DAMS
Today there are more than 50,000 large dams around the world, which play an important role in life of communities and their economic development. Current estimates suggest that 30-40% of irrigated land worldwide relies on dams. Hydropower supplies about one-fourth of the world's total electric power supply. The world's two most populous countries, China and India, are relying heavily on dams for their power requirements.
India's increasing demand for water for intensive irrigated agriculture, for generating electricity, and for consumption in urban and industrial centers, has been met by large dams. Dams ensure supply of water for domestic use throughout the year, provide water for agriculture, industry and hydropower generation.
In spite of the above mentioned advantages, there are several serious environmental problems also, resulting from the construction of dams. Dams alter river flows, change nature's flood control mechanisms such as wetlands and flood plains, distort the lives of local people and destroys habitats of wild plant and animal species. Irrigation to support cash crops quite often leads to unequal distribution of water. Landholders nearby the canals get the lion's share of water, while the poor and small farmers get less, who are seriously affected by water shortage.
The major problems created by dams can be briefed as follows.
1. Fragmentation and physical transformation of rivers.
2. Serious impacts on riparian ecosystems.
3. Social consequences due to displacement of people.
4. Water logging and salinisation of surrounding lands.
5. Dislodging animal populations, damaging their habitat and cutting off their migration routes.
6. Disruption to fishing, boating and free use of water for different purposes. 7. Emission of greenhouse gases from reservoirs due to rotting vegetation in catchment areas.
The negative impacts of dams are more on indigenous and tribal people because their livelihood, culture and spiritual life would be affected. At the same time, the benefits from dams quite often do not reach such people. For example, in India, of the millions of people were displaced by dams, 40% to 50% were tribal people, who account for only 8% of our population.
Conflicts over dams have heightened in the last two decades because of their social and environmental impacts and failure to achieve targets and promised benefits. The relative advantages and disadvantages of dams can be summarised as follows.
Advantages of dams
1. Low cost, pollution free method for generation of electricity for a pretty long period.
2. The lake that forms behind the dam can be used for water sports and pleasure activities. Large dams are tourist attractions and good sources of income.
3. Dam water can be used for irrigation purposes.
4. Dams help to reduce the impact of floods.
5. Dams can be used for aquaculture.
Disadvantages of dams
1. Construction of dams is extremely expensive and time consuming. They become profitable only after decades of operation. 2. Dams submerge large areas of highly fertile land and cause destruction of natural environment.
3. People living in villages and towns around the dam areas get dislocated. They lose their farms and businesses. Rehabilitation of such people is a very difficult task.
4. Construction of large dams can cause serious geological damages like earth-quakes, landslides, etc.
5. Old dams are to be decommissioned which involves huge expenditure manpower and dislocations.
6. When a dam is built, it blocks the progress of a river and the people downstream are affected thereby. Such a situation always lead to conflicts between neighbouring states and countries.
7. Building a large dam alters the natural water level causing much distress to various kinds of plants and animals.
From the above discussions it can be concluded that the construction of dams is inevitable, but should be carried out only after proper environment impact studies and careful planning to reduce the losses and displacements to men, animals and plants.
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