引用本文:白玉洁,张风宝,杨明义,李占斌,张加琼.急陡黄土坡面薄层水流水力学参数变化特征[J].土壤学报,2018,55(3):641-649. DOI:10.11766/trxb201710310307
BAI Yujie,ZHANG Fengbao,YANG Mingyi,LI Zhanbin,ZHANG Jiaqiong.Variation of Hydraulic Parameters of Shallow Flow on Steep Loess Slope[J].Acta Pedologica Sinica,2018,55(3):641-649. DOI:10.11766/trxb201710310307
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急陡黄土坡面薄层水流水力学参数变化特征
白玉洁1, 张风宝1, 杨明义1, 李占斌2, 张加琼1
1.黄土高原土壤侵蚀与旱地农业国家重点实验室(西北农林科技大学水土保持研究所);2.中国科学院水利部水土保持研究所
摘要:
为探明降雨条件下黄土急陡坡坡面薄层水流水力学特性,采用室内模拟降雨的方法,研究了6个坡度(25°、30°、35°、40°、45°和50°)和3个雨强(1.0 mm min-1、1.5 mm min-1和2.0 mm min-1)组合条件下坡面薄层水流水力学参数的变化规律。结果表明:(1)坡度相同时,流速随雨强的增加而增大;雨强相同时,坡度对薄层水流流速的影响存在临界效应(40°~45°),小于临界坡度,流速随坡度的增加而增大,大于临界坡度,流速随坡度增加而减小。(2)各坡度条件下,坡面薄层水流的平均径流水深随降雨强度增加呈平稳增长趋势;相同雨强时,径流深随坡度的增大有减小趋势。(3)黄土急陡坡坡面雷诺数(Re)整体较小(远小于580),试验条件下坡面薄层径流属于层流且水流处于层流中的失稳区;弗劳德数(Fr)大于0.8,薄层水流属于急流。(4)阻力系数(f)随着降雨强度增加而增大,随着坡度的增加而减小。(5)方差分析结果显示,雨强、坡度及二者交互作用对急陡坡坡面薄层水流水力学参数均有显著影响(p<0.01),但流速、弗劳德数和阻力系数的变化主要受坡度控制,而径流深和雷诺数的变化主要受雨强控制。
关键词:  模拟降雨  急陡坡  薄层水流  水力学参数
基金项目:国家自然科学基金项目(41571130082、41330858、41371283)和国家重点研发计划项目(2016YFC0402406)
Variation of Hydraulic Parameters of Shallow Flow on Steep Loess Slope
BAI Yujie1, ZHANG Fengbao1, YANG Mingyi1, LI Zhanbin2, ZHANG Jiaqiong1
1.State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University;2.Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources
Abstract:
【Objective】Hydraulic characteristics of shallow flow are essential to elucidating mechanisms of soil erosion and sediment yield on the slope. However, most of the studies in this aspect have been reported on slopes less than 25° in gradient. This paper is oriented to study hydraulic characteristics of steep loess slopes (25°~50°), in an attempt to lay down a foundation for elucidating in-depth relationships of the hydraulic characteristics of shallow water flow on slopes with slope soil erosion. 【Method】An indoor experiment was carried out simulating rainfalls on steep loess slopes. The experiment was designed to have only one soil type (loessal soil), three rainfall intensity (1.0mm min-1, 1.5 mm min-1 and 2.0 mm min-1) and six slope gradient (25°, 30°, 35°, 40°, 45° and 50°) with the aid of perforated metal flumes (3 m in length, 1 m in width and 0.30 m in depth). Runoff, sediment and flow velocity on the slopes were observed, relative to rainfall intensity and slope gradient. 【Result】Results show: (1) Flow velocity increased with rising rainfall intensity on slopes the same in gradient, and under the same rainfall intensity, the effect of slope gradient on flow velocity exhibited a critical point in gradient, that is, between 40° and 45° under the same rainfall intensity. On slopes with gradient lower than the critical point, flow velocity increased with rising slope gradient, whereas on slopes with gradient higher than the point, flow velocity decreased with rising slope gradient. (2) Mean runoff depth increased steadily with rising rainfall intensity on all slopes regardless of gradient; but decreased with rising slope gradient under rainfalls the same in intensity. (3) Reynolds numbers of steep loess slopes were on the whole relatively small, often far below 580. In this study shallow flows on slopes were of laminar flow in destabilized layers, while shallow flows with Froude number beyond 0.8 were of rush. And (4) Darcy-Weisbach resistance coefficient (f) was positively related to rainfall intensity and negatively to slope gradient. 【Conclusion】Rainfall intensity, slope gradient and interactions between these two factors all have significant effects on hydrodynamic parameters (p<0.01) of shallow flow on steep slopes, but flow velocity, Froude number and Darcy-Weisbach resistance of the shallow flow varied mainly with slope gradient, while runoff depth and Reynolds number did mainly with rainfall intensity.
Key words:  Simulated rainfall  Steep slope  Shallow flow  Hydraulic parameters