Anti-scourability of Soils and Its Influencing Factors under Typical Ecological Restoration Models in Dry-Hot Valley Regions

[Objective] Dry-hot valley regions are characterized by fragile ecological environment and severe soil erosion. Clarifying the differences in soil anti-scourability and the influencing factors under different ecological restoration models is crucial for revealing the soil anti-scourability mechanism and optimizing ecological restoration measures in this region. [Methods] The drawdown zone of Wudongde Hydropower Station in the dry-hot valley of the Jinsha River was selected as the study area. Three typical ecological restoration models were designed, namely tree forest land, slope-to-terrace + farmland, and shrub-grassland. Undisturbed soil samples were collected from three soil layers (0-20 cm, 20-40 cm, and 40-60 cm), and anti-scourability tests were conducted. The anti-scourability indices and runoff sediment amounts of each soil layer under different models at different scouring times were measured. Physicochemical indicators such as soil bulk density, water content, and particle composition were determined through laboratory experiments, and the influencing factors of soil anti-scourability were identified through correlation analysis. [Results] (1) Different ecological restoration models and soil layer depths significantly affected soil anti-scourability. The anti-scourability indice of tree forest land was the largest (0.566 L/g), followed by slope-to-terrace+farmland (0.501 L/g) and shrub-grassland (0.428 L/g). The total runoff sediment yield exhibited an opposite trend, with the shrub-grassland showing the highest value, 28.03% higher than that of the tree forest land. As soil depth increased, the anti-scourability indices of all three ecological restoration models demonstrated significant declining trend. For all three models, the runoff sediment concentration dropped rapidly during the initial scouring period (0-6 min) and stabilized after 6-10 minutes, while the anti-scourability indices exhibited regular temporal patterns that could be fitted by either quadratic or power functions(R2> 0.92 in all cases).(2) Significant differences in soil particle composition and particle fractal dimension were observed among the three models, reflecting variations in soil structural stability. Coarse silt (35.82%-46.10%, mean 41.85%) dominated the particle composition, while coarse sand (0-1.93%, mean 0.42%) was the least abundant fraction. The contents of clay, coarse clay, and fine silt followed the order of shrub-grassland > slope-to-terrace + farmland > tree forest land, whereas fine sand and coarse sand showed the opposite trend, with the highest values in the tree forest land and the lowest in the shrub-grassland. The soil particle fractal dimension ranged from 2.540 to 2.648, with the shrub-grassland exhibiting the highest values, followed by slope-to-terrace + farmland and then tree forest land (all differences significant), indicating that the tree forest land’s soil structure is more stable, which is favorable for soil anti-scourability. (3) Anti-scourability index exhibited significant correlations with multiple physicochemical indicators. Negative correlations were observed between anti-scourability index and soil bulk density, fine clay, coarse clay, fine silt, coarse silt, cumulative eroded soil mass, and fractal dimension, whereas positive correlations were found with fine sand and coarse sand contents. Water content showed a positive correlation with anti-scourability index during the early scouring stage (1-6 min) but turned negative in the later stage (7-10 min). Among these factors, fine clay content and particle fractal dimension demonstrated the most pronounced influences on the anti-scourability index. [Conclusions] Among the three typical ecological restoration models in dry-hot valley regions, tree forest model effectively enhances soil anti-scourability, followed by slope-to-terrace + farmland model. Soil particle composition and structural characteristics significantly affect anti-scourability performance, with fine clay content and particle fractal dimension being the dominant factors. For future ecological restoration measures in drawdown zones, it is recommended to prioritize tree-dominated and tree-shrub-grass composite configuration, tailored to regional topography and soil structural features, to improve soil anti-scourability.