长江河口上边界床沙粒径的长期变化及其原因

大通水文站和泥沙观测断面位于长江河口的上边界。长江下游从大通（潮区界）至长江口门的距离长达680 km。20世纪80年代以来,长江流域日趋强烈的人类活动,显著改变了长江入海水文和泥沙数量和特性,从而对长江下游至河口动力地貌和动力沉积产生了显著影响。主要研究长江潮区界大通断面20世纪50年代以来床沙粒径的长期变化。1977~2004年床沙粒径 (〖WTBX〗d〖WTBZ〗50) 有一稳定增大的趋势,这主要是对上游河道悬沙来量持续减少的响应。值得注意的是床沙粗化过程是发生在该河床长期加积的背景上的。研究表明：导致床沙粒径粗化的原因,主要是上游河段进入本河段床沙粒径的增加和本河段冲淤过程中悬沙与床沙颗粒的交换。随着三峡水库的正常运行和其它大型水库的建设,预计未来几十年长江上游悬沙来量将进一步大幅度下降,可以预计,长江潮区界河段的床沙粒径将继续呈现增大的趋势。〖     

葛洲坝水利工程对长江中游生态水文特征的影响

为了满足人类社会经济发展要求而修建的水利工程,不可避免地对生态环境造成了巨大影响。从生态水文学角度对长江中游的生态水文特征进行了研究。借鉴国外已有的研究成果,建立了一套指标体系包括长期指标、高流量指标、低流量指标、平均变化指标、涨水落水指标和月流量指标,通过分析指标的变化来评价水利水电工程对生态环境的影响。长江中游是最重要的家鱼自然繁殖区,利用建立的指标体系量化并分析了葛洲坝建坝前后长江中游的生态水文特征变化。分析认为,葛洲坝的修建主要影响涨水落水,对其它生态水文特征影响不大;对于鱼类,涨水过程是刺激鱼类产卵的必要条件,葛洲坝的修建对鱼类产卵造成了一定影响。     

Undamming Rivers: A Review of the Ecological Impacts of Dam Removal

Dam removal continues to garner attention as a potential river restoration tool. The increasing possibility of dam removal through the FERC relicensing process, as well as through federal and state agency actions, makes a critical examination of the ecological benefits and costs essential. This paper reviews the possible ecological impacts of dam removal using various case studies. Restoration of an unregulated flow regime has resulted in increased biotic diversity through the enhancement of preferred spawning grounds or other habitat. By returning riverine conditions and sediment transport to formerly impounded areas, riffle/pool sequences, gravel, and cobble have reappeared, along with increases in biotic diversity. Fish passage has been another benefit of dam removal. However, the disappearance of the reservoir may also affect certain publicly desirable fisheries. Short-term ecological impacts of dam removal include an increased sediment load that may cause suffocation and abrasion to various biota and habitats. However, several recorded dam removals have suggested that the increased sediment load caused by removal should be a short-term effect. Preremoval studies for contaminated sediment may be effective at controlling toxic release problems. Although monitoring and dam removal studies are limited, a continued examination of the possible ecological impacts is important for quantifying the resistance and resilience of aquatic ecosystems. Dam removal, although controversial, is an important alternative for river restoration.     

剑潭大坝对东江惠州河段浮游植物的影响研究

根据2006年4月、8月和12月月初的采样调查,对剑潭大坝蓄水前后浮游植物种类、组成在时间和空间上的变化进行研究,并探讨富营养化要素对浮游植物结构和数量的影响。结果表明,剑潭大坝下闸蓄水后：（1）浮游植物的数量和结构发生了一定的变化。3年期间,总物种数呈现下降趋势;剑潭大坝处采样点浮游植物群落结构变化明显;（2）季节性变化明显,丰水期以蓝藻为优势,枯水期以蓝藻绿藻共同占据优势;（3）在剑潭大坝正常运行一年后,剑潭大坝处叶绿素a显著增加,浮游植物现存量出现一个峰值,这反应了偏高的营养盐含量为浮游植物的生长创造了有利条件。最后作者针对剑潭大坝蓄水后的负面影响,提出了有关防治措施与建议。     

Evaluation of the efficiency of some sediment trapping methods after a Mediterranean forest fire

Forest fires are common in Mediterranean environments and may become increasingly more frequent as the climate changes. Destruction of the forest cover and litter layer leads to greater overland flow and increased erosion rates. The greatest risk occurs during the first rainstorms following a major fire, so local authorities must act quickly to put erosion control methods in place in order to avoid excessive post-fire sediment loads in river channels. Deciding on which methods to use requires accurate knowledge of their impact on sediment load and an estimate of their cost efficiency. The objective of this study was to evaluate the efficiency of Log Debris Dams (LDDs) and a sedimentation basin for their effectiveness in trapping sediments. Paired sub-catchments were studied to quantify the amount of sediments trapped in stream channels by a series of LDDs and a sedimentation basin. Cost efficiency was evaluated for each of the measures as a function of the cost per unit volume of sediments trapped. In addition, grain size analyses were performed to characterise the nature of the sediments trapped. A third sediment trapping method, Log Erosion Barriers (LEBs) was evaluated more superficially than the first two and conclusions regarding this method are tentative. LDDs trapped a mean volume of 1.57 m³ per unit (median = 1.28 m³); mean LDD height was 105.4 cm (std. dev. = 21.9 cm), and mean height of trapped sediments was only 50.0 cm (std. dev. = 22.9 cm), showing that the traps were only half filled. Sediment height was limited by the presence of gaps between logs or branches that allowed runoff to flow through. Comparison of the textural characteristics of slope and trapped sediments showed distinct sorting: particles greater than 20 mm were not mobilised from the slopes during the study period, sediments in the medium to coarse sand size fractions were trapped preferentially by the LDDs, and sediments in the sedimentation basin were enriched by clay and silt sized (<0.050 mm) particles as coarser sediments were trapped upstream by the LDDs. Cost efficiency of LDDs was estimated at about 143 € m⁻³ for the LDDs and 217 € m⁻³ for the sedimentation basin at the time of sampling. The LDDs are therefore a cost effective method of trapping sediments, but they can only be used when pine trees or straight-trunked trees are locally available. In this case, they should be combined with LEBs, which had a cost efficiency estimated at about 250 € m⁻³. Installation of the LEBs had not been optimised and they have the advantage of trapping sediments on the slopes where they can continue to play an ecological role, so this method can give better results with more care. Sedimentation basins can be emptied if necessary and are useful in areas where pine trees are not available and where the site can be secured.     

Interactions between scientific uncertainty and flood management decisions: Two case studies in Colorado

Flood management policies in the United States rely on scientific information about the frequency and intensity of extreme precipitation and runoff. Yet, the available information is inherently uncertain because of the complexity of meteorological and hydrological processes. In mountainous areas, flood risk can vary greatly even within short distances depending on local climate, topography, soil characteristics, and land use. This paper describes two Colorado cases in which policy makers were presented with conflicting scientific estimates: revision of the Fort Collins floodplain map and modification of the Cherry Creek Dam. The case studies demonstrate that uncertainty can have substantial impacts on regulatory processes, public safety, and costs. The analysis considers the differing perspectives of various participants in the flood management processes, illustrating the interplay between uncertainties attributable to scientific issues and values issues. It suggests that attempts to provide a single “best” estimate do not necessarily meet the decision needs of all stakeholders. Conclusions indicate a need to improve communication about uncertainty when scientific estimates areprovided to decision makers. Furthermore, in highly controversial decisions, it may be necessary to reframe the discussion to consider the values issues raised by scientific uncertainty.     

Political benefits as barriers to assessment of environmental costs in Brazil's Amazonian development planning: The example of the Jatapu Dam in Roraima

Development projects are rapidly changing the landscape in Brazilian Amazonia. Environmental impact assessments have been required since 1986, and the regulatory system is evolving as precedents are set by each new development project. The Jatapu Dam in Roraima provides an illustration of underlying impediments to assessment of environmental costs and to due consideration being given to these assessments when decisions are made. The high priority placed on the dam by the Roraima state government is unexplainable in terms of economic returns. The place of the dam in a long-term political strategy provides the best of several possible explanations, any one of which is incompatible with a rational weighing of economic and environmental costs and benefits. A number of lessons can be drawn from the experience of Jatapu, but some of the problems have no solution. The barriers to rational decision making illustrated by Jatapu apply to development projects in many parts of the world.     

国外私人水坝安全管理政策及其对我国的启示

小型水坝数目多 ,分布广 ,安全管理困难。笔者研究了西方发达国家的私人水坝管理政策的基本准则、主要内容、管理方案的选取等问题 ,并针对我国处于产权市场化改革的水利工程的安全管理问题提出了几点具体建议     

三峡库区小江支流沉积物硝化反硝化速率在蓄水期和泄水期的特征

三峡库区是新形成的生态系统,沉积物特征较之成库前有显著改变;研究库区小江支流——南河沉积物的硝化与反硝化过程可以为库区氮素管理提供科学依据,而反季节蓄水和泄水,沉积物-水界面硝化与反硝化速率特征鲜见报道.实验选取库区开县南河沉积物为研究对象,在2015年泄水期(8月)和蓄水期(11月)采集上、下游以及南河与小流域菁林溪交汇处沉积物样品,测定其理化指标;同时通过实验室模拟沉积物水环境,以乙炔抑制法测定泄水期与蓄水期沉积物的硝化反硝化速率.结果表明,蓄水期沉积物总氮(total nitrogen,TN)、铵态氮(ammonium nitrogen,NH_4~+-N)、硝态氮(Nitrate nitrogen,NO_3~--N)及总有机碳(total organic carbon,TOC)等理化指标均显著高于泄水期(P0.05),这说明蓄水期有外源物质入库;沉积物硝化速率在蓄水期[194.06μmol·(m~2·h)~(-1)]显著高于泄水期[16.52μmol·(m~2·h)~(-1)],且硝化速率与沉积物理化特征(TN、NH_4~+-N、NO_3~--N、TOC)存在显著正相关;沉积物反硝化速率则与硝化速率相反,泄水期[647.20μmol·(m~2·h)~(-1)]高于蓄水期[24.04μmol·(m~2·h)~(-1)],其与沉积物理化指标(TN、NH_4~+-N、NO_3~--N)呈显著负相关.