含沙水流和坡面糙度对红壤团聚体输移破坏影响

发布时间：2018-04-28 08:17

本文选题：坡面水流 + 红壤团聚体　；参考：《华中农业大学》2017年硕士论文

【摘要】：我国南方红壤丘陵区人口密度大,丘陵坡地利用率高,土壤侵蚀退化严重。同时,该区域降雨集中且强度大,分散的地表径流由于受到地形影响逐渐集中,从而冲刷地表而产生坡面侵蚀。本研究选取第四纪红黏土发育的红壤作为研究对象,系统的分析了不同水流含沙量和坡面糙度条件下,坡面流水力学特性的变化及其对红壤团聚体破坏剥蚀的影响,从机理层面揭示坡面流内团聚体输移破坏规律。主要取得的结论如下:1.通过对5种模拟糙度和6种不同冲刷距离组合下3种粒径的红壤团聚体在坡面水流内的剥蚀破坏规律的研究得出:(1)在相同运移距离条件下,随粒径和糙度的增加团聚体剥蚀破坏程度呈增加趋势,与粒径相比,糙度对剥蚀破坏程度的影响更大。(2)相同模拟糙度下,随着运移距离的增加,剥蚀率均呈抛物线形先增大后减小的趋势;各运移距离下,7~5 mm粒径团聚体的剥蚀率随糙度的增加而增加;5~3 mm和3~1 mm粒径团聚体在各运移距离内随糙度的增加变化规律不一致。(3)团聚体剥蚀破坏程度随径流水深、阻力系数、水流剪切力的增加均呈幂函数减小后趋于平缓的趋势,且大粒径较小粒径变化趋势更明显;但是不同糙度下,水深对团聚体剥蚀破坏程度的影响还需在多坡度流量条件下进行进一步探索。2.选取单一粒径的红壤团聚体,在4种坡度、5种流量和5种模拟糙度条件下进行冲刷试验,详细分析水力学特性的变化及其对团聚体破坏剥蚀的影响。(1)相同糙度条件下,小坡度(8.8%~17.6%)时,随流量的增加,团聚体剥蚀程度下降;而在较陡坡度(26.8%~36.4%)和下垫面糙度较大时,Wr/Wi值随流量变化规律有所不同,在大流量(1.0 L·s-1~1.2 L·s-1)条件下Wr/Wi值均有不同程度的下降。(2)在各糙度下,平均流速和水流剪切力随坡度和流量的增加而增加;径流水深随流量的增加而增加,随坡度的增加而减小,而阻力系数的变化却与之相反。随着下垫面糙度的增加,径流水深、阻力系数以及水流剪切力呈增加趋势,而平均流速呈减小趋势。(3)多个坡度和流量组合下,Wr/Wi值随径流水深变化无明显规律,但单一糙度中,Wr/Wi(%)值均随径流水深的增加呈现幂函数增加的趋势;在不同糙度和单一糙度下,Wr/Wi值均随阻力系数和水流剪切力的增加呈幂函数减小趋势。3.选取单一粒径的红壤团聚体,在2种坡度、5种流量和5种不同浑水条件下进行冲刷,详细分析水力学特性的变化及其对团聚体破坏剥蚀的影响。(1)清水条件下,Wr/Wi值随流量的增加而增加,表现为团聚体剥蚀破坏程度的随流量的增加而下降;所有处理中,Wr/Wi值均随含沙量的增大呈现幂函数的减小趋势。(2)随着供沙量和流量的增加,水深均呈增加趋势;在两种坡度条件下,流量、供沙量及其之间的交互作用对水深的影响均表现为:流量供沙量交互作用。五种流量下,随着供沙量的增加,平均流速、雷诺数和弗汝德数均呈减小趋势,坡面流呈现出由紊流急流向层流缓流发展的趋势。各流量下,阻力系数随供沙量的增加而变大,且大坡度(15°)条件下表现更为明显。在各坡度和供沙量组合条件下,阻力系数均随雷诺数的增加呈幂函数减小趋势,且有较好的相关性。(3)在相同流量中,Wr/Wi(%)值随径流水深、水流剪切力的增加呈幂函数降低趋势,综合所有不同含沙量数据,Wr/Wi(%)值随径流水深和水流剪切力变化无明显规律。本试验条件中Wr/Wi(%)所有值均随着阻力系数的增大呈幂函数形式减小,团聚体剥蚀破坏程度随阻力系数增加而增加。
[Abstract]:The red soil hilly area of southern China has a large population density, high utilization rate of hilly slope land and severe soil erosion. At the same time, the rainfall concentration and intensity are large and the scattered surface runoff is gradually concentrated due to the topography effect, thus erosion on the surface of the surface. The red soil developed in the Quaternary red clay is selected as the research object. The variation of hydraulic characteristics of slope surface flow under the conditions of different flow sediment and slope roughness and its effect on the destruction and erosion of red soil aggregates are analyzed systematically. The failure rules of aggregate transport in the slope flow are revealed from the mechanism level. The main conclusions are as follows: 1. by combining 5 kinds of simulated roughness and 6 different scour distances. The erosion damage law of red soil aggregates with grain size in the flow of slope is studied. (1) under the same migration distance, the erosion damage degree of aggregate increases with the increase of particle size and roughness. Compared with the particle size, roughness has a greater impact on the degree of erosion damage. (2) under the same simulated roughness, with the increase of migration distance, peeling off. The erosion rate increases first and then decreases, and the erosion rate of 7~5 mm particle aggregates increases with the increase of roughness, and the variation of 5~3 mm and 3~1 mm aggregates with the increase of roughness is not consistent with the roughness. (3) the degree of erosion and destruction of aggregates follows the depth of runoff, the coefficient of resistance and the shear force of the flow. The increase of the power function tends to be slow after the power function decreases, and the large particle size is more obvious than the small size. But under the different roughness, the influence of the depth of water on the erosion degree of the aggregate should be further explored under the condition of the multi slope flow and the single particle size of the red soil aggregate should be selected by.2., in 4 kinds of slope, 5 kinds of flow and 5 kinds of simulation. Under the roughness condition, the change of the hydraulic characteristics and its effect on the damage and erosion of aggregates were analyzed in detail. (1) the erosion degree of aggregates decreased with the increase of the flow rate under the same roughness (8.8%~17.6%), while the Wr/Wi value changed with the flow rate at the higher gradient (26.8%~ 36.4%) and the lower surface roughness. Under the conditions of large flow (1 L. S-1~1.2 L. S-1), the Wr/Wi value decreased in varying degrees. (2) under the roughness, the average flow velocity and flow shear force increased with the increase of slope and flow; the depth of water increased with the increase of the flow rate, and decreased with the increase of the gradient, but the change of the resistance coefficient was opposite to the underlying surface. The increase of roughness, water depth, drag coefficient and flow shear force showed an increasing trend, and the average flow velocity decreased. (3) under the combination of multiple slopes and flow, there was no obvious law of Wr/Wi value with the depth of water flow, but in the single roughness, Wr/Wi (%) value increased with the increase of the depth of water flow; in different roughness and single. Under the roughness, the Wr/Wi value decreases with the increase of the resistance coefficient and the increase of the flow shear force.3., the single particle size of red soil aggregates is selected, and the 2 gradient, 5 flow and 5 different muddy water conditions are scoured. The variation of the hydraulic characteristics and its effect on the destruction and erosion of the aggregates are analyzed in detail. (1) the value of Wr/Wi under clear water conditions. With the increase of flow, the degree of erosion and destruction of aggregates decreased with the increase of flow rate; in all treatment, the Wr/Wi value decreased with the increase of sediment content. (2) with the increase of sediment supply and flow, the depth of water increased; under the two gradient conditions, the flow, the amount of sediment supply and the interaction between them The effect of the effect on water depth is the interaction of flow supply. Under five kinds of flow, the average flow rate, Reynolds number and Froude number decrease with the increase of sediment supply, and the slope flow shows a trend from turbulent flow to laminar flow. The resistance coefficient increases with the increase of sediment supply and the large slope (15 degrees) under each flow. Under the conditions of slope and sand supply, the resistance coefficient decreases with the increase of the Reynolds number, and has a better correlation. (3) in the same flow, the Wr/Wi (%) value is deep with the diameter flow, the increase of the flow shear force decreases with the power function, and the Wr/Wi (%) value is integrated with all the different sediment content data. There is no obvious law of changing the depth of water and the shear force of water flow. All the values of Wr/Wi (%) decrease in the form of power function with the increase of the resistance coefficient, and the erosion degree of the aggregate increases with the increase of the drag coefficient.

【学位授予单位】：华中农业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S157.1

【参考文献】