– DAMS –
The basic idea of a dam is simple: block the passage of a river down a valley, and its waters will rise to form a man-made lake. Then the water can be piped or channelled to dry areas where it is needed for irrigation , wjuch is supplying crops with water. Besides this, flooding can be controlled and the water-power can be used to turn turbines which generate electricity – the cheapest way of producing it.
Many great dams have been built throughout the world. When they were built, especially in developing countries, their planners predicted a tremendous improvement in the living conditions of the people who would receive the water and electric power. Many of these hopes have been realized and there has been a great improvement in the living conditions, but experience shows that dams can create new problems while solving others.
A survey was recently carried out into the effects of dams that have been built in the past 25 years. It was found that in some cases the dams provided less irrigation and less hydro-electric power than the planners had anticipated. And in certain instances, the presence of the dams was actually causing damage to the environment.
Damming a river does a great deal more than create a huge reservoir of water. Because the water trapped in the lake is no longer flowing rapidly, much of the silt – sand, soil or mud carried along by a river – is deposited on the bottom of the lake. When this happens, the land below the dam may actually lose its fertility because it is silt that makes the land fertile , or productive.
An outstanding example of the unforeseen ill-effects can be observed in the Nile Valley. The lands north of the Aswan High Dam are no longer getting the vast quantities of silt which the annual flood used to deposit on them.
Instead, the large quantities of silt are accumulating on the bottom of the man-made Lake Nasser behind the dam. On the other hand, while losing rich silt and minerals, the dam water may pick up some chemicals which may have extremely harmful effects. For example, the waters of the Volta Dam in Ghana have caused the destruction of some of the country’s richest cocoa cations.
IMPACTS OF DAMS
A. Write the meaning of each word.
1. Line 4, ‘irrigation’ is
2. Line 9, ‘tremendous* means
3. Line 21, ‘silt* is
4. Line 24, ‘fertile* means
5. Line 26, ‘vast’ means
B. Mark the statements as True (T) or False (F).
1. The survey showed that ali dams that have been built in the past 25 years provide very little hydro-electric power.
2. According to the results of the survey, some dams damage the environment.
3. Some cocoa plantations in Ghana were destroyed because of the harmful chemicals in the waters of the Volta Dam.
C. 1. Give the three reasons for building dams.
2. Why is silt deposited on the bottom of the lake?
3. What happens when silt is deposited on the bottom of the lake?
4. Where did the annual flood in the Nile Valley use to deposit the silt?