Influence of cascade reservoirs on spatiotemporal variations of hydrogeochemistry in Jinsha River

River hydrogeochemistry offers necessary guidance for effective water environmental management.However,the influence of cascade reservoirs on river hydrogeochemistry remains unknown.In this study,the Jinsha River,the headwaters of the Yangtze River of China,was selected to investigate the spatiotemporal variations of hydrogeochemistry after the construction of six cascade reservoirs.Major ions,total dissolved solids,electrical conductivity,and pH values of sampled water in the upper natural reaches and lower reservoir-regulated reaches were analyzed in both flood and dry seasons.The results of Piper diagram and Gibbs plots showed that the hydrogeochemistry of the Jinsha River was naturally controlled by both evaporation-crystallization and carbonate weathering processes,but it was also artificially affected by reservoirs.The impoundment of cascade reservoirs affected the hydrodynamic condition of the river.The river flow in the flood season was reduced by approximately 24.5%,altering the proportions of water sources and leading to notable hydrogeochemical alterations in reservoir-regulated reaches.Conversely,river hydrogeochemistry generally remained unchanged in the dry season,owing to the insignificant effect of cascade reservoirs on river flow.In contrast to what has been observed in previous studies of individual reservoirs,the cumulative influence of cascade reservoirs on the Jinsha River flow regime did not cause abrupt hydrogeochemical changes between the upstream and downstream areas of each reservoir.Moreover,the water quality assessments revealed that the impoundment of cascade reservoirs improved downstream irrigational water quality,with lower Na~+ ratio values in the flood season.This study provides the earliest evaluation of cascade reservoir influence on the hydrogeochemistry of the Jinsha River.The findings of this study can be used as a reference for scientific guidelines for future environmental management of cascade reservoirs in large rivers.     

三峡水库2003年蓄水对长江中下游水情影响分析

三峡工程经过近10 a的建设于2003年6月上旬蓄水至135 m,工程进入围堰发电运行期,10月由于航运等方面的需要,水库第2次蓄水至139 m.水库蓄水减少了上游来水,使中下游的水情发生了相应的变化,其变化也引起了社会各界的关心.根据三峡水库的蓄水情况,对2003年三峡水库蓄水期间长江中下游主要站螺山、汉口、大通站水位、流量进行研究,分析三峡水库蓄水对长江中下游水情的影响.     

河流生态流量特征图及生态流量评价方法

以水电站大坝下游河道为研究对象,从分析天然日流量特征出发,基于月中值流量和月内典型特征流量绘制了河流生态流量特征图,作为水库下泄生态流量的确定依据。基于此河流生态流量特征图,建立了判断生态流量满足程度的7 d流量偏差率、7 d生态需水保证率、月均生态需水适宜度及基于此3个指标的生态需水综合指标,并给出了各指标的评价依据和评价方法。结果表明,河流生态流量特征图符合各时段河流天然流量的基本特征,可作为指导水库生态泄流的依据;所建立的生态流量评价方法能够反映实际下泄流量与天然流量的变化程度,可用于评价河流的生态流量满足程度。     

Effects of an upland impoundment on structural and functional properties of a small stream in a basaltic plateau (golan heights,Israel)

The aim of the study was to evaluate the impact of an upland storage reservoir, typical of the series of reservoirs in the Golan Heights basaltic plateau, on structural and functional properties of the downstream ecosystem, in the vicinity of the reservoir, shortly after damming. The effect of impoundment on water quality conditions may be divided into winter-spring, and summer periods. In the former, the impoundment seems to lengthen the period of flow of runoff quality water. This is evident by the elevated winter and spring turbidities and the higher concentrations of suspended solids below the reservoir. In summer, water quality below the reservoir is controlled by the consequences of stratification in the reservoir. The hypolimnial release results in depression of the maximal temperature and narrowing of the daily and seasonal temperature variations. It supplies water enriched in nutrients and low in oxygen, suspended solids and turbidity. The macroinvertebrate community responds to impoundment in density changes and shifting of dominance. We hypothesize that the thermal effect of hypolimnial release from warm monomictic reservoirs on the invertebrate community of warm streams will differ from an equivalent thermal change caused by cold dimictic reservoirs in cold, temperate zone, streams. The effect of impoundment on functional properties of the ecosystem are most pronounced. The rate of production of benthic algae biomass below the reservoir increased by more than two orders of magnitude, but the effect diminished downstream. The rate of processing of plant material below the reservoir was lower than above the reservoir. Further investigation is needed to clarify this effect. Changes in reservoir operation are recommended to diminish the effects of impoundment.     

Immediate downstream effects of the Petit-Saut dam on young neotropical fish in a large tributary of the Sinnamary River (French Guiana,South America)

The effects of artificially low runoffs in the Sinnamary River, French Guiana, South America, on flow patterns and on richness and abundance of young fish in Venus Creek, one of its main downstream tributaries were examined. After Petit-Saut dam's gates were closed, the areas adjacent to this tributary were never once flooded for the entire duration of the rainy season. The daily maximal averages of water speed at the tributary's mouth were found to be significantly increased. Young fish sampled using light-traps were less abundant and less diverse after dam closure. Young Characiformes appeared to be the most affected by these flow disturbances. These findings enabled us to develop a conceptual model of the consequences of impoundment on young fish assemblages through the modifications of tributaries and associated floodplains hydrology. Because of flow reduction in the river during the first year of impoundment, young fish that previously had a tendency of being trapped in tributaries and flooded areas were then at risk of being flushed away. The pattern of flow release by dam operations is known to be very different from natural flow variations. The consequences for downstream tributaries will be similar to those of channelization: lack of adjacent flooding areas and higher rates of downstream water transfer. How the recovery of downstream fish assemblages will occur is discussed. © 1998 John Wiley & Sons, Ltd.     

Mitigation of cold‐water thermal pollution downstream of a large dam with the use of a novel thermal curtain

Hypolimnial releases from dams during periods of thermal stratification modify the downstream riverine thermal regime by decreasing water temperature and reducing natural diel thermal variability. This cold‐water thermal pollution in rivers can persist for hundreds of kilometres downstream of dams and impact important ecological processes such as fish spawning. To mitigate this problem, a first‐of‐its‐kind thermal curtain was fitted to the large bottom release Burrendong Dam on the Macquarie River, Australia. The thermal curtain acts by directing warmer, near‐surface epilimnial water to the low‐level hypolimnial offtake. This study aimed to test the efficacy of the thermal curtain by measuring temperatures before and after the curtains installation, quantifying the magnitude and extent of cold‐water thermal pollution along the Macquarie River downstream of Burrendong Dam. Epilimnial releases with use of the curtain increased diel temperature ranges and the mean monthly water temperature below the dam. Epilimnial releases with use of the curtain increased diel temperature ranges from 0.9°C to 2.5°C and reduced the difference between the mean monthly water temperature of an upstream control and a downstream site by up to 3.5°C. A comparison of the monthly temperature means along the river, indicated that thermal recovery, whereby temperatures returned to within the natural range of upstream temperatures occurred 45 km downstream of the dam during summer when the thermal curtain was deployed, compared with approximately 200 km prior to deployment of the curtain. Our study suggests that the use of thermal curtains can reduce cold‐water thermal pollution and improve ecological outcomes for river ecosystems downstream of dams.     

补偿中华鲟产卵场水动力环境的梯级水库联合生态调度研究

三峡—葛洲坝梯级水利枢纽工程的建设和运行阻隔了长江部分洄游鱼类的洄游通道,梯级水库的联合调度运行改变了坝下河道天然径流过程,对被迫在坝下形成新产卵场的珍稀水生物中华鲟的产卵繁殖产生一定影响。为有效保护中华鲟资源,在明确梯级水库调度运行与中华鲟产卵场产卵适合度相关性分析的基础上,提出优化三峡下泄流量和葛洲坝运行方式相结合的三峡—葛洲坝梯级水库生态调度方式,以补偿中华鲟产卵栖息所需的河流生境。通过以三峡水库的实际来流过程输入水库生态调度模型,得出中华鲟产卵期(每年10—12月)补偿其产卵栖息水环境的梯级水库联合生态调度方式。根据梯级水库生态调度与现有调度结果进行分析比较结果表明:梯级水库联合生态调度可在满足三峡水库常规调度目标的基础上同时满足中华鲟产卵所需的生态流量,配合葛洲坝电厂优化调度运行方式,可有效增加坝下中华鲟产卵场水动力环境产卵适合度,补偿梯级水库运行对中华鲟产卵生境造成的不利影响。     

Influence of dams on river water‐quality signatures at event and seasonal scales: The Sélune River (France) case study

Dams and reservoirs are known to disturb river‐water composition, among other impacts, with potential implications for downstream river ecosystems and water uses. Existing studies have emphasized the variable influence of dams on water composition according to the element, its speciation (dissolved vs. particulate), reservoir properties (residence times), reservoir functions (e.g., hydropower, irrigation), and management (water releases). A now common approach to analyzing hydrological, geochemical, and biological controls on element export from unregulated rivers is to study hydrochemical signatures such as concentration‐flow relationships. We investigated a case study to analyze hydrochemical signatures of a regulated river (Sélune River, western France) upstream and downstream of a chain of two hydropower dams, assuming that the dams disturbed the river's signatures, and that those disturbances would provide information about processes occurring in the reservoirs. Both seasonal and event‐scale signatures were analyzed over two contrasting hydrological years and a range of storm events. The dams induced a chemostatic downstream response to storm events whenever elements were diluted or concentrated upstream. Dams did not disturb the seasonality of major anions but did modify silica and phosphorus concentration‐flow relationships, especially during low flow. Such changes in dynamics of river‐water composition may affect downstream biological communities. This study presents an initial state of the hydrochemical signature of the downstream river, before the removal of the two dams.     

Toledo Bend reservoir and geomorphic response in the lower Sabine River

Downstream geomorphic responses of stream channels to dams are complex, variable, and difficult to predict, apparently because the effects of local geological, hydrological, and operational details confound and complicate efforts to apply models and generalizations to individual streams. This sort of complex geomorphic response characterizes the Sabine River, along the Texas and Louisiana border, downstream of the Toledo Bend dam and reservoir. Toledo Bend controls the flow of water and essentially prevents the flux of sediment from three‐quarters of the drainage basin to the lower Sabine River. Although the channel is scoured immediately downstream of the dam, further downstream there is little evidence of major changes in sediment transport or deposition, sand supply, or channel morphology attributable to the impoundment. Channels are actively shifting, banks are eroding, and sandbars are migrating, but not in any discernibly different way than before the dam was constructed. The Sabine River continues to transport sand downstream, and alluvial floodplains continue to accrete. The relatively small geomorphic response can be attributed to several factors. While dam releases are unnaturally flashy and abrupt on a day‐to‐day basis, the long‐term pattern of releases combined with some downstream smoothing creates a flow regime in the lower basin which mimics the pre‐dam regime, at least at monthly and annual time scales. Sediment production within the lower Sabine basin is sufficient to satisfy the river's sediment transport capacity and maintain pre‐dam alluvial sedimentation regimes. Toledo Bend reservoir has a capacity: annual inflow ratio of 1.2 and impounds 74% of the Sabine drainage basin, yet there has been minimal geomorphic response in the lower river, which may seem counterintuitive. However, the complex linked geomorphic processes of discharge, sediment transport and loads, tributary inputs, and channel erosion include interactions which might increase as well as decrease sediment loads. Furthermore, if a stream is transport‐limited before impoundment, the reduced sediment supply after damming may have limited impact. Copyright © 2003 John Wiley & Sons, Ltd.     

浅谈桂林防洪及漓江补水工程的生态调度

漓江补水工程中的生态调度包括如下4个方面：①建立水库群联合多目标生态调度模型;②确保卜放河道内最小生态需水量;③建设分层取水设施,降低低温水影响;④优化初期蓄水调度方式,确保不断流。通过在设计过程各个层面上的生态调度运用,实现了合理配置水资源、保护漓江生态环境的目标。     

Modification of temperature behaviour through regulation of a British river system

The effects of flow regulation on temperature behaviour in the River Exe, Devon, U.K. have been studied, and attention is given to the local impact of impoundment and its downstream persistence. Temperature levels and seasonal thermal regime are considered as well as diel temperature fluctuations and temperatures during extreme weather conditions. Variations in temperature during individual reservoir releases have also been monitored. The impact of impoundment has been to make the stream environment immediately below the dam more homothermous so that temperatures rearely rise above 17·5°C or fall below 2·0°C, and monthyl average diel ranges are < 3 and < 1°C in summer and winter months respectively. In contrast to other reservoirs in Britain and abroad, this effect has been largely caused by increased groundwater flow downstream from the reservoir following impoundment. Regulation has also affected downstream temperature behaviour and has moderated the thermal regime of the Exe mainstream. This influence is generally restricted to a distance of up to 20 km from the dam, but in conditions of hot weather and low flows it may extend to almost 40 km from the impoundment.     

The impact of river regulation on invertebrate communities in the U.K.

The impact of river regulation on invertebrates has received comparatively little attention in the U.K., with most studies concentrating on the effects of impoundment. During dam construction invertebrate diversity and abundance decreases. Longer term alterations in community structure (which usually extend for a relatively short distance downstream) reflect changes in flow, substrate, temperature, and water quality. In particular adverse effects on invertebrates have been attributed to a reduction in substrate heterogeneity together with an accumulation of sediment. Responses to impoundment within and between taxonomic groups are highly variable. In general Ephemeroptera and Coleoptera are reduced. Of the Plecoptera the Perlodidae and Chloroperlidae are more likely to be adversely affected than the Nemouridae or Leuctridae. The impact of impoundment on net-spinning Trichoptera varies with reductions in some populations and enhancement in others. Simuliids are usually restricted, probably because of a lack of suitable oviposition or attachment sites. Freshets released from reservoirs increase the level of invertebrate drift. However, the full consequences of impoundment on drift, recolonization, and upstream migration have yet to be assessed. There is some evidence that modified temperature regimes cause extended egg hatching periods and alter larval growth rates but further studies are needed. Little is known of the effects of inter-river transfers on invertebrates, but it has been suggested that changes in flow velocity, water chemistry, suspended solids, and temperature together with translocation of organisms are all likely to be important. The limited information available for groundwater schemes indicates that they are not detrimental to invertebrates. Their impact, however, is dependent upon factors such as the extent and timing of flow augmentation. It is suggested that there is scope for positive management of invertebrate communities through river regulation, although at present attitudes and practices do not encourage this. Many gaps in our knowledge still remain and these are discussed in relation to future research needs.     

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.     

溪洛渡、向家坝水库与三峡水库联合蓄水调度研究

由于溪洛渡、向家坝水库与三峡水库蓄水时间上的同步性,使三峡水库蓄水难度进一步加大,进而影响其综合效益的发挥。为满足下游地区在蓄水期对上游梯级水库下泄流量的新要求,研究金沙江溪洛渡、向家坝水库与三峡水库联合蓄水调度方案,优化梯级水库蓄水过程。在综合分析防洪、泥沙、库区、发电及供水等指标基础上,推荐梯级水库蓄水调度方案。防洪、库区淹没及泥沙淤积的影响分析表明,所提方案可进一步缓解下游地区的供水压力,对金沙江梯级水库联合蓄水调度一定实践指导意义。     

雅砻江和金沙江中下游梯级水库联合优化调度建模及应用Ⅱ——联合优化调度规则分析

为提升长江上游水资源利用效率,在“雅砻江和金沙江中下游梯级水库联合优化调度建模及应用Ⅰ—联合优化调度潜力分析”的基础上,进一步探究了雅砻江和金沙江中下游梯级上下游水库间和不同梯级间的运行规律,绘制了联合优化调度图,并分析了相关电站的蓄放水次序。研究表明:汛前金中、雅砻江梯级水库与金下梯级各水库消落开始次序宜为两河口—龙盘—锦屏一级—二滩—向家坝—白鹤滩—溪洛渡—乌东德,总体消落思路为上游水库优先消落,尽可能的保持下游溪洛渡、乌东德等电站高水位运行,提高流域整体发电效益;汛末各水库蓄水开始次序宜为锦屏一级—龙盘/二滩—两河口—乌东德—白鹤滩/溪洛渡—向家坝,总体蓄水思路为上游水库优先释放防洪库容开始蓄水,减轻下游防洪压力,且来水偏丰年份的蓄水时间相应有所推迟。     

Responses of the sediment system of a regulated river to a scour valve release: Llyn Clywedog,mid-Wales,U.K.

In March 1985 engineering tests of scour valves at the base of the Llyn Clywedog regulating reservoir resulted in a controlled peak release discharge of 53m³ s^?1 into regulated reaches of the upper Severn. To exploit this unusual opportunity, simple monitoring systems were set up within the first 50 km downstream to assess the morphological effects on bed and banks and the movement of bed and suspended sediments. The interpretation of suspended sediment transport patterns became the major analytical task following the release, since bedload and morphological impacts were minimal. In comparison with natural floods, the scour valve release exhibited suspended sediment concentrations usually associated with a five-year event, but with a complex time and space pattern resulting from the release strategy. Wet antecedent conditions and the short duration of the scour valve release help to explain why impacts on the downstream channel were, otherwise, much more restricted than those of a water resource test release in 1975. Since scour releases can be planned with greater flexibility than major water resource releases, indications are that they should be made ‘on the back of’ natural high flows, although sensitive sites may require protection.     

THE COMBINED EFFECTS OF FLOW REGULATION AND AN ARTIFICIAL FLOW RELEASE ON A REGULATED RIVER

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.     

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.     

EFFECTS OF FLOW RELEASES ON MACROINVERTEBRATE ASSEMBLAGES IN THE INDIAN AND HUDSON RIVERS IN THE ADIRONDACK MOUNTAINS OF NORTHERN NEW YORK

The effects of flow releases (daily during spring and four times weekly during summer) from a small impoundment on macroinvertebrate assemblages in the lower Indian River and upper Hudson River of northern New York were assessed during the summers of 2005 and 2006. Community indices, feeding guilds, dominant species and Bray–Curtis similarities at three sites on the Indian River, below a regulated impoundment, were compared with those at four control sites on the Cedar River, below a run‐of‐the‐river impoundment of comparable size. The same indices at four less‐likely affected sites on the Hudson River, below the mouth of the Indian River, were compared with those at an upstream control site on the Hudson River. Results show that the function and apparent health of macroinvertebrate communities were generally unaffected by atypical flow regimes and/or altered water quality at study reaches downstream from both dams in the Indian, Cedar and Hudson Rivers. The lentic nature of releases from both impoundments, however, produced significant changes in the structure of assemblages at Indian and Cedar River sites immediately downstream from both dams, moderate effects at two Indian River sites 2.4 and 4.0 km downstream from its dam, little or no effect at three Cedar River sites 7.2–34.2 km downstream from its dam, and no effect at any Hudson River site. Bray–Curtis similarities indicate that assemblages did not differ significantly among sites within similar impact categories. The paucity of scrapers at all Indian River sites, and the predominance of filter‐feeding Simulium gouldingi and Pisidium compressum immediately below Abanakee dam, show that only minor differences in dominant species and trophic structure of macroinvertebrate communities occurred at affected sites in the Indian River compared to the Cedar River. Thus, flow releases had only a small, localized effect on macroinvertebrate communities in the Indian River. Copyright © 2011 John Wiley & Sons, Ltd.     

Including environmental flow requirements as part of real‐time water resource management

South African water resources legislation requires that environmental flow requirements are included as part of water resource management. An operational management method is presented that relies upon simulating natural flow conditions based on inputs of near real‐time observations of rainfall and a set of operating rules. The operating rules define the reservoir releases and water use supply curtailments that ensure downstream environmental flow objectives will be met. The focus is on managing the variability of continuous low flows, while a suitable method for managing event‐based high flow releases remains elusive. The main limitation to the successful implementation of the low flow approach is the lack of legislated control over run‐of‐river water abstractions. While this limitation is expected to be overcome, as the provisions of new legislation are implemented, water managers may still lack the capacity to exercise the necessary controls over abstraction. There is no reason why the method could not be applied outside South Africa, given compatibility in the definition of environmental flow requirements. Copyright © 2008 John Wiley & Sons, Ltd.