Biofilm Responses to Flow Regulation by Dams in Mediterranean Rivers

Dams regulate downstream hydrology and modify water quality, which in turn can impinge on the biota, especially in rivers naturally subject to large hydrological variability, such as those under Mediterranean climate. The effect of dams on biofilms was analysed in three tributaries (Cinca, Siurana and Montsant) of the Ebro River (NE Spain). We hypothesized that flow regulation would lead to lower spatial variability of biofilms on the streambed and to a decrease in their metabolic rate per unit biomass, especially during low flow periods. Biofilm characteristics were studied in five transects evenly spaced along river reaches upstream (control) and downstream (impact) of dams in each river, along with riverbed granulometry, hydraulics and water chemistry. Chlorophyll‐a, respiratory activity, photosynthetic capacity and efficiency, and extracellular enzymatic activities (β‐d ‐glucosidase, alkaline phosphatase and leucine‐amino‐peptidase) of epilithic biofilms were measured in different seasons. Spatial variability of chemical and biological variables was reduced downstream of the dams. Chlorophyll‐a concentration, photosynthetic efficiency and respiration capacity were higher in impact than in control reaches, but generally, low inorganic phosphorus concentrations resulted in comparable phosphatase activities downstream and upstream of dams. On the other hand, β‐d ‐glucosidase and leucine‐amino‐peptidase activities were higher at impact reaches. Biofilms were thicker and metabolically more active at the impact reaches, with higher ability to transform dissolved organic matter. Overall, results from this study provide evidence that dams can largely affect the structure and activity of river biofilms, with foreseeable important consequences for river ecosystem functioning. Copyright © 2014 John Wiley & Sons, Ltd.     

Plant dispersal along rivers fragmented by dams

To understand the influence of dams on connectivity of riparian plant communities along rivers, we examined plant dispersal by water (hydrochory) and riparian plant community attributes upstream and downstream from dams on two rivers in the southern Rocky Mountains, Colorado, USA. Drifting plant propagules were collected from the water column along reaches upstream and downstream from dams to examine the longitudinal and temporal variation in seed‐pool species composition and concentration of water‐transported seeds. Similarities between species composition of the hydrochoric seed pool and local standing riparian vegetation were used to evaluate the degree of longitudinal connectivity along river corridors and to isolate the relative contributions of local versus regional species pools to hydrochoric species composition. Furthermore, several synthetic attributes (longevity, origin, life‐form and dispersal mode) and species composition of riparian plant communities were examined to explore the effects of interrupted propagule dispersal on standing vegetation. We estimated that as many as 120 million seeds were transported via hydrochory along free‐flowing reaches of the Rocky Mountain streams in a single growing season. Seed concentration (seeds/m³) in the water column was reduced by 70–94% along reaches downstream from dams compared to free‐flowing reaches. The similarity in species composition of hydrochoric seeds and local standing vegetation was nearly two times greater downstream from reservoirs compared to upstream. This suggests that hydrochory complements local species pools by importing seeds from throughout the upstream catchment area along free‐flowing river reaches, but that hydrochoric seeds are derived primarily from local sources along regulated river reaches. Species richness recovers as a function of downstream distance from contributions of standing vegetation and seeds from tributary streams. Hydrochory may extend the period over which viable seeds of a parent population are dispersed. Even after dispersal of parent populations has terminated, seeds may continue to be available due to residence time in water transport. This extension of the ‘effective dispersal window’ of some species may exceed two weeks or more and may influence the likelihood of successful establishment. In this study, synthetic attributes of riparian vegetation did not differ significantly between free‐flowing and regulated reaches, whereas formal statistical comparisons of community composition upstream and downstream from reservoirs indicate that there are differences in community composition upstream and downstream from dams. These findings suggest that the consequences of 50 to 100 years of fragmentation result in community‐wide effects along Rocky Mountain streams and that these effects may be partially explained by dam‐caused disruption in connectivity of plant populations. Copyright © 2005 John Wiley & Sons, Ltd.     

Storm effects on nitrogen flux and longitudinal variability in a river–reservoir system

Sustainable management of the nitrogen (N) cycle remains a considerable global challenge that has major implications for aquatic ecosystems. Dams play a critical yet often neglected role in addressing this challenge as they increase hydraulic residence time and denitrification potential. However, during storm events when the majority of N loading occurs, less is known about the effects dams have on N fate and transport processes. Here, we examined the flux of N species and phosphorus (P) and longitudinal profiles of nitrate (NO₃^?) along a sixth‐order river–reservoir system at baseflow and across the falling limb of a multiday, 1‐year storm hydrograph. During the storm event, the reservoir reduced total NO₃^? flux by 19.1% and P flux by 12.7%. On the contrary, ammonium (NH₄⁺) fluxes were 200% higher downstream of the dam in comparison with fluxes into the reservoir, indicating that there was a substantial net export of NH₄⁺ from the reservoir during the storm event. Longitudinally along the river to reservoir transition, a breakpoint of statistical significance was identified, highlighting the sharp contrast between NO₃^? concentrations within the river and reservoir. Results suggest that frequent storm events such as the one presented here can greatly alter N removal processes in river–reservoir systems. Overall, this study highlights the need to better understand the role that storm events play in river–reservoir N cycling dynamics.     

Spatial and seasonal variations in δ13C AND δ15N of particulate organic matter in a dam‐controlled subtropical river

Alteration of stream flow by artificial dams has been observed to be a significant factor for river water environmental changes. Therefore, understanding the biogeochemical processes occurring in the dam‐controlled rivers is important for water resource management. In this paper, δ¹³C and δ¹⁵N signatures of particulate organic matter (POM) in a dam‐controlled subtropical river, Beijiang River, in south China are reported for their spatial and seasonal distributions. POM affected by reservoirs is lighter in δ¹³C and heavier in δ¹⁵N relative to unaffected POM. In April, POM δ¹³C and δ¹⁵N values show less spatial variation in the mainstem, and suggest relatively greater contributions of terrestrial organic matter (OM) to POM. This could be related to the onset of summer monsoon that caused an abrupt increase in terrestrial input to the river by the monsoon‐induced enhancement of rainfall and runoff. In August and December, however, POM isotopic values for the sites affected by the Feilaixia dam reservoir in the middle of the river show marked changes, suggesting aquatic plankton proliferation in the reservoir during the times. Upstream from the reservoirs, POM isotopes are seasonally less varied and suggest mainly terrestrial origin. However, the isotopic signals of aquatic plankton proliferation in the reservoir in August and December is imprinted on the POM isotopic compositions downstream the reservoir, indicating far‐reaching influences of the reservoir on the downstream water environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Simulating system‐wide effects of reducing irrigation withdrawals in a disputed river basin

Stakeholders in river systems often target larger upstream water consumers as an intuitive solution for increasing flows for downstream ecological needs. Within regulated river systems, simplistic panaceas may have unexpected and unintended results at a watershed level. The Apalachicola–Chattahoochee–Flint River Basin is a large watershed in the south‐eastern United States whose management has been the source of conflict for several decades. This paper tests the hypothesis of whether a reduction in consumptive losses to Flint River flows through the large‐scale implementation of water‐saving agricultural irrigation technologies and practices will have a positive effect on downstream ecosystem water requirements in the Apalachicola River. An existing integrated reservoir/reach model was used to explore multiple irrigation water use scenarios. Because of current federal reservoir operating rules in the Chattahoochee River, irrigation decreases in the Flint River do not always directly translate to elevated flows downstream in the Apalachicola River. In drought years, a large percentage of the Flint River water savings is captured as greater storage volume at upstream Chattahoochee reservoirs because of a requirement to supplement downstream flows to a prescribed minimum level. In nondrought years, the majority of irrigation decreases translate to increased flow in the Apalachicola River. Given these simulation results, public policy decisions need to be formulated with regard to what portion of the Flint River water savings from changing irrigation practices in drought years should be allocated to the upstream Chattahoochee storage reservoirs and what portion to supporting downstream environmental and social needs in the Apalachicola watershed.     

Impacts of dam construction on streamflows during drought periods in the Upper Colorado River Basin,Texas

The purpose of this study was to assess the impacts of dam construction on streamflow during a severe drought in the upper Colorado River basin (TX), upstream of Lake Buchanan reservoir. The region has experienced severe, prolonged droughts over the past century. To ameliorate the effects of drought, and increase water storage for use during dry periods, several dams were constructed on the mainstem and tributaries of the Colorado River upstream of Lake Buchanan since the late‐1940s. Analysis of flow at the gauge above Lake Buchanan indicated streamflow was significantly reduced during the recent drought (2009–2014), compared with streamflows during the ‘drought of record’ (1950–1957). The construction of these upstream dams reduced streamflow by intercepting and storing water. It is concluded that building reservoirs in the western portion of the basin, largely in response to past droughts, although increasing water supplies for local uses, exacerbated the downstream effects of the hydrological drought, essentially making it the worst in recorded history.     

Discharge pulses of hydroelectric dams and their effects in the downstream limnological conditions: a case study in a large tropical river (SE Brazil)

To address daily fluctuations in electricity demands, the quantities of water passing through the turbines of hydropower plants can vary significantly (up to fourfold) during a 24‐h cycle. This study evaluates the effects of hourly variations in water discharges on the limnological conditions observed in two below‐dam river stretches. The study reservoirs, Capivara and Taquaruçu, are the 9th and 10th reservoirs in a cascade of dams in the Paranapanema River in south‐east Brazil. The reservoirs exhibit different trophic conditions, water retention times, thermal regimes and spillway positions. Capivara Reservoir is deeper, meso‐eutrophic, with a high water retention time and hypolimnetic discharges (32 m) varying between 500 and 1400 m³ s^?1. In contrast, Taquaruçu Reservoir is relatively shallow, oligo‐mesotrophic, and has a low retention time, with water discharges varying between 500 and 2000 m³ s^?1. Its turbine water intake zone also is more superficial (7 m). For two periods of the year, winter and summer, profiles of limnological measurements were developed in the lacustrine (above‐dam site) zones of the reservoirs, as well as in the downstream river stretches (below‐dam site). In both cases, the sampling was carried out at 4‐h intervals over a complete nictemeral cycle. The results demonstrated that the reservoir operating regime (water discharge variations) promoted significant differences in the conditions of the river below the dams, especially for water velocity, turbidity, and nutrient and suspended solids concentrations. The reservoir physical characteristics, including depth, thermal stratification and outlet structure, are also key factors influencing the limnology and water quality at the below‐dam sampling sites. In the case of Capivara Reservoir, for example, the low dissolved oxygen concentration (<5.0 mg L^?1) in its bottom water layer was transferred to the downstream river stretches during the summer. These study results demonstrated that it is important to continue such investigations as a means of verifying whether or not these high‐amplitude/low‐frequency variations could negatively affect the downstream river biota.     

The role of the hyporheic zone in the nitrogen dynamics of a semi‐arid gravel bed stream located downstream of a heavily polluted reservoir (Tafna wadi,Algeria)

Nitrogen retention was measured along the Tafna wadi downstream of a heavily polluted reservoir in North‐West Algeria to understand the role of the hyporheic zone (HZ) in nitrogen dynamics. Nutrient concentrations were measured monthly for 2 years within the bed sediments of a 300 m reach located 20 km downstream from the dam. Due to strong hydrological fluctuations hyporheic water was analysed during natural low and high water (HW) periods, and during water reservoir releases. Nutrient concentrations in surface water (SW) increased during water releases and in the HZ during the low water (LW) periods. Surface/hyporheic water interactions were characterized by determining the vertical hydraulic gradient (VHG) and the chemical signature of the ground water (GW). The latter was obtained from regional GW monitoring. Hyporheic chemistry was strongly influenced by patterns of surface flow. Hyporheic and SWs had similar chloride concentrations during high flow when they were significantly lower than those of the regional GW. GW was generally richer in nitrates and nitrites, but was lower in ammonium concentrations than interstitial and river waters. Nitrates decreased significantly from upstream to downstream within the HZ throughout the hydrological period even though temporal fluctuations were high. Ammonium concentrations in interstitial water (IW) were significantly higher than in SW and generally increased from upstream to downstream. This study demonstrates the importance of the HZ in altering the dissolved inorganic nitrogen composition and concentrations of heavily polluted arid streams. The study is of interest because it documents a large ‘natural experiment’ that being the effect of periodic water release from a reservoir with serious water quality problems on the water quality dynamics (particularly nitrogen) of subsurface and SWs downstream. Copyright © 2008 John Wiley & Sons, Ltd.     

SHIP‐LOCK–INDUCED SURGES IN AN IMPOUNDED RIVER AND THEIR IMPACT ON SUBDAILY FLOW VELOCITY VARIATION

The majority of large rivers are fragmented by dams, and navigation is often supported by the installation of ship locks. Despite their ubiquitous existence, the effect of ship locks on river basin hydrodynamics is rarely considered in an environmental context. Ship‐lock operation induces single‐wave crests or troughs called surges, which propagate along the basin and are subject to reflection at the up‐ and downstream impoundments. We used pressure sensors and acoustic Doppler current profiler measurements to investigate the effects of up‐ and downstream ship locking on the water level and the current velocity dynamics in a 12.9‐km‐long basin of the impounded river Saar (Germany). Ship lifting at the lower dam and the associated water export from the basin results in a negative surge propagating upstream, whereas a descending ship‐lock operation at the upper dam of the basin creates a positive surge propagating downstream. Both types of waves are subject to positive reflection at the opposing dams. Frequent lock operations lead to a complex pattern of multiple superimposing surges. The resulting water level fluctuations are comparable in magnitude with those associated with discharge variations due to hydropower peaking but occur at much shorter timescales. Associated with the water surface displacement during wave passage is a corresponding increase or decrease of the longitudinal current velocity. The magnitude of wave‐induced velocity fluctuations can exceed mean flow velocities by a factor of three and, depending on wave type and direction, can result in a reversal of the main flow direction of the river. Because of their longevity of several hours and superposition effects, ship‐lock–induced surges govern 66.3% and 45.4% of the subdaily variations in flow velocity and water level, respectively. This article concludes with a discussion of the potential effects of lock‐induced flow dynamics in impoundments on oxygen dynamics and methane ebullition. Copyright © 2013 John Wiley & Sons, Ltd.     

向家坝水电站泥沙淤积计算

为了研究上游为两个水库共同调度的情况下水库泥沙的淤积特性,选取了金沙江干流向家坝水电站作为研究对象.采用自主开发的一维非恒定流泥沙冲淤计算数学模型对向家坝水电站水库泥沙淤积进行了计算,具体对水库库区泥沙淤积、水库河床纵剖面变化、水库库容损失、水库排沙比、库区坝前泥沙淤积厚度作了计算,进一步分析泥沙淤积形态、泥沙淤积速度、库容损失以及排沙比的变化特点,得出了以下结论:由于上游水库的调度作用,使库区来水来沙较天然大不相同,导致库区泥沙淤积呈现带状淤积为主;前期泥沙淤积速度较慢,以后逐年加快,接近平衡时,淤积速度才又减慢;库容损失逐年增加;排沙比较大,水库运行前期排沙比较大但逐年减小,以后又逐年增大至水库淤积平衡.此外,还简要介绍了向家坝、溪洛渡以及雅砻江上的二滩电站的联合运行的综合拦沙效应.     

河流水电梯级开发水温累积影响研究

从流域开发对河流水温结构的影响方面进行分析,采用现场观测和数学模型计算相结合的方法,对水库水温结构进行研究,同时,对梯级电站下泄水温的累积影响进行数值模拟研究。研究结果表明,高坝大库对河流水温改变大,对水温累积影响的贡献大;流域开发程度越高,累积影响越大,5个梯级比3个梯级累积影响大。这一定量研究成果体现了梯级电站的水温累积影响和群体效应,可推进梯级水电站对河流水温影响的研究进程,并为研究大型电站运行减缓下泄低温水的对策措施提供依据和参考。     

Reservoir Management in the Duero Basin (Spain): Impact on River Regimes and the Response to Environmental Change

The climatic conditions of the Iberian Peninsula result in an imbalance between water availability and demand, which is largely managed through the many dams that were built during the 20th century. However, dam operations modify the natural functioning of rivers and related subsystems. In this study we investigated the effect of reservoirs on river regimes in the Duero basin, which is one of the largest river basins in Spain. This involved calculation of a modified impoundment ratio index, and assessment of the correlations between monthly inflows and outflows. Water resources in the basin have decreased markedly during the last five decades, so we also studied how patterns of management have adapted to less water availability in the region. A significant correlation was found between the level of impoundment and the alteration of river regimes by dams. The degree of regulation was highly dependent on annual inflows into the reservoir, and consequently alterations to river regimes were more intense during dry years. The basic pattern of flow regulation involved the storage of water during winter and spring in preparation for high water demand in summer, when natural flows are low. A combination of trend and cluster analyses revealed three responses of reservoir managers to decreasing inflows during the study period: (i) for several reservoirs the level of storage was reduced; (ii) for many reservoirs, particularly those for hydropower production, the storages were increased; and (iii) for the remainder the storage levels were maintained by adjusting the outflows to the decreasing inflows. The results suggest the absence of a common approach to reservoir management, and the dominance of other interests over environmental concerns, particularly in the context of hydrological change in the basin.     

三峡水库运行期设计洪水及汛控水位初探

考虑长江上游水库群调蓄对三峡水库设计洪水的影响,采用最可能组成法和典型年法推求干支流控制站洪水的地区组成,构建多输入单输出(MISO)系统模型模拟向家坝至三峡水库未控区间的洪水过程,研究探讨三峡水库运行期设计洪水及汛期防洪控制水位(汛控水位)。结果表明:长江上游干支流梯级水库的调蓄作用对三峡水库设计洪水影响显著;三峡运行期千年一遇设计洪峰流量为81 136 m3/s,3、7、15和30 d洪量分别为188.2、386.3、727.4和1320.9亿m3,相比建设期设计值分别削减了18.2%、23.8%、20.6%、20.2%和16.9%;在不降低防洪标准的前提下,三峡水库运行期汛控水位(155 m)比建设期汛限水位(145 m)抬高了10 m,这不仅有利于库区航运、维护库岸稳定、保护消落区生态环境,还可增发电量、减少蓄水期对洞庭湖和鄱阳湖的影响,经济社会和生态环境效益巨大。     

Peaking hydropower and fish assemblages: an example from the Tallapoosa River,AL

Dams alter many aspects of riverine environments and can have broad effects on aquatic organisms and habitats both upstream and downstream. While dams and associated reservoirs can provide many services to people (hydropower, recreation, flood control, and navigation), they can also negatively affect riverine ecosystems. In particular, hydropeaking dams affect downstream fish habitats by increasing variability in discharge and temperature. To assess the effects of Harris Dam on the Tallapoosa River, AL, operating under an adaptive management plan implemented in 2005, we sampled fish for community analyses from four sites on the river: three in the regulated reach downstream of the dam, and one unregulated site upstream. Fish were collected every other month using boat/barge electrofishing. We used Shannon's H, nonmetric multidimensional scaling (NMDS), a multiresponse permutation procedure (MRPP), and indicator species analysis to quantify patterns in fish assemblage structure and determine how assemblages varied among sites. NMDS and MRPP indicated significant fish assemblage differences among sites, with the tailrace fish assemblage being distinct from the other downstream sites and sites becoming more similar to the upstream, unregulated site (relative to fish assemblages) with distance downstream of the tailrace. The tailrace fish assemblage included higher proportions of rheophilic species that may be better suited to variable and/or high flows. Altered fish assemblages demonstrated continued effects of Harris Dam on the downstream aquatic systems, particularly close to the dam. These effects may indicate that further mitigation should be considered depending on conservation and management goals.     

Effects of river regulation on aquatic macrophyte growth and floods in the Hadejia‐Nguru Wetlands and flow in the Yobe River,northern Nigeria; implications for future water management

The Hadejia River is a tributary of the Yobe River in semi‐arid northern Nigeria and is regulated by two major dams. The other main tributary is uncontrolled. Comparison of the discharge data for the controlled and uncontrolled rivers shows an average decrease of 33% in annual flow in the upstream part of the Hadejia River. The total annual flow and the peak flow in the Hadejia River further downstream, just above the Hadejia‐Nguru Wetlands (HNW), however, did not show a significant reduction in discharge. This is related to a relatively small river flow reduction at lower flows in the upstream part of the Hadejia River and the fact that the formal large upstream water users are not (yet) working at full capacity. The major impact of the dams on the downstream part of the river is the change in regime from ephemeral to perennial. The introduced dry season flows created favourable circumstances for the development of aquatic macrophyte blockages in the HNW. Owing to these blockages, the Hadejia River stopped contributing to the flow in the Yobe River for much of the year. Furthermore, after the completion of the dams, the timing of the floods in the HNW became less predictable. Suggestions for improvement of water management are made. These comprise engineering structures, including a flow diversion structure to regulate flows in the HNW, implementation of environmentally acceptable river flow strategies and water allocation management. Copyright © 2002 John Wiley & Sons, Ltd.     

反调节作用下的梯级水库短期优化调度研究

为充分发挥上游大型水电站的调峰作用,保障下游供水、生态流量等供给,在下游建设反调节水库的梯级水库运行模式应运而生。目前,对水库反调节的研究多侧重于下库对上库出库流量或发电水头单方面的调节,并未将两者结合考虑。针对上述情况,以堵河流域潘口-小漩梯级水库为例,结合该梯级中“以电定水”与“以水定电”运行模式并存的生产实际,综合考虑小漩对潘口出库水量的调蓄作用以及对潘口尾水的顶托作用,建立了潘口-小漩梯级水库短期优化调度模型,并采用改进的POA算法对模型进行求解。计算结果表明：抬高小漩水库运行水位并保持其机组位于高效率区运行能够提升梯级水电站整体的发电效益。     

滦河流域大中型闸坝水文生态效应

为揭示滦河流域水库对下游河流水文影响,辨析其生态效应,建立了流域闸坝水生态效应评估体系,运用河流影响因子(RI)法评估了闪电河、庙宫、潘家口和桃林口水库的水生态效应,进一步运用水文变化范围(RVA)法评估了潘家口水库的水生态效应。结果表明:1各水库对水文的影响程度为:潘家口桃林口闪电河庙宫,水库的水文效应同时受其级别(库容)和河流原始径流量影响,小型河流水库的水文生态效应不容忽视。2潘家口水库IHA指标(RVA法)总改变度为0.88,第1~2组指标发生了高度改变(0.91),第3~5组指标发生中度改变(0.45),强烈改变了鱼类洄游、底栖生物和植物群落等生态过程。生态水文同步监测与生态模型构建将有助于提升河流生态系统预警能力,为河流生态恢复提供科学依据和技术工具。     

Waterfall formation at a desert river–reservoir delta isolates endangered fishes

Unforeseen interactions of dams and declining water availability have formed new obstacles to recovering endemic and endangered big‐river fishes. During a recent trend of drying climate and declining reservoir water levels in the Southwestern United States, a large waterfall has formed on two separate occasions (1989–1995 and 2001–present) in the transition zone between the San Juan River and Lake Powell reservoir because of deposited sediments. Since recovery plans for two large‐bodied endangered fish species, razorback sucker (Xyrauchen texanus) and Colorado pikeminnow (Ptychocheilus lucius), include annual stockings in the San Juan River, this waterfall potentially blocks upstream movement of individuals that moved downstream from the river into the reservoir. To quantify the temporal variation in abundance of endangered fishes aggregating downstream of the waterfall and determine population demographics, we remotely monitored and sampled in spring 2015, 2016, and 2017 when these fish were thought to move upstream to spawn. Additionally, we used an open population model applied to tagged fish detected in 2017 to estimate population sizes. Colorado pikeminnow were so infrequently encountered (<30 individuals) that population estimates were not performed. Razorback sucker captures from sampling (335), and detections from remote monitoring (943) showed high abundance across all 3 years. The razorback sucker population estimate for 2017 alone was 755 individuals and, relative to recent population estimates ranging from ~2,000 to ~4,000 individuals, suggests that a substantial population exists seasonally downstream of this barrier. Barriers to fish movement in rivers above reservoirs are not unique; thus, the formation of this waterfall exemplifies how water development and hydrology can interact to cause unforeseen changes to a riverscape.     

Determining the effects of dams on subdaily variation in river flows at a whole‐basin scale

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.     

梯级水电开发中生态保护分析与生态水头理念及确定原则

在分析水电开发对生态环境影响及原因的基础上,归纳了近年来水电站建设运行中生态保护措施的研究进展,包括过鱼设施的建设、鱼类增殖放流站的构建、大坝下游河道断面生态流量的确定和梯级水电站水库生态调度,并阐释了这些措施在河流梯级水电开发生态保护中的不足,提出了河流梯级水电开发水头与生态水头协同确定的理念,界定了基于河流自然生境和原生生态及物种保护的生态水头的概念、内涵与确定原则,给出了生态水头规划的综合优化方法。