Variation of rill cross-sections with gravel and aggregating soil in the Dry-Hot Valley (SW China)

Cross-sectional morphology is an effective approach for calculating rill volume and revealing the mechanism for rill development. In this study, the law governing the temporal–spatial variation in rill cross-section (RCS) under interbedded clay and gravel conditions was investigated by a scouring experiment. A high-flow scouring experiment was conducted in a field plot under heterogeneous soil conditions in the Yuanmou Dry-Hot Valley using 3D laser scanning and ArcGIS techniques. Morphological index system including the size and derived proportional parameters was established to accurately reveal the dynamic process of the rill erosion–sediment sections based on temporal–spatial scale. The study indicated that the RCS size under gravel and soil aggregates showed an irregular variation over different periods, and the variation of RCS morphology tends to be nonlinear. The area of rill cross-section at the middle of the rill was much larger than that of the rill head and the rill mouth, and the fluctuations in RCS along the rill depended heavily on the soil texture heterogeneity. In addition, there were extreme variations in rill erosion direction for different rill parts, i.e., rill head, body, and mouth, and the highly significant asymmetry in RCS distributed along the rill under increasing scouring duration in the Yuanmou Dry-Hot valley. Temporal variations in RCS morphology were opposite to spatial variations by comparing the same morphology parameter. Nonlinear fluctuation trends and asymmetric shapes were observed in the variation of RCS on slopes with soils and gravels.