模拟草被覆盖下坡面水流阻力特性试验研究

Experimental Study on Overland Flow Resistance Characteristics Under Simulated Grass Cover

探究植被覆盖下的坡面流阻力特性对土壤侵蚀模型的建立有着重要意义。通过3个坡度、7个流量和10个草被覆盖度下的定床冲刷实验,系统分析坡面薄层水流的流型流态与阻力特性。实验结果表明,坡面水流流态受到草被覆盖度与坡度的综合影响,主要分布在层流区及过渡流区。通过等效粗糙度和坡面水流流动阻力规律,推导出等效阻力系数f_(e)的计算公式,公式表明草被覆盖度是影响水流阻力的重要因素,f_(e)值随覆盖度增加而整体增大,实验结果显示当覆盖度在0%~37.68%的范围内时,等效阻力系数始终小于1.5;而当覆盖度在56.52%~94.2%的范围内时,f_(e)由0.697~3.042增长至2.440~14.393。淹没度及雷诺数对等效阻力系数的影响与覆盖度密切相关,覆盖度低于18.84%时,等效阻力系数随淹没度与雷诺数的增加而呈减小趋势;而当覆盖度高于65.94%时,等效阻力系数随淹没度与雷诺数的增加而以较大的速率上升。研究结果以期为水土流失综合治理提供理论支撑。

It is important to explore the resistance characteristics of overland flow under vegetation cover for the establishment of soil erosion model. In this study, the flow pattern and resistance characteristics of slope thin-layer flow were systematically analyzed through fixed-bed scouring experiments under three slopes, seven flows, and ten types of grass covers. The experimental results showed that the slope flow pattern was aff_(e)cted by the interactive influence of grass cover and slope, which were mainly distributed in laminar and transition flow areas.Using the equivalent roughness and the law of resistance on overland flow, a calculation formula for the equivalent resistance coefficient was derived. The formula shows that grass cover is an important factor that aff_(e)cts the flow resistance, and the equivalent resistance coefficient increases with the increase of coverage. The experimental results also showed that when the coverage was in the range of 0%~37.68%, the equivalent resistance coefficient was always less than 1.5;when the coverage was in the range of 56.52%~94.2%, the equivalent resistance coefficient increased from 0.697 to 3.042 to 2.440 to 14.393. The influence of submergence and Reynolds number on the equivalent resistance coefficient was closely related to the coverage. When the coverage was less than 18.84%, the equivalent resistance coefficient decreased with the increase of the submergence and Reynolds number;when the coverage was higher than 65.94%, the equivalent drag coefficient increased at a large rate with the increase of the submergence and Reynolds number. The results are expected to provide theoretical support for the comprehensive control of soil and water loss.