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1.
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. 相似文献
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通过连续4年对黄河内蒙古段河道28条大断面进行测量,提取测次间河岸蚀淤量,分析了2011-2014年间汛期和非汛期黄河内蒙古段河岸蚀退与淤进速率频率分布特征,以及河岸蚀退和淤进与水沙因子的关系。结果显示侵蚀性岸段占64%,平均蚀退速率0.147m/d;淤积性岸段占31%,平均淤进速率0.335m/d。不论蚀退还是淤进的速率频率分布都表现为明显的正偏,其对数值都呈现为正态分布。河岸蚀淤量统计结果显示河槽缩窄趋势近期已减缓。河岸蚀退速率与淤进速率都与流量成正相关,分析揭示河岸蚀退速率及淤进速率与水沙因子的关系主要是河岸蚀淤响应洪枯期流量变化而调整的结果。 相似文献
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DAI Wen-hong TANG Hong-wu State Key Laboratory of Hydrology-Water Resources Hydraulic Engineering College of Water Conservancy Hydropower Engineering Hohai University Nanjing China 《水动力学研究与进展(B辑)》2010,22(2):214-220
This article presents a mathematical model of the plane evolution of alluvial meandering streams,through downstream migration and lateral expansion of meander loops.Under the conditions prevailing in natural streams,the channel centerlines follow sine-generated curves,with an assumed steady-state turbulent and subcritical flow,of large width-to-depth ratio(≥ 15,for example) and small Froude number(Fr ).The plane deformation of the channel is caused by the action on the banks of the convective vertically-averaged meandering flow.The growth(migration and expansion) of meander loops is attributed to the regime-trend.The computational results of the model show that the obtained migration and expansion patterns of the meander loops are in good agreement with those of observations and measurements in similar meandering streams. 相似文献
4.
河岸淘刷及其对河岸崩塌的影响 总被引：9，自引：0，他引：9
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。 相似文献
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We measured patterns of river channel migration and cutoff between 1904 and 1997 on a 160 km meandering alluvial reach of the Sacramento River by intersecting a sequential set of river channel centrelines mapped from a field survey and aerial photography. We identified approximate dates and locations of cutoffs and quantified cutoff dimensions. Twenty‐seven chute and 11 partial cutoffs occurred over this 93‐year time interval, with an average of one cutoff approximately every 2.5 years or 0.0029 cutoffs per kilometre per year. The average rate of lateral channel change was over the study period was 5.5 ± 0.6 m year?1 (approximately 0.02 channel widths per year) due to progressive migration and cutoff combined. An average of 5% of the total channel length moved laterally via chute cutoff at a rate of 22.1 ± 3.3 m year?1 versus 94% of channel length that moved via progressive migration at a rate of 4.7 ± 0.5 m year?1. The remaining 1% of channel length migrated via partial cutoff at a rate of 13.0 ± 2.8 m year?1. Although channel cutoff was less predominant mode of channel change than progressive migration in terms of channel length, an average of 20% of the total floodplain area change between successive centrelines was attributable to cutoffs. Peak cutoff frequency was concentrated temporally between 1964 and 1987 and was also spatially clustered in specific active sub‐reaches along the valley axis over the entire study period. We hypothesize that the probability of channel cutoff is a function of both channel geometry and discharge. Bends that experienced chute cutoff displayed an average sinuosity of 1.97 ± 0.1, an average radius of curvature of 2.1 ± 0.2 channel widths and an average entrance angle of 111 ± 7°, as opposed to average values for bends migrating progressively of 1.31 ± 0.01, 2.8 ± 0.1 and 66 ± 1°, respectively. The sinuosity of Sacramento River bends experiencing chute cutoff appears to have been consistently declining from 2.25 ± 0.35 channel widths in 1904 to 1.54 ± 0.23 channel widths in 1987. We hypothesize that this trend may be due in part to the influence of land‐use changes, such as the conversion of riparian forest to agriculture, on the ‘erodibility’ of bank and floodplain materials. For the post‐dam flow regime (1937 on), cutoff frequency was significantly correlated with an estimate of cumulative overbank flow. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
7.
In contrast to the generally accepted stabilizing effects of riparian vegetation, the surcharge of trees on riverbanks has been widely implicated as a source of bank instability. Fieldwork conducted along the Latrobe River in Victoria, Australia shows that the bank‐destabilizing effects of surcharge, due to silver wattle (Acacia dealbata), are minimal. Field observations indicate that it is unlikely that the weight of silver wattles growing on an otherwise stable bank section will directly cause mass failure. Observations of deep‐seated failures and silver wattle stands on the Latrobe River indicate that where average‐sized slump‐blocks support an average number of average‐sized silver wattles, the trees represent only 4.1% of the total saturated slump mass. Infinite slope stability analysis indicates a threshold of around 48° where banks become prone to shallow‐planar slide failures as they steepen. Where bank sections are inherently unstable and prone to shallow‐planar slide failure, the additional weight of the trees may contribute to overall instability. However, manipulation of other stability parameters within reasonable constraints negates the effect of surcharge so it is not possible to demonstrate conclusively a destabilizing influence of silver wattles. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
8.
为了解滨河植被对河湾横向迁移的作用,以及河湾迁移对滨河植被群落分布的影响,对黄河源区兰木错曲弯曲河段崩塌块、凹岸植被生物量和凸岸植被多样性进行现场调查统计,给出了河湾迁移速率的估算方法。结果表明:其迁移速率与凹岸植被生物量呈指数关系;河湾凸岸边滩的泥沙沉积在不同重现期洪水作用下,形成不同的植被条带,对应于5种典型的植被群落;河湾的横向迁移对滨河植被生态系统具有调节作用,形成一种牧草先增多后减少再增多的草场更新机制,原生演替不断循环进行,以维持草场的长期可持续放牧功能。 相似文献
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Since European settlement in the early 1800s, 66 artificial meander cut-offs have been created in the lower Latrobe River, Victoria. Contemporary waterway management practices include the reinstatement of a selection of these cut-off meanders to slow water flows and reduce river bed and bank instability. Infill sediments were collected from a range of depths from one of these meanders prior to its reinstatement to estimate the potential for remobilization of any sediment pollutants into the waterway. The characteristics of collected sediments were described and sediments were analysed for a range of pollutants including heavy metals, total petroleum hydrocarbons, monoaromatic hydrocarbons, organochlorine pesticides, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). Metal concentrations in the fine (<63 μm) sediment fraction increased with increasing sample depth; however, only increases in cadmium, chromium and mercury concentrations were statistically significant. Statistically significant increases in mercury concentrations with depth were also present in the entire sediment fraction. With the exception of mercury, concentrations of all metals assessed in meander sediments were similar to those reported as being at background concentrations. Mercury concentrations, although elevated, were below concentrations reported to adversely effect riverine biota. Concentrations of organochlorine pesticides, polychlorinated biphenyls, total petroleum hydrocarbons, monoaromatic hydrocarbons and polycyclic aromatic hydrocarbons were all below detection limits in the entire sediment fraction. As a consequence, reinstatement of the meander as part of a waterway management programme is unlikely to release significant quantities of sediment-partitioned pollutants into the mainstream waterway. 相似文献
10.
In this study, we evaluate the use of riparian tree‐geometry and bank‐characteristic data in developing riverbank stability forecasts at four study sites along a mercury‐contaminated reach of the South River, Virginia. Our forecast data set includes measurements of tree diameter, lean angle and percent root‐plate undercut, coupled with bank characteristics included in the Pfankuch Index. Stepwise comparisons and statistical analyses of our tree‐geometry data reveal that lean angle and percent root‐plate undercut are effective measures for discriminating between riparian tree populations at eroding and stable banks, with the strongest discriminant power from the percent root‐plate undercut. Our stability forecasts, using both tree and bank characteristics, agree with long‐term observations, underscoring the value of rarely used tree‐geometry data in such evaluations. The application of these results is important in long study reaches where forecasts of erosion potential from contaminated banks are required to develop mitigation strategies, but direct measurements of bank stability are not feasible. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
11.
H. Nakagawa H. Zhang Y. Baba K. Kawaike H. Teraguchi 《Journal of Flood Risk Management》2013,6(4):345-359
Severe bank erosion is one of the most challenging problems in the management of large rivers in Bangladesh. This paper describes the detailed flow patterns around typical bank‐protection works on the Brahmaputra/Jamuna River as well as their morphological implications. Based on field surveys at several locations along this large alluvial river that are highly susceptible to erosion, attempts are made to clarify the flow fields and mechanisms of bank erosion. The performance of existing measures such as revetments and spur dykes are evaluated, and possible solutions for further enhancements are proposed. It is found that existing conventional works are generally huge in both size and cost, potentially exerting great disturbances on the river's dynamism and ecosystem. That said, the Bandal – a historied and indigenous structure – is cost‐effective and environmentally friendly. This study suggests the recurrent use of Bandal‐like structures for channel stabilisation and flood management of the braided Brahmaputra/Jamuna River. 相似文献
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M. L. Keefer G. A. Taylor D. F. Garletts C. K. Helms G. A. Gauthier T. M. Pierce C. C. Caudill 《河流研究与利用》2013,29(4):483-492
Many high‐head dams in Oregon's Willamette River basin were constructed without fish passage facilities for downstream migrants. Instead, fish pass dams via hydroelectric turbines, surface spillways or deep‐water regulating outlets. The availability of these routes varies seasonally with dam operations and reservoir depth, which can fluctuate by tens of meters. To assess how dam and reservoir operations affect fish movement timing and survival, we used rotary screw traps below three Willamette basin dams and at two riverine sites above reservoirs. Traps were operated 2950 days over 8 years, and >195 000 fish were collected. Samples above reservoirs were primarily native salmonids (Oncorhynchus spp.), daces (Rhinichthys spp.) and sculpins (Cottus spp.), while those below dams were often dominated by non‐native Centrarchidae. Capture rates at riverine sites were highest from late winter to early summer, coincident with juvenile Chinook salmon emigration. Conversely, collection below dams was largely restricted to late fall and winter when reservoirs were drawn down to annual lows and discharge was high. We hypothesize that winter operations facilitated fish access to dam turbines and regulating outlets, whereas spring–summer operations entrapped fish in reservoirs and restricted volitional downstream passage. Total fish mortality was ≤2% at riverine sites and was 36–69% below dams. Estimates were highest for non‐native species and juvenile Chinook salmon. Fatal injuries were consistent with traumas related to pressure, shear and contact and there were size‐related and morphology‐related risk differences. Mitigation opportunities include fish bypass system development, retrofits for existing routes and seasonally appropriate reservoir draw down to allow fish passage. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
14.
周素芳 《水利水电科技进展》2004,24(3):36-38
介绍钱塘江北岸明清老海塘概况和工程自然条件 .提出运用板桩防冲墙技术解决塘脚防冲技术难题 ,并研制出可以遥控操作的多功能打桩机 .该技术在海宁明清海塘塘脚防冲工程中应用9 9km ,节省投资 5 2 0 0万元 ,并已在类似工程中推广应用 . 相似文献
15.
为探讨植被根系对河岸冲刷过程的影响作用,取新疆塔里木河岸坡原状土,选取当地优势灌木红柳、乔木胡杨根系,通过室内水槽试验,分析不同植被根系对河岸冲刷起防护作用的贡献率。结果表明:①无根系河岸水下淘刷形式主要为圆弧状,下部抗冲能力差;有根系河岸的淘刷形式主要为三角形,下部抗冲能力强,上部悬空层的稳定性好。②根系的网络固土作用使河岸的抗冲能力提高12%~42%;相同植被根系河岸,根系的布置方式对河岸的固土能力有显著差异,V型根系的固土作用优于竖直型;不同植被根系河岸,红柳根系的固土能力大于胡杨根系,平均提高27%。③根土胶结崩塌体堆积形式主要为三角形,且堆积体的占比大于无根系崩塌体;红柳根系胶结崩塌体的分解速率最慢;根系牵拉系数可作为反应根系对河床防护作用贡献的参数,实际计算中可按1.15~2.52进行估算。研究结果可为塔里木河河道岸坡防护提供理论参考。 相似文献
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为了给靠近黄河岸坡的基础能源工厂的安全建设与运行管理提供技术支持,针对黄河岸坡厚层黄土及下伏泥岩的典型岩性组合特征,通过选取黄河中游某电厂典型近厂区岸坡断面,模拟集中暴雨、河流洪水、岸坡人为扰动等不良条件,利用Morgenstern-Prince边坡极限平衡理论与基于流固耦合理论的有限元计算方法,分析了岸坡的稳定性和坡面侵蚀规律。结果表明:岸坡长期遭遇降雨、河流洪水侵蚀、河道演变及人工扰动等的循环作用,易引起侧蚀、临空面变陡失稳;随着降雨及洪水等不利因素的增多,近厂区岸坡坡面水平变形影响范围将扩大;以水平变形量0.1 m为非稳定区判别标准,计算断面受降雨及洪水影响较大,其深度剥蚀发生在坡面,暴雨及洪水期水平剥蚀发生速率为4.0 m/d;以安全系数1.30为评判标准,计算断面受降雨及洪水影响相对较大,洪水期断面趋于失稳状态;河道演变造成的岸坡坡角改变对计算断面的影响较大,失稳的临界坡角为40°。 相似文献
17.
Michael Mansfield;John Shelley;Christopher Haring; 《河流研究与利用》2024,40(8):1595-1601
The purpose of this research is to analyze the headcut propagation and downstream sediment yield as a result of a low-head dam failure. While frameworks have been presented elsewhere to track headcut propagation from a dam failure/removal, little research has been conducted to calculate the downstream sediment yield of the resulting headcut. The sediment yield is of particular interest when a reservoir is located downstream of the headcut. This paper estimates the increased sediment yield to Tuttle Creek Lake as a result of a low-head dam failure on the Big Blue River. From 2018 to 2022, the headcut contributed an estimated 859,000 m3 of sediment to Tuttle Creek Lake. Erosion is unlikely to continue due to the presence of natural grade control provided by boulder riffles and bedrock. 相似文献
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This paper examines ecosystem restoration practices that focus on water temperature reductions in the upper mainstem Willamette River, Oregon, for the benefit of endangered salmonids and other native cold‐water species. The analysis integrates hydrologic, natural science and economic models to determine the cost‐effectiveness of alternative water temperature reduction strategies. A temperature model is used to simulate the effects of combinations of upstream riparian shading and flow augmentations on downstream water temperatures. Costs associated with these strategies are estimated and consist of the opportunity costs of lost agricultural production and recreation opportunities due to flow releases from an up‐stream reservoir. Temperature reductions from another strategy, hyporheic flow enhancement, are also examined. Restoration strategies associated with enhanced hyporheic cooling consist of removal/reconnection of current obstacles to the creation of dynamic river channel complexity. The observed reduction of summer water temperatures associated with enhanced channel complexity indicates that restoring hyporheic flow processes is more likely to achieve cost‐effective temperature reductions and meet the total maximum daily load (TMDL) target than conventional approaches that rely on increased riparian shading or/and combinations of flow augmentation. Although the costs associated with the hyporheic flow enhancement approach are substantial, the effects of such a long‐term ecological improvement of the floodplain are expected to assist the recovery of salmonid populations and provide ancillary benefits to society. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
19.
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。 相似文献
20.
近60年渭河下游自然裁弯成因分析 总被引：1，自引：0，他引：1
渭河下游是典型的弯曲型河道,过去60年频繁地发生自然裁弯,其触发原因、形成过程和演变规律缺少深入的研究。渭河下游的裁弯是河湾横向演变到一定阶段后在汛期洪水冲刷作用下发生临界突变,直接影响河道平面形态、上下游河床冲淤和局部河段的防洪安全。基于原型观测、水沙数据(1960-2013)和遥感影像(1990-2015),分析了渭河下游裁弯事件的水沙条件、影响因素和裁弯时空演变过程及其原因。渭河下游发生的18次裁弯的主要原因是受三门峡建库后渭河下游边界条件的改变,包括潼关侵蚀基准面淤积抬高,凸岸边滩及内侧平原缺少粘性成分,抗冲性差,同时也受渭河下游来水来沙条件的变化及其高含沙洪水的影响。 相似文献