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Drainage Area


Date: 2015-10-07; view: 545.


The Amazon Basin, the largest drainage basin in the world, covers about 40 percent of South America, an area of approximately 7 050 000 square kilometres (2 720 000 sq mi). It gathers its waters from 5 degrees north latitude to 20 degrees south latitude. Its most remote sources are found on the inter-Andean plateau, just a short distance from the Pacific Ocean.

The Amazon River and its tributaries are characterized by extensive forested areas that become flooded every rainy season. Every year the river rises more than 9 metres (30 ft), flooding the surrounding forests, known as várzea ("flooded forests"). The Amazon's flooded forests are the most extensive example of this habitat type in the world. In an average dry season, 110 000 square kilometres (42 000 sq mi) of land are water-covered, while in the wet season, the flooded area of the Amazon Basin rises to 350 000 square kilometres (140 000 sq mi).

The quantity of water released by the Amazon to the Atlantic Ocean is enormous: up to 300 000 cubic metres per second (11 000 000 cu ft/s) in the rainy season, with an average of 209 000 cubic metres per second (7 400 000 cu ft/s) from 1973 to 1990. The Amazon is responsible for about 20% of the Earth's freshwater entering the ocean. The river pushes a vast plume of freshwater into the ocean. The plume is about 400 kilometres (250 mi) long and between 100 and 200 kilometres (62 and 120 mi) wide. The freshwater, being lighter, overrides the salty ocean, diluting the salinity and altering the color of the ocean surface over an area up to 1 000 000 square miles (2 600 000 km2) large. For centuries ships have reported freshwater near the Amazon's mouth yet well out of sight of land in what otherwise seemed to be the open ocean.

The Atlantic has sufficient wave & tidal energy to carry most of the Amazon's sediments out to sea, thus the Amazon does not form a true delta. The great deltas of the world are all in relatively protected bodies of water while the Amazon empties directly into the turbulent Atlantic.

The bore is the reason the Amazon does not have a protruding delta; the ocean rapidly carries away the vast volume of silt carried by the Amazon, making it impossible for a delta to grow past the shoreline.

 

Exercise 7. Read the text above “Drainage Area” once again and answer the following questions:

 

1. Where does the Amazon gather its waters from?

2. How does the level of the river change in the rainy season?

3. What is the quantity of water released by the Amazon to the Atlantic Ocean?

4. What is the size of the plume in the Atlantic Ocean?

5. Why doesn't the Amazon form a true delta?

6. Why isn't silt deposited in delta past the shoreline?

Exercise 8. Read the following text “Origins” and fill in the gaps with the words given below:

 


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Amazon River | Origins
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