淹没状态下河道植物偏斜高度与糙率的关系

利用室内变坡水槽,模拟了复式河道滩地3种植物对漫滩水流的干扰作用,并借助声学多普勒测速仪(ADV)施测了不同垂线、不同测点的瞬时流速,计算了不同条件下的河道糙率。基于水动力及植物柔性变形分析,建立了淹没状态下的植物河道糙率计算的基本关系,反映出糙率值不仅与水流动力条件有关,还与植物类型、淹没高度、布置及其自身力学性能有关,同时,利用试验资料及理论分析成果,进一步获取了植物河道的附加糙率值,借此分析与评价河道植物对水流阻力的影响程度。     

Impact of the channelization‐induced incision of the Skawa and Wisłoka Rivers,southern Poland,on the conditions of overbank deposition

The impact of river incision in response to channelization on the conditions of overbank deposition is shown by the study of two montane rivers from the upper Vistula drainage basin, southern Poland. The Wisl/oka River had insufficient energy to destroy the river‐control structures and remained laterally stable in the course of the channel downcutting. Under such conditions, the incision has raised the relative elevation of the floodplain above the river bed, thereby reducing considerably the frequency of overbank flows, and increasing concentration of suspended sediment transport within the incised channel. On the high‐energy Skawa, the long periods of incision of the channelized river alternated with the shorter periods of lateral channel migration over the twentieth century. This has led to the formation of an incised meander belt, within which flood flows are constricted, and where the high velocities of the floodplain flows inhibit overbank deposition. Field observations confirm an insignificant role played nowadays by floodplain sedimentation in the valleys of both rivers. This study shows that the potential of the floodplains of the Carpathian tributaries to the Vistula for sediment storage has been dramatically reduced over the few past decades as a result of the channelization‐induced incision of the rivers. The frequency of overbank flows has decreased considerably on the rivers draining the eastern part of the Polish Carpathians, and the majority of the suspended sediment is routed within the resultant enlarged channels. In the western part of the mountains, high velocities of the floodplain flows restrict overbank deposition on the narrow floodplains developed along incised channels. Copyright © 2001 John Wiley & Sons, Ltd.     

Enhanced Channel Division Method for Estimation of Discharge in Meandering Compound Channel

Accurate prediction of shear force distribution along the boundary in open channels is a key to the solution of numerous hydraulic problems. The problem becomes more complicated for meandering compound channels. A model is developed for predicting the percentage of shear force at the floodplain (%S_fp) of two-stage meandering channels using gene-expression programming (GEP) by considering five dimensionless parameters viz. the width ratio, relative depth, sinuosity, bed slope, and meander belt width ratio as the inputs in the model. Basing on the %S_fp, the apparent shear force along the division lines of separation in compound channels is selected for discharge calculation using the conventional channel division methods. An Enhanced Channel Division Method (ECDM) is introduced to calculate discharge by assuming interface line at main channel and floodplain junction. A modified variable-inclined (MVI) interface is suggested having zero apparent shear determined from flow contribution in the main channel and floodplain. The MVI interface is further used to calculate discharge in the meandering compound channels. Performance of the GEP model is tested against other analytical methods of calculating %S_fp. Error between the observed and calculated discharges using the MVI interface is found to be the minimum when compared to other interface methods. The enhance channel division method is successfully applied for validating the two available overbank discharge values for the river Baitarani at Anandapur (drainage area of 8570 sq. km), giving the minimum errors of 0.31% and 1.02% for flow depths of 7.5 m and 8.63 m, respectively.

     

有植被的河道水流紊动特性模型试验研究

通过物理模型试验,研究了有植被的河道水流紊动特性.试验结果表明,在复式断面河道滩地种植柔性植被后,滩地糙率增大,水流紊动更为剧烈,河道水流紊动强度峰值由原先的滩槽交界区转移到滩地区.滩地的水流紊动强度沿程递减;滩槽交界区的水流紊动强度沿程不断增大;主槽的水流紊动强度主要与床面糙率有关,滩地植被影响了滩地水流的归槽时间,使主槽水流流速沿程增大.     

太湖流域平原河网分流比影响因素

以太湖流域典型分汊河道为例,构建河道二维水动力模型,研究平原河网分流比主要影响因素及其作用机理,并运用岭回归建立了平原河网分流比预测方程。结果表明:平原河网分流比与糙率、支汊过水宽度比、水位差呈正相关关系,与干流流量呈负相关关系,与分汊角度关系复杂;干流流量和支汊过水宽度比是影响分流比的主要因素;构建的多因素平原河网分流比综合预测方程可用于预测平原河网分汊河道分流比。     

黄河下游过渡型河段漫滩洪水演进规律探讨

利用黄河下游高村至孙口河段漫滩洪水观测资料 ,分析了过渡型河段漫滩洪水演进规律及其影响因素 .结果表明 :过渡型河段河槽弯曲 ,滩地多、面积大、连通性差 ,在险工、护滩控导工程控制下 ,主槽相对稳定 ,河道横向淤积分布不均 ,主槽冲淤变化大 ,滩地低洼、蓄滞洪能力大 .滩地蓄滞洪能力、主槽排洪能力与不同量级不同类型洪水的不同组合 ,是造成漫滩洪水洪峰流量削减、洪峰形状变形、传播时间变化的主要原因     

黄河下游典型河段滩槽分界二维洪水数值模拟

采用平面二维水沙数学模型,在黄河下游河道现存生产堤条件下,针对典型洪水进行洪水模拟计算研究。通过对黄河下游典型河段的洪水数值模拟,分析研究该区域洪水演进、漫滩及河势变化状况、滩槽流速分布及单宽流量分布,给出滩槽分流比及滩区不同程度的淹没范围。这一研究对于明确滩槽范围、为滩区受洪水灾害补偿提供明确范围、为滩区发展创造良好环境及维持黄河健康生命具有非常重要的意义。     

Multi‐annual contemporary flood event overbank sedimentation within the vegetated lower Orinoco floodplain,Venezuela

Multi‐annual contemporary flood event overbank sedimentation rates were quantified on the World's third largest river in terms of discharge, the tropical lower Orinoco. We discuss the role of variables at the basin and reach scales that contributed to the complexity of spatio‐temporal overbank sediment deposition patterns. Monitored in situ plots were characterized by distance to the main channel, hydroperiod, different geomorphological units, and vegetation cover. Flood event sedimentation rates showed a high spatial variability ranging from the absence of sediment deposition up to 225.46 kg m^‐2 yr^‐1. Banks and levees received relatively high amounts of sediment (39.6 kg m^‐2 yr^‐1), whereas observed mean sedimentation rates on the more distant floodplain and backswamps tended to be lower (17.7 kg m^‐2 yr^‐1). Significant differences in sedimentation rates were observed in two major vegetation types: dense herbaceous and shrubby vegetation (42.2 kg m^‐2 yr^‐1) and floodplain forest (12.7 kg m^‐2 yr^‐1). However, overbank sedimentation patterns also reflected imbricated hydrosedimentary and biogeomorphological vegetation feedbacks that co‐construct fluvial landforms. The incidence of an El Niño–Southern Oscillation–La Niña episode during the study period on sediment availability and floodplain sedimentation suggests that within whitewater rivers, where suspended sediment concentrations are naturally high, hydrological connectivity seems to be more important for floodplain sedimentation than variations in suspended sediment concentrations. These results may provide a good basis for future biogeomorphological investigation projects using complementary methodologies, in order to better anticipate global change and fluctuations in the occurrence, strength or duration of El Niño–La Niña episodes in the tropical zone and their consequences for flood discharge and sediment dynamics during channel–floodplain exchanges.     

Sediment storage and shallow groundwater response to beaver dam analogues in the Colorado Front Range,USA

Enthusiasm for using beaver dam analogues (BDAs) to restore incised channels and riparian corridors has been increasing. BDAs are expected to create a similar channel response to natural beaver dams by causing channel bed aggradation and overbank flow, which subsequently raise water tables and support vegetation growth. However, lack of funding for monitoring projects post‐restoration has limited research on whether BDAs actually cause expected channel change in the Front Range and elsewhere. Geomorphic and hydrologic response to BDAs was monitored in two watersheds 1 year post‐restoration. BDAs were studied at Fish Creek, a steep mountainous catchment, and Campbell Creek, a lower gradient piedmont catchment from May to October 2018. At each restoration site, the upstream‐ and downstream‐most BDAs were chosen for intensive study in comparison with unrestored reference reaches. Monitoring focused on quantifying sediment volumes in BDA ponds and recording changes to stream stage and riparian groundwater. Despite differences in physical basin characteristics, BDA pools at both sites stored similar volumes of sediment and stored more sediment than reference pools. Sediment storage is positively correlated to BDA height and pool surface area. However, BDAs did not have a significant influence on shallow groundwater. The lack of groundwater response proximal to BDAs could indicate that local watershed factors have a stronger influence on groundwater response than restoration design 1 year post‐restoration. Systematic, long‐term studies of channel and floodplain response to BDAs are needed to better understand how BDAs will influence geomorphology and hydrology.     

HYDRAULICS OF COMPOUND CHANNEL WITH VEGETATED FLOODPLAINS

1. INTRODUCTIONThe Pearl River delta is often subject to typhoons and heavy rainfalls. Big waves generated by typhoons cause scouring, even collapsing and breaching of river embankments. Facts have proved that the effectiveness for wind and ship wave prot…     

RESEARCH ON SYSTEM DYNAMICS MODEL OF CONVEYANCE CAPACITY IN SYMMETRIC COMPOUND CHANNELS

Stage-discharge curves are particularly important in river basin management. For a compound channel, the stage-discharge curve is often difficult to be extrapolated to yield estimates of level for a given frequency of flow. By analyzing a large number of experimental data from Science and Engineering Research Council Flood Channel Facility (SERCFCF) and applying system dynamics method, the authors established system dynamics model of conveyance capacity when rivers flow in an overbank mode, spilling onto the adjoining flood plain. The model was applied to a compound channel. And the corresponding simulated results are shown to attain high accurcy.     

淤滩与刷槽之间没有必然的联系

实测资料与动床摸型试验均表明,在洪水过程中淤滩与刷槽虽然同时发生,但它们之间并没有必然的联系。在多沙河流上洪水漫滩必然会造成滩地淤积,并在滩唇形成自然堤,阻断滩槽水流交换;主槽的冲刷发生在涨水期,在落水期不管含沙量大小,河床均处于淤积状态。漫滩后的清水在滩地上流动缓慢,远远小于主槽水流的运动速度,因此漫滩水往往在落水期才能汇入主槽,且只能起到减少主槽淤积的作用,无法改变由于洪水的非恒定性形成的落水期河床必然淤积的状态。实测资料表明,含沙量100~200 kg/m3的不漫滩洪水在涨水期仍可造成主槽的强烈冲刷。     

Hydraulic effects of aquatic weeds in U.K. rivers

The effects of large aquatic plants (aquatic macrophytes) have been given limited attention in literature dealing with open channel flow. This is despite a large number of river channels in the U.K. being affected by profuse growths of these plants. This paper contributes to three major areas in relation to aquatic macrophytes and river channels. First, a literature review examines four areas of vegetated channel research. Early work on vegetated channels concentrated upon grass-lined farm drainage channels in the U.S.A. This was complemented by flume studies of predominantly artificial vegetative roughness elements. The review discusses research into large aquatic plants in stream channels, and the discussion draws together a number of disparate areas of research into vegetated channels including theoretical considerations. Secondly, the paper discusses results obtained from laboratory flume experiments, using real plants, and field monitoring on the River Ebble, Wiltshire, U.K. The relationship between discharge and Manning's roughness coefficient (n) is examined. Field monitoring results are presented as generalizations in the relationship between Manning's n when the monitoring sites were vegetated and unvegetated. The relationship between plant cover in the channel and Manning's n is also examined. Two measurements of plant cover are employed: the percentage cross-sectional area of channel vegetated, and biomass per unit area. The field data for Manning's n and discharge are then discussed in detail in a case study of one site on the River Ebble. Finally, the results obtained from field monitoring are compared to previous research. In the light of these comparisons and detailed examination of the field and flume data, a conceptual model of the effects of aquatic plant growth on channel roughness, mean flow depth, and flow stage is represented. Using this model, an estimate can be made of the likely effect of changing plant cover and discharge on flow stage in an open channel.     

Numerical simulation of overbank flood discharges

A full computer based investigation of the factors influencing the modelling of overbank flood discharges has been carried out. Several floods of differing magnitudes and peak curvatures were routed down regular channels using an implicit finite difference scheme and the influence of time and distance steps used for the numerical solution of the flow equations were investigated. Spillage over sharp crested weirs was assumed to satisfactorily simulate the overbank flood discharge; the importance of a correct estimation of the coefficient of discharge was also checked. It was shown that sensibly chosen values of the time step had little effect on the simulations. This was also true for the value of the coefficient of discharge when the sideweir flow was predominately drowned, but not for free flow conditions. It was also shown that close spacing of computational nodes was required at the onset of overbank flow to accurately simulate the overflow and also model the occurrence of large water level gradients.     

Lithological controls influence river form in contrasting sub-catchments: The Scamander and Avenue Rivers,Tasmania

Bedrock influence on river channel form is difficult to assess, with many catchments dominated by glacial erosion and with blanketing sediments from both pluvial and fluvial sources. The Scamander catchment in Tasmania lacks glacial history and features two bedrock-confined sub-catchments of similar area and maximum flow length, but one dominated by Mathinna Group sedimentary rocks, and the other with large areas in granite lithology. Lithology types, stream network parameters and near stream slope angles were analysed using geographical information systems, and results of stream cross sections, channel form and planforms were compared for each lithology. Results showed that granite features low gradient, shallow streams with channel slope cross sections of <10°. Granite channels are irregular and dominated by large boulders that create channel roughness and resist incision. Weathering products of coarse quartz sand provide anchorages for in-channel vegetation. By contrast, sedimentary Mathinna Group rocks feature steeply incised trough-like channels, with near-channel hillslope gradients mostly between 30° and 50°. Rectangular blocks disintegrate to gravel cobbles on the channel bed, providing poor anchorage for vegetation. Mathinna lithology influences steep, low roughness channels, and stable, incised recurved meanders formed by river interaction with vertical layers of resistant rock. The resistant bedrock lithology is demonstrated in this study to influence varied river planforms, near-channel slope gradients, channel sediments and cross sections.     

Depositional response of a headwater stream to channelization,East Central Illinois,USA

Channelization typically modifies the energy regime and sediment transport capacity of rivers, triggering morphologic adjustments. Most past studies of channelization have focused on erosional responses involving channel incision and widening. Depositional adjustments to channelization, although noted in previous work, have not been documented in detail. This study investigates the depositional response of the Spoon River, a headwater agricultural stream in Illinois, USA, to channelization. Historical aerial and ground‐based photography show that channelization of the Spoon River in the early 20th century produced a wide, deep trapezoidal drainage channel. Following this channelization, unvegetated alternate and mid‐channel bars developed on the bottom of the ditch. Sedimentological analysis of bar stratigraphy indicates that the bars grew through vertical accretion of horizontal sheets of sand‐and‐gravel bedload and organic‐rich drapes of fine‐grained suspended load. The horizontal sheets of sand and gravel are consistent with the braided conditions shown on historical photographs. Late‐stage bar growth appears to have been dominated by progressive overbank deposition of suspended load as indicated by the presence of a thick, fine‐grained organic‐rich A horizon immediately below the surface of each bar. The development of a soil layer also suggests that the bars are stable—an inference supported by the thick grass cover on the bar surfaces. The net result of the depositional response is the formation of a meandering channel flanked by a discontinuous floodplain on the bottom of the ditch. The construction of a wide ditch relative to original stream size is a key factor promoting a depositional response to channelization. Allowing or actively promoting floodplain elements to form in overwidened ditches may be a viable management option for improving the environmental quality of channelized agricultural streams. The Spoon River has a diverse fish community compared to channelized streams in East Central Illinois that lack a meandering low‐flow channel. This morphological configuration apparently enhances geomorphological and ecological variability while sustaining the drainage function of the ditch. Copyright © 2003 John Wiley & Sons, Ltd.     

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.     

植被作用下的复式河槽漫滩水流紊动特性

分别选取塑料吸管、鸭毛和塑料大草模拟乔木、灌木和野草，通过水槽试验，探讨了不同滩地植物作用下的浸滩水流紊动特性。试验结果表明，纵向、横向和垂向三个方向的脉动流速基本满足正态分布；时均流速与采样时间的长短有关；横向动量交换比垂向动量交换大，横向动量基本上是主槽向滩地传递；不同的滩地植物对水流的紊动强度的影响不同。滩地种植植物后，水流的紊动强度增强。纵向和垂向的紊动强度相当，都服从S型分布。     

FISH RECRUITMENT IS INFLUENCED BY RIVER FLOWS AND FLOODPLAIN INUNDATION AT APALACHICOLA RIVER,FLORIDA

High human demand for limited water resources often results in water allocation trade‐offs between human needs and natural flow regimes. Therefore, knowledge of ecosystem function in response to varying streamflow conditions is necessary for informing water allocation decisions. Our objective was to evaluate relationships between river flow and fish recruitment and growth patterns at the Apalachicola River, Florida, a regulated river, during 2003–2010. To test relationships of fish recruitment and growth as responses to river discharge, we used linear regression of (i) empirical catch in fall, (ii) back‐calculated catch, via cohort‐specific catch curves, and (iii) mean total length in fall of age 0 largemouth bass Micropterus salmoides, redear sunfish Lepomis microlophus and spotted sucker Minytrema melanops against spring–summer discharge measures in Apalachicola River. Empirical catch rates in fall for all three species showed positive and significant relationships to river discharge that sustained floodplain inundation during spring–summer. Back‐calculated catch at age 0 for the same species showed positive relationships to discharge measures, but possibly because of low sample sizes (n = 4–6), these linear regressions were not statistically significant. Mean total length for age 0 largemouth bass in fall showed a positive and significant relationship to spring–summer discharge; however, size in fall for age 0 redear sunfish and spotted sucker showed no relation to spring–summer discharge. Our results showed clear linkages among river discharge, floodplain inundation and fish recruitment, and they have implications for water management and allocation in the Apalachicola River basin. Managed flow regimes that reduce the frequency and duration of floodplain inundation during spring–summer will likely reduce stream fish recruitment. Copyright © 2012 John Wiley & Sons, Ltd.     

CES模型计算复式河槽过流能力及方法对比

复式河槽的洪水漫滩后,滩槽水流相互作用,在滩槽交界处形成动量交换,若直接采用曼宁公式进行水力计算将产生很大误差。应用CES(Conveyance Estimation System)模型首先计算了不同复式河槽的垂线平均流速,并结合英国科学工程研究理事会洪水水槽设备(SERC-FCF)的试验资料进行了验证,进而分析了不同形态复式河槽的水流特性;然后通过对比分析CES模型与经验方法(湿周修正法、断面分割法)和理论方法(谢汉祥法、刘沛清法、河槽协同度法)计算流量时的精度,论证了该模型在复式河槽水力计算中的优越性。结果表明,由CES模型计算的断面垂线平均流速分布符合复式河槽的水流特性且与实测资料吻合良好,较之其他模型方法,该模型能适用于任意形态复式河槽的流量计算且精度较高。