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1.
Urban rivers are often engineered to increase flood conveyance and stabilize channel size and position. This paper analyses habitat surveys of 180 urban river stretches of differing engineering type from four river basins (river Tame, West Midlands, UK; tributaries of the lower river Thames, UK; river Botic, Prague, Czech Republic; river Emscher, North‐Rhine Westphalia, Germany). Kruskal–Wallis tests identify significant differences in extent and/or frequency of flow types, bank and bed physical habitats, and vegetation characteristics associated with different styles of engineering. Principal Components Analysis identifies four key environmental gradients in the data set: sediment supply and retention; extent and diversity of in‐channel vegetation and riparian trees; bed and bank sediment calibre; flow type energy and complexity. These gradients discriminate stretches of differing planform, cross section and reinforcement and are significantly correlated with indices of degree and type of bank and bed reinforcement, pollution and presence of alien nuisance plant species. The analytical results illustrate statistically significant associations between different styles and levels of engineering intervention and the number and nature of physical habitats present in urban rivers. The results provide a basis for filtering sites for potential remedial measures prior to site‐specific surveys and modelling, for comparing sites and for tracking trajectories of change at sites that are subject to changes in channel engineering. They provide evidence that river condition and degree of engineering are not inversely related in a simple linear way, and that engineering of urban river channels, in the form of mixed, patchy reinforcement can contribute a great deal to habitat diversity where other controls on flow heterogeneity are more difficult to manipulate. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

2.
Critical to restoring the nature conservation value of many river corridors is an understanding of how alluvial landscapes will respond to cessation of river management and land use practices that have previously degraded the environment. This paper analyses changes in valley floor landforms and vegetation patch dynamics, in relation to fluvial disturbance, over a period of almost 100 years following flood embankment abandonment on a wandering gravel‐bed river, namely the River Tummel, Scotland. Such rivers were once typical of many draining upland areas of northern maritime Europe. Prior to abandonment the valley floor landscape was agriculturally dominated and the river for the most part was single thread confined between flood embankments. The pattern of landform change and vegetation patch development over time following a decision in 1903 not to maintain embankments was tracked by geomorphic and land cover mapping utilizing successive sets of aerial photography for the period 1946 to 1994. A historical context for these changes was also feasible because the channel planform in 1900 and earlier channel planform changes dating back to 1753 were known due to the availability of old maps and earlier geomorphic studies. The land cover mapping was validated by comparison of results produced from the interpretation work on the 1994 aerial photographs with the field‐based UK National Vegetation Classification protocol. The findings of the study illustrate that bordering the River Tummel fluvial landforms and vegetation patch mosaics, presumably resembling those that occurred before valley floor land use intensification, evolved in less than 50 years after flood embankment abandonment with a resultant increase in habitat diversity. The change relates primarily to flood‐induced channel planform change and moderate levels of fluvial disturbance. The general significance of this change to plant species diversity on the valley floor of the River Tummel and elsewhere is discussed as is possible implications of the upstream impoundment and scenarios for climatically induced changes in flood frequency and magnitude. The overall outcome is the strong possibility that simple changes in river management and land use practices could result in re‐establishment of the nature conservation value of similar river corridors in Europe over the medium term without active restoration efforts. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

3.
This paper quantifies patterns of discharge and temperature variation in the regulated river Lyon and the adjacent, unregulated river Lochay (Scotland) and assesses the importance of these patterns for benthic invertebrate community structure. Invertebrates were sampled at sites in each catchment in autumn, winter and spring during the 2002–2003 hydrological year. Metrics were used to characterize the discharge and temperature regimes in the period immediately preceding invertebrate sample collection. Metric values were then used in a canonical correspondence analysis (CCA) of the invertebrate sample data, in order to assess the significance of individual metrics and the overall importance of flow and temperature variability for community structure. The variance in the invertebrate data explained by this CCA was compared to that from a CCA using a range of environmental data from the sites (stream‐bed algal cover, channel hydraulic, sedimentary and water quality characteristics). This comparison allowed assessment of the relative importance of environmental variables versus hydrologic and thermal regimes. Invertebrate communities in the Lyon were relatively poor and uneven, with Ephemeroptera, Plecoptera and Coleoptera poorly represented. Distinct site and seasonal clusters were evident in the CCA ordination biplots, with Lyon and Lochay sites separated in dimensions represented by geometric mean sediment size, water temperature and algal cover. The cumulative variance values from ordinations using the discharge and temperature metrics were consistently highest, suggesting that differences in invertebrate communities showed a stronger relation to patterns of discharge and temperature variability than to the broader suite of environmental conditions. Although there were marked thermal differences between sites, temperature metrics appeared no more important than discharge metrics in explaining differences in invertebrate community structure. A number of the temperature and discharge metrics appeared similarly important, suggesting that no one aspect of the hydrothermal regime was any more important than others in helping to understand differences in invertebrate community between the study sites. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

4.
We conducted a regional classification and analysis of riverine floodplain physical features that represent key attributes of salmon rearing habitats. Riverine habitat classifications, including floodplain area and river channel complexity, were derived at moderate (30 m) spatial resolution using multispectral Landsat imagery and global terrain data (90 m) encompassing over 3 400 000 km2 and most North Pacific Rim (NPR) salmon rivers. Similar classifications were derived using finer scale (i.e. ≤ 2.4‐m resolution) remote sensing data over a smaller set of 31 regionally representative flood plains. A suite of physical habitat metrics (e.g. channel sinuosity, nodes, floodplain width) were derived from each dataset and used to assess the congruence between similar habitat features at the different spatial scales and to evaluate the utility of moderate scale geospatial data for determining abundance of selected juvenile salmon habitats relative to fine scale remote sensing measurements. The resulting habitat metrics corresponded favorably (p < 0.0001) between the moderate scale and the fine scale floodplain classifications; a subset of these metrics (channel nodes and maximum floodplain width) also were strong indicators (R2 > 0.5, p < 0.0001) of floodplain habitats defined from the finer scale analysis. These relationships were used to estimate the abundance and distribution of three critical shallow water floodplain habitats for juvenile salmon (parafluvial and orthofluvial springs, and shallow shore) across the entire NPR domain. The resulting database provides a potential tool to evaluate and prioritize salmon conservation efforts both within individual river systems and across major catchments on the basis of physical habitat distribution and abundance. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

5.
应用有限体积法建立了河道平面二维水流泥沙数学模型并将模型应用于典型河段的计算,验证了模型的计算精度.设置了不同来水来沙条件和沙坑几何边界条件,将本模型应用于几种工况的理想矩形河道中矩形沙坑影响模拟研究,计算表明采砂对河道的正常演变产生影响,影响结果与离沙坑的距离、沙坑的深度和面积大小以及来水来沙情况等因素有关.初步分析了在采沙规划中可控制采沙影响后果的措施.  相似文献   

6.
This paper presents the first study of the benthic invertebrate assemblages of the upper section of the Paraguay River, a major tributary to the Pantanal wetland in Brazil. Thirty‐eight sites were sampled along a 200 km section below the city of Cáceres in November 2000. Sixty‐nine species and morphospecies were identified, which were dominated by Oligochaeta and Chironomidae. Mean density of benthic invertebrates varied between 72 and 10 354 m?2 in the meandering sector of the river, 3611–49 629 m?2 in the straight–transitional sectors, 682–5962 m?2 in the floodplain lakes, and 1704–2208 m?2 in floodplain channels. Highest densities were attained in sand‐gravel sediments dominated by the psammophilous oligochaete Narapa bonettoi. The Shannon diversity index ranged from 0.75 to 2.08 and was highest in floodplain lakes. Statistical analysis (UPGMA and CCA) revealed that benthic assemblages in the floodplain habitats were clearly distinct from the riverine habitats. In the river channel, the habitats were distinguished by grain size while the floodplain habitats were mostly determined by current and silt‐clay concentration (floodplain channels) or by organic matter concentration (floodplain lakes). Conservation efforts in the Upper Paraguay area should aim to maintain the flood pulse as a permanent source of spatial and temporal habitat heterogeneity. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

7.
挟沙水流的冲刷率及河床惯性的研究   总被引:5,自引:1,他引:4  
在清水水流河床冲刷率的实验研究基础上,本文进一步研究了挟涉水流来沙率对冲刷率的影响。结果说明挟抄水流的冲刷率随来沙率与水流输沙力欠饱和度之比以负指数律降低。当来水挟抄率与水流饱和输抄率相等时,冲刷率降刊0。河床惯性是河床在非恒定流中一种重要的动力学性质。利用河床惯性与冲刷率的关系测量了各种沙样的河床惯性值。发现河床惯性随床沙颗粒分选系数增大而增大,分选系数很大时趋近于极限值50t/Tn0。利用河床惯性和河床变形方程得出了冲刷过程中水流输沙率沿程和随时间的变化规律,结果说明水流输沙率欠饱和度向下游以负指数律下降,这与冲刷率随实际水流挟沙率与欠饱和度之比以指数率下降的规律有耜同意义。河床惯性愈大,实际水流输沙率增长得愈慢。河床惯性与于容重及摩阻流速之比构成的无困次数A。代表河床变形和水流实际挟沙量对水流挟沙力变化的响应程度。  相似文献   

8.
砂质河床与砾石河床的河型判别研究   总被引:2,自引:0,他引:2  
许炯心 《水利学报》2002,33(10):0014-0020
砂质河床与砾石河床在水力学特征与泥沙运动特征方面都有较大差异,由此导致了河型特征的差异。本研究以世界上近200条河流的资料为基础,在建立同时适用于砂质与砾石河床河型判别统一关系方面进行了尝试。以水流切力、河流功率以及无量纲切力Sd/D50来表示水流强度,而以宽深比和无量纲河宽来间接反映河岸约束性,从而在一定程度上克服了河岸约束性难以定量表达的困难。研究发现,上述水流强度变量和河岸约束性变量的组合关系,在具有不同河型的砂质与砾石河床之间表现出较大的差异,从而实现了对砂质河床与砾石河床河型的定量判别,得到了一系列的沙质与砾石河床河型的判别关系。  相似文献   

9.
‘River widenings’ are commonly used in river restoration to allow channel movement within a spatially limited area. Restoration seeks to restore fluvial processes and to re‐establish a more natural riparian community. This study investigates the performance of five river widenings in Switzerland, focusing on the re‐establishment of riparian (semi‐)terrestrial habitats and species, and highlights some factors that seem to influence their performance. The restoration projects are compared with pre‐restoration conditions and near‐natural conditions, which are assumed to represent the worst‐ and best‐case conditions along a gradient of naturalness. Fuzzy ordination of vegetation data and calculation of landscape metrics based on habitat maps revealed marked differences between the degree of naturalness achieved by each individual restoration project. However, in general river widenings were found to increase the in‐stream habitat heterogeneity and enhanced the establishment of pioneer habitats and riparian plants. Analyses of species pools based on a hierarchic list of indicator species and correspondence analysis showed that the ability of river widenings to host typical riparian species and to increase local plant diversity strongly depends on the distance to near‐natural stretches. Species dispersal and establishment might be hampered by decisions taken outside the scope of the restoration project. Therefore we conclude that action on the catchment scale is needed to maximize the benefits of local management. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

10.
River management in New Zealand's laterally active gravelly rivers has permitted floodplain development and protection of agricultural resources and infrastructure. Management of these dynamic systems has been hailed as a success for the approaches adopted, namely straightening and confining the river using bank protection and managing riverbed levels by gravel extraction. However, this activity also impacts river morphological/habitat diversity and potential gravel resource, by replacing broad riparian corridors with narrower channels and reducing lateral connectivity with the floodplain. This paper quantifies river behaviour in three laterally confined reaches in the upper Motueka River over a 7‐year period, using annual high‐resolution ground surveys to address the nature of morphological change and associated sediment flux in these reaches with a view to informing management of the gravel resource. Surveys between 2004 and 2010 acquired data to construct digital elevation models (DEMs) of the active riverbed in three ~1‐km‐long reaches. Morphological budgeting based on differencing between successive DEM surfaces reveals complex spatial and temporal patterns of erosion and deposition, demonstrating complex reach dynamics. Overall, volumetric changes suggest these narrowed reaches have been net exporters of sediment, associated with continued channel degradation. This has left bar features, traditionally the focus of gravel extraction in the reaches, relatively isolated from all but extreme flows, limiting replenishment of the gravel resource. The paper demonstrates the utility of riverbed DEMs as a potential tool to frame river character and behaviour at the reach scale in gravel‐bed rivers, thereby providing an important contribution to holistic river management in these systems. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

11.
Geomorphologists are becoming increasingly interested in assessing morphologic structure and the diversity and/or complexity in morphologic structure across multiple scales within river systems. Unfortunately, many of our existing tools/variables are unsuitable for this task because they do not work across multiple scales or with changing discharges. Asymmetry is one variable that can be used to either include or exclude variations in flow stage and that can be assessed across multiple scales. Existing asymmetry indices, however, are limited in scope and largely focus on only cross‐sectional form. This study examines three existing asymmetry indices in the cross‐stream and downstream planes (for cross‐sections and riffle or pools, respectively) and develops nine new asymmetry indices that incorporate vertical, cross‐stream and downstream asymmetry for bed elements (e.g. riffle crests, pool troughs, riffle entrance slope), bedforms (pools or riffles) and bar units (pool‐riffle sequences) to investigate the utility of asymmetry as a measure of morphologic structure and diversity in fluvial systems. These 12 indices are field tested on the Embarras River in East Central Illinois, USA. The results of this study indicate that there is considerable morphologic diversity in bed elements, bedforms and bar units both at bankfull and also with varying flow stage. This multi‐scale, multidimensional, multistage variability in morphologic structure highlights the complexity of natural river systems. The highly variable nature of fluvial form within a reach has important implications for river restoration and/or assessments of physical habitat or river health especially in instances where pools, riffles or pool‐riffle sequences are the focus of study. In general the most robust and useful combination of asymmetry indices for most applications includes A* and AL1 for bed elements and bedforms and AL3, AW and AH for bar units. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

12.
A total of 436 logs were used to create 20 engineered log jams (ELJs) in a 1.1 km reach of the Williams River, NSW, Australia, a gravel‐bed river that has been desnagged and had most of its riparian vegetation removed over the last 200 years. The experiment was designed to test the effectiveness of reintroducing woody debris (WD) as a means of improving channel stability and recreating habitat diversity. The study assessed geomorphic and ecological responses to introducing woody habitat by comparing paired test and control reaches. Channel characteristics (e.g. bedforms, bars, texture) within test and control reaches were assessed before and after wood placement to quantify the morphological variability induced by the ELJs in the test reach. Since construction in September 2000, the ELJs have been subjected to five overtopping flows, three of which were larger than the mean annual flood. A high‐resolution three‐dimensional survey of both reaches was completed after major bed‐mobilizing flows. Cumulative changes induced by consecutive floods were also assessed. After 12 months, the major geomorphologic changes in the test reach included an increase in pool and riffle area and pool depth; the addition of a pool–riffle sequence; an increase by 0.5–1 m in pool–riffle amplitude; a net gain of 40 m3 of sediment storage per 1000 m2 of channel area (while the control reach experienced a net loss of 15 m3/1000 m2 over the same period); and a substantial increase in the spatial complexity of bed‐material distribution. Fish assemblages in the test reach showed an increase in species richness and abundance, and reduced temporal variability compared to the reference reach, suggesting that the changes in physical habitat were beneficial to fish at the reach scale. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

13.
The habitat templet approach was used in a scale‐sensitive bioindicator assessment for the ecological integrity of riverbanks and for specific responses to river management. Ground beetle habitat templets were derived from a catchment‐scale sampling, integrating the overall variety of bank types. This coarse‐filter analysis was integrated in the reach‐scale fine‐filtering approaches of community responses to habitat integrity and river management impacts. Higher species diversity was associated with the higher heterogeneity in bank habitats of the un‐navigable river reaches. The abundant presence of habitat specialists in the riverbank zone allows a habitat integrity assessment based on the habitat templet indicator species. Significant responses were detected for channel morphology in the width‐to‐depth ratio and for hydrological regime in peak frequency and peak velocity, enabling the development of evaluation methods for the impact assessment of river management and flood protection strategies. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

14.
15.
Bank stabilization is increasing along large rivers as urban areas expand, and the need to protect infrastructure increases in the face of changing climate and flow patterns, but the cumulative effects of different stabilization approaches on reach‐scale biodiversity are not well understood. We investigated physical habitat characteristics and macroinvertebrate community composition and diversity for four shore‐zone habitat types across nested spatial scales over two sampling occasions. Distinct physical conditions were evident for riprap, beach and willow (mixed trees dominated by Salix spp.) habitats, reflecting variations in the combinations of shade, water velocity and substrate size/type, but there was wide variation in habitat conditions for mixed willow‐riprap sites. Additive biodiversity partitioning decomposed reach (γ) diversity into within (α) and among (β1) sample, among habitat (β2), and among site (β3) components, and highlighted significant effects of all spatial scales on macroinvertebrate diversity. Low autumn water levels led to truncated species accumulation curves at beach sites where macrophyte beds that supported macroinvertebrates became stranded, or elevated species accumulation curves for exposed willow‐riprap sites where the river benthos was sampled during hydrological disconnection of bank habitats. Spring and autumn differences in macroinvertebrate community composition were stronger than differences between habitat types. Our findings (a) highlight the interacting effect of river level with shore‐zone habitat function, and (b) underscore the importance of maintaining a diversity of bank habitat types at multiple sites along river shore‐zones to maximize macroinvertebrate diversity.  相似文献   

16.
Prediction of changes to in‐stream ecology are highly desirable if decisions on river management, such as those relating to water abstractions, effluent discharges or modifications to the river channel, are to be justified to stakeholders. The physical habitat simulation (PHABSIM) system is a well‐established hydro‐ecological model that provides a suite of tools for the numerical modelling of hydraulic habitat suitability for fish and invertebrate species. In the UK, the most high‐profile PHABSIM studies have focused on rural, groundwater‐dominated rivers and have related to low flow issues. Conversely, there have been few studies of urban rivers. This paper focuses on the application of PHABSIM to urban rivers and demonstrates how sensitivity analyses can be used to assess uncertainty in PHABSIM applications. Results show that physical habitat predictions are sensitive to changes in habitat suitability indices, hydraulic model calibration and the temporal resolution of flow time‐series. Results show that there is greater suitable physical habitat over a wider range of flows in a less engineered river channel when compared to a more engineered channel. The work emphasizes the need for accurate information relating to the response of fish and other organisms to high velocities. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

17.
In this paper, we use a system‐wide census of large river and floodplain habitat features to evaluate influences of valley form and land use on salmon habitats along 2,237 km of river in the Puget Sound region of Washington State, USA. We classified the study area by geomorphic process domains to examine differences in natural potential to form floodplain habitats among valley types, and by dominant land cover to examine land use influences on habitat abundance and complexity. We evaluated differences in aquatic habitat among strata in terms of metrics that quantify the length of main channels, side channels, braid channels, and area of wood jams. Among geomorphic process domains, habitat metrics standardized by main channel length were lowest in canyons where there is limited channel migration and less potential to create side channels or braids, and highest in post‐glacial and mountain valleys where island‐braided channels tend to form. Habitat complexity was lower in glacial valleys (generally meandering channels) than in post‐glacial valleys. Habitat abundance and complexity decreased with increasing degree of human influence, with all metrics being highest in areas classified as forested and lowest in areas classified as developed. Using multiple‐year aerial photography, we assessed the ability of our methods to measure habitat changes through time in the Cedar and Elwha Rivers, both of which have recent habitat restoration activity. We were able to parse out sources of habitat improvement or degradation through time, including natural processes, restoration, or development. Our investigation indicates that aerial photography can be an effective and practical method for regional monitoring of status and trends in numerous habitats.  相似文献   

18.
Despite considerable effort, predicting habitat preferences for freshwater mussels has remained elusive. This study identified four parameters that correlate with bed stability to decipher fine‐scale spatial patterning of habitat use by the western pearl shell mussel (Margaritifera falcata) in the Trinity River of Northern California. Logistic regression analysis correctly predicted the occurrence of 83% of mussel bed areas based on water depth, velocity, substrate size, and distance to the stream bank as estimated from hydrodynamic modelling of low‐flow conditions. These parameters coincide with bed stability at high flow and provide support for the ‘refugia hypothesis’. Our data clearly demonstrate that mussel beds occupied the most stable portions of the riverbed; however, habitat was partitioned with one of their primary host fish, Chinook salmon (Oncorhynchus tshawytscha), a species that also requires stable bed areas for spawning. Mussels occupied significantly deeper and lower velocity areas that were closer to the streambank compared with spawning salmon, but where habitats directly overlapped (30% of potential mussel habitat) mussels were excluded because the act of spawning disturbs the riverbed. By necessity, mussels and salmon must co‐exist, but results of this study indicate that they compete for stable bed areas that may be limiting in dynamic river systems. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

19.
River regulation can alter the structural complexity and natural dynamics of river ecosystems substantially with negative consequences for aquatic insects. However, there have been few studies of regulation effects on the export of emergent insects into terrestrial ecosystems. In northern Scandinavia, we compared emerged aquatic insect and terrestrial invertebrate biomass between four strongly regulated and four free‐flowing rivers using fortnightly measurements at three upland‐forest blocks in each over one summer. The biomass of emerged aquatic insects was significantly lower along regulated rivers than free‐flowing rivers. Biomass in Linyphiidae, Opiliones, Staphylinidae, total Coleoptera, Formicidae and total terrestrial invertebrates was also lower along regulated rivers. Aquatic insect biomass did not explain the entire regulation effect on terrestrial invertebrates but did explain significant variations among Linyphiidae, total Coleoptera, Formicidae and total terrestrial biomass. Variations in Formicidae also explained significant variance among several terrestrial taxa, suggesting some keystone role in this group. Overall, our results suggest that river regulation affects upland‐forest invertebrate communities, with at least some of these effects arising from links between aquatic emergence and terrestrial predators. The data highlight the need to consider areas beyond the riparian zone when assessing the effects of river regulation. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

20.
将河流动力学与数学中的分形理论相结合,以河床冲淤较为剧烈的三峡坝下游典型分汊河段为例,分析了河床表面分形维数(BSD)的变化及其与相应河段平面、纵剖面、横断面冲淤调整特点的关系。结果表明:BSD具有时空变异性,一方面不同类型河段BSD是不同的,其可在一定程度上反映河型,甚至河型亚类的差异;另一方面同一河段BSD随河床冲淤进程亦发生相应变化,其与河床形态调整存在着必然联系。同时,BSD值与典型剖面形态的复杂程度呈正相关性,可从整体上描述河床表面形态冲淤起伏的剧烈程度。BSD作为河床表面形态冲淤起伏程度的定量工具,其在河流动力学领域中的河势量化分析、河型判别及河道形态阻力计算等方面将具有一定的参考价值。  相似文献   

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