黄土模拟小流域降雨侵蚀中地面坡度的空间变异

Slope Variation of Small Tested Loess Watershed under Erosion of Rainfall

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貌的发育特征。研究结果表明:1)在不同的侵蚀发育阶段,黄土地貌平均坡度及坡度组合持续变化。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。2)黄土地貌地面坡度及其组合形态的变异不仅能有效表征黄土高原地貌形态的空间变异规律,也可以对黄土地貌侵蚀规律和它产生的时间规律进行高分辨率的地貌认识和划分。

The topographic feature is one of the main factors that influence the process of soil erosion and sediment yield of small watershed. It is very necessary to quantitate the topographic feature of small watershed and get the correlative parameters rapidly. According to the process resemble principle and statistic analysis of the topographic feature of small watershed on the Loess Plateau, the small tested watershed is designed. Based on 25 artificial simulated rainfalls, the dynamic development process of the topographic feature of the tested small watershed is studied by means of photogrammetry and GIS technology. DEMs at nine different erosion levels were picked up with a high precision and resolution. The spatial variation of slope and its composition derived from these DEMs are mainly discussed through comparison analysis and experimental validation. The result shows： firstly, in the process of rainfall erosion, the velocity of the increase of the surface mean-slope is increasing during erosion prophase and decreasing during erosion activity stage. The decrease of smoother slope balanced with the increase of steeper slope at erosion critical angle, namely, the proportion of erosion critical angle histogram resultants is keeping almost steady. In addition, the variation of slope composition reflects not only the spatial variation of loess morphology, but also the rule of loess erosion and the developing process as well.