草被覆盖度下坡面流流速变化及缓流机制研究

Flow velocity change and slow-flow mechanism of overland flow under different vegetation coverage

坡面薄层水流是黄土区土壤侵蚀发生的直接动力条件,探究植被覆盖条件下坡面流水动力学特性及缓流机制,有助于揭示土壤侵蚀发生的水动力学机理。在水槽坡度为12°条件下,通过9个草被覆盖度、7个流量的组合试验,研究了不同植被覆盖度下坡面水流流速变化和缓流机制。结果表明:坡面流流速随着覆盖度的增加整体呈减小的趋势;缓流系数随覆盖度的增加呈先增大后减小的变化规律,当覆盖度大于47.66%时,缓流系数随覆盖度的增加显著减小;以覆盖度47.66%为临界值,高、低覆盖度下缓流系数随雷诺数的变化规律有所不同。最后,建立了模拟草被下的坡面流流速和缓流系数拟合公式,验证结果表明,拟合公式精度较高,可为建立土壤侵蚀预报模型提供参考。

The overland flow plays an important role in the process of soil erosion in loess areas,the study of overland flow dynamics and slow-flow mechanism under vegetation coverage is fundamental for understanding the cause of soil erosion.Here,flume experiments of slopes of 12°under different combinations of nine vegetation coverage and seven flow rates were carried out to analyze the variation of flow velocity and slow-flow mechanism.The results show that the overland flow velocity generally decreased with the increase of the vegetation coverage,whereas the slow-flow coefficient first increased then decreased with the increase of the coverage.When the vegetation coverage was larger than 47.66%,the slow-flow coefficient decreased significantly with the increase of the coverage.So,47.66%was the critical value of the coverage,the changes of the slow-flow coefficient with those of the Reynolds number under high or low vegetation coverage followed different patterns around this tipping point.Finally,the formulas for calculating the velocity and slow-flow coefficient under the simulated vegetation coverage were then derived.The verification result shows that the formulas have high accuracy and can provide theoretical reference for the prediction of soil erosion.