A Hydro-electric dam is a barrier across flowing water that obstructs, directs or slows down the flow, often creating a reservoir, lake or impoundment. A Hydro-electric dam is a barrier that divides water.Hydro-electric Dams generally serve the primary purpose of retaining water. The tallest dam in the world is the 300 meter high Nurek dam in Tajikistan. Hydroelectricity is electricity produced by hydropower.It is a renewable source of energy, produces no waste, and does not produce carbon dioxide (CO2) which contributes to greenhouse gases. Hydroelectricity now supplies about 715,000 or 19% of world electricity (16% in 2003), accounting for over 63% of the total electricity from renewables in 2005।Although large hydroelectric installations generate most of the world's hydroelectricity, small hydro schemes are particularly popular in China, which has over 50% of world small hydro capacity।
Functions of a Hydro-electric Dams !!!!!
Hydropower- is the force or energy of moving water. It may be captured for some useful purpose.
Irrigation- is the artificial application of water to the soil usually for assisting in growing crops.
Flood control- is a feature of many communication protocols designed to prevent overwhelming of a destination receiver.
Navigation- is the process of planning, recording, and controlling the movement of a craft or vehicle from one place to another.
Tourism- is travel for predominantly recreational or leisure purposes or the provision of services to support this leisure travel.
Supply water for human use- In coastal areas, human use of a sub-surface water source may cause the direction .... roughly 5 have a connection to a piped water supply at home.
Advantages of Hydro-electric Dams
- Hydro-electric Dams gather drinking water for people.
- Hydro-electric Dams help farmers bring water to their farms.
- Hydro-electric Dams help create power and electricity from water.
- Hydro-electric Dams keep areas from flooding.
- Hydro-electric Dams create lakes for people to swim or sail on.
Big Dams Big Dillemas
LISTING THE HARMFUL EFFECTS OF DAM TO THE ENVIRONMENT
EFFECT ON RIVERS
Hydroelectric Dams affect many ecological aspects of a river. Rivers depend on the constant disturbance of a certain tolerance. Dams slow the river and this disturbance may damage or destroy this pattern of ecology. Temperature is also another problem that dams create. Rivers tend to have fairly homogeneous temperatures. Reservoirs have layered temperatures, warm on the top and cold on the bottom; in addition often it is water from the colder (lower) layer which is released downstream, and this may have a different dissolved oxygen content than before. Organisms depending upon a regular cycle of temperatures may be unable to adapt; the balance of other fauna (especially plant life and microscopic fauna) may be affected by the change of oxygen content.
EFFECT ON AQUATIC LIFE
When Hydro-electric dams are constructed, they instantly alter the body of water they are installed in. In many instances, dams are constructed to control the flow of water, in rivers such as the Nile. The first thing to be affected by a dam is the flow of sediment, which is usually picked up along banks and stream beds and carried downstream. Sediment collects behind dams, rather than continuing to flow out with the river, and as a result, the water bed below the dam eventually becomes rocky and scoured clean of sediment. Aquatic plants are unable to thrive, and the nutrients in the sediment that nourish fish and other aquatic life are no longer available, sometimes causing extinction in large numbers. The most obvious impact that a dam has on fish is that it obstructs migration. For some fish species, such as salmon, which spawn in rivers and then swim out to sea, this can be devastating. For others, being unable to pass dams means that there is not as much species diversity. Many dams in the latter part of the 20th century were built with fish ladders and other modifications designed to allow the passage of fish, but many fish are unable to use the ladders or die in the machinery of the dam. Dams also decrease the rate of migration, exposing sensitive fish species to predators that may lurk in slower flowing water.
A CONCRETE IS NO FRIEND TO A RIVER
Hydro-electric Dams were once considered magnificent feats of engineering. But the perspective on dams has changed. Ambs says dams slow down river currents, block the migration of fish, and flood valuable wildlife habitat.
"As I like to say, one of the worst things that you can do to a river, short of pumping raw sewage directly into it, is to dump a chunk of concrete into it. And we knew that removing these dams would have a tremendous beneficial impact on the riverside ecosystem. What even we did not appreciate was just how significant and how quickly the river would recover." Before the first dam was removed from the Baraboo River, the Wisconsin Department of Natural Resources examined the reservoir behind it. There were 11 species of fish in it, and the dominant one was carp. Ambs says that situation changed quickly.
"Eighteen months later, after the dam had been removed, they found 24 species of fish, and the dominant specie was smallmouth bass. Dissolved oxygen levels were way up. Nutrient loading, which had been a real problem, was way down. As we like to say, it really was proof positive that if you remove the dam, the fish will come." When the final dam is taken out, 120 miles of the Baraboo River will again flow freely. Ambs says that might be the longest stretch of river in the United States ever restored by removal of a dam.
POPULATION RELOCATION!!!!
Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In many cases, no amount of compensation can replace ancestral and cultural attachments to places that have spiritual value to the displaced population. Additionally, historically and culturally important sites can be flooded and lost. Such problems have arisen at the Three Gorges Dam project in China, the Clyde Dam in New Zealand and the Ilısu Dam in Southeastern Turkey.
SOIL EROSION
- Soil may be detached and moved by water wind or tillage.
- Erosion’s removal of the upper horizons of the soil results in a reduction in soil quality i.e. a diminution of the soil’s suitability for agriculture or other vegetation. This is because the eroded upper horizons tend to be the most nutrient-rich. Erosion removes the cream of the soil”.
- 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. A major example of soil erosion problems is the Aswan Dam. One of the reasons dams are built is to prevent flooding. However, most ecosystems which experience flooding are adapted to this and many animal species depend on the floods for various lifecycle stages, such as reproduction and hatching.
- Annual floods also deposit nutrients and replenish wetlands.
DAM FAILURE
- Failures of large dams, while rare, are potentially serious — the Banqiao Dam failure in Southern China resulted in the deaths of 171,000 people and left millions homeless. Dams may be subject to enemy bombardment during wartime, sabotage and terrorism. Smaller dams and micro hydro facilities are less vulnerable to these threats.
- The creation of a dam in a geologically inappropriate location may cause disasters like the one of the Vajont Dam in Italy, where almost 2000 people died, in 1963
HEALTH IMPACT
The influence of the project and its labour on the health of the local communities needs to be studied urgently. The Targeted Intervention (TI) programme under the Sikkim State Aids Control Society has already undertaken AIDS and Sexually Transmitted Diseases (STD) awareness programms in the entire project site through a few local NGOs. The program identifies migrant workers like those who are employed by the Teesta V project as a vulnerable group. There is reason to believe that the number of persons with STDs has gone up tremendously after the project started.
- 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.
CHANGES TO EARTH ROTATION
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 by 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.
REHABILITATION AND REsTTLEMENT OF PEOPLE
RESETTLEMENT TARGET
The overall objective of resettlement and rehabilitation is to ensure that the affected production base will be restored, the affected labor force will be re-employed, and income and livelihood of affected people will be improved or at least restored to their previous levels before resettlement.
- As much as possible the resettler’s grain production level will be self-sufficient after resettlement.
- The income per capita shall be recovered to the standard before resettlement.
- The affected public infrastructures, school, hospitals, social welfare level, natural environment and traffic condition etc. shall be improved after resettlement.
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