Complete the summary below.
Choose NO MORE THAN TWO WORDS from the passage for each answer.
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.
The Eco- Impact of the Canyon Dam
Floods are peopled nightmare. In the past, canyon was raged by flood every year. The snow from far Wyoming would melt in the season of and caused a flood flow peak in Colorado river. In the four decades after people built the Glen Canyon dam, it only could gather together from tiny, undammed tributaries.
Humpback chub population reduced, why?
Then, several species disappeared including Colorado pike-minnow, and the round-tail chub. Meanwhile, some moved in such as fathead minnows, channel catfish and . The non-stopped flow leaded to the washing away of the sediment out of the canyon, which poses great threat to the chubs because it has poor away from predators. In addition, the volume of available behind the dam was too tow to rebuild the bars and flooding became more serious.
AI explanationShows the answer. Tap to open.
Question Focus: Synonym match - summary mentions season when snow melts; passage specifies the season
Correct Answer: Spring
Why this is correct: The summary says the snow from Wyoming would melt in a certain season. The passage clearly states Spring Snow would melt and cause floods, so the exact word needed is Spring.
Passage Reference: 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.
Common Mistake: Students may write spring season or springtime, but you must copy the exact word from the passage. Writing extra words breaks the word limit. This is a word limit trap.
Paraphrasing: Passage: 'Spring Snow ... would melt' = Summary: 'the snow ... would melt in the season of ___'
Tips: When the summary mentions a season, scan the passage for capitalized season words.
Key Vocabulary:
- melt = turn from ice to water
- rage = happen strongly
Question Focus: Direct word match - what the dam could gather
Correct Answer: Sediment
Passage Reference: 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.
Why this is correct: The summary says the dam could only gather something from tiny tributaries. The passage clearly says the only thing collected was sediment, so that is the correct word.
Common Mistake: Students may write sand because sand is mentioned later, but here the passage specifically says sediment. This is a context shift trap.
Paraphrasing: Passage: 'the only sediment that it has collected' = Summary: 'it only could gather ___ together'
Tips: Do not jump ahead in the passage. The summary follows passage order.
Key Vocabulary:
- sediment = material like sand and mud
- tributaries = small rivers
Question Focus: List completion - disappearing species
Correct Answer: Razorback sucker
Passage Reference: 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.
Why this is correct: The summary lists species that disappeared. The passage names the razorback sucker as one of them, so those exact words complete the list.
Common Mistake: Students may choose Colorado pike-minnow again, but it is already written in the summary. Repeating it misses the next item. This is a wrong section trap.
Paraphrasing: Passage: 'These include the Colorado pike-minnow, the razorback sucker' = Summary: 'including Colorado pike-minnow, ___'
Tips: When you see a list, copy the next item exactly as written in the passage.
Key Vocabulary:
- vanish = disappear
- species = types of animals
Question Focus: List completion - invasive species moving in
Correct Answer: Common carp
Passage Reference: 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.
Why this is correct: The summary mentions species that moved in. The passage lists fathead minnows, channel catfish and common carp, so common carp completes the list.
Common Mistake: Students may write channel catfish, but that species is already mentioned just before the gap. This is a repetition trap.
Paraphrasing: Passage: 'fathead minnows, channel catfish and common carp' = Summary: 'fathead minnows, channel catfish and ___'
Tips: Check what words are already written before the gap so you do not repeat them.
Key Vocabulary:
- alien species = non-native animals
- move in = start living there
Question Focus: Cause-effect - why chubs are threatened
Correct Answer: Visibility
Passage Reference: 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.
Why this is correct: The summary says sediment loss threatens chubs because it has poor something away from predators. The passage explains the chub depended on poor visibility to hide, so the missing word is visibility.
Common Mistake: Students may write water or sediment, but the passage focuses on how cloudy water reduced visibility. This is a partial truth trap.
Paraphrasing: Passage: 'poor visibility created by the thick, red water' = Summary: 'it has poor ___ away from predators'
Tips: Grammar clues like adjectives help you decide the word type you need.
Key Vocabulary:
- visibility = how well you can see
- vulnerable = easy to attack
Question Focus: Specific detail - material behind the dam
Correct Answer: sand
Passage Reference: 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.
Why this is correct: The summary mentions the volume available behind the dam was too low. The passage clearly states the volume of sand was too low, so the correct word is sand.
Common Mistake: Students may write sediment, but in this part the passage is more specific and says sand. This is a specific detail trap.
Paraphrasing: Passage: 'the volume of sand available behind the dam was too low' = Summary: 'the volume of ___ available behind the dam'
Tips: Use the exact word used in that paragraph, even if a similar word appeared earlier.
Key Vocabulary:
- volume = amount
- sandbank = raised area of sand
General Tips:
- Summary completion questions follow passage order. Use the previous gap to find the next answer faster.
- Always copy the exact word from the passage. Do not change it to a synonym.
- Check the word limit carefully. Extra words make the answer wrong.
- Use grammar clues around the gap to decide if you need a noun, verb, or adjective.
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