Large Dams Research Articles

Seismic and structural health monitoring systems for large dams: theoretical, computational and practical innovations

This paper is focused on the study of the dynamic behaviour of two large arch dams, and it presents some innovations for the improvement of Seismic and Structural Health Monitoring (SSHM) systems for dams. The work describes a methodology based on the integrated use of software for automatic monitoring data analysis and of computational 3D finite element (3DFE) models for dam dynamic behaviour simulation. The monitoring data analysis software was developed for automatic modal identification, in order to obtain natural frequencies and mode shapes, for automatic detection of vibrations induced by seismic events, to be distinguished from those caused by other operational sources, and for comparison between results retrieved from measured vibrations and numerical results from 3DFE modelling. The numerical simulations are carried out using a 3DFE program developed for dynamic analysis of dam-reservoir-foundation systems, based on a solid–fluid coupled formulation and considering the dam-water dynamic interaction, including calculation modules for complex modal analysis and for linear and non-linear seismic analysis. The case studies are two large arch dams that have been under continuous dynamic monitoring over the last ten years: Cabril dam (132 m high), the highest dam in Portugal, and Cahora Bassa dam (170 m high), in Mozambique, one of the highest dams in Africa. The SSHM systems installed in both dams have similar schemes and were designed to continuously record accelerations in several locations at the upper part of the dam body and near the dam-foundation interface, using uniaxial and triaxial accelerometers. The most significant experimental results from continuous dynamic monitoring are presented and compared with numerical results for both dams, with emphasis on the evolution of natural frequencies over time, including the vibration mode shapes for various water levels, and on the measured accelerations during low-intensity seismic events. Furthermore, the main results of non-linear seismic response simulations are provided, considering the effects due to joint movements and tensile and compressive concrete damage, aiming to assess the seismic performance of both dams based on the Endurance Time Analysis method.

Spatiotemporal Variation in Distribution, Size, and Relative Abundance within a Salish Sea Nearshore Forage Fish Community

AbstractForage fish are schooling species commonly occurring in both offshore pelagic and nearshore coastal habitats. Beyond use by some species for spawning, the dynamics of nearshore habitat use are not well understood. The objective of our study was to evaluate the spring–summer dynamics of forage fish occurrence in nearshore habitats of the Strait of Juan de Fuca, Washington. We suspected that habitat changes resulting from removal of two large dams on the Elwha River (2009–2011) may have altered fish presence and abundance. Monthly beach seine sampling in four regions along 40 km of shoreline was conducted from April to September between 2006 and 2019. We caught nearly 600,000 fish, comprising 82 different species. Nine species of forage fish accounted for 81.7% of all fishes caught; most were classified as postlarvae and juveniles based on size. There were spatial differences in the forage fish assemblage between two of our sites but no discernable year effects and no obvious impact of dam removal on forage community composition. Three species represented 78.8% of the catch: Pacific Herring Clupea pallasii, Pacific Sand Lance Ammodytes hexapterus, and Surf Smelt Hypomesus pretiosus. We used a Bayesian generalized linear mixed model to evaluate spatial and temporal variability in the probability of occurrence of these species. Each species exhibited a unique pattern of intra‐annual, interannual, and regional fluctuations. Pacific Herring occurrence progressively increased monthly, Pacific Sand Lance occurrence decreased, and Surf Smelt probability of occurrence peaked in June. Temporal variations in distribution and abundance of these species are likely driven by life history differences and biological requirements. We speculate that specific characteristics of each region, including proximity to spawning areas, spawn timing, extant current patterns, and ecosystem processes, drove variations in distribution between species.

The Small Dams Safety Index (SDSI): a tool for small dams safety assessment

ABSTRACT There is a great number of small dams around the world, usually built in private rural properties, for irrigation, animal watering or aquaculture; as they are getting old, the probability of a failure increases. In Brazil, the Brazilian National Policy of Dam Safety was approved, but it is intended only for large dams, unless it is classified with medium or high Associated Potential Damage. Usually, risk analysis methods are used to assess the safety of a dam, but this may be unfeasible for small dams, as it is costly and time-consuming, which is not affordable for small dams’ managers. This article proposed the Small Dams Safety Index (SDSI), which is a matrix with classification criteria to evaluate the safety of small dams. Besides providing a general level of the safety of a dam, it also helps to prioritize actions of maintenance, allowing the small dam’s manager to optimize time and financial resources.

Evaluation of soil erosion in Northern Algeria watershed using SWAT and RUSLE models

Soil water erosion is a major phenomenon that threatens almost all watersheds in the Mediterranean area, nowadays. The worsening of this phenomenon in Algeria affects soil capacity to ensure its ecological functions and socio-economic purposes which depend on it. Concurrently, the storage capacity of Algeria dams has considerably decreased as a result of excessive silting. The above issue motivated this study, which aims to establish mechanisms for prioritizing to improve the economic efficiency of agricultural land and the long-term viability of dams in the largest metropolitan basin of Algeria ‘Coastal Algiers 2a basin’. This basin, which is urbanized over 50% of its area, contains six large dams with a total capacity of 540 Million m3 and one of the most important agricultural zones in Algeria. Common decision support frameworks have been implemented to predict the areas that are potentially exposed to erosion and sediment deposition threatening the dam capacity using the Soil and Water Assessment Tool (SWAT) and the Revised Universal Soil Loss Equation (RUSLE). To achieve this, rainfall, climatic, hydrometric, land use, soil, digital elevation, and satellite data were used by the two spatially soil loss models. The results show a dependency between the two statistical models with respect to low, medium and high erosion risk areas and its evolution from the eastern to the western region of the watershed. Regarding the deposition of sediments at the dams, the two models only partially explain the rate of sediments observed at the level of the dams’ basins whose relative errors exceed 4%, 8%, 60%, 30% and 40% respectively for the Meurad, Bouroumi, Keddara, Boukerdane and El Hamiz dams. The canonical analysis (CC) revealed that the average slope, vegetation cover and the available water capacity in the soil of the basin are the most important parameters influencing the soil loss provided by the two models.

Advocacy Coalition Framework in Environmental Governance Studies: Explaining Major Policy Change for A Large Dam Removal in Japan

This paper applied the Advocacy Coalition Framework (ACF) to environmental governance studies and examined the validity of policy change hypotheses in Japan, where few ACF studies exist despite the seemingly appropriate conditions to apply the ACF. While environmental governance has been studied for several decades, there is no prevailing research framework. I used the ACF to explain the policy process leading to Japan’s first large dam removal, a critical case of major policy change in environmental governance. Using data from interviews and newspaper articles, I identified advocacy coalitions, the events leading to the policy change, and the changes in coalition resources through discourse network analysis and other methods used in the ACF literature. Consequently, I found that the policy change hypotheses were valid and that coalition resources were significant intervening variables that lead to policy change. However, I also found the need for further refinements of the policy change hypotheses in the ACF. This paper confirms the utility of the ACF’s policy change hypotheses and research methods to understand the complex dynamics of environmental governance.

Hydrologic balance and inundation dynamics of Southeast Asia's largest inland lake altered by hydropower dams in the Mekong River basin

Inland lakes have been increasingly impacted by climate change and human activities, leading to unprecedented environmental consequences. Among many rapidly changing lakes is the Tonlé Sap Lake (TSL) in Cambodia—Southeast Asia's largest inland lake—which is under growing threats from altered flows and inundation dynamics due to compounding effects of climate change and dam construction in the Mekong River basin (MRB). While previous studies have examined the potential causes of recent changes in open water areas, a mechanistic quantification of the lake's shifting hydrologic balance and inundation dynamics due to natural climate variability and dam operations is lacking. Here, using a hydrological-hydrodynamic modeling system that includes the major dams in the MRB, we show that while climate variability has been a key driver of inter-decadal variabilities in the lake's water balance, the operation of Mekong dams has exerted a growing influence—especially after 2010—on the Mekong flood pulse, Tonlé Sap River's flow reversal, and the TSL's inundation dynamics. The dam-induced dampening of the Mekong's peak discharge increased from 1–2% during 1979–2009 to ~7% in the 2010s, causing comparable alterations in the peak of inflow from the Mekong into TSL. More crucially, during the 2010s, the dams caused a reduction in annual inflow volume into TSL by 10–25% and shortened the annual inundation duration by up to 15 days in the lake's periphery. Further, seasonally inundated areas decreased (increased) most substantially by ~245 km2 or ~3% (~270 km2 or ~6%) in August (April) during the 2010s. These results demonstrate that Mekong dams have already caused substantial alterations in the hydrologic balance and inundation dynamics of the TSL. Our findings offer critical insights relevant for improved transboundary water management and decision making in light of growing concerns about the adverse impacts of large dams in the MRB.

Hydrological effects of large dams in Chilean rivers

Study regionEight rivers regulated by large dams located in three hydro-climatic zones along the Chilean latitudinal gradient. Study focusWe performed a multi-temporal scale analysis of flow records and we used data from official gauging stations to characterise the non-altered and the altered river regimes to determine the magnitude and persistence of the hydrological alteration downstream from large dams in Chile. These analyses provide relevant information to improve the understanding of such alterations, and a conceptual basis for assessing future impacts as the country plans to build a series of large dams in the coming years. New hydrological insights for the regionThe mean annual runoff was reduced in all the study rivers. The monthly flows of the rivers from the northern arid zone were the most affected by the dams. The magnitude and frequency of floods decreased in all the study rivers. Moreover, northern drier river systems did not recover their hydrological conditions in the distance downstream of the dams, probably due to transmission losses and water extractions and diversions; in contrast, southern rivers partially recovered their flow regimes with distance downstream, mainly due to the inflows from permanent non-regulated tributaries. So far, this is the first study in Chile that comprehensively analyses the hydrological effects of large dams.

Predicting Hydrological Drought Alert Levels Using Supervised Machine-Learning Classifiers

Reliable drought prediction is a global challenge in disaster-prone regions around the world. Data-driven models such as machine-learning (ML) classifiers have recently received considerable attention from water resources planners and managers. In this study, we applied several ML classifiers, including decision tree (DT), naive Bayes (NB), random forest (RF), and support vector machine (SVM) to the prediction of hydrological drought classes. Daily data of precipitation, reservoir inflow, and reservoir volume collected from three large dams (Andong, Chungju, and Seomjin) in South Korea were used as classifier input to predict hydrological drought alert levels. A comparison of the accuracy and computation time of each ML classifier revealed that the classifiers were capable of predicting hydrological drought alert levels, with the SVM achieving outstanding performance in terms of accuracy (97%) and precision (89%) and the NB exhibiting superior computational time (0.63 sec). The results of this study indicated that the ML classifiers can be effective predictors of hydrological drought classes and can provide warnings of drought conditions.

AN INVENTIVE CONCRETE PAVEMENT BY USING NYLON CRYSTAL AS A PARTIAL REPLACEMENT OF CEMENT

Transportation is a major developing sector in India, and required for good quality of roads, railways and airways is high. Concrete has occupied an important place in construction industry in the past few decades and it is used widely in all types of constructions ranging from small buildings to large infrastructural dams or reservoirs. Cement is major ingredient of concrete. The cost of cement is increasing day by day due to its limited availability and large demand. In the present study an attempt been made on concrete and also an experimental investigation on the concrete using Nylon Crystal. Experimental studies were performed on plain cement concrete and replacement of cement with Nylon crystal is done. In this study the concrete mix were prepared by using Nylon crystal from 1% to soon by weight of cement were added partially to the mixes. A comparative analysis has been carried out for concrete to that of the Nylon crystal reinforced concrete in relation to their compressive strength, split tension strength and flexural strength properties. The concrete made with Nylon crystal performed well in terms of compressive strength, split tension strength and flexural strength showed higher performance at the age of 7, 28, 60 and 90 days than conventional concrete. And also Bond Strength by using cylinders and two different types of acid attack is done to determine the Bond Strength and compressive strength both on conventional concrete and Nylon crystal reinforced concrete. Key Words: Acid Attack, Bond Strength, Compressive Strength, Flexural Strength, Nylon Crystal, Split Tensile Strength.

Identifying hydrologic reference stations to understand changes in water resources across Vietnam - a data-driven approach

Among the impacts of climate change and variabilities, change in the terrestrial water cycle has been investigated extensively due to the importance of water resources to the Earth System. The detection and attribution of changes in river flows, however, are usually complicated by the impacts of on-ground human activities such as urbanization or dam construction that have altered flow regimes. As a result, hydrological reference stations – gauges measuring river flows of catchments that are unregulated - have been identified in many countries to provide streamflow records that are suitable for climate studies. Such a network, to the best of our knowledge, has not been promoted widely in Vietnam, making it difficult to determine the actual impact of climate change and variability to river flow regimes at the national scale. To address this limitation, this study uses a data-driven approach to identify stations that have not been influenced substantially by human activities for Vietnam. Specifically, we have carefully assessed streamflow records at 68 locations that are not influenced by tidal regime to identify stations with relatively good data quality. The drainage area associated with each of these stations was then delineated following international standards, and then used to identify catchments that were not associated with large dams. The catchment boundary was also used to extract land surface information, available through an ensemble of different satellite-based data products, to further identify catchments that are not featured by large urban areas, or experienced a substantial change in land cover during the 2000-2019 period. Using these criteria, this study suggested two subsets of stations distributed across the countries, providing a good starting point for future investigations into the impacts of climate change on water resources in Vietnam. The investigation also suggests that more investments are required to maintain and expand the hydrologic reference network for Vietnam.

Deep Learning Segmentation of Satellite Imagery Identifies Aquatic Vegetation Associated with Snail Intermediate Hosts of Schistosomiasis in Senegal, Africa

Schistosomiasis is a debilitating parasitic disease of poverty that affects more than 200 million people worldwide, mostly in sub-Saharan Africa, and is clearly associated with the construction of dams and water resource management infrastructure in tropical and subtropical areas. Changes to hydrology and salinity linked to water infrastructure development may create conditions favorable to the aquatic vegetation that is suitable habitat for the intermediate snail hosts of schistosome parasites. With thousands of small and large water reservoirs, irrigation canals, and dams developed or under construction in Africa, it is crucial to accurately assess the spatial distribution of high-risk environments that are habitat for freshwater snail intermediate hosts of schistosomiasis in rapidly changing ecosystems. Yet, standard techniques for monitoring snails are labor-intensive, time-consuming, and provide information limited to the small areas that can be manually sampled. Consequently, in low-income countries where schistosomiasis control is most needed, there are formidable challenges to identifying potential transmission hotspots for targeted medical and environmental interventions. In this study, we developed a new framework to map the spatial distribution of suitable snail habitat across large spatial scales in the Senegal River Basin by integrating satellite data, high-definition, low-cost drone imagery, and an artificial intelligence (AI)-powered computer vision technique called semantic segmentation. A deep learning model (U-Net) was built to automatically analyze high-resolution satellite imagery to produce segmentation maps of aquatic vegetation, with a fast and robust generalized prediction that proved more accurate than a more commonly used random forest approach. Accurate and up-to-date knowledge of areas at highest risk for disease transmission can increase the effectiveness of control interventions by targeting habitat of disease-carrying snails. With the deployment of this new framework, local governments or health actors might better target environmental interventions to where and when they are most needed in an integrated effort to reach the goal of schistosomiasis elimination.

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.

Development of a flow‐sensitive macroinvertebrate index for Australian rivers

AbstractHydrologically sensitive macroinvertebrate indices have been developed in Europe, the Americas and New Zealand to serve many purposes such as monitoring ecological responses to drought, flow regulation, water extraction and the provision of environmental flows. We created an Australian Macroinvertebrate Flow Index (AMFI) based on relative current‐velocity preferences of numerous Australian invertebrate families and genera, derived from a large dataset composited from past biomonitoring programs. We tested the new index with datasets independent from those used for its derivation, showing that it correlated strongly with current velocity and responded mostly as expected to discharge fluctuations downstream of a large dam. A genus‐level version was more responsive than a family‐level version, but the sensitivity of the family‐level version was improved by the incorporation of weighting based on taxon abundance. We suggest possible uses of the new index and recommend further development and testing, particularly in relation to intermittent streams and environmental flows.

Deduction of ultimate equilibrium limit states for concrete gravity dams keyed into rock mass foundations based on large displacement analysis

Concrete gravity dams are mass concrete structures, often built on rock mass foundations, conceived to rely upon their weight for stability. To prevent sliding, these structures are usually keyed/embedded into the foundation, a good construction practice particularly relevant in medium to high intensity seismic zones. In stability analysis, the extra strength obtained by keying the dam into the foundation is usually either neglected or taken as a passive resistance, which, such as explored in this paper, do not reflect the real structural response in pre-collapse situations. Limit state philosophy requires the ultimate equilibrium conditions to be expressed as accurately as possible. In this paper, the rigid-body equilibrium of a wedgy model representing the dam and a downstream rock wedge is analyzed according to the large displacement regime. Failure mechanisms were identified, analytically described and numerically validated. Application to two Portuguese large concrete gravity dams led to safety factors considerably larger than those computed assuming the usual practice. The proposed approach is intended to support probabilistic and/or semi-probabilistic methodologies for safety assessment of concrete gravity dams, in the design and feasibility phases, in which the limit state approach is inherently followed.

Ecological connectivity of the upper Rhône River: Upstream fish passage at two successive large hydroelectric dams for partially migratory species

The restoration of migration pathways for fish is crucial for the maintenance of populations in a worldwide context of increasing river fragmentation due to the development of dams. Studies aiming at quantifying fish passage at dams through fishway efficiency estimates concern few species, mostly diadromous. Data are lacking regarding most potamodromous species, despite their need to move to complete their life cycles. This study aimed to evaluate the efficiency of two vertical slot fishways for upstream fish migration on two consecutive run-of-the-river hydropower dams (Verbois and Chancy-Pougny) on the Rhône River. Radiotelemetry and PIT-tagging were used together (1) to describe the behaviour of fish under the dams and (2) to quantify entrance probability and passage efficiency of the fishways, for three potamodromous, partially migratory species, comprising of two cyprinids (Barbus barbus and Squalius cephalus) and one salmonid (Salmo trutta). The study revealed that fish preferentially moved upstream of the dam beside the gates, independently of their opening, rather than in the main flow of the turbines. While the passability of fishways did not differ among species (68% for all species), the attractiveness was dependent on the dam/fishway, the species and some individual characteristics such as fish body length and condition. A few fish remained below the gates or near the fishway for a long time, up to several months, without being able to detect the entrance. Overall, results revealed a lower efficiency of the fishways for trout than for the two cyprinids. Attraction was pointed out as the major limiting factor to the efficiency of the Verbois fishway for barbel and trout. Overall, results suggested to better account for fish motivation (migratory behaviour) to assess fishway efficiency for these species.

Dynamic Modeling Framework of Sediment Trapped by Check-Dam Networks: A Case Study of a Typical Watershed on the Chinese Loess Plateau

Check-dam construction is an effective and widely used method for sediment trapping in the Yellow River Basin and other places over the world that are prone to severe soil erosion. Quantitative estimations of the dynamic sediment trapped by check dams are necessary for evaluating the effects of check dams and planning the construction of new ones. In this study, we propose a new framework, named soil and water assessment tool (SWAT)–dynamic check dam (DCDam), for modeling the sediment trapped by check dams dynamically, by integrating the widely utilized SWAT model and a newly developed module called DCDam. We then applied this framework to a typical loess watershed, the Yan River Basin, to assess the time-varying effects of check-dam networks over the past 60 years (1957–2016). The DCDam module generated a specific check-dam network to conceptualize the complex connections at each time step (monthly). In addition, the streamflow and sediment load simulated by using the SWAT model were employed to force the sediment routing in the check-dam network. The evaluation results revealed that the SWAT-DCDam framework performed satisfactorily, with an overestimation of 11.50%, in simulating sediment trapped by check dams, when compared with a field survey of the accumulated sediment deposition. For the Yan River Basin, our results indicated that the designed structural parameters of check dams have evolved over the past 60 years, with higher dams (37.14% and 9.22% increase for large dams and medium dams, respectively) but smaller controlled areas (46.03% and 10.56% decrease for large dams and medium dams, respectively) in recent years. Sediment retained by check dams contributed to approximately 15.00% of the total sediment load reduction in the Yan River during 1970–2016. Thus, our developed framework can be a promising tool for evaluating check-dam effects, and this study can provide valuable information and support to decision-making for soil and water conservation and check-dam planning and management.

Upgrading mechanical and electrical systems

In carrying out maintenance and rehabilitation investigations of three large overseas dams, there was a need to address the issue of providing up-to-date technology against sustainability. The dams were built in the 1970s and used proven technology from that period. As a result of reduced investment, maintenance had been neglected for some time, resulting in much of the dam equipment being relegated from automatic to manual operation; in some cases, relying on operator knowledge and use of ‘work-arounds’. The challenge for the investigation was to return the dam equipment to full functionality and take advantage of developments in technology, while providing a sustainable solution. The balance between a state-of-the-art technical solution that meets accepted international standards and practices, and operational sustainability can be difficult to attain, particularly in developing countries. The experience and knowledge of engineers who design or manage dams can encourage the use of innovative solutions, which may be at odds with the knowledge and training of those maintaining the dam, and availability of spare parts and service support. This paper will discuss how the balance of sustainability, reliability and redundancy affects the choice of design and, through examples, why there may not always be a single solution.

Wavelet Analysis of Dam Injection and Discharge in Three Gorges Dam and Reservoir with Precipitation and River Discharge

The Yangtze River has been the primary support of the resources and transportation of China. The Three Gorges Dam and Reservoir on the Yangtze River is one of the world’s largest dams. The influence caused by the dam and reservoir on the river system has been overwhelming and destructive. For better water resource use and flood-prevention planning, more understanding is needed regarding the dam’s impact on river discharge, regional precipitation, and frequency of extreme rainfall events. This study aims to analyze the changes in river discharge and regional precipitation records before and after the construction of the Three Gorges Dam. This research examines temporal correlations among these data by collecting daily dam injection and dam discharge records, the precipitation from ground stations, and river discharge. The time series are analyzed with the wavelet analysis. The precipitation datasets decrease in wavelet magnitude after 1998 when the dam was built in the wavelet analysis. The annual cycle, shown as a bright year line through the time range, still exists in the analysis result after 1998, but the magnitude of the annual cycle has reduced. The river discharge shows a decrease of wavelet magnitude at the three downstream locations. The possible explanation of this pattern could be the human-controlled dam discharge. The constant water level maintained in the reservoir by human control would slow down the flow speed and stabilize it.

Making space for indigenous law in state‐led decisions about hydropower dams: Lessons from environmental assessments in Canada and Brazil

AbstractThe article examines the environmental impact assessment of hydropower dams as an opportunity for applying indigenous laws. Although indigenous laws of affected communities exist and have guided the management of land and natural resources for millennia, they have not yet occupied a significant place in state‐led decision making. Consequently, decisions to approve dams, based on state laws and officials' discretionary power, affect indigenous peoples in distinct and profound ways. The analysis is based on the comparison between two decision‐making processes—Site C (Canada) and Belo Monte (Brazil) dams. The methodology includes the application of principles from the environmental justice literature, the analysis of interviews, case law and legislation. The article concludes that environmental justice for indigenous peoples in environmental decision making of projects with significant impacts, such as large dams, requires recognizing and making institutional spaces for implementing indigenous laws.