How can a beaver dam help to reduce flooding downstream?
For several hundred years, there were no beavers in Britain. Hunted for their thick fur and for an oily scent used in medicine, they had vanished from the rivers by the sixteenth century. In recent years, however, small groups have been released under careful supervision, and the results have surprised scientists.
A beaver is nature's engineer. It fells small trees with its sharp front teeth and uses the branches, mud and stones to build dams across streams. Behind each dam, the water spreads into pools and marshy patches. These slow the flow of the river, so that after heavy rain the water is released gradually instead of rushing downstream. Fish, frogs, dragonflies and water birds move into the new wetlands.
Not everyone is delighted. Some farmers point out that a dam can flood a field of crops, and that gnawed trees along a riverbank may fall across paths or fences. 'I like wildlife as much as anyone,' says one farmer, 'but I cannot grow wheat under a pond.'
Conservation groups reply that most problems can be managed. Pipes can be fitted through dams to keep the water at a safe level, and young trees can be wrapped in wire. The question, they argue, is not whether beavers should return but how people and beavers can share the same land.
A beaver is nature's engineer. It fells small trees with its sharp front teeth and uses the branches, mud and stones to build dams across streams. Behind each dam, the water spreads into pools and marshy patches. These slow the flow of the river, so that after heavy rain the water is released gradually instead of rushing downstream. Fish, frogs, dragonflies and water birds move into the new wetlands.
Not everyone is delighted. Some farmers point out that a dam can flood a field of crops, and that gnawed trees along a riverbank may fall across paths or fences. 'I like wildlife as much as anyone,' says one farmer, 'but I cannot grow wheat under a pond.'
Conservation groups reply that most problems can be managed. Pipes can be fitted through dams to keep the water at a safe level, and young trees can be wrapped in wire. The question, they argue, is not whether beavers should return but how people and beavers can share the same land.
Answer and explanation
Correct answer: A. It slows the river so that water is released gradually.
- Step 1: The second paragraph says pools slow the flow of the river. Step 2. After heavy rain the water comes down gradually instead of rushing. Answer: It slows the river so that water is released gradually. Why not the others: It stops water from ever leaving the stream.: The text says water is released, only more slowly. It makes the river bed deeper than it was before.: This Depth of the river bed is not mentioned. It carries floodwater away through hidden pipes.: This Pipes are only mentioned as a farmer's solution.
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