Water, a substance almost as old as the earth itself, covers about three quarters of the planet's surface. It is a very simple molecule, composed of two hydrogen atoms and one oxygen atom, but vital to life on the planet. Water is found in every cell of every plant and animal in the world, and life could not exist without it.
Water moves through the earth's natural systems in what is called the water cycle. The same water molecule may be in a river one day, the sky the next day, on the tip of a glacier the following day, and eventually released back into the atmosphere when the glacier's tip melts. The water molecule itself never changes; it simply changes its location.
As with sunlight, humans have benefited from the energy made available by the presence and movement of water. Waterwheels, turned by the flow of a stream or river pushing against the wooden wheels' paddles, had many uses such as grinding grain into flour, and later, for generating electricity. Dams were also used as early as 1660 in Raj Putana, India, where a marble structure was built to divert water for irrigation and for drinking. Once the principles of electricity became widely known, dams were built to generate electricity. Today, dams are the main tool used to produce hydropower, although water power is still used to turn some waterwheels, grind grain, and pump water. Hydropower produces many benefits, from low-cost electricity to recreational areas, but the social and environmental impacts are equally substantial, making this a controversial source of alternative energy.
Harnessing the Water Cycle
That a water molecule changes its location during the water cycle process is quite important to the production of hydropower. Many water molecules that fall onto mountain glaciers or into mountain streams eventually find a path down the mountain and to the ocean. Humans harness the energy of the moving water by constructing dams along the rivers that carry this water. Using the power of water flow to generate electricity is referred to as hydroelectricity.
A dam, also called a hydroelectric power plant, is basically a large concrete structure that blocks the flow of a river. The base of a dam is quite thick and must be set
into the bottom of the river. The top of a dam is not as thick and must rise far above the surface of the water. A dam constructed in this manner creates a reservoir of water behind it that looks like a large lake.
To be able to produce electricity, the water from the reservoir must travel through the dam. Power plant operators use a sluice gate, or a controllable opening in the dam, to allow a regulated amount of water to flow through the dam. Because of the pressure from the backed up water in the reservoir, the water entering the sluice gate moves very fast. As the water travels through the dam it flows past turbines which are connected to a generator. Similar to the wind-powered generators, water-powered generators have a large pole inside with metal wires wrapped around it. On the inside walls of
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the generator there are magnets and as the turbine poles spin, the magnets also whirl about the metal wires and draw electrons from them. These electrons are sent down other wires as electricity.
The amount of hydroelectricity a dam can produce is related to the amount of water available to send through the dam and the rate at which the water flows. The larger the amount of water in the reservoir and the faster that it flows through the dam, the more electricity the dam can produce.
Hydroelectricity accounts for about 10 percent of the electricity produced in the United States. Much of this hydroelectricity is produced at about three hundred different dams, most of which are located in the western United States. The largest of these dams is the Grand Coulee Dam in Washington State. This dam produces about 6,465,000 kilowatts, enough power to continuously satisfy the energy needs of about 250,000 homes.
Other countries in the world rely on hydroelectricity even more than the United States. It is estimated that seven out of ten Canadian homes are powered by hydroelectricity. Hydropower provides Norway with 95 percent of its electrical power and Switzerland with 74 percent. These countries have developed almost every available site on their waterways for producing hydroelectricity.
The largest dam built to date is the Itaipú along the Paraná River in South America. This dam is a joint venture between the countries of Brazil and Paraguay. The sheer amount of building materials and effort that went into the construction of this dam is enormous. The steel and iron used to build this dam would have made 380 Eiffel Towers. According to the American Society of Civil Engineers, the Itaipú Dam workers "reenacted the labor of Hercules; they shifted the course of the seventh largest river in the world and removed more than 50 million tons of earth and rock. The true marvel of Itaipú, though, is its powerhouse . . . a single building that [continuously] puts out 12,600 megawatts—enough to power most of California."21
China is currently constructing a dam even larger than the Itaipú Dam. The Three Gorges Dam on the Yangtze River in China, expected to be completed by 2009, will produce enough electricity to power over 6 million homes, which is about three times that of the South American dam.
Hydroelectricity accounts for 80 percent of the renewable energy used in the United States. It is naturally replenished as water travels through the water cycle and provides rivers with water on a continuous basis—both day and night and throughout the seasons. There is never a time when water is not flowing because there is never a full interruption of the water cycle.
Hydroelectricity is also a nonpolluting source of electricity. There are no emissions released by the burning of fuels. The National Hydropower Association estimates that using hydropower instead of burning fossil fuels to create electricity reduces the amount of carbon dioxide released into the atmosphere by about 77 million metric tons. This amount is equivalent to the amount of exhaust from 62.2 million cars being driven for a year, which is about half the cars in the United States.
Hydropower is considered a nonpolluting source of energy for other reasons. Hydropower does not require steam to be released into the atmosphere like several other forms of energy production. Steam can alter weather patterns and requires large quantities of water from the surrounding environment. There are also no chemicals required in the production of hydroelectricity that would have to be disposed of in the environment. Last, since most dams tend to be located in rather remote areas, there is no noise pollution to contend with.
The cost of building a hydroelectric power plant varies widely because each one is built to suit its location. Once such a plant is built, however, the cost to maintain and operate it is fairly minimal in comparison to the income a dam provides the power company. Rarely does a dam need to be shut down for maintenance and even more rarely does a dam break. The life expectancy of any given dam tends to be two to ten times that of a coal or nuclear power plant, which can last up to fifty years. The cost of producing one kilowatt of hydroelectricity is about four cents. This is comparable to the cost of generating power by burning fossil fuels. For many utility companies, the construction of a dam is a wise financial decision in this regard.
The Benefits of Reservoirs
The basic structure of a dam also allows people to benefit beyond the production of electricity. The reservoir, or lake, that builds up behind the dam serves to provide a continual flow of water. It also makes larger amounts of water available to farmers to use downriver during the summer growing season. Under natural conditions, this water would travel from the glaciers on mountaintops to the ocean during the spring runoff, and farmers would have little water to irrigate with. Since the water is reserved for later, it is available for irrigating fields in the spring and early summer.
Many homes in the United States not only receive their electric power from hydroelectric plants but also get their drinking water from the reservoir. For this reason, water treatment plants are often built near a reservoir. The water treatment plants clean the water of harmful bacteria and sediments so that people may use the water in their homes.
The reservoirs behind dams provide recreational opportunities such as boating, water skiing, and fishing. People also like to hike and camp in the natural areas surrounding the reservoirs, or spend time watching the wildlife that is attracted to the water.
Many hydroelectric dams capitalize on this aspect of their power plants. Duke Power, a company that operates thirty-one hydro projects in North and South Carolina, leases much of the land around their hydroelectric plants to state agencies. These agencies then provide the public with recreational opportunities, such as swimming, boating, hiking, and fishing. In addition, Duke Power has designed and built the Duke Environmental Center, located on the banks of one of their reservoirs, allowing scientists to monitor the overall health of the reservoir waters. The center also serves to educate the public about the benefits of hydropower and its impact on wildlife.
The Social Impacts
Although the water cycle itself is not greatly impacted in the way it is presently being used to produce power, there are many social and ecological impacts. Hydroelectricity requires water to be dammed in a reservoir. The reservoirs behind a dam are often massive. The Glen Canyon Dam, located on the border of Utah and Arizona, virtually drowned the canyon. This meant that all of the people living in that area of about 266 square miles had to be relocated.
It is estimated that when the Three Gorges Dam is completed in China, about 1.9 million people will have to be relocated. This is similar to moving all of the people out of a large city. While some new industries may be created along the Three Gorges Dam, providing employment opportunities for displaced farmers, the transition will be difficult for these people. The end result is that many lives are interrupted and forced in new directions.
After the people are moved from a reservoir site, there are often other social impacts. Historical buildings are sometimes submerged and towns that were once vibrant and bustling become silenced beneath the waters of a reservoir. Reservoir waters can decimate lands and ritual sites that are sacred to Native Americans. For example, in 1942 the Grand Coulee Dam on the Columbia River took away one of the largest fishing sites in the western United States at Kettle Falls, Washington. Before that time, Native Americans, and later white settlers, came from as far as Oregon, Idaho, Montana, and Canada to participate in the annual salmon harvest at the falls, called by the Native Americans "Shwan-ate-kee," meaning "deep-sounding waters." The harvest provided not only food for the winter but served as a time for social and ceremonial interactions and trading. Once a reservoir is established, there is no going back to re-create the history of the towns and areas hidden beneath its waters.
When reservoirs are created, they also alter the natural flow of a river. Water that once ran cold and clear down a mountain becomes a large lake that is heated by the sun and often becomes murky from mountain runoff. This ecological change in the water can have unforeseen consequences.
The Aswan Dam in Egypt provides a good example of these consequences. The reservoir there became so warm that a certain kind of parasitic worm began to flourish. Because the reservoir not only served to power many cities in Egypt but was also a source of drinking water, the number of cases of people getting sick and dying from ingesting the parasitic worm went up by about 75 percent. The Aswan Dam is now monitored closely for water temperatures, but people are still wary of drinking from its reservoir.
Another ecological impact of hydroelectricity involves the movement of sediments down the river. Sediments are small particles of soil that are rich in minerals and nutrients. It is made up of decaying plants and animals as well as worn-away bits of rock. The health of animals that live in and along the river depends upon sediment and its minerals.
Usually sediment flows from a mountaintop to the ocean down the course of a river. When a river is dammed, however, the reservoir that is created can act as a large trap for sediment, stopping its downstream progress. Sediment does not go through the dam, and the plants and animals in and along the river downstream from the dam do not get to benefit from the nutrients it provides. At the same time, the animals that live in and along the reservoir get too much of the built-up sediment. It can clog the gills and breathing ways of the aquatic life. The sediment can also slowly poison the animals and plants living in the water. When there is too much sediment in the water, aquatic animals and plants become sick and often die.
The restricted flow of water that a dam imposes also affects wildlife in other ways. Fish, such as salmon, are hatched in riverbeds high in the mountains. These salmon grow into smolts that travel down the river and out to the sea. After several years they return to their original hatch site to spawn and lay their eggs. Dams affect these migrating fish as they head both downstream and upstream.
Young smolts coming down a river to the sea face a huge challenge. Many of these smolts must travel through the internal structures of the dam as they make their journey to the sea. Turbines spin them about and sometimes their bodies are crushed. The Northwest Power Planning Council's Independent Science Group conducted studies in which they established that approximately 15 percent of smolts traveling downstream are killed at each dam. Because many rivers have far more than one dam, these deaths greatly impact salmon populations in the long run.
Fish migrating upstream often find it just as difficult to get past the barriers of a dam. These salmon must navigate the huge distance from the river below a dam to the reservoir waters being held back by the dam. In an effort to solve this problem, many hydroelectric power plant owners install fish ladders, which are a series of cascading pools through which the fish can jump, but these are of little help. Fish are often too tired to face the raging waters and make the sometimes ten- to twenty-foot leaps up the fish ladder. After repeated attempts to climb the fish ladder, many of these salmon perish at the base of a dam. They never make it to their hatch site and never spawn.
The Future of Hydropower
Waterwheels have been used through the ages. The earliest known reference is from around 400 b.c. in the writings of Greek poet Antipater, who wrote of the freedom from toil that the waterwheel provides. From the beginning of modern history the United States has used waterwheels and, later, hydroelectric power plants. Americans understand how hydroelectricity is produced far better than any other renewable resource. They feel comfortable with it, and this comfort goes a long way in helping this renewable resource to flourish.
Currently, only about 2 percent of the rivers in America are free-flowing and not dammed in any manner. This number seems very low and worries many people that Americans are taking advantage of a natural system beyond its capacity to produce. There are many environmental groups seeking to protect these last free rivers. The Wild and Scenic Rivers Act of 1968 protects many of these remaining rivers. It aims to give certain scenic rivers the status of National Parks and protect them from being developed for hydroelectricity.
On the other hand, there are over seventy-five thousand dams along American rivers. Approximately three hundred of them produce substantial amounts of hydroelectricity. The vast majority of the rest of the dams provide irrigation water for farmers; however, many utility companies feel these dams could better serve the energy needs of America if they were accessed for producing hydroelectricity.
Still other groups believe the best sites for generating power from water have already been established. This leaves the country with two options. The first option is for hydroelectric plants to find better ways to maximize the power available at current sites. At present, the majority of dams have an 85 percent efficiency rate. This means dams have the capacity to extract 85 percent of the energy from the movement of water and turn it into electricity. This is quite a high efficiency rate, much higher than burning fossil fuels, which has only a 15 percent efficiency rate for combustion engines. However, many scientists believe it will be hard to improve upon the design of modern dams.
The other option is to start importing more hydroelectricity from neighboring countries such as Canada, which is considered an excellent candidate for such a solution. Canada is rich in fast-flowing rivers with many potential hydroelectric sites that have not yet been developed. Its population is much smaller than the United States' and so it has lower energy needs. As a nation, it already relies heavily on hydroelectricity and has many well-established hydroelectric plants. For these reasons, Canada is being carefully considered as a possible source of electricity to satisfy the energy needs of the American market.
Worldwide, the growth of hydroelectricity is impressive. Already, 20 percent of the electricity produced in the world comes from hydroelectricity. As developing countries seek to bring more power to their countries, they are looking at their major rivers to determine if they can possibly develop sites for hydroelectricity. Laos is currently in the process of developing a 680-megawatt dam that would satisfy the energy needs of most of their citizens. It would also allow for greater economic development within the country as electrical energy is brought to local businesses. With projects such as this in development, it is felt hydroelectricity will become the most established form of renewable energy throughout the world in the decades to come.