Abstract
A typical gully sub-basin with a complex geomorphological form is used to do a model test of gravity erosion of loess by considering the sequence of slopes in a prototype gully creating a sequence of underlying surface forms in the upper reaches. The results show that the runoff from heavy rainfall is the main external force for the erosion of loess, and also is an important influencing factor to stimulate and intensify the development of gravity erosion. The soil structure and the height of the critical surface have a direct impact on the possibility of gravity erosion. Spatially, the upper section of the drainage channel mainly experiences undercutting and headcut erosion, the middle section mainly experiences lateral erosion and gravity erosion, and the lower section alternately experiences sedimentation or alluvial erosion. Rainfall splash erosion produces a large amount of sand to yield high concentration mud flows in the middle and lower sections of the channel. Because of the mud flows the flood flow is obviously larger than the runoff volume formed by rainfall in a small watershed. The flood formed by high-intensity rainfall brings a large amount of sediment into the downstream rivers along the channel, indicating that under the condition that high-intensity rainfall on the Loess Plateau, lots sediment will enter the Yellow River, and the erosion deformation occurs on all slopes. Further the steep slope drainage flow causes undercutting and lateral erosion, and the soil body moves down along the slope under the action of gravity. The gully in the middle section still experience sediment washing in both depth and width, and the downstream gully continues to experiences sedimentation due to the reduction of the gradient, reflecting the adaptive adjustment of water flow and the boundary. Headcut erosion occurred on almost all slopes during different periods of rainfall, while gravity erosion mostly occurred on steep slope sections during periods of high-intensity rainfall.
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