黄土细沟侵蚀径流水动力学特性研究

发布时间：2019-01-09 10:07

【摘要】：土地资源的损失已成为全球性的资源环境问题,而中国等发展中国家所面临的状况尤为严重。细沟沟道中的水流携带着大量的泥沙,加剧细沟的土壤侵蚀和水土流失。细沟水流侵蚀力和搬运能力均远远大于雨滴打击和坡面片状水流所具有的侵蚀力和搬运力,坡面水蚀动力和细沟发育过程相互影响、相互作用,同时又受流量、坡度和坡长等外界条件的影响。本文以黄土为研究对象,采用室内放水冲刷的方法在12m长土槽上进行细沟径流侵蚀研究,分别在5个坡度(5。,10°,15°,20°,25°)和3个流量(2,4,8 L/min)控制条件下研究黄土细沟径流流速沿坡长变化的规律,分析细沟侵蚀形态变化过程、细沟径流流速与流量和坡度的关系,侵蚀产沙量与细沟径流流速的关系,以探究黄土发生细沟侵蚀时的临界剪切力和最大剥蚀率。本研究对于揭示坡面土壤侵蚀过程及其内在规律、建立土壤侵蚀物理模型、提高土壤侵蚀预测和预报水平,具有重要的理论意义和实际应用价值。本研究得到以下结论：(1)细沟冲刷后形成的细沟深度呈现随着坡长的增加细沟深度先增加后减小的趋势。距放水口0～2m段,细沟深度具有最大值；大坡度大流量时距放水口0.5 m左右细沟深度出现最大值。表明在放水冲刷试验中距放水口0-2 m处细沟侵蚀最强。细沟内跌穴出现沿坡长分布具有随机性,细沟深度在沿坡长发育过程中呈现波动性。(2)黄土细沟侵蚀中坡度和流量是影响细沟径流流速的主要因素,流速随坡度和流量增加而增加。细沟径流平均流速与坡度、流量成幂函数关系,拟合经验公式为v=1.488·q0.342S0.644。坡度一定条件下,细沟径流流速与放水流量之间呈幂函数关系：v=α.Qb,相关分析表明随着流量变化,细沟流速可以用经验公式很好的拟合。(3)细沟径流流速沿坡长0-8 m时呈现迅速增加的加速状态,在8-12 m坡长段细沟径流流速增加速度减缓,流速变化趋于平衡,细沟侵蚀达到动态平衡。细沟径流流速与坡长之间存在幂函数关系,拟合经验公式为v=c.Ld。拟合系数c的变化范围为0.1772～0.8836,指数d变化范围为0.0747～0.3265。(4)细沟径流剪切力随坡长的变化可用幂函数方程描述：τ=k·Ln,其中系数n的值均为负数,表明径流剪切力随坡长变化呈递减趋势；系数k表现为坡度相同时,流量越大k值越大；当流量相同时,随着坡度的增加k值也会逐渐增大。k值变化与径流剪切力在不同坡度和流量条件下的变化趋势相同,因此k值可以用来描述径流剪切力随坡度和流量变化的分布特征。(5)试验坡度和水流流量对径流泥沙含量和径流剪切力的影响是相似的,都会随着坡度和流量的增大而增大,但是影响关系是不同步的,即径流泥沙含量的耦合作用效果要大于径流剪切力。细沟内径流剪切力随着泥沙含量的增加呈减小趋势,径流剪切力与泥沙含量之间的关系可以用线性函数表达为：τ=m+p·c。(6)径流剪切力和剥蚀率是研究径流对细沟内泥沙侵蚀强度的指标,细沟内剥蚀率呈现随坡长增加而递减的分布特征,细沟内径流剪切力与径流剥蚀率呈显著线性关系,且随径流剪切力值增大径流剥蚀率也增大,二者之间的关系可以用线性方程来模拟：Drmax=a+b·x。计算得到本试验土壤的可蚀性参数Kd值为0.1361 kg/(m2·s),临界剪切力T0值为0.2367 N/m2。
[Abstract]:The loss of land resources has become a global resource environment problem, and the situation of the developing countries such as China is particularly serious. The water flow in the channel of the fine trench carries a large amount of sediment, which increases the soil erosion and soil erosion of the fine trench. The erosion force and handling capacity of the water flow of the fine trench are much larger than that of the raindrop striking and surface-like water flow, and the interaction and interaction between the water erosion power and the fine trench development process of the slope surface are influenced by the external conditions such as flow, slope and slope length. In this paper, on the basis of loess as the research object, the runoff erosion of the fine trench is carried out on the 12m long soil tank by using the method of indoor water discharge and erosion, and the law of the change of the flow velocity along the slope of the loess fine trench is studied under the control conditions of 5 slope (5., 10 掳, 15 掳, 20 掳, 25 掳) and 3 flow (2, 4, 8 L/ min), respectively. The relationship between the flow velocity of the fine trench and the flow rate and the slope of the fine trench is analyzed, and the relationship between the sediment concentration and the flow velocity of the fine trench is analyzed to study the critical shear and the maximum erosion rate at the time of the fine trench erosion in the loess. The study is of great theoretical significance and practical application value to reveal the process of soil erosion and its internal law in the slope surface, to establish a physical model of soil erosion, to improve the prediction and forecast of soil erosion. The following conclusions are obtained in this study: (1) The depth of the fine trench formed after the fine trench is washed is shown to decrease with the increase of the slope length and the depth of the fine trench. The depth of the fine trench has a maximum value from 0 to 2m of the water discharge port, and the maximum value of the depth of the fine trench at the distance of about 0.5 m from the water outlet when the large-grade large flow is large. It is shown that the erosion of the fine trench at 0-2m from the water outlet is the strongest in the water-discharge flushing test. There is randomness in the long distribution along the slope, and the depth of the fine trench presents the fluctuation in the course of the long development of the slope. (2) The slope and flow rate in the erosion of the fine trench of the loess are the main factors that affect the flow velocity of the fine trench, and the flow velocity is increased with the increase of the slope and the flow rate. The average flow velocity of the fine channel runoff is the power function relation with the slope and the flow rate, and the fitting experience formula is v = 1. 488. q0. 342so. 644. There is a power function relation between the flow velocity of the fine trench and the discharge water flow under a certain condition: v = 1. Qb, the correlation analysis shows that with the change of flow, the flow rate of the fine channel can be well fitted with the empirical formula. (3) The flow velocity of the fine trench is increased rapidly along the slope length of 0-8 m, and the velocity of the flow velocity of the fine channel in the long section of the 8-12 m slope is reduced, the flow rate change tends to be balanced, and the erosion of the fine trench reaches the dynamic balance. There is a power function relation between the flow velocity of the fine channel and the length of the slope, and the formula of the fitting experience is v = c. Ld. The variation range of the fit coefficient c is 0.1772-0.8836, and the variation range of the index d is 0.0747-0.3265. (4) The shear force of the fine trench can be described by the power function equation with the change of the slope length: xt = k. Ln, where the value of the coefficient n is negative, indicating that the runoff shearing force is decreasing with the change of the slope length; when the coefficient k is the same as the slope, the greater the value of the higher k value of the flow; and when the flow is the same, As the slope increases, the value of k also increases. The k-value change is the same as that of the runoff shearing force under different slope and flow conditions, so the k-value can be used to describe the distribution characteristics of the runoff shearing force with the change of the slope and the flow rate. (5) The effect of the test slope and the flow rate on the runoff and sediment content and the runoff shear force is similar, which will increase with the increase of the slope and the flow rate, but the influence relation is not synchronous, that is, the coupling effect of the runoff and sediment content is greater than the runoff shearing force. The flow shear force in the fine trench decreases with the increase of the sediment content, and the relation between the runoff shear force and the sediment content can be expressed by the linear function as: m = m + p 路 c. (6) The runoff shearing force and the denudation rate are the index of the study run-off on the erosion intensity of the sediment in the fine trench. The erosion rate in the fine trench presents a decreasing distribution characteristic along with the increase of the slope length, and the runoff shear force in the fine trench is linearly related to the runoff and denudation rate, and the runoff erosion rate is increased along with the runoff shearing force value, and the relationship between the two is simulated by the linear equation: Drmax = a + b 路 x. The Kd value of the soil in this test is 0.1361 kg/ (m2 路 s), and the critical shear force T0 is 0.2367N/ m2.
【学位授予单位】：西南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：S157

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