This document supports for Hoover Dam presentation.

1. Foreword
Beside the Statue of Liberty and Golden Gate bridge, United State of America has
another structure which show the face of the USA industrial power in early 20th century; the
Hoover dam. People are already known a lot of the advantages of the great Hoover dam, but the
disadvantages of Hoover dam, special in negative effects on environment, are not popular at all.
People must understand that hydraulic structures such as Hoover dam are not as good as people
thought. Therefore, now we need a research about the negative effects of Hoover dam on
environment so that we can come to the balance of economy and environment in future hydraulic
structures.
Figure 1.1: Hoover Dam, taken from above
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2. I. Overview of Hoover Dam:
In 1929, the Great Depression, which known as Dark Tuesday, began from Wall Street,
New York, USA, when stock value dropped suddenly, and it spread out quickly from stock
market to commercial business and industry of every countries in the world. Thousands of banks
were closed; factories were stopped manufacture, unemployed rate rose while GDP of the World
fell. According to Britannica Encyclopedia1, 11000 in 25000 banks were bankrupted; so we can
imagine how huge it was. Each country had its own way to reproduce, but they could classify
them in two ways. The first way was become a fascist country such as Germany, Italia, Japan,
and Spain. The second way was to make something for labors do while they had nothing to do
such as building a great structure. USA had done it well by building the Hoover dam in 1931(1*).
Hoover dam was located on Colorado River, the natural canyon border between Arizona
State and Nevada State. If we begin from Las Vegas, we need about an hour to drive to Hoover
dam location. The name of the dam is taken from the name of 31st USA president, Mr. Herbert
Hoover. Herbert Hoover was the person who planned building a huge dam on Colorado River,
and with the help of him, Colorado compact, which Arizona, California, Colorado, Nevada, New
Mexico, Utah and Wyoming agreement to device amount of river’s water, was signed. For the
result that Hoover brought to USA, the huge dam on Colorado River was named after him (2*).
Hoover dam can be a huge dam because it had the 1st rank of biggest dam in the world
right after it construction completed in 1935, and at the present time, it is being 38th rank. It cost
49 million US dollars to build. People needed to move 1150000 cubic meters of raw material to
begin construct. Thousands worker worked in great construction for the result: Hoover dam, the
(3*)
Concrete Arch Gravity dam which has 379m high, 221m tall and 201m wide at its base .
According to Wikipedia, Hoover was designed for 17 turbine generators for 2078 MW installed
capacity. 17 turbine generators were supported by 35200 cubic meters of Lake Mead, which
created by the holding stream of the dam (7*).
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3. Figure 1.2: Herbert Hoover
A huge structure usually has some big troubles. Hoover Dam used a huge amount of
concretes, so it faces a deathly problem. Concrete heats up when it dries, so that, the dam might
be broken if people did not make it cool down. If people let the dam cool down in the natural
way, it would take the dam 125 years to finish. Anyway, they soon came up with a solution. A
lot of 25mm-diameter pipes were put inside the body of Hoover dam, and then people pumped
water in those pipes. The result was the Hoover Dam which is still standing at the present.
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4. II. Hoover Dam and its negative effects on environment:
Hoover Dam is a marvelous arch dam; represent the great efforts and the height of
architecture of human. It shows the world a beautiful face with so many advantages such as a
source of clean hydropower, an impressive wonder, etc. However, behind the positive
appearance, Hoover dam causes a lot of negative effects on the environment: riverbed lowering,
greenhouse gases ejecting, ecosystem destroying and problems about the water itself.
1. Riverbed lowering:
After Hoover dam was constructed, people gradually realized that the groundwater table
was getting deeper. The reason for that phenomenon was the lowering of Colorado riverbed.
During 9 years, the water stored in Lake Mead kept digging the riverbed and it made the riverbed
(4*)
below Hoover dam get 4 meters deeper . The groundwater became deeper, and it brought
along with it a bunch of bad effects. Many plants in the floodplain were threatened, because they
could not reach the new depth of the groundwater table.
2. Greenhouse gases ejecting:
The hydropower dams are supposed to help decrease the global warming problems by
reducing the greenhouse gases. If people use electricity from hydropower plants instead of those
made from fossil fuel, there will be less greenhouse gases. It is logical! However, the dams
themselves are a great source of greenhouse gases. A study created by National Institute for
Research in the Amazon pointed out that hydropower dams can release greenhouse gases from
their reservoirs (5*). These gases are carbon dioxide (CO2) and methane (CH4), which is 25-times
stronger than carbon dioxide.
This is the valley of Colorado River, before Hoover dam was built. There were many
trees along side the river (Figure 2.1).
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5. Colorado River
Figure 2.1
When the dam was completed, the water from upstream was stored behind the dam,
forming its reservoir. Hoover dam has Lake Mead as its reservoir – the largest reservoir in the
United States. It expands to the length of 180km after the dam, contains approximately 35 km³ of
water. It covers all the trees in 640 sq km of valley (7*) (Figure 2.2).
The water covered
the valley
Figure 2.2
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6. Because the trees were covered in water, they could not obtain any more sunlight and
oxygen, and they died. Then, under the process of bacteria, these trees rotted. As they rotted,
they released carbon dioxide and methane and these gases went from the bottom of the lake to
the surface as bubbles (Figure 2.3).
CO2 and CH4
Figure 2.3
The bubbles reached the surface, and they ejected all the gases into the air (Figure 2.4).
CO2 and CH4
released
Figure 2.4
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7. But it was not just the plants created the greenhouse gases, the soil and animals can do it
too. The soil contains a large amount of nutritive substance, and as it was stored behind the dam,
it just rotted. Just the same as animals and fish which died there, the soil released methane and
nitrous oxide into the air (8*).
3. Ecosystem destroying:
The Hoover Dam ecosystem, a part of the Mojave Desert, is home to a number of animal
species, including the bighorn sheep, coyote, ground squirrel, ringtail cat and the endangered
desert tortoise. The desert tortoise in particular has suffered the impact of the Hoover Dam
through the disruption of nesting grounds and destruction of nests by construction and visitors.
The roadrunner, golden eagle and turkey vulture are just a few of the bird species found in the
area, and the desert is also home to scorpions, tarantulas, rattlesnakes and lizards. Attempts to
avoid altering the bighorn sheep's natural environment guided the original construction plans of
the highway and dam, but more considerations of Hoover Dam wildlife were included in the
Hoover Dam Bypass Project. The Hoover Dam Bypass Project was initiated in the 1980s to
alleviate the impact of road traffic and potential road hazards on area wildlife by providing an
alternate river crossing. This project provided Hoover Dam wildlife crossing areas and tortoise
protection policies for the construction of the dam, with the hopes of minimizing the impact of
new construction on wildlife.
The deserts animals in the Hover Dam ecosystem live in a delicate balance that
depends on specialized plant life to survive. A range of cactus types, desert flowers and bushes
and nettles provide the basis of a fragile food chain. Plant life has been affected by the change in
the Colorado River watershed and the harnessing of water flow, the erosion of the riverbanks and
the pollution resulting from increased vehicle traffic. The draws of the Lake Mead recreational
area and the Hoover Dam visitor center also have increased the human impact of individuals
through foot traffic, damage or removal of plants and litter.
Several species of native and introduced fish that live in the Colorado River also have
felt the impact of Hoover Dam. The catfish, sunfish and other fishes inhabiting the Hoover Dam
ecosystem have been affected by a number of specific aspects of the dam, most notably the
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8. change in water temperature. The Hoover Dam turbines lower the water temperature drastically,
which resulted in the immediate extinction of several species of warm-water wish after the dam's
completion in 1936. Furthermore, introduction of rainbow trout, which are cold-water fish, for
recreational fishing has created competition with native species for resources. The impact of
Hoover Dam also includes significant yearly erosion of the banks of the river as a result of
poured concrete preventing natural silt deposits. This erosion has also affected the feeding and
reproductive environments of the native species of fish.
4. Problems with the water:
The water is stored behind Hoover dam and it often is released from some depth, so the
temperature of the water below the dam is usually not as high as it would be before the dam is
there. The water flow’s temperature often remains unchanged, not affected by the natural
seasonal variations that would have been the case in the free-flowing river. Similarly, the
chemistry of the water may be altered. The free-flowing water usually has higher oxygen level
and lower dissolved salts level than the water in the Lake Mead.
The water is impounded, and the potential of evaporation increases many times. Lake
Mead has the great surface of 640 sp km, thousands of times larger than the Colorado River’s
surface. Because of such extensive area, the water lost by evaporation must be considered. The
evaporation losses in Lake Mead in one year can be as great as 350 billion gal (1.3 trillion liters)
(6*)
.
III. Conclusion:
As you see, Hoover Dam has a lot of negative effects on environment of Colorado River,
but we cannot destroy it. It is a wonder not only for USA but also for the World; moreover, its
electricity production is safer than the work of nuclear power plants. What we discover from
Hoover Dam can be useful for creating future hydraulic structures. We need to consider the
environment before constructing such enormous structure; economic and environmental aspects
must be balance so that we will not have to regret any more.
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9. Appendix
Hoover dam picture:
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10. 10

11. Stone Angel
Lake Mead
Lake Mead map
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12. Hoover dam map
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13. Chart of Colorado riverbed lowering.
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14. Reference
1. http://www.britannica.com/EBchecked/topic/243118/Great-Depression
2. http://en.wikipedia.org/wiki/Great_Depression
3. http://en.wikipedia.org/wiki/Hoover_Dam
4. http://www.internationalrivers.org/en/africa/environmental-impacts-large-dams-
african-examples
5. http://en.wikipedia.org/wiki/Dam#Environmental_impact
6. http://science.jrank.org/pages/1942/Dams-Impact-dams.html
7. http://en.wikipedia.org/wiki/Lake_Mead
8. http://www.news.com.au/worlds-dams-are-contributing-to-global-warming/story-
e6frfkp9-1111114339063
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