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Holston River

Holston River

] The Holston River is a major river system of southwestern Virginia and East Tennessee. The three major forks of the Holston (its North, Middle and South Forks) rise in southwestern Virginia and have their confluence near Kingsport, Tennessee. From there the river flows roughly southwestward until it reaches its confluence with the French Broad River just east of downtown Knoxville, Tennessee. This confluence is considered to be the headwaters of the Tennessee River. The Holston River valley is greatly developed for electrical power generation, both with hydroelectric dams and coal-fired steam plants. In its upper reaches some of these plants are controlled by private interests; in the downstream portion they are owned by the United States Government's Tennessee Valley Authority.

East Tennessee

Image:East Tennessee.png

East Tennessee is a name given to approximately the eastern third of the state of Tennessee. Unlike the names given to regions or portions of many of the American states, the term East Tennessee can be precisely defined. It is the portion of the state located within the Eastern Time Zone and four counties in the Central Time Zone, namely Bledsoe, Cumberland, Marion, and Sequatchie Counties. East Tennessee is noted for its mountains, particularly the Great Smoky Mountains portion of the Blue Ridge Mountains, but in fact has many and varied landforms.

Cities

The major cities of East Tennessee are Knoxville and Chattanooga. Other important cities include the "Tri-Cities" of Kingsport, Johnson City, and Bristol, located in the extreme northeasternmost part of the state, an area previously and traditionally referred to as Upper East Tennessee, although today the term Northeast Tennessee is preferred. Bristol

Higher Education

East Tennessee is noted for the presence of many institutions of higher learning, perhaps most notably the Knoxville and Chattanooga campuses of the University of Tennessee and East Tennessee State University in Johnson City.

Industry

Knoxville and Chattanooga also contain major operations of the Tennessee Valley Authority. The U.S. nuclear weapons program was largely developed during World War II at Oak Ridge. Kingsport is the home of Tennessee's largest single industial employer in Eastman Chemical Company, formerly the chemical division of Kodak, and the Aluminum Company of America, now Alcoa, initially attracted to the area by its potential for low-cost hydroelectric development, still maintains a major operation in its namesake town of Alcoa, just south of Knoxville.

Politics

East Tennessee is the only part of the state--and one of the few in the South--which has consistently voted Republican since Reconstruction. The region was the only area of the state that didn't practice slavery on a wide scale. It was the only region to oppose secession before the Civil War, and as a result became an early base for the then-new Republican Party. This allegiance has continued to this day. The state's 1st and 2nd Congressional Districts, based in the Tri-Cities and Knoxville respectively, are considered to be so heavily Republican that Republican nomination is tantamount to a general election victory. When Tennessee seceded from the Union in 1861, the 1st and 2nd Districts' congressmen were the only ones not to resign from the House. Similarly the only Senator from a seceding State who remained in the Senate was Andrew Johnson, by background from Greeneville. The 2nd District has been held by Republicans continuously since 1857; the 1st has been held by Republicans for all but two years since 1861. Democrats do slightly better in the 3rd District, based in Chattanooga, but that district has not supported a Democrat for president since 1956. Despite the regional Republican majority, there are significant Democratic enclaves in Hamilton, Knox and Washington counties—home to Chattanooga, Knoxville and Johnson City respectively, and also home to the three largest colleges in the region (two UT campuses and ETSU).

Geography

Unlike the geographic designations of regions of most U.S. states, the term East Tennessee has legal as well as socioeconomic meaning. East Tennessee, along with Middle Tennessee and West Tennessee, comprises one of the state's three Grand Divisions. According to the Tennessee State Constitution, no more than two of the state Tennessee Supreme Court's five justices can come from any one Grand Division. A similar rule applies to certain other commissions and boards as well, to prevent them from showing a geographic bias. Category:Geography of Tennessee

French Broad River

The French Broad River flows from near Rosman in Transylvania County, North Carolina, into Tennessee. Its confluence with the Holston River at Knoxville, Tennessee is considered to be the headwaters of the Tennessee River. It was originally named for being one of two broad rivers in western North Carolina . The one which flowed into formerly French territory was named the French Broad, and the other which stayed in English territory (the American colonies) was named the English Broad, now just the Broad River. The lower portion of the river is the site of a major hydroelectric dam development of the Tennessee Valley Authority, Douglas Dam, which is one of the larger TVA developments on a Tennessee River tributary stream. Douglas, like many of the older TVA facilites in East Tennessee, was initially developed largely to meet the power demands entailed by World War II, particularly the atomic weapons plant at Oak Ridge. The river begins west of the Eastern Continental Divide, and therefore actually flows northwest through the Appalachian Mountains. The river flows through the city of Asheville, North Carolina, where it picks up the Swannanoa River. Of interest is that the French Broad river is often cited as the 3rd oldest river in the world, only predated by the Nile and the New River.

External links

- [http://www.riverlink.org/ RiverLink] Category:Rivers of North Carolina Category:Rivers of Tennessee Category:Tennessee River

Tennessee River

The Tennessee River is the largest tributary of the Ohio River. It is approximately 650 mi (1,046 km) long, and located in the southeastern United States, in the Tennessee Valley.

Course

The Tennessee River is formed at the confluence of the Holston and French Broad Rivers on the east side of Knoxville, Tennessee, and is the only river on earth that flows in all cardinal directions. From Knoxville, it flows southwest through East Tennessee toward Chattanooga before crossing into Alabama. It loops through north Alabama, creating some of the most beautiful scenary in the country. Eventually the Tennessee forms a small part of the state's border with Mississippi, before returning to Tennessee. At this point, it defines the boundary between Tennessee's other two traditional regions, Middle and West Tennessee. The Tennessee-Tombigbee Waterway, a U.S. Army Corps of Engineers project providing navigation on the Tombigbee River and a link to the Port of Mobile, enters the Tennessee near the Tennessee-Alabama-Mississippi boundary corner. This waterway reduces the navigation distance from Tennessee, north Alabama, and northern Mississippi to the Gulf of Mexico by hundreds of miles. The final part of the Tennessee's run is in Kentucky, where it separates the Jackson Purchase from the rest of the state. It then flows into the Ohio River at Paducah, Kentucky.

Dams

The river has been dammed numerous times, primarily by Tennessee Valley Authority projects. The placement of the TVA's Kentucky Dam on the Tennessee and the Corps' Barkley Dam on the Cumberland River directly led to the creation of Land Between the Lakes. A navigation canal located at Grand Rivers, Kentucky links Kentucky Lake (the reservoir behind Kentucky Dam) and Lake Barkley (the reservoir behind Barkley Dam). The canal allows for a shorter trip for river traffic going from the Tennessee to most of the Ohio River, and for traffic going down the Cumberland River toward the Mississippi.

Popular culture

- Cormac McCarthy's 1979 novel Suttree concerns a man who forsakes his life of privilege to become a fisherman along the Tennessee River in Knoxville in the early 1950s.
- The song "Tennessee River" was recorded by the country music band Alabama in 1980.

Cities and towns along the Tennessee River

- Bridgeport, Alabama
- Chattanooga, Tennessee
- Clifton, Tennessee
- Crump, Tennessee
- Decatur, Alabama
- Florence, Alabama
- Grand Rivers, Kentucky
- Guntersville, Alabama
- Harrison, Tennessee
- Killen, Alabama
- Knoxville, Tennessee
- Lakesite, Tennessee
- Langston, Alabama
- Lenoir City, Tennessee
- Loudon, Tennessee
- New Johnsonville, Tennessee
- Paducah, Kentucky
- Redstone Arsenal, Alabama
- Saltillo, Tennessee
- Savannah, Tennessee
- Sheffield, Alabama
- Signal Mountain, Tennessee
- South Pittsburg, Tennessee
- Triana, Alabama
- Waterloo, Alabama

External links

- [http://reference.allrefer.com/gazetteer/us-categories/tennessee-river.html Tennessee Rivers]
- [http://www.riversofalabama.org/Tennessee/TENNESSEE.htm Map of Tennessee River in Alabama]

Electricity

Electricity is a general term applied to phenomena involving a fundamental property of matter called an electric charge. This article will introduce and explain some of the basic principles of electricity.

Related concepts

being radiated as light as the air of Earth's atmosphere is shifted from gas to plasma and back. ]] In casual usage, the term electricity is applied to several related concepts that are better identified by more precise terms.
- Electric charge: a fundamental conserved property of some subatomic particles, which determines their electromagnetic interactions. Electrically charged matter is influenced by, and produces, electromagnetic fields.
- Electric field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity.
- Electric potential the potential energy per unit charge associated with a static (time-invariant) electric field.
- Electric current: a movement or flow of electrically charged particles.
- Electrical energy: energy made available by the flow of electric charge through a conductor or from the forces between charged particles.
- Electric power: The rate at which electric energy is converted into another form, such as light, heat, or mechanical energy (or converted from another form into electric energy).

History

Ancient

According to Thales of Miletus, writing circa 600 BCE, a form of electricity was known to the Ancient Greeks who found that rubbing fur on various substances, such as amber, would cause a particular attraction between the two. The Greeks noted that the amber buttons could attract light objects such as hair and that if they rubbed the amber for long enough they could even get a spark to jump. The origin of the word "electricity" is from the Greek word ēlektron, a word the ancient Greeks used for both "amber" and "electrum," and derives from an old root, ēlek- = "shine." The same word was used for both amber and electrum, probably because of the pale yellow color of some varieties of electrum (see electrum). An object found in Iraq in 1938, dated to about 250 BCE and called the Baghdad Battery, resembles a galvanic cell and is believed by some to have been used for electroplating. Additionally, some egyptologists associate the ancient goddess Hathor with artificial light (see Hathor temple). But, remaining unproven are the conjectures that these and other similar ancient artifacts had electrical function and that their associated ancient technology contributed to the development of modern electrical knowledge.

Modern

In 1600 the English scientist William Gilbert returned to the subject in De Magnete, and coined the modern Latin word electricus from ηλεκτρον (elektron), the Greek word for "amber", which soon gave rise to the English words electric and electricity. He was followed in 1660 by Otto von Guericke, who is regarded as having invented an early electrostatic generator. Other European pioneers were Robert Boyle, who in 1675 stated that electric attraction and repulsion can act across a vacuum; Stephen Gray, who in 1729 classified materials as conductors and insulators; and C. F. Du Fay, who first identified the two types of electricity that would later be called positive and negative. The Leyden jar, a type of capacitor for electrical energy in large quantities, was invented at Leiden University by Pieter van Musschenbroek in 1745. William Watson, experimenting with the Leyden jar, discovered in 1747 that a discharge of static electricity was equivalent to an electric current. In June, 1752, Benjamin Franklin promoted his investigations of electricity and theories through the famous, though extremely dangerous, experiment of flying a kite during a thunderstorm. Following these experiments he invented a lightning rod and established the link between lightning and electricity. If Franklin did fly a kite in a storm, he did not do it the way it is often described (as it would have been dramatic but fatal). It was either Franklin (more frequently) or Ebenezer Kinnersley of Philadelphia (less frequently) who created the convention of positive and negative electricity. Franklin's observations aided later scientists such as Michael Faraday, Luigi Galvani, Alessandro Volta, André-Marie Ampère, and Georg Simon Ohm whose work provided the basis for modern electrical technology. The work of Faraday, Volta, Ampere, and Ohm is honored by society, in that fundamental units of electrical measurement are named after them. Volta worked with chemicals and discovered that chemical reactions could be used to create positively charged anodes and negatively charged cathodes. When a conductor was attached between these, the difference in the electrical potential (also known as voltage) drives a current between them through the conductor. The potential difference between two points is measured in units of volts in recognition of Volta's work. The invention of the electric telegraph showed that commercial and practical use could be made of electrical phenomena. By the end of the 19th century electrical engineering became a distinct profession, separate from the physicist or inventor. The late 19th and early 20th century produced such giants of electrical engineering as Nikola Tesla, inventor of the polyphase induction motor; Samuel Morse, inventor of the telegraph; Antonio Meucci, an inventor of the telephone; Thomas Edison inventor of the phonograph and a practical incandescent light bulb; George Westinghouse, inventor of the electric locomotive; Charles Steinmetz, theoretician of alternating current; Alexander Graham Bell, another inventor of the telephone and founder of a sucessful telephone business. The rapid advance of electrical technology in the latter 19th and early 20th centuries lead to commercial rivalry such as the so-called War of the Currents), between Edison's direct-current system or Westinghouse's alternating-current method. Often concurrent research in widely scattered locations lead to multiple claims to the invention of a device or system.

Electric charge

Electric charge is a property of certain subatomic particles (e.g., electrons and protons) which interacts with electromagnetic fields and causes attractive and repulsive forces between them. Electric charge gives rise to one of the four fundamental forces of nature, and is a conserved property of matter that can be quantified. In this sense, the phrase "quantity of electricity" is used interchangeably with the phrases "charge of electricity" and "quantity of charge." There are two types of charge: we call one kind of charge positive and the other negative. Through experimentation, we find that like-charged objects repel and opposite-charged objects attract one another. The magnitude of the force of attraction or repulsion is given by Coulomb's law.

Electric field

The concept of electric field was introduced by Michael Faraday. The electrical field force acts between two charges, in the same way that the gravitational field force acts between two masses. However, electric field is a little bit different. Gravitational force depends on mass, whereas electric force depends on the electric charge on both objects. A positive charge exerts away from the object and a negative charge pulls towards the object equally in all directions; thus it is symetric. The most common experience with electric charge in everyday life is that of static cling - when two particular types of materials are rubbed together, they tend to stick together, at least for a while.

Electric potential

The electric potential difference between two points is defined as the work done per unit charge (against electrical forces) in moving a positive point charge slowly between two points. If one of the points is taken to be a reference point with zero potential, then the electric potential at any point can be defined in terms of the work done per unit charge in moving a positive point charge from that reference point to the point at which the potential is to be determined. For isolated charges, the reference point is usually taken to be infinity. The potential is measured in volts. (1 volt = 1 joule/coulomb) The electric potential is analogous to temperature: there is a different temperature at every point in space, and the temperature gradients indicates the direction of heat flows. Similarly, there is an electric potential at every point in space, and its gradient in the the electric field indicates where charges move.

Electric current

The electric charge which occurs naturally within conductors can be forced to flow, while the charges within insulators are locked in place and cannot be moved. Devices that use charge flow principles in materials are called electronic devices. A flow of electric charge is called an electric current. A direct current (DC) is a unidirectional flow; alternating current (AC) is a flow whose time average is zero, but whose energy capability (RMS level) is not zero. With AC the electric current repeatedly changes direction. Electric current is measured in Amperes Ohm's Law is an important relationship describing the behaviour of electric currents: See also: electrical conduction For historical reasons, electric current is said to flow from the most positive part of a circuit to the most negative part. The electric current thus defined is called conventional current. It is now known that, depending on the conditions, an electric current can consist of a flow of charged particles in either direction, or even in both directions at once. The positive-to-negative convention is widely used to simplify this situation. If another definition is used - for example, "electron current" - it should be explicitly stated.

Electrical energy

Electrical energy, is the flow of electrons or ions. When electrons are flowing through a wire or through hundreds of feet of air in the case of lightning it is because they are being forced to do so by an electrical field. A force is exerted on the electrons and they move. Work is done on the charged particles. A force is pushing them through a distance. More properly, they are moving from outer orbitals of one atom to another, being pushed by the electromotive force. While the electrons are in motion they contain kinetic energy. Consquently, atomic level electricity is a form of kinetic energy.

Electric power

Electric power is the capacity of the circuit for performing work in a particular amount of time. When a charge moves in a conductor, work is done by that charge. Devices can be made which convert this work into heat (Electric arc furnaces), light (light bulbs and Fluorescent lamps), or motion, i.e. kinetic energy (electric motors). The unit for all forms of power is the watt (symbol: W). In practice, however, this is generally reserved for the real power component. Apparent power is conventionally expressed in volt-amperes (VA) since it is the simple multiple of rms voltage and current. The unit for reactive power is given the special name "VAR", which stands for volt-amperes-reactive.

SI electricity units

External links

- [http://amasci.com/miscon/whatis.html What is electricity?]
- [http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=electricity Merriam-Webster: Electricity]
- [http://www.bibliomania.com/2/9/72/119/21387/1.html Tyndall: Faraday as Discovery: Identity of Electricities]
- [http://www.eia.doe.gov/fuelelectric.html US Energy Department Statistics]
- [http://www.mouthshut.com/readreview/38842-1.html How to save on your electricity bills]
- [http://users.pandora.be/worldstandards/electricity.htm Electricity around the world]
- [http://www.tufts.edu/as/wright_center/fellows/bob_morse_04/ A Comprehensive Collection of Franklin’s Electrical Works: The Electrical Writings of Benjamin Franklin], Created and Collected by Robert A. Morse (2004)
- [http://www.telesensoryview.com/steverosecom/Articles/UnderstandingBasicElectri.html Understanding Electricity and some Electronics in 10 minutes](Steve Rose, Maui)
- [http://amasci.com/miscon/eleca.html Electricity Misconceptions]
- ko:전기 ja:電気 simple:Electricity

Dam

:This article discusses structures for water impoundment. For other meanings, see dam (disambiguation). dam (disambiguation), Australia, was engineered to withstand a once-in-5000-years flood event]] A dam is a barrier across flowing water that obstructs, directs or retards the flow, often creating a reservoir, lake or impoundment. Most dams have a section called a spillway, over which or through which it is intended that water will flow either intermittently or continuously.

Types of dams

lake]] Dams may be classified according to structure, intended purpose or height. Based on structure and material used, dams are classified as timber dams, embankment dams or masonry dams, with several subtypes. Intended purposes include providing water for irrigation or town or city water supply, improving navigation, generating hydroelectric power, creating recreation areas or habitat for fish and wildlife, flood control and containing effluent from industrial sites such as mines or factories. Few dams serve all of these purposes but some multi-purpose dams serve more than one. According to height, a large dam is higher than 15 metres and a major dam is over 150 metres in height. Alternatively, a low dam is less than 30 m high; a medium-height dam is between 30 and 100 m high, and a high dam is over 100 m high. What is sometimes called a saddle dam is actually a dike, a wall built at the edge of a lake to protect nearby land from flooding. This is similar to a levee, which is a wall built along a river or stream to protect adjacent land from flooding. An overflow dam is designed to be overtopped. A weir is a type of small overflow dam that can be used for flow measurement. A check dam is a small dam designed to reduce flow velocity and control soil erosion. A dry dam is a dam designed to control flooding. It normally holds back no water and allows the channel to flow freely, except during periods of intense flow that would otherwise cause flooding downstream.

Diversionary dams

A diversionary dam is a dam that does not completely block a river. Some of the flow is siphoned off into a separate lake, in front of which is the dam.

Timber dams

The timber dam is rarely used by humans because of its short lifespan and the limitation in height to which it can be built. The locations where timber dams are most economical to build are those where timber is plentiful, cement is costly and difficult to transport, and only a submerged diversion dam is required. Timber dams used to be more numerous, but most have been replaced with concrete, especially those in industrialized countries. A few timber dams are still in use, however. Timber is the basic material used by beavers, often with the addition of mud or stones.

Embankment dams

Embankment dams are made from fill material not joined by mortar, and have two main types, rockfill and earth dams. Embankment dams rely on their weight to hold back water, like the gravity dams made from concrete.

Rock-fill dams

beaver Rock-fill dams are embankments of loose rock with either a watertight upstream face of concrete slabs or timber or a watertight core. Where suitable rock is at hand, a minimum of transportation of materials can be realized with this type of dam. Like the earth embankment, rock-fill dams usually resist damage from earthquakes quite well. However, water infiltration may cause liquefaction at embankment dams during an earthquake. This problem can be eliminated by keeping the susceptible material dry. New Melones Dam is a rock-fill dam.

Earth dams

New Melones Dam Earth dams, also called earthen and earth-fill dams, are constructed as a simple homogeneous embankment of well-compacted earth, sometimes with a watertight concrete or clay core or upstream face, or sometimes with a hydraulic fill to produce a watertight core. A type of temporary earth dam occasionally used in high latitudes is the frozen-core dam, in which a coolant is circulated through pipes inside the dam to maintain a watertight region of permafrost within it. Oroville Dam is an example of an earth dam, and is the tallest dam in the United States.

Masonry dams

Masonry dams are of either the gravity or the arch type.

Gravity dams

arch.]] In a gravity dam, stability is secured by making it of such a size and shape that it will resist overturning, sliding and crushing at the toe. The dam will not overturn provided that the moment around the turning point, caused by the water pressure is smaller than the moment caused by the weight of the dam. This is the case if the resultant force of water pressure and weight falls within the base of the dam. However, in order to prevent tensile stress at the upstream face and excessive compressive stress at the downstream face, the dam cross section is usually designed so that the resultant falls within the middle third at all elevations of the cross section (the core). For this type of dam, good impervious foundations are essential. When situated on a suitable site, a gravity dam inspires more confidence in the layman than any other type; it has mass that lends an atmosphere of permanence, stability, and safety. When built on a carefully studied foundation with stresses calculated from completely evaluated loads, the gravity dam probably represents the best developed example of the art of dam building. This is significant because the fear of flood is a strong motivator in many regions, and has resulted in gravity dams being built in some instances where an arch dam would have been more economical. Gravity dams are classified as "solid" or "hollow." The solid form is the more widely used of the two, though the hollow dam is frequently more economical to construct. Gravity dams can also be classified as "overflow" (spillway) and "non-overflow." Grand Coulee Dam is a solid gravity dam and Itaipu Dam is a hollow gravity dam.

Arch dams

Itaipu Dam] In the arch dam, stability is obtained by a combination of arch and gravity action. If the upstream face is vertical the entire weight of the dam must be carried to the foundation by gravity, while the distribution of the normal hydrostatic pressure between vertical cantilever and arch action will depend upon the stiffness of the dam in a vertical and horizontal direction. When the upstream face is sloped the distribution is more complicated. The normal component of the weight of the arch ring may be taken by the arch action, while the normal hydrostatic pressure will be distributed as described above. For this type of dam, firm reliable supports at the abutments (either buttress or canyon side wall) are more important. The most desirable place for an arch dam is a narrow canyon with steep side walls composed of sound rock. The safety of an arch dam is dependent on the strength of the side wall abutments, hence not only should the arch be well seated on the side walls but also the character of the rock should be carefully inspected. Two types of single-arch dams are in use, namely the constant-angle and the constant-radius dam. The constant-radius type employs the same face radius at all elevations of the dam, which means that as the channel grows narrower towards the bottom of the dam the central angle subtended by the face of the dam becomes smaller. Jones Falls Dam, in Canada, is a constant radius dam. In a constant-angle dam, also known as a variable radius dam, this subtended angle is kept a constant and the variation in distance between the abutments at various levels are taken care of by varying the radii. Constant-radius dams are much less common than constant-angle dams. Parker Dam is a constant-angle arch dam. The multiple-arch dam consists of a number of single-arch dams with concrete buttresses as the supporting abutments. The multiple-arch dam does not require as many buttresses as the hollow gravity type, but requires good rock foundation because the buttress loads are heavy. See Geotechnical engineering.

Cofferdams

Geotechnical engineering. ]] A cofferdam is a sometimes temporary barrier constructed to exclude water from an area that is normally submerged. Made commonly of wood, concrete or steel sheet piling, cofferdams are used to allow construction on the foundation of permanent dams, bridges, and similar structures. When the project is completed, the cofferdam may be demolished. See also causeway and retaining wall.

Spillways

retaining wall soon after first fill]] A spillway is a section of a dam designed to pass water from the upstream side of a dam to the downstream side. Many spillways have floodgates designed to control the flow through the spillway. A service spillway or primary spillway passes normal flow. An auxiliary spillway releases flow in excess of the capacity of the service spillway. An emergency spillway is designed for extreme conditions, such as a serious malfunction of the service spillway. A fuse-plug spillway is a low embankment designed to be overtopped and washed away in the event of a large flood. Any cavitation or turbulence of the water flowing over the spillway slowly eats the dam. To minimize that erosion (especially with maximum water elevation at the crest), the downstream face of the spillway is ordinarily made an ogee curve. It was the inadequate design of the spillway that caused the overtopping of a dam that caused the infamous Johnstown Flood.

Other considerations

The best place for building a dam is a narrow part of a deep river valley; the valley sides can then act as natural walls. The primary function of the dam's structure is to fill the gap in the natural reservoir line left by the stream channel. The sites are usually those where the gap becomes a minimum for the required storage capacity. The most economical arrangement is often a composite structure such as a masonry dam flanked by earth embankments. The current use of the land to be flooded should be dispensable. Significant other engineering considerations when building a dam include
- permeability of the surrounding rock or soil
- earthquake faults
- peak flood flows
- reservoir silting
- environmental impacts on river fisheries, forests and wildlife (see fish ladder)
- impacts on human habitations
- compensation for land being flooded as well as population resettlement
- removal of toxic materials and buildings from the proposed reservoir area fish ladder] Dam failures are generally catastrophic if the structure is breached or significantly damaged. Routine monitoring of seepage from drains in, and around, larger dams is necessary to anticipate any problems and permit remedial action to be taken before structural failure occurs. Most dams incorporate mechanisms to permit the reservoir to be lowered or even drained in the event of such problems. Another solution can be rock grouting - pressure pumping portland cement slurry into weak fractured rock.

Environmental impacts

([http://www.canadiangeographic.ca/magazine/ND05/indepth/environment.asp Source]: Canadian Geographic) More than half of the world’s large rivers have been dammed, regulating and flooding approximately 400,000 square kilometres of land worldwide. These diversions have an effect on diverse ecosystems and habitats around the globe, replacing them with uniform structures and reservoirs and ultimately changing the way otherwise balanced, stable ecosystems function.

Stream flow

The life of a river is closely tied to its stream flow, which constantly fluctuates. Damming a river and altering its flow pattern generates a number of physical and biological impacts. The disruption of a river’s flow obstructs its’ natural current and affects the water’s habitat. One of the largest impacts a lack of current has on a river is the sediment flow, which is normally carried down the river by the current. When trapped by a dam, the sediment is held in the reservoir and settles to the bottom while clear water containing very little sediment is released down the river. Over time, the easily erodible material from the riverbed is carried away with no sediment being deposited to replace it. This leaves a rocky stream bed, resulting in a poorer habitat for aquatic fauna.

Barrier to migration

The most visible and obvious effect of dams is that they fragment rivers and make migration difficult for fish and other aquatic life. Species, such as salmon and eels that migrate to spawn, may not make it to their destination or may suffer injury or death while travelling through turbines or over spillways. Fish that do make it through are often disoriented and become more susceptible to predators. Some dams are equipped with fish passage structures, or fish ladders, to attempt to accommodate the migration of a river’s aquatic life. Questions have been raised as to whether fish ladders are actually too stressful for an adult fish and that its’ chances for successful spawning is reduced.

Water quality impacts

When water is held in the reservoir of a dam, the quality of water is affected in several ways, the extent of which depending on how long it is held there. The initial creation of a reservoir on a floodplain submerges the existing vegetation and soil, causing much of the organic material to decompose over time which can deplete oxygen from the water supply. The establishment of a deep reservoir will almost always lead to thermal stratification during summer months. Water warmed by the sun forms an upper warm layer called the Epilimnion which is well oxygenated. The bulk of the water is held in the lower, cold unmixed layer, the Hypolimnion. This cold water receives relatively little light, has no contact with the air and is often depleted in oxygen. The boundary between these two layers is the thermocline. Where draw-off towers or sluices in dams release water from the Hypolimnion into the downstream river, the water discharged may be unusually cold and may be low in oxygen and high in metals such as Manganese. All these propoerties can have seriously adverse effects on the normal biota of a river. Mercury, which can exist at very low levels in the soil in inorganic forms in the soil, may be transformed by bacteria into methyl mercury once the soil is flooded if the benthic conditions become substantially anoxic. Methyl mercury is a cumulative toxin to veterbrate species and may enter the food chain from consumption of reservoir fish. Such circumstances are theoretically possible but very rare in practice.

Examples of dams

- Three Gorges Dam, China
- Itaipu Dam, Brazil/Paraguay
- Aswan Dam, Egypt
- Grande Dixence Dam, Switzerland
- Benmore Dam, New Zealand
- Glen Canyon Dam, United States
- Grand Coulee Dam, United States
- Hoover Dam, United States
- Hume Dam, Australia
- Kariba Dam, Zambia/Zimbabwe
- Vishvesvaraya Dam, India
- Mactaquac Dam, Canada
- Inga Dam, Democratic Republic of Congo
- Lockport Powerhouse, United States
- Lake Pedder - Lake Gordon, Australia
- Snowy Mountains Scheme, Australia

Failed dams

- South Fork Dam - 1889
- St. Francis Dam - 1928
- Malpasset - 1959
- Vajont Dam - 1961
- Baldwin Hills Dam - 1963
- Buffalo Creek Flood - 1972
- Banqiao and Shimantan Dams - 1975
- Teton Dam - 1976
- Kelly Barnes Dam - 1977
- Lawn Lake Dam - 1982
- Opuha Dam - 1997
- Camará Dam - 2004
- Shakidor Dam - 2005

External links

- [http://www.icold-cigb.org/ International Commission On Large Dams (ICOLD)]
- [http://www.structurae.de/en/structures/stype/s3.cfm Structurae: Dams and Retaining Structures]
- [http://www.iucn.org/themes/ceesp/Publications/SL/CT/Ballad%20-%20Part%202.pdf The Ballad of Ecological Awareness] (pdf)
- [http://www.usbr.gov/pmts/hydraulics_lab/pubs/manuals/SmallDams.pdf "Design of Small Dams", US Bureau of Reclamation, 65MB pdf]
- [http://http://www.canadiangeographic.ca/magazine/ND05/indepth/environment.asp "Dam science"] Canadian Geographic
- Category:Buildings and structures Category:Engineering Category:Civil engineering ko:댐 ja:ダム th:เขื่อน

Coal

Coal is a fossil fuel extracted from the ground by deep mining, coal mining (open-pit mining or strip mining). It is a readily combustible black or brownish-black sedimentary rock. It is composed primarily of carbon and hydrocarbons, along with assorted other elements, including sulfur. Often associated with the Industrial Revolution, coal remains an enormously important fuel and is the most common source of electricity world-wide. In the United States, for example, the burning of coal generates over half the electricity consumed by the population. United States

Etymology and folklore

Coal is thought ultimately to derive its name from the Old English col but this actually meant charcoal at the time; coal was not mined prior to the late Middle Ages; i.e. after ca. 1000 AD. Mineral coal was referred to as sea-coal, either because it was found on beaches occasionally having fallen from the exposed coal seams above, or because it was easier to transport by sea rather than on the very poor road system (in London, England there is still a sea coal road/lane where the coal merchants conducted their business). It is associated with the astrological sign Capricorn. It is carried by thieves to protect them from detection and to help them to escape when pursued. It is an element of a popular ritual associated with New Year's Eve. To dream of burning coals is a symbol of disappointment, trouble, affliction and loss, unless they are burning brightly, when the symbol gives promise of uplifting and advancement. Santa Claus is said to leave a lump of coal instead of Christmas presents in the stockings of naughty children.

Composition and creation

Carbonacous material forms more than 50 percent by weight and more than 70 percent by volume of coal (this includes inherent moisture). Coal is formed from plant remains that have been compacted, hardened, chemically altered, and metamorphosed by heat and pressure over geologic time. Much coal was formed from ancient plants that grew in swamp ecosystems. When such plants died, their biomass was deposited in anaerobic, aquatic environments where low oxygen levels prevented their decay and oxidation (rotting and release of carbon dioxide). Successive generations of this type of plant growth and death formed thick deposits of unoxidized organic matter that were subsequently covered by sediments and compacted into carbonaceous deposits such as peat or bituminous or anthracite coal. Evidence of the types of plants that contributed to carbonaceous deposits can occasionally be found in the shale and sandstone sediments that overlie coal deposits, and, with special techniques, within the coal itself. The greatest coal-forming time in geologic history was during the Carboniferous era (280 to 345 million years ago).

Types of coal

As geological processes apply pressure to peat over time, it is transformed successively into:
- Lignite - also referred to as brown coal, is the lowest rank of coal and used almost exclusively as fuel for steam-electric power generation. Jet is a compact form of lignite that is sometimes polished and has been used as an ornamental stone since the Iron Age.
- Sub-bituminous coal - whose properties range from those of lignite to those of bituminous coal and are used primarily as fuel for steam-electric power generation.
- Bituminous coal - a dense coal, usually black, sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat and power applications in manufacturing and to make coke.
- Anthracite - the highest rank, used primarily for residential and commercial space heating.

Uses

Anthracite]

Coal as fuel

:See also Clean coal Coal is primarily used as a solid fuel to produce heat through combustion. World coal consumption is about 5,800 million short tons (5.3 petagrams) annually, of which about 75% is used for electricity production. The region including China and India uses about 1,700 million short tons (1.5 Pg) annually, forecast to exceed 3,000 million short tons (2.7 Pg) in 2025. The USA consumes about 1,100 million short tons (1.0 Pg) of coal each year, using 90% of it for generation of electricity. Coal is the fastest growing energy source in the world, with coal use increasing by 25% for the three-year period ending in December 2004 (BP Statistical Energy Review, June 2005). When coal is used in electricity generation, it is generally pulverized and then burned. The heat produced is used to create steam, which is then used to spin turbines which turn generators and create electricity. Approximately 40% of the Earth's current electricity production is powered by coal, and the total known deposits recoverable by current technologies are sufficient for 300 years' use at current rates (see World Coal Reserves, below). A promising, more energy efficient way of using coal for electricity production would be via solid-oxide fuel cells or molten-carbonate fuel cells (or any oxygen ion transport based fuel cells that do not discriminate between fuels, as long as they consume oxygen), which would be able to get 60%-85% combined efficiency (direct electricity + waste heat steam turbine), compared to 30-40% currently possible with only steam turbines. Currently these fuel cell technologies can only process gaseous fuels, and they are also sensitive to sulfur poisoning, issues which would first have to be worked out before large scale commercial success is possible with coal. As far as gaseous fuels go, one idea is pulverized coal in a gas carrier (nitrogen), especially if the resulting carbon dioxide is sequestered, and has to be separated anyway from the carrier. A better idea is coal gasification with water, then the water recycled.

Gasification

High prices of oil and natural gas are leading to increased interest in "BTU Conversion" technologies such as coal gasification, methanation, liquefacation, and solidification. In the past, coal was converted to make coal gas, which was piped to customers to burn for illumination, heating, and cooking. At present, the safer natural gas is used instead. South Africa still uses gasification of coal for much of its petrochemical needs. Gasification is also a possibility for future energy use, as it generally burns hotter and cleaner than conventional coal, can spin a more efficient gas turbine rather than a steam turbine, and makes capturing carbon dioxide for later sequestration much much easier.

Liquefaction

Coal can also be converted into liquid fuels like gasoline or diesel by several different processes. The Fischer-Tropsch process of indirect synthesis of liquid hydrocarbons was used in Nazi Germany, and for many years by Sasol in South Africa - in both cases, because those regimes were politically isolated and unable to purchase crude oil on the open market. Coal would be gasified to make syngas (a balanced purified mixture of CO and H₂ gas) and the syngas condensed using Fischer-Tropsch catalysts to make light hydrocarbons which are further processed into gasoline and diesel. Syngas can also be converted to methanol: which can be used as a fuel, fuel additive, or further processed into gasoline via the Mobil M-gas process. A direct liquefaction process Bergius process (liquefaction by hydrogenation) is also available but has not been used outside Germany, where such processes were operated both during World War I and World War II. SASOL in South Africa has experimented with direct hydrogenation. Several other direct liquefaction processes have been developed, among these being the SRC-I and SRC-II (Solvent Refined Coal) processes developed by Gulf Oil and implemented as pilot plants in the United States in the 1960's and 1970's. Yet another process to manufacture liquid hydrocarbons from coal is low temperature carbonization (LTC). Coal is coked at temperatures between 450 and 700 °C compared to 800 to 1000 °C for metalurgical coke. These temperatures optimize the production of coal tars richer in lighter hydrocarbons than normal coal tar. The coal tar is then further processed into fuels. The process was developed by Lewis Karrick, an oil shale technologist at the U.S. Bureau of Mines in the 1920s. All of these liquid fuel production methods release carbon dioxide (CO₂) in the conversion process. Carbon dioxide sequestration is proposed to avoid releasing it into the atmosphere. As CO₂ is one of the process streams, sequestration is easier than from flue gases produced in combustion of coal with air, where CO₂ is diluted by nitrogen and other gases. Coal liquefaction is one of the backstop technologies that limit escalation of oil prices. Estimates of the cost of producing liquid fuels from coal suggest that domestic U.S. production of fuel from coal becomes cost-competitive with oil priced at around 35 USD per barrel , (break-even cost), which is well above historical averages - but is now viable due to the spike in oil prices in 2004-2005. . Among commercially mature technologies, advantage for indirect coal liquefaction over direct coal liquefaction are reported by Williams and Larson (2003). Estimates are reported for sites in China where break-even cost for coal liquefaction may be in the range between 25 to 35 USD/barrel of oil.

Coking and use of coke

Coke is a solid carbonaceous residue derived from low-ash, low-sulfur bituminous coal from which the volatile constituents are driven off by baking in an oven without oxygen at temperatures as high as 1,000 °C (2,000 °F) so that the fixed carbon and residual ash are fused together. Coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. Coke from coal is grey, hard, and porous and has a heating value of 24.8 million Btu/ton (29.6 MJ/kg). Byproducts of this conversion of coal to coke include coal-tar, ammonia, light oils, and "coal-gas". Petroleum coke is the solid residue obtained in oil refining, which resembles coke but contains too many impurities to be useful in metallurgical applications.

Harmful effects of coal burning

Combustion of coal, like any other compound containing carbon, produces carbon dioxide (CO₂), along with varying amounts of sulfur dioxide (SO₂) depending on where it was mined. Sulfur dioxide reacts with water to form sulfurous acid. If sulfur dioxide is discharged into the atmosphere, it reacts with water vapor and is eventually returned to the Earth as acid rain. Emissions from coal-fired power plants represent the largest source of artificial carbon dioxide emissions, according to most climate scientists a primary cause of global warming. Many other pollutants are present in coal power station emissions. Some studies claim that coal power plant emissions are responsible for tens of thousands of premature deaths annually in the United States alone. Modern power plants utilize a variety of techniques to limit the harmfulness of their waste products and improve the efficiency of burning, though these techniques are not widely implemented in some countries, as they add to the capital cost of the power plant. To eliminate CO₂ emissions from coal plants, carbon sequestration has been proposed but is not yet in large-scale use. Coal also contains many trace elements, including arsenic and mercury, which are dangerous if released into the environment. Coal also contains low levels of uranium, thorium, and other naturally-occurring radioactive isotopes whose release into the environment may lead to radioactive contamination. While these substances are trace impurities, if a great deal of coal is burned, significant amounts of these substances are released. If coal liquefaction or gasification is used to make petrochemicals, a great deal of carbon dioxide is produced in the process. If a carbon tax was introduced and sufficient CO₂ was not captured, the economics of such processes would be significantly less attractive. However, if sequestration or some other process were used to dispose of this by-product, fuels produced from this process would be less polluting. Some process do not have a much greater total impact on carbon dioxide levels than ones refined from petroleum. Others may be less polluting still. Research in this field is ongoing.

Coal fires

There are hundreds of coal fires burning around the world. Those burning underground can be difficult to locate and many can not be extinguished. Fires can cause the ground above to subside, combustion gases are dangerous to life, and breaking out to the surface can initiate surface wildfires. Coal seams can be set on fire by spontaneous combustion or contact with a mine fire or surface fire. A grass fire in a coal area can set dozens of coal seams on fire. Coal fires in China burn 120 million tons of coal a year, emitting 360 million metric tons of carbon dioxide. This amounts to 2-3% of the annual worldwide production of CO₂ from fossil fuels, or as much as emitted from all of the cars and light trucks in the United States. In the United States , a trash fire was lit in the borough landfill located in an abandoned Anthracite strip mine pit in the portion of the Coal Region called Centralia, Pennsylvania from 1962. It burns underground today, 40 years later. The reddish siltstone rock that caps many ridges and buttes in the Powder River Basin (Wyoming), and in western North Dakota is called porcelanite, which also may resemble the coal burning waste "clinker" or volcanic "scoria." Clinker is rock that has been fused by the natural burning of coal. In the case of the Powder River Basin approximately 27 to 54 billion metric tons of coal burned within the past three million years. Wild coal fires in the area were reported by the Lewis and Clark expedition as well as explorers and settlers in the area. The Australian Burning Mountain was originally believed to be a volcano, but the smoke and ash comes from a coal fire which may have been burning for 5,000 years.

World coal reserves

It has been estimated that, as of 1996, there is around one exagram (1 × 10¹⁵ kg) of total coal reserves economically accessible using current mining technology, approximately half of it being hard coal. The energy value of all the world's coal is well over 100,000 quadrillion Btu (100 zettajoules). There probably is enough coal to last for 300 years. However, this estimate assumes no rise in population, and no increased use of coal to attempt to compensate for the depletion of natural gas and petroleum. A recent (2003) study by scientist Gregson Vaux, which takes those factors into account, estimates that coal could peak in the United States as early as 2046, on average. "Peak" doesn't mean coal will disappear, but defines the time after which no matter what efforts are expended coal production will begin to decline in quantity and energy content. The disappearance of coal will occur much later, around the year 2267, assuming all other factors do not change, which they naturally will. Gregson Vaux The United States Department of Energy uses estimates of coal reserves in the region of 1,081,279 million short tons, which is about 4,786 BBOE (billion barrels of oil equivalent) . The amount of coal burned during 2001 was calculated as 2.337 GTOE (gigatonnes of oil equivalent), which is about 46 MBOED (million barrels of oil equivalent per day) . At that rate those reserves will last 285 years. As a comparison natural gas provided 51 MBOED, and oil 76 MBD (million barrels per day) during 2001.

External links

- [http://www.msnbc.msn.com/id/5174391/ MSNBC report on coal pollution health effects in the United States]
- [http://www.uic.com.au/nip83.htm Clean coal technologies]
- [http://www.ucsusa.org/CoalvsWind/brief.coal.html Use of coal gas in fuel cells]
- [http://www.jcoal.or.jp/overview_en/gijutsu.html Advanced methods of using coal] (Japanese Coal Energy Center)

References

- , also [http://www.ieiglobal.org/ESDVol7No4/dclversussicl.pdf] # # # # # # # # # # # # # # # # # # #
- Category:Sedimentary rocks Category:Rocks ja:石炭

United States/Government

The federal government of the United States was established by the United States Constitution. United States politics is dominated by the two major parties, the Republican Party and the Democratic Party. There are several other groups or parties of minor political significance.

Federal, state and local governments

The federal entity created by the Constitution is the dominant feature of the American governmental system. However, every person outside the capital is subject to at least three governing bodies: the federal government, a state, and a county (Note: county government has been abolished in some places, see New England and Town Meeting, the town/city fulfills this level of government). Within an incorporated entity, such as a city, they are also subject to the local government and possibly a district. Each level has its own political system (subject to constraints at higher levels). This multiplicity of jurisdictions reflects the country's history. The federal government was created by former colonies that had been established separately and had governed themselves independently of the others. Within these colonies were counties and towns with varying levels of development and therefore different administrative needs. Rather than replacing the states' legal systems with a unitary government, the Constitutional Convention chose to keep the states largely self-governing. As the country expanded, it admitted new states modeled on the existing ones.

State government

Before their independence, colonies governed themselves separately under the authority of the British Crown. In the early years of the republic, prior to the adoption of the Constitution, each state was virtually an autonomous unit. The delegates to the Constitutional Convention sought a stronger, more viable federal union, but they could not ignore state traditions, nor the interests of state politicians. In general, matters that lie entirely within state borders are the exclusive concern of state governments. These include internal communications; regulations relating to property, industry, business, and public utilities; the state criminal code; and working conditions within the state. Within this context, the federal government requires that state governments must be republican in form and that they adopt no laws that contradict or violate the federal Constitution or the laws and treaties of the United States. There are, of course, many areas of overlap between state and federal jurisdictions. Particularly in recent years, the federal government has assumed ever broadening responsibility in such matters as health, education, welfare, transportation, and housing and urban development. But where the federal government exercises such responsibility in the states, programs are usually adopted on the basis of cooperation between the two levels of government, rather than as an imposition from above. Like the national government, state governments have three branches: executive, legislative, and judicial; these are roughly equivalent in function and scope to their national counterparts. The chief executive of a state is the governor, elected by popular vote, typically for a four-year term (although in a few states the term is two years). Except for Nebraska, which has one legislative body, all states have a bicameral legislature, with the upper house usually called the Senate and the lower house called the House of Representatives, the House of Delegates, or the General Assembly. To confuse matters further, some states refer to the entire state legislature as the "General Assembly", with two houses therein. In most states, senators serve four-year terms, and members of the lower house serve two-year terms. The constitutions of the various states differ in some details but generally follow a pattern similar to that of the federal Constitution, including a statement of the rights of the people and a plan for organizing the government. On such matters as the operation of businesses, banks, public utilities, and charitable institutions, state constitutions are often more detailed and explicit than the federal one. Each state constitution, however, provides that the final authority belongs to the people, and sets certain standards and principles as the foundation of government.

City government

Once predominantly rural, the United States is today a highly urbanized country, and about 80 percent of its citizens now live in towns, large cities, or suburbs of cities. This statistic makes city governments critically important in the overall pattern of American government. To a greater extent than on the federal or state level, the city directly serves the needs of the people, providing everything from police and fire protection to sanitary codes, health regulations, education, public transportation, and housing. The business of running America's major cities is enormously complex. In terms of population alone, New York City is larger than 41 of the 50 states. It is often said that, next to the presidency, the most difficult executive position in the country is that of mayor of New York. City governments are chartered by states, and their charters detail the objectives and powers of the municipal government. But in many respects the cities function independently of the states. For most big cities, however, cooperation with both state and federal organizations is essential to meeting the needs of their residents. Types of city governments vary widely across the nation. However, almost all have some kind of central council, elected by the voters, and an executive officer, assisted by various department heads, to manage the city's affairs. There are three general types of city government: the mayor-council, the commission, and the council-manager. These are the pure forms; many cities have developed a combination of two or three of them. Mayor-Council. This is the oldest form of city government in the United States and, until the beginning of the 20th century, was used by nearly all American cities. Its structure is similar to that of the state and national governments, with an elected mayor as chief of the executive branch and an elected council that represents the various neighborhoods forming the legislative branch. The mayor appoints heads of city departments and other officials, sometimes with the approval of the council. He or she has the power of veto over ordinances — the laws of the city — and frequently is responsible for preparing the city's budget. The council passes city ordinances, sets the tax rate on property, and apportions money among the various city departments. As cities have grown, council seats have usually come to represent more than a single neighborhood. The Commission. This combines both the legislative and executive functions in one group of officials, usually three or more in number, elected city-wide. Each commissioner supervises the work of one or more city departments. One is named chairperson of the body and is often called the mayor, although his or her power is equivalent to that of the other commissioners. Council-Manager. The city manager is a response to the increasing complexity of urban problems, which require management expertise not often possessed by elected public officials. The answer has been to entrust most of the executive powers, including law enforcement and provision of services, to a highly trained and experienced professional city manager. The city manager plan has been adopted by a growing number of cities. Under this plan, a small, elected council makes the city ordinances and sets policy, but hires a paid administrator, also called a city manager, to carry out its decisions. The manager draws up the city budget and supervises most of the departments. Usually, there is no set term; the manager serves as long as the council is satisfied with his or her work.

County government

The county is a subdivision of the state, sometimes — but not always — containing two or more townships and several villages. New York City is so large that it is divided into five separate boroughs, each a county in its own right. On the other hand, Arlington County, Virginia, just across the Potomac River from Washington, D.C., is both an urbanized and suburban area, governed by a unitary county administration. What has happened, in these cases, is known as consolidated city-county government, which is also used by several other larger U.S. cities. In most U.S. counties, one town or city is designated as the county seat, and this is where the government offices are located and where the board of commissioners or supervisors meets. In small counties, boards are chosen by the county as a whole; in the larger ones, supervisors represent separate districts or townships. The board levies taxes; borrows and appropriates money; fixes the salaries of county employees; supervises elections; builds and maintains highways and bridges; and administers national, state, and county welfare programs. In some New England states, counties do not have any governmental function and are simply a division of land.

Town and village government

Thousands of municipal jurisdictions are too small to qualify as city governments. These are chartered as towns and villages and deal with such strictly local needs as paving and lighting the streets; ensuring a water supply; providing police and fire protection; establishing local health regulations; arranging for garbage, sewage, and other waste disposal; collecting local taxes to support governmental operations; and, in cooperation with the state and county, directly administering the local school system. Note that in many states the term "town" does not have any specific meaning--it is simply an informal term applied to populated places (both incorporated and unincorporated municipalities). And in some states, the term town is equivalent to how civil townships are used in other states. The government is usually entrusted to an elected board or council, which may be known by a variety of names: town or village council, board of selectmen, board of supervisors, board of commissioners. The board may have a chairperson or president who functions as chief executive officer, or there may be an elected mayor. Governmental employees may include a clerk, treasurer, police and fire officers, and health and welfare officers. One unique aspect of local government, found mostly in the New England region of the United States, is the "town meeting." Once a year — sometimes more often if needed — the registered voters of the town meet in open session to elect officers, debate local issues, and pass laws for operating the government. As a body, they decide on road construction and repair, construction of public buildings and facilities, tax rates, and the town budget. The town meeting, which has existed for more than two centuries, is often cited as the purest form of direct democracy, in which the governmental power is not delegated, but is exercised directly and regularly by all the people.

Other local governments

The federal, state, and local governments covered here by no means include the whole spectrum of American governmental units. The U.S. Bureau of the Census (part of the Commerce Department) has identified no less than 84,955 local governmental units in the United States, including counties, municipalities, townships, school districts, and special districts. Americans have come to rely on their governments to perform a wide variety of tasks which, in the early days of the republic, people did for themselves. In colonial days, there were few police officers or firefighters, even in the large cities; governments provided neither street lights nor street cleaners. To a large extent, people protected their own property and saw to their families' needs. In modern times, meeting these needs is usually seen as the responsibility of the whole community, acting through the agency of one or more levels of government. Even in small towns, the police, fire, welfare, and health department functions are exercised by governments. Hence, the bewildering array of jurisdictions.

Participation

Suffrage is nearly universal for citizens 18 years of age and older. A major remaining exception is the District of Columbia, where residents have no representation whatsoever in the US Senate; only a non-voting "delegate" in the House; and an extremely weak "home rule" city government. Also, US voting rights can be restricted as a result of felony conviction (such laws vary widely by state). The most significant fact about politics in the United States, especially at the national level, is that successful participation requires large amounts of money, especially for television advertising. This money is very difficult to raise by appeals to a mass base, although the Republican Party has had some success, as has Howard Dean with his Internet appeals. Both parties must depend on wealthy donors and organizations - traditionally the Democrats depended on donations from organized labor while the Republicans relied on business donations. Since 1984, however, the Democrats' business donations have surpassed those from labor organizations. This dependency on donors is controversial, and has led to laws limiting spending on political campaigns being enacted; as a complicating factor due to the United States Constitution, opponents of campaign finance laws cite the First Amendment's guarantee of free speech, and challenge campaign finance laws on grounds that they attempt to circumscribe their constitutionally-guaranteed rights. Even when laws are upheld, the complication of compliance with the First Amendment requires careful and cautious drafting of legislation, leading to laws that are still fairly limited in scope, especially in comparison to those of other countries such as the United Kingdom, France or Canada. Some would allege that funding practices commonplace in the United States would likely be considered political corruption elsewhere.

Political culture

Most schools in the United States teach the Declaration of Independence, Constitution, Bill of Rights, and the writings of the Founding Fathers as the definition of the country's governing ideology. Among the core tenets of this ideology are the following:
- The government is answerable to citizens, who may change it through elections.
- The government's power in matters of religion, expression, and law enforcement should be limited to prevent abuse of power.
- The laws should attach no special privilege to any citizen (that is, citizens should be equal before the law).
- Individuals and political parties debate how this ideology applies to particular circumstances, and may disagree openly with any of it. At the time of the United States's founding, the economy was predominantly one of private business, and state governments left welfare issues to private or local initiative. The United States government has largely accepted the system of private enterprise and opposed broad grants of support to citizens, although the experience of the Great Depression challenged both positions. As a result the US tends to be ideologically oriented toward capitalism in contrast with the social democratic cultures in Europe. Prior to World War II the United States pursued a policy of isolationism in foreign affairs by not taking sides in conflicts between foreign powers. The country abandoned this policy when it became a superpower, but the country remains skeptical of internationalism. The ideology of the incumbent President and the President's advisors largely determines the government's attitude in foreign affairs.

Political parties

See also: Republican Party, Democratic Party, Puerto Rico political parties Many of America's Founding Fathers hated the thought of political parties. They were sure quarreling factions would be more interested in contending with each other than in working for the common good. They wanted individual citizens to vote for individual candidates, without the interference of organized groups — but this was not to be. By the 1790s, different views of the new country's proper course had already developed, and those who held these opposing views tried to win support for their cause by banding together. The followers of Alexander Hamilton, the Hamiltonian faction, took up the name "Federalist"; they favored a strong central government that would support the interests of commerce and industry. The followers of Thomas Jefferson, the Jeffersonians and then the "Anti-Federalists," took up the name Democrat-Republicans" (not to be confused with the modern Republican party); they preferred a decentralized agrarian republic in which the federal government had limited power. By 1828, the Federalists had disappeared as an organization, replaced by the Whigs, brought to life in opposition to the election that year of President Andrew Jackson. Jackson's presidency split the Republican party: Jacksonians became the "Democratic-Republicans" and those following the leadership of John Quincy Adams became the "National Republicans." The Democratic-Republicans quickly shortened their name to the Democratic party, and the two-party system, still in existence today, was born. The United States thus has exceptionally old political parties. In the 1850s, the issue of slavery took center stage, with disagreement in particular over the question of whether or not slavery should be permitted in the country's new territories in the West. The Whig Party straddled the issue and sank to its death; it was replaced in 1854 by the Republican Party, whose primary policy was that slavery be excluded from all the territories. Just six years later, this new party captured the presidency when Abraham Lincoln won the election of 1860. By then, parties were well established as the country's dominant political organizations, and party allegiance had become an important part of most people's consciousness. Party loyalty was passed from fathers to sons, and party activities — including spectacular campaign events, complete with uniformed marching groups and torchlight parades — were a part of the social life of many communities. By the 1920s, however, this boisterous folksiness had diminished. Municipal reforms, civil service reform, corrupt practices acts, and presidential primaries to replace the power of politicians at national conventions had all helped to clean up politics — and make it quite a bit less fun. How did the two-party system develop in the United States? America has historically had many minor or third political parties. They tend to serve a means to advocate polices that eventually are adopted by the two major political parties, i.e. the abolishment of slavery, and child labor laws. Some of these third political parties such as the Socialist Party, the Farmer Labor Party and the Populist Party developed an impressive degree of support, although limited electoral success. Most officials in America are elected from single-member districts and win office by beating out their opponents in a system for determining winners called first-past-the-post — the one who gets the pluarity wins, (which is not the same thing as actually getting a majority of votes). While some cities and the state of Illinois did experiment with proportional representation, the United States Congress banned the usage of that alternative voting method for federal legislative elections in 1967. This, too, encourages the two-party system; see Duverger's law. Another critical factor has been ballot access law. Originally voters went to the polls and publicly stated which candidate they supported, later on this developed into a process whereby each political party would create its own ballot and thus the voter would put the party's ballot into the voting box. In the late nineteenth century, states became to adopt the Australian Secret Ballot Method and it eventually became the national standard. The secret ballot method ensured that the privacy of voters would be protected (hence government jobs could no longer be awarded to loyal voters) and each state would be responsible for creating one official ballot. The fact that states legislators were dominated by Democrats and Republicans provided an opportunity to possible discriminatory laws against minor political parties, yet such laws did not start to arise until the first Red Scare that hit America after World War I. State legislators became to enact tough laws that made it harder for minor political parties to run candidates for office by requiring a high number of petition signatures from citizens and decreasing the length of time that such a petition could legally be circulated. The election laws encourages the creation of a duopoly: one party in power, the other out. If those who are "out" band together, they have a better chance of beating those who are "in." Occasionally a third party does come along and receive a considerable share of the vote, although usually not for very long. The most successful third parties in recent years have been H. Ross Perot's Reform Party, which won 8% of the vote in the presidential election of 1996 (Perot himself won 19% of the vote in 1992, but the Reform Party did not yet exist) and the Libertarian Party, which has more than 400 members in elected office. Jesse Ventura became the only Reform Party candidate to win statewide office when he was elected governor of Minnesota in 1998. Only two independents currently hold federal office - Senator James Jeffords (though he often votes with Democrats and sits with them in their closed meetings) and Congressman Bernie Sanders, both of Vermont (Vermont has only one House seat). However, Jeffords was elected as a Republican, and has yet to face re-election since leaving the GOP. Most third parties have a hard time surviving, though, because one or both of the major parties often adopt their most popular issues, and thus their voters. Also, voters who might otherwise favor a third party often hesitate to give them their votes because they are perceived as not having any realistic chance of winning, or because they fear their support for a third party will the divide the vote and cause the defeat of the major party candidate more favorable than the other. It should also be noted that while almost all elected officials do identify with a political party, the political parties of the United States are much more individualistic than in other political systems (i.e. in a parliamentary system). More often than not, party members will "toe the line" and support their party's policies, but it is important to note that they are free to vote against their own party and vote with the opposition ("cross the aisle") if a particular policy is counter to the priorities and interests of their constituents. Recent examples of this can be seen in such highly controversial matters as Social Security reform, the federal budget, and some environmental policies. "In America the same political labels — Democratic and Republican — cover virtually all public officeholders, and therefore most voters are everywhere mobilized in the name of these two parties," says Nelson W. Polsby, professor of political science, in the book New Federalist Papers: Essays in Defense of the Constitution. "Yet Democrats and Republicans are not everywhere the same. Variations — sometimes subtle, sometimes blatant — in the 50 political cultures of the states yield considerable differences overall in what it means to be, or to vote, Democratic or Republican. These differences suggest that one may be justified in referring to the American two-party system as masking something more like a hundred-party system." The commonwealth of Puerto Rico has separate political parties. The main ones are the New Progressive Party of Puerto Rico, Popular Democratic Party of Puerto Rico, and the Puerto Rican Independence Party.
Organization of American political parties
Unlike in some countries, American political parties are very loosely organized. The two major parties, in particular, have no formal organization at the national level that controls membership, activities, or policy positions, though some state affiliates do. Thus, for an American to say that he or she is a member of the Democratic or Republican party, is quite different from a Briton's stating that he or she is a member of the Labour party. In the United States, one can often become a "member" of a party, merely by stating that fact. In some U.S. states, a voter can register as a member of one or another party or vote in the primary election for one or another party, but such participation does not restrict one's choices in any way; nor does it give a person any particular rights or obligations with respect to the party. A person may choose to attend meetings of one local party committee one day and another party committee the next day. The sole factor that brings one "closer to the action" is the quantity and quality of participation in party activities and the ability to persuade others in attendance to give one responsibility. Party identification becomes somewhat formalized when a person runs for partisan office. In most states, this means declaring oneself a candidate for the nomination of a particular party and intent to enter that party's primary election for an office. A party committee may choose to en

Holston River

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