三峡工程运用后上荆江典型河段岸坡稳定性分析

根据三峡水库蓄水前后的实测地形和水文资料,分析了上荆江河段的水沙变化特性和该河段平滩河槽下的冲刷情况。结合三峡工程后续岸坡影响处理的工程实践,选择杨家垴至罗家潭段、学堂洲段、沙市城区、公安河弯、耀新民堤段、郝穴河弯段和南五洲等河段,进行了三峡水库蓄水运用后的岸坡稳定性分析。结合已有的预测结果及岸坡稳定的分析,指出上荆江河段岸坡存在崩塌隐患的地段。     

下荆江熊家洲至城陵矶弯曲型河段河床调整规律

三峡水库运用后, 坝下游水沙过程发生了较大调整, 对下荆江熊家洲至城陵矶弯曲型河段河床冲淤演变造成较大影响, 从而对本河段河势稳定、防洪、航运等可能造成不利的影响, 基于此, 根据最新实测资料分析水沙条件变 化及其对本河段河床调整规律的影响。研究成果显示: 三峡水库运用后, 水流含沙量大幅减小, 且水库调蓄导致熊 家洲至城陵矶河段在枯水期径流量明显增加, 使弯道主流长期偏向于凸岸, 引起凸岸边滩大幅冲刷, 这是近期该河段发生“撇弯切滩”的主要原因之一; 随着三峡上游干支流水库群陆续建成运用, 坝下游河道将会长期遭受清水冲 刷, 河床仍将呈单向冲刷下切的趋势, 弯顶段主流平面摆动仍将较大, 弯道顶冲点也将相应下移, 导致主流贴岸距离 进一步下延, 引起河道岸线的崩退, 未来一段时期内典型弯曲型河道的局部河势变化仍将明显。     

三峡工程运用初期监利河段河势变化预测

监利河段是下荆江变化最剧烈的河段之一,三峡工程运用后,下泄含沙量减小,该河段冲淤调整将更为明显.采用河道平面二维水沙数学模型,对监利河段在三峡工程蓄水运用初期可能产生的河床冲淤及河势变化进行了计算分析研究.结果表明:监利河段总体河势变化不大,但河床冲淤较为剧烈,断面冲深扩大,局部岸段和乌龟洲右缘部位崩退,乌龟洲左汊萎缩...     

长江荆江河段七弓岭弯道主流撇弯原因初探

三峡水库蓄水运行后,荆江河段发生了普遍冲刷,下荆江尾闾七弓岭弯道主流出现撇弯现象。分析了七弓岭弯道的历史演变和形成过程,以及近期岸线、深泓线和河床冲淤的变化,并与已有的丹江口水库蓄水后坝下游撇弯切滩的分析成果进行对比,探究了七弓岭弯道发生撇弯的原因。结果表明,七弓岭弯道撇弯主要和来水来沙量及过程、河道形态及河床地质条件、江湖关系等因素有关。其河道勘测分析成果可为下荆江河道综合整治提供参考。     

下荆江七弓岭弯道裁弯的水情效应研究

三峡水库蓄水运用以来，下荆江七弓岭弯道段出现凸岸侧冲刷、凹岸侧淤积的现象，八姓洲狭颈宽度因崩岸缩短，存在裁弯的风险。基于原型观测资料，分析七弓岭弯道裁弯具体位置，设计裁弯新河道，建立长江中游-洞庭湖一二维耦合非恒定流模型，评估典型工况下七弓岭弯道裁弯带来的水情效应。结果表明，七弓岭弯道裁弯将造成汛期高洪水位下城陵矶水位升高0.03～0.04 m,枯期藕池口分流比减少0.09%、断流天数增加5 d,监利站月均水位下降0.04～0.11 m、七里山站月均水位上升0.01～0.04 m等影响。研究成果可为判断城陵矶附近防洪形势及提出相关应急预案提供技术支撑，对保障区域防洪安全及江湖汇流段治理和防护具有参考价值。     

下荆江七弓岭弯道崩岸机理研究

三峡水库蓄水以来,下荆江末端七弓岭弯道颈口上下游河岸的崩岸速率加快,极有可能发生崩岸型颈口裁弯,导致下荆江河道强烈冲刷和河势横向调整。采用水文资料、遥感影像、野外调查和BSTEM数值模拟相结合的方法,分析了七弓岭弯道60余年平面形态变化,颈口上下游的崩岸速率及主控因素,揭示其崩岸过程与机理。七弓岭河段河岸上层为密集的芦苇根系,剪切式和悬臂式崩岸兼有,上游侧崩岸速率约为12.5 m/a,上游颈口处崩岸速率大于八姓洲其他部位,而下游侧略有淤积。考虑到潜水位变化和坡脚冲刷作用,在持续相同流量条件下比实际水位流量过程的崩岸速率更大。     

丹江口水库蓄水以来汉江中下游河床冲淤变化研究

丹江口水库蓄水运用后,汉江中下游河床发生了显著调整。为了加深对水库调蓄影响下汉江中下游河床整体冲淤规律的认识,根据大量实测资料,对汉江中下游水沙与河床冲淤变化进行了较为系统的分析。结果表明:丹江口水库蓄水运用后,汉江中下游洪峰削减,枯水期流量增大,中水期延长,径流年内分配更加均匀,坝下游输沙总量大幅度减少。南水北调中线工程运行后,径流年内分配更趋均匀,坝下游输沙量进一步减少。1978～2020年,丹江口至河口河段平滩河槽冲刷了10.75亿m3,冲刷强度自上而下逐步减小;中游丹江口至碾盘山河段仍是冲刷发展最为剧烈的河段。近期河床演变分析结果表明:丹江口至襄阳河段洲滩变化较大,江心滩面积有所淤长且整体下移;襄阳至碾盘山河段洲滩、汊道基本稳定,河道游荡性减弱;碾盘山至仙桃河段深泓线横向摆动频繁,洲滩冲淤变化较为剧烈;仙桃至河口河段河床演变强度相对较小,但局部弯道有裁弯取直现象发生。分析成果可为汉江中下游防洪减灾、规划设计、河道治理、采砂管理、航道整治等提供参考。     

长江中游宜都至松滋河口段近期河床演变分析

近几十年来,受上游多座水库和各种涉水建筑物不断兴建的影响,长江中游宜都至松滋河口段河道边界条件和水沙条件相应发生了显著变化,河道将表现出新的演变特性,对下游河道防洪、航运、岸线利用、水环境、生态修复等可能产生一定影响。通过分析枝城水文站近期水沙变化特性和近20 a来河道地形实测资料以及开展一维水沙数学模型计算,探讨了长江中游宜都至松滋河口段近期河道演变特性。研究成果表明:多年来荆江三口分流比一直处于下降趋势,三峡水库蓄水运用前分沙比也呈现下降趋势,但蓄水运用后与蓄水运用前(1999～2002年)相比,分沙比平均值明显增加。受三峡水库蓄水后清水下泄影响,研究河段河床纵向冲刷剧烈,床沙粗化后中值粒径增大趋势明显,洲滩萎缩、深槽扩展,但2013年以来冲刷速率明显趋缓,且河道平面形态、水流主流和河势均保持基本稳定。预计今后一段时间内该河段河床冲刷幅度将有所减小并逐渐趋于平衡,研究河段河势不会发生重大变化。     

下荆江熊家洲河段平面形态与河床冲淤变化

熊家洲河段位于长江中游下荆江尾端,其平面形态从顺直过渡到微弯再逐渐演变成S型,是目前荆江最为弯曲的河段。受水沙条件、河岸边界条件、自然裁弯和人工裁弯等因素影响,局部河势调整频繁。熊家洲凸岸斜槽裁弯形成新河槽,导致主流与支汊成为共生的分汊河势,改变了熊家洲出口段水流条件,进而影响下游七弓岭弯道崩岸速率和河床冲淤。为全面分析熊家洲河段平面形态演变过程和河床冲淤变化,选取枯水期遥感影像数据及沿程代表性断面进行分析。结果表明:熊家洲河段整体向下游蠕动且河道展宽,熊家洲弯道新生河槽呈冲刷扩大趋势,7 a平均展宽70 m;出流沿程断面深槽从左岸向右岸方向发展,熊家洲下游的深泓线偏向右岸;三峡水库建成运行后,深泓线开始贴近七弓岭凸岸,而原深槽回淤形成2个沙洲,经过七弓岭弯顶后逐渐向凹岸偏移,出熊家洲弯道后河道沿程呈现冲刷下切趋势。研究成果对目前该段河势控制工程的实施提供了参考意见,为下一步研究三峡水库运行的河势控制提出了思路。     

荆江窑监大河段河床演变关联性研究

为了弄清长江中游弯曲分汊河型与单一微弯河型演变的关联性,有必要开展荆江窑监大河段(由窑监河段和大马洲水道组成)河床演变的关联性研究。在分析窑监河段河床演变的基础上,研究了窑监大河段来水水沙条件和边界条件变化对河床演变的影响,重点探讨了窑监河段变化与大马洲水道主流、洲滩、航道条件变化的关联性。结果表明,在窑监河段河床变化的影响下,大马洲水道进口段弯曲狭窄,出口过渡段航道条件变差。     

长江和畅洲左汊潜坝工程对汊道演变的影响

长江镇扬河段和畅洲左汊潜坝工程是首次在长江主汊中采用全断面潜坝形式实施的汊道控制工程,工程建成后使和畅洲左汊分流比上升的势头得到有效遏制,基本实现了工程预期目标。为研究潜坝工程对和畅洲汊道近期演变的影响,比较了潜坝工程建成前后汊道平面、断面、分流比、槽蓄量等要素的变化;分析了来水来沙条件、上游河势变化、河床边界条件等因素对汊道的影响;从两汊道阻力变化对比、相对引水深变化及上游流速分布的改变等方面,初步探讨了潜坝工程对汊道的影响机理。结果表明,潜坝工程建成后和畅洲汊道发生了有利变化,而潜坝工程是和畅洲汊道近期演变朝着有利方向变化的主要因素。     

长江下游马鞍山河段河道治理初步研究

 归纳总结了长江马鞍山河段基本情况、近期河道演变特点和河道治理概况;根据现有河势条件及近年崩岸险情,分析指出了目前本河段存在的主要问题;结合河道治理规划情况,探讨了下一步河道治理措施。研究认为：河势调整工程是该河段整治的关键,重点是通过数学模型和河工模型试验研究提出河势调整工程方案;主要是在左岸新河口一带布置导流工程和上下何家洲及心滩串沟封堵并岸工程,并辅以江心洲尾的何家洲尾挖槽工程。鉴于整治工程的紧迫性和时效性,建议相关部门尽快开展相关前期工作,为整治工程早日实施创造条件,进而实现该河段河势的稳定。     

EFFECTS OF FLOW DYNAMICS ON THE AQUATIC‐TERRESTRIAL TRANSITION ZONE (ATTZ) OF LOWER MISSOURI RIVER SANDBARS WITH IMPLICATIONS FOR SELECTED BIOTA

Sandbars are an important aquatic terrestrial transition zone (ATTZ) in the active channel of rivers that provide a variety of habitat conditions for riverine biota. Channelization and flow regulation in many large rivers have diminished sandbar habitats and their rehabilitation is a priority. We developed sandbar‐specific models of discharge‐area relationships to determine how changes in flow regime affect the area of different habitat types within the submerged sandbar ATTZ (depth) and exposed sandbar ATTZ (elevation) for a representative sample of Lower Missouri River sandbars. We defined six different structural habitat types within the sandbar ATTZ based on depth or exposed elevation ranges that are important to different biota during at least part of their annual cycle for either survival or reproduction. Scenarios included the modelled natural flow regime, current managed flow regime and two environmental flow options, all modelled within the contemporary river active channel. Thirteen point and wing‐dike sandbars were evaluated under four different flow scenarios to explore the effects of flow regime on seasonal habitat availability for foraging of migratory shorebirds and wading birds, nesting of softshell turtles and nursery of riverine fishes. Managed flows provided more foraging habitat for shorebirds and wading birds and more nursery habitat for riverine fishes within the channelized reach sandbar ATTZ than the natural flow regime or modelled environmental flows. Reduced summer flows occurring under natural and environmental flow alternatives increased exposed sandbar nesting habitat for softshell turtle hatchling emergence. Results reveal how management of channelized and flow regulated large rivers could benefit from a modelling framework that couples hydrologic and geomorphic characteristics to predict habitat conditions for a variety of biota. Published in 2011 by John Wiley & Sons, Ltd.     

Effects of spates of different magnitudes on a Phragmites japonica population on a sandbar of a frequently disturbed river

In flow‐regulated rivers, natural flow patterns and related sedimentation processes are disturbed, thus interrupting the magnitude and duration of spates. We hypothesized that this in turn might alter the impact of spates on plant communities inhabiting sandbars along the river channel. In order to test this hypothesis, the effects of spates of different magnitudes and durations on spatial variation and composition of a Phragmites japonica Steud. community on a sandbar during a 2‐year period were investigated. The flow variation of the river was continuously monitored, and the spates were categorized as small, medium or large, based on the magnitude (depth). Growth parameters (shoot length and shoot density), above‐ and belowground biomass of the plant community and the quantity of litter retained within selected quadrats, and ash‐free dry weight (AFDW) of the soil were observed at seven different locations: two each at the extreme upstream, middle and extreme downstream and one location in the downstream reaches of the sandbar. Our results showed that the aboveground biomass declined due to large‐scale spates; however, these spates triggered the formation of secondary shoots if sediments were accumulated as a result of the spates. Conversely, the aboveground biomass did not recover if the substrate was eroded. Accumulated litter beneath shoots was easily washed away due to spates, positively affecting shoot re‐growth. The effects of spates on the P. japonica plant community depended highly on the location of the plants on the sandbar and the magnitude and duration of the spates. The different erosion–sedimentation processes, depending on the local river channel morphology and spate types, significantly affected the growth and morphological characteristics of P. japonica population. Copyright © 2008 John Wiley & Sons, Ltd.     

长江下游镇扬河段河道演变及整治研究

长江镇扬河段是长江下游变化最剧烈的河段之一,近百年来其河道变化主要表现在世业洲洲头的不断崩退、左汊的缓慢发展及汇流后的主流不断右移,六圩弯道凹凸岸互换后的凹岸持续崩坍及弯道向下游不断的发展,和畅洲汊道由多汊演变为鹅头型双汊河道后发生主、支汊易位及左汊的持续发展等。其演变过程颇为复杂,河道整治难度较大。通过分析镇扬河段的河势特点及近百年来河道的演变特点,结合已实施的整治工程,分析了该河段工程的整治效果,总结了工程的整治经验,并且针对目前河段存在的主要问题提出了整治建议。     

长江中下游阻隔性河段特征及成因初步研究

长江中下游长河段长时段的演变资料分析表明河势调整往往会向下游传递,但是部分河段却能阻隔这种河势调整的传递效应,称之为阻隔性河段。统计表明,阻隔性河段应同时具有单一微弯的平面形态、凹岸抗冲性较强且中上段无挑流节点、河宽随水位变化率不超过45等三个特征。进一步分析表明,这种河段具有阻隔性的根本原因是其能够归顺不同流量级的主流平面位置,使得无论上游河势如何调整,其出流的主流平面位置基本稳定,为下游河段提供相对稳定的入流条件。河道整治过程中,宜抓住有利时机塑造阻隔性河段效果,无阻隔性影响的长河段宜自上而下系统规划整治,对大幅度崩岸、滩体大幅萎缩等可能破坏阻隔性的变化应及时整治,防止阻隔性丧失。     

Influence of Riparian and Watershed Alterations on Sandbars in a Great Plains River

Anthropogenic alterations have caused sandbar habitats in rivers and the biota dependent on them to decline. Restoring large river sandbars may be needed as these habitats are important components of river ecosystems and provide essential habitat to terrestrial and aquatic organisms. We quantified factors within the riparian zone of the Kansas River, USA, and within its tributaries that influenced sandbar size and density using aerial photographs and land use/land cover (LULC) data. We developed, a priori, 16 linear regression models focused on LULC at the local, adjacent upstream river bend, and the segment (18–44 km upstream) scales and used an information theoretic approach to determine what alterations best predicted the size and density of sandbars. Variation in sandbar density was best explained by the LULC within contributing tributaries at the segment scale, which indicated reduced sandbar density with increased forest cover within tributary watersheds. Similarly, LULC within contributing tributary watersheds at the segment scale best explained variation in sandbar size. These models indicated that sandbar size increased with agriculture and forest and decreased with urban cover within tributary watersheds. Our findings suggest that sediment supply and delivery from upstream tributary watersheds may be influential on sandbars within the Kansas River and that preserving natural grassland and reducing woody encroachment within tributary watersheds in Great Plains rivers may help improve sediment delivery to help restore natural river function. Copyright © 2014 John Wiley & Sons, Ltd.     

长江沙市河段近期河道演变分析

沙市河段是上荆江河势较为复杂的河段之一,也是航道治理的重点河段之一。根据三峡水库蓄水以来沙市河段实测地形资料以及沙市水文站的实测水文资料,从来水来沙、深泓平面、洲滩、深槽以及横断面变化等方面系统分析了沙市河段的近期河道演变特性。结果表明:(1)三峡水库蓄水后,沙市河段整体呈现冲刷的趋势,深泓平面摆动集中在分汊段,沿程洲滩冲刷萎缩,横断面冲淤时有发生,20 m深槽冲刷发展,接近贯通。(2)受到沿程护岸工程以及洲滩守护工程等的影响,该河段总体河势基本稳定,但局部河段内仍会有所调整。(3)河段尚未达到冲淤平衡,未来一段时间内,河段仍将以冲刷为主,若无人工干预,滩槽演变趋势将延续近期的变化,由此对防洪、航运等方面带来的影响值得关注。     

EROSION OF RIVER SANDBARS BY DIURNAL STAGE FLUCTUATIONS IN THE COLORADO RIVER IN THE MARBLE AND GRAND CANYONS: FULL‐SCALE LABORATORY EXPERIMENTS

This research examines the mass failure and seepage erosion of sandbars due to rapid fluctuations in river stage using a full‐scale laboratory model. Hydroelectric dams operated to provide electricity at peak demand produce rapid river stage fluctuations. During decreasing river stage, the groundwater table becomes higher than the river stage, increasing pore water pressures and exfiltrating groundwater. This can cause seepage erosion and mass failures in the banks and bars. In the Colorado River in the Marble and Grand Canyons, maximal downramp and upramp rates have been imposed on the Glen Canyon Dam operations. Our experiments research the efficacy of these discharge ramp rate restrictions to reduce sandbar erosion. The laboratory model consists of a two‐dimensional sandbar face (8 m long, 2.5 m high and 0.5 m wide). Multiple experiments were conducted in a range of slopes, varying from 12° to 26°. An analysis of historical and current ramp rates at 47 locations along the river provided the basis of laboratory downramp rates in the range from 0.1 to 0.6 m h^?1. Results show that bank stability is reached at a slope of approximately 14°. The erosion of intermediate slopes (18° – 22°) is controlled by seepage erosion, whereas the erosion of steep slopes (26°) is governed by mass failures. Erosion rates per diurnal cycle do not depend on ramp rates, but they increase with sandbar steepness. Therefore, steep sandbar faces would rapidly erode by mass failure and seepage erosion to shallower stable slopes in the absence of other erosion processes, regardless of dam discharge ramp rates. Our experiments only address seepage erosion and mass failure; increasing the daily magnitude and/or duration of peak discharge may increase the erosion of bars by turbulent sediment transport. Copyright © 2012 John Wiley & Sons, Ltd.     

基于河势变化条件的张靖过江通道线位比选分析

长江澄通河段福姜沙段多汊并存,受上游径流和下游潮流双重作用,水动力条件和河床演变复杂。拟建张靖过江通道线位,南岸在张家港市十字港附近,北岸在靖江市新六助港-夏仕港之间,横跨福姜沙及福左、福右汊道。过福右汊道拟采用隧道工程(A线),过福左汊道有桥梁工程(A1线)和隧道工程(A2)两种方案。采用实测资料对近期张靖过江通道拟选线位上下游附近河势变化、河床稳定性等进行了研究,就工程河段滩槽、深泓稳定性和河床断面、冲淤变化等进行了对比分析。通过分析,推荐采用河床较为稳定的"A+A1"线位方案作为张靖过江通道方案。研究成果可为工程设计和决策提供技术依据