Note for Hoover Dam


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Note for Hoover Dam

  1. 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 1
  2. 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*). 2
  3. 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. 3
  4. 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). 4
  5. 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 5
  6. 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 6
  7. 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 7
  8. 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. 8
  9. 9. Appendix Hoover dam picture: 9
  10. 10. 10
  11. 11. Stone Angel Lake Mead Lake Mead map 11
  12. 12. Hoover dam map 12
  13. 13. Chart of Colorado riverbed lowering. 13
  14. 14. Reference 1. 2. 3. 4. african-examples 5. 6. 7. 8. e6frfkp9-1111114339063 14