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1.
Jonathan D. Phillips 《河流研究与利用》2013,29(2):149-160
Oxbow lakes, sloughs and other floodplain depressions associated with former channel positions are critical elements of floodplain hydrology, geomorphology and ecology. They comprise key elements of wetland and aquatic habitats and have important influence on the storage and routing of floodwaters. The hydrological connectivity between active river channels and floodplain depressions varies considerably in a qualitative sense, even within a single fluvial system. Several oxbows, sloughs and paleochannels were examined on the lower Sabine River, Texas/Louisiana, during a period of high but sub‐bankfull flow as well as at lower flows. Six different types of surface water connectivity with the main, active channel were identified: (i) flow through—a portion of the river flow regularly passes through the feature and returns to the main channel; (ii) flood channel—there is no hydraulic connection at normal flows, but at high flows the channels convey discharge, at least part of which returns to the main channel; (iii) fill and spill—the features fill to a threshold level at high flows and then overflow (mainly via ephemeral channels) into flood basins; (iv) fill and drain—the features fill at high river discharges but do not (except in large floods) overflow because as river discharge declines, water drains back to the river; (v) tributary occupied—tributaries draining to the abandoned channel continue to occupy it, flowing through it to the active channel; and (vi) disconnected—no flow is exchanged except during large floods. The age or stage of infilling and the relative elevation of abandoned channels are important first‐order controls of hydrological connectivity, but the lateral distance from the active channel is poorly related. Other critical controls are whether the cutoff section receives tributary input and whether a tie channel forms. The alluvial valley geomorphic context—specifically the presence of a meander belt ridge and flood basins—is also critical. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
2.
河道地形的多样性决定了河流栖息地物理生境的多样性,对水生生物物种丰度、多样性程度有重要影响。三峡水库蓄水后,下游河道河床发生显著冲淤调整,河道地形多样性也随之变化。使用2003、2018年长江三峡水库下游宜昌-城陵矶河段固定断面实测地形数据,基于河道纵向多样性、横向多样性、水深方向生境完整性指标,构建多样性综合指标,分析三峡水库蓄水后不同河型、不同河段栖息地地形多样性变化差异性及成因。结果表明：不同河型地形多样性不同,不同河段地形多样性也相应的存在差异,弯曲河型峰度系数低,低滩占比大,多样性高于其他河型,由弯曲河型为主构成的下荆江河段多样性也最高。水库蓄水后,下游河段地形多样性总体降低,但不同河型、不同河段地形多样性变化不同：顺直河型平滩水位、枯水位下峰度系数均增加,分汊河型枯水位峰度系数整体增加,而弯曲河型平滩水位下峰度系数减小,以弯曲河型为主的下荆江河段峰度系数减小。蓄水后不同河型冲淤调整的差异性是导致多样性变化趋势不同的内在机制。研究成果可为认识人类活动影响下河流栖息地变化提供支持。 相似文献
3.
This paper presents the results of an investigation into environmental controls on vegetation dynamics on gravel bars. Such environments are a hotspot of threatened plant biodiversity and the dynamics of their vegetation reflect a range of processes that should be indicative of the integrity of the wider floodplain ecosystem. The study was undertaken on a 2 ha mid‐channel gravel bar complex that evolved over two decades, in response to several high magnitude flood events (including two with a return period in excess of 25 years), on a ‘wandering’ reach of the River Tummel, Scotland. Over 180 plant species, including a number of national or regional scarcities, had colonized. The fluvial chronology of the site was documented via sequential sets of aerial photography that revealed a number of discrete surfaces created by individual floods. Environmental heterogeneity, both within and between fluvial units, was investigated by field sampling of vegetation and abiotic variables at 66 locations. The fluvial surfaces were assigned to five habitat classes that ranged in age from two to approximately 20 years, from fine gravel to cobbles, and maintained an elevation range of up to 2.5 metres above low flow river levels. Multivariate analysis highlighted the relative importance of elevation, grain size, moisture content and infiltration and trapping of fines in controlling plant species composition. After standardizing sampling effort the habitat mosaic was found to support on average 1.36 times more species than an equivalent sample of any one habitat. In terms of biodiversity and river management, our results emphasize the importance of sustaining fluvial processes that preserve the habitat mosaic in order to conserve the characteristic biota of gravel bar complexes and river channel islands. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
4.
Dead wood pieces, especially when organized in jams, play an important geomorphic role in streams because of the effects on flow hydraulics, pool formation and sediments storage. The increase in stream morphological diversity and complexity also exerts an important ecological role. This work reports on geomorphic role of large wood (LW) pieces and jams in a third‐order mountain stream located in the Southern Tierra del Fuego (Argentina), and draining an old‐growth Nothofagus‐forested basin not influenced by the beavers damming activity. Even if the in‐stream number of wood pieces (length >1 m; diameter >0.1 m) is comparable to that observed in other climatic areas, the slow growth of the Nothofagus forest causes a lower wood abundance in terms of volumetric load. Because of the relatively small dimensions of the surveyed LW pieces, almost 70% of them demonstrated to have been fluvial transported and also the wood jams reflect the apparent dynamic nature of wood in the channel. Wood jams exert a significant influence on the channel morphology, representing almost half of the drop caused by steps and being responsible for the creation of 30% of the pools. LW‐forced pool volume is strongly and positively correlated to the height of the LW jam. The geomorphic influence of LW jams is also exerted by a considerable sediment storing capacity. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
5.
黄河源区支流白河和黑河位于青藏高原东北部若尔盖盆地的东部,河道蜿蜒曲折,是典型弯曲型河流,研究其弯曲河道的一般形态规律,有利于认识青藏高原弯曲河流的发育条件和形态特征。基于遥感图像、DEM和野外调查,利用ArcGIS提取了白河和黑河的河网,计算了沿程的纵比降,并测算了河道宽度、弯曲度、河谷宽度和牛轭湖数量。白河和黑河的统计河段平均弯曲度分别为1.68和2.46,黑河平均弯曲度大于白河的主要原因是黑河的多年平均流量和河道纵比降均小于白河。白河单位河长的牛轭湖数量沿程由多变少,黑河单位河长的牛轭湖数量沿程趋于均匀,且牛轭湖数量多于白河,说明黑河沿程保持更高的自然裁弯频率。 相似文献
6.
Thomas C. Wagner;Romy Woellner;Veronika Kloska;Johannes Kollmann; 《河流研究与利用》2024,40(6):1125-1141
Channel migration, furcation, and vegetation succession are characteristic processes of braided gravel rivers in Alpine regions. These are associated with a frequent turnover of large parts of the active floodplain. However, more than one century of river regulation has reduced or destroyed most of these ecosystem dynamics. More recently, there have been attempts to restore at least some sections of degraded rivers, while there is little monitoring of the biogeomorphological dynamics of such rivers. Thus, we did a four-year analysis of four representative sections of the upper River Isar in Southern Germany differing in their degree of naturalness. Dynamics of channels, gravel bars, and vegetation were recorded by drone images, and braiding and gravel indices were calculated. When comparing the near-natural, semi-natural, degraded or restored sections, there was a gradient of decreasing channel migration, gravel bank expansion, and bank erosion due to a reduced turnover frequency. Biogeomorphological variation among years correlated with log peak discharge within the four sections. In addition, the cover and height growth of vegetation increased with river degradation, and channel migration was positively related to the braiding index. The total turnover of the active river corridor and of the vegetation were positively correlated with log peak discharge within the four sections. The floodplain dynamics of the restored section were improved compared to the degraded section but did not reach a near-natural state. Thus, Alpine river sections with contrasting degrees of naturalness differ in terms of habitat turnover and vegetation succession, and these characteristics can only partially be restored by local measures. 相似文献
7.
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
8.
C. J. Legleiter 《河流研究与利用》2015,31(10):1328-1343
Recent reservoir construction on Savery Creek provided an opportunity to examine the downstream effects of a dam on a small, meandering channel. The new dam, completed in 2005, modified the flow regime by reducing the magnitude of spring peaks and increasing baseflows, including a second period of high discharge in the fall. A time series of remotely sensed data spanning 1980–2011 was used to measure lateral migration rates, quantify areas of erosion and deposition, and map spatial patterns of channel change. Both migration rates, and gross erosion and deposition increased during the post‐dam era, although 2 years of exceptionally large snowmelt runoff also occurred during this time. Net sediment flux inferred from the image time series was negative for both the upper and lower reaches for the first photo pair after the dam's completion but became positive for the most recent photos. Detailed topographic surveys of five individual meander bends were used to produce digital elevation models of difference and infer bed material transport rates. For three sites located in the upper reach, downstream increases in transport rate implied a sediment deficit satisfied through channel incision and/or bank erosion. For two sites in the lower reach where sediment supply was greater, larger values of gross erosion were balanced by enhanced deposition and transport rates stabilized or increased along each bend. Together, these results suggest that Savery Creek has entered a period of adjustment as the channel adapts to altered, dam‐regulated supplies of water and sediment. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
9.
三门峡水库建库前渭河下游淤积状况分析 总被引：2，自引：1，他引：1
历史文献记载,渭河“水浅,沙深”。由汉至唐因渭河淤浅不能通航,多次另行开挖漕渠为京师运粮,三门峡水库建成前,渭河华县、咸阳、道口的同流量水位年平均上升0.020-0.089m,渭河下游也是淤积上升的,潼关是渭河下游侵蚀基面,潼关高程年平均上升0.035m,渭河下游与潼关高程是相互作用、相互影响而同步上升的。 相似文献
10.
分析黄河下游游荡型河道河势的时空演变规律,为进一步认识黄河下游河道演变特征、开展河道整治提供理论支撑和实践价值。在系统收集、整理1960-2015年黄河下游游荡型河段典型断面的河势观测资料基础上,利用Mann-Kendall趋势检验和Fisher断点检验方法分析1960-2015年黄河下游游荡型河道典型断面多年平均河宽及主流线迁移速率变化情况。结果表明:近60年黄河下游游荡型河道在平面形态上呈藕节状分布,而其主流线调整速率的时空分布规律并不显著;黄河下游于店断面、禅房断面是平面藕节状分布的关键节点,将全河段划分为3段(第一段铁谢至于店断面,河宽均值为1 627m;第二段于店至禅房断面,河宽均值为1 477m;第三段禅房至高村断面,河宽均值为1 074m)。 相似文献