【作者】 魏霞；

【导师】 李占斌；

【作者基本信息】 西安理工大学 ， 水利工程， 2008， 博士

【摘要】 本文针对目前坡沟系统研究中的薄弱环节和亟待解决的问题,分别利用室内概化坡沟系统模型和野外天然变坡地形,采用放水冲刷试验来研究和完善坡沟系统的侵蚀产沙理论。根据黄土高原的坡沟地貌特征,建立室内坡沟系统概化模型,结合REE示踪技术,采用室内放水冲刷试验,研究了坡沟系统的径流水动力学特性、坡沟系统的侵蚀产沙过程、坡沟系统的径流侵蚀动力、坡沟系统侵蚀泥沙来源等问题。利用野外坡沟系统的放水冲刷试验,研究了草被覆盖对坡沟系统的水动力学特性的调控作用、坡沟系统的侵蚀产沙过程随坡底和沟底两种不同位置时侵蚀产沙的差异、坡沟系统的侵蚀产沙过程随着坡底和沟底草被覆盖度的变化、坡沟系统的侵蚀产沙过程随着坡沟系统不同坡长组合的变化等问题。用野外收集到的坡面改修梯田工程资料,研究了坡改梯工程措施的实施对坡沟系统的入渗过程、产流产沙过程的调控作用;根据收集到的沟道淤地坝工程资料,分析了淤地坝工程措施的实施对来自坝空流域坡沟系统径流泥沙和侵蚀产沙粒径的调控;应用有限元分析软件,研究了淤地坝工程措施对坡沟系统重力侵蚀的调控作用。通过三年来相关的试验与研究工作,取得以下结论:（1）在本论文试验的坡沟系统中,径流雷诺数Re、径流弗罗德数Fr和流速V随流量和坡位的不同变化较大。在实验流量范围内,坡沟系统的Re变化位于342.3～858.8之间,Re都小于900,说明整个试验过程中,坡沟系统的径流处于层流状态。Fr变化位于1.36～8.92之间;均都大于1,说明在整个试验过程中,坡沟系统径流处于急流状态。（2）REE示踪研究结果表明,坡沟系统的侵蚀量主要来自坡面,坡面顶端2m的侵蚀量占坡沟系统总侵蚀量的50%～75%;坡面各示踪侵蚀带侵蚀量大小顺序依次为:La元素示踪带（坡顶断面）＞Ce元素示踪带（与坡顶断面相邻的坡中断面）＞Tb元素示踪带（坡底断面）＞Sm元素示踪带（与坡底断面相邻的坡中断面）,但Q=12L/min时例外;沟坡各侵蚀带侵蚀量大小次序依次为:Eu元素示踪带（沟顶断面）＞Yb元素示踪带（沟坡中间断面）＞Dy元素示踪带（沟底断面）,但小流量Q=6L/min和Q=8L/min时例外;流量相同时,随着冲刷历时的延长,坡沟系统侵蚀率呈波动变化趋势,陆续达到最大,然后又逐渐减小;且随冲刷流量的增大,侵蚀率达到最大值的时间越来越短。（3）坡沟系统中的侵蚀率与径流能耗或单宽水流功率之间呈现显著的幂函数关系,函数的通式为:y=ax^-b,其中,y为侵蚀率,x为能耗或者单宽水流功率,a、b为大于零的常数。并且能耗与侵蚀率之间的相关性大于单宽水流功率与侵蚀率之间的相关性。坡沟系统中的侵蚀率与径流剪切力之间呈现出线性相关性,但是相关关系不如能耗和功率关系显著,本研究中的坡沟系统在用径流剪切力、径流能耗、水流功率三个参数进行描述时,径流能耗效果最好,水流功率次之,径流剪切力相对最差。（4）相同冲刷流量下,不论草被布设在坡沟系统的坡底还是沟底,随着草被覆盖度从30%增大至50%,坡沟系统的Re、Fr和V均呈现出明显的增长趋势,但随着草被覆盖度继续增大至70%时,Re、Fr、V又呈现出明显的递减趋势。相同流量相同草被覆盖度下,坡沟系统的Re、Fr和V随着冲刷历时的增大呈现出波动的变化趋势,增减趋势不是很明显;相同草被覆盖度下Re、Fr、V随着冲刷流量的增大而增大;草在沟时的Re、Fr、V略大于草在坡底时相应的Re、Fr、V。（5）不论草被布设在坡底还是沟底,当草被覆盖度相同时,随着放水流量的增大,坡沟系统的产流总量呈现出增大的趋势。同一流量下,坡沟系统的产流量随着草被覆盖度的变化不同,当草被在坡底时,坡沟系统的产流量的变化为:当Q=14L/min时,0%＞50%＞30%＞原状＞70%;当Q=18L/min和Q=22L/min时,50%＞0%＞原状＞30%＞70%。当草被在沟底时,坡沟系统的产流量的变化为:当Q=14L/min时,0%＞50%＞30%＞原状＞70%;当Q=18L/min和Q=22L/min时,原状＞70%＞50%＞30%＞0%。（6）坡沟系统的产沙总量随着草被覆盖位置的变化相差较大。当草被布设在坡底时,草被覆盖度为原状时,随着流量的增大,坡沟系统的产沙量呈现出先减小后增大的趋势;草被覆盖度为50%时,随着流量的增大,坡沟系统的产沙量呈现出先增大后减小的趋势;草被覆盖度为70%、30%和剪草裸坡时,随着放水流量的增大,坡沟系统的产沙总量呈现出逐渐增大的趋势。当草被布设在沟底时,草被覆盖度为原状、70%和剪草裸坡时,随着放水流量的增大,坡沟系统的产沙总量呈现出逐渐增大的趋势;草被覆盖度为50%和30%时,随着流量的增大,坡沟系统的产沙量呈现出先减小后增大的趋势。（7）在本实验设计的坡长和流量范围内,长坡长的产沙量大于短坡长的产沙量,相同草被覆盖度和相同流量下,长坡长的坡沟系统的侵蚀产沙过程较短坡长的侵蚀产沙过程剧烈,各坡长情况下产沙量随着流量和盖度的变化呈现出不同的变化趋势。（8）相同冲刷流量下,坡沟系统的侵蚀产沙过程随着坡面草被覆盖度的增大呈现先增大后减小的趋势。即当草被覆盖度由30%增大至50%时,坡沟系统的产沙速率增大,但随着草被覆盖度继续增大至70%时,坡沟系统的产沙速率又出现减小的趋势。坡沟系统的产沙速率随着沟坡的草被覆盖度的变化呈现出类似坡面草被覆盖度的变化,但这种变化不如坡面显著。相同覆盖度的草被布设在坡沟系统的沟底时的侵蚀产沙过程较草被布设在坡底时的侵蚀产沙过程剧烈,这说明在本实验设计的坡沟系统实验中,草被布设在坡底时的减沙作用较显著,而沟底的减沙作用不如坡底显著。（9）坡改梯工程措施能够增大坡沟系统的入渗量,伴随着入渗量的增多,土壤中的养分的流失量减小,利于作物高产稳产。在一定的暴雨洪水范围内,坡改梯措施改变了坡耕地原有的坡度,使坡面的产流产沙量大幅度减小,对坡面产流产沙量进行了有效控制,从而有效控制了相应坡沟系统的坡面（上方）来水来沙量。（10）沟道淤地坝工程措施的实施,能够就地拦蓄淤地坝所在坡沟系统的产流产沙量,使得出口的水沙量减小,长流水沟道的基流量增大,出口泥沙中值粒径减小,说明淤地坝不但能有效拦蓄洪水泥沙,而且可以减小粗泥沙对下游河道的危害。随着淤积厚度的增大,淤地坝系所在沟道两侧的坡沟系统的稳定性越来越好,重力侵蚀量或侵蚀潜力也越来越小,说明淤地坝工程措施对坡沟系统的重力侵蚀具有较强的调控作用。更多还原

【Abstract】 On the basis of literatures reviewing on the slope-gully system development from domestic and abroad, the theory of erosion sediment yield of slope-gully system was researched and perfected by aiming at the weak neck and urgent problems to solve in the process of research of slope-gully systems, using slope-gully systems physical model and field crude slope-gully landform, adopting runoff scouring method. According to typical physiognomy of slope-gully systems in Loess Plateau, the slope-gully systems physical model was established. Hydrodynamics characteristic, the process of erosion sediment yield, erosion motivity, the origin of erosion sediment yield were all researched by integrating with rare-earth element tracing technology and adopting scouring method. The adjust-control effect of grassland coverage to hydrodynamics characteristic, the difference of sediment yield process under grassland in slope and gully, the variation of erosion sediment yield process with grassland coverage, the variation of erosion sediment yield process with slope length of slope-gully system were all studied by scouring with field slope-gully systems experiment. Furthermore, according to data of sloping fields reformed to terraced fields collected from field investigation, adjust and control effect of terrace on the process of infiltration , flow generation and sediment yield of slope-gully systems were studied . At the same time, adjust and control effect of check dam on flow generation and sediment yield from the slope-gully systems and its grain composition were studied by the collected data. Based on finite element software, adjust and control effect of check dam on gravity erosion. The following conclusions were obtained:(1) Main runoff dynamic parameters, including Reynolds number, Froude numbers andvelocity in slope-gully systems, varied greatly with runoff discharge and slope position.In this experiment, Reynolds number varied between 342.3 and 858.8, all of which was smaller than 900, and indicated that runoff in the slope-gully system was laminar flow. Froude numbers varied between 1.36 and 8.92 in the erosion processes, and showed that the runoff of the slope-gully systems were turbulent flow.(2) Analysis of sediement source by rare-earth element tracing method indicated that the proportion of sediment from slope was greater than that from gully in the experiment, and sediment from the top two meters on the slope accounted for more than 50% of the total sediment yield. Except for sediment under the runoff discharge of 12L/min, sediment from various element tracing belt in the slope was in the order of La>Ce>Tb >Sm. Sediment from various element tracing belt in the gully was in order of Eu>Yb >Dy, excep for sediment under the runoff discharge of 6L/min and 8L/min. Erosion ratio increased fluctuantly with time under the same runoff discharge. And time sediment reached its peak value decreased with the increase of runoff discharge.(3) The relationship between the erosion rate of the slope-gully systems and the runoff energy consumption or the runoff power per unit width were all established as power function( y = ax~b, where a and b were constants; y was erosion rate of slope-gully systems; x was runoff energy consumption or runoff power per unit width of slope-gully systems). What’s more, the correlation between the erosion rate and runoff energy consumption was larger than that the erosion rate and the runoff power per unit width. The relationship between the erosion rate of the slope-gully systems and the runoff shear stress was established as linear function. Result demonstrated that in the process of erosion description with three parameters were in the order of runoff energy consumption > runoff power > runoff shear stress.(4) Reynolds number Re, Fuluode number Fr and velocity of runoff V, were all showed a distinct increscent tendency with the grassland coverage increasing from 30% to 50 %, but were all showed a distinct decreasing tendency with the grassland coverage increasing from 50% to 70 % under the same condition of scouring flow without reference to the grass location of slope and gully in the slope-gully systems. Re, Fr and V were all showd a fluctuant tendency with the time duration, and the change was not very clear under the same condition of scouring flow and grassland coverage. The values of three parameters of Re, Fr and V gradully augmented with the increase of the scouring flow under the same grass coverage. When grassland in gully, the three parameters of Re, Fr and V was slightly larger than that in slope.(5) The gross amount of runoff generation from the slope-gully becomes large with the increasing scouring flow under the same grass coverage without reference to the grass location of slope and gully in the slope-gully systems. The gross amount of runoff generation from the slope-gully shows different change characteristics with the difference of the grass coverage under the same scouring flow. When grassland was in the slope, the change law of the gross amount of runoff generation with different grass coverage was as follows: 0%>50%>30%>original state>70% under the condition of Q=14L/min, 50% >0%> original state > 30% > 70% under the condition of Q=18L/minor Q=22L/min. When grassland was in the gully, the change law of the gross amount of runoff generation was as follows: 0%>50%>30%>original state>70% under the condition of Q=14L/min, original state>70%>50%>30%>0%under the condition of Q=18L/minor Q=22L/min.(6) Sediment yield from the slope-gully systems varied a lot with with the changes of vegetation location. When the grass was located in the slope and the grassland coverage was same, the total sediment yield was showed several changing trendency as follows: 1) for the original state of grass coverage, the total sediment yield decreased firstly and then increased with the increase scouring flow; 2) for the 50 percent of grass coverage, the total sediment yield increased firstly and then decreased with the increase scouring flow; 3) for the other grass coverages, the total sediment yield increases with the increase scouring flow. When the grass was in the slope and the grassland coverage was same, the total sediment yield was showed several change trendency as follows: 1) for the 30 percent or 50 percent of the grass coverage, the total sediment yield decreased firstly and then increased with the increase scouring flow; 2) for the other grass coverages, the total sediment yield increased with the increase scouring flow.(7) Slope length and vegetation cover had deep effect on sediment yield. Results by runoff scouring indicated that sediment yield from long slope was larger than that from short slope. Under the same vegetation cover and same runoff discharge, sediment yield from long slope-gully system was more exquisite than that from short slope-gully system. That is to say, within the range of designed slope length and scouring discharge, sediment yield of slope-gully systems was more exquisite with the augmentation of slope length.(8) Under the same runoff discharge, soil erosion in the slope-gully systems increased firstly and then decreased with the increase of vegetation cover. When vegetation cover on the slope increased from 30% to 50%, sediment yield in the slope gully system increased, and then decreased when vegetation cover increased to 70%. Changes of runoff and sediment yield with vegetation cover on gully showed similar trendComparison of sediment yield with different vegetation cover location indicated that sediment reduction with vegetation cover at the bottom of the slope was much larger than that with vegetation cover at the bottom of the gully.(9) Reforming slopeland to terraced fields improved soil infiltration, reduced nutrient loss, and consequently improved land productivity. At the same time, terrace changed the slope gradient, reduced the runoff yield, and consequently reduced sediment yield and improved stability of slope-gully system.(10) Check dam was effective in reducing soil and water loss, resulted in increasing base flow and decrease in grain composition. Further analysis indicated that with the increase of alluvial height, stability of slope-gully system increased, and gravity erosion or potential was decreased too. That is to say, check dam can adjust and control gravity of slope-gully systems effectively.更多还原