草被覆盖度下坡面流流速变化及缓流机制研究

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。

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

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.