Impact Of Large Dams Research Articles

Impacts of large dams on Amazonian floodplain bird communities

Impacts of large dams on Amazonian floodplain bird communities

The impact of large dams on sediment deposition and channel adjustment: a case study at the Huanghuacheng Reach in the Three Gorges Reservoir, China

The impact of large dams on sediment deposition and channel adjustment: a case study at the Huanghuacheng Reach in the Three Gorges Reservoir, China

Water Security in Africa in the Age of Global Climate Change

Abstract This essay explores the multiple ways in which the nexuses between water scarcity and climate change are socially and historically grounded in ordinary people's lived experiences and are embedded in specific fields of power. Here we specifically delineate four critical dimensions in which the water crises confronting the African continent in an age of climate change are clearly expressed: the increasing scarcity, privatization, and commodification of water in urban centers; the impact of large dams on the countryside; the health consequences of water shortages and how they, in turn, affect other aspects of people's experiences, sociopolitical dynamics, and well-being, broadly conceived; and water governance and the politics of water at the local, national, and transnational levels. These overarching themes form the collective basis for the host of essays in this volume that provide rich accounts of conflicts and struggles over water use and how these tensions have been mitigated.

The impact of large dams on fluvial sedimentation: The Iron Gates Reservoir on the Danube River

Dam construction is one of the major human pressures impacting fluvial processes, including topography and hydro-sedimentary flows, as a result of the change in flow regime from fluvial to fluvial-lacustrine. This article investigates geomorphic changes at Iron Gates I, the largest reservoir on the Danube River, completed in 1972 for hydropower and navigation. The study focuses on a gulf area that emerged at the mouth of the Cerna River into the reservoir, highlighting spatial changes in topography and sediment distribution, based on a diachronic analysis of two datasets before and after the dam was built: one extracted from historical topographic maps and the other obtained from a bathymetric echo sounding survey, integrated within a GIS analysis. The results reveal the dominance of the sedimentation process, with an alluvium layer thickness up to 14 m. The current sediment pattern has changed the submerged morphology, leading to the formation of an alluvial fan at the mouth of the Cerna River and of a sedimentary bar between the Cerna Gulf and the Danube River’s channel. The siltation process together with the current underwater morphology limits ship traffic and the storage capacity of the reservoir.

Longitudinal transport timescales in a large dammed river - The Changjiang River

As a key component of the global water cycle, river flow transports both freshwater and biotic/abiotic matters from land to sea, while in recent decades its rhythm has been strongly disturbed by human activities, especially damming. Yet little is known about the long-distance transport processes along the world's major fluvial systems and the impact of large dams on their timescales. Here, taking the Changjiang River (Yangtze River) as an example, we built a hydrodynamics-based model to investigate the water age and residence time in the mainstream from the upper reach ~700 km upstream of the Three Gorges Dam (TGD) to the estuary ~1900 km downstream of the TGD. We find that since the mainstream was dammed by the TGD, the water age increases significantly by approximately 2 to 5 times from the estuary to the dam. Downstream of the dam the longitudinal ageing rate of water becomes discordant in an annual cycle, and the replenished discharge in dry season accelerates the water transport. Due to the stationary assumption, the widely applied hydraulic residence time of water is substantially larger and smaller than the age-based dynamic residence time in the large reservoir during the impounding and releasing periods, respectively.

Malaria around large dams in Africa: effect of environmental and transmission endemicity factors

BackgroundThe impact of large dams on malaria has received widespread attention. However, understanding how dam topography and transmission endemicity influence malaria incidences is limited.MethodsData from the European Commission’s Joint Research Center and Shuttle Radar Topography Mission were used to determine reservoir perimeters and shoreline slope of African dams. Georeferenced data from the Malaria Atlas Project (MAP) were used to estimate malaria incidence rates in communities near reservoir shorelines. Population data from the WorldPop database were used to estimate the population at risk of malaria around dams in stable and unstable areas.ResultsThe data showed that people living near (< 5 km) large dams in sub-Saharan Africa grew from 14.4 million in 2000 to 18.7 million in 2015. Overall, across sub-Saharan Africa between 0.7 and 1.6 million malaria cases per year are attributable to large dams. Whilst annual malaria incidence declined markedly in both stable and unstable areas between 2000 and 2015, the malaria impact of dams appeared to increase in unstable areas, but decreased in stable areas. Shoreline slope was found to be the most important malaria risk factor in dam-affected geographies, explaining 41–82% (P < 0.001) of the variation in malaria incidence around reservoirs.ConclusionGentler, more gradual shoreline slopes were associated with much greater malaria risk. Dam-related environmental variables such as dam topography and shoreline slopes are an important factor that should be considered in efforts to predict and control malaria around dams.

Reviews and syntheses: Dams, water quality and tropical reservoir stratification

Abstract. The impact of large dams is a popular topic in environmental science, but the importance of altered water quality as a driver of ecological impacts is often missing from such discussions. This is partly because information on the relationship between dams and water quality is relatively sparse and fragmentary, especially for low-latitude developing countries where dam building is now concentrated. In this paper, we review and synthesize information on the effects of damming on water quality with a special focus on low latitudes. We find that two ultimate physical processes drive most water quality changes: the trapping of sediments and nutrients, and thermal stratification in reservoirs. Since stratification emerges as an important driver and there is ambiguity in the literature regarding the stratification behavior of water bodies in the tropics, we synthesize data and literature on the 54 largest low-latitude reservoirs to assess their mixing behavior using three classification schemes. Direct observations from literature as well as classifications based on climate and/or morphometry suggest that most, if not all, low-latitude reservoirs will stratify on at least a seasonal basis. This finding suggests that low-latitude dams have the potential to discharge cooler, anoxic deep water, which can degrade downstream ecosystems by altering thermal regimes or causing hypoxic stress. Many of these reservoirs are also capable of efficient trapping of sediments and bed load, transforming or destroying downstream ecosystems, such as floodplains and deltas. Water quality impacts imposed by stratification and sediment trapping can be mitigated through a variety of approaches, but implementation often meets physical or financial constraints. The impending construction of thousands of planned low-latitude dams will alter water quality throughout tropical and subtropical rivers. These changes and associated environmental impacts need to be better understood by better baseline data and more sophisticated predictors of reservoir stratification behavior. Improved environmental impact assessments and dam designs have the potential to mitigate both existing and future potential impacts.

The impact of large dams on the autochthonous, threatened freshwater ichthyofauna of Greece: Current knowledge and gaps to be fulfilled

The impact of large dams on the autochthonous, threatened freshwater ichthyofauna of Greece: Current knowledge and gaps to be fulfilled

Malaria impact of large dams at different eco-epidemiological settings in Ethiopia

BackgroundDams are important to ensure food security and promote economic development in sub-Saharan Africa. However, a poor understanding of the negative public health consequences from issues such as malaria could affect their intended advantages. This study aims to compare the malaria situation across elevation and proximity to dams. Such information may contribute to better understand how dams affect malaria in different eco-epidemiological settings.MethodsLarval and adult mosquitoes were collected from dam and non-dam villages around the Kesem (lowland), Koka (midland), and Koga (highland) dams in Ethiopia between October 2013 and July 2014. Determination of blood meal sources and detection of Plasmodium falciparum sporozoites was done using enzyme-linked immunosorbent assay (ELISA). Five years of monthly malaria case data (2010–2014) were also collected from health centers in the study villages.ResultsMean monthly malaria incidence was two- and ten-fold higher in the lowland dam village than in midland and highland dam villages, respectively. The total surface area of anopheline breeding habitats and the mean larval density was significantly higher in the lowland dam village compared with the midland and highland dam villages. Similarly, the mean monthly malaria incidence and anopheline larval density was generally higher in the dam villages than in the non-dam villages in all the three dam settings. Anopheles arabiensis, Anopheles pharoensis, and Anopheles funestus s.l. were the most common species, largely collected from lowland and midland dam villages. Larvae of these species were mainly found in reservoir shoreline puddles and irrigation canals. The mean adult anopheline density was significantly higher in the lowland dam village than in the midland and highland dam villages. The annual entomological inoculation rate (EIR) of An. arabiensis, An. funestus s.l., and An. pharoensis in the lowland dam village was 129.8, 47.8, and 33.3 infective bites per person per annum, respectively. The annual EIR of An. arabiensis and An. pharoensis was 6.3 and 3.2 times higher in the lowland dam village than in the midland dam village.ConclusionsThis study found that the presence of dams intensifies malaria transmission in lowland and midland ecological settings. Dam and irrigation management practices that could reduce vector abundance and malaria transmission need to be developed for these regions.

Impact of dams on global biodiversity: A scientometric analysis

The extensive damming of rivers around the world, regardless their economic purpose, has changed the river landscapes and led to serious ecological consequences for the biological organisms associated with these ecosystems. In the present study, a scientometric analysis was performed aiming to assess temporal trends of the scientific production related to environmental concerns about the impact of large dams on biodiversity worldwide. On this context, a bibliographic review of the scientific works of this area, using the research platform “Web of Science” searching for the keywords “dam impact” or “dam effect” and “bio*diversity” in the subject line. The results showed that, despite the publication number increase in the field, these studies are clearly more abundant in temperate regions, which have less biological diversity. Although much of the planned hydroelectric expansion is expected to occur in the tropics, which have most of the world’s biodiversity, the biological knowledge about the species in these places is still very little. The lack of studies in these areas may mask the impact intensity and extent of dams on biodiversity and also induce decision-makers to adopt inefficient management strategies.Keywords: Freshwater ecosystem, review, reservoir.

Together we can do more – environmental consciousness in the South African dam construction sector (1945-1980)

For several thousand years societies have diverted and dammed up rivers to meet their increasing water needs. The Industrial Revolution ushered in the modern era of water resource development, which has led to the construction of an estimated 50 000 large dams worldwide.Rising concerns over the state of natural resources following the Second World War resulted in the emergence of public anti-dam lobby groups who used protest and advocacy to place pressure on authorities to cease dam construction activities and improve environmental legislation. While these actions proved successful in many countries this approach has led to conflict between environmental groups and dam authorities.South Africa is highly dependent on dams for stable and regular water supply. The country’s 320 largest dams together store some 66% of the country’s mean annual runoff. In contrast with the global environmental movement, institutionalisation of the environment occurred within the water engineering sector not as a result of outside pressures but due to rising concerns from water engineers themselves.In the absence of strong adversarial environmental non-governmental organisations, improved management of the impact of large dams grew out of early cooperation between department officials and aquatic scientists, especially around the sustainable management of water resources in KwaZulu-Natal, as this article illustrates. This trend towards negotiation and collaboration led to the country’s main developer of large dams, the Department of Water Affairs, instituting voluntary environmental policies from 1980.Keywords: History, dams, rivers, history, environmental movement, environmental consciousness, water, aquatic science, engineering, cooperation

Impacts of large dams on downstream fluvial sedimentation: An example of the Three Gorges Dam (TGD) on the Changjiang (Yangtze River)

Summary Under the influence of climate and human activities, fluvial systems have natural ability to make adjustments so that the river hydrology, sediment movement, and channel morphology are in dynamic equilibrium. Taking the Changjiang (Yangtze River) for example. In the early stages after the Three Gorges Dam (TGD) began operational ten years ago, the suspended sediment content (SSC) and fluxes in the middle and lower reaches of the river decreased noticeably. At present, they appear to be in a stable state on the decadal scale. Although the river runoff has not shown any trends, the water level in the river decreased appreciably in time. In the meantime, channel down cutting along the thalweg almost existed throughout the river course. The riverbed has turned from depositional before the dam construction to erosional afterwards. In other words, the riverbed had turned from being sediment sinks to sediment sources. In the main channel of the Changjiang between Yichang and Nanjing, a distance of 1300 km, the riverbed sedimentation mode displays strong, intermediate, and weak erosion depending on the closeness to the TGD.

Impacts of large dams on riparian vegetation: applying global experience to the case of China’s Three Gorges Dam

Dams are widely recognised as having significant negative consequences for the surrounding natural ecosystems and environment. China’s Three Gorges Dam, being one of the largest in the world, stands to inflict more damage than most for numerous reasons. This paper reviews the current knowledge on the impacts of dams and impoundments with regard to reservoir riparian vegetation in order to apply this knowledge to the Three Gorges Project. It also summarises research performed to date on the effects of the Three Gorges Dam on the local riparian zone and vegetation. The known and potential outcomes for local plant communities are examined in terms of their responses to the increased water levels, altered hydrological characteristics and other adverse effects associated with the construction of the dam. Vegetation responses will be diverse and change over time, but will ultimately result in a markedly different landscape and riparian zone within the Three Gorges Reservoir. These changes will take place through a loss of previous vegetation, potential invasion by exotics and result from the significant alteration in hydrological regimes and also erosion and sedimentation processes influencing and creating novel plant communities. Management of the environmental consequences of the Three Gorges Project should take into account factors associated with these processes, in order to facilitate vegetation recovery in the reservoir and to conserve biodiversity of the surrounding ecosystems.

Impacts of large dams on downstream flow conditions of rivers: Aggradation and reduction of the Medjerda channel capacity downstream of the Sidi Salem dam (Tunisia)

Summary Since the opening of the Sidi Salem dam on the watercourse of the Medjerda, in 1981, an alarming narrowing of the riverbed in the lower valley has been observed. This geo-morphological change is attributed to different factors ranking from the reduction in the discharge flows, which used to clean out the riverbed to the periodic releases of turbid water undertaken to remove the silt deposition inside the reservoir, which increased the sediment deposition in the downstream channel. Other smaller hydraulic projects are also held responsible for the loss of the water velocity including a series of concrete sills meant to raise water levels, numerous cross bridges and the management of the downstream Laroussia dam regulating the discharge from the Cap Bon canal. The above anthropogenic factors, in conjunction with natural topographical conditions characterized by a generally shallow slope and a very sinuous watercourse, led to an extremely rapid aggradation of the downstream channel-bed. This paper proposes an analysis of this process and argues that the resulting reduction in channel capacity is one of the major causes of the large floods experienced in the country since 1996.

Impact of weirs on fish communities in a piedmont stream

AbstractThe impact of large dams on fish communities is much better documented than that of weirs. This paper investigates the influence of weirs on fish community patterns along a piedmont river (the River Viaur). Presence/absence of species was obtained distant from a weir (NW), and immediately downstream (DW) and immediately upstream (UW) of the weir. More than half of the species captured were non‐native, probably introduced when upstream reservoirs were built. Most of these species were eurytopic or limnophilic. Species richness at UW sites and the number of introduced species found at each site did not depend on the distance from the source (DFS). UW sites had more introduced and limnophilic species than NW sites. Conversely, NW had more rheophilic species than UW. Furthermore, total species richness (SRT) was higher at DW than NW suggesting a direct influence of the weir on the downstream community. UW sites were characterized by the presence of tench, roach and bleak which were scarce in NW sites where brown trout predominated. Weirs appear to modify habitat to favour the colonization of introduced species, and therefore have influenced the structure of fish communities. The study underlines the importance of local conditions in artificially‐influenced rivers. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Review of Dams and Disease: Ecological Design and Health Impacts of Large Dams, Canals and Irrigation Systems by William R. Jobin

Review of <i>Dams and Disease: Ecological Design and Health Impacts of Large Dams, Canals and Irrigation Systems</i> by William R. Jobin