Hydroelectric Dams

Intro

Hydroelectric dams have both advantages and disadvantages to society and nature. They supply humans with the electricity we need, from computers to light bulbs. Dams also supply us with our water, giving us a reliable source to go to when we need it. Dams also have some drawbacks. They can emit greenhouse gases, such as methane and carbon dioxide. Dams also harm nature, by destroying habitats and cutting off migration routes. Humans also take a hit when it comes to dams. Dams have forced millions of people to relocate their entire lifestyle to another location and make it work there. Finally, the water quality is a major factor when it comes to spreading diseases such as malaria schistosomiasis, and river blindness. Hydroelectric dams positively and negatively affect our lives, so are they worth it?

2A How Electricity Is Made

Some people may not know, but hydroelectric and coal-fired power plants both produce electricity in a similar way. The Turbine, a propeller-like piece, is moved by a power source, which turns a metal shaft in an electric generator. An electric generator is the motor that produces the electricity. The power source for the hydroelectric power plant is water, but in the coal-fired power plant, the source is the steam from the coal. From there, the results are the same.

Dams are designed to be built on a river with a large drop in elevation. Near the bottom of the dam, water is taken from the reservoir, the water behind the dam, and puts it through the water intake. Trash is collected by the trash rack located at the entrance of the penstock. The water falls down the water intake, through the penstock, to the turbine. The turbine is moved by this water, which in turn moves the shaft connected to the transformer to produce power. This power goes up power lines from the dam and into use by society. After the water goes by the turbine, it passes through the tailrace into the river past the dam.

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2B Classification

Dams can come in a variety of shapes. The shape used for a dam is determined by how the dam will be utilized, funding, the materials available, and how much water is going to be retained by the dam. There are four main types of dams built:

· Embankment

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· Gravity

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· Buttress

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· Arch

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The most common dam is the embankment. Made of locally available material, such as rocks, gravel, sand, and clay, these dams resist the flow of water by their weight. Water can flow into and through the dam because of the permeable materials used. The structure can not be all permeable so the clay protects the structure and its purpose. Since the materials for these dams are local, and the construction process for these dams is relatively simple, the cost to build this dam is much lower compared to other types of dams. Gravity dams also hold back water by their weight. This type of dam is usually built on a solid rock foundation, with the rest created of cement or masonry. The spillway designs of embankment dams are normally where gravity dams are built. This is because of the stable, solid nature of the dam is favored by many. Arch dams are created to resist water by their upstream-facing arch. Arch dams are usually made of concrete and found in narrow canyons. These dams need good contact between the bedrock and the concrete in which it is created to ensure stability and prevent leakage. The final type of dam is the buttress. These dams are no longer economically viable, because of the steel framework and the labor needed for construction and maintenance. Buttress dams are usually made in wide valleys where solid bedrock is not available.

The general purpose, or the way it was designed, is another way to classify a dam. Storage dams can provide a reliable source of water for a short or long period of time. These dams can provide a variety of uses once built. The can be used for hydroelectric power generation, irrigation, recreation, and community water supply. Storage dams can capture water runoff for the use of livestock during dry summer months. Diversion dams are created to move a body of water to another location. They do this by typically elevating a body of water to allow that water to move and change direction. Common uses for this type of dam are to supply irrigation canals or put water into a storage reservoir for industrial or public use. A detention dam is the last type of dam classified by a general purpose. Detention dams minimize the impact of flooding by slowing or stooping the flow rate to a particular channel. They can also be used to recharge the subsurface groundwater system. Debris dams, a type of detention dam, are used to trap sediment and debris carried by floods.

2C Early Uses

More than eight thousand years ago, the Sumerians built an irrigation-based civilization between the Tigris and Euphrates Rivers. This shows that man has need and has found ways to get the water he needs to survive. The Mediterranean, the Middle East, Central America and China all had low dams by the first contrary B.C. They had limited technology that kept their dams down. This was until the fifth century, when a thirty-four meter high dam was constructed in Sri Lanka, making it the world’s highest dam. That record would stand for the next millennium. (http://www.ehso.com/ehshome/energydams.htm#03Civilization 2009)

Hydroelectricity and the idea of producing electricity by water came into America in 1882. H.F. Rogers was a paper manufacturer with a problem, he need to supply light to his two paper mills and a house. The development of the electric generator, improvements in the hydraulic turbine, and a growing demand for electricity all pushed Rogers to produce the first commercial hydroelectric power plant, supplied with water from the Fox River in Wisconsin. He created a 12.5 kilowatt generator becoming the first person to successfully engineer a hydroelectric power plant.

2D Modern Dams

Dams can come in a variety of shapes and sizes for different uses in the world. The International Commission on Large Dams (ICOLD) says a large dam is over fifteen meters high, but their definition also includes dams five to fifteen meters high that hold over three million cubic meters of water. There are about 40,000 large dams and 800,000 smaller dams hat have been constructed. Half of the world’s dams that exceed fifteen meters in height are located in China. In total, all of the world’s dams are expected to hold around 6,000 cubic kilometers of water. Turkey, China, Iran, China, and Japan account for sixty-seven percent of the worldwide dams built since 2003. $2 trillion was been spend on the construction of dams within the twentieth century alone, with around 1,600 large dams built annually. Sixty percent of the 227 largest rivers in the world have some type of construction done, from canals, dams, and diversions. Nineteen percent of the globe’s electricity comes from hydroelectricity. One-third of the countries in the world rely on hydroelectricity for more that fifty percent of their total electricity.

(http://www.panda.org/what_we_do/footprint/water/dams_initiative/quick_facts/)

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Some dams are famous for pictures or their location. The Hoover Dam, on the border of Arizona and Nevada, has been a necessary resource for the growth of the American Southwest. Lake Mead is the reservoir created by the Colorado River, the river the Hoover Dam is holding back. Of the thirty-five billion cubic meters of water held back, 15,000 cubic meters of water is released from the dam every second. The dams’ seventeen generators create four billion kilowatt-hours of electricity each year. This electricity serves over 1.3 million people in the surrounding area.

The Three Gorges Dam, the largest dam in the world, is located in China. The 1.3 mile across, 610 feet tall structure holds water from the Yangtze River valley in a reservoir that extends 350 miles upstream. Although the dam was completed until 2006, the hydroelectrically facility was not completed until 2009. This facility has the capacity to produce 18,200 megawatts of electricity, equal to fifteen nuclear power plants. The Three Gorges Dam has had many catastrophic floods in the last 2,000 years. In 1954, a flood was reported to have killed 30,000 people. More recently, in 1998, 4,000 people were killed and over one million left homeless when a flood occurred. That same flood caused $24 billion in economic losses.

3 Advantages

Dams can provide a variety of uses for the everyday use of society. They provide flood control by slowing the amount of water entering an area. This excess water can also be transferred to nearby areas for irrigation use. In a dam’s reservoir, wildlife and fish populations can flourish, providing shelter and food year-round. Human’s can also benefit from the creation of a dam. The reservoir can provide a place to have outdoor activities, such as hunting, fishing, and even picnicking. Once treated, the stored water can be used by the public for drinking, or for industrial use.

4A Emissions/ Air Pollution

Power plants running on fossil fuels can sometimes create less carbon dioxide and methane than hydroelectric dams. These amounts vary from dam to dam, but some dams create a significant amount of the greenhouse gases. In one study, scientists studying the emissions of the Curuá-Una dam in Pará, Brazil, estimate that the amount of greenhouse gas emissions were three-and-a-half times greater than if that same electricity was created from oil. Scientists think that because the trees and plants that were in the reservoir when it initially flooded had died and rotted. The plant matter then settled and started to decompose on the bottom of the reservoir without any oxygen. This caused a buildup of methane, which was released into the atmosphere when water passed through the dam’s turbines. Even though methane is twenty-one times stronger than carbon dioxide with its effect on global warming, it goes unchecked because scientists cannot agree on how significant methane really is.

4B Environmental Damage

The magnitude of the destruction a dam can cause is often correlated with its size. Before dams are built, rivers and the waters flow rates vary in response to weather conditions. But, once a dam is constructed the rate at which the water below the dam flows is restricted. Dams release water constantly, but usually more during times of need, instead of being dictated by nature. Also, sediment that is carried by the incoming water settles to the bottom of the reservoir. This increases the erosive potential of the outgoing water. The water can affect shorelines and the biological productivity of coastal areas all because of sediment deprivation.

People use dams and reservoirs for many outdoor activities. People can enjoy swimming, boating, diving fishing, and water skiing. This is one viewpoint that causes conflict with other environmentalists who want the natural river system restored. In the Colorado River, where the 2,300 kilometers of water would flow freely and create a rich delta in Mexico, now has ten dams in it and the water can be recycled as many as eighteen times. This means the nutrition is not getting to where it needs to be and the environment is suffering. The delta is now dry except for years when there is exceptional rainfall. Because the environment changed, native species may not be able to adapt to their new surroundings. As a result, nonnative vegetation, including trees and small shrubs from Eurasia, has invaded the banks of the river.

Fish migration routes are big concerns when building dams. Huge declines in anadromous fish, such as salmon, steelhead, shad, and sturgeon, have been caused by the dams built. Dams, along with over population and fishing, have caused the shad and sturgeon to virtually disappear from the U.S. Atlantic coast, and salmon from many rivers in Europe and the American West and Northeast. In the Chesapeake Bay watershed, fish must be trucked to their spawning grounds. $50 million had been spend by the public and utilities over a twenty year time period on fish ladders and passages on the Susquehanna River, a spawning ground for fish coming from the Chesapeake Bay. 20% of the world’s 10,000 freshwater fish have become extinct, threatened, or endangered in recent decades.

Dams not only effect the fish and wildlife, but the overall health of the river and its water. They can alter the riverbed, downstream floodplains, and even coastal deltas. This can ultimately lead to lower groundwater tables, an accumulation of toxic materials, and even increase flood risks. It is estimated that wetland areas have see a decrease of water by fifty percent as a result of dams.

4C How Are Humans Effected?

Humans are affected in many negative ways. Approximately forty to eighty million people have been displaced from the construction of dams worldwide. Yet the migration, compensation, and resettlement given are often not enough. This can cause social disruption and higher population densities in resettlement areas. Poor hygiene and related diseases are common in these communities. People may also not know how to make a living. With the natural ecosystem disrupted the livelihoods of millions of people downstream who depend on wetlands, fisheries, and the regular sediment deposits may be in jeopardy.

One prime example of human life being disrupted is the Three Gorges Dam in China. This dam has submerged thirteen cities, 140 towns, and 1,350 villages. This adds up to 1.3 million people displaced. Some people complained that the housing they received as settlement is so expensive that they cannot pay the rent. Some have even taken from their saving, because only forty-five of the 181 building went to higher ground. Since these buildings did not move, over 20,000 people lose their jobs. By the year 2020, it is estimated that another 530,000 people will have to be relocated because 178 kilometers of the riverbank is expected to collapse. (http://www.internationalrivers.org/files/3Gorges_FINAL.pdf 2009)

4D Water Quality