美国拆坝统计分析

对美国1921~2013年共计1 093座水坝拆除进行了信息统计,从拆坝数量、大坝规模、筑坝材料、坝龄等方面系统分析了美国拆坝现状,并从生态、经济、安全方面分析拆坝的主要原因。统计结果表明水坝拆除现象在美国一直存在,且至今为止美国所拆除的主要为小型水坝、旧坝、病险坝。对美国经济发展有重要影响的水坝不仅未被拆除,还不断得到维护,水坝在美国的经济和社会发展中仍贡献着重要力量。     

拆坝对鱼类资源的影响及生态保护修复技术措施探讨

文章结合我国水坝对鱼类资源影响的现状,针对我国退役水库拆除后河流生态环境改变对鱼类资源的影响因素进行分析,探讨拆坝后保护修复鱼类资源的工程技术措施。     

浅析美国建坝与拆坝

分析了美国101座建坝(坝高100 m或库容30亿m3以上)和248座拆坝(1999~2005年)的特征。得出如下结论:①20世纪60年代为美国建坝高峰期,建坝集中于中西部偏远地区的小河或大河支流上,密西西比河干流未建坝;建坝开发目标依次为防洪、供水灌溉、发电、旅游生态、航运,坝型依次为土石坝、重力坝、堆石坝、拱坝、混合坝及其他;最大坝高234 m,最大库容348.5亿m3。②拆坝的建坝时间为1708~1970年,拆坝的坝高大多小于5 m,最大坝高18 m,拆除的主要是建在小支流或溪沟上的老、弃、废和"无名"坝;拆坝的原因依次为"生态环境"、"水坝安全"、"经济效益"和"泥沙淤积"。③美国建坝与拆坝具有"中西部河流建大坝、东部小河拆小坝"的总体特征。     

美国拆坝情况简析

美国1999～2003年底前共拆坝168座,所拆的坝绝大多数为小型坝,寿命超过使用年限、功能已丧失或本身就是病险坝,且维修费用高昂,拆除是最经济的选择.在拆除过程中非常注重对拆坝环境影响的观测与评价.美国拆坝的原则和经验可供我国借鉴.     

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。     

小型低水头坝围堰拆除设计的流量频率分布选择

建围堰是水坝安全拆除的第1步。小型低水头坝拆除所需时间通常为几个月。为减少围堰修建费用,通常需要在低水时期进行水坝拆除,因此围堰的设计应根据水坝拆除期间相应的河流流量系列而不是全年流量系列进行。对近期拆除的俄勒冈州桑迪（Sandy）河上马莫特（Marmot）坝的时均和日均流量记录,按4种拆坝期限进行分析,期限长达1～4个月（7-10月）。为代表现场的最大流量系列,将三一矩比率图和概率图相关关系系数法用来选择皮尔逊Ⅲ型,二参数和三参数的对数正态概率分布函数。从水文工程角度看,建议拆坝的最优时间期限为3个月（7～9月）。根据年最大流量系列估算的流量设计值较高,会导致围堰设计不经济。     

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。     

美国退役水坝的拆除

老坝处理方案之一是将已达到使用寿命的水坝退役和拆除。仅在美国就已拆除450多座水坝,其中有些为大型水坝。通过分析最近美国水坝拆除的典型事例,探讨了与水坝拆除有关的费用、泥沙管理、趋势以及方法。     

我所看到的美国水电（之十）——从格伦峡谷协会等反坝组织看美国的拆坝运动

美国拆除水坝的原因：一是很多水坝到了使用寿命期 二是维修成本以及构成的安全威胁与日俱增 三是已经产生了一些不建水坝也能满足人类需求的方法 四是因为在美国,建坝决策越来越公开化,环保主义者、公用事业、工程技术以及水电施工等各方面都可以在听证会上发表意见,法律法规也从环境生态角度,对水电开发施加了很多限制.     

我所看到的美国水电(之十)——从格伦峡谷协会等反坝组织看美国的拆坝运动

美国拆除水坝的原因:一是很多水坝到了使用寿命期;二是维修成本以及构成的安全威胁与日俱增;三是已经产生了一些不建水坝也能满足人类需求的方法;四是因为在美国,建坝决策越来越公开化,环保主义者、公用事业、工程技术以及水电施工等各方面都可以在听证会上发表意见,法律法规也从环境生态角度,对水电开发施加了很多限制.     

美国大坝安全管理现状分析及启示

简要介绍了美国大坝建设管理的现状和大坝安全管理发展的几个阶段.重点结合美国1996年水资源法案确定“美国国家大坝安全计划(NDSP)“立项以来开展的工作,对大坝安全管理体制、工作重点、研究方向和主要成果等进行了归纳和总结.对我国大坝安全管理工作提出了建议,认为必须制定一个长远的战略计划,以适应当前及未来大坝安全管理的需求;整合我国现有各部门、各级机构的大坝安全管理中的技术力量,从法律上确定水库大坝安全管理体制,统一协调和指导我国水库大坝安全管理的行政和技术工作;急需建立适合我国国情的水库大坝安全管理技术体系,将水库大坝的安全管理贯穿于工程的规划、设计、施工以及运行的全过程;呼吁国家与水利部、有关部门加大对大坝安全管理技术研究的科研投入.     

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.     

Physical and Biological Responses to an Alternative Removal Strategy of a Moderate‐sized Dam in Washington,USA

Dam removal is an increasingly practised river restoration technique, and ecological responses vary with watershed, dam and reservoir properties, and removal strategies. Moderate‐sized dams, like Hemlock Dam (7.9 m tall and 56 m wide), are large enough that removal effects could be significant, but small enough that mitigation may be possible through a modified dam removal strategy. The removal of Hemlock Dam in Washington State, USA, was designed to limit channel erosion and improve fish passage and habitat by excavating stored fine sediment and reconstructing a channel in the former 6‐ha reservoir. Prior to dam removal, summer daily water temperatures downstream from the dam increased and remained warm long into the night. Afterwards, a more natural diel temperature regime was restored, although daily maximum temperatures remained high. A short‐lived turbidity pulse occurred soon after re‐watering of the channel, but was otherwise similar to background levels. Substrate shifted from sand to gravel–cobble in the former reservoir and from boulder to gravel–cobble downstream of the dam. Initially, macroinvertebrate assemblage richness and abundance was low in the project area, but within 2 years, post‐removal reaches upstream and downstream of the dam had diverse and abundant communities. The excavation of stored sediment and channel restoration as part of the dam removal strategy restored river continuity and improved benthic habitat while minimizing downstream sedimentation. This study provides a comparison of ecological effects with other dam removal strategies and can inform expectations of response time and magnitude. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.     

Geomorphic Responses to a Large Check‐Dam Removal on a Mountain River in Taiwan

The ability to understand and predict the impacts of dam removal in river systems is important, especially as dam decommissioning is becoming increasingly popular. In this study, we document the morphological and sediment impact of the removal of Chijiawan Check Dam in May 2011; a 13‐m‐high dam located on a coarse‐grained, steep mountain river channel in Taiwan. An estimated 0.2 million m³ of sediment had accumulated within the impoundment before its removal. Longitudinal and bankfull cross‐sectional surveys and a detailed sediment textural survey were undertaken along a 3.2‐km study reach of the Chijiawan Creek between 2010 and 2012. A rotating knickpoint with migration rates of up to 22 m/day was observed along the study reach, following dam removal. The rate and character of channel change, associated with the dam removal, appear to be driven as much by channel morphology and distance from the dam as by the hydrology variability. Our results suggested that relatively small amounts of sediment were eroded during the first 3 weeks following dam removal because of low discharge conditions. However, after 1 and 15 months, 10 and 75% of the sediment that had accumulated within former impounded was eroded, respectively. Sites near the former dam had a sediment texture that reflected the transport of released sediment, and this suggested that basin‐wide sediment processes exerted a strong influence. The removal of Chijiawan Dam offers unique insight on how sediment processes can drive river channel responses to sediment pulses may vary with discharge and sediment load, in areas subject to remarkably high flows and sediment loads. Copyright © 2015 John Wiley & Sons, Ltd.     

Modelling Evaluation of Dam Removal in the Context of River Ecosystem Restoration

Applications of environmental models may provide imperative information to enable informed decision‐making of river management actions, which are often made in the face of high system complexity and uncertainty. We applied Hydrologic Engineering Centers River Analysis System(HEC‐RAS) and Curvilinear Hydrodynamics Three‐Dimensional (CH3D) models to aid in the decision‐making of the proposed removal of the Masten Dam, a small, ‘run‐of‐the‐river’ dam on the Loxahatchee River, a federally designated ‘Wild and Scenic River’ in south‐east coast of Florida (USA). Anthropogenic alteration of the system has led to changing hydroperiods and salinity regimes in the floodplain. Both models are calibrated against measured data taken at varying temporal and spatial scales. The HEC‐RAS modelling results show that removal of the Masten Dam would lower water levels in the upstream riverine reach, leading to reduced soil moisture or inundation in the floodplain. The CH3D modelling results indicate that dam removal would increase river salinity during the dry season in the tidal reach where salinity compliance for environmental flow regulation is measured. These environmental changes would exert additional stress on freshwater vegetation communities in the floodplain. Given the scarcity of water resources in the region, removal of the Masten Dam would not offer an effective restoration strategy. This study demonstrates not only the need for evaluation of dam removal on a case‐by‐case basis but also the usefulness of environmental models in providing the technical basis for such management decisions. Copyright © 2014 John Wiley & Sons, Ltd.     

美国奥罗维尔坝溢洪道事故分析与启示

奥罗维尔坝溢洪道事故为美国大坝安全管理敲响了警钟,也提醒世界各国应足够重视大坝安全管理。在全面梳理奥罗维尔坝历次重大风险事件的基础上,系统阐述了2017年美国奥罗维尔坝主溢洪道、应急溢洪道事故的详细过程,深入分析事故发生的原因。分析表明,此次事故的发生是工程设计、施工建设、运行管理多方面长期积累的系统性问题,其中设计与施工缺陷是先天不足,运行维护和应急管理及其相关机制的缺陷是后天隐患。本文由此次事故反映的问题获得启示,从设计、建设、运行及应急管理方面对我国大坝安全管理提出了建议,呼吁相关部门加快建立贯穿大坝全生命周期的风险管理体系。     

美国奥洛维尔水库的工程安全管理问题简析

2017年2月,美国加利福尼亚州奥洛维尔水库出现了严重的溢洪道冲刷破坏事故,引起国际水利水电工程界强烈关注。本文分别介绍了美国地方政府所属大坝的安全管理基本情况和加利福尼亚州所辖大坝安全管理情况,探讨了奥洛维尔工程安全管理存在的问题,分析了工程应急响应的组织模式。从工程安全管理上看,奥洛维尔水库事故出现事故的原因,核心在于安全管理权责不匹配、责任缺位与越权管理并存;监督检查流于形式、运行维护费用投入不足、风险评估不科学等,也是导致事故出现的管理方面原因。     

推进大坝安全信息化建设提高大坝安全管理水平

水电站大坝安全直接关系到社会公共安全与人民生命财产安全,已得到了政府和水电站业主的高度重视.始于上世纪八十年代的大坝安全定期检查工作,推进了消缺和补强加固工作的开展,显著改善了大坝的安全状况.但据了解,相当数量的水电站大坝安全管理手段仍较落后,仍停留在传统手工作业阶段,没有及时跟上企业乃至整个社会的信息化步伐.为此,国家电监会颁发了《水电站大坝运行安全信息报送办法》和《水电站大坝运行安全信息化建设规划》,旨在提高全行业的大坝安全管理信息化水平.本文分析了大坝安全管理和信息化建设的现状,就如何推进大坝安全信息化工作,提出了具体的技术方案和实施要求.     

Fracturing dams,fractured data: Empirical trends and characteristics of existing and removed dams in the United States

Dam removals in the United States continue to accelerate in pace and scope, but no national analyses have examined how removed dams compare with existing dam stock. Here, we review and analyse the best available national data on dams from the National Inventory of Dams (NID), dam removals from American Rivers, the U.S. Geological Survey, and the National River Restoration Science Synthesis databases to compare trends and characteristics of removed versus existing dams in the United States. If historical trends continue, by 2050 the United States can expect between 4,000 and 36,000 total removals, including 2,000–10,000 removals of NID dams. Best‐fit regression models estimate total costs between $50.5 million and $25.1 billion (mean $10.5 billion, median $416.5 million) for all removals and $29.6 million to $18.9 billion (mean $7.2 billion, median $285 million) for NID removals, a significant cost savings over present stated dam rehabilitation needs. Structural characteristics and ages of documented removals are not representative of existing dams, with privately owned hydroelectric dams subject to public oversight and water supply dams the most disproportionately removed. We conclude that dam removal science would benefit from the creation of an interdisciplinary framework for studying dams as environmental, social, and technological interventions, facilitated by transparent datasets around dams and removals and reflexive research approaches that combine statistical approaches with place‐based analyses.     

LONG‐TERM IMPLICATIONS OF DAM REMOVAL FOR MACROINVERTEBRATE COMMUNITIES IN MICHIGAN AND WISCONSIN RIVERS,UNITED STATES

The removal of the numerous ageing dams in the United States has become an important stream restoration technique. The extent to which the ecological damage done to streams by dams is reversed upon removal is unknown, especially on decadal time scales. The objectives of this study were to determine if macroinvertebrate assemblages within rivers recover following the removal of a dam and to estimate the time needed for recovery. A space‐for‐time substitution approach was used on eight rivers in various stages of recovery following a dam removal, ranging from <1 to 40 years post‐removal. Within each river, macroinvertebrates were sampled in a zone unaffected by the dam removal (reference zone) and two zones impacted by the dam removal (former impoundment and downstream zone). Insects were identified to the family level and placed into functional feeding groups. Various macroinvertebrate community metrics were compared between impacted and unimpacted zones to evaluate the extent of recovery, and plotted over time since removal to develop a temporal trajectory of recovery. Generally, the macroinvertebrate community recovered 3–7 years following removal both in terms of taxonomic similarity and richness, although densities could take decades to recover. Dam removals are a beneficial restoration technique, yet the recovery of important stream components can be variable and may take longer than previous research has suggested. Having realistic expectations of the ecological ramifications of dam removal efforts is paramount in ensuring the success and thus potential of future projects. Copyright © 2011 John Wiley & Sons, Ltd.