Morphology and influencing factors of rills in the steep slope in Yuanmou Dry-Hot Valley (SW China)

It is very important to understand rill morphology in order to understand its dynamics. To reveal the morphology and influencing factors of rills in the steep slope (RSS) in the Yuanmou Dry-Hot Valley, the total station, photogrammetric technique and microtopographic profiler were used to obtain the parameters of the cross sections and longitudinal profiles of the RSS, and 12 parameters were used to characterize the rill morphology. The results show that the morphology of rills clearly varied between each layer; the topography, soil properties and ferruginous cemented layer all exerted important influences on the rill morphology. The average depth decreased with increasing slope length, and the depths dominated by silt and sand were larger than that dominated by clay. The average width and average width/depth ratio increased with increasing slope length, and the width and the width/depth ratio that was dominated by clay was larger than that dominated by silt and sand. The shape ratio of the rill cross section ranged from 0.50 to 0.58, and the shape of the cross-section gradually changed from narrow and deep to wide and shallow with increasing slope length. Concave-convex degree tended to be larger in the segment with ferruginous cement. In the longitudinal profile, the gradient gradually decreased with decreasing slope gradient and increasing slope length. The presence of the ferruginous cemented layer and topsoil crust resulted in abnormal changes in the shape of the rill. It is helpful to further understand the mechanisms of rill erosion under different conditions.