Knowledge Resource Center for Ecological Environment in Arid Area
| 黄河上游沙漠宽谷段高含沙洪水灾害机理与河型响应 | |
| 其他题名 | Mechanisms of hyper-concentrated flow disasters and channel pattern responses in the desert reach of the upstream Yellow River |
| 王之君 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 拓万全 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 高含沙洪水是携带一定含量粘性细颗粒的水流在某种水沙与河床边界条件下所形成的一种含沙浓度较高的特殊水流现象，在汛期天然河流中时有发生。区别于清水水流和一般挟沙水流，高含沙洪水在其物理特性、流动特性及对河床演变的作用等方面表现出较大差异。干旱区河流因汛期持续而集中的高含沙洪水引发的高含沙泥流灾害，通常对水利工程、工农业生产乃至河流生态系统带来巨大的影响和损失，其随机性和突发性类似于山区河流上所发生的泥石流。黄河上游沙漠宽谷段十大孔兑沙漠流域及沙漠干流河段频发的高含沙洪水，是该区独特且季节交替的风水复合侵蚀作用的结果。流域支流高含沙洪水（泥流）入汇及干流风沙水沙过程导致黄河上游沙漠宽谷段小水决口，泥沙冰凌等自然灾害及主槽萎缩，河流改道、地上悬等河型演变。因此，深入系统地开展风水两相作用下高含沙洪水灾害机理及河型响应研究，对于维护黄河健康、保障流域生态环境系统稳定而言，显得尤为迫切且意义重大。研究对丰富沙漠河流泥沙动力学及风水复合土壤侵蚀理论体系而言，具有重要的科学意义；对干旱区沙质河道水利工程设计、运行及防灾减灾而言，亦具有重要的实践指导价值。长期以来，干旱区沙漠系统与河流系统的研究处于分离状态，有关沙漠与河流相互作用的研究，却鲜有系统深入的报道。本研究以黄河上游沙漠宽谷段为主要研究区域，基于该区域典型的风水两相作用，分别从十大孔兑沙漠流域小尺度和干流沙漠河段中尺度出发，系统研究流域风水复合侵蚀作用诱发高含沙洪水（泥流）灾害过程机理及流域产沙与干流水沙关系及河床演变的内在联系；并将该区域离散型沙漠粗沙泥流与陇南山区粘性泥（石）流进行对比，以期深入探索两类高含沙泥流运动机理之异同；在借鉴陇南山区粘性泥石流入汇白龙江导致河型演变成果的基础上，深入认知黄河上游沙漠宽谷段十大孔兑高含沙洪水入汇对河床演变的影响和作用。研究选取十大孔兑典型支流苏达拉尔沙漠小流域建立沙漠泥流观测场，并选择陇南山区G212线（兰州-重庆）高速公路沿线泥石流频发区作为参照，同步设计建造粘性泥流运动机理直槽概化模型试验台，分别采用野外观测、调研分析、河道钻孔、模型试验、数值模拟、理论分析等手段，取得了较为丰富的研究成果。基于十大孔兑流域泥沙过程物理图景的侵蚀产输沙动力学机理初步分析，为下一步建立风沙—水沙—河道模拟系统，开展全流域泥沙过程机理研究指明了方向，打下了坚实的基础。（1）季节交替的风水复合侵蚀过程，是黄河上游沙漠宽谷段十大孔兑沙漠流域高含沙洪水（泥流）灾害的诱因。高含沙洪水的发生、发展和演变，是全流域不同部位风水复合侵蚀过程的叠加和反映。首次提出的最优粒度指标OGI（C＞0.08mm/C＜0.05mm），直观反映了高含沙洪水中砒沙岩细颗粒与沙漠粗沙颗粒组分的对比消长关系。产流区暴雨洪水泥沙中细颗粒含量（C＜0.05mm）的多少直接关系到山洪能否演变为高含沙洪水，而粗颗粒含量的多少（C＞0.08mm）则关系到高含沙洪水能否演变为泥流灾害，当且仅当流域风水两相侵蚀程度相当时，才有可能发生高含沙洪水，流域风水侵蚀产沙比约为1：1；经与其他孔兑乃至黄河中游黄土高原流域高支流含沙洪水（泥流）要素的系统对比，提出判定黄河上游沙漠宽谷段干旱区沙漠流域高含沙洪水发生的临界含沙量标准为γ0=500kg/m3；同时建议做好产流区水土保持综合治理工作，防治土壤侵蚀，进而有效控制和减缓高含沙洪水及泥流灾害发生。（2）干流沙漠河段独特的风沙水沙两相作用，尤其是十大孔兑高含沙洪水（泥流）入汇，加速了该河段河床淤积、河道摆动及由辫状河流向弯曲型河流过渡演变的过程。刘家峡与龙羊峡水库的运行彻底改变了黄河上游的水沙特性，区间风沙的加入进一步使得沙漠宽谷段的水沙搭配关系失衡。首次区分并明确了含量仅占悬移质泥沙组分的10%的床沙质对研究区河段河床演变起到的重要作用。床沙质为区间沙漠粗沙颗粒（0.08~0.25mm），且在一定的水流条件下活跃于悬移质与推移质之间，河床活动层厚度约1m；根据沙漠粗沙床沙质的这一运动特性，判定研究区上段辫状河段输沙特性为粗细泥沙混合运动模式；下段弯曲型河流则为以悬沙为主导的输沙模式。根据提出的河床稳定性指标K，初步得到辫状河段（K=0.238）较之弯曲河段（K=0.647）而言不稳定的结论，并与河型分类稳定性理论判定的结果相一致，这对沙质河段水利工程设计、施工与运行管理而言，有重要的参考意义。根据研究据结果预测：随着上游水利工程拦沙能力的下降，未来沙漠宽谷段流域沙漠侵蚀对区间水沙关系乃至河床演变将起到重要作用，进而提出搞好沙漠宽谷段沙漠流域水土保持综合治理工作，维护黄河健康及生态系统稳定的工程建议。（3）十大孔兑流域泥沙过程机理，须区分覆沙坡沟系统和沙丘沟谷系统分别研究。基于坡面风水复合侵蚀、沙丘沟谷重力侵蚀、沙丘前移及沟道落淤、高含沙洪水运移等侵蚀产沙子过程进行了流域泥沙动力学机理初步分析，并依托十大孔兑苏达拉尔沟沙漠沟道观测结果开展了高含沙洪水输沙过程三维数值模拟。模拟基于湍流两相流模型，重点分析了流场流线、速度梯度及泥沙浓度等主要参量的变化，从现象、本质、结果的角度解释了高含沙洪水水流运动及泥沙运移机理，模拟结果与实测结果定性吻合，但仍有诸多改进优化之处。以风蚀过程动力学机理为重点，耦合风水复合侵蚀过程，建立符合流域侵蚀沙产物理图景的全流域泥沙动力学机理模型，是下一步研究的重点所在。（4）泥石流的起动符合尖点突变理论模型。首次提出将液固比Sr（泥石流体中水体体积与固体体积之比）作为衡量泥石流起动的状态参量，并强调：坡度一定时，细颗粒含量大小决定了各类泥石流的起动模式。就陇南山区白龙江流域而言：小于1mm细颗粒含量15%以下时，泥石流常以突然起动模式为主，细颗粒含量15~30%之间时，多以渐变模式起动，而细颗粒含量30%以上时，逐渐表现为缓慢起动的特点；相应的泥石流体流动特性，也随细颗粒含量的增加由波状阵性流转变为均匀流（层流）状态，可通过改变其主要的运动控制参量，一定程度上预防并控制其发生发展方向；粘性泥流沟道内的运动堆积可视为整体力学行为，按一维静力学方法分析判定其临界条件，并将其作为复杂条件下动力学数值计算的有益补充；堆积型态呈抛物线型，可作为致灾范围估算的依据。（5）以甘肃陇南山区白龙江流域为代表的粘性泥（石）流，因细颗粒含量较大，其运动特性表现出明显的非牛顿流体的性质，而以黄河上游沙漠流域为代表的支流离散型沙漠粗沙泥流，则仍然表现为两相高含沙紊流，具有非牛顿流体的特点；二者都属于自然界常见的高含沙洪水的极端模式；黄河上游沙漠宽谷段干流的高含沙洪水，其水沙特性则因细颗粒含量的变化而介于两个极端模式之间，总体仍以两相紊流为主；泥沙颗粒靠湍流扰动而悬浮输移，河床展宽或比降变缓时，发生泥沙分选和淤积。（6）黄河上游沙漠宽谷段支流高含沙泥流入汇与白龙江流域甘肃陇南段粘性泥（石）流入汇对河床演变的影响，分别代表平原河流和山区河流河床演变的典型情况，其对河床演变的加速作用过程相似，主要取决于入汇作用于主流作用之间的消长关系。支流高含沙泥流或泥石流入汇对主河水沙搭配关系与河床边界条件产生影响，河床演变是对水沙关系及河床边界条件变化的滞后响应。 |
| 英文摘要 | Hyper-concentrated flow is a special natural phenomenon often occurring on river channel during flood season, of which the development is attributed to certain amount of fine sediment and the related water-sdeiment relationship and even the boundary conditions of river bed as well. Compared with clear water flow and sediment-laden flow, hyper-concentrated flow shows a significant difference in physical and flow characteristics and even fluvial process-related river bed evolution. In arid zones, hyper-concentrated flows in flood seasons always developes into hyper-concentrated mud flow disasters due to high rainfall intensity, leading to severe influence and loss on hydropower structures, industrial and agriculatural production and even ecological stability of river systems. The stochastic and castasprophic occurring characteristics of hyper-concentrated flows is to some extent similar with those of debris flows in mountain areas. The hyper-concentrated flows ouucuring at the desert reach of the upstream Yellow River due to aeolian and fluvial interactions (AFIs) has long been the dominant factor of the disasters such as flood overflow, ice jam, mainstream shrinking, channel lateral shift, river bed evolution and so on. Therefore, it is of great importance and a pressing need to study systematically and deeply the mechanisms of hyper-concentrated flow disasters and channel pattern responses in order to maintain the sustainable development of the ecological system of the Yellow River. It is of great scientific significance in enriching the theoretical systems of desert&river sediment dynamics and soil eriosin induced by AFIs, and is of primary guiding significance in controlling disasters and the design and operation of hydropwer structures on the sand-bed reach of rivers in arid zones.Aeolian and fluvial processes have long been studied separately and there are still few studies reporting the interactions between river and desert systems, especially the aeolian process-induced hyper-concentrated (AHC) flows. Study on the inter-relationships between hyper-concentrated flows and river bed evolution were carried out in desert watershed and mainstream channel scale, respectively, based on the typical AFI phenomenon in the desert reach of the upstream Yellow River. In order to distinguish noncohesive mudflows fromviscous mudflows, the Longnan mountain areas along G212 (Lanzhou-Chongqing highway) where cohesive debris flows occurs frequently were chose as a comparison and reference site. Based on the comparison of the similarity of the two areas in mudflow confluence and the related channel pattern responses, the mechanisms of river bed evolution in response to hyper-concentrated flow confluence were identified in detail. To facilitate our study, we chose the Sudalaer desert watershed in ten tributaries to establish a field site for hyper-concentrated flow observation, and constructed a generalized indoor model test instrument for cohesive mud flow testing. By means of field observation, investigation and analysis, channel bed drilling, model test, numerial simulation and theoretical analysis, many benefical results were concluded, while the following study laying emphsis on soil erosion and sediment dynamics in watershed scale was prepared adequately through the preliminary theoretical analysis based on the physical processes of the individual aeolian and fluvial erosion, in order to eatabliash the comprehensive aeolian-fluvial simulating system.(1) This study reports findings, from a more integrated perspective of aeolian-fluvial dynamics and describes the characteristics of AHC flows in response to severe AFI in the SDC in the upstream area of the Yellow River. AHC flows appear to be a natural consequence of seasonal alternate AFIs. Our analysis results indicate that there is an optimal grain size ratio of different grain size sediment contents in the flows, indicating the severity of the effects of aeolian and fluvial erosion on different earth surface materials. The sediment yield ratio of aeolian erosion to fluvial erosion is 1:1. Following the OGI (C>0.08/C<0.05mm) we proposed for the first time, with respect to the SSC of AHC flows , the SSC γ0=500 m3/s was suggested as the threshold value for the occurrence of AHC flows in arid desert watersheds in the upstream area of the Yellow River. Because AHC flows always show very high rates of sediment transport and lead to deleterious downstream effects on the river system and ecology, comprehensive governing of soil erosion in the upstream gully-dissected slopes is suggested as an essential and effective method for controlling AHC flows.(2) The severe noncohesive sand bank erosion and hyper-concentrated mudflows inputhave been undoubtedly accelerating the self-forming process of the available alluvial channel. The wash-load and bed material-load in suspension were distinguished for the first time while laying emphasis on the role of bed material in shaping channel morphology of the alluvial desert reach in the Yellow River. The bed material load composed of medium and coarse sediment (0.08-0.25mm), although only a small fraction of 10% on average, are active in saltation as bed-load, which indicates that the study channel reach should be transitional channel or transitional to labile, with a 1-m-thick active surface layer on the bed. In addition, the primary river stability indicator (K) adapted to the two channel stretches were proposed and calculated by introducing the D50 and bank-full discharge instead of Maximum discharge. The calculated values shows that the meandering channel (K=0.647) is more stable than the braded channel (K=0.238), which is of primary guiding significance for alluvial river stability prediction. Deterioration in runoff-sediment relations is increasingly threatening the health of the upper Yellow River. Accordingly, with the decline of the sediment trapping ability of existing reservoirs in the future, erosion rates will increasingly affect the fluvial sediment characteristics and even the channel morphology development.(3) It is rational and necessary to study the soil erosion and sediment transport in the ten tributaries area from the perspective of aeolian sand-covered hillslope and aeloian dunes-desert channel systems, respectively. Preliminary theoretical analysis of sediment dynamics of individual erosion processes such as hillslope erosion induced by AFIs, gravitational erosion in gullies, aeoian dunes migration and deposition, hyper-concentrated flows routing in channels were conducted, combined with three dimensional mumerical simulation of the hyper-concentrated flow in the Sudalaer desert channel. The numerical simulation are based on turbulene model and focused on the variation of flow field, velocity gradient and sediment concentration, explaining the sediment transport dynamics in substance. The simulation results agreed qualitatively well with the measured results while indicating that the following emphasis should be aeolian erosion and the fulfillment of the physically-based sediment dynamics model in watershed scale.(4) The initiation mode of debris flows obey the cusp castasprophe theory. Sr（volumeratio of water and solid material）were proposed for the first time as the state parameter demonstrating the initiation of debris flows. The content of fine particles is critical in deciding the initiation modes undercertain bed slope. As far as the Longnan mountain areas is concerned, if the content of fine particle (<1 mm) is below 15%, the initiation mode shoud be castasprophic, and if the content of fine particle is between 15~30%, the initiation mode shows a gradual mode, whlie the content of fine particle exceeds 30%, debris flows will start to move as a low-starting mode. According to this criteria, we can predict and control the occurrence and development of debris flows to some extent by appropriate engineering measures. In addition, the accumulation type of viscous mud flow in the channel is a parabola style, which can be considered as a integrated mechanical behavior and analysized by one-dimensional atatics theory for predicting the scope of disaster and as a beneficial supplement of the complex dynamic simulation.(5) The viscous debirs (mud) flows occurring at Baillongjiang watershed are reprenstative of Binghanm fluid due to large amount of fine particles. However, the noncohesive hyper-concentrated mud flows in the desert watershed of ten tributaries area are still Newtonian fluid, showing a two-phase turbulent flow characteristics. Both the two types are extreme form commonly occurring in natural rivers. The hyper-concentrated flows in the mainstream of the upstream Yellow River is two-phase turbulent flow dominant, of which coarse sediment originating from local desert maintain in suspension by flow turbulence while settling under certain inflow and boundary conditions.(6) The confluence of viscous debris flows occurring at Longnan mountain area and that of hyper-concentrated flows in the desert reach of the upstreamYellow River and the related channel pattern responses represent lowland river and mountainous river, respectively. The physical mechanisms in accelerating the river bed evolution are similar, dependeing on the dynamic relationship between tributary and mainstream. The effect of hyper-concentrated flows through tributary confluence alters the water-sdeiment relationship in mainstream and even the boundary conditions ofchannel bed, leading to a hysteresis response of channel patterns. |
| 中文关键词 | 高含沙洪水 ; 河床演变 ; 泥沙动力学 ; 沙漠 ; 黄河上游 |
| 英文关键词 | hyper-concentrated flow river bed evolution sediment dynamics desert the upstream Yellow river |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287844 |
| 推荐引用方式 GB/T 7714 | 王之君. 黄河上游沙漠宽谷段高含沙洪水灾害机理与河型响应[D]. 中国科学院大学,2017. |
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