砾石覆盖对坡面流水动力学特性试验研究

发布时间：2018-02-24 04:40

本文关键词： 紫色土覆盖度粒径水动力学特性细沟侵蚀　出处：《华中农业大学》2015年硕士论文　论文类型：学位论文

【摘要】：紫色土是一种初育土,结构疏松,母岩裂隙发育,极易风化,土壤侵蚀十分强烈。由于紫色土风化程度浅,砾石含量高成为了紫色土主要特征之一。坡面薄层水流是土壤水蚀过程的主要动力,水动力学特性与坡面侵蚀密切相关,而砾石覆盖和粒径大小对坡面薄层水流水动力学参数有着重要影响,开展不同砾石覆盖度和不同砾石粒径大小对坡面流水动力学参数变化的研究,不仅能够深入认识砾石对坡面侵蚀的作用机理及其影响,更重要的是能够为紫色土地区水土保持措施规划以及水土流失治理方案提供科学依据。本试验以三峡库区秭归县王家桥小流域的紫色土为研究对象,选用光滑的鹅卵石并设置了5种砾石覆盖度(0、10%、20%、30%和40%),四种粒径大小(0.5-1 cm、1-2 cm、2-4 cm和4-6 cm)以及三种冲刷流量(2 L/min、4 L/min和6 L/min),坡度设置为5度,通过室内模拟冲刷实验(土槽2 m×0.5 m×0.15 m),对紫色土坡面流水动力学特性及细沟侵蚀含沙量变化的主要研究结论如下:(1)随着砾石覆盖度的增大,流速和弗劳德数有减小的趋势;径流深、水流剪切力、水流功率、阻力系数和曼宁糙率系数等都有增大的趋势,雷诺数变化不明显;细沟内雷诺数、平均流速、径流深和水流剪切力要比细沟间大;细沟内阻力系数和曼宁糙率系数一般要比细沟间小,特别是在覆盖度较大的条件下差异更为显著;随着冲刷流量的增大,雷诺数、径流深、水流剪切力等有增大的趋势。(2)径流含沙量随着冲刷流量增大而增大,随着砾石覆盖度的增大而减小。不同砾石覆盖度下径流含沙量变化趋势基本相同,在冲刷流量较大时(6 L/min)表现为先增大后减小,最后趋于平稳的趋势;在冲刷流量较小时(2 L/min),径流含沙量一直缓慢增大;细沟在无砾石覆盖时比有砾石覆盖发育快,在冲刷流量大时比冲刷流量小时发育快,径流含沙量的变化与细沟形态发育以及水流剪切力密切相关。(3)随着砾石粒径的增大,阻力系数和曼宁糙率系数等有减小的趋势;流速、径流深、水流剪切力、水流功率等有增大的趋势,雷诺数变化不明显;细沟内雷诺数、平均流速、径流深和水流剪切力要比细沟间大;细沟内阻力系数和曼宁糙率系数一般要比细沟间小;随着冲刷流量的增大,雷诺数、径流深、水流剪切力等有增大的趋势;相同冲刷流量下,随着砾石粒径的增大,侵蚀量不断增大。
[Abstract]:Purple soil is a kind of initial fertility soil with loose structure, the fissures of parent rock develop easily weathering, and soil erosion is very strong. High gravel content has become one of the main characteristics of purple soil. Thin layer flow is the main driving force of soil erosion, and hydrodynamic characteristics are closely related to slope erosion. The gravel coverage and particle size have an important influence on the hydrodynamic parameters of thin layer water income on the slope surface. Not only can the action mechanism of gravel on slope erosion and its effect on slope erosion be deeply understood, More importantly, it can provide a scientific basis for the planning of soil and water conservation measures and soil erosion control schemes in purple soil areas. This experiment takes the purple soil in the Wangjiaqiao small watershed of Zigui County, three Gorges Reservoir area, as the research object. The smooth cobblestones were selected and five kinds of gravel coverage were set up, including 30% and 40%, four sizes of 0.5 ~ (-1) cm ~ (2) cm ~ (2) ~ (2) cm ~ (2) and 4 ~ (6) cm), and three kinds of scour flow rates of 2 L / min and 6 L / min, with a slope of 5 degrees. Through the indoor simulated scour experiment (soil trough 2 m 脳 0.5 m 脳 0.15 m), the main research on the dynamic characteristics of income on the purple soil slope and the change of sediment content of rill erosion are as follows: 1) with the increase of gravel coverage, the velocity of flow and the Froude number decrease; Runoff depth, flow shear force, flow power, resistance coefficient and Manning roughness coefficient are all increasing, Reynolds number is not obvious, Reynolds number, average velocity, runoff depth and flow shear force are larger than those between the gullies. The resistance coefficient and Manning roughness coefficient in the rill are generally smaller than those between the furrows, especially under the condition of large coverage, the Reynolds number and runoff depth increase with the increase of scour discharge. The runoff sediment content increases with the increase of scour discharge and decreases with the increase of gravel coverage. When the scour flow is larger, the runoff sediment content increases slowly when the scour flow is larger, then increases, then decreases, and finally tends to steady. When the scour flow is less than 2 L / min, the sediment content in the runoff increases slowly, and the sediment content in the rill develops faster than the gravel cover when the scour flow is small. With the increase of gravel particle size, the resistance coefficient and the Manning roughness coefficient decrease with the increase of gravelly particle size, and the velocity of flow, the change of runoff sediment content is closely related to the development of rill shape and flow shear force. Runoff depth, flow shear force, flow power and so on have an increasing tendency, Reynolds number is not obvious, Reynolds number, mean velocity, runoff depth and flow shear force are larger than those between gullies. The resistance coefficient and Manning roughness coefficient in the rill are generally smaller than those between the furrows; with the increase of scour flow, Reynolds number, runoff depth, flow shear force and so on, there is an increasing trend, and at the same scour flow rate, with the increase of gravel particle size, The amount of erosion is increasing.
【学位授予单位】：华中农业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：S157

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