在降雨侵蚀中黄土地面坡度变化的高分辨研究

运用近景数字摄影测量方法，获得在不同人工降雨时段黄土模拟小流域高精度、高分辨率的DEM数据，并以地面坡度及其组合形态的变化为切入点，通过对比分析和理论验证，探讨黄土小流域降雨侵蚀过程中地面坡度变化特征，在更宏观空间尺度和高分辨的时间尺度上，揭示黄土地貌形成与发育特征。研究结果表明：1）在较好地维持黄土的土壤结构与抗蚀特征，较真实地模拟自然降雨的条件下，模拟流域地面的变化能很好地反映自然地面的发育进程。2）在降雨侵蚀过程中，黄土小流域地面坡度呈现持续性变化规律，平均坡度在地貌发育幼年期呈加速增长趋势，到了壮年期增长幅度呈递减性变化；坡度组合以侵蚀临界角度为轴点呈持续逆转变化，侵蚀临界坡度单元所占面积基本保持稳定。3）黄土地面坡度的变化，一方面受地表物质被侵蚀和迁移程度的影响，另一方面，也是沟间地、沟坡地和沟底地空间面积重新分配的结果。

The Study with High Precision and High Resolution of Spatial Variation of Slope at Small Loess Watershed with the Erosion of Rainfall

As a key process of surface erosion,the formation of a drainage basin is the results of long-time reciprocity of different factors affecting the surface erosion.It has been a significant task to depict precisely the processes and features of physiognomy development at regional scale.This research probes into the temporal-spatial process of drainage development of Loess Plateau on the basis of a carefully designed experiment.In the experiment,the development of a simulated loess watershed is tested under the condition of manual rainfall.The typical drainage features of Loess Plateau are abstracted and generalized in the process.Through 25 times stimulating rainfall of different intensity and epochs,the drainage has turn from the infinitive smooth shallow watershed into a rough and fragmented terrain.A close-range photogrammetry survey is employed in this experiment,per which a series of high precision and resolution DEM of the drainage is established,which could be applied in investigating the dynamic development features of the drainage.In addition,the mean slope and slope composition of the whole and part of drainage basin are extracted and analyzed.Furthermore,the loess physiognomy form and its development features are discovered in a more macro spatial scale and higher precise temporal scale.1) The stimulation result can effectively reflect the truth if those experimental conditions,i.e. loess soil structure,stimulated rainfall,is adjusted in accord with the true situation;2) The slope of loess drainage varies all through the rainfall erosion process.Regarding the drainage basin at primitive experiment stage to be the infancy period of relief development,an accelerated increasing of the mean slope is presented.While in the adulthood,the increasing range is descending.The durative variances of slope combinations turn suddenly different at the erosion critical angle with the corresponding areas of erosion critical slope basically stable.3) The variances of slope in Loess areas are influenced by the degree of erosion and deposition of loess soil.On the other hand,the composition of different terrain type area contributes a lot to the variation of slope spectrum as well.