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.     

河岸临界崩塌高度的研究

从河床冲刷下切与河岸应力的变化关系出发,分析了陡坡和垂直岸滩的崩塌挫落机制。在河床冲刷下切或者岸滩淘刷的过程中,黏性岸滩会出现纵向裂隙,促使河流岸滩崩塌。通过河岸崩塌体的稳定分析,导出折线河岸初次崩塌及二次崩塌的临界崩塌高度公式。河岸崩塌高度主要取决于河岸边界、水流因子、渗流强度、河道冲淤和岸坡土质等方面的因素。当河岸高度大于临界崩塌高度时,河岸发生崩塌。利用天然河岸崩塌高度的研究成果与模型沙崩塌高度的试验资料检验岸滩崩塌高度公式的合理性,证实了计算结果与实际基本相符。     

游艇波浪侵蚀长港河河岸的计算分析

船行波导致的河岸侵蚀对土地资源和堤防构成威胁。游艇体量小,其危害往往被忽视,然而快速航行的游艇会对河岸产生严重损坏。目前量化评估船行波侵蚀河岸的文献很少。建立船行波引起河岸侵蚀后退的估算模型,并结合鄂州市长港河侵蚀进行实例计算。研究过程由三部分组成:一是现场勘测和调研,包括采集河岸土样,测量河道特征参数,调查长港河船舶类型、船舶技术参数及各类船舶每天航行频次;二是开展室内土工试验,测定土样颗粒级配曲线和临界剪应力,以评估河岸的抗侵蚀性;三是开展河岸侵蚀的数值计算,包括计算游艇船行波要素,采用侧向侵蚀模型计算河岸侵蚀率。计算结果表明,在游艇船行波侵蚀作用下,长港河河岸年平均侵蚀后退54.4 cm,与现场调研结果基本相符。     

Experimental measurements of river-bank erosion caused by boat-generated waves on the gordon river,Tasmania

Erosion of natural river banks by boat-generated waves is an increasingly serious problem on the navigable reaches of many rivers, particularly on the middle and estuarine reaches. An experiment designed to link bank erosion rates with easily measured wave characteristics, conducted on the scenic lower Gordon River in Tasmania, provides information useful for river management. Within a boat-generated wave train a number of characteristics were measured and most showed a high correlation with measured rates of bank retreat. Maximum wave height within the train is the simplest measure and is associated with a major threshold in erosive energy on unconsolidated sandy alluvium at wave heights of 30 to 35 cm. At maximum wave heights above 35 cm all but the most resistant bank sediments erode. Reducing maximum wave heights to < 30 cm by limiting boat speeds, and reducing the frequency of boat passages, caused a dramatic decline in bank erosion along the river.     

河岸淘刷及其对河岸崩塌的影响

通过研究河岸岸脚淘刷机理与岸滩稳定性，把岸脚淘刷与岸滩崩塌有机地连接在一起。在分析岸滩泥沙起动特点和顺直河段剪切力分布的基础上，指出在同样的水流条件下，河岸泥沙比河底泥沙更容易起动和冲刷，顺直河道的河岸冲刷主要发生在岸边的中下部或岸脚的地方。借用水流泥沙运动理论、水流动力理论和水流涡流理论就弯曲河道的淘刷机理进行了分析探讨，指出在主流和副流的共同作用下，弯道进口处的凸岸、弯道及其出口处的凹岸都属于高剪切力区。河岸淘刷严重，其中凹岸岸脚处的剪切力最大、淘刷最严重。河岸的侧向冲刷，特别是岸（堤）脚的冲刷，导致岸滩泥沙块体的滑力（矩）增加。阻滑力（矩）减小，相应的稳定系数减小，当冲刷到一定程度，岸滩崩塌。     

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。     

冲积河流岸滩崩退模式与崩退速率

为研究冲积河流的侧向演变过程并开展模拟预测,采用河道冲刷及河岸稳定性等理论探讨岸滩的崩退模式和崩退速率。根据河岸崩塌机理及崩体塌落到水中后冲刷形式的不同,提出3种岸滩崩退模式,分别为挫崩滑塌冲刷崩退模式、挫崩倒塌冲刷崩退模式和落崩冲刷崩退模式。结合河岸的侧向淘刷、河床的纵向冲刷以及河岸崩塌的临界状态,推导了3种岸滩崩退模式的崩退速率计算公式,并利用长江和黄河的水文、河岸资料进行检验。结果表明:长江和黄河的河岸岸滩崩退速率估算值与实际崩退速率基本相符,所建立的岸滩崩退模式和崩退速率计算公式是合理的。     

Putting down roots: Afforestation and bank cohesion of Icelandic Rivers

Riparian vegetation is widely recognized as a critical component of functioning fluvial systems. Human pressures on woody vegetation including riparian areas have had lasting effects, especially at high latitude. In Iceland, prior to human settlement, native downy birch woodlands covered approximately 15%–40% of the land area compared to 1%–2% today. Afforestation efforts include planting seedlings, protecting native forest remnants, and acquiring land areas as national forests. The planted and protected nature of vegetation along rivers within forests provides a unique opportunity to evaluate the various taxa within riparian zones and the channel stabilizing characteristics of the vegetation used in afforestation. We investigated bank properties, sediment textures, and root characteristics within riparian zones along four rivers in forests in Iceland. Bank sediment textures are dominantly sandy loam overlying coarser textures. Undercut banks are common because of erosion of the less cohesive subsurface layer. Quantitative root data indicate that the woody taxa have greater root densities, rooting depths, and more complex root structures than forbs or graminoids. The native downy birch has the highest root densities, with <1 mm roots most abundant. Modeling of added bank cohesion indicates that willow provides up to six times and birch up to four times more added cohesion to the coarse sediment textures comprising stream banks compared to no vegetation. We conclude that planting and protecting the native birch and willow helps to reduce bank erosion, especially where long-term grazing exclusion can be maintained.     

冲积河道冲刷过程中横向展宽的初步模拟

本文首先描述了冲积河道横向展宽现象，分析了河岸横向冲刷、崩塌的机理及展 宽原因。然后建立细沙河流一维非均匀悬移质泥沙数学模型，同时结合河道横向展宽模式，预测冲积河道冲刷过程中，粘性土组成的河岸的横向展宽过程。此外，还分析了不同来水来沙条件及河岸土体特性对河道横向展宽和河床冲刷的影响，指出了影响冲积河道横向展宽的主要因素。     

受损河岸生态修复技术

我国中小河流的护岸工程只考虑工程的耐久性多采用混凝土护岸的基本模式,忽视河流的生态功能,破坏了河流的各种生态过程,导致河流污染严重,生态作用越来越小。本文提出了基于生物多样化保护的受损河岸生态修复技术及其评价指标。     

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。     

黄河下游游荡性河道双岸整治方案研究

作者针对黄河下游游荡性河槽极为宽浅，河床极不稳定，目前的河道整治宽度过大，不利于洪水期控导河势与河床的集中冲刷，必须双岸同时整治，缩窄河宽；从有利于排洪输沙需求出发，应按洪水较顺直河势，因地制宜，因势利导的原则规划流路。两岸同时整治后，在小浪底水库下泄清水冲刷期，可控制滩地坍塌、河槽展宽，使冲刷向纵深方向发展，有利于使河槽过流能力迅速增大。为水库泥沙多年调节排沙期利用洪水集中排沙入海创造条件，使近期作用与远期整治效果紧密结合。形成窄深、归顺 、稳定、且有窄槽宽滩的输水输沙通道。     

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。     

河道岸滩稳定性综合评价方法

为了评价河岸边界条件和河流动力条件对岸滩稳定性的影响,以河道岸滩崩塌影响因子层次结构模型和权重系数为基础,将定性指标定量化和定量指标标准化,构造了枯水期和洪水期岸滩稳定综合评价函数,提出了考虑多种因素影响的岸滩稳定性综合评价方法。对拟定的3种不同土壤性质、边界条件和水动力条件的河段岸滩稳定性评价结果表明,岸滩稳定性综合评价过程和评价方法是合理的。     

黑龙江省国境界河江岸坍塌原因分析

黑龙江省境内国境界河总长度为2075km，由于界河历年江岸的冲刷、切滩改道、主流变化和岔道发展，造成界河国土流失，情况非常严重，通过对江岸坍塌分析，找出其主要原因为地形因素、气象因素、河床地质因素、人为因素和弯道环流作用因素所造成的，从而为今后国土防护工程提出更加可靠的工程措施。     

The Influence of Logjams on Largemouth Bass (Micropterus Salmoides) Concentrations on the Lower Roanoke River,a Large Sand‐Bed River

This study examines the relation between logjams and largemouth bass (Micropterus salmoides) on the alluvial sand‐bed lower Roanoke River. Disparate data sets from previous bank erosion, fisheries, and large wood studies were used to compare the distribution of largemouth bass with logjam frequency. Logjams are related to the frequency of bank mass wasting increasing from near an upstream dam to the middle reach of the study segment and then decreasing as the river approaches sea level. The highest concentration of largemouth bass and logjams was in the middle reach (110 fish per hour and 21 jams per km). Another measure of largemouth bass distribution, fish biomass density (g h^?1), had a similar trend with logjams and was a better predictor of fish distribution versus logjams (R² = 0.6 and 0.8 and p = 0.08 and 0.02 for fish per hour and g h^?1 versus logjam, respectively). We theorize that the preference for adult bass to congregate near logjams indicates the use of the jams as feeding areas. The results of a principal component analysis indicate that fish biomass concentration is much more related to logjam frequency than channel geometry (width, depth, and bank height), bed grain size, bank erosion, or turbidity. The results of this research support recent studies on in‐channel wood and fisheries: Logjams appear to be important for maintaining, or increasing, both largemouth bass numbers and total biomass of fish in large eastern North American rivers. Persistent logjams, important as habitat, exist where relatively undisturbed river reaches allow for bank erosion inputs of wood and available anchoring locations. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

植物消波消浪研究综述

植物护岸是生物治河措施之一．简要介绍了种植植物消波消浪，保护土壤，避免水土流失，固滩固岸，防浪护堤的作用，以及植物消浪的实验研究．     

中国冲积大河的河型分布与成因

结合遥感影像、野外调查和水沙数据,以冲积大河为研究对象,分析中国大河的河型分布及成因。中国大河的冲积河段以弯曲与辫状河型为主,局部河段为分汊与网状河型。综合考虑河型分布的一般性和特殊性,认为相对输沙率(来沙量与输沙能力之比)、相对河岸侵蚀切应力(近岸水流切应力与河岸临界抗冲切应力之比)和河谷地形控制(如节点和宽度)是决定河型成因的3个最主要的因素。     

Matching the critical portion of the flow duration curve to minimise changes in modelled excess shear.

Hydrologic and hydraulic modeling in the USEPA Stormwater Management Model (SWMM) were used to examine the effectiveness of typical stormwater management practices in reducing the potential for stream erosion. Fifty-year continuous simulations were used to produce flow duration curves and stream erosion rates for a variety of critical shear stress values representative of both cohesive and non-cohesive sediments. An excess shear stress erosion potential index was used to evaluate changes in erosion between undeveloped conditions of a 10 hectare watershed and four variations of post-development stormwater control. Evaluation of flow duration curves showed that when development takes place, the duration of mid- to low-range discharges increase significantly, especially when detention practices are applied. In channels with low entrainment thresholds for bed and bank materials, e.g. sands and highly erodible clays, the significant increase of the duration of mid- to low-range discharges results in erosion potential index values greater than two regardless of the detention practices used. Overcontrol detention resulted in erosion potential index values of less than one, indicating a loss of erosion potential for bed materials such as most gravels (d(s) > 6 mm) and resistant clays that have critical shear stress values greater than four Pa.     

Historical changes in hydrology,geomorphology, and floodplain vegetation of the Willamette River,Oregon

Historical trends in hydrology, geomorphology, and floodplain vegetation provide fundamental contexts for designing future management of large rivers, an area of fluvial research extensively informed by studies of historical channel dynamics. Changes in hydrology, channel structure, floodplain forests, and large wood were documented for the 273‐km main stem of the Willamette River from 1850 to present. Reduced sediment supply and frequency and magnitude of floods have decreased channel mobility and incised channels, leading to fewer gravel bars, islands, and side channels. Human alteration of channel morphology, vegetation, and bank hardening has exacerbated channel simplification caused by reductions in floods, sediment supply, and inputs of wood. A substantial number of floodplain channels reoccupied remnants of previous active channels inundated during recent floods, demonstrating functional but often forgotten role of historical geomorphic structure in modern floodplains and flood processes. In most reaches, area of floodplain forests in 1990 was only 10% to 25% of the area of forests in 1850. Abundance of wood in the wetted channel was generally greater in reaches with higher abundances of floodplain forests. Future trajectories will be influenced by legacies of the historical river but increasingly will reflect evolution of a new river shaped by human development, changing climate, and emerging hydrogeomorphic and vegetation processes. Understanding historical characteristics and anticipating future rates and patterns of ecosystem change provide fundamental contexts for restoring biophysical processes and structure in a large floodplain river.