| TRUE | if the statement agrees with the information |
| FALSE | if the statement contradicts the information |
| NOT GIVEN | if there is no information on this |
Dirty river but clean water
Floods can occur in rivers when the flow rate exceeds the capacity of the river channel, particularly at bends or meanders in the waterway. Floods often cause damage to homes and businesses if they are in the natural flood plains of rivers. While riverine flood damage can be eliminated by moving away from rivers and other bodies of water, people have traditionally lived and worked by rivers because the land is usually flat and fertile and because rivers provide easy travel and access to commerce and industry.
A. FIRE and flood are two of humanity’s worst nightmares. People have, therefore, always sought to control them. Forest fires are snuffed out quickly. The flow of rivers is regulated by weirs and dams. At least, that is how it used to be. But foresters have learned that forests need fires to clear out the brush and even to get seeds to germinate. And a similar revelation is now dawning on hydrologists. Rivers 一 and the ecosystems they support — need floods. That is why a man-made torrent has been surging down the Grand Canyon. By Thursday March 6th it was running at full throttle, which was expected to be sustained for 60 hours.
B. Floods once raged through the canyon every year. Spring Snow from as far away as Wyoming would melt and swell the Colorado river to a flow that averaged around 1,500 cubic metres (50,000 cubic feet) a second. Every eight years or so, that figure rose to almost 3,000 cubic metres. These floods infused the river with sediment, carved its beaches and built its sandbars.
C. However, in the four decades since the building of the Glen Canyon dam, just upstream of the Grand Canyon, the only sediment that it has collected has come from tiny, undammed tributaries. Even that has not been much use as those tributaries are not powerful enough to distribute the sediment in an ecologically valuable way.
D. This lack of flooding has harmed local wildlife. The humpback chub, for example, thrived in the rust-red waters of the Colorado. Recently, though, its population has crashed. At first sight, it looked as if the reason was that the chub were being eaten by trout introduced for sport fishing in the mid-20th century. But trout and chub co-existed until the Glen Canyon dam was built, so something else is going on. Steve Gloss, of the United States’ Geological Survey (USGS), reckons that the chub’s decline is the result of their losing their most valuable natural defense, the Colorado’s rusty sediment. The chub were well adapted to the poor visibility created by the thick, red water which gave the river its name, and depended on it to hide from predators. Without the cloudy water the chub became vulnerable.
E. And the chub are not alone. In the years since the Glen Canyon dam was built, several species have vanished altogether. These include the Colorado pike-minnow, the razorback sucker and the round-tail chub. Meanwhile, aliens including fathead minnows, channel catfish and common carp, which would have been hard, put to survive in the savage waters of the undammed canyon, have moved in.
F. So flooding is the obvious answer. Unfortunately, it is easier said than done. Floods were sent down the Grand Canyon in 1996 and 2004 and the results were mixed. In 1996 the flood was allowed to go on too long. To start with, all seemed well. The floodwaters built up sandbanks and infused the river with sediment. Eventually, however, the continued flow washed most of the sediment out of the canyon. This problem was avoided in 2004, but unfortunately, on that occasion, the volume of sand available behind the dam was too low to rebuild the sandbanks. This time, the USGS is convinced that things will be better. The amount of sediment available is three times greater than it was in 2004. So if a flood is going to do some good, this is the time to unleash one.
G. Even so, it may turn out to be an empty gesture. At less than 1,200 cubic metres a second, this flood is smaller than even an average spring flood, let alone one of the mightier deluges of the past. Those glorious inundations moved massive quantities of sediment through the Grand Canyon, wiping the slate dirty, and making a muddy mess of silt and muck that would make modem river rafters cringe.
AI explanationShows the answer. Tap to open.
Question Focus: Comparing severity of damage from fire and flood
Correct Answer: NOT GIVEN
Why this is correct: The passage says fire and flood are both terrible, but it never compares which one causes more damage. There is no sentence saying fire damage is worse than flood damage. So the correct answer is NOT GIVEN.
Passage Reference: A. FIRE and flood are two of humanity's worst nightmares. People have, therefore, always sought to control them. Forest fires are snuffed out quickly. The flow of rivers is regulated by weirs and dams.
Common Mistake: Students often choose FALSE because they expect a comparison. But the passage does not say the opposite either. This is a Not Given trap.
Paraphrasing: Passage: 'two of humanity's worst nightmares' = Statement: 'damage caused by fire is worse than flood'
Tips: Do not assume comparisons. If the passage does not clearly compare A and B, the answer is NOT GIVEN.
Key Vocabulary:
- nightmares = very bad experiences
- regulate = control
Question Focus: Specific flood measurements and frequency
Correct Answer: FALSE
Passage Reference: B. Every eight years or so, that figure rose to almost 3,000 cubic metres. Spring Snow from as far away as Wyoming would melt and swell the Colorado river to a flow that averaged around 1,500 cubic metres a second.
Why this is correct: The passage clearly says floods reached almost 3,000 cubic metres every eight years, not 1,500. The statement mixes up the average flow with the peak flow, so it is wrong.
Common Mistake: Students see the number 1,500 and choose TRUE without checking the time phrase. This is a Partial truth trap.
Paraphrasing: Passage: 'almost 3,000 cubic metres every eight years' = Statement: 'almost 1500 cubic meters every eight years'
Tips: Always check numbers and time expressions together. IELTS often swaps them to trick you.
Key Vocabulary:
- average = usual level
- peaks = reaches the highest level
Question Focus: Impact of sediment from tributaries
Correct Answer: NOT GIVEN
Passage Reference: C. the only sediment that it has collected has come from tiny, undammed tributaries. Even that has not been much use as those tributaries are not powerful enough to distribute the sediment in an ecologically valuable way.
Why this is correct: The passage says the sediment from tributaries is not useful ecologically, but it does not clearly say their overall impact is little. The statement makes a general judgement that the passage does not directly state.
Common Mistake: Students often mark TRUE because it sounds logical. But IELTS needs exact meaning from the text. This is a Not Given trap.
Paraphrasing: Passage: 'not powerful enough to distribute the sediment in an ecologically valuable way' = Statement: 'has little impact'
Tips: Be careful with general words like 'little impact'. If the passage does not clearly say this, choose NOT GIVEN.
Key Vocabulary:
- tributaries = smaller rivers
- sediment = sand and mud
Question Focus: Cause of humpback chub decline
Correct Answer: FALSE
Passage Reference: D. At first sight, it looked as if the reason was that the chub were being eaten by trout. But trout and chub co-existed until the Glen Canyon dam was built, so something else is going on.
Why this is correct: The passage clearly says trout are not always the cause of the chub decline. It explains that chub and trout lived together before, so the statement is the opposite of the passage.
Common Mistake: Students miss the contrast word 'But' and think trout are the reason. This is a Contradiction trap.
Paraphrasing: Passage: 'something else is going on' = Statement: 'always caused by trout'
Tips: Watch for contrast words like 'but' or 'however'. They often signal FALSE answers.
Key Vocabulary:
- co-existed = lived together
- decline = decrease
Question Focus: Initial results of the 1996 artificial flood
Correct Answer: TRUE
Passage Reference: F. To start with, all seemed well. The floodwaters built up sandbanks and infused the river with sediment. Eventually, however, the continued flow washed most of the sediment out of the canyon.
Why this is correct: The passage clearly says that at the beginning, the flood appeared successful. This directly matches the statement, so the answer is TRUE.
Common Mistake: Some students focus only on the final failure and choose FALSE. This is a Wrong section trap.
Paraphrasing: Passage: 'To start with, all seemed well' = Statement: 'achieved success partly at the very beginning'
Tips: Read the whole description. IELTS may ask about the beginning, not the final result.
Key Vocabulary:
- infused = filled
- sediment = sand and mud
Question Focus: Comparing artificial flood size with natural floods
Correct Answer: TRUE
Passage Reference: G. At less than 1,200 cubic metres a second, this flood is smaller than even an average spring flood.
Why this is correct: The passage directly says the current artificial flood is smaller than an average natural flood. This is a clear match, so the answer is TRUE.
Common Mistake: Students sometimes overthink and look for extra conditions. This is a straightforward Synonym match.
Paraphrasing: Passage: 'smaller than even an average spring flood' = Statement: 'smaller than an average natural flood'
Tips: When wording matches clearly, trust it and move on. Do not overanalyse.
Key Vocabulary:
- yield = amount
- average = usual
Question Focus: Water quality during mighty floods
Correct Answer: NOT GIVEN
Passage Reference: G. Those glorious inundations moved massive quantities of sediment through the Grand Canyon, wiping the slate dirty, and making a muddy mess of silt and muck.
Why this is correct: The passage actually describes the water as muddy and dirty, but it does not directly discuss water quality using terms like clean or high quality. The statement adds ideas not stated in the passage.
Common Mistake: Students use their own logic that fast floods mean clean water. This is a Not Given trap.
Paraphrasing: Passage: 'muddy mess of silt and muck' = Statement: 'clean and high quality water'
Tips: Never add your own interpretation. Stick strictly to the words in the passage.
Key Vocabulary:
- inundations = floods
- silt = fine sand
General Tips:
- TFNG questions follow passage order. Use the previous answer location to find the next one faster.
- If the passage does not clearly say something is wrong, do not choose FALSE. Choose NOT GIVEN.
- Numbers and time phrases are common traps. Always check them carefully.
- Words like 'always' and 'never' are dangerous. They often signal FALSE answers.
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