【作者】 赵纯清；

【导师】 蔡崇法；

【作者基本信息】 华中农业大学 ， 土壤学， 2014， 博士

【摘要】 在我国南方湿润、半湿润丘陵地区,坡地面积大且是重要的耕地资源。由于不合理的坡地利用,加上南方地区雨量大、降雨强度大的影响,坡地发生沟蚀十分常见。由于汇聚了较多的水流,冲刷动能较大,对坡地侵蚀严重,造成坡地大量的水土流失。本文拟采用植物篱技术防治南方地区坡地沟蚀为目的,以南方地区坡地形成的沟道为研究对象,通过自主设计的室内模拟冲蚀水槽装置,在较大径流量冲刷条件下,对沟道径流的水力特性和径流挟沙力进行试验研究。分析了植物篱在径流中的受力和形变、植物篱拦挡下的径流钝体绕流和对径流动能的影响,试验研究了不同植物篱拦挡模式对径流水力特性及挟沙力的影响,取得的主要结论如下：1.在调查南方地区发生沟蚀的坡地地形、沟道径流特点的前提下,自主设计并制造了一种适合沟道侵蚀室内模拟试验的冲蚀水槽装置。该装置可进行无土、填土冲蚀试验和植物篱拦挡试验等。满足试验坡度为1°、5°、15°、25°、径流量为0-0.13m3/min、泥沙浓度为0～100g/L的径流冲刷试验要求,并可满足槽底糙度为0.01、0.02的试验要求。整体装置具有结构紧凑、占用空间少,试验操作方便等特点。2.无植物篱拦挡时,通过改变冲蚀槽底糙度,在设定4种试验坡度分别对应4种流量试验条件下,对沟道径流的水力特性进行了试验研究。研究得出了浅沟径流的挟沙力与坡度和流量的定量关系(糙度0.01),并对径流挟沙时不同粒径泥沙的沉积特性进行了分析。(1)沟道径流属于薄层水流范畴,槽底糙度对径流流速影响明显,槽底糙度越大,流速越小；流速随着流量、坡度的增加而增大且呈现幂函数增加关系(R2=0.98,p<0.05),径流水深随着流量的增加而增大,随着坡度的增加而减小,它们之间的关系符合幂函数关系(R2=0.98,p<0.05)。(2)试验得出沟道径流的雷诺数(Re)在842～5467之间,沟道水流流态属于紊流,水流雷诺数的大小与径流量呈现较好的正相关性,流量越大,雷诺数越大。坡度和槽底糙度对水流的雷诺数影响不明显；沟道径流的佛汝德数(Fr)在1.05～18.89之间,属于急流范畴,流量对佛汝德数的影响不明显,坡度和槽底糙度对佛汝德数的影响明显,它们的值越大,佛汝德数越小。(3)沟道径流的挟沙力与流量和坡度有关,径流挟沙力随流量的增加而增大、随着坡度的增加挟沙力急剧增加,通过回归分析得出的挟沙力模型为：T=292.95X0.98Y0.22(R2=0.93P<0.05)。流量对同一粒径泥沙沉积影响不明显,坡度对同一粒径泥沙沉积影响显著。坡度为1°时,径流对2-4mm泥沙的输移力较大,对0.02-2mm、小于0.02mmm粒径泥沙输移力较小；大坡度(15°、25。)时,小于0.02mmm粒径泥沙沉积量较多,2-4mm、0.02-2mm粒径泥沙颗粒沉积较少。3.通过力学分析和物理方法推演,对径流中的泥沙受力、侵蚀产沙、植物篱受力形变和径流钝体绕流进行了研究,结果表明：在径流作用和植物篱阻挡下,泥沙受到径流拖曳力、上举力、黏结力、渗透压力、重力、浮力和植物篱拦挡引起的阻力作用,径流发生产沙的剪切力至少大于水压引起的摩擦力、土壤黏结力引起的摩擦力和植物篱拦挡引起的阻力之和；植物篱形变的主要动力是径流水头压力,植物篱最大绕度方程为：植物篱转角方程为：并分析了植物篱布置时需要考虑植物篱变形因素的原因；在植物篱拦挡下,钝体绕流的宽度与流量呈正相关,与流速呈负相关的线性关系,植物篱对径流的阻挡影响径流的流线,径流沿流线的交叉碰撞和叠加导致其动能的消耗,降低了径流的侵蚀力。4.确定紫穗槐和蓑草在5cmX5cm、1OcmX10cm拦挡模式(糙度0.01)、4种坡度分别对应4种流量的条件下,对拦挡下的径流的水力特性进行试验研究,并研究了不同拦挡模式下径流的挟沙力、拦挡效果及不同粒径泥沙的沉积特性。(1)在植物篱拦挡下,径流流速与单宽流量、坡度呈幂函数增加关系(R2=0.98P<0.05)；蓑草5cmX5cm拦挡模式在小坡度(1°、5°)时可以大大降低径流的流速,但在大坡度时对流速的影响较小,其它3种拦挡模式在坡度为1°时对流速影响有限,坡度为5°、15。、25°时对流速影响不明显。径流深度与单宽流量、坡度呈幂函数关系(R2=0.98P<0.05)；植物篱拦挡时径流深度随径流量的增加而增大,在坡度为1°时增长较快,但在5°、15°、25。时增长缓慢。小坡度时径流深度较深,大坡度时径流深度较浅,大坡度时径流深度之间的极差较小。(2)植物篱拦挡下水流流态仍属于紊流流态。植物篱的拦挡、坡度对沟道径流的雷诺数影响不明显,流量是影响水雷诺数的主控因素。坡度对佛汝德数的影响十分明显,其中蓑草在5cm X5cm模式拦挡下坡度为1°时,径流属于缓流,其它情况均为急流。(3)在植物篱拦挡下,小坡度时径流的挟沙力随流量的增加而增大,径流量是影响径流挟沙力的主要因素；在大坡度时,径流的挟沙力很大,坡度是影响径流挟沙力的主要因素；4种模式的拦沙能力分别为蓑草5cmx5cm>紫穗槐5cmx5cm>蓑草>10cmxl0cm>紫穗槐10cmx10cm;流量对同一粒径泥沙沉积影响不明显,坡度对同一粒径泥沙沉积影响显著。在蓑草拦挡下,坡度为1°时,较大粒径的泥沙颗粒发生输移,较小颗粒泥沙易于沉积；坡度为50时,2～4mm泥沙沉积相对量较少,0.02～2mm粒径泥沙易于输移。对于0.02mm以下粒径泥沙,在坡度为1°、5°时,植物篱对该粒径泥沙拦挡效果较差。更多还原

【Abstract】 In the humid and semi-humid hilly area in South China, there are plenty of the slope land and it’s important arable resource, the gully erosion is very common phenomenon because of the influence of the unreasonable land use and heavy rainfall. Because much water is collectted in the gully, and it has larger erosion kinetic energy leading soil and water loss away, so the slope land erosion is serious. The purpose of this paper was using the hedgerow technology to prevent the gully erosion in south area, and the object was the gully formed in the southern slope land, under the conditions of the large runoff, experimental studied hydraulic characteristics and transporting sediments capacity of gully flow through simulation erosion flume device designed by ourselves. Analyzed not only the stress and deformation of hedgerow, but also the effects of hedgerow block on the runoff kinetic energy and the runoff around a blunt body, and experimental studied the effects of different hedgerow block on hydraulic characteristics and transporting sediments capacity of gully flow, the main results were as follows:1. According to character of the gully flow and the slope land of gully erosion in the south area, we designed a kind of erosion flume device which was suitable for gully erosion simulation experiment indoor. This device could complete a variety of experiment including soilless and soil erosion experiment, hedgerow block experiment and so on. Experiment condition included that slope gradient is1°,5°,15°,25°, the flow discharge is0-0.13m3/min, the sediment concentration is0-100g/L, the roughness is0.01and0.02. The whole device is characteristic of compact structure, less space occupation, convenient experiment operation.2. By using different roughness at the bottom of erosion flume and no hedgerow block, under the conditions of4kinds of experiment slope gradient corresponding to4kinds of flow discharge, experimental studied the hydraulic characteristics of gully flow. The results showed the quantitative relationship between the transporting sediments capacity of ephemeral gully flow and the slope gradient and the flow discharge (rigesity was0.01), and analyzed the deposition character of different size sediments.(1) The ephemeral gully flow belongs to the laminar flow, roughness of the erosion flume had obvious effect on the flow velocity, the results showed that the bigger roughness was, the smaller the velocity was; the flow velocity increased with increasing both of the flow discharge and of the slope gradient, the relationship was the increasing power function (R2=0.98,p<0.05),the water depth increased with increasing of the flow discharge and it reduced with the increase of the slope gradient, the relationship was the power function (R2=0.98,P<0.05).(2) The experiment results showed Reynolds number (Re) was842-5467, gully flow was turbulent flow, there was a good positive correlation between Reynolds number and flow discharge, the more the flow discharge was, the bigger Reynolds number was. The slope gradient and roughness of erosion flume wasn’t obvious effects on Reynolds number; the Froude number (Fr) is1.051-8.89, gully flow belonged to the torrent, the flow wasn’t obvious effect on the Froude number, the slope gradient and roughness of the flume had obvious effect on Froude number, the bigger their value was, the smaller Froude number was.(3) The transporting sediments capacity of gully flow was related to the flow discharge and the slope gradient, it increased with the increasing of the flow discharge and increased sharply with the increase of the slope gradient, the transporting sediments capacity model was T=292.95X0.98Y0.22by the regression analysis (R2=0.93P<0.05). The flow discharge had little effect on the same size sediments deposition but the slope gradient had obvious effect. When the slope gradient was1°, the transporting sediments capacity to2-4mm sediments was larger, but it was smaller to0.02-2mm and less than0.02mm sediments; when the slope gradient was larger(15°,25°), the size of sediments deposition was more to less than0.02mm sediments, but it is less to2-4mmand0.02-2mm sediment.3. The experiment had studied sediment stress, erosion and sediment yield, hedgerow deformation and the runoff around a blunt body by using mechanical analysis and physical reduction, the results showed that the sediment was stopped by drag force, lift force, cohesion force, osmotic pressure, gravity, and buoyancy because of the runoff and hedgerow block, so sediment yield shear force caused by the runoff is at least more than the total friction caused by the water pressure, soil cohesion and the resistance caused by hedgerow block; The Hedgerow deformation power was mainly come from the runoff head pressure, Hedgerow maximum deflection formula was hedgerow angle formula was and analyzed the causes of hedgerow deformation when laid hedgerow; under the condition of the hedgerow block, the water width around a blunt body was positive linear correlation to flow discharge but negative to the flow velocity, the hedgerow block influenced streamline of runoff, runoff collision and stack on the crossing of streamline, so the kinetic energy of runoff was reduced, the erosion force of runoff was also reduced.4. When Amorpha fruticosa or Juncus effusus laying mode was5cm×5cm and10cm×10cm (roughness was0.01), under the conditions of4kinds of the slope gradient corresponding to4kinds of the flow discharge, experimental studied the hydraulic characteristics of the runoff, the transporting sediments capacity, block effects and the different size sediments deposition character.(1) Under the conditions of the hedgerow block, the relationship between the flow velocity, the flow unit discharge and the slope gradient was a power function (R2=0.98P<0.05); When the Juncus effusus was in5cm×5cm mode block and the slope gradient was smaller (1°nd5°), the flow velocity reduced greatly, in the large slope gradient, the velocity changes were smaller; the other3kinds of block mode had few effects on the velocity. The relationship between water depth and the unit discharge, the slope gradient was a power function (R2=0.98P<.05); under the condition of hedgerow block, the water depth increased with the increase of the flow discharge, however, it increased rapidly when the slope gradient was in1°and slow in5°,15°,25°. In the small slope, the water depth was deeper, in the large slope, the water depth was relatively shallow and the change range of the water depth was smaller.(2)Under the condition of the hedgerow block, the flow pattern belonged to the turbulent flow. Hedgerows block and the slope gradient had few effects on Reynolds number, the flow discharge was the main factors of influencing Reynolds number. The slope gradient had obvious effect on Froude number, when the Juncus effusus was5cm×5cm mode block and the slope gradient was1°, the gully flow belongs to the slow flow, the others belongs to the torrent.(3)Under the condition of the hedgerow block, in the small slope, the transporting sediments capacity increased with the increase of the flow discharge, the flow discharge was the main factor of influencing transporting sediments capacity. In the large slope, the transporting sediments capacity was very large, so the slope gradient was the main factor. The transporting sediments capacity of4modes were Juncus effusus5cm×5cm> Amorpha fruticosa5cm×5cm> Juncus effusus10cm×10cm> Amorpha fruticosa10cm×1Ocm; the flow discharge hadn’t obvious effect on the same size sediment deposition but the slope gradient was obvious to it. Under the condition of the Juncus effusus block, when the slope gradient was1°, the large size sediments was easy to be transported, but the small size was deposited more; when the slope gradient was5°, the2-4mm sediments was deposited more, the0.02-2mm sediment was easy to be transported. When the slope was1°or5°, the hedgerow bock hadn’t obvious effect on deposition of less than0.02-2mm sediments.更多还原