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471.
The upstream migration of adult anadromous salmonids in the Columbia River Basin (CRB) has been dramatically altered and fish may be experiencing energetically costly delays at dams. To explore this notion, we estimated the energetic costs of migration and reproduction of Yakima River‐bound spring Chinook salmon Oncorhynchus tshawytscha using a sequential analysis of their proximate composition (i.e., percent water, fat, protein, and ash). Tissues (muscle, viscera, and gonad) were sampled from fish near the start of their migration (Bonneville Dam), at a mid point (Roza Dam, 510 km upstream from Bonneville Dam) and from fresh carcasses on the spawning grounds (about 100 km above Roza Dam). At Bonneville Dam, the energy reserves of these fish were remarkably high, primarily due to the high percentage of fat in the muscle (18–20%; energy content over 11 kJ g?1). The median travel time for fish from Bonneville to Roza Dam was 27 d and ranged from 18 to 42 d. Fish lost from 6 to 17% of their energy density in muscle, depending on travel time. On average, fish taking a relatively long time for migration between dams used from 5 to 8% more energy from the muscle than faster fish. From the time they passed Bonneville Dam to death, these fish, depending on gender, used 95–99% of their muscle and 73–86% of their visceral lipid stores. Also, both sexes used about 32% of their muscular and very little of their visceral protein stores. However, we were unable to relate energy use and reproductive success to migration history. Our results suggest a possible influence of the CRB hydroelectric system on adult salmonid energetics. Published in 2006 by John Wiley & Sons, Ltd. 相似文献
472.
本文根据大坝安全工作的长期实践和研究,论述了依法治坝、科学防灾的做法及重要性;论述了大坝安全工作以人为本,加强管理、开展非工程措施工作,打造绿色工程的做法及重大意义。最后,阐述了新世纪中国的大坝安全工作应立足于社会、经济、环境的协调和可持续发展。 相似文献
473.
Damming and regulating the flow of rivers is a widespread issue and can have a significant impact on resident biota. The Tongariro River, central North Island, New Zealand, has a flow regime that is regulated by two hydroelectric dams along its length, and it has been suggested that ‘flushing flows’ would assist benthic communities by removing ‘nuisance’ periphyton growth forms that typically occur in autumn. We assessed whether (i) damming has altered periphyton and macroinvertebrate communities downstream of the Rangipo Dam and (ii) whether the release of a flow pulse equivalent to 50 times the baseflow is sufficient to (a) move the substrate in the section of river downstream of this dam and (b) impact benthic periphyton and macroinvertebrate communities. Downstream macroinvertebrate communities were impacted by the presence of the dam, but periphyton was not. No movement of substrate occurred downstream of the dam as a result of the flow release, which was likely because of naturally high embeddedness and armouring of substrate. Periphyton biomass and macroinvertebrate density were not affected by the release indicating that larger releases would be required to have any effect on benthic communities downstream of this dam. This study highlights the importance of considering natural bed structure and sediment dynamics when using flow releases downstream of dams to control periphyton. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
474.
Julie K. H. Zimmerman Benjamin H. Letcher Keith H. Nislow Kimberly A. Lutz Francis J. Magilligan 《河流研究与利用》2010,26(10):1246-1260
River regulation can alter the frequency and magnitude of subdaily flow variations causing major impacts on ecological structure and function. We developed an approach to quantify subdaily flow variation for multiple sites across a large watershed to assess the potential impacts of different dam operations (flood control, run‐of‐river hydropower and peaking hydropower) on natural communities. We used hourly flow data over a 9‐year period from 30 stream gages throughout the Connecticut River basin to calculate four metrics of subdaily flow variation and to compare sites downstream of dams with unregulated sites. Our objectives were to (1) determine the temporal scale of data needed to characterize subdaily variability; (2) compare the frequency of days with high subdaily flow variation downstream of dams and unregulated sites; (3) analyse the magnitude of subdaily variation at all sites and (4) identify individual sites that had subdaily variation significantly higher than unregulated locations. We found that estimates of flow variability based on daily mean flow data were not sufficient to characterize subdaily flow patterns. Alteration of subdaily flows was evident in the number of days natural ranges of variability were exceeded, rather than in the magnitude of subdaily variation, suggesting that all rivers may exhibit highly variable subdaily flows, but altered rivers exhibit this variability more frequently. Peaking hydropower facilities had the most highly altered subdaily flows; however, we observed significantly altered ranges of subdaily variability downstream of some flood‐control and run‐of‐river hydropower dams. Our analysis can be used to identify situations where dam operating procedures could be modified to reduce the level of hydrologic alteration. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
475.
Natural flood regimes provide a wide array of important ecological functions. Our goal is to assess the hydrologic impact of dams on flood flows throughout the United States. Regional regression models of the median annual 1‐day maximum flow were developed as a function of natural watershed characteristics, dam storage, and population density. Most of the regressions have adjusted R2 values in excess of 0.80, and overall the models covered 78% of the area of the continental U.S. Alteration of flood flows is present in every region of the country, and is more severe west of the Mississippi and especially in the southern Great Plains, desert Southwest, and northern California. The percent of U.S. rivers with greater than a 25% reduction in the median annual flood is 55% for large rivers, 25% for medium rivers, and 10% for small rivers. The majority of freshwater ecoregions in the country have at least 10% of their rivers with 25% or greater alteration in all three river size classes. A simple model based on the ratio of dam storage to mean annual runoff was developed for assessing alteration in ungauged rivers, and was found to be generally useful for classifying rivers into categories of potential alteration. Overall, we document the alteration of natural flood flows across the U.S. in more detail than has been previously accomplished, and demonstrate the efficacy of multivariate regional regression models and other indicators for assessing hydrologic alteration. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
476.
In the last decade many research projects have been developed concerning the breaching of embankment dams. In particular in the framework of the IMPACT Project, results were provided for five large scale field tests and for 22 laboratory tests, so providing the basis for a better comprehension of the breach enlargement process, but also giving useful data for numerical modelling. This paper presents the results of the simulations of some of these tests, where the erosion is triggered by the overtopping of the dam. The simulations were carried out through a physically based model proposed by Macchione. The numerical results confirmed the soundness of the physical basis of the model. 相似文献
477.
Michael Bliss Singer 《河流研究与利用》2007,23(1):55-72
This paper reports basinwide patterns of hydrograph alteration via statistical and graphical analysis from a network of long‐term streamflow gauges located various distances downstream of major dams and confluences in the Sacramento River basin in California, USA. Streamflow data from 10 gauging stations downstream of major dams were divided into hydrologic series corresponding to the periods before and after dam construction. Pre‐ and post‐dam flows were compared with respect to hydrograph characteristics representing frequency, magnitude and shape: annual flood peak, annual flow trough, annual flood volume, time to flood peak, flood drawdown time and interarrival time. The use of such a suite of characteristics within a statistical and graphical framework allows for generalising distinct strategies of flood control operation that can be identified without any a priori knowledge of operations rules. Dam operation is highly dependent on the ratio of reservoir capacity to annual flood volume (impounded runoff index). Dams with high values of this index generally completely cut off flood peaks thus reducing time to peak, drawdown time and annual flood volume. Those with low values conduct early and late flow releases to extend the hydrograph, increasing time to peak, drawdown time and annual flood volume. The analyses reveal minimal flood control benefits from foothill dams in the lower Sacramento River (i.e. dissipation of the down‐valley flood control signal). The lower part of the basin is instead reliant on a weir and bypass system to control lowland flooding. Data from a control gauge (i.e. with no upstream dams) suggest a background signature of global climate change expressed as shortened flood hydrograph falling limbs and lengthened flood interarrival times at low exceedence probabilities. This research has implications for flood control, water resource management, aquatic and riparian ecosystems and for rehabilitation strategies involving flow alteration and/or manipulation of sediment supplies. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
478.
Relatively little is known about the downstream migration of landlocked stocks of Atlantic salmon Salmo salar L. smolts, as earlier migration studies have generally focused on upstream migration. However, in watersheds with many hydroelectric plants (HEPs), multiplicative loss of downstream‐migrating salmon smolts can be high, contributing to population declines or extirpations. Here we report the results from a study of wild landlocked Atlantic salmon smolts in the River Klarälven. Salmon smolts, tagged with acoustic transmitters, were released at different locations and followed as they passed 37 receivers along a 180‐km‐long river segment, including eight dams as well as free‐flowing control stretches. We found that 16% of the smolts successfully migrated along the entire river segment. Most losses occurred during HEP passages, with 76% of the smolts being lost during these passages, which contrasts with the 8% smolt loss along unregulated control stretches. Migration speed was 83% slower along regulated stretches than along unregulated stretches. The observed lower migration speed at regulated stretches was dependent on fish size, with large fish moving slower than small fish. Discharge affected migration speed but not losses. As previously shown for anadromous populations, our study of landlocked salmon demonstrates similar negative effects of multiple passages of HEPs by downstream‐migrating smolts. On the basis of this and previous migration studies, we advocate using a holistic approach in the management and conservation of migratory fish in regulated rivers, which includes safe passage for both upstream‐ and downstream‐migrating fish. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
479.
针对土石坝运行安全综合评价中评价指标之间存在相关性及人为设定的权重恒定不变的问题,通过决策实验室法(DEMATEL)分析指标内部联系,联合变权理论(VWT)依据指标状态值对指标权重进行修正,得到了一种考虑指标相关性及指标状态值的优化权重。并探究了常权权重与优化权重对各评价指标的权重和评价结果的影响,识别影响土石坝运行安全综合评价的关键指标。结合云模型能有效处理监测信息和评价过程中存在的不确定问题的优点,构建了权重优化-云模型的土石坝运行安全综合评价模型。以和龙水库的土石坝为研究对象,研究结果表明：评价云生成的云滴大部分落在“安全”与“基本安全”之间;结合云相似度计算结果,和龙水库与“安全”和“基本安全”的相似度分别为32.3%和16.7%,由最大相似度原则确定评价结果为“安全”。与常权权重相比,两者的评价结果一致,但对“安全”的隶属度从40.6%降低到了32.3%,体现了指标相关性及指标状态值对评价结果的影响。评价结果与和龙水库现状吻合,印证了本文模型的准确性和可行性,且该方法考虑了指标相关性及实测指标对权重的影响,并结合云模型从定量和定性两个角度评估了土石坝的运行状态,能够更加真实有效地反应大坝的安全状况,可为大坝的安全评价提供参考。 相似文献
480.
针对传统“黑箱”模型可以预测却无法解释拱坝变形的缺陷,利用Shapley Additive Explanation(SHAP)理论对特高拱坝的机器学习变形预测模型进行解构分析,分析水压、温度、时效对特高拱坝不同部位径向水平位移的影响规律。构建特高拱坝变形监测数据的轻量梯度提升算法（Light Gradient Boosting Machine,LightGBM）黑箱预测模型,利用SHAP对存在多重共线性的因子进行剔除,再从整个因子集和单个样本两个角度分析不同影响因子对模型变形预测的贡献度;通过分析拉西瓦特高拱坝坝肩、坝基、拱冠等不同部位的径向水平位移与影响因子间的关系,发现时效因子对高程越高、越靠近拱冠位置的径向水平位移影响越大,温度因子主要影响靠近拱冠位置的径向水平位移,水压因子主要影响高程较高位置的径向水平位移,而坝基和深入坝肩岩体测点的径向水平位移几乎不受水位、温度的影响。解决了以往“黑箱”变形预测模型可视性差、内部机理不明的问题,根据可解释模型得到的相关规律可为特高拱坝的工作性态分析和运行管理提供借鉴。 相似文献