IMHE OpenIR
干热河谷冲沟沟头溯源侵蚀过程的动力学机制
Alternative TitleDynamic Mechanism during Gully Headward Erosion Process in the Dry-Hot Valley Region
张宝军
Subtype博士
Thesis Advisor熊东红
2017
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline土壤学
Keyword径流水动力特征 侵蚀产沙特征 地形变化特征 动力学机制 沟头溯源侵蚀
Abstract金沙江干热河谷冲沟侵蚀强烈,以沟头溯源侵蚀过程为主,陡立跌坎是活跃沟头的重要形态特征之一。本研究通过构建不同跌坎高度沟头原位模拟试验平台,采用放水冲刷试验和高精度近景摄影测量方法,研究了沟头侵蚀过程中的径流水动力特征、侵蚀产沙特征及地形变化特征,查明了侵蚀过程中沟头径流能量转化、耗散特征及崩塌发生的临界条件,揭示了冲沟沟头溯源侵蚀过程的动力学机制。这不但对于深刻揭示该区域冲沟侵蚀发生发展规律具有重要意义,而且对于采取针对性的冲沟治理措施具有重要的实践指导意义。主要研究结论及取得的创新性认识如下:⑴ 查明了沟头溯源侵蚀过程中的径流水动力学特征,阐明了沟头径流能量变化特征及跌坎高度对其影响机理沟头沟壁跌坎在坡面径流冲刷过程中对水动力特性影响显著。坡面径流在沟头部位能耗大,且能耗随沟壁跌坎高度增大呈显著增加趋势,50~75 cm之间存在引起沟头径流能耗突然增大的临界跌坎高度。当沟壁跌坎高度超过75 cm时,沟头部位径流能耗超过50%,且75 cm和50 cm沟头能耗比值(2.61和2.21)显著高于其它相邻高度沟头径流能耗比值(1.03~1.47)。沟壁跌坎高度对沟头径流跌水侵蚀冲刷能力影响显著,径流跌水势能转化量和剪切力随跌坎高度增大均显著增大。沟壁跌坎高度每增大25 cm,120 L/min和150 L/min两种流量跌水势能转化量分别平均增加4.89 J/s和6.10 J/s,跌水剪切力分别平均增加24.1 Pa和22.2 Pa。沟壁跌坎高度差异相比径流量大小,可能对径流水动力特征的改变影响更为显著。⑵ 查明了沟头溯源侵蚀过程中的侵蚀产沙特征,阐明了沟头跌坎高度对侵蚀产沙效应的影响机制干热河谷冲沟侵蚀过程中,径流量、沟头跌坎高度对径流产输沙特征影响显著,干湿交替作用或崩塌发生是导致水土耦合失衡特征突出的重要原因。径流含沙量随时间整体呈幂函数降低趋势,期间干湿交替作用或崩塌发生会引起径流泥沙含量突然增大,导致水土耦合失衡突出;径流平均含沙量随径流量和沟壁跌坎高度增大均呈增大趋势,150 L/min流量时各小区径流平均含沙量与120 L/min流量相比表现为1.05~1.30的倍数关系,径流平均泥沙含量随跌坎高度增大呈指数增加趋势。沟头部位侵蚀量对总侵蚀量贡献大,验证了干热河谷冲沟水土耦合失衡主要集中在活跃沟头部位的野外判定。各小区沟头部位面积占总面积17.2%~27.3%,但沟头侵蚀量贡献在24.8%~71.0%和27.3% ~71.1%之间,显著超过其面积比例,说明沟头部位侵蚀贡献大,水土耦合失衡最为突出。沟壁跌坎高度对沟头侵蚀量及其贡献影响显著,75 cm是引起沟头溯源侵蚀特征突变的临界跌坎高度,这为干热河谷沟头活跃程度划分及采用科学的沟头溯源侵蚀治理对策提供重要理论依据。沟头部位侵蚀量随跌坎高度增大呈指数增长趋势,对总侵蚀量贡献呈线性或对数增长趋势;当沟壁跌坎高度大于75 cm时,沟头侵蚀量贡献均达到50%以上,认为75 cm是影响沟头溯源侵蚀过程中水土耦合失衡效应突变的临界跌坎高度。⑶ 阐明了沟头溯源侵蚀过程中的地形变化特征,揭示了跌坎高度对其影响机制集水区和沟床部位地形变化主要以垂直下切为主,两者下切深度随时间变化特征表现出差异,且沟床部位下切变化更为剧烈。冲刷试验后,集水区和沟床沿径流流路下切深度随时间均呈显著线性增长趋势,部位整体平均下切深度随时间在集水区呈对数函数变化,在沟床呈线性变化;各小区沟床与集水区沿径流流路下切深度呈现1.49~3.64倍关系。干热河谷冲沟侵蚀过程中,沟头部位地形变化最为剧烈,包括沟壁底部跌穴垂直下切和沟壁后退,且沟壁跌坎高度对地形变化特征影响显著。沟头平均侵蚀厚度随时间呈线性或对数增长趋势,是集水区平均下切深度的1.74~8.92倍,是沟床平均下切深度的1.08~3.20倍(120 L/min);随沟壁跌坎高度增大,沟头部位平均侵蚀厚度和跌穴平均下切深度分别呈指数和对数增长趋势。⑷ 阐明了沟头溯源侵蚀过程的动力学机制,初步探索建立了沟头土体崩塌稳定性模型径流水动力作用是冲沟沟头溯源侵蚀过程中的主导作用,由于沟壁跌坎高度不同引起的径流能量转化、耗散和剪切力特性差异,导致地形变化特征和产输沙特征差异,两者变化特征与径流能量变化特征有必然联系。径流总能耗与总侵蚀量和累计产沙量之间、沟头部位径流能耗与沟头侵蚀量之间、各部位径流能耗与其地形平均下切变化和沿径流流路下切深度变化之间,均在0.01水平上呈显著正相关;径流跌水平均势能转化量和平均剪切力与沟头部位平均侵蚀速率之间在0.01水平上显著线性正相关,平均剪切力与与跌穴平均下切速率在0.05水平上显著正相关。沟头崩塌是干热河谷冲沟溯源侵蚀主要重力作用过程,是沟头溯源侵蚀过程中水土耦合失衡的一种突出表现;基于极限平衡理论,综合考虑水力和地形条件,初步探索建立了沟头土体崩塌稳定性模型。沟头崩塌土体稳定性受土壤质量含水量、内凹洞高度、崩塌距离和裂缝深度等多种因素的共同影响。沟头土体稳定性系数,随裂缝发育深度增大呈现显著的对数函数减小趋势,随土壤含水量增大呈现显著的指数函数降低趋势,随内凹洞发育高度增大呈显著线性降低趋势。此外,土壤临界含水量随崩塌距离、内凹洞发育高度和裂缝深度的增大均呈现降低趋势。比较野外试验沟头崩塌时土壤含水量与模型模拟崩塌土壤临界含水量,模型可靠度达到了80%左右。沟头土体崩塌稳定性模型的建立,对干热河谷沟头崩塌发生预测具有重要理论参考意义。综合以上研究结论,沟头部位(包括跌坎)在冲沟侵蚀过程中扮演极为重要的角色。沟头部位径流能量、侵蚀地形及产沙特征变化均较为突出,今后在干热河谷开展冲沟侵蚀研究及生态治理应重点关注沟头部位;沟头跌坎对沟头溯源侵蚀特征影响显著,临界跌坎高度的确定,为不同活跃程度沟头生态治理提供重要理论依据。
Other AbstractGully erosion is very severe in the Yuanmou Dry-hot Valley Region, dominated by the headward erosion process, which is characterized by steep gully headcuts. Based on an in situ active bank gully head, five experimental platforms were constructed with the different headcut height. During the gully headcut erosion process, the runoff hydrodynamic properties, erosion and sediment yield characteristics and landform change characteristics were determined using in-situ runoff scouring experiment and 3D photo-reconstruction method. The experimental results not only explored the transfer and dissipation laws of concentrated flow energy and the critical conditions of soil collapse based on the Limit Equilibrium Theory, but also preliminary revealed the dynamic mechanism during the gully headward erosion process. The results of the study will be of great significance to reveal the laws of gully initiation and development and provide pertinent gully control measure in this region. The main results were showed in following aspects:⑴ Analyzed the runoff hydrodynamic properties during the gully headward erosion process, and proved the change characteristics of the runoff energy and the effects of headcut height on them in gully head.During the gully headward erosion process, gully headcut showed significant effects on the change of runoff hydrodynamic properties. Compared to the upstream drainage area and downstream gully bed, gully head has experienced much more runoff energy dissipations, and the energy consumptions showd significantly linear increasing trend as the headcut height increased. In particular, there may be a criticle headcut height between 50 and 75 cm causing the energy dissipations a sudden increase. When the headcut height was over 75 cm, runoff energy consumption was more than 50% in gully head; and the runoff energy consumption ratio of 75 cm and 50 cm (2.61 and 2.21) were significant higher than any other ratios between other adjacent heights (1.03 ~ 1.47).Furthermore, gully headcut height showed significant effects on the free jet erosivity. Both the transformed potential energy and shear stress increased as the headcut height increased. When the headcut height increased by 25 cm, the transformed potential energy would increase by approximately 4.89 J s-1 and 6.10 J s-1 on average, while the shear stress would increase by approximately 24.1 Pa and 22.2 Pa on average, under the flow discharge of 120 L min-1 and 150 L min-1, separately. Headcut height seemed to show more significant effects on the hydrodynamic changes than the flow discharge during the gully head erosion process in the Dry-hot valley region.⑵ Studied the erosion and sediment yield characteristics during the gully headward erosion process, and proved the effects of headcut height on them.During the gully headward erosion process, the flow discharge and headcut height both showed significant effects on the sediment, and the alternating dry and wet conditions or the mass failures are the important causes of the sudden increase in runoff sediment. Runoff sediment concentration almost showed a power-function decline trend over time during the gully headward erosion process; however, runoff sediment concentration could increase suddenly due to the alternating dry and wet conditions or the mass failures. Mean runoff sediment concentration also increased as the flow discharge and headcut height increased. The average sediment concentrations of 150 L min-1 tests were 1.05 ~ 1.30 times as large as the sediment concentrations of 120 L min-1 tests. And the average runoff sediment concentration showed an exponential increasing trend as the headcut height increased. The soil loss volume in gully head has made a much bigger conctribution of the total soil loss volume, which proved the field determination that gully erosion and sediment yield mainly concentrated on the active gully head positions in the Dry-hot valley region. The soil loss volume showed the logarithmic growth trend over time under 120 L/min, and more than 50% almost occurred in the initial 50 min. The surface area of gully head occupy 17.2% ~ 27.3% of a total, however, the contribution of soil loss in gully heads were 24.8% ~ 71.0% and 27.3% ~ 71.0%, separately, which were much higher than the area ratio.During the gully headward erosion process, the headcut height also showed significant effects on the soil loss volume in gully head and its contribution. 75 cm may be the critical headcut height to cause the gully headward erosion characteristics a sudden change, which provided important theoretical basis for the hot dry valley gully head activity division and the scientific headward erosion control measures in the Dry-hot valley region. The soil loss volume in gully heads also showed a significantly expontenial growth trend as the headcut height increased, while their contributions to the total soil loss showed linear or logarithmic growth trend. In particular, the soil loss volume in gully head has also appeared a sudden increase with the headcut height increasing from 50 cm to 75 cm, and the gully head erosion contribution all exceeded 50% while the headcut height was more than 75 cm. So 75 cm could be viewed as the critical headcut hight causing a sudden change of erosion and sediment yield characteristics during the gully headward erosion process.⑶ Revealed the landform change characteristics during the gully headward erosion process, and proved the effects of headcut height on them.Vertical incisions were determined to be the dominant soil erosion process for the upstream areas and downstream gully beds. However, the incised depth changes over time showed differences between the two parts, and the incision seemed to be more intense in the gully bed. After the whole scouring test, the incision depths along the flow path both showed significant linear increasing trend over time in the upstream area and gully bed, while a logarithmic growth trend and linear growth trend were observed in the changes of mean incision depth of whole upstream area and gully bed, separately. The mean incision depths along the flow path in the gully bed were 1.49 ~ 3.64 times as large as in the upstream area.Furthermore, during the gully headward erosion process, gully head position has experienced the most severe landform change, which included the vertical incision and headcut retreat, and the headcut height also showed significant effects on the landform change characteristics. The mean erosion rate in gully heads and the mean incision depth of plunge pool both increased as the scouring tests progressed and as the headcut height increased, especially, which were much higher than the incision depths in the upstream area and gully bed. The mean erosion rate in gully heads showed linear and logarithmic trend over time under the flow discharge of 120 L min-1, which were 1.74~8.92 and 1.08~3.20 times as large as the mean incision depeth in the upstream area and gully bed, separately. Furthermore, as the headcut height increased, the average soil erosion rate in gully heads showed a significantly expontenial increase trend, while the mean incision depth of plunge pool showed a logarithmic growth trend.⑷ Revealed the dynamic mechanism during the gully headward erosion process, and preliminarily established the stability model of the mass failure. The hydrodynamic force played the dominant role during the gully headward erosion process. The runoff energy consumption and transformation differences due to the different headcut height, has caused the differences of landform change and sediment characteristics. Especially, the erosion and sediment yield characteristics and landform change characteristics during the gully headward erosion process both had the positive connections with the runoff energy consumption and transformation. The runoff energy consumptions all showed significant correlations with the soil loss volume, the cumulative sediment yield and landform change at the 0.01 level respectively. Furthermore, there were also significant correlations between the energy transformation and the shear stress of jet flow and the average soil erosion rate at the 0.01 level in gully heads, while there were significant correlations between the shear stress of jet flow and the incision rate of plunge pool at the 0.05 level. Gully head collapse has been viewed as the main way during the gully headward erosion process, which was also a prominent feature of imbalance of soil and water after the impending the soil reaching the ultimate equilibrium state. Therefore, considering of the hydrodynamic and topographic conditions, a soil mass stability model was preliminarily established based on the Limit Equilibrium Theory. The soil mass stability was affected by various factors, such as the soil water content, concave hole height, collapse distance and crack depth. The soil mass stability showed a significantly logarithmic decreasing trend as the crack depth increased, and showed a significantly expontential decreasing trend as the soil water content increased, and showed a significantly linear decreasing trend as the concave hole height increased. Furthermore, while the mass failure happens, the criticle soil water content almost showed a decreasing trend as the concave hole height, crack depth and collapse distance increased. Although the field validation results did not coincide exactly with the model simulation results, if the soil water content ratio was viewed as the evaluation criteria, it can also be concluded the model reliability reached about 80%. The result indicated that this soil mass stability model still has some reference value to forecast the gully head collapse in the Dry-hot valley region.Based on the above research conclusions, it was proved that gully head position (including the headcut) played a significant role during the gully erosion process in the Dry-hot valley region. The changes of runoff energy, landform and sediment yield all showed the most prominent in the gully head, which concluded that gully head position should need more attention while studied the gully erosion and environmental control in the future. Furthermore, the gully headcut height showed significant effects on the headcut erosion characteristics. The determination of the critical headcut height has provided the important theoretical basis for the ecological managements of different active gully heads. 
Pages165
Language中文
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/24598
Affiliation中国科学院成都山地灾害与环境研究所
First Author Affilication中国科学院水利部成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
张宝军. 干热河谷冲沟沟头溯源侵蚀过程的动力学机制[D]. 北京. 中国科学院大学,2017.
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