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The construction of large dams always change the relationship of water and land that destroy the existing ecosystem balance whereas in many cases, has taken thousands of years to create. Now, there are around 40,000 large dams that obstruct the world’s rivers, completely changing their circulation systems. This is not going to occur without dire environmental impacts. About past few years, the negative impacts of dams have become so familiar that most of countries had to stop building them altogether and are now forced to invest their money into fixing the problems created by existing dams.
Construction of the dam does not necessarily only bring benefits. But on the other hand there are adverse effects of dam construction that existed before and after construction must be considered. It will not only affect the construction environment, but can be up to the river mouth. Among the effects of dam construction is:-
ECOLOGICAL SYSTEM PROBLEMS
No doubt the problem will arise in our ecosystem. It is usually starts from the beginning of the constructions until the affected downstream natural river. Many cases studies and much information can not be used as reference material before extinct. Indirectly, the genetic diversity of biological resources and destroyed. Many endangered species of aquatic animals, land, forest issues.
Construction of dams required extensive land clearing without any control. As in Bakun and at Lake Chini has a significant impact and can be seen clearly. The most obvious example of the Bakun dam has destroyed the natural habitat of 70.000 hectares of Singapore. Another example is the dam of Lake Chini, Pahang is also clear that there are 60 hectares of forest. Vegetative damaged ecosystems and hence have an impact on wildlife. Disturbed the natural habitat and cause the organism to find a new habitat or the continued extinction of the area.
Extinction of flora and fauna, and disruption
In Temenggor, dam have been identified as causes of this problem with the number of fish in the Sungai Perak terubuk decreasing. Another problem is the transfer of animals from the forest to the occupation. This causes problems for local residents who live nearby. As an example was the construction of ordinary dam at Bakun. This problem will increase if no action is taken and control.
Other example, the reproduction of freshwater turtles is threatened by this situation. It also prevents the passage of freshwater turtles and fish and thus interferes with their breeding habits and movements.
In rivers with biologically productive estuaries, both marine and fish and also shellfish suffer from the changes in water flow and quality. Changes in fresh and quality water flows and the salinity balance in an estuary will alter species distribution and breeding pattern of fish. Furthermore, changes in nutrient levels and decrease in the quality of the river water can also gives bad impacts on the productivity of the fish.
These changes can also have major effects on marine species which is the feed of their life cycle in the marine, or are influenced by water quality changes in the coastal areas. The greatest impact on wildlife will come from loss of habitat. This is as result from the reservoir filling and land use changes in the catchment area. Migratory patterns of wildlife and the fish may be disrupted by the dam. This will make the aquatic fauna, include waterfowl, amphibians and reptiles can increase because of the construction of dam.
Water pollution / Water quality
Usually, the river will be effect on soil erosion and the silt occurs during the construction and disposal of water. Because of that, the water becomes brown and it was caused of a problem for growth of aquatic plants. But on the other hand, the river will be a shortage of minerals due to system problems slowed the flow of water caused water dam. Then, rate of mineral and oxygen was decreasing. Further problems arise when people cultivated their crops. The used of pesticides can not be drained and recycled in a river. The material from the construction of dam itself which is the steel consumption rates also affect water quality when water is released from the dam.
The obvious changes occur in the timing of flow, quality, quantity and use of water, aquatic biota, and sedimentation in the river basin. The area of influence of a dam construction projects extend from the upper limits of the catchment of the reservoir to as far downstream as the marine and coast or offshore zone. While there are direct environment impacts related with the construction of the dam for examples, dust, erosion, borrow and the disposal problems. The greatest impacts result from the impoundment of water, flooding of land to form the dam and alteration of water flow downstream. These effects also have direct impacts on soils, vegetation, wildlife and wild lands, fisheries, climate and also the human populations in that area.
Construction of the dam has an adverse impact on river hydro ecosystem. Other disadvantages are affected fish population in the river if the construction of the dam occurred at the upper river. That situation took place on the Temenggor Dam, Bersia Kenering. Deep study was done in Lake Chenderoh. Fishery catches in the dam is low and only 22 species were captured, and 15 of them consisted of fish caught by family Cyprinid. Most using drift nets, and this small shows lack large fish in that dam. Results show catch per unit effort will be between (2.7 – 12.8 kg. per fisherman-day with a value between RM4.94-32.43-per-day fishing.
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