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。     

Bank‐derived material dominates fluvial sediment in a suburban Chesapeake Bay watershed

Excess fine sediment is a leading cause of ecological degradation within the Chesapeake Bay watershed. To effectively target sediment mitigation measures, it is necessary to identify and quantify the delivery of sediment sources to local waterbodies. This study examines the contributions of sediment sources within Upper Difficult Run, a suburbanized watershed in Fairfax County, Virginia. A source sediment library was constructed from stream banks, forest soils, and road dust. Target sediments were collected from fine channel deposits and suspended sediment during 16 storm events from 2008 to 2012. Apportionment of targets to sources was performed using Sed_SAT, a publicly available toolkit for sediment fingerprinting. Bed sediment was dominated by stream bank material (mean: 98%), with minor contributions from forests (2%). Suspended fine sediments were also dominated by stream banks (suspended sediment concentration‐weighted mean: 91%), with minor contributions from roads (8%) and forests (<1%). Stream banks dominated at all discharges, and on the rising limb and at peak flow, sediment concentrations increased due to bank material rather than surface erosion. Sediment budget data indicated that direct bank erosion was insufficient to account for the suspended load derived from stream banks. However, bank‐derived sediment re‐mobilized from in‐channel storage could account for this difference and, combined, resulted in a sediment delivery ratio of 0.847 for all bank‐derived sediments. Results demonstrate that stream bank erosion is responsible for the majority of fine sediment in this suburban watershed of the Chesapeake Bay drainage area. Thus, management actions to control upland sources of sediment may have limited effect on the sediment conditions of Upper Difficult Run, whereas efforts focusing on bank stabilization, channel restoration, and/or stormwater management to reduce bank erosion may improve the ecological condition of these waterbodies.     

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。     

Effect of fine sediment deposition and channel works on periphyton biomass in the Makomanai River,northern Japan

The Makomanai River in northern Japan has suffered considerable fine sediment deposition, especially in a reach where channel works have been constructed. Four contiguous reaches were examined for deposition of fine sediment and the effects of such on periphyton biomass; two of the reaches had channel works and bank protection, respectively, the other two being unmodified. The influence of fine sedimentation on epilithic periphyton biomass (chlorophyll a weight and organic matter weight) and the autotrophic index (AI), and the relationship between these and hydraulic variables was emphasized. Fine sediment increased, chlorophyll a decreased and AI increased in the reach with channel works and in the unmodified reach immediately upstream. In addition, the current velocity and Froude number tended to decrease in the reach with channel works. Correlation analysis showed that with an increase in fine sediment, chlorophyll a decreased and non‐living periphyton, indicated by AI, increased. It was also confirmed that fine sediment increased with an increase in weight of periphyton organic matter and decreased with an increase in current velocity or Froude number. These results suggest that accumulation of fine sediment, which substantially reduces light penetration for photosynthesis under low current velocity conditions, results in lowered periphyton levels. The channel works have lowered the current velocity, thus promoting deposition of fine sediment and an increase in non‐living periphyton. Copyright © 2002 John Wiley & Sons, Ltd.     

细颗粒原状土起动流速试验研究

为了得到更为客观科学的泥沙基本活动规律,利用有压矩形管进行了细颗粒泥沙起动试验。试验结果表明,管内水压力对细颗粒泥沙的起动有重要影响,水压力越大,管中泥沙起动断面平均流速和起动切应力越大。根据有压矩形管的水流分布特性和水压特点,将矩形管中水流转换为普通明渠水流,转换得到的明渠中泥沙起动垂线平均流速与试验矩形管中泥沙起动断面平均流速基本相同,验证了利用有压矩形管进行细颗粒泥沙起动流速试验的可行性和代表性。在试验矩形管与实际明渠的泥沙起动流速转换过程中,并未考虑不同水柱高度下曼宁糙率系数的变化,这方面还有待进一步研究。     

黄河宁蒙河段冲淤演变特点及趋势分析

通过分析黄河宁蒙河段冲淤演变及河槽过洪能力变化,进一步认识宁蒙河段冲淤演变规律,并根据下河沿水文站设计水沙条件,估算宁蒙河段2020年、2030年的冲淤变化趋势。分析表明:近期宁蒙河段输沙能力降低,巴彦高勒、三湖河口、昭君坟断面平滩流量呈减小趋势,河道淤积加重,支流淤堵干流情况加重。根据下河沿设计水沙条件推算头道拐水沙量以及区间引沙量,采用沙量平衡法,考虑区间支流来沙、区间风沙入黄情况,预估下河沿～头道拐冲淤量,2020年水平,宁蒙河段年均淤积0.78亿t;2030年水平,宁蒙河段年均淤积0.80亿t。     

Downstream effects of diversion dams on sediment and hydraulic conditions of Rocky Mountain streams

Reduced streamflow via flow diversion has the potential to limit the sediment‐transport capacity of downstream channels and lead to accumulation of fine sediments and habitat degradation. To investigate, we examined the effects of variable levels of flow diversion on fine‐sediment deposition, hydraulic conditions and geomorphic alteration. Our study consisted of a detailed field analysis pairing reaches above and below diversion dams on 13 mountain streams in north‐central Colorado and southern Wyoming USA. Diversions are ubiquitous across the American West, yet previous comparative studies on the effects of flow diversion have yielded mixed results. Through application of strict site‐selection criteria, multiple fine‐sediment measures, and an intensive sampling scheme, this study found that channels downstream of diversions contained significantly more fine sediment and slow‐flowing habitat as compared to upstream control reaches. Susceptibility to fine‐sediment accumulation was associated with decreasing basin size, decreasing bankfull depth and smaller d₈₄, and it appears to be magnified in streams of less than 3% slope. Copyright © 2010 John Wiley & Sons, Ltd.     

Reach‐scale interactions between aquatic plants and physical habitat: River Frome,Dorset

Substrate and flow velocity are two key physical factors influencing the distribution of aquatic plants. These two controls are closely related and reflect interactions between flow regime, quantity and calibre of sediment supplied to and bounding river channels, and channel dimensions. Seasonal growth of aquatic plants has important impacts upon flow resistance, flow velocities and sediment dynamics. This paper focuses upon the reach scale and the aggregate impact of the seasonal growth of aquatic plants on the meso‐habitat characteristics of chalk rivers. It provides a contribution to the broader literature by illustrating how submerged and emergent macrophytes interact with one another at the reach scale to control flow patterns and the retention of fine sediment. The research was conducted within the River Frome, Dorset, UK. Four sets of observations from 2004 of the seasonal growth of aquatic plants, flow velocity behaviour and the storage of fine sediment are presented. Aggregate velocity behaviour over the four observation periods is classified using agglomerative, hierarchical cluster analysis. The spatial arrangement of patches exhibiting different aggregate velocity behaviour are explored and the degree to which velocity behaviour can be attributed to physical characteristics of patches and the growth of aquatic plants is discussed. Conclusions include: (i) patterns of aggregate velocity behaviour within reaches are strongly influenced by macrophyte growth; (ii) average fine sediment deposition is higher around emergents such as Sparganium erectum than submerged plants such as Ranunculus penicillatus subsp. pseudofluitans; (iii) complementary flow patterns evolve across the river channel as aquatic macrophytes grow and it appears that this allows marginal emergents to scavenge fine sediment from faster flow velocity threads that become diverted towards the channel edges. (iv) These processes are important for mesohabitat evolution and maintenance, and they also contribute to patterns of bank erosion and aggradation. Copyright © 2006 John Wiley & Sons, Ltd.     

新水沙条件下黄河下游泥沙均衡配置方案

由于自然气候条件的变化和人类活动的影响,黄河下游的来沙量大幅减少,为了维护黄河下游河槽均衡稳定、治理"二级悬河",合理利用泥沙资源,开展黄河下游泥沙均衡配置研究。采用黄河下游泥沙均衡配置数学模型,按照新水沙条件和配置模式,计算了黄河下游泥沙均衡配置方案,计算结果表明,来水来沙条件对泥沙配置状况的影响较大,一般年来水量约260亿m3条件下,如果年来沙量少于4亿t左右,黄河下游河槽不淤积萎缩,修建防护堤对增大平滩流量有一定作用,滩区放淤可以改善泥沙分布状况。通过对各配置方案综合评价,提出了建议方案及不同配置方式的泥沙配置比例。     

黄河干流泥沙分布状况及存在问题

利用实测资料系统分析了1950.7-2005.6不同时期黄河干流泥沙分布特点。通过上游宁蒙河段河道冲淤量、主槽平滩流量,中游龙潼河段河道冲淤量、潼关高程、三门峡水库拦沙量、小浪底水库拦沙量,下游主槽冲淤量、滩地冲淤量、主槽平滩流量、二级悬河状况、以及出口断面沙量等参数的变化,综合分析了不同时期不同来水来沙条件下,黄河干流泥沙分布引起的问题。提出了有利于减轻黄河干流泥沙淤积灾害的建议。     

Geomorphic applications of stream‐gage information

In the United States, several thousand stream gages provide what typically is the only source of continuous, long‐term streamflow and channel‐geometry information for the locations being monitored. In this paper, the geomorphic content of stream‐gage information, previous and potential applications of stream‐gage information in fluvial geomorphic research and various possible limitations are described. Documented applications include studies of hydraulic geometry, channel bankfull characteristics, sediment transport and channel geomorphic response to various types of disturbance. Potential applications include studies to determine the geomorphic effectiveness of large floods and in‐stream habitat change in response to disturbance. For certain applications, various spatial, temporal and data limitations may render the stream‐gage information of limited use; however, such information often is of considerable value to enable or enhance geomorphic investigations. Published in 2008 by John Wiley & Sons, Ltd.     

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。     

黄河下游泥沙沉积汇对入海悬移质泥沙粒度的影响

黄河下游泥沙沉积汇在黄河流域系统的泥沙收支平衡(Sediment budget)中起着重要的作用。通过河床主槽中泥沙的淤积和冲刷,运动泥沙的组成发生变化;通过滩地上泥沙淤积和河岸坍塌,河漫滩上前期淤积的泥沙与洪水所挟带的泥沙发生交换,使悬移质泥沙的组成发生变化。泥沙冲淤量对不同粒径组入海泥沙百分比的影响是不同的。小于0.01mm细泥沙的百分比与下游河道淤积量呈正相关,0.025~0.05mm和大于0.05mm的较粗泥沙的百分比与下游河道淤积量呈负相关。入海泥沙平均粒径与深泓年摆幅之间也存在着负相关关系。自20世纪60年代,中期以来,特别是自80年代中期以来,由于黄河下游径流量显著减小,黄河下游河道发生萎缩,河宽减小,因而主流线的摆动幅度也显著减小。这使得原来十分强烈的河岸侵蚀和滩槽泥沙交换强度大为减弱,主槽洪水得到的来自河岸侵蚀的细粒泥沙越来越少,因而使入海泥沙粒径变粗。     

塔里木河河槽形态调整特点及影响因素Symbol`@@

为确定塔里木河干流河槽形态调整过程及特点,根据2005—2013年实测水沙数据及断面资料等,分析了塔里木河河槽形态演变特点及影响因素。结果表明:2005—2009年中上游河段河槽逐渐萎缩,平滩面积总体呈下降趋势;2010—2013年汛期水流冲刷强度增大,游荡型河段平滩河槽形态主要体现为横向调整,断面趋于宽浅,过渡段相对稳定,弯曲型河段汛期水流冲刷强度变化趋势与游荡型河段一致,期间平滩河宽变化较小,断面朝窄深方向发展;2009—2011年游荡型河段和过渡段纵比降减幅分别为1.7%和3.0%,河床比降趋于调平,弯曲型河段纵比降增幅为1.6%,河床略微冲刷;水流冲刷强度能够较好地响应河槽形态变化,可用于预测塔里木河平滩河槽形态冲淤情况。中上游河岸土体在近岸水流作用下容易分解,稳定性差,在一定程度上加快了河床调整过程。     

浑水淤积层的防渗性能分析

浑水中含有较多的细小颗粒,在水库渗漏过程中,泥沙逐渐沉积、下渗,在库底形成一弱透水的淤积层,且浑水入渗对库底地层起到充填挤压、渗透固结和改良作用,提高原地层的密实度,降低库盆的渗漏。经对多个水库的实例分析研究表明:一定厚度的浑水淤积层,能够改善库底地层结构,提高抗渗透能力,减小渗漏量,可作为提高库底抗渗性能的工程措施。     

三峡工程运用后宜枝河段平滩流量调整特点

三峡水库蓄水运用后,清水下泄使得坝下游宜枝河段发生显著冲刷,河道过流能力也相应调整。宜枝河段(包括宜昌及宜都两河段)断面形态复杂,且过流能力沿程差异较大,河段平均的平滩流量更能反映其综合过流能力。采用基于对数转换的几何平均与断面间距加权平均相结合的方法,分别计算了宜昌及宜都河段2002—2013年各年汛后的平滩流量,分析了河床冲淤变化对河段平滩流量的影响,同时还建立了两河段平滩流量与前5 a汛期平均水流冲刷强度的经验关系。结果表明当河段冲刷时,平滩流量增大,反之则减小;宜昌河段平滩流量与水流强度相关性系数较低,为0.64,而在宜都河段为0.94,表明宜都河段对上游水沙条件变化的响应较宜昌河段更为显著。     

水库淤积控制与功能恢复研究进展与展望

世界上几乎所有水库都面临着泥沙淤积问题,淤积造成水库功能性、安全性和综合效益的降低已成为亟待解决的技术难题。已建水库的库容长期保持和可持续利用,以及已淤损库容的有效恢复,已成为解决水资源短缺的一种重要途径。本文简要介绍了近年来国内外在水库淤积基础研究方面的进展,从减少入库泥沙、水动力减淤和淤损库容恢复三个方面论述了水库淤积控制与功能恢复技术。未来需要加强水动力和人工措施共同作用下水库泥沙运动过程研究,研发淤损水库库容恢复及淤积物处理利用技术,建立水库功能影响评价模型,提出不同类型区水库功能恢复措施及策略。     

三峡库区细沙输移运动状态的水槽试验研究

三峡库区内淤积泥沙均属细颗粒泥沙范畴,运动规律较为复杂。依靠传统泥沙理论即以挟沙力为判断标准,所得冲淤情况与实际观测情况有所出入,需进行进一步研究。在三峡库区典型淤沙河段——皇华城河段现场观测的基础上,通过水槽试验研究库区细颗粒泥沙的运动特点,对不同水深流速下细颗粒泥沙的运动状态进行归类整理,发现其淤积过程可根据水深与流速的不同划分为3个区域,即冲刷区、相对平衡输送区及淤积区,并指出用流速作为判断细沙输移状态的标准更符合库区实际冲淤情况。     

以水流挟沙力和河床演变规律研究调水调沙的主要水沙指标

冲积性河流的河床在输水输沙过程中,调节流量及含沙量和泥沙组成(调水调沙)可以调节河床水力几何形态和水流挟沙力,追求水沙输运和河床演变的相对平衡。在分析水流挟沙力和河槽水力形态规律的基础上,研究调水调沙的流量、含沙量等主要水沙指标,可以解决河道输沙减淤和河槽相对稳定问题。     

SEDIMENT TRANSPORT AND FLOW DYNAMICS AROUND A RESTORED POOL IN A FISH HABITAT REHABILITATION PROJECT: FIELD AND 3D NUMERICAL MODELLING EXPERIMENTS

Few studies have examined sediment transport patterns around in‐stream structures used to enhance fish habitat despite the importance of this variable in the successful design of stream restoration schemes. The objective of this study is to examine interactions between the (excavated) pool morphology, flow and sediment transport in a restored reach of the Nicolet River (Quebec, Canada). Bedload transport was investigated using passive integrated transponder (PIT) tagged particles that were followed from positions upstream of a pair of current deflectors which were designed to maintain the excavated pool downstream. Three‐dimensional numerical simulations of the flow field at various flow stages (with emerged or submerged deflectors) were used to relate near‐bed velocity and bed shear stress to transport patterns and to assess the impact of varying the pool location and geometry on the flow field and water surface profiles. Results show that from 2005 to 2008, of the 117 pit‐tagged particles that fell in the pool, only 27 are known to have exited. None of the 30 largest rocks entering the pool escaped. Bed shear stress values simulated at high and peak flow (slightly above bankfull level) are not sufficient to move the largest rocks in the pool exit zone. Simulations also reveal a complex water surface topography when flow is above the height of deflectors, with negative water surface slope in the pool zone. When modifying the pool geometry so that the deepest zones are close to the apex of the in‐stream structures instead of in the centre of the channel, both water surface slope and near‐bed velocity patterns are greatly modified. Understanding the interactions between excavated pools, bedload and 3D velocity patterns around in‐stream structures is essential for long‐term success of fish habitat restoration projects, and using 3D models to test various designs of artificial pools is a promising approach. Copyright © 2011 John Wiley & Sons, Ltd.