Soil Erosion Process Under the Combined Action of Water and Gravity on Red Soil Slope

[Objective] Soil erosion is one of the most important ecological and environmental problems in the world. It is of great significance to reveal the coupling mechanism of water and gravity combined erosion by analyzing the water and sediment process of water and gravity combined erosion under different conditions and its synergistic change law with gravel content. [Methods] Two types of soil, with no gravel and gravel content of 40%, were set up. Through the method of artificial simulation of continuous rainfall in the field, the influence of gravel content on soil erosion process and its synergistic change rule under the combined action of water and gravity were discussed. [Results] (1) Gravel-free soil did not produce runoff under two rainfalls. The gravel-containing soil did not produce runoff under the first rainfall, but started to produce runoff at 36 min under the second rainfall. The initial runoff time basically tended to advance with the increase of rainfall times, and the range of variation was 8~36 min. (2) The total runoff of each rainfall in the gravel soil was 8.97, 63.9, 70.8, 79.7 and 127.5 L, respectively. The runoff process in the later stage of each rainfall was basically the same, and the runoff rate decreased gradually. (3) The total sediment yield of each rainfall was 0.26, 10.6, 5.74, 3.15, 9.37 g, the erosion rate of the gravel soil fluctuated greatly under each rainfall, but the overall trend decreased in the later stage of rainfall. (4) Gravity erosion occurred in the non-gravel soil during the second rainfall. The erosion amount was 106.37 × 103 cm3, and the deposition amount was 76.28 × 103 cm3. Under the third rainfall, a small area of collapse occurred in the middle and lower part of the gravel soil, and the amount of gravity erosion was 6.08 × 103 cm3. [Conclusion] The research results can provide a theoretical basis for analyzing the coupling mechanism of water and gravity combined erosion forces.