【作者】 屈贵贤；

【导师】 王建； 高正荣；

【作者基本信息】 南京师范大学 ， 自然地理学， 2014， 博士

【摘要】 自然与人为双重影响下的河流变化过程研究,是当前国际地球科学研究的一个前沿课题。长江作为人类活动最强烈的河流以及在很大程度上受季风气候影响、水沙变率很大的河流,是研究河流过程对自然与人为作用响应的理想河流。长江干流河床近五十年来的冲淤变化和调整,是自然环境变化和人类活动双重影响的结果,已经成为国内外关注的一个研究热点。三峡工程运行以来,由于来沙量的减少,不仅导致中游近坝河段遭受强烈冲刷,并且还导致长江河口岸滩的侵蚀。而下游河段,尤其是位于潮区界和潮流界附近的大通--江阴河段冲淤变化如何,是怎么响应的,还缺乏系统的研究。本文在地理信息系统和数字高程模型技术的支撑下,对长江下游大通-江阴河段六个时期(1959、1969、1983、1992、2003、2008)的河道地形图进行了分析处理,建立了河道水下地形数据库,选取其中三个年份(1969、2003、2008)的数据建立了数字高程模型,对研究河段的形态特征、冲淤变化及其成因机制进行了系统分析。发现了对于三峡工程影响的一种新的响应机制,发现了上、中、下三段不同的冲淤变化特征和响应模式,揭示出该河段河床冲淤变化随着深度增大而增大的规律。对于深化长江受自然与人为影响的响应机制的认识,以及指导长江流域和河道工程建设等,均具有重要的意义。主要结论如下：(1)该河段对于三峡大坝影响的响应,与其它河段有所不同。在三峡大坝建成后的前五年(2003-2008),该河段平均来说并没有随着上游来沙量的减少而发生冲刷,而是发生了淤积。原因在于该段位于潮区界和潮流界变动比较敏感的河段,三峡蓄水后,洪水流量减少,导致洪水期潮区界上移,水力坡度减小。净淤积量为47822.45万立方米。(2)该河段的上、中、下三段的冲淤变化,表现出不同的变化特征和响应模式。三峡蓄水运行后(2003-2008),上段由小幅冲淤交替转为以冲刷为主,中段由冲刷转为淤积,下段由淤积转为冲刷。这是因为,三峡蓄水后,到达大通站的泥沙量减少,因此上段(大通-芜湖河段)发生冲刷。进入中段(芜湖-镇江河段)后,一方面由于上段冲刷使得含沙量得以补充,挟沙能力下降,另一方面由于潮区界上移导致河流纵比降减小,使得径流流速下降,挟沙能力进一步降低,从而造成河床淤积。进入研究河段下段,由于同时受到径流与潮流双重作用,落潮时落潮流与径流同向叠加,流速增大,同时含沙量因泥沙在中段落淤而有所下降,此时挟沙能力增强,从而导致下段发生冲刷。(3)不同类型河道对冲淤的响应也存在差异。弯道河床演变特征表现为深槽下切和深泓左右摆动,其次表现为对岸浅滩的淤积。不稳定的汊道段则表现为左右汊冲淤调整加剧,深槽下切或淤积,汉道入口和出口的深泓左右摆动为其主要特征。节点段,深泓位置无较大变化,河段入口和出口处断面冲淤显著。(4)由于受到河岸工程的影响,大部分河段的横向冲淤(摆动)受到限制。河床冲淤变化主要表现为10米等深线附近及其以下深槽的冲淤,以及沿着河道方向的纵向冲淤变化。(5)该河段近五十年,由于受到河道工程的影响,河床宽度存在着减小的趋势。其中,1983-1992年间,河宽缩窄约11.9%。江心洲的发育逐渐趋于稳定。(6)在受人类活动影响较小的自然状态下,上下游河段之间在河床演变中具有较好的关联性。节点段主泓的位置变化对下游河段的演变具有直接影响。护岸工程的实施,对稳定节点段河势作用显著。近期,各分汉河段之间的上下游关联性有减弱趋势。更多还原

【Abstract】 Research on river channel changes caused by nature and human being has attracted increasing attention worldwide due to the economic, social, and environmental significance of these changes. As the most important river in China, the Yangtze River has been tremendously influenced by human activities as well as monsoon climate variation. The changes in water and solid in the river make it an ideal study area for understanding how natural events and human actions can impact the characteristics of a river. Therefore, the research that focused on the sedimentation and erosion of the river channel, indicating the river channel change has received a large amount of attention in fluvial geomorphology research. The sedimentation-erosion changes in the Yangtze River and the adjustment of its main course in recent decades can be attributed to both natural environmental change and human activities.After the Three Gorge’s reservoir impoundment, the bed in the middle reach of the Yangtze River scoured strongly, especially the reach close to the dam. The quantity of material that goes into the sea decreased and the trend of cut-and-fill sedimentation has changed. However, the response from the lower reach of the Yangtze River is unknown, which needs to be further investigated.The hydrodynamic condition of the lower reach of the Yangzte River, from Datong to Jiangyin, is different from the one of middle reach and estuary. So the feature of channel’s response to the hydrodynamic condition should be distinctive. Consequently, this study aims to study the characteristics and causes of channel change in the lower reach of the Yangtze River, which is beneficial to understand deeply the response from big river to the natural factors and human activities. To evaluate the dynamic changes of sedimentation and erosion of the Datong-Jiangyin reach of the lower Yangtze River from1959to2008, database of six periods of underwater topography were designed and constructed, with the help of GIS technology, on the basis of the Datong-Jiangyin River Relief Map in1959,1969,1983,1992,2003and2008. Digital Elevation Model (DEM) were constructed based on the data of map in1969,2003and2008. Changes in channel width and area of channel and mid-bar were investigated to understand the planform change. Bed-level adjustments were identified both by comparing available topographic longitudinal and vertical profiles and volume changes of different years. Based on the above critical studies, the major contribution of this dissertation are summarized as follows: (1) It is different from other reaches of the Yangtze River that the channel’s response to the Three Gorge. Although the sediment supply from upstream decreased, sediments amounts to478,224.5thousand cubic metres deposited in Datong--Jiangyin reach owing to the increasing action of tide between2003to2008.(2) Inner differences exist in the filling and scouring process for the river reach between Datong and Jiangyin. Due to the reduction of sediment from the upper reach of the Yangzte River, the upper reach between Datong and Jiangyin were scoured. In the middle reach between Datong and Jiangyin, the sediment concentration increases gradually, the tidal effection moves up,so that the sediment transport capacity of flow decreases and sand falls on the river bed. In the lower reach between Datong and Jiangyin, due to the same direction of ebb-current flow and runoff, flow velocities increases and could carry more sediment, so this reach was scoured.(3) Due to the different type of channel, the beds’ filling and scouring process are also different. In bend reach, the channel change focuses on the incision and main flow’s moving from side to side. Unstable branching adjusted strongly,with one branch filled and the other scoured. In node reach,the location of main flow had no change.(4) The planform of most reaches was confined by revetments, so the filling and scouring process occoured below the elevation of-10meters and adjusted longitudinally. The main area of deposit transfered from the lower reach to the middle reach. The center of erosion changed from the middle reach to the upper reach.(5) The dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel(up to11.9%from1983to1992). Mid sandbars become more and more stable. The main reason can be ascribed to the effection of river-training works.(6) In a state of nature, the channel change of adjacent reaches is relevant. The location change of main flow in node reach has a tremendous impacts on the channel change of the following reach. The shore protection engineerings play an important role on the stability of the node reach’s river bed. Recently, the relevant relationship between up and down reaches declines.更多还原