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. 1
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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
1
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 rivers 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*). 2
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. 3
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). 4
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 km 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 5
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 6
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 7
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 flows 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 Rivers 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. 8