Dams are structures built across rivers for flood control, navigation, water supply, energy production, and recreation. They may have locks, spillways, or power plants. The Tennessee Valley Authority system is an example of a dam that serves all functions. Dams aid in navigation and flood control with locks and spillways. They generate hydroelectric power and provide constant water levels for recreation and water supply.
Dams are one of mankind’s oldest innovations. People may have borrowed the idea from beavers, but human ingenuity has taken dam building to incredible heights. These structures perform many functions: flood control, navigation, water supply, energy production, and even recreation.
Essentially, dams are buildings, usually constructed of concrete, across a river to support the water on one side. Depending on its purpose, it may have locks and a series of gates, called spillways, or it may have just a power plant and turbines. A good example of those that serve all of the above functions are those in the Tennessee Valley Authority system in the southeastern United States. Many of the TVA dams have become vital parts of the river’s ecosystem.
One hundred years ago, the Tennessee River was wild and narrow, running its 600 miles (about 965 km) from East Tennessee, down through northern Alabama, and then turning north, back into West Tennessee, before emptying into the Ohio River in Paducah, Kentucky. The river overflowed each spring, and treacherous shoals in northwest Alabama made navigation dangerous. With the advent of the Tennessee Valley Authority and the building of dams on the river, Tennessee became one of the largest shipping lanes in the country.
Dams that aid in navigation have locks and spillways, which also aid in flood control. A lock is a gated chamber built into the side of a structure. Using gravity, the block can be filled by the water above the dam and emptied into the water below. The boats can then navigate through the locks and continue their journey.
Spillways are gates built into dams. They open and close, letting the water pass, so as to lower the level of the lake above the structure. This aids in navigation because it helps maintain a constant water depth in the main channel of the river. It also helps with flood control, as too much water from one part of the river can be moved to other parts of the river that are not at risk of flooding.
Power generation is another primary purpose of dams. Water flows through turbines, which drive generators to produce energy. The kinetic energy required to spin the turbines comes from the force of the water falling into the turbines and turning their blades to power the generators. Hydroelectric power is much cheaper and more environmentally friendly than many other generation methods.
Recreation on a river also benefits from these facilities. Again, because they keep the water level constant, boaters and anglers can count on safe water levels for their activities. The environment can also benefit, as lake levels can be lowered in winter, for example, exposing mudflats and other soils that help support the overwintering of waterfowl in the area. Dams also help keep water supplies constant, which is crucial in times of drought.
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