河道改造对弯曲河段的水力影响模拟研究

以浏阳河朝正垸急弯河段为例 ,采用MIKE21水动力平面二维水流 -泥沙模型先进行率定 ,综合考虑长沙枢纽运行后湘江水位抬升对浏阳河下游的顶托与浏阳河不同频率洪水的叠加作用 ,采用该模型对上游直线段、弯段、下游直线段的水文变化、流速变化及冲淤情势进行多工况模拟.结果表明 :对于弯曲河道尽管改造拓宽弯曲段 ,在凸岸水流流速增大 ,可能存在冲刷 ,凹岸局部会产生淤积 ,在近邻弯曲下游段凹岸局部还会产生水位壅高.结果可指导本河段防洪规划设计 ,对类似工程也具有借鉴意义.     

三峡工程运用后荆江不同河型河道演变分析

利用三峡工程运用以来实测水沙和地形资料,分析荆江河道分汊、弯曲、顺直等河型调整的规律,并对其变化原因进行探讨.三峡工程运用以后,分汊型河道变化主要表现为凸岸支汊发展;弯曲型河道演变特点为凹岸深槽淤积,凸岸边滩冲刷,断面形态由偏“V”单槽向“W”型双槽转化;顺直型河道变化特点是两岸交错边滩冲刷,深槽淤积,河道断面向宽平方向发展,深泓年内变化频繁.从水流能量的角度,探讨了荆江不同河型河道调整的原因.由于三峡工程运用后荆江特别是下荆江河段水流输沙所需要的弯曲度明显较建库前小,因此弯曲河段凸岸边滩冲刷以减小水流弯曲度,是响应上游水沙变化的重要方式.     

二维水沙数学模型在复杂河道治理中的应用

本文结合北江下游具体河段，针对河段弯曲及河道分汊的特性，考虑岸滩崩塌展宽进行边界处理，建立了二维平原型弯曲河道水沙数学模型，正确地计算模拟了河段中大江心洲和丁坝的绕流阻水现象，准确地处理了滩地漫水、鱼塘及挖沙坑蓄水及其对河道演化趋势的影响，为河道的科学治理提供了依据。在计算方法上，本文采用了二维有限元的方法，可进行网格自动剖分和局部加密计算模拟。     

长江宜都段水流运动特性及河床冲淤演变分析

长江宜都河段为一典型低水弯曲分汊河段。利用2005年实测河道地形与水流资料，在5种不同入口流量条件下，计算模拟了河段内的水流。以此为实例研究了弯曲分汊河道水流的运动特性，包括河道流速分布的沿程变化、水面纵比降的变化和水流动力轴线年内的摆动等，并探讨了弯曲分汊河段水流运动与河床冲淤演变之间的关系。研究成果为航运、防洪、取水等部门提供了基本资料。     

低成本河道绿化带养护模式的探讨

河道绿化带是实现"水清"、"岸绿"、"景美"的清水河道建设的重要组成部分,但河道绿化带建设完成后,往往由于资金不足、管理制度不健全等原因,使得河道绿化带常常面临养护不足的状态.根据多年的实际工作经验,从河道绿化带的管理措施与施工措施的角度,总结出一套行之有效的分段分区域低成本河道绿化带养护模式,并简要介绍嘉兴市水利局在实行这种养护模式下所取得的经济效益和社会效益.     

三峡库区巫山新县城库岸塌岸的防护

水库蓄水及运行过程中，岸坡所处的地质环境将发生显著改变，河道发生壅水，水位抬高，水深加大，水面变宽，浪蚀作用加剧，破坏了原来河谷岸坡的自然平衡条件，从而引起岸坡稳定性的变化并产生库岸再造。巫山新县城一带库岸冲沟发育，岸线弯曲。地质条件复杂。三峡水库蓄水后再造强烈及不稳定库岸长达5.38km，根据不同的岩层，岩性特征和库岸再造类型及防护对象综合确定防护措施。     

弯曲河道对水流流态影响数值模拟

蜿蜒型河流是冲积平原常见的河型之一。针对具体河流的特定自然条件,需要对不同河道形态下的河道特性做出预测,以便选择和调整相应方案。采用集水动力模块、泥沙输运模块、污染物运移模块和水质预测模块为一体的环境流体动力学模型,利用计算机进行数值模拟,对京郊某弯曲河道3种河道形态在50年一遇洪水过程下进行数值模拟,在此基础上对3种工况下河道的水流特性进行分析,发现工况一弯道处凸岸流速先增加后减小,凹岸流速先减小后增大,凹岸水位明显高于凸岸水位;工况二两岸流速分布较为对称,叉道起到分洪滞洪作用;工况三两岸水流摆动现象不如工况一明显,衬砌工程量较小,并提出相应河道保护措施。     

河道凹岸冲刷防护研究

在天然弯曲河道中往往存在着冲刷现象。通过物理模拟河道的方法得出,在弯道处由于凹岸漩涡、横向流速以及弯道环流的作用形成了凹岸冲刷、凸岸淤积的现象。为了保护岸基及路基安全,提出了相应的防护措施。     

城镇河流保护性治理的思路与实践——松潘县岷江川主寺河段生态护岸工程规划设计

近年来,城市河流滨水景观的建设愈来愈被人们所重视,在河流综合治理规划设计中,如何在保证河道基本功能的前提下,体现河道的自然本性,再现区域的文化特性,使其达到"水宁、河动、岸绿、景美"的理想目标,是规划设计师目前面临的重要挑战。以松潘县岷江川主寺河段生态护岸工程规划设计为例,通过对高原地区河流水文特征、地质特点、植被分布及特色文化等背景资料的研究分析,探讨了高原河道岸坡稳定、河滨生态修复与区域特色文化再现等规划设计方法及对策,以供类似河道的综合治理参考。     

河北承德县滦河生态治理研究

以人水和谐、生态健康作为工程总体定位,运用生态水工学理念对河北承德县滦河进行生态治理.分析了滦河区域的现状,详细介绍了沿河建筑物的布置,河道断面、河道防洪、岸坡防护的设计.滦河生态治理实践将为北方城市河流治理提供借鉴.     

荆江河段崩岸机理及多尺度模拟方法

三峡工程运用后,进入荆江河段的水沙条件大幅度改变,导致近期崩岸频繁发生,影响局部河段的河势稳定及河道防洪安全。荆江段河岸组成一般为上层黏性土、下层沙土的二元结构,在近岸水流冲刷及河道水位涨落过程中受多种因素作用而发生崩塌。以往崩岸模拟考虑因素少,且相关参数难以量化确定。将河流动力学与土力学结合,提出了荆江段河岸土体物理特性与抗剪、抗冲及抗拉强度三大力学特性的量化指标,建立了上、下荆江二元结构河岸稳定性的计算方法,揭示了坡脚冲刷、潜水位变化等因素对岸坡稳定性的影响;提出了河岸崩退过程的多尺度模拟方法,将崩岸力学模型与水沙数学模型耦合,不仅能模拟河道内水沙输移及床面冲淤过程,而且还能模拟不同二元结构河岸的崩退过程。将建立的模型应用于荆江河段典型断面、长河段及局部河段的崩岸过程模拟,计算结果与实测值总体符合较好。提出的多尺度模拟方法为荆江崩岸预测提供了理论与技术基础。     

船闸布置在弯道凹凸岸附近时通航条件分析

统计了枢纽中通航建筑物的布置现状,阐述了枢纽中船闸布置的有关规定,重点对通航建筑物布置在凹岸或凸岸附近时的边界、水流和航行条件作综合分析.分析表明:船闸布置在凹岸时的有利条件多于凸岸;当船闸引航道口门区处在弯道段时,会受斜向水流与弯道水流的共同作用,增加船舶(队)进出口门的难度;当连接段处在弯道段时,船舶(队)受到弯道水流与航线夹角和船队轴线与航线夹角的双重作用,船舶操舵较顺直河段困难.同时需研究船舶(队)回转半径与操舵角的关系.     

冲积河流崩岸机理、数值模拟及预警技术研究进展

冲积河流崩岸不仅影响河势稳定,而且威胁两岸堤防等重要涉水工程安全。近年来由于上游来水来沙变化及水库运用等影响,长江中下游及黄河下游河段河床冲刷,崩岸现象突出,增大了河道防洪压力。从崩岸机理、数值模拟及监测预警技术3个方面总结了冲积河流崩岸的研究进展,指出了仍待解决的几个关键问题。在崩岸机理方面,阐明了崩岸发生的力学条件及影响因素,但需深化研究各因素之间的相互作用。崩岸数值模拟方法的快速发展为崩岸预测提供了有效的技术手段,但需更为全面地考虑崩岸机理,并有效刻画河岸边界条件的沿程变化。在监测预警技术方面,通常以局部岸段的地形及水沙条件监测为主,崩岸预警等级划分指标及方法多以经验法为主,需建立统一的、完善的评估体系。     

Determination of bank erodibility for natural and anthropogenic bank materials using a model of lateral migration and observed erosion along the Willamette River,Oregon, USA

Many large rivers flow through a variety of geologic materials. Within the span of several kilometres, bends may alternately flow against recently reworked sediments, older, more indurated sediments or highly resistant materials. As sediment size, cementation, and other properties strongly influence the erodibility of river banks, erosion rates and channel planform are likely to vary significantly along the length of large rivers. In order to assess the role of bank materials on bank erosion rates, we develop a method for detecting relative differences in erodibility between bank materials along large floodplains. By coupling historic patterns of channel change with a simple model of bank erodibility we are able to track relative changes in bank erodibility among time intervals and bank materials. We apply our analysis to the upper Willamette River, in northwestern Oregon for three time periods: 1850–1895, 1895–1932 and 1972–1995 and compute relative differences in bank erodibility for Holocene alluvium, partially cemented Pleistocene gravels, and revetments constructed in the 20th century. Although the Willamette is fundamentally an anastomosing river, we apply the model to single‐thread portions of the channel that evolved through lateral migration. Our simple model of bank erodibility reveals that for all three‐time periods, banks composed of Holocene alluvium are at least 2–5 times more erodible than banks composed of Pleistocene gravels. Revetment installed in the 20th century is highly resistant to erosion and is at least 10 times less erodible than Pleistocene gravels. Copyright © 2006 John Wiley & Sons, Ltd.     

Quantifying the effect of riparian forest versus agricultural vegetation on river meander migration rates,central Sacramento River,California, USA

Riparian forest vegetation is widely believed to protect riverbanks from erosion, but few studies have quantified the effect of riparian vegetation removal on rates of river channel migration. Measured historical changes in a river channel centreline, combined with mapped changes in floodplain vegetation, provide an opportunity to test how riparian vegetation cover affects the erodibility of riverbanks. We analysed meander migration patterns from 1896 to 1997 for the central reach of the Sacramento River between Red Bluff and Colusa, using channel planform and vegetation cover data compiled from maps and aerial photography. We used a numerical model of meander migration to back‐calculate local values for bank erodibility (i.e. the susceptibility of bank materials to erosion via lateral channel migration, normalized for variations in near‐bank flow velocities due to channel curvature). A comparison of migration rates for approximately 50 years before and after the construction of Shasta dam suggests that bank migration rates and erodibility increased roughly 50%, despite significant flow regulation, as riparian floodplains were progressively converted to agriculture. A comparison of migration rates and bank erodibilities between 1949 and 1997, for reaches bordered by riparian forest versus agriculture, shows that agricultural floodplains are 80 to 150% more erodible than riparian forest floodplains. An improved understanding of the effect of floodplain vegetation on river channel migration will aid efforts to predict future patterns of meander migration for different river management and restoration scenarios. Copyright © 2004 John Wiley & Sons, Ltd.     

四川省茂县城区岷江河道治理段岸墙形式的比选分析

针对山区河道纵坡大、水流急、推移质较多的特点,以及重建两岸生态环境的要求,堤防断面形式综合分析比较了复式断面、扶壁式岸墙、格宾石笼重力式岸墙、悬臂式岸墙等几种形式,并最后予以选定。     

新水沙情势下长江中下游干流岸线保护研究——以扬中市2017年江堤崩岸治理为例

近十几年来随着水沙情势的显著变化,长江中下游干流崩岸险情频发,加强崩岸治理和岸线保护是沿江防洪安全和经济发展的重要保障。在梳理三峡水库蓄水以来坝下游水沙情势变化、河道冲刷和崩岸情况的基础上,以2017年11月江苏省扬中市江堤崩岸为例,分析崩岸段近期河道演变特征和地勘资料,认为河槽持续冲刷下切贴岸及二元土质结构河岸是崩塌的主要原因,而2016~2017年连续大洪水加了快崩岸的发生。崩岸发生后立即实施了窝塘抢护并修筑临时挡水子堤,随后实施完成干堤复建和窝塘上下游岸线守护工程,实现了2018年成功度汛。此次崩岸的特点和原因在长江中下游较为典型,对崩岸治理与岸线保护具有启示作用。     

黄河源草甸型弯曲河流的悬臂式崩岸机制

弯曲河流的滨河草甸对抑制河岸崩塌和维持河湾蜿蜒具有重要作用。2011—2014年,在黄河源区兰木错曲的弯曲河段对河岸植被根系、崩塌块几何尺寸、根土复合体物理和力学特性等开展野外调查,并通过原位拉拔试验测定河岸崩塌面植被根系抗拉强度,进而分析草甸型弯曲河道的崩岸机制。草甸型弯曲河流的滨河植被根系网络具有较强缠绕和固结土体作用,河岸根系的力学特性是抑制凹岸崩岸的关键因子。近岸水流淘刷作用集中于根系作用范围以下的砂卵石层,当砂卵石层被淘刷至上部悬空,在自重作用下达到临界状况,河岸沿纵深方向出现贯穿性裂缝,最后崩塌块垮塌贴住河岸。崩块的破坏形式以悬臂式张拉破坏为主。崩塌块的植被根系长度与崩塌块厚度呈明显对数函数关系,其体积也随根系长度增大而增加。分析草甸型弯曲河流的新崩岸模式,建立了近岸根土复合体崩岸的临界力矩平衡方程,并简化得到崩塌块的临界宽度表达式。崩塌块体的临界宽度是崩塌块根系长度和根系产生的抗拉强度增量的函数,临界宽度的计算值与实测值较为符合。     

若尔盖高原泥炭型弯曲河道崩岸过程模拟

崩岸在河床演变和河型转化中发挥重要作用,促使河岸横向移动和河道蜿蜒。2011—2016年黄河源若尔盖高原的弯曲河流野外调查表明,泥炭型弯曲河流的崩岸是河岸上部泥炭层在自重作用下发生的悬臂式崩岸。针对泥炭型河岸的悬臂式崩岸,采用BSTEM模型分析其岸坡稳定性,并模拟河岸侵蚀和崩塌过程。泥炭层的含水率是河岸稳定的关键因子,泥炭层含水率的增加,既增强河岸崩塌的驱动力,也减弱抵抗河岸崩塌的抗剪力,对河岸稳定不利。河岸二元物质组成的厚度对河岸稳定性有较大影响,其泥炭层厚度的增加,可提高河岸稳定性,但是河岸下部粉沙层厚度的增加,则会降低河岸的稳定性。     

Two-Dimensional Composite Mathematical Alluvial Model for the Braided Reach in the Lower Yellow River

Abstract

The fluvial processes are considerably complicated in the braided reach of the Lower Yellow River, and the lateral or transverse channel deformation process is especially pronounced. The state-of-the-art of simulation techniques for the channel deformation in the Lower Yellow River was analyzed in this paper, and such a conclusion was drawn that existing mathematical alluvial models only can simulate the longitudinal channel deformation and cannot simulate such the lateral deformation as lateral erosion and failure of bank. Then a new two-dimensional (2D) composite model was developed herein, consisting of a 2D flow and sediment transport submodel and a riverbank-erosion submodel. This model not only can simulate the longitudinal and lateral channel deformations, but also can be used to simulate the fluvial processes of natural alluvial rivers with complex bed morphology. Through using the proposed composite model, the flood routing and channel deformation processes during the August 1982 flood were simulated. The maximum stage along the reach and the discharge hydrograph at the outlet so obtained were in good agreement with the observed data. Simulated results of the channel deformation processes showed that during the flood season, the main channel scours and the flood plain deposits; during the dry season, the main channel deposits and banks of the floodplain retreat due to lateral erosion by the flow and failure under gravity. Such results accord with the annual varying law of bed scouring and deposition in the braided reach.