Rill morphology change and its effect on erosion and sediment yield on loess slope

Abstract: The rill morphology changes directly affect the slope hydrological process, and thus forms a mutual feedback effect with runoff yield and concentration, sediment yield and transport. This process embodies the relationship between the elements of water erosion dynamics on the slope, and is a key scientific problem in understanding the physical process of erosion and sediment yield. Morphological development of rill on slope forms a micro relief dynamic response system with soil erosion driven by rainfall. To reveal the formation mechanism of this system, scientific quantification is the key problem. In the past research, one-factor quantification parameter based on mathematical statistics was used, which was hard to express the complexity of the whole system effectively. In this paper, the influence of rill morphology evolution on runoff and sediment process was studied. The rainfall, rill evolution, runoff and sediment yield were used as a hydrodynamic coupling system to study the rill morphological characteristics and implementation methods, to reveal the law of spatial and temporal differentiation of rill morphology, and clarify the quantitative response of rill morphology to rainfall-runoff and sediment yield. The aim of this study was to break through the unresolved spatial variability problem in the existing water erosion prediction model, and to provide scientific basis for the prediction of soil erosion process. The indoor simulated rainfall experiment was conducted to reveal the variation regularity of the rill boundary and the response of the erosion and sediment yield under the fixed slope gradient (20°) and 3 rainfall intensities (66, 94, 127 mm/h). The parameters such as rill cumulative length, mean width and depth were used to describe the change of the rill morphology with the rainfall. Results show that the effect of rainfall intensity on rill length is significant, the change of rill width is influenced by the rainfall duration, and the change of rill depth shows a strong differentiation rule with the rainfall intensity. Rill morphology parameters are not independent of each other, and there is a clear correlation between them. This shows that the evolution of rill morphology is not a one-dimensional development process, but a multi-dimensional change process. Sediment yield is affected by the development of rill. There is a logarithmic function relationship between the rill morphology and the sediment concentration and erosion rate. The results show that the formation and development of the rill are closely related to the water and sediment yield on the slope, and the influence of rill forwarding, rill wall expansion and rill bed undercutting on the sediment yield is basically the same. This study can provide basic data for the establishment of rill erosion dynamic model.