Quasi‐equilibrium conditions of urban gravel‐bed stream channels in southern Ontario,Canada

Urban gravel‐bed stream channels in southern Ontario, Canada identified to be in a state of quasi‐equilibrium have been studied over the past 15 years and compared against rural gravel bed stream channels of the same hydrophysiographic region. Bankfull width and depth versus bankfull discharge were not found to increase as a function of increasing urbanization as has been found in many other studies. The observed annual frequency of bankfull discharge was typically less than a 1‐year return period with many sites ranging between 2 and 18 bankfull events per year with higher intensity and shorter duration urban flood responses, which further identified significant limitations in using annual peak discharge methods for predicting morphological forming flows in urban watersheds. The cumulative volume of bankfull and larger flood events from the urban stream channels were very similar to the same annual event volumes in the rural comparison study reaches. Bed material supply was found to decrease with increasing urbanization and the reduction in bed material supply appears to be off‐set by the smaller bankfull channel width, depth and access to floodplains during large flood events. Field evidence may also suggest a even greater reduction in channel width trajectory, relative to the rural setting, with expansive floodplains to maintain quasi‐equilibrium conditions as bed material supply continues to decrease with increased anthropogenic activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessing channel geometry in response to land use disturbance in a low-relief,glacially conditioned setting

Bankfull stage, the highest flow elevation contained by a river channel before overbank flooding occurs, is the presumed threshold for channel morphological change. At bankfull, the channel boundary experiences the highest shear stress, producing somewhat predictable hydraulic relationships and a cross-sectional form. However, land use and glacial conditioning can profoundly impact a channel's geomorphic responses. Two common methods characterize bankfull flow: one based on flow frequency and other based on channel form. This study considers a simplified approach to identify upstream land use relative to estimates of bankfull flow versus a channel's geometric form. The approach compares archived geomorphic surveys of 140 river reaches in southern Ontario, Canada, to 2-year flood quantiles modelled from historical flood data of 207 gauge stations. Flood frequency analysis determines that annual maximum series (AMS) datasets, fitted to optimized probabilistic distributions, underestimate discharge for low-magnitude, high-frequency flood events compared to partial duration series (PDS) datasets. For smaller drainage areas (<100 km²) associated with an extensive agricultural activity and/or urbanization, the estimates of bankfull discharge (Q_bf) generated by cross-sectional channel geometry are greater than the gauge-derived Q₂ values. Channels impacted by high levels of upstream land use disturbance show statistically significant lower width-to-depth ratios (p < 0.001) and a trend towards a finer D₅₀ bed material, suggesting enhanced surface runoff delivering more mobile finer sediments and channel confinement or incision. This research quantifies the formative bankfull stage to better understand the link between land use and a channel's ‘natural’ hydrogeomorphic response in a low-relief, glacially conditioned setting.     

Effect of urbanization on stream hydraulics

Urbanization results in major changes to stream morphology and hydrology with the latter often cited as a primary stressor of urban stream ecosystems. These modifications unequivocally alter stream hydraulics, but little is known about such impacts. Hydraulic changes due to urbanization were demonstrated using two‐dimensional hydrodynamic model simulations, comparing urban and non‐urban stream reaches. We investigated three ecologically relevant hydraulic characteristics: bed mobilization, retentive habitat, and floodplain inundation, using hydraulic metrics bed shear stress, shallow slow‐water habitat (SSWH) area, and floodplain inundation area. We hypothesized that urbanization would substantially increase bed mobilization, decrease retentive habitat, and due to increased channel size would decrease floodplain inundation. Relative percent area of bed disturbance was 4 times higher, compared with that of the non‐urban stream at bankfull discharge. SSWH availability rapidly diminished in the urban stream as discharge increased, with SSWH area and patch size 2 times smaller than the non‐urban stream for a frequently occurring flow 0.7 times bankfull discharge. Floodplain inundation decreased in frequency and duration. These results demonstrate changes in hydraulics due to urbanization that may impact on physical habitat in streams. New “water sensitive” approaches to stormwater management could be enhanced by specification of hydraulic regimes capable of supporting healthy stream habitats. We propose that a complete management approach should include the goals of restoration and protection of natural hydraulic processes, particularly those that support ecological and geomorphic functioning of streams.     

维持黄河下游河槽排洪输沙能力方案分析

利用黄河下游水动力学泥沙冲淤数学模型,采用3个20年设计水沙系列对河段的冲淤及平滩流量的变化进行了计算与分析,结果表明:①各水沙系列的前10年,下游各河段均处于沿程冲刷状态,而后10年各河段则出现了淤积;②只有系列2能维持整个下游河道的平滩流量在4000 m3/s以上;③各系列前10年塑造河槽阶段的水沙过程均比较合理,基本实现了平滩流量稳定增大的目的,后10年河道平滩流量则出现了不同程度的减小;④应尽量控制小浪底出库含沙量不超过200 kg/m3且细泥沙比重在75%以上。     

Downstream Regime Relations for Single‐Thread Channels

New empirically derived downstream hydraulic geometry relations are developed for single‐thread gravel/cobble‐bed and sand‐bed channels using the independent variables bankfull discharge, channel slope, and median bed grain size. Differences in channel response to the controlling variables are observed between gravel/cobble‐bed and sand‐bed channels. It is found that the inclusion of channel slope into regime relations is necessary for accurate channel geometry predictions and that bed grain size becomes an unnecessary variable. Accuracy of predictions is superior to many existing relations and comparable with those that already include slope as an independent variable. Variability of prediction errors is comparable with existing relations. Applications and implications of the new relations are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

LARGE‐WOOD LOADING FROM NATURAL AND ENGINEERED PROCESSES AT THE WATERSHED SCALE

Large wood, both live and dead, is essential for producing complex habitat in many streams, especially in forested watersheds that support salmonid populations. The addition of engineered wood structures is a common approach taken in many streams where past watershed management practices have resulted in reduced wood loading. We examined six 300‐m stream reaches in the Lagunitas Creek watershed, Northern California, to determine (i) the distribution of large wood in the bankfull channel and 10‐year floodplain, (ii) the influence of large wood on the size and distribution of pools and (iii) whether streams with engineered wood structures had greater diversity of pool habitat to support salmonid populations. We found that the amount of large wood in the bankfull channel and the amount available for recruitment from the 10‐year floodplain were highly variable among and within reaches examined and largely dependent on the local geomorphic setting. Stream reaches with engineered wood structures had elevated pool frequencies relative to reaches without these structures, suggesting a higher capacity to support salmonids during critical life stages. Among large wood pieces that had a strong influence on pool formation, 23% had an attached root wad and 66% were part of a cluster. All of the study reaches we examined had lower volumes of large wood in their bankfull channels than similar stream types with natural wood‐loading levels, suggesting that increased additions of large wood could provide ecosystem benefits over time. These principles can be understood and transferred effectively to other watersheds using a framework of wood‐loading process domains. Copyright © 2012 John Wiley & Sons, Ltd.     

Monitoring the channel process of a stream restoration project in an urbanizing watershed: a case study of Kelley Creek,Oregon, USA

Pacific Northwest (PNW) streams in the United States were impacted by the 20th century development, when removal of instream structure and channelization degraded an aquatic habitat. The lower Kelley Creek in southeast Portland, USA was channelized during the 1930's Works Progress Administration (WPA) projects. Stream restoration reintroduced pool‐riffle sequences and heterogeneous substrates to protect salmonids while mitigating impacts from flooding. We investigated whether the restored pool‐riffle morphology changed substantially following effective discharge events. We examined channel forms for four reaches representing three time periods—pre‐development (two reference reaches), development and restoration. We conducted thalweg profiles, cross‐sections and pebble counts along the reaches to examine how channel geometry, residual pool dimensions and particle size distribution changed following effective discharge events. The effective discharge flows altered the restoration reach more substantially than the reference reaches. The restoration reach decreased in median particle size, and its cross‐sectional geometry aggraded near its margins. However, the residual pool morphology remained in equilibrium. Richardson Creek's reference reach degraded at the substrate level, while Kelley Creek's reference reach remained in equilibrium. The restoration reach's aggradation may have resulted from sedimentation along the nearby Johnson Creek. In contrast, Richardson Creek's degradation occurred as upstream land use may have augmented flows. Stream channels with low gradient pool‐riffle morphologies are ideal for salmonid spawning and rearing and should be protected and restored within urban corridors. The findings of our study suggest that the connectivity of streams and the dynamic fluvial geomorphology of stream channels should be considered for stream restoration projects in humid temperate climates. Copyright © 2008 John Wiley & Sons, Ltd.     

水沙变异条件下黄河下游河道横断面形态特征研究

通过对黄河下游各水文站1950～2003年实测资料的分析，探讨了过去50多年间黄河下游河道横断面形态变化过程及其与来水量的响应关系。分析得出，过去50多年间，黄河下游河道主河槽发生了明显的淤积萎缩，游荡性河段的萎缩程度大于弯曲性河段，平滩面积呈明显减小的趋势，宽深比有增大的趋势，但各河段河型没有发生转化；平滩面积随年来水量和当年最大洪峰流量的增加而增大，宽深比随来沙系数的增加而增大。由黄河下游排沙比与来水来沙的关系分析表明，黄河下游花园口～利津河段不淤积的花园口临界年均来沙系数约为0.012，临界年平均流量约为1850m3/s。综合分析认为，在目前下游河道来水偏枯的条件下，下游河道的平滩流量不宜也不可能太大，从维持中水河槽和满足流域经济社会发展需要考虑，在花园口年来水量为200～250亿m3时，花园口控制洪峰流量在4000m3/s左右、年均来沙系数不大于0.012的来水来沙过程比较合适。     

Use of L-Moments Approach for Regional Flood Frequency Analysis in Sicily, Italy

Extremely great floods are among environmental events with the most disastrous consequences for the entire world. Estimates of their return periods and design values are of great importance in hydrologic modeling, engineering practice for water resources and reservoirs design and management, planning for weather-related emergencies, etc. Regional flood frequency analysis resolves the problem of estimating the extreme flood events for catchments having short data records or ungauged catchments. This paper analyzes annual maximum peak flood discharge data recorded from more than 50 stream flow gauging sites in Sicily, Italy, in order to derive regional flood frequency curves. First these data are analyzed to point out some problems concerning the homogeneity of the single time series. On the basis of the L-moments and using cluster analysis techniques, the entire region is subdivided in five subregions whose homogeneity is tested using the L-moments based heterogeneity measure. Comparative regional flood frequency analysis studies are carried out employing the L-moments based commonly used frequency distributions. Based on the L-moment ratio diagram and other statistic criteria, generalized extreme value (GEV) distribution is identified as the robust distribution for the study area. Regional flood frequency relationships are developed to estimate floods at various return periods for gauged and ungauged catchments in different subregions of the Sicily. These relationships have been implemented using the L-moment based GEV distribution and a regional relation between mean annual peak flood and some geomorphologic and climatic parameters of catchments.     

Estimating discharge in gravel‐bed river using non‐contact ground‐penetrating and surface‐velocity radars

Discharge measurement is a critical task for gravel‐bed channels. Under high‐flow conditions, the elevation of the riverbed changes significantly by intensive torrential flow. The stage–discharge relations commonly used for stream discharge estimation may no longer be adequate. The contact‐type velocity measuring is also subject to measurement errors and/or instrument failures by the high‐flow velocities, driftwood, stumps, and debris. This study developed a new real‐time method to estimate river discharge in gravel‐bed channels. A systematic measuring technology combining ground‐penetrating radar and surface‐velocity radar was employed. The rating curves representing the relations of water surface velocity to the channel cross‐sectional mean velocity and flow area were established. Stream discharge was then deduced from the resulting mean velocity and flow area. The proposed method was examined in a steep gravel‐bed reach of the Cho‐Shui River in central Taiwan. The estimated stream discharge during three flood events were compared to the prediction by using the stage–discharge relation and the index‐velocity method. The proposed method of this study is capable of computing reasonable values of discharge for an entire flood hydrograph, whereas the other two methods tend to produce large extrapolation errors. Moreover, when the computed discharge is used in 2D flood flow simulation, the proposed method demonstrates better performance than the commonly used stage–discharge and index‐velocity methods.     

平滩流量下弯曲分汊河道水力要素的突变性特征

平滩流量下的水力特性对分汊河道的滩槽冲淤、分流分沙比及污染物的输移等均有较大的影响。以长江中游戴家洲河段为原型,通过开展概化定床模型试验,分析了弯曲分汊河道不同特征流量下水动力特性的沿程差异性和平滩流量下分汊河道不同区域水力要素的突变特性。试验结果表明:纵比降沿程变化规律为分流区小流量下沿程增加、大流量下沿程减小,凸岸汊道与之相反,而凹岸汊道沿程增加;在平滩流量附近,分流区水面纵比降出现极大值、沿程比降变幅出现极小值,主流线、最大床面切应力所处位置由凹岸汊道转移至凸岸汊道。试验结果为水沙变异条件下分汊河道冲淤机制的研究提供了基础。     

黄河下游造床流量的变化及其对河槽的影响

本文通过计算黄河下游的第一造床流量和第二造床流量,分析了黄河下游河槽的萎缩过程。第一造床流量与年水沙量的关系分析表明,黄河下游的深槽平浅滩流量700～1000m3/s是相对稳定的,恒定流的平衡输沙能力约为18～21kg/m3。通过小浪底水库拦粗排细年平均拦沙约3亿t,并在汛期强化调水调沙运用,基本可以控制黄河下游河槽的淤积萎缩。第二造床流量和平滩流量的关系分析表明黄河下游恢复和维持平滩流量约4000m3/s的中水河槽是比较合理的。根据小浪底水库调水调沙运用状况,提出了恢复和维持黄河下游稳定中水河槽的措施,并探讨了强化小浪底水库调水调沙运用的方案。     

Influences of environmental conditions on macrophyte communities in drought‐affected headwater streams

A 10‐year study of groundwater‐dominated headwater streams in the chalklands of southern England has highlighted the major influence that stream flow has on the composition of in‐channel macrophyte communities. Macrophytes supply much of the physical structure within these headwater channels, as well as providing habitats for a rich assemblage of higher life forms, some of them specialized and rare. The overall influence of stream flow however, is modulated by many environmental factors operating at diverse spatial scales. Data describing the relevant environmental variables were accumulated for six chalk streams in the Thames basin and related directly to the vegetation record by means of Canonical Correspondence Analysis, correlation tests and other analyses, to reveal the circumstances in which communities would be likely to thrive and those in which they would be negatively impacted by variations in stream flow. It was found that local topography and channel dimensions had a direct influence on the composition of communities at local level and that land use and rates of water abstraction had an underlying, but no less important, influence at catchment level. The species most associated with positive species diversity were those of sluggish flow and damp margins indicating the importance of velocity and moisture gradients across the channel in producing a full manifestation of the flora. Strong negative correlations were produced by non‐aquatic grasses and herbs, which represent prolonged periods of channel desiccation. The environmental parameters most associated with positive diversity were high local water stages, wide channels and a high degree of semi‐natural land use within the catchment. Steep channel gradients were strongly associated with negative diversity. The results have confirmed that optimal channel conditions, as exemplified by the classic ‘winterbourne’ with its low‐flow channel, extensive margins, gently sloping banks and high seasonal inundation, will produce good conditions for species diversity and make communities more resistant to the effects of drought. These conditions can be enhanced through sensitive catchment management that encourages rainfall percolation, limits abstractions and seeks to maintain a low intensity of landcover management. Copyright © 2006 John Wiley & Sons, Ltd.     

An Evaluation of the Stream Simulation Culvert Design Method in Washington State

Stream simulation has become an increasingly common culvert design method around the world. It is based on the assumption that geologic and hydraulic conditions in natural channels define passage characteristics for migrating fish and that water crossing structures that imitate these conditions can then achieve those same passage characteristics. This study expands on an initial evaluation of 19 culverts in 2003 to 50 culverts and includes methods and analyses comparing hydraulic characteristics based on cross sections, profile variation, and bed texture between each culvert and its paired reference reach situated in an adjacent section of the natural channel of each stream. Taken as a group, these culverts simulate bed texture, 100‐year recurrence interval flood velocity and 2‐year flood width but did not simulate thalweg complexity or other hydraulic metrics. Culvert span, relative to the bankfull width of the stream, does not by itself determine whether the culvert simulates the reference reach. Of the 50 culverts, many of which experienced record floods, only one showed significant bed degradation. Copyright © 2014 John Wiley & Sons, Ltd.     

Reservoir Flood Routing Considering the Non-Stationarity of Flood Series in North China

Owing to the increasing anthropogenic activities, flood frequency analysis and flood control scheduling of reservoir become more and more complicated because of the non-stationarity of flood series. This paper aims to assess the effects that non-stationary flood series, which is affected by land use change of Daqing River Basin (in North China), has induced on the reservoir flood routing. And the analysis has been carried out in Xidayang Reservoir, which is located in south branch of Daqing River Basin of North China. In this paper, the annual maximum peak discharge series and the annual maximum flood volume (1-day, 3-day and 6-day) series of Xidayang Reservoir were selected to detect their variation using three steps change point diagnosis. Mixed distribution was employed to fit the non-stationary flood series, estimating parameters by simulated annealing algorithm. The results indicate that (1) mixed distribution provided a more appropriate and superior fit than conventional distribution (P3 distribution) to non-stationary flood series, (2) design flood values estimated by mixed distribution reduced by 0.03 %–20.24 % with different return periods compared with the results computed by conventional P3 distribution, and (3) through reservoir flood routing, the maximum water level and maximum discharge with various return periods considering the series’ non-stationarity also showed a decrease by up to 0.56 m and 81.68 % respectively compared with the results regardless of the series’ non-stationarity. These results provide a significant theoretical basis for flood control and water resources management in Daqing River Basin.     

黄河下游塑槽输沙需水量计算方法

本文从能量平衡原理出发分析了挟沙水流的能量耗散机理及水流塑槽和输沙能量的分配模式,河道水流能量的消耗主要用于塑槽和输沙两个方面,即一部分水流能量用来克服河床边界阻力,维持一定的河道主槽;另一部分则用于输送水流中挟带的泥沙,维持河道的输沙平衡。根据水流能量的这一分配模式,并结合水沙条件对平滩流量的累积影响作用,建立了塑槽输沙需水量的计算方法。将该方法用于黄河下游各主要测站的塑槽输沙需水量计算,取得了较好的效果。以三黑小的来水来沙为输入条件,得到了黄河下游河道塑槽输沙需水量的计算公式,并给出了维持黄河下游平滩流量为4000m3/s的塑槽输沙需水量区间。     

黄河下游平滩流量不同确定方法的比较

平滩流量是主槽过流能力的一个重要指标,准确估算各断面平滩流量大小是黄河下游水沙调控的一项内容。本文首先阐述了平滩流量的概念,并结合黄河下游不同年代的实测横断面形态特征,给出了确定主槽范围及平滩高程的原则。接着评述了国内外已有确定平滩流量的方法,并分析了断面平滩流量四种确定方法各自的优缺点及适用范围。最后以下游花园口断面为例,给出了四种计算方法所得平滩流量的结果及其差别。通过比较认为,本文提出的采用一维水动力学模型确定平滩流量的方法所得结果较为合理。     

黄河下游河道断面形态参数变化与主河槽萎缩趋势分析

本文采用时间序列分析的方法对黄河下游河道断面形态参数变化趋势及其变异点进行了分析，分析结果表明从20世纪50年代以来，断面形态参数发生了趋势性变化，特别是90年代以来各站平滩流量和平滩面积均有显著的下降趋势，花园口站、高村站和利津站平滩河宽出现了显著下降趋势，花园口站、艾山站平均水深显著下降，高村站和艾山站的平滩水位显著抬高，艾山站的宽深比也有显著增大的趋势。黄河下游河道主河槽萎缩的最显著特征就是断面平滩流量和平滩面积的显著下降，相应的平滩河宽、平均水深、最大水深出现不同程度的下降，另外可能还伴随着平滩水位和断面宽深比的上升。黄河下游河道主河槽在70年代开始初步萎缩，90年代以后进入严重萎缩期。     

黄河下游河道断面形态参数变化与主河槽萎缩趋势分析

采用时间序列分析法对黄河下游河道断面形态参数变化趋势及其变异点进行了分析。结果表明从20世纪50年代以来,特别是90年代以来黄河下游花园口站、高村站、艾山站和利津站断面形态参数发生了趋势性变化,主河槽变化的最显著特征就是断面平滩流量下降,相应的平滩面积、平滩河宽、平均水深、最大水深均出现不同程度的减小,平滩宽深比增大。变异点分析表明黄河下游河道主河槽总体上在1970—1975年开始萎缩,1990年以后进入严重萎缩期。     

长江武汉河段平滩及枯水河槽形态近期调整的机理研究

依据实测水沙及地形资料,分析了长江武汉河段近期平滩及枯水河槽形态的调整特点,确定了其与来水来沙及河床边界条件等因素之间的相关关系.三峡工程运用后,进入武汉河段的沙量大幅度减小(汉口站年均沙量仅为1.03亿t/a),河床冲刷较为显著,2001-2016年该河段平滩河槽累计冲刷量近1亿m3.平滩及枯水河槽形态参数计算表明:...