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The Three Gorges Dam in China cost USD37 billion to build. It created a reservoir hundreds of feet deep and nearly 400 miles long. To achieve this, 13 cities, 140 towns and more than 1600 villages had to be evacuated and then inundated. The dam generates 11 times as much power as the Hoover Dam in the United States.

The Three Gorges Dam, built across three gorges in the Yangtze River, was supposed to control flooding on that river. Yet, 2010 saw the worst flood in years. There is now a USD 62 billion project to divert water to China's scorched Northern region. Northern China has half the population of the country but only 15 % of its freshwater.

The ambitious Three Gorges Dam was first envisioned in 1919. Much of the approach to the project did not take into account the warnings of various scientific groups and activists. More often than not, it was in direct contradiction to scientific recommendations. The massive quantity of water dammed up is said to slow Earth's rotation. This may sound far-fetched. But is must be noted that the detonation of the largest bomb by Russia is said to have produced a sonic wave that went round the Earth twice. Our region has been suffering the haze for more than twenty years due to massive fires in a neighbouring country. The point to be noted is that man is capable of projects and activity massive enough to have a tangible effect on the planet as a whole.

The environmental consequences of large dam include direct impacts to the biological, chemical and physical properties of rivers and the stream-side environments. Fish that migrate upstream to spawn can lose access to their spawning grounds when rivers are dammed up. In some parts of the world, small side streams connect the upper and lower parts of the dammed river to create a path for the fish to move upstream and find their natural spawning grounds.

Dams trap sediments that are an integral part of physical processes and habitats downstream, including productive deltas, barrier islands, fertile floodplains and coastal wetlands. Damming slows the water flow. From a free-flowing river the body of water becomes an artificial slack-water reservoir. This completely changes the environment of the river as a body of water. Aquatic plants and animals suffer to adapt to the change in temperature, chemical composition, dissolved oxygen levels and physical properties of the river that becomes a reservoir. Non-native and invasive species move in to the detriment of the river's natural communities of plants and animals.

The greatest sustained environmental impacts of dams are the alteration in the river's flow and transportation of sediment downriver. Areas of the river's reaches, the natural seepage of water to the sides are disrupted. This dewatering severely affects the life forms contained in these areas. The ecological web of the river system is adversely altered.

Some sediment naturally replenish downstream ecosystems. Riverbeds downstream of dams are typically eroded by several meters within the first decade itself. This damage can extend for hundreds of kilometres below a dam. This deepening of the riverbed will lower groundwater tables along the river. Plants will lose their supply of groundwater as will human communities who draw from wells. Invertebrates and fish lose this riverbed environment for natural spawning.

Dams also have a significant effect on the atmosphere. Most reservoirs in the tropics show a significant increase to greenhouse gas emissions. Large dams have led to the extinction of many fish and other aquatic species, the disappearance of birds in floodplains, huge losses of forest, wetland and farmland, erosion of coastal deltas and many other negative impacts that cannot be reversed.

   

Answer the following questions using complete sentences

 

1.

From paragraph 1, how much did the Three Gorges Dam cost ?

 

2.

(a) From paragraph 1, how long is the reservoir of the Three Gorges Dam ?

(b) From paragraph 1, in terms of power generation, how does the Three Gorges Dam compare with the Hoover Dam ?

 

3.

(a) From paragraph 4, how are fish that move upstream to spawn affected by dams ?

(b) From paragraph 6, what are the two sustained environmental impacts of dams ?

 

4.

(a) In your own words, what does the term non-native species mean ?

(b) What is the negative effect on the environment of dams in the tropics ?

 

5.

What characteristic in dams outweigh the benefit of a continuous supply of electricity ?

 

6.

Based on the passage, write a summary of :

How dams should only be the last recourse as a source of electricity.

How dams affect an ecosystem.

 

 

 

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Answers
 

1.

It cost USD 37 billion.
 

2.

(a) It is 400 miles long.

(b) The Three Gorges Dam produces 11 times as much electricity as the Hoover Dam.

 

3.

(a) They lose access to their natural spawning grounds.

(b)

(i) Alteration in the river's flow.

(ii) Transportation of sediment downriver.

 

4.

(a) The term non-native species refers to species that do not belong to the community of plants or animals that naturally live in the river.

(b) There is a significant increase in the emission of greenhouse gases.

 

5.

Characteristic: The environmental impact of dams far outweighs the benefit of electric power.

Reason: Dams permanently change not just the ecosystem within the river dammed, but also adversely affects the areas adjoining the rivers that have been sustained by the presence of the river and the river's flow.

  6. Dams for electricity should be a choice only when all other options have been exhausted. There are ample scientific results and studies to show hat dams permanently after the river and its adjoining areas to the detriment of the flora and fauna that naturally exist there. Man has to co-exist with all the flora and fauna of this world. More importantly, biodiversity has to be maintained. Man's knowledge of plants and animals is still young. There could be many plants and animals that will become the source of medicines and other useful products that await discovery. The negative effects of dams are chemical, physical and biological. The price that nature has to pay for hydro-electric power for mankind is totally unjustifiable.
 
 
 
 
 

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Comprehension 1

 

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