Vegetation community response to hydrologic and geomorphic changes following dam removal

Dam removal can restore fish passage, natural flow regimes, sediment transport in streams, dispersal of organic matter, and drift of aquatic insects. However, dam removal also impacts the riparian vegetation, with both immediate and delayed responses. In this study, we measure vegetation change at the Merrimack Village Dam site on the Souhegan River in Merrimack, NH, USA. The August 2008 removal caused a ~3‐m drop in water level and rapid erosion of impounded sediment, with ~50% removed in the first 3 months. Terrace, floodplain, and wetland communities were surveyed in summer 2007, 2009, 2014, and 2015. Temporal change was quantified using Analysis of Similarity on the Bray–Curtis dissimilarity matrix. Only herbaceous vegetation closest to the river channel and in the off‐channel wetland changed significantly. The herbaceous plots directly adjacent to the impoundment eroded to bare sand in 2009, but by 2014, the original riparian fringe community had re‐established in the newly developed floodplain. Between 2007 and 2014, the off‐channel wetland area changed from aquatic species to a stable terrestrial community that persisted without significant change in 2015. The vegetation response was greatest in areas with the largest geomorphic and hydrologic change. These included the channel margin where erosion and bank slumping created an unstable scarp. The mid‐channel island and off‐channel wetland were strongly affected by the lowered water table. However, large unvegetated areas never persisted nor did the areal coverage of invasive species expand, which are two frequent concerns of dam removal stakeholders.     

Effects of dam removal on brook trout in a Wisconsin stream

Dams create barriers to fish migration and dispersal in drainage basins, and the removal of dams is often viewed as a means of increasing habitat availability and restoring migratory routes of several fish species. However, these barriers can also isolate and protect native taxa from aggressive downstream invaders. We examined fish community composition two years prior to and two years after the removal of a pair of low‐head dams from Boulder Creek, Wisconsin, U.S.A. in 2003 to determine if removal of these potential barriers affected the resident population of native brook trout (Salvelinus fontinalis). Despite the presence of other taxa in the downstream reaches, and in other similar streams adjacent to the Boulder Creek (including the brown trout, Salmo trutta), no new species had colonized the Boulder Creek in the two years following dam removal. The adults catch per unit effort (CPUE) was lower and the young‐of‐the‐year catch per unit effort (YOY CPUE) was higher in 2005 than in 2001 in all reaches, but the magnitude of these changes was substantially larger in the two dam‐affected sample reaches relative to an upstream reference reach, indicating a localized effect of the removal. Total length of the adults and the YOY and the adult body condition did not vary between years or among reaches. Thus, despite changes in numbers of adults and the YOYs in some sections of the stream, the lack of new fish species invading Boulder Creek and the limited extent of population change in brook trout indicate that dam removal had a minor effect on these native salmonids in the first two years of the post‐removal. Copyright © 2007 John Wiley & Sons, Ltd.     

Downstream benthic responses to small dam removal in a coldwater stream

Increased awareness of the negative effects of dams combined with an aging dam infrastructure has led to an increase in dam removals. However, ecological responses of downstream biota to such actions are poorly understood. We examined the influence of a pair of small dam removals on downstream periphyton and macroinvertebrates in Boulder Creek, WI (USA). The dams were 180 m apart and both were removed on 9 July 2003. We monitored algae and macroinvertebrates as well as habitat characteristics for approximately 2 months before and after the removals upstream and downstream from the two dams, and continued our observations over a similar period (mid‐May to mid‐July) the following summer. After the removals, an initial release of sediment significantly increased the proportion of fine sediments in the downstream reach and buried benthic substrate. This burial led to a 60% reduction in chlorophyll in the downstream reach the week following removal, while concentrations increased in the upstream reference reach. Similarly, macroinvertebrate densities 2 weeks post‐removal were lower relative to pre‐removal densities and were associated with declines of ephemeropterans, trichopterans and dipterans. Examination of Trichoptera genera demonstrated substantial changes in this assemblage associated with diminished densities of the formerly dominant genus Brachycentrus. Algal and invertebrate populations increased in the weeks after the dam removal, but did not reach densities similar to the upstream reference reach. In the following year, both periphyton and invertebrate densities were lower in the downstream reach, suggesting a long‐term effect of the removal. Thus, effects of the dam removal were alternatively positive or negative over time, and indicate that the time scale of consideration has a strong effect on the interpretation of the consequences of this management activity. Copyright © 2008 John Wiley & Sons, Ltd.     

美国退役坝拆除背景与原因剖析

为全面、客观反映美国退役坝拆除的真实情况,通过文献检索和专题调研,在综述美国退役坝拆除背景及现状的基础上,分析了美国拆坝的主要原因,即环境、安全和经济因素。案例研究表明,美国拆坝旨在消除老化坝的安全风险,恢复溯河性鱼类洄游以及节省无成本效益的开支。水坝退役是水坝生命周期管理中的一个重要阶段,拆坝并不意味着不能建坝,目前水电仍然是美国最大的可再生能源电力来源。美国在水坝退役方面的理念和经验可为我国水库降等与报废管理提供借鉴。     

桎木水库溃坝及小型水库安全分析

本文通过娄底市的水库溃坝特别是桎木水库溃坝事件,初步探讨了小型水库安全管理问题。     

Pacific lamprey recolonization of a Pacific Northwest river following dam removal

Recolonization of Pacific lampreys Entosphenus tridentatus into historically used freshwater habitats in the United States Pacific Northwest was evaluated in the White Salmon River basin after removal of Condit Dam. Pacific lamprey population declines are of concern, and passage barrier removal is often recommended for conservation. Condit Dam on the White Salmon River in Washington was a complete barrier to fish migrating upstream for nearly 100 years, was breached in 2011, and was removed by 2012. Distribution of larval Pacific lampreys was estimated before and after removal of Condit Dam using either backpack or deepwater electrofishing. Larval detection probabilities were calculated for the basin, and sample efforts were refined to ensure at least 80% confidence that larvae were absent when not detected. Pacific lampreys were not present upstream of Condit Dam before it was removed but were present in areas downstream of the dam. After dam removal, Pacific lamprey larvae were collected upstream of the former dam site from four reaches of the mainstem White Salmon River, indicating a recent recolonization event. Pacific lampreys were absent from the river mouth area before the dam was removed but were found in newly created habitat at the mouth after dam removal. Pacific lampreys naturally recolonized the White Salmon River basin within a few years after dam removal. Removing dams and providing passage opportunity can allow Pacific lampreys to distribute into vacant areas and may help reverse population declines.     

创建中国坝库工程的遗产保护科学

我国坝库工程与遗产保护的关系十分密切。传统的坝库工程降低了所涉文化遗产的“原真性”和自然遗产的“原整性”。加强遗产保护,要求坝库工程科学创造新的文化遗产保护方式,在注重生物多样性、突出景观美学、重视工程寿命设计等方面不断完善知识体系。     

Modelling the effects of dam removal on migratory walleye (Sander vitreus) early life‐history stages

Many dams in the USA have outlived their intended purpose and an increasing number are being considered for removal. Yet, quantitative studies of the potential physical, biological and ecological responses are needed to assess dam removal decisions. In this paper, the responses of migratory walleye (Sander vitreus) to increased spawning habitat availability as a result of dam removal was studied by comparing scenarios with and without a high‐head dam in the Sandusky River (Ohio), a major tributary to Lake Erie. A conceptual, ecological model was proposed to define the relationship between hydrodynamics and walleye spawning, egg hatching, larval drift and survival. A mathematical, ecological model of the early life‐history stages was then developed and coupled with time series of depth and velocity predictions over the spawning grounds from a 1‐D hydrodynamic model. Model simulations were run for 1984–1993 for both the with‐ and without‐dam scenarios to assess the potential benefit of dam removal. The simulation results demonstrated that velocity, depth and water temperature are major factors influencing adult walleye spawning success. Without the dam, 10 times the amount of spawning habitat would be available for walleye to spawn. This increase in spawning habitat area resulted in up to five times the total egg deposition and seven times the larval output to the nursing grounds, based on the assumption that 5% of the walleye population of Lake Erie migrated up the Sandusky River to spawn. We concluded that the spawning habitat in the current condition (with the dam) is limiting and additional spawning habitat upstream could significantly increase the number of larval walleye drifting to Lake Erie. The model sensitivity analysis showed that the number of walleye migrating up the river in spring is the dominant factor for larval recruitment to the lake. Copyright © 2006 John Wiley & Sons, Ltd.     

我国小型水库大坝安全问题探讨

在我国已建成的8．5万多座水库中，小型水库近8．2万座，约占96％，这些小型水库在防洪、灌溉、供水、发电和改善生态与环境等方面发挥了巨大的作用，但多种原因造成病险率高，也形成了极大的威胁．在对我国小型水库大坝安全现状及病险特点与机理进行分析的基础上，总结小型水库大坝安全管理的状况及亟待解决的关键问题。     

高坝水库放空要求及设施设计研究

高坝水库调节能力强,在流域梯级开发和防灾减灾中发挥重要作用,但其面临的风险也客观存在,一旦失事后果不堪设想。水库放空或降水位能力是经济社会发展新阶段对大坝风险防控和应急管理提出的新要求。本文给出水库放空的定义、目的及分类,系统阐述了放空水头比、放空库容比、库水位降速等水库放空能力评价指标,梳理了国内外对水库放空的要求,选取我国25座典型高坝水库进行放空能力分析。结果表明：高坝水库放空水头比介于17.5%～71.8%,均值为42.7%;放空库容比介于47.2%～99.2%,均值为81.7%;放空时间介于7.2～123 d,均值为42.7 d;库水降速介于0.71～9.03 m/d,均值为3.0 m/d。从实践来看,高坝水库放空能力受总库容、放空水位、坝型等工程特性参数影响,也受河流形态、河谷形状和库盆特点等因素影响。据此对水库放空设施设计中的入库流量、放空指标、启动条件和分级决策模式等关键问题进行了分析,对我国水利水电工程行业水库放空设施设计和应急管理有一定参考意义。     

美国百年拆坝历史回顾

自1912年至今,美国拆坝历史已有百年之久,期间拆坝共计1108座。从拆坝数量、分布范围、坝高和坝龄等多个角度对这些闸坝的资料进行分析比较,得出不同年代美国的拆坝特点:1980年以前拆坝数量少,分布范围较小,但闸坝的负面影响及拆坝必要性开始被人们所认识;20世纪80年代以后拆坝数量和范围逐渐扩大,坝高仍小于20 m,拆坝原因以生态修复为主,且更加关注闸坝安全问题;20世纪90年代拆坝数量继续扩大,拆坝高度实现突破,编制完成《大坝及水电设施退役导则》;21世纪,拆坝数量、高度和长度都打破以往记录,被拆闸坝以混凝土坝为主且绝大多数超过了使用寿命。同时,分析表明,闸坝的拆除与当时的社会经济状况有着密不可分的联系。     

我国水库大坝安全监测与管理的新动态

论述了我国水库大坝安全面临的新形势,介绍了风险评价技术和风险管理在水库大坝安全方面的应用,强调了小型水库的安全问题以及安全监测技术在防洪减灾和洪水资源利用中的应用。     

退役坝拆除现状及其影响研究进展综述

我国降等与报废水库逐年增加,大坝退役拆除成为必然趋势。针对退役坝拆除问题,从各国拆坝数量、拆坝地区分布、拆坝原因和拆坝相关政策入手,对国内外大坝拆除现状进行分析总结,并对拆坝后对生态环境和社会经济产生的影响进行综述。研究发现国内外关于拆坝影响研究多为定性分析,缺少定量分析和一套切实可行的计算方法,且多为单因素研究,缺乏综合影响因素评估分析。由此展望未来的拆坝影响研究中应由定性分析向定量分析转变,并耦合水动力、泥沙、生物响应、水生环境等多方面因素,构建拆坝影响的综合评估体系。     

Large dam removal and early spontaneous riparian vegetation recruitment on alluvium in a former reservoir: Lessons learned from the pre‐removal phase of the Sélune River project (France)

The restoration of ecological continuity along the Sélune River (Normandy, France) involves the removal of two tall hydroelectric dams (36 m removed in 2019 and 16 m in 2021), a project without precedent in Europe. During the pre‐removal phase (2014–2018), we performed scientific monitoring of the vegetation that was colonizing alluvium in the former dam reservoir (length: 19 km; surface area: 151 ha). Our study aimed to analyse if spontaneous vegetation could ecologically restore the riparian zone and help maintain fine sediment after dam removal. We used colonization indicators related to vegetation structure, taxonomic richness and diversity, and composition. These indicators were calculated at two spatial scales (local, at a single site, and broad, along the reservoir). The aim was to (a) characterize the spontaneously established species pool; (b) analyse longitudinal patterns in vegetation colonization; and (c) assess temporal changes in the species community. Our results show that diverse plant communities have developed. Slight differences in longitudinal and lateral patterns existed; they were linked with habitat heterogeneity and the reservoir's slow pace of draining. We observed fast spontaneous terrestrialization, which has resulted in cover stabilization, decreased diversity, and the development of herbaceous riverbank communities, with very few invasive species. This finding suggests stabilization potential is high and passive ecological restoration could occur, at least locally. Further analyses focusing on functional traits could help inform future management decisions regarding revegetation on reservoir alluvium.     

浅析小型水库坝下涵管险情原因与防范措施

通过对小型水库坝下涵管除险加固的形式、设计方法、施工质量控制及出险原因等方面的归纳和分析,提出防止坝下涵管险情的应对措施.     

闻喜县土石坝溃坝原因与防治对策

山西省闻喜县土石坝工程兴建于20世纪50～70年代,经过40余年的运行,水库数量锐减过半,现存水库带病运行,已成防洪的心腹之患。从洪水漫顶、坝体质量、地震和管理不当四个方面介绍了导致土石坝溃坝的原因,并详细说明针对不同原因应采取的除险加固措施。     

大坝加高后新老坝体结合问题

大连市英那河水库扩建工程将原来大坝加高15.1 m,本文介绍了大坝加高方式,新老坝坝体结合和加高后 坝体稳定分析。     

Learning from dam removal monitoring: Challenges to selecting experimental design and establishing significance of outcomes

As the decommissioning of dams becomes a common restoration technique, decisions about dam removals must be based on sound predictions of expected outcomes. Results of past and ongoing dam removal monitoring are an important source of information that practitioners may utilize to evolve predictive and decision‐making tools, emphasizing the need for thorough and defensible documentation of dam removal outcomes. However, as dam removals challenge many basic assumptions of conventional experimental designs and data analysis techniques, the quality of information available to aid decision‐making may be questionable or misleading. Nevertheless, some study design principles and analysis procedures may be robust to the challenges presented by dam removal research. To assist managers in undertaking dam removal monitoring, this article discusses the assets and limitations of monitoring and analysis options available for dam removal studies, with emphasis on selecting a rigorous experimental design and determining significance of results. As the chosen monitoring design will influence the appropriateness of applying standard analytical methods, particularly statistical hypothesis testing, researchers should carefully consider constraints inherent to dam removal studies when designing a monitoring plan and assigning significance to observed changes. Ecological significance is often the most justifiable method for framing significance of dam removal outcomes, though it may be complicated by identification of environmentally significant thresholds. Another alternative is evaluation of the practical significance of results, when observed changes exceed measurement error and background variability. Establishing practical significance may be informative when statistical and ecological significance is inappropriate or impossible to determine. Copyright © 2010 John Wiley & Sons, Ltd.     

Short-term effects on Unionid mussel density and distribution before and after low-head dam removal in northern New York

Unionid mussel populations have declined in many environments, particularly those that were altered by human activities such as dam construction and removal. The Fort Covington Dam blocked the Salmon River in northern New York upriver of its confluence with a smaller tributary, the Little Salmon River. This dam was removed in 2009. My study compared the mean ranked density of mussels in both rivers for the pre-removal period (2005–2008) to the post-removal period (2009–2012) with special attention to Lampsilis cariosa and Margaritifera margaritifera. Systematic sampling was used at six riffles and double sampling at four glides divided between the Salmon and Little Salmon rivers from 2005 through 2012. The Little Salmon River served as a control. Mean ranked adult mussel density was not significantly different between the two rivers in the pre-removal period but was significantly greater in the Little Salmon River after dam removal. Living mussels of 13 species were collected dominated by Elliptio complanata. Dam removal did not affect sediment sorting, porosity, water chemistry, or mussel species distribution. Rapid dewatering of the reservoir led to stranding and death of mussels in the reservoir and in the adjacent ponds. Increased water velocity, exacerbated by rain, mobilized sediment that buried a potentially large mussel bed downstream of the dam where Lampsilis cardium and L. cariosa were abundant, which showed little recovery by 2013.     

白石碾压混凝土坝坝体芯样评定

白石水库位于辽宁省西部大凌河干流上,采用RCD方法施工。本文通过对坝体碾压混凝土的均质性、密实性、抗渗性、结构强度和层间稳定性的综合评定,证明坝体碾压混凝土符合设计要求,并且达到优良标准。