Mention any one ecological problem caused by building large same
Answers
The construction of large dams completely change the relationship of water and land, destroying the existing ecosystem balance, which in many cases, has taken thousands of years to create. Currently there are around 40,000 large dams which abstract the World’s rivers, completing changing their circulation system this is not going to occur without dire environmental impacts.
Throughout the past few years, the negative impacts of dams have become so well known that most countries (including India) have stopped building them altogether and are now forced to invest their money into fixing the problems created by existing dams.
Some environmental problems caused by dams are as follow:
(i) Soil Erosion:
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One of the first problems with dams is the erosion of land. Dams hold back the sediment load normally found in a river flow, depriving the downstream of this. In order to make up for the sediments, the downstream water erodes its channels and banks. This lowering of the riverbed threatens vegetation and river wildlife.
One of the reason dams are built is to prevent flooding. However, most ecosystems which experience flooding are adopted and many animal species depend on the floods for various life cycle stages, such as reproduction and hatching. Annual floods also deposit nutrients and replenish wetlands. A major example of soil erosion problems is the Aswan Dam.
(ii) Species Extinction:
Fisheries become an increasingly important source of food supply more attention is being paid to the harmful effects of dams on many fish and marine mammal populations. The vast majority of large dams do not include proper bypass systems for these animals, interfering with their life cycles and sometimes even forcing species to extinction.
(iii) Spread of Disease:
Dam reservoirs in tropical areas, due to their slow-movement, are literally breeding grounds for mosquitoes, snails and flies, the vectors that carry malaria, Schistosomiasis and river blindness
(iv) Changes to Earth’s Rotation:
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Nasa geophysicist Dr. Benjamin Fong Chao found evidence that large dams cause changes to the earth’s rotation, because of the shift of water weight from oceans to reservoirs. Because of the number of dams which have been built, the Earth’s daily rotation has apparently sped up eight-millionths of a second since the 1950s. Chao said it is the first time human activity has been shown to have a measurable effect on the Earth’s motion.
(v) Sedimentation:
It is the process by which larger sediments in water entering a reservoir are deposited as its upper end forming a delta and steadily raising the level of the upper reaches of the reservoir. This causes flooding due to its bank water effect, and in the case of the Sardar Sarovar Dam, this process shortens the utility of the dam.
(vi) Siltation:
It is the outcome of silt being deposited at the bottom of the reservoir, which inevitably reduces the utility of the dam. In the case of SSP there is the possibility of premature siltation, which decides the life span of a reservoir. Siltation reduces the water storage capacity of the reservoir, undermines its effectiveness for power-generation, irrigation and flood control and renders it usefulness in the long term.
(vi) Water logging:
Rich soils in the states of Punjab and Haryana have been robbed for their use because of water logging. The Indian Institute of science estimates that 40 percent of the command area for Sardar Sarovar Dam will become waterlogged. This area contains black cotton soils which are particularly prove to water logging under perennial irrigation due to high water retention capacity. Soils become water logged and crop yields fall.
(viii) Salinisation:
The arid and semi-arid areas are incapable of handling large amounts of water brought by irrigation. Irrigation water has more saline content and adds more salt to the system leading to the increase of salinisation. Changes in the salt regime can affect the entire ecosystem and disrupt breeding of fishes. Large areas on the river banks are likely to be affected by an increased quality of salt after dam construction. In total, over 32,000 hectares of land have been submerged by the Sardar Sarovar Dam, 13,000 of which is forest land and 11,000 hectares of agricultural land.
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