| As the world's most researched value of geographical regions in the world,the Loess Plateau has the special geographical location,the typical climate environment,and unique soil conditions.There is loess deposition more than two million years and persistent strong modern water erosion,and has formed complex and orderly diverse loess landform pattern.Scientifically quantifying the typical characteristics of loess landforms and systematically expressing its spatial differentiation pattern has become one of the important contents of landform research,which has important scientific significance for deepening the cognition of loess landform.In previous studies,it is more concerned about reflecting the local landforms morphology at a specific angle,and it lacks a comprehensive description of the morphology development characteristics.it was difficult to effectively reveal the overall geomorphologic development from multiple perspectives in the large region.This study takes the natural complete watershed with stable scale as the basic unit,grasps closely the spatial entities such as ditch along the valley,the valley network,and the boundary of the watershed,and their combined relationships,and analyzes their morphological characteristics in depth.Google Earth image with better than 1m high-definition and Aster 30m DEM as data sources,scientifically selected 90 watershed sample plots and designed experiments to accurately extract physical element characteristics such as watershed boundary lines,gully lines and gully networks,and further build a quantitative index system of landform development can effectively realize the quantitative expression of the characteristics of 90 complete watersheds in the study area.Moreover,a comprehensive factor analysis method is used to comprehensively quantify the degree of landform morphological development in the Loess Gully Erosion Region,and explore the relationship between the degree of watershed landform development and soil erosion and its environmental factors,so that reveal the watershed landform development degree.The main conclusions are:(1)Accurately mining index factors that have clear geographical significance and rich information characteristics for watershed landforms development,including surface Nibble Degree,Gully Density,Shoulder-line Density,Elevation Approximation,Area Elevation Integration,Difference of Average Slope,Ratio of Main Branch and Trench,Moran Index and Fragmentation Degree,and build a quantitative index system that effectively reflects the landform and morphological development of the loess gully erosion region.(2)Based on the factor analysis method of information characteristics synthesis,the information characteristics transmitted by the quantification factors system of watershed geomorphology from various perspectives are explored,and an information synthesis model of river basin landform morphology development is established so that achieve a comprehensive quantitative assessment of the development of watershed landform morphology,and comprehensively and systematically reflect the overall development of the watershed landform morphology.(3)A stage characteristics of geomorphic morphology development were explored by combining qualitative and quantitative methods.From the global trend of landscape development degree appear gradient features from south to north,showing a good continuity,high value appears in the Yellow River from north to south through Shaanxi Shenmu,Baode to Lin County of Shanxi Province,as well as the Wuding river basin,these areas belong to regional geomorphic mature stage.Respectively,the low-value areas are mainly located in the loess tableland in the south and the residual tableland in the southern Qingyang.(4)It can be seen from the soil erosion that the strong erosion in the loess gully erosion region occurs in the loess inclined beam area of Gansu Qingyang,the middle and upper reaches of the Yanhe river basin,the Wuding river basin and the eastern area where the Yellow River flows from north to south.The high value areas of comprehensive geomorphologic development degree are mainly concentrated in the northern part of Yanhe river basin,Wuding river basin and the eastern part of the middle reaches of the Yellow River,which indicates that soil erosion and comprehensive landform development degree have good synchronization characteristics in space except for some places such as Gansu Qingyang and Shaanxi Wuqi.In the past 20 years,since the implementation of the project of returning farmland to forests,national policy guidance and ecological management projects have been able to take measures in accordance with local conditions and adopt precise measures,effectively alleviating regional ecological and environmental pressures,conforming to the distribution pattern of regional geomorphological development,and playing a significant positive role in regional soil and water conservation and ecological environment.Regarding the current situation of the ecological environment in the Loess Gully Erosion Area,it is still necessary to strengthen the scientific implementation of soil and water conservation services and integrated watershed management measures in combination with the characteristics of regional erosion and sediment production and landforms development degree,and to strongly control energy mining activities in the middle of the Yellow River to curb water and soil Loss phenomenon,further ensure good ecological benefits and sustainable ecological environment. |
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