20-11-2012, 02:16 PM
DISADVANTAGES OF DAMS
disadvantages of dams.doc (Size: 26 KB / Downloads: 56)
Dams reduce the amount of available water by increasing evaporative loss. This is more of a problem in warmer areas since evaporation is a factor of temperature, but it doesn't mean that rainfall increases in the same area. Rainfall is itself a factor of water vapour in the atmosphere and temperature, so the water evaporated from a given dam may travel many kilometres (including out to sea) before it falls as rain.
There can be significant problems from reduced flows on the affected streams below the dam. The vegetation will change, stream banks will move, and the stream will be occasionally polluted with cold water released from the dam (the water is cold because it comes from the bottom of the dam). It is not uncommon for the ecology of a stream to not be well understood, and the environmental changes may have negatively influence the ecosystem. The changes to the size of the water column, the force of flow and the fact that dams make water flows more regular can all affect species adapted to the specific hydrology of a given stream.
The placement of the dam can displace peoples who live in the valley to be flooded. There are many examples of political problems arising when poor peoples are not adequately provided for. There may also be problems for downstream agriculturalists who may have relied on more water volumes.
• dams detract from natural settings, ruin nature's work
• dams have inundated the spawning grounds of fish
• dams have inhibited the seasonal migration of fish
• dams have endangered some species of fish
• dams may have inundated the potential for archaeological findings
Dams are extremely expensive to build and must be built to a very high standard.
The high cost of dam construction means that they must operate for many decades to become profitable.
The flooding of large areas of land means that the natural environment is destroyed.
People living in villages and towns that are in the valley to be flooded, must move out. This means that they lose their farms and businesses. In some countries, people are forcibly removed so that hydro-power schemes can go ahead.
The building of large dams can cause serious geological damage. For example, the building of the Hoover Dam in the USA triggered a number of earth quakes and has depressed the earth's surface at its location.
Although modern planning and design of dams is good, in the past old dams have been known to be breached (the dam gives under the weight of water in the lake). This has led to deaths and flooding.
Dams built blocking the progress of a river in one country usually means that the water supply from the same river in the following country is out of their control. This can lead to serious problems between neighbouring countries.
Building a large dam alters the natural water table level. For example, the building of the Aswan Dam in Egypt has altered the level of the water table. This is slowly leading to damage of many of its ancient monuments as salts and destructive minerals are deposited in the stone work from 'rising damp' caused by the changing water table level
Hydropower dams can damage the surrounding environment and alter the quality of the water by creating low dissolved oxygen levels, which impacts fish and the surrounding ecosystems. They also take up a great deal of space and can impose on animal, plant, and even human environments.
Fish populations can be impacted if fish cannot migrate upstream past impoundment dams to spawning grounds or if they cannot migrate downstream to the ocean. Upstream fish passage can be aided using fish ladders or elevators, or by trapping and hauling the fish upstream by truck. Downstream fish passage is aided by diverting fish from turbine intakes using screens or racks or even underwater lights and sounds, and by maintaining a minimum spill flow past the turbine.
Hydropower can impact water quality and flow. Hydropower plants can cause low dissolved oxygen levels in the water, a problem that is harmful to riparian (riverbank) habitats and is addressed using various aeration techniques, which oxygenate the water. Maintaining minimum flows of water downstream of a hydropower installation is also critical for the survival of riparian habitats.
Hydropower plants can be impacted by drought. When water is not available, the hydropower plants can't produce electricity.
New hydropower facilities impact the local environment and may compete with other uses for the land. Those alternative uses may be more highly valued than electricity generation. Humans, flora, and fauna may lose their natural habitat. Local cultures and historical sites may be flooded. Some older hydropower facilities may have historic value, so renovations of these facilities must also be sensitive to such preservation concerns and to impacts on plant and animal life.
By 2020, it is projected that the percentage of power obtained from hydropower dams will decrease to around four percent because no new plants are in the works, and because more money is being invested in other alternative energy sources such as solar power and wind power. .