Dams can have both negative and positive environmental effects. Dams have both intended and unforeseen consequences, though good consequences can occur both intentionally and unintentionally. Each of these dam-related effects may be unavoidable in their entirety, reducible, or completely preventable. Until recently, the majority of dams’ negative social and environmental consequences were overlooked. Even today, such effects are only partially reflected in the financial and economic studies of the project. While the direct costs of reforestation, catchment area remediation, and relocating and rehabilitating project affected individuals (PAPs) may be reflected in a financial analysis, many other expenditures go unaccounted for. Furthermore, many of the environmental and social costs are difficult to quantify financially.
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The reservoir’s effects
The overall repercussions are social; all economic and environmental impacts have social consequences. Unlike economic consequences, which are all primarily social in character, environmental repercussions affect not just human civilization but also other natural factors. Dams Have Beneficial Environmental Effects Catchment Benefits The environmental clearance conditions for the most recent developments involve the treatment of the catchment region. There are enormous environmental benefits when this treatment is properly carried out and results in the recovery of natural forests and other ecosystems in the catchment region. Wetland species, particularly water birds, benefit from the establishment of a reservoir. Animals and plants in the surrounding areas may be able to get water from the reservoir.
A dam’s construction can contribute to the degradation of its catchment. For example, during and after dam building, the extraction of cooking fuel by the labour force, as well as greater access to the forests, destroys catchment forests. The increased activity in the area, as well as the construction of roads and other infrastructure, add to the pressure on the forests. This causes more silt to flow into the reservoir, shortening the dam’s life and posing a risk to its safety, as well as its equipment and machinery. Degraded catchments also result in unpredictable water flows, resulting in shortages during the dry season as well as surpluses during heavy rain and cloudbursts, endangering the dam’s stability. The destruction of the environment.
Following construction, where woods are submerged beneath the reservoir, the pressures on surviving forests, especially in catchments, increase dramatically. Furthermore, when catchments are damaged, the local community’s access to biomass is harmed. This frequently leads to additional deterioration. Catchment Area Treatment is a popular recommendation for avoiding the harmful effects of dams on catchments and degraded catchments on dams (CAT). However, there are numerous issues with the present CAT system.Treatment that is not appropriate The main CAT activity should be massive plantation and vegetative cover rejuvenation. To ensure that trees live and regenerate, the issues that caused the catchment’s degradation in the first place must be addressed.
Local communities must be involved for this to be successful. This, however, nearly never occurs. As a result, even when treated, catchments rapidly degrade. Treatment was postponed. The treatment of catchments must be finished prior to impoundment in order to be effective. Unfortunately, this does not occur, and the substantial amount of silt produced by the treatment process, as well as that from untreated catchments, is deposited in the reservoir. Inadequate area Treatments recent years, there has been a growing trend to address only the ‘directly draining’ reservoir, which is a scientifically ridiculous idea, rather than the entire ‘seriously degraded’ catchment. Issues with Ownership Kuch of the catchment that needs to be treated is private land, and treatment can only be effective if the landowners collaborate.
Dams Have a Negative Impact on the Environment
Mining and quarrying for construction materials have a variety of effects.The dirt, stones, and sand needed to build dams and canals are frequently mined and quarried near the dam or canal site. Such extraction can have negative environmental consequences, including increased dust pollution, wildlife disturbance, and vegetation destruction. The scars and pits left by such mining and quarrying (also known as borrow pits) remain as environmental eyesores and can have a negative influence on the dam and canals. Backwater build-up has a number of negative consequences.When a free-flowing river meets a relatively static reservoir, back-pressure builds up, resulting in a backwater. This has the potential to devastate the upstream environment as well as inflict property damage. Backwaters can form as well.
Construction activities, such as river diversion through a tunnel, have a significant negative influence on the aquatic ecosystem. Even before the dam is finished, vulnerable species with limited distribution or low tolerance may become extinct. The obstruction of a river and the construction of a lake has a substantial impact on the river’s ecological conditions, harming species and the ecosystem. Pressure, temperature, oxygen levels, and even the chemical and physical properties of the water all fluctuate. Furthermore, disrupting the flow of water disrupts ecological continuity. This is especially true for fish species whose travel up to their spawning habitats is obstructed by the dam. Many other species, however, are harmed, though not as severely.
Submergence of forests
As soon as the impoundment begins, enormous swaths of forest and other ecosystems, such as grasslands and wetlands, are submerged. Forests are being flooded. For 60 dams, data on forest submergence was available. Based on these figures, the average forest area flooded per dam is around 4,879 ha. As a result, the 1,877 dams erected between 1980 and 2000 flooded 9,157,883 hectares (approximately 9.1 million hectares) of forest.According to the CWC, the average forest submergence per project was 2,400 ha, based on a study of 116 projects (details not available). Even if this is right, the total submergence between 1980 and 2000 would have been 4,504,800 hectares (roughly four and a half million hectares). The most commonly suggested mitigating action.
The performance of state governments in compensating afforestation has not been sufficient, according to the Ministry of Environment and Forests. Only 46% of the land set aside for afforestation had been taken up as of 1997. Furthermore, a plantation cannot replace a natural forest. As a result, even if formal ‘compensation’ for forest losses in terms of forest area exists, the true ecological and biodiversity losses that natural forest destruction entails cannot be compensated. Losses of wildlife Aside from trees, the reservoir and dam have an impact on other ecosystems as well as different wildlife and flora species. Unfortunately, there has been little attempt to examine the influence on flora and wildlife, as well as non-forest habitats, until lately. Even in places where research was done.
Impacts on human health
Vector breeding poses a severe hazard to reservoirs in tropical regions of the world, particularly those below 1,000 metres in elevation. Mosquitoes, which are vectors of malaria, filaria, dengue fever, and other diseases, reproduce in little pools of water generated on the reservoir’s margins when the water level rises and falls. Dams have also been observed to increase the number of schistosomiasis-carrying snails in some places. The link between the spread of vector-borne diseases like malaria and irrigation projects has been thoroughly researched and proven. Malaria was reported to have increased following impoundment in a number of projects, including Sriramsagar and Ukai. Following the outbreak of malaria in the Raichur district of Karnataka, the district became extremely endemic.
The two most prevalent reactions to the threat to human health are the establishment of primary health centres and the spraying of pesticides. Regrettably, the first is more of a cure than a preventive measure. Furthermore, the efficacy of insecticides is debatable. Furthermore, the use of chemical pesticides causes various health risks that must be studied and addressed.
Large dams not only harm biological diversity, but also cause flooding of land.
Removal of natural vegetation and infiltration or leakage from constructed reservoirs or dams can bring the level of the watertable.
Dams effect hydraulic cycles in rivers by impounding sediment, and creating groundwater pressure downstream.