Dams

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The Environmental and Water Issues

A study of dams and its impact on the environment and water quality

History suggests that the earliest of the dams were built about seven thousand years ago . The purpose , technology operation and impact of the dam on the lives of people at those times were obviously different from these now . The uses and benefits of the dams are well known like irrigation , decrease severity of drought and increase agricultural production . Although today 's technology makes it possible for the construction of

large , multi-purpose , easy managed dams , they come with a very high , irreversible price , devastation of the environment

The first report to highlight the negative impacts of dams and large-scale water engineering projects was the report `The Careless Technology ' published in 1972 (Conference Report which was based on the 1968 conference on dams . The conference was jointly sponsored by the Center for Biology of Natural Systems Washington University and The Conservation Foundation . According to the World Commission on Dams (WCD Report ) inundation of the river areas lead to the loss of forests and wildlife habitat , loss of certain species and aquatic biodiversity . The impacts on the ecosystem by dams are more negative than being positive , including cumulative impacts on water quality and natural flooding . Reservoirs emit green house gases due to rotting of vegetation and carbon inflows from catchments , with the emission levels being highly variable

The obstruction of free flowing rivers for dams has several physical and biological impacts and directly influences the natural ecosystem . When river flows , the current carries sediment along its path , while simultaneously depositing it , thus ensuring even sedimentation throughout its path . Sediment deposition and riverbed erosion occurs when the current carries the sediment only to be deposited by obstruction at the foot of the dam . Very little sediment is further carried along the path for deposition by the shallow waters leading to erosion of the riverbed . Erosion and sedimentation triggers a series of hydrologic , ecological and economic impacts . The migration of fishes and other marine species are also seriously affected by dams Several species that migrate seasonally as part of their breeding cycle cannot reach their intended suitable place . Some dams have passage structures or fish ladders for fishes to pass through , which however is stressful for bigger fishes . For instance , the salmon population on the Columbia river dropped drastically once the dam was built , although there were fish ladders . The salmon were unable to swim upstream during the breeding season

The quality of any stored water is deteriorated depending on the amount of time it is held there and water held by dam is no exemption . The quality of river water when held for long time is affected by change in temperature , loss of nutrients , flooding and decomposition of forests etc . As the vegetation is completely submerged by the reservoir , the organic matter is gradually decomposed , depleting the oxygen from water . The conversion of fresh water into salty water is also one of the unwanted side...