Reading Practice
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,alwayssought 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 brash and even to get seeds to germinate. And a similar
revelation is now – dawning on hydrologists. Rivers – 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 asWyoming 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 upstreamof 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, thrivedin the rust-redwaters 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, severalspecies 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
move din.
F
So flooding is the obvious answer.
Unfortunately, it is easier said than done. Floodswere 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 asecond, 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 modern river rafters cringe.
Questions 1-7
Do
the following statements agree with the information given in Reading Passage?
In
boxes 1-7 on your answer sheet,
write
TRUE if the statement agrees with the information
FALSE if the statement contradicts the information
NOT
GIVEN if there is no information on this
1..................... Damage caused by fire is worse than that
caused by flood.
2..................... The flood peaks at almost 1500 cubic meters
every eight years.
3..................... Contribution of sediments delivered by
tributaries has little impact.
4..................... Decreasing number of chubs is always caused
by introducing of trout since mid 20th century.
5..................... It seemed that the artificial flood in 1996
had achieved success partly at the very beginning.
6..................... In fact, the yield of artificial flood water
is smaller than an average natural flood at present.
7..................... Mighty floods drove fast moving flows with
clean and high quality water.
Questions 8-13
Complete
the summary below.
Choose
NO MORE THAN TWO WORDS from the passage for each answer.
Write
your answers in boxes 8-13 on your
answer sheet.
The eco-impact of the Canyon Dam
Floods are people’s nightmare. In the past, canyon was
raged by flood every year. The snow from far Wyoming would melt in the season
of 8..................... and caused
a flood flow peak in Colorado river. In the four decades after people built the
Glen Canyon dam, it only could gather 9.....................
together from tiny, undammed tributaries.
Humpback chub population on reduced, why?
Then, several species disappeared including Colorado
pike-minnow, 10.....................
and the round-tail chub. Meanwhile, some moved in such as fathead minnows,
channel catfish and 11......................
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 12..................... away from
predators. In addition, the volume of 13.....................
available behind the dam was too low to rebuild the bars and flooding became
more serious.
Solution:
|
1. NOT GIVEN |
8. spring |
|
2. FALSE |
9. sediment |
|
3. TRUE |
10. razorback sucker |
|
4. FALSE |
11. common carp |
|
5. TRUE |
12. visibility |
|
6. TRUE |
13. sand |
7.
NOT GIVEN
PASSWORD: 14MAY2025
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