细沟流侵蚀产沙及断面形态研究

发布时间：2018-03-18 13:02

本文选题：细沟流　切入点：水动力学特性　出处：《西北农林科技大学》2017年硕士论文　论文类型：学位论文

【摘要】：黄土高原水土流失问题是整个中国乃至世界水土流失最为严重的地区,流失面积占整体75%以上。其中细沟侵蚀是黄土坡面上最主要侵蚀方式之一,占水土流失面积一半以上。水动力学条件和床面土壤条件是细沟侵蚀的两个主要因素,而细沟侵蚀产沙和纵横断面形态发育过程与径流水动力学参数相辅相成。系统分析细沟水动力学特性及径流产沙量和断面形态发育影响因素对深入研究细沟侵蚀机理有一定价值。本文通过室内冲刷试验,基于黄河中游多沙粗沙区的陕西省神木县沙黄土以及关中平原区杨凌当地X土两种土壤,分别研究了沙黄土(坡度:3°、9°、15°;流量:2.4、3.6、4.8、6.0、7.2L/min)和X土(坡度:2°、4°、6°、8°、10°、12°;流量:8、16、24、32、40L/min)在流量和坡度完全组合试验条件下,径流水动力学特征、径流产沙机理以及沟道纵横断面几何形态发育。主要得出以下结论:(1)细沟平均流速、水深均与流量和坡度呈幂函数关系,相较于坡度,流速和水深与流量的关系更为显著,分析是因为与床面阻力构成有关。弗劳德数大致在0.96~1.30之间,床面形态属于动平床过渡区,通过对比分析发现,床面能态与土壤粘粒含量和中值粒径有关。雷诺数变化范围为:307~1465,可知细沟水流流态处在过渡区范畴。水流阻力系数与雷诺数的相关性并不显著,这与明渠水流中紊流粗糙区的阻力特征比较类似。(2)横断面方向上,横断面宽深比随坡度的增大而减小,说明下切和溯源侵蚀是细沟发育过程中主要的侵蚀方式,而沟壁坍塌侵蚀作用比较微弱。且与最佳断面所对应的宽深比相差较远,即床面还未达到稳定状态。横断面形态指标随冲刷历时和坡度的增加而增大,并逐渐趋近于梯形水力最佳断面对应的横断面形态指标。随距顶距离的增加,横断面指标逐渐减小,随着流程长度的增加,细沟断面形态由宽深状逐渐变窄,同时细沟侵蚀深度也减小。纵横面形态系数范围为:0.60δ11.26。纵横面形态系数与坡度呈正相关,与流量相关性不大。糙率系数和消能率均与纵横面形态系数呈幂函数增加。(3)随着距顶距离增大,断面均速呈波动性增加。断面均速与流量和断面呈0.001水平的极显著性相关,而和坡度关系不大。含沙量与流量、坡度的关系可用幂函数描述,且均呈极显著性相关。径流切应力和有效水流功率与侵蚀产沙量的关系分别为线性和幂函数形式,其中有效水流功率能更好的描述细沟侵蚀产沙。水流挟沙饱和系数随坡度和流量的增大而增大,由于试验土壤粘性较大,坡度对土壤输移的贡献不及土壤颗粒粘聚力的作用,挟沙饱和系数随坡度的增加其增加趋势减缓。
[Abstract]:The problem of soil and water loss in the Loess Plateau is the most serious in China and the world, and the area of soil erosion is more than 75%. The rill erosion is one of the most important erosion methods on the loess slope. The hydrodynamic condition and the bed soil condition are the two main factors of rill erosion. The development process of sediment yield and cross section and runoff hydrodynamic parameters are complementary to each other. A systematic analysis of the hydrodynamic characteristics of rill gullies and the influence factors of sediment yield and section shape development on the study of rill erosion. The mechanism has certain value. Based on the sandy loess in Shenmu County, Shaanxi Province, in the middle reaches of the Yellow River, and Yang Ling local X soil in Guanzhong Plain, The runoff hydrodynamics characteristics of sandy loess (slope: 3 掳/ 9 掳/ 15 掳; flow: 2. 4 / 3. 64.86.0 / 7.2L / min) and X soil (0: 2 掳/ 4 掳/ 6 掳/ 8 掳/ 8 掳/ 10 掳/ 12 掳) were studied respectively under the conditions of combined flow and slope tests. The main conclusions are as follows: (1) the average velocity and depth of the rill have a power function relationship with the flow rate and the gradient. Compared with the slope, the relationship between the velocity and depth of water and the flow rate is more significant. The Froude number is approximately between 0.96 and 1.30, and the bed shape belongs to the transitional zone of moving flat bed. The energy state of the bed surface is related to the clay content and the median particle size of the soil. The Reynolds number varies in the range of 1: 307 ~ 1465, which shows that the flow pattern of the rill is in the transition zone, and the correlation between the flow resistance coefficient and the Reynolds number is not significant. This is similar to the resistance characteristics of turbulent rough area in open channel flow. In the cross section direction, the ratio of width to depth of cross section decreases with the increase of slope, which indicates that undercutting and traceability erosion are the main erosion modes during the development of rill trenches. The ratio of width to depth corresponding to the optimum section is far different, that is, the bed surface has not reached a stable state. The cross section shape index increases with the increase of scour duration and slope. With the increase of the distance from the top to the top, the cross section index gradually decreased, and with the increase of the flow length, the shape of the rill section gradually became narrower from the wide to the deep shape, and the cross section shape of the trapezoidal hydraulic optimum section gradually decreased with the increase of the distance from the top to the top. At the same time, the depth of rill erosion also decreased. The shape coefficient of vertical and horizontal plane was in the range of: 0.60 未 11.26. The shape coefficient of vertical and horizontal plane was positively correlated with the slope. The roughness coefficient and energy dissipation coefficient were increased by power function with the shape coefficient of vertical and transverse plane. (3) with the increase of the distance from the top to the top, the average velocity of the section increased and the average velocity of the section increased, and the average velocity of the section was significantly correlated with the flow rate and the cross section at the level of 0.001. The relationship between sediment content and discharge and slope can be described by power function, and the relationship between runoff shear stress and effective flow power and erosion sediment yield is linear and power function, respectively. The effective flow power can better describe the sediment yield of rill erosion. The saturated coefficient of sediment transport increases with the increase of slope and flow rate, and the contribution of slope to soil transport is not as good as that of soil particle cohesion due to the large viscosity of experimental soil. The increasing trend of sediment saturation coefficient decreases with the increase of slope.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S157.1

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