Large Hydropower Dams Research Articles

Longitudinal Recovery of Suspended Sediment Downstream of Large Dams in the US

AbstractDams disrupt the natural flow of water and sediment along rivers. Reservoirs trap a significant amount of sediment, which substantially alters downstream hydrology, channel morphology, and sediment transport capacity. The longitudinal recovery of suspended sediment concentration (SSC) along rivers is potentially a new metric for estimating downstream responses to dams over space, rather than time, but is rarely quantified due to the lack of spatial SSC data. Satellites can estimate SSC along rivers where no field data exist and provide a high enough spatial resolution for assessing downstream recovery at the scale of tens to hundreds of kilometers. Here, we use a recently published database of spatially explicit SSC observations derived from Landsat to quantify if a river recovers or not, the SSC recovery percentage, and SSC recovery length downstream of large dams across the Contiguous United States (CONUS). Rivers recover SSC downstream of most dams (71%). The chance of a river recovering and the length of river required to recover SSC is associated primarily with the size of the reservoir (mean storage, km3) and the size of the river (mean discharge, m3/s). Rivers were more likely to recover SSC downstream of run‐of‐river, navigation dams compared to large storage or hydropower dams. Our results suggest that rivers typically recover suspended sediment downstream of dams, influenced by factors like dam storage, purpose, and river channel characteristics.

The Don Sahong Dam in Laos: Political Ecology, Infrastructure, and the Changing Spatialities of Impacts on Fish and People

The Don Sahong Hydropower Project (DSHPP), located in the Khone Falls area of Khong District, Champasak Province, southern Laos, near the border with Cambodia, has been amongst the most controversial hydropower dams in the Mekong River Basin. Despite considerable regional and international opposition, the dam was finally constructed, becoming commercially operational in 2020. In 2011, I expressed serious concerns about the project's potential impacts on long-distance migratory fish and associated fisheries, especially fish that migrate from Cambodia and Vietnam up the Mekong River to Laos and Thailand. However, my concerns have somewhat changed along with the circumstances, although they continue to focus on dam impacts on migratory fish. I am now particularly concerned about the indirect impacts of the DSHPP on the fishing livelihoods in the Khone Falls area, and the impacts of the dam on fish larvae and fish passing through the dam's turbines when migrating downstream. Using a political ecology approach, this paper considers how infrastructure, in this case a large hydropower dam located on the Mekong River, has altered the spatialities associated with the project in particular ways.

Unique diet and Philonema sp. infections in reservoir‐rearing juvenile Chinook Salmon

AbstractObjectiveDams and reservoirs can alter juvenile growth and survival of migratory salmonids through several physical and biological mechanisms. Juvenile Chinook Salmon Oncorhynchus tshawytscha that are produced upstream of large hydropower dams may have associated passage mortality, but the reservoirs created by these dams can support rapid growth. Characterizing the biotic drivers of growth and mortality in reservoirs may aid in understanding the cumulative effects of river impoundments on migratory salmonid populations. The purpose of this study was to understand how reservoirs facilitate rapid growth in juvenile Chinook Salmon.MethodsWe analyzed stomach contents to determine diet composition throughout the summer and fall. We also recorded prevalence of the parasitic nematode Philonema sp. in the coeloms of fish.ResultWe found that juvenile Chinook Salmon frequently consumed young‐of‐year centrarchids, which likely contributed to rapid growth. Piscivory was highest from July through October and decreased with surface temperature from November through December. Correspondingly, zooplankton and arthropod consumption increased in November and December. Prevalence of visible Philonema sp. infections in the coelom was high (34.6%), negatively associated with time, and nonlinearly associated with fork length.ConclusionThese findings reveal unique diet patterns and suggest potential parasite‐associated mortality in reservoir‐rearing Chinook Salmon, but more detailed studies across a longer time scale are needed to robustly assess the population‐level effects of this parasite.

Poverty-Food Insecurity Nexus in the Post-Construction Context of a Large Hydropower Dam in the Brazilian Amazon.

Within the 2030 Sustainable Development Agenda, large hydropower dams are positioned as a sustainable energy source, notwithstanding their adverse impacts on societies and ecosystems. This study contributed to ongoing discussions about the persistence of critical social issues, even after the investments of large amounts of resources in areas impacted by the construction of large hydropower dams. Our study focused on food insecurity and evaluated this issue in the city of Altamira in the Brazilian Amazon, which has been profoundly socially and economically impacted by the construction, between 2011 and 2015, of Brazil's second-largest dam, namely, Belo Monte. A survey in Altamira city featured a 500-household random sample. Structural equation modeling showed conditioning factors of 60% of the population experiencing varying food insecurity degrees. Poverty, female-led households, lower education, youth, and unemployment were strongly linked to higher food insecurity. Crowded, officially impacted, and resettled households also faced heightened food insecurity. Our findings underscore the food insecurity conditions in the region impacted by the Belo Monte dam, emphasizing the need to take into account this crucial issue while planning and implementing hydropower dams.

Effects of regulation on open‐water flows in the lower Peace River, Canada, and implications for the recharge of Peace‐Athabasca Delta basins

AbstractDownstream impacts of large hydropower dams are often neglected or underestimated, especially for areas situated at long distances from a dam. Naturalization of the flow hydrograph is an important step in assessing hydro‐ecological and socio‐economic impacts of regulation. Using reservoir inflows, a recently developed, lagged‐flow naturalization method is applied to the lower portion of the regulated Peace River, which forms the northern boundary of the Peace‐Athabasca Delta (PAD). The PAD is a Ramsar wetland of international importance that depends on overland flooding for recharge of its high‐elevation or “perched” basins. Such flooding can be caused by ice jams during the spring breakup of the ice cover or by exceptionally high runoff during open‐water flow conditions. Herein, the focus is on the latter type of event and the resulting recharge of basins located within the Peace sector of the PAD. For the period 1972–2017, regulation has reduced open‐water flow peaks by ~4100 m3/s on average, while limiting the possibility of overbank flooding from the Peace River during the summer. Consistent with earlier findings on spring breakup flows, naturalized open‐water peaks do not exhibit a temporal trend. Recharge of non‐perched basins can also occur with moderately high flows that cause no overland flooding but generate flow reversals in Peace River tributaries. In turn, this mechanism can deliver river water to various basins either directly or via connecting channels. Our results show that flow‐based variables that index the hydrological sustenance of non‐perched basins have been significantly reduced by regulation.

Flood pulses and fish species coexistence in tropical rivers - a theoretical food web model

AbstractFreshwater fish diversity reaches its zenith in large tropical rivers. Although the origins of this diversity have been relatively well studied, the mechanisms that maintain high fish diversity in tropical rivers remain largely unknown. It has been hypothesized that the annual flood pulse, a perennial feature of many lowland rivers in the tropics, reduces competitive exclusion and consequently promotes species coexistence. During the high-water season, superabundant allochthonous resources and relatively low fish density may reduce intra- and interspecific competition. During the low-water season on the other hand, resource availability is low and predation pressure high, offsetting competitive differences between species and controlling fish population sizes. Here, we tested the potential role of these mechanisms for species coexistence using a food web model where fish species exhibit strong differences in competition strength and compete for finite resources. We simulated fish interactions when a regular flood pulse was either present or absent. We found that extinction rates in the simulations without an annual flood pulse were consistently higher when compared to those with a flood pulse, indicating more species could coexist when a regular annual flood pulse is present. If the flood pulse is a relevant mechanism for fish species coexistence, as our model results suggest, then flood pulse changes could result in species extinctions and lower fish diversity. Deforestation, climate change, and the construction of large hydropower dams are current drivers of hydrological change across the tropics, increasing the urgency to understand the role of natural flooding regimes for the maintenance of tropical freshwater fish diversity.

The impact of hydropower dam construction on malaria incidence: Space-time analysis in the Brazilian Amazon.

During the first two decades of the 21st century, Brazil carried out massive public investments on infrastructure projects, such as large hydropower dams, with potential impact on population health. Here we characterize local malaria transmission and its potential spread during the construction of three large hydropower dams in the Brazilian Amazon. We focus on Porto Velho (PVH), in Rondônia state, where the Santo Antônio and Jirau dams were built (2008-2013), and Altamira region (ATM), in Pará state, where the construction of the Belo Monte dam took place (2011-2016). Analyzed data cover 4 years before, 6 years during, and 4 years after each dam construction. In total, we utilized malaria case notifications entered into the electronic malaria notification system of the Ministry of Health of Brazil between January 2004 and December 2020 (n = 39,977,167 malaria notifications). First, we used Interrupted Time-Series Analysis (ITSA) to assess temporal changes in malaria notifications in the study sites. Then, we conducted a space-time cluster analysis to investigate the potential of malaria spread from the study sites (sources) to elsewhere (sinks). Finally, we present the sociodemographic characteristics of exported cases over time using multivariate logistic regressions. Our results show that there was no upsurge in malaria cases in the study sites and exported cases did not trigger outbreaks in other localities. Exported malaria infections originating from PVH and ATM were typically found in working age literate males involved in mining, farming or traveling. We suggest that efficient control measures, such as ensuring timely diagnosis and treatment; fostering integrated vector control; promoting health education; and prevention, detection and containment of outbreaks, if properly implemented and sustained, may prevent local and introduced malaria outbreaks during and after hydropower dam construction in the Amazon.

Os efeitos do represamento fluvial sobre pescadores artesanais no Médio Rio Tocantins, Brasil

Abstract: Aim The present study investigated the social impacts caused by the construction of a large hydropower dam (Lajeado Dam) on artisanal fishers in the Middle Tocantins River, evaluating how the impoundment affected fishing techniques (locations, transport and gears), operation (income, effort and costs), and fisher’s well-being. Methods The study interviewed 30 artisanal fishers (Colony Z-04, Porto Nacional, TO) between August and October 2018 with the application of a structured questionnaire. Results Results indicated that fishing is socially important as a source of income and occupation, carried out essentially by men with low levels of formal education. Fishers reported, however, significant changes in the fishery system after the impoundment of the Tocantins River. The main fishing area was maintained, but fishers abandoned some sites. There were significant changes in fishing equipment, with an increase in the use of aluminum boats and outboard engines, and a reduction in the use of various gears, replaced by the use of gillnets. Almost all fishers (96.6%) declared that fishing effort and the financial costs increased after damming. Many also reported an increase in financial income (70%), but part reported a decrease, no change or could not say. The majority reported that the impoundment damaged the fishing activity (80%) and their well-being (individual and their families; 83.3%); dissatisfaction with the profession also increased. Conclusions Results indicated that the impoundment created by Lajeado Dam impacted several aspects of artisanal fisheries in the Middle Tocantins, with a wide perception of damage, which indicates that working conditions of fishers have declined. This information is relevant and can support fisheries management in the Tocantins River Basin, in order to balance societal demands with sustainability goals and fisher’s needs.

Generalizing Trends in Upstream American Eel Movements at Four East Coast Hydropower Projects

Abstract Dams impede the upstream migration of juvenile American Eel Anguilla rostrata, limiting their access to freshwater habitat and potentially contributing to population declines across their range. The implementation of fishways at large hydropower dams help restore access to upstream habitat and represents a long-term dataset of American Eel captures. We analyzed the relationships between eel captures and select environmental variables (river discharge, water temperature, and lunar illumination) at four hydropower projects on east coast rivers with a comparable decade of data and sampling techniques: Roanoke Rapids Dam on the Roanoke River in North Carolina, Conowingo Dam on the Susquehanna River in Maryland, Holyoke Dam on the Connecticut River in Massachusetts, and the Moses-Saunders Dam on St. Lawrence River in New York and Canada. The number of eels captured varied among projects, from year to year, and seasonally. American Eel are opportunistic in their upstream movements, with peak movement events associated with high flows, increased water temperature, and low lunar illumination. Our results suggest that systems altered by hydropower dams offer unique challenges to American Eel migrants and that a multitude of factors play a role in the timing of upstream movements.

Hydropeaking impacts on riverine plants downstream from the world's largest hydropower dam, the Three Gorges Dam

Hydropeaking has become a global issue because of extensive hydropower dam construction worldwide. Yet, its ecological impacts on riverine ecosystems are not well studied. We explored the effects of hydropeaking on riverine plants, based on data from a ~300 km reach downstream of the world's largest hydropower dam, the Three Gorges Dam. We tested three hypotheses relating to hydropeaking impacts on species elevational distributions, assemblage structure and species-specific biomass patterns by generalized linear mixed modelling and joint species distribution modelling. We found that, first, hydropeaking greatly shaped species elevational ranges, leading to expansions of herbs to high elevations and shifting species dominance at low elevations. Secondly, we detected contrasting effects of hydropeaking on assemblage-level characteristics of herbs. The inundation induced by hydropeaking had strong effects on assemblage composition and biomass allocation, where more biomass was allocated to belowground part. Hydropeaking blurred the species richness-biomass relationship, although it had little effect on species richness or plot-level biomass. Thirdly, hydropeaking induced inundation was the most important covariate driving species biomass patterns of riverine plants, although complex species-specific effects were identified, and random effects were often large in fitted models. We concluded that hydropeaking likely acted as a major driver of plant community assembly in rivers with a hydropower dam. Conservation and restoration of riverine plants can benefit from the inclusion of water level management in operational schemes of hydropower dams, especially during the early life history stages.

Social perception assessment of hydropower sustainability: A stepwise logistic regression modeling

Hydropower dams could benefit the three dimensions of sustainability of the river basins where they are deployed. However, experiences from large hydropower projects worldwide taught that large hydropower dams may cause serious social and environmental concerns that ultimately derive into public disapproval. Hydropower industries are increasingly aware that public support is a determining factor that could restrict the development of large hydropower projects, and hence industries have started to take action. Recently, a large hydropower industry from Colombia has implemented actions aimed at sustainability to improve the environmental and social welfare of territories without deviating from the business core. However, formulating effective sustainability policies that consider the different viewpoints of industrials, policymakers, and the general community is challenging. Hence, here we aim to identify cause-effect correlations between the impact management actions taken by the firm and the public perception of the impacts caused by two large hydropower dams in the Colombian Andes. To this end, we performed 50 stepwise logistic regressions between ad-hoc impact management perception indices (predictor variables) and impact perception variables (response variables). The data is based on a 25-question survey assessing the public perceptions of 694 respondents from two river basins and three social groups. Findings revealed 28 significant correlations between impacts and impact management, showing that the corporate actions for environmental protection play a crucial role in the public attitudes on sustainability. Our findings may provide guidelines to develop tailored policies aimed at sustainability in the hydropower sector of developing countries.

Alteration of River Flow and Flood Dynamics by Existing and Planned Hydropower Dams in the Amazon River Basin

AbstractHydropower dams have received increased global attention due to their detrimental socioenvironmental ramifications. Such attention has led to an increase in studies on the impacts of reservoir operation on river flow; however, a holistic understanding of the compounded effects of hydropower dams on different hydrological characteristics is lacking, especially for large river basins such as the Amazon where hydropower development is on the rise. Here, we mechanistically quantify the historical impacts of existing dams and the potential impacts of the collective operation of existing and planned dams on a basin‐wide scale in the Amazon for the 1981–2019 period. We build on the recently developed high‐resolution (3‐arcmin; ∼5 km) river‐floodplain‐reservoir model, the CaMa‐Flood‐Dam, which is enhanced to realistically simulate hydropower dam operation considering maximized power production. Flood simulations are further downscaled to 3 arc‐seconds (∼90 m) resolution to investigate the impacts of dams on fine‐scale flood dynamics across the basin. Results indicate that existing dams have substantially altered downstream river flow and flooding patterns across the Amazon River basin. Specifically, large dams in the Amazonian subbasins, including the Xingu, Madeira, and Tocantins, have altered downstream river flow amplitude by up to 3 orders of magnitude. Further, the collective operation of existing and planned dams could increasingly alter river flow patterns, causing ∼10% decrease in flood duration in many parts of the Amazon mainstem. Our results provide quantitative evidence on the severity of the hydrologic impacts of large hydropower dams and have important implications for sustainable hydropower operation and development in the Amazon and worldwide.

MR and stacked GRUs neural network combined model and its application for deformation prediction of concrete dam

Deformation prediction is crucial to dam safety management and economical operation. However, most existing prediction techniques, such as statistical methods, support vector machine based models and other traditional machine learning methods, fail to consider the dynamic evolution characteristics of dam deformation and just treat this process as a problem of static fitting, which leads to the fact that these models not only have limited prediction accuracy and generalization ability, but also can hardly carry out long-term prediction. This study proposed a statistical-deep learning combined strategy to improve the accuracy and stability of concrete dam deformation prediction and realize long-term prediction. The multiple regression (MR) model is utilized to decompose the observed displacement into four components: hydrostatic, temperature, aging and reminder. Then the stacked gated recurrent units (GRUs) neural network is employed to explore the berried chaotic and dynamic change mechanism in the remainder component and make prediction based on historical data. Meanwhile, the other three components are predicted by the fitted MR model. Finally, the predicted displacement is obtained by aggregating the results of the MR model and the stacked GRUs neural network. A large hydropower dam on the Yellow River is introduced to demonstrate the application of the proposed strategy. Results show that the model proposed in this paper achieves excellent performance in both prediction accuracy and stability in long-term prediction tasks. In a one-year arc dam deformation prediction, the relative root mean square error of the proposed model is as small as 1.34%, and the R2 is as big as 0.9981. The proposed model has certain engineering application value in the long-term prediction of concrete dam deformation.

Population connectivity of aquatic insects in a dam‐regulated, desert river

AbstractHumans have exaggerated natural habitat fragmentation, negatively impacting species dispersal and reducing population connectivity. Habitat fragmentation can be especially detrimental in freshwater populations, whose dispersal is already constrained by the river network structure. Aquatic insects, for instance, are generally limited to two primary modes of dispersal: downstream drift in the aquatic juvenile life stages and flight during the terrestrial winged adult stage. Yet the impacts of large hydropower dams can make rivers uninhabitable for incoming (drifting) juvenile insects, with remaining refugia found only in tributaries. The ability of adult aquatic insects to traverse such river stretches in search of suitable tributary habitat likely depends on factors such as species‐specific dispersal ability and distance between tributaries. To explore the intersection of natural and human‐induced habitat fragmentation on aquatic insect dispersal ability, we quantified population genetics of three taxa with varying dispersal abilities, a caddisfly (Hydropsychidae, Hydropsyche oslari), a mayfly (Baetidae: Fallceon quilleri), and a water strider (Veliidae: Rhagovelia distincta), throughout tributaries of the Colorado River in the Grand Canyon, Arizona, USA. Using 2bRAD reduced genome sequencing and landscape genetics analyses, we revealed a strong pattern of isolation by distance among mayfly populations. This contrasts with caddisfly and water strider populations, which were largely panmictic. Analysis of thousands of informative single nucleotide polymorphisms showed that realized dispersal ability may not be accurately predicted by species traits for these widespread species. Principal components analysis revealed a strong division between caddisfly populations upstream and downstream of Havasu Creek (279 km through the 390 km study reach), suggesting that the geography of the Grand Canyon imposes a dispersal barrier for this species. Our use of genetic tools in the Grand Canyon to understand population structure has enabled us to elucidate dispersal barriers for aquatic insects. Ultimately, these data may be useful in informing effective conservation management plans for understudied organisms of conservation interest.

Responding to transboundary water challenges in the Vietnamese Mekong Delta: In search of institutional fit

AbstractThe operations of large hydropower dams in the Mekong basin, while posing detrimental transboundary effects downstream, are not fully recognised in Vietnamese government policies, especially at the regional scale. This study adopts the concept of institutional fit to investigate policy gaps in addressing the transboundary water challenges characterised by falling floodwater flows and accelerating saltwater intrusion in the Vietnamese Mekong Delta. Based on interviews with key stakeholders (including central and provincial government officials, environmental experts, and academics) as well as desk reviews of policy documents, we argue that, while the transboundary water repercussions are increasingly evident on the ground, they are not adequately factored in water policies and strategic development planning for the delta. This study suggests that failure to incorporate co‐evolving effects of climate change and Mekong‐wide hydropower dynamics into local water governance will cause institutional constraints to tackle water stressors (too much or too little water) over the long term. Achieving institutional fit will therefore help align the national water policy framework with local development strategies and reduce policy‐practice gaps at the delta scale. To this end, two key aspects need to be considered: first, how, and in which forms, innovative management decisions and water governance policies can be effectively undertaken towards securing the living delta and its resilience to present and future environmental risks; and second, how reframed water policy and development agendas can holistically capture and resolve the transboundary hydrological problems, while leveraging the Vietnamese government's policy engagement at higher levels to address related impacts.

Future hydropower operations in the Zambezi River basin: Climate impacts and adaptation capacity

AbstractSouthern Africa could experience major hydrological changes in coming decades, bringing drastic changes to hydropower. Focusing on four large hydropower dams in the Kafue and Zambezi Rivers (Itezhi‐Tezhi, Kafue Gorge Upper, Kariba, and Cahora Bassa), accounting for over 90% of the installed capacity in the basin, this study analyzed how these dams have altered river flows in the past, and how hydropower generation could be affected by future climate change and water use scenarios based on dynamically downscaled simulations from the Fifth Coupled Model Intercomparison Project for a Representative Concentration Pathway of 8.5 W/m2. Future climate change could affect reservoir levels by decreasing water inflows and by increasing evaporation. Results showed a decrease in median annual water levels for all reservoirs, with largest changes expected at Itezhi‐Tezhi (−1.3 to −3.3 m), followed by Cahora Bassa (−0.8 to −2.8 m), Kariba (−0.2 to −0.9), and Kafue Gorge (0.1–0.2 m). Flows downstream of dams show a consistent negative trend, with mean annual flow changes of −30% to −49% at the furthest downstream gauge. The combined reduction in water levels and flows could result in decreases on average annual hydropower generation and increases in interannual variability; annual generation could decrease by −61% to −28% at Kariba, by −51% to −21% at Itezhi‐Tezhi, by −7% to −39% at Kafue Gorge, and −27% to −9% at Cahora Bassa. Reservoir operation optimization could marginally offset the projected changes in hydropower generation, with largest gains for Kariba (+6%) and Cahora Bassa (+10%). Overall, opportunities to offset losses via operations would probably decrease with the expected drier climate and escalating reduction in river discharge and water availability. Given these negative projections, it is becoming critical to adapt and coordinate reservoir operations to best cope with the expected challenging future in this important river basin.

Riverbed deformation and its response to human intervention on the lower reaches of the Yangtze River

AbstractThe operation of the world's largest hydropower dam, the Three Gorges Dam (TGD), has significantly influenced the middle and lower reaches of the Yangtze River (YR). However, research has not been conducted on the impact of local engineering projects on the evolution of the tidal channel of the YR. This study used historical water depth and level data to analyze the factors influencing riverbed deformation in the Nanjing reach of the tidal channel of the YR. Moreover, the effect of local engineering projects on riverbed deformation in the study area was quantitatively analyzed. Our results indicated that between 1998 and 2013, ~78.26 × 106 m3 of sediment accumulated in the study area. The goose‐head bifurcated section of this reach exhibited the most significant change in riverbed deformation during this period. Between 1998 and 2013, 46.97 × 106 m3 of sediment accumulated in this section, the riverbed elevation increased by 1.01 m, and the thalweg increased by 2.78 m. Quantitative analysis of the volume of sediment accumulated in the near‐bank area indicated that revetment engineering accounted for >40% of the accumulation. The results of this study provide a more accurate understanding of channel deformation in the lower reaches of the YR. Moreover, the results will improve the prediction accuracy of river channel evolution and assist in channel regulation and future local engineering construction projects.

Impacts of loss of free-flowing rivers on global freshwater megafauna

The fragmentation of free-flowing rivers (FFRs) through major infrastructure development remains a pivotal threat to global freshwater biodiversity. More than 3400 large hydropower dams (>1 MW) are either planned or under construction, posing threats to freshwater megafauna (i.e., freshwater animals that can reach 30 kg). Here, we investigate the global patterns of river connectivity within distribution ranges of freshwater megafauna and explore how these patterns could change in the future. We found that the susceptibility of freshwater megafauna to reduced river connectivity in different dimensions depends on their life history. Freshwater megafauna taxa with a short accumulated length or low percentage of FFRs in their distribution ranges are more likely to be threatened. On average, there is higher freshwater megafauna richness in FFRs with proposed dams than in rivers that would remain free-flowing in the future or that are already fragmented. If all the proposed dams were built, 94 (18.9%) out of 497 remaining FFRs >500 km that provide habitat for freshwater megafauna would lose their free-flowing status. Our results highlight the reduced connectivity of rivers currently inhabited by freshwater megafauna and the future intensification of river fragmentation in megafauna-rich basins. Research and conservation efforts, including life-history studies, identification of critical habitats, updates of IUCN Red List assessments, advanced communication of the potential impacts on ecosystem services and livelihoods of affected communities, and strategic siting, design, and operations of proposed dams are urgently needed to safeguard freshwater megafauna and overall freshwater biodiversity.

Hydropeaking intensity and dam proximity limit aquatic invertebrate diversity in the Colorado River Basin

AbstractRiver biodiversity is threatened globally by hydropower dams, and there is a need to understand how dam management favors certain species while filtering out others. We examined aquatic invertebrate communities within the tailwaters 0–24 km downstream of seven large hydropower dams in the Colorado River Basin of the western United States. We quantified aquatic invertebrate dominance, richness, abundance, and biomass at multiple locations within individual tailwaters and across the basin and identified biological community responses associated with dam operations and distance from dam. We found that each tailwater was dominated by 3–7 invertebrate taxa, accounting for 95% of total abundance. Half of these dominant taxa were non‐insect, non‐flying species and thus were unavailable to terrestrial consumers. Consistent with previous studies, aquatic insects and sensitive taxa were negatively associated with hydropeaking intensity (magnitude of daily flow fluctuations associated with hydropower generation), which limits the composition and potentially the quality of the invertebrate food base. While total invertebrate abundance and biomass did not change with increasing distance downstream from dams, insect and sensitive taxa richness, abundance, and biomass all increased, suggesting that impacts of hydropeaking are most acute immediately downstream of dams. Our results demonstrate that tailwaters experiencing hydropeaking support high abundances of aquatic invertebrate, but the diversity of these communities is low.

Numerical and experimental characterization of splitter blade impact on pump as turbine performance.

Several rivers and streams are available in Africa and Asian regions with great potentials not applicable for constructing large hydropower dams but feasible for small and mini hydro generation. This study strive for investigating the impact of splitter blade on pump as turbine performance considering different speed and flow rates. Two specific centrifugal pump models one with six blades without splitter and another with four blades and four splitters were used for the study. The inlet diameter and outlet diameters of both impellers were 104 mm/116 mm, and 160 mm respectively at a designed flow rate Q = 12.5 m3/h, head H = 16 m, rotational speed n = 1450 rpm and efficiency of 56%, outlet impeller width of 0.006 m, a blade outlet angle of 30° was used for the study. CFD simulations were conducted with the use of k-ε turbulence model. The influence of splitter blade position on the performance of pump as turbine in the selected specific pumps with and without splitter blades has been investigated both experimentally and numerically at three different flow rates and rotational speed. The simulated data were in good agreement with the experimental results, the maximum deviation error between the CFD and test for each model are 5.6%, 2.6%, for the head and efficiency; 7.5% and 3.6% at different flow conditions.