Knowledge Resource Center for Ecological Environment in Arid Area
| 内蒙古十大孔兑流域地貌发育动力机制及其沉积响应 | |
| 其他题名 | Dynamical Mechanism of Geomorphic Evolution and Its Sedimentary Responses in Ten Kongdui Watersheds in Inner Mongolia of China |
| 顾畛逵 | |
| 出版年 | 2018 |
| 学位类型 | 博士 |
| 导师 | 师长兴 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 十大孔兑（孔兑，洪水沟，蒙古语）是黄河内蒙古段南岸的十条支流，历来具有较强的侵蚀产沙特性，洪水易发且产沙量大，流域下游以及汇入段的黄河都饱受泥沙淤积之害。为了治理好流域内泥沙淤积和水土流失问题，诸多学者开展过大量研究，主要集中在产沙量估算、水沙变化规律分析、风-水两相作用以及地表沉积特征分析等几个方面，但这些研究均是针对于短时间尺度上的特征分析，并未从地貌演化角度对地表环境进行过研究。实际的地貌演化过程是复杂而漫长的，本文从宏观角度对流域地貌发育动力以及沉积特征进行了研究，进一步完善了对区域地理环境的认识，为相关战略治理措施的制定和工程实施提供指导依据。文中以DEM数据、地质资料和气候数据为基础，首先通过地貌量化参数对流域地貌及其发育动力机制进行了研究。在进行一系列地貌参数提取之前，借助面积-高程积分值分析了地貌尺度表达的空间效应，并将其作为相关地貌参数提取时的尺度参照。然后在此基础上根据一系列地貌参数对流域内构造活动强度特征、纵剖面的发育动力特征和流域沟壑区侵蚀谷横断面的演化模式等方面进行了分析。与此同时，结合探地雷达数据和沉积粒度特征开展了对流域下游沉积环境的调查，分析了流域下游和典型风-水两相区的河道沉积环境特征。对于流域地貌特征的尺度效应来讲，地貌空间特征分异性较大的尺度主要集中在6.2km和22.5km附近的两种直径窗口之下。受北部阴山山脉区的影响，区域内的面积-高程积分值会随着分析尺度的增加而减小。进一步通过分析构造地貌指标、纵剖面和横剖面特征后发现，流域构造活动强度以西部大于东部、自西向东趋于减弱为特点，均为中-弱强度；构造隆升强度大于侵蚀下切强度，整体表现为隆升状态，其中西部隆升速度高于东部流域。流域内侵蚀区域主要分布在上游，侵蚀发生以来的总侵蚀量大约为4006亿t（按密度2.425t/m3估算），历史平均侵蚀速率远低于现代水平。除壕庆河外，各主河道纵剖面侵蚀演变阶段为早期，说明下游河段将长期接受沉积。纵剖面凹度值自西向东趋于增加，主要受构造隆升快慢影响。流域隆升速率在东西方向上的差异大致起始于上新世前后，西部流域海拔增长较快，能够使得纵剖面因受侵蚀而降低的高程得以弥补，而东部流域纵剖面由于隆升速度慢，外营力的作用结果相对凸显，纵剖面下凹程度略大，侵蚀演进程度相对较高。在各主河道内及主河道之间，河流功率值的空间差异一般较大，西部流域河道平均功率整体上要大于东部流域，其中最大的为西柳沟，最小的为壕庆河，高值区一般在中游河段，下游段河流功率下降明显，因而导致淤积。上游沟壑区最大谷宽和最大谷深均出现在中部的罕台川，尺度均值以中部大、东西两侧略小为特点。宽深比的最大值不超过140，绝大部分在20?80以内。谷宽和谷深的变化具有较大相关性，表明横剖面演化过程中侧向侵蚀和下切侵蚀现象并存，根据线性公式，当侵蚀谷向两侧拓宽100m时，谷底下切量约为1.34?1.07m。侵蚀谷侧向侵蚀和横剖面的不对称程度在自西向东方向上存在增加的趋势，但与区域整体的侵蚀演化阶段无显著关系。下游河段沉积严重，对其沉积特征的研究显示，在10m深度范围内的沉积地层存在两个主要的雷达反射层，上层反射相的厚度在2?4m之间，反射频率略低。反射相主要为水平或者近水平层理。空白反射、倾斜反射、不连续、波状、杂乱状及侵蚀填充反射也以小尺度形式在一定程度上存在，表明区域内主要沉积模式为垂向加积过程，很少遭受大规模的侵蚀活动和后期河流过程较大的改造。沉积物主要由砂质和粉砂质组成，分选性较差，河床相和河漫滩相较为多见，直接的风成堆积物在地层记录中极少见。迥异大规模沉积的是，在西柳沟流域下游河段发现了规模较大的深切河道侵蚀填充结构，大概位于冲积扇的扇顶附近，处于晚更新世地层之上，根据气候变化特点，推断其可能形成于早全新世（11.9至4ka B.P.）。在这些流域中，罕台川流域在历史时期具有高含沙水流多发的特点，其次为西柳沟流域，这可能与其上游东胜隆起区的暴雨风暴中心位置有关。对于风-水两相河道内沉积粒度与外营力以及地貌条件的关系，以黑赖沟为典型流域的分析结果显示，上游河段河床沉积物主要受径流和风力作用影响；中游河段主要受河流作用影响，沉积颗粒最粗、分选性也最差，沉积颗粒的大小主要反映水力作用大小而与风力作用关系不大。由于河流功率在中-下游河段下降很快，粗颗粒难以被搬运到下游河段。下游河段受库布齐沙漠影响较大，风力作用相对增强，会将河道西侧的颗粒带入河道并对颗粒分选性产生一定影响，但粒径值不会大于0.88f。与水力和风力作用相比，地貌侵蚀演化特征对河道沉积颗粒影响不显著。总之，河流作用对河道沉积粒度特征起主要作用，风力作用次之。 |
| 英文摘要 | The ten Kongduis (large arroyos in Inner Mongolian) are tributaries of the Inner Mongolia reach of Yellow River. They are characterized by intensive erosion and high floods with a high sediment concentration. The lower reaches of the Kongduis and the Yellow River are suffering from heavy sedimentation. To manage the sedimentation and soil erosion in these watersheds, many scholars have done a lot of researches, mainly concentrating in the sediment yield estimation, the analysis of laws of flow and sediment changes, interactions of the Aeolian-fluvial process and the grain size characteristics of the earth surface. However, all these works focus on the short timescale and are not done from the perspective of landform evolution, which is not conducive to foresee the long-term trend of geographic environment change. As the evolution of landforms is complex, and its history is long, the research on the dynamics of landform evolution and sedimentary features can further improve the understanding of regional geographical environments, providing the basic knowledge for the formulation of relevant strategic governance measures.Based on DEM data, geological data and climatic data, this paper firstly studies the geomorphic features and the dynamical mechanisms by geomorphic parameters. Before a series of geomorphic parameter values are extracted, the spatial effect of geomorphic scale expression is analyzed by using the hypsometric integral value, and it is regarded as the reference scale during the extraction of geomorphological parameters. Furthermore, the intensity of tectonic activity and its changing trend, formation mechanism of longitudinal profiles and the evolution characteristics of the cross sections of the valleys in the upper basins were analyzed. Also, the sedimentary environment survey and analysis were carried out in the lower river channels and floodplains of some basins by ground-penetrating radar and grain size analysis.For the scale effects of the watershed geomorphic feature, the spatial heterogeneity of geomorphic features is more obvious under the two diameter windows, 6.2km and 22. 5km. For the further analysis, geometric parameters, the longitudinal profiles of the main stream, and cross sections of valley and gullies of the Kongduis were extracted from DEM. Some findings are achieved as follows. The intensity of the tectonic activity is on the middle-weak level and is higher in the west basins than in the east basins. The uplift rate of the basin is greater than erosion rate. Main bodies of the basins are still dominated by the tectonic uplift. The erosion of the basin is mainly concentrated on the upper reaches with a total erosion volume of about 40.6 billion t (estimated at 2.425t/m3) since the tectonic uplift occurred. The current erosion rate is much higher than the historical average since the Quaternary. The shapes of main channel profile show the early stage of erosion evolution, suggesting that the upper reaches will be eroded and the downstream plains will be silted up in the long run. Each longitudinal profile shows a concave shape, and the concavity value tends to increase from west to east Kongduis due to differences in tectonic activity. Compared with the tectonic activity, the fluvial action is more limited and not significant. The maximum concavity value occurs in the lower reaches of longitudinal profiles, inhibiting the sediment transport. The larger the concave value is, the smaller the sediment transport capacity is. The differences in the uplift rate between the east and the west basins occurred around the Pliocene. The elevations of the longitudinal profiles of the west have been increasing as a result of the higher uplift rate than erosion rate there. The effect of external force on the east longitudinal profiles is relatively prominent, resulting in the larger concavity values and the characteristics of a later stage of erosion evolution. Great differences of the stream power of the main channel exist along the channel. The high values of the stream power are distributed in the middle reaches and decrease downstream significantly, so deposition occurs in the lower reaches, forming alluvial fans. The average stream powers of the western channels are greater than that of the eastern ones, with the largest in the Xiliugou and the smallest in the Haoqinghe. For cross-sectional features, the maximum values of valley width and valley depth appear in the Hantaichuan watershed located in central part of the Kongdui basins and decrease to the east and west sides, which may be related to the rainstorm center in the middle reaches of the basin. The width/depth ratio of valleys is in the range from 20 to 80 with a maximum of about 140. The valley width has a scale dependence on valley depth, suggesting that lateral erosion and downcutting coexist. According to the linear relationship, the valley depth will increase about 1.34?1.07m when the valley broadens about 100m. The lateral erosion intensity increases and the valley slope decreases from west to east. Besides, cross-section shapes become more complex from west to east and there is no significant relationship between the geometric parameters of cross sections and the erosion evolution of watersheds.The sedimentation in the lower reaches of the basin is serious, the study results of the downstream sedimentary areas show that the radar facies of sedimentary strata are dominated by horizontal or sub-horizontal shape on a large scale, suggesting that the deposition process on the alluvial fans has been dominated by a vertical accretion pattern. The reflection features like reflection free, inclined reflections, discontinuous, undula, chaotic, sinuous reflections and channel fill exist to a lesser extent. However, a few GPR sections send signs of strong erosion, and the one in the upper Xiliugou fan reveals that erosion had been active likely during the early Holocene and the channel position should be relatively fixed, indicating that sediment accumulation has been slow in the upper part of the alluvial fan since the early Holocene. Sedimentary strata in the alluvial fans are mainly composed by sand and silt deposited in the fluvial environment and are rarely affected by aeolian reworking, and the deposits in the west are more poorly sorted and coarser than those in the east, likely suggesting different hydrodynamic conditions in the east and west. In these basins, Hantaichuan was easily characterized by hyperconcentrated flows during the historical period, followed by the Xiliugou, which may be related to the storm center in the Dongsheng uplift area.For the characteristics of Aeolian-fluvial environments, the main stream of Heilaigou, as a typical one, was investigated. The relationship between the sedimentation characteristics and the external forces and the geomorphic conditions was analyzed. The results show that the upper stream is controlled by both fluvial and wind processes. The riverbed sediments in the middle stream are sorted worse than those in the upper stream and are affected mainly by fluvial processes. The particles of the downstream riverbed are likely contributed by the Kubuqi Desert. The size of particles on the riverbed depends on the hydrodynamic conditions but has not a significant association with the evolution of landform. Sorting is related to both the hydrodynamic conditions and wind action significantly. Riverbed deposits brought in by winds likely become finer from the lower to the upper reaches and are not coarser than 0.88f. Generally speaking for the channel, the hydrodynamic forces play a major role in sedimentation characteristics of the riverbed, followed by wind actions. |
| 中文关键词 | 十大孔兑 ; 地貌演化 ; 动力特征 ; GPR ; 沉积环境 |
| 英文关键词 | Arroyo landform evolution dynamic characteristic GPR sedimentary environment |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院地理科学与资源研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288072 |
| 推荐引用方式 GB/T 7714 | 顾畛逵. 内蒙古十大孔兑流域地貌发育动力机制及其沉积响应[D]. 中国科学院大学,2018. |
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