the prediction model of the slope shape type conversion.The experiment shows that the regression equations of the width and depth have a good simulation effect.Incision depth and profile curvature have a significant effect on the widening and downcutting of the gully.Moreover,the established Markov model can better predict the transformation of the slope shape of gully cross section.This study has explored the morphological characteristics and evolution of gully cross-section,and the conversion law of the morphological types of the slope intersected with the cross-section,which is of great significance for revealing the external performance and internal mechanism of the gully morphology.