A sluice is a water channel controlled at its head by a gate. A mill race, flume, penstock or lade is a sluice channelling water toward a water mill; the terms sluice, sluice gate, knife gate, slide gate are used interchangeably in the water and wastewater control industry. A sluice gate is traditionally a wood or metal barrier sliding in grooves that are set in the sides of the waterway. Sluice gates control water levels and flow rates in rivers and canals, they are used in wastewater treatment plants and to recover minerals in mining operations, in watermills. "Sluice gate" refers to a movable gate allowing water to flow under it. When a sluice is lowered, water may spill over the top. A mechanism drives the sluice up or down; this may be a simple, hand-operated, chain pulled/lowered, worm drive or rack-and-pinion drive, or it may be electrically or hydraulically powered. Flap sluice gate A automatic type, controlled by the pressure head across it, it is a gate hinged at the top. When pressure is from one side, the gate is kept closed.
Vertical rising sluice gate A plate sliding in the vertical direction, which may be controlled by machinery. Radial sluice gate A structure, where a small part of a cylindrical surface serves as the gate, supported by radial constructions going through the cylinder's radius. On occasion, a counterweight is provided. Rising sector sluice gate Also a part of a cylindrical surface, which rests at the bottom of the channel and rises by rotating around its centre. Needle sluice A sluice formed by a number of thin needles held against a solid frame through water pressure as in a needle dam. Fan gate This type of gate was invented by the Dutch hydraulic engineer Jan Blanken in 1808, he was Inspector-General for Waterstaat of the Kingdom of Holland at the time.. The Fan door has the special property that it can open in the direction of high water using water pressure; this gate type was used to purposely inundate certain regions, for instance in the case of the Hollandic Water Line. Nowadays this type of gate can still be found for example in Gouda.
The design of a Fan gate is shown in the image on the left. The sluice has a separate chamber that can be filled with water and is separated on the high-water-level side of the sluice by a large door; when a tube connecting the separate chamber with the high-water-level side of the sluice is opened, the water level, with that the water pressure in this chamber, will rise to the same level as that on the high-water-level side. The surface area of the door separating the chamber from the high-water-level side of the sluice is larger than that of the door closing the sluice. Since pressures are equal this results into a net force. In the mountains of the United States, sluices transported logs from steep hillsides to downslope sawmill ponds or yarding areas. Nineteenth-century logging was traditionally a winter activity for men who spent summers working on farms. Where there were freezing nights, water might be applied to logging sluices every night so a fresh coating of slippery ice would reduce friction of logs placed in the sluice the following morning.
Sluice boxes are used in the recovery of black sands and other minerals from placer deposits during placer mining operations. They may be small-scale, as used in prospecting, or much larger, as in commercial operations, where the material is first screened using a trommel or screening plant. Typical sluices have transverse riffles over a carpet, which trap the heavy minerals and other valuable minerals; the result is a concentrate. Wood Traditionally wood was the material of choice for sluice gates. Cast iron Cast iron has been popular; this material is great at keeping the strength needed. Stainless steel In most cases, stainless steel is lighter than the older cast iron material. Fibre-reinforced plastic In modern times, newer materials such as fibre-reinforced plastic are being used to build sluices; these modern technologies have many of the attributes of the older materials, while introducing advantages such as corrosion resistance and much lighter weights. In the Somerset Levels, sluice gates are known as clyce.
Most of the inhabitants of Guyana refer to sluices as kokers. Sinhala people in Sri Lanka who had an ancient civilization based on harvested rain water, refer to sluices as Horovuwa. Floodgate Gatehouse – An structure to house a sluice gate Lock Zijlstra – A Dutch name referring to one who lives near a sluice Control lock Crittenden, H. Temple; the Maine Scenic Route. McClain Printing. Moody, Linwood W.. The Maine Two-Footers. Howell-North. Cornwall, L. Peter & Farrell, Jack W.. Ride the Sandy River. Pacific Fast Mail. Soar Valley Sluice Gates Salt/Fresh water separating Sluice Complex
A siphon is a device that involves the flow of liquids through a tube. In a narrower sense, the word refers to a tube in an inverted'U' shape, which causes a liquid to flow upward, above the surface of a reservoir, with no pump, but powered by the fall of the liquid as it flows down the tube under the pull of gravity discharging at a level lower than the surface of the reservoir from which it came. There are two leading theories about how siphons cause liquid to flow uphill, against gravity, without being pumped, powered only by gravity; the traditional theory for centuries was that gravity pulling the liquid down on the exit side of the siphon resulted in reduced pressure at the top of the siphon. Atmospheric pressure was able to push the liquid from the upper reservoir, up into the reduced pressure at the top of the siphon, like in a barometer or drinking straw, over. However, it has been demonstrated that siphons can operate in a vacuum and to heights exceeding the barometric height of the liquid.
The cohesion tension theory of siphon operation has been advocated, where the liquid is pulled over the siphon in a way similar to the chain model. It need not be one theory or the other, correct, but rather both theories may be correct in different circumstances of ambient pressure; the atmospheric pressure with gravity theory cannot explain siphons in vacuum, where there is no significant atmospheric pressure. But the cohesion tension with gravity theory cannot explain CO2 gas siphons, siphons working despite bubbles, the flying droplet siphon, where gases do not exert significant pulling forces, liquids not in contact cannot exert a cohesive tension force. All known published theories in modern times recognize Bernoulli's equation as a decent approximation to idealized, friction-free siphon operation. Egyptian reliefs from 1500 BC depict siphons used to extract liquids from large storage jars. There is physical evidence for the use of siphons by Greek engineers in the 3rd century BC at Pergamon.
Hero of Alexandria wrote extensively about siphons in the treatise Pneumatica. The Banu Musa brothers of 9th-century Baghdad invented a double-concentric siphon, which they described in their Book of Ingenious Devices; the edition edited by Hill includes an analysis of the double-concentric siphon. Siphons were studied further in the 17th century, in the context of suction pumps with an eye to understanding the maximum height of pumps and the apparent vacuum at the top of early barometers; this was explained by Galileo Galilei via the theory of horror vacui, which dates to Aristotle, which Galileo restated as resintenza del vacuo, but this was subsequently disproved by workers, notably Evangelista Torricelli and Blaise Pascal – see barometer: history. A practical siphon, operating at typical atmospheric pressures and tube heights, works because gravity pulling down on the taller column of liquid leaves reduced pressure at the top of the siphon; this reduced pressure at the top means gravity pulling down on the shorter column of liquid is not sufficient to keep the liquid stationary against the atmospheric pressure pushing it up into the reduced pressure zone at the top of the siphon.
So the liquid flows from the higher pressure area of the upper reservoir, up to the lower pressure zone at the top of the siphon, over the top, with the help of gravity and a taller column of liquid, down to the higher pressure zone at the exit. The chain model is a useful but not accurate conceptual model of a siphon; the chain model helps to understand how a siphon can cause liquid to flow uphill, powered only by the downward force of gravity. A siphon can sometimes be thought of a little like a chain hanging over a pulley, with one end of the chain piled on a higher surface than the other. Since the length of chain on the shorter side is lighter than the length of chain on the taller side, the heavier chain on the taller side will move down and pull up the chain on the lighter side. Similar to a siphon, the chain model is just powered by gravity acting on the heavier side, there is no violation of conservation of energy, because the chain is just moving from a higher to a lower location, as the liquid does in a siphon.
There are a number of problems with the chain model of a siphon, understanding these differences helps to explain the actual workings of siphons. First, unlike in the chain model of the siphon, it is not the weight on the taller side compared to the shorter side, that matters. Rather it is the difference in height from the reservoir surfaces to the top of the siphon, that determines the balance of pressure. For example, if the tube from the upper reservoir to the top of the siphon has a much larger diameter than the taller section of tube from the lower reservoir to the top of the siphon, the shorter upper section of the siphon may have a much larger weight of liquid in it, yet the lighter volume of liquid in the down tube can pull liquid up the fatter up tube, the siphon can function normally. Another difference is that under most practical circumstances, dissolved gases, vapor pressure, lack of adhesion with tube walls, conspire to render the tensile strength within the liquid ineffective for siphoning.
Thus, unlike a chain which has significant tensile strength, liquids have little tensile strength under typical siphon conditions, therefore the liquid on the rising side cannot be pulled up, in the way the chain is pulled up on the rising side. An occasional misunderstanding of siphons is
The Gadsden Purchase is a 29,670-square-mile region of present-day southern Arizona and southwestern New Mexico that the United States acquired from Mexico by the Treaty of Mesilla that took effect on June 8, 1854. The purchase included lands south of the Gila River and west of the Rio Grande which the U. S. needed to build a transcontinental railroad along a deep southern route, which the Southern Pacific Railroad completed in 1881–1883. The purchase aimed to resolve other border issues; the first draft was signed on December 30, 1853, by James Gadsden, U. S. ambassador to Mexico, by Antonio López de Santa Anna, president of Mexico. The U. S. Senate voted in favor of ratifying it with amendments on April 25, 1854, transmitted it to President Franklin Pierce. Mexico's government and its General Congress or Congress of the Union took final approval action on June 8, 1854, when the treaty took effect; the purchase was the last substantial territorial acquisition in the contiguous United States, defined the Mexico–United States border.
The financially-strapped government of Santa Anna agreed to the sale, which netted Mexico $10 million. After the devastating loss of Mexican territory to the U. S. in the Mexican–American War and the continued filibustering by U. S. citizens, Santa Anna may have calculated it was better to yield territory by treaty and receive payment rather than have the territory seized by the U. S; as the railroad age evolved, business-oriented Southerners saw that a railroad linking the South with the Pacific Coast would expand trade opportunities. They thought the topography of the southern portion of the original boundary line was too mountainous to allow a direct route. Projected southern railroad routes tended to veer to the north as they proceeded eastward, which would favor connections with northern railroads and favor northern seaports. Southerners saw that to avoid the mountains, a route with a southeastern terminus might need to swing south into what was still Mexican territory; the administration of President Pierce influenced by Secretary of War Jefferson Davis, saw an opportunity to acquire land for the railroad, as well as to acquire significant other territory from northern Mexico.
In those years, the debate over slavery in the United States entered into many other debates, as the acquisition of new territory opened the question of whether it would be slave or free territory. In January 1845 Asa Whitney of New York state presented the United States Congress with the first plan to construct a transcontinental railroad. Although Congress took no action on his proposal, a commercial convention of 1845 in Memphis took up the issue. Prominent attendees included John C. Calhoun, Clement C. Clay, Sr. John Bell, William Gwin, Edmund P. Gaines, but it was James Gadsden of South Carolina, influential in the convention's recommending a southern route for the proposed railroad; the route was to end in San Diego or Mazatlán. Southerners hoped that such a route would ensure southern prosperity while opening the "West to southern influence and settlement". Southern interest in railroads in general, the Pacific railroad in particular, accelerated after the conclusion of the Mexican–American War in 1848.
During that war, topographical officers William H. Emory and James W. Abert had conducted surveys that demonstrated the feasibility of a railroad's originating in El Paso or western Arkansas and ending in San Diego. J. D. B. DeBow, the editor of DeBow's Review, Gadsden both publicized within the South the benefits of building this railroad. Gadsden had become the president of the South Carolina Canal and Rail Road Company in 1839. Gadsden wanted to connect all Southern railroads into one sectional network, he was concerned that the increasing railroad construction in the North was shifting trade in lumber and manufacturing goods from the traditional north–south route based on the Ohio and Mississippi rivers to an east–west axis that would bypass the South. He saw Charleston, his home town, losing its prominence as a seaport. In addition, many Southern business interests feared that a northern transcontinental route would exclude the South from trade with the Orient. Other Southerners argued for diversification from a plantation economy to keep the South independent of northern bankers.
In October 1849, the southern interests held a convention to discuss railroads in Memphis, in response to a convention in St. Louis earlier that fall which discussed a northern route; the Memphis convention overwhelmingly advocated the construction of a route beginning there, to connect with an El Paso, Texas to San Diego, California line. Disagreement arose only over the issue of financing; the convention president, Matthew Fontaine Maury of Virginia, preferred strict private financing, whereas John Bell and others thought that federal land grants to railroad developers would be necessary. Gadsden supported nullification in 1831; when California was admitted to the Union as a free state in 1850, he advocated secession by South Carolina. Gadsden considered slavery "a social blessing" and abolitionists "the greatest curse of the nation"; when the secession proposal failed, Gadsden worked with his cousin Isaac Edward Holmes, a lawyer in San Francisco since 1851
A flood is an overflow of water that submerges land, dry. In the sense of "flowing water", the word may be applied to the inflow of the tide. Floods are an area of study of the discipline hydrology and are of significant concern in agriculture, civil engineering and public health. Flooding may occur as an overflow of water from water bodies, such as a river, lake, or ocean, in which the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries, or it may occur due to an accumulation of rainwater on saturated ground in an areal flood. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, these changes in size are unlikely to be considered significant unless they flood property or drown domestic animals. Floods can occur in rivers when the flow rate exceeds the capacity of the river channel at bends or meanders in the waterway. Floods cause damage to homes and businesses if they are in the natural flood plains of rivers.
While riverine flood damage can be eliminated by moving away from rivers and other bodies of water, people have traditionally lived and worked by rivers because the land is flat and fertile and because rivers provide easy travel and access to commerce and industry. Some floods develop while others such as flash floods can develop in just a few minutes and without visible signs of rain. Additionally, floods can be local, impacting a neighborhood or community, or large, affecting entire river basins; the word "flood" comes from a word common to Germanic languages. Floods can happen on flat or low-lying areas when water is supplied by rainfall or snowmelt more than it can either infiltrate or run off; the excess accumulates in place, sometimes to hazardous depths. Surface soil can become saturated, which stops infiltration, where the water table is shallow, such as a floodplain, or from intense rain from one or a series of storms. Infiltration is slow to negligible through frozen ground, concrete, paving, or roofs.
Areal flooding begins in flat areas like floodplains and in local depressions not connected to a stream channel, because the velocity of overland flow depends on the surface slope. Endorheic basins may experience areal flooding during periods when precipitation exceeds evaporation. Floods occur in all types of river and stream channels, from the smallest ephemeral streams in humid zones to normally-dry channels in arid climates to the world's largest rivers; when overland flow occurs on tilled fields, it can result in a muddy flood where sediments are picked up by run off and carried as suspended matter or bed load. Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, debris, or beaver dams. Slow-rising floods most occur in large rivers with large catchment areas; the increase in flow may be the result of sustained rainfall, rapid snow melt, monsoons, or tropical cyclones. However, large rivers may have rapid flooding events in areas with dry climate, since they may have large basins but small river channels and rainfall can be intense in smaller areas of those basins.
Rapid flooding events, including flash floods, more occur on smaller rivers, rivers with steep valleys, rivers that flow for much of their length over impermeable terrain, or normally-dry channels. The cause may be localized convective precipitation or sudden release from an upstream impoundment created behind a dam, landslide, or glacier. In one instance, a flash flood killed eight people enjoying the water on a Sunday afternoon at a popular waterfall in a narrow canyon. Without any observed rainfall, the flow rate increased from about 50 to 1,500 cubic feet per second in just one minute. Two larger floods occurred at the same site within a week, but no one was at the waterfall on those days; the deadly flood resulted from a thunderstorm over part of the drainage basin, where steep, bare rock slopes are common and the thin soil was saturated. Flash floods are the most common flood type in normally-dry channels in arid zones, known as arroyos in the southwest United States and many other names elsewhere.
In that setting, the first flood water to arrive is depleted. The leading edge of the flood thus advances more than and higher flows; as a result, the rising limb of the hydrograph becomes quicker as the flood moves downstream, until the flow rate is so great that the depletion by wetting soil becomes insignificant. Flooding in estuaries is caused by a combination of sea tidal surges caused by winds and low barometric pressure, they may be exacerbated by high upstream river flow. Coastal areas may be flooded by storm events at sea, resulting in waves over-topping defenses or in severe cases by tsunami or tropical cyclones. A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category. Research from the NHC explains: "Storm surge is an abnormal rise of water generated by a storm and above the predicted astronomical tides. Storm surge should not be confused with storm tide, defined as the water level rise due to the combination of storm surge and the astronomical tide.
This rise in water level can cause extreme flooding in coastal areas when storm surge coincides with normal high tide, resulting in storm tides reaching up to 20 feet or more in some cases." Urban flooding is the inundation of land or property in a built environment in more densely populated areas, caused by rainfall overwhelmi
Civilian Conservation Corps
The Civilian Conservation Corps was a public work relief program that operated from 1933 to 1942 in the United States for unemployed, unmarried men. For young men ages 18–25, it was expanded to ages 17–28. Robert Fechner was the first director of the agency, succeeded by James McEntee following Fechner's death; the CCC was a major part of President Franklin D. Roosevelt's New Deal that provided unskilled manual labor jobs related to the conservation and development of natural resources in rural lands owned by federal and local governments; the CCC was designed to provide jobs for young men and to relieve families who had difficulty finding jobs during the Great Depression in the United States. Maximum enrollment at any one time was 300,000. Through the course of its nine years in operation, 3 million young men participated in the CCC, which provided them with shelter and food, together with a wage of $30 per month; the American public made the CCC the most popular of all the New Deal programs.
Sources written at the time claimed an individual's enrollment in the CCC led to improved physical condition, heightened morale, increased employability. The CCC led to a greater public awareness and appreciation of the outdoors and the nation's natural resources, the continued need for a planned, comprehensive national program for the protection and development of natural resources; the CCC operated separate programs for Native Americans. 15,000 Native Americans participated in the program, helping them weather the Great Depression. By 1942, with World War II and the draft in operation, the need for work relief declined, Congress voted to close the program; as governor of New York, Franklin Delano Roosevelt had run a similar program on a much smaller scale. Long interested in conservation, as president, he proposed to Congress a full-scale national program on March 21, 1933: I propose to create to be used in complex work, not interfering with normal employment and confining itself to forestry, the prevention of soil erosion, flood control, similar projects.
I call your attention to the fact that this type of work is of definite, practical value, not only through the prevention of great present financial loss but as a means of creating future national wealth. He promised this law would provide 250,000 young men with meals, housing and medical care for working in the national forests and other government properties; the Emergency Conservation Work Act was introduced to Congress the same day and enacted by voice vote on March 31. Roosevelt issued Executive Order 6101 on April 5, 1933, which established the CCC organization and appointed a director, Robert Fechner, a former labor union official who served until 1939; the organization and administration of the CCC was a new experiment in operations for a federal government agency. The order indicated that the program was to be supervised jointly by four government departments: Labor, which recruited the young men, which operated the camps, Agriculture and Interior, which organized and supervised the work projects.
A CCC Advisory Council was composed of a representative from each of the supervising departments. In addition, the Office of Education and Veterans Administration participated in the program. To end the opposition from labor unions Roosevelt chose Robert Fechner, vice president of the International Association of Machinists and Aerospace Workers, as director of the corps. William Green, head of the American Federation of Labor, was taken to the first camp to demonstrate that there would be no job training involved beyond simple manual labor. Reserve officers from the U. S. Army were in charge of the camps. General Douglas MacArthur was placed in charge of the program but said that the number of Army officers and soldiers assigned to the camps was affecting the readiness of the Regular Army, but the Army found numerous benefits in the program. When the draft began in 1940, the policy was to make CCC alumni sergeants. CCC provided command experience to Organized Reserve Corps officers. Through the CCC, the Regular Army could assess the leadership performance of both Regular and Reserve Officers.
The CCC provided lessons which the Army used in developing its wartime and mobilization plans for training camps. The legislation and mobilization of the program occurred quite rapidly. Roosevelt made his request to Congress on March 21, 1933; the first CCC enrollee was selected April 8, subsequent lists of unemployed men were supplied by state and local welfare and relief agencies for immediate enrollment. On April 17, the first camp, NF-1, Camp Roosevelt, was established at George Washington National Forest near Luray, Virginia. On June 18, the first of 161 soil erosion control camps was opened, in Alabama. By July 1, 1933 there were 1,463 working camps with 250,000 junior enrollees; the typical CCC enrollee was a U. S. citizen, unemployed male, 18–25 years of age. His family was on local relief; each enrollee volunteered and, upon passing a physical exam and/or a period of conditioning, was required to serve a minimum six-month period, with the
Pumping stations are facilities including pumps and equipment for pumping fluids from one place to another. They are used for a variety of infrastructure systems, such as the supply of water to canals, the drainage of low-lying land, the removal of sewage to processing sites. A pumping station is, by definition, an integral part of a pumped-storage hydroelectricity installation. In countries with canal systems, pumping stations are frequent; because of the way the system of canal locks work, water is lost from the upper part of a canal each time a vessel passes through. Most lock gates are not watertight, so some water leaks from the higher levels of the canal to those lower down; the water has to be replaced or the upper levels of the canal would not hold enough water to be navigable. Canals are fed by diverting water from streams and rivers into the upper parts of the canal, but if no suitable source is available, a pumping station can be used to maintain the water level. An excellent example of a canal pumping station is the Claverton Pumping Station on the Kennet and Avon Canal in southern England, United Kingdom.
This pumps water from the nearby River Avon to the canal using pumps driven by a waterwheel, powered by the river. Where no external water supply is available, back pumping systems may be employed. Water is extracted from the canal below the lowest lock of a flight and is pumped back to the top of the flight, ready for the next boat to pass through; such installations are small.. When low-lying areas of land are drained, the general method is to dig drainage ditches. However, if the area is below sea level it is necessary to pump the water upwards into water channels that drain into the sea; the Victorians understood this concept, in the United Kingdom they built pumping stations with water pumps, powered by steam engines to accomplish this task. In Lincolnshire, large areas of wetland at sea level, called The Fens, were turned into rich arable farmland by this method; the land is full of nutrients because of the accumulation of sedimentary mud that created the land initially. Elsewhere, pumping stations are used to remove water that has found its way into low-lying areas as a result of leakage or flooding.
In more recent times, a "package pumping station" provides an efficient and economic way of installing a drainage system. They are suitable for mechanical building services collection and pumping of liquids like surface water, wastewater or sewage from areas where drainage by gravity is not possible. A package pumping station is an integrated system, built in a housing manufactured from strong, impact-resistant materials such as precast concrete, polyethylene, or glass-reinforced plastic; the unit is supplied with internal pipework fitted, pre-assembled ready for installation into the ground, after which the submersible pumps and control equipment are fitted. Features may include controls for automatic operation. Traditional site constructed systems have the valve vault components installed in a separate structure. Having two structural components can lead to serious site problems such as uneven settling between components which results in stress on, failure of the pipes and connections between components.
The development of a packaged pump station system combined all components into a single housing which not only eliminates uneven settling issues, but pre-plumbing and outfitting each unit prior to installation can reduce the cost and time involved with civil work and site labor. Pumping stations in sewage collection systems are designed to handle raw sewage, fed from underground gravity pipelines. Sewage is fed into and stored in a pit known as a wet well; the well is equipped with electrical instrumentation to detect the level of sewage present. When the sewage level rises to a predetermined point, a pump will be started to lift the sewage upward through a pressurized pipe system called a sewer force main if the sewage is transported some significant distance; the pumping station may be called a lift station if the pump discharges into a nearby gravity manhole. From here the cycle starts all over again until the sewage reaches its point of destination—usually a treatment plant. By this method, pumping stations are used to move waste to higher elevations.
In the case of high sewage flows into the well additional pumps will be used. If this is insufficient, or in the case of failure of the pumping station, a backup in the sewer system can occur, leading to a sanitary sewer overflow—the discharge of raw sewage into the environment. Sewage pumping stations are designed so that one pump or one set of pumps will handle normal peak flow conditions. Redundancy is built into the system so that in the event that any one pump is out of service, the remaining pump or pumps will handle the designed flow; the storage volume of the wet well between the "pump on" and "pump off" settings is designed to minimize pump starts and stops, but is not so long a retention time as to allow the sewage in the wet well to go septic. Sewage pumps are always end-suction centrifugal pumps with open impellers and are specially designed with a large open passage so as to avoid clogging with debris or winding stringy debris onto the impeller. A four pole or six pole AC induction motor drives the pump.
Rather than provide large open passages, some pumps smaller sewage pumps macerate any solids within the
The United States of America known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico; the State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean; the U. S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The diverse geography and wildlife of the United States make it one of the world's 17 megadiverse countries.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century; the United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies following the French and Indian War led to the American Revolution, which began in 1775, the subsequent Declaration of Independence in 1776; the war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties; the United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery.
By the end of the century, the United States had extended into the Pacific Ocean, its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power; the United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U. S. Moon landing; the end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower. The United States is the world's oldest surviving federation, it is a representative democracy.
The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, other international organizations. The United States is a developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for a quarter of global GDP; the U. S. economy is post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U. S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country. Despite wide income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, human development, per capita GDP, worker productivity.
The United States is the foremost military power in the world, making up a third of global military spending, is a leading political and scientific force internationally. In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci; the first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq. to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort; the first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776. The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the'United States of America'".
The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence; this draft of the document did not surface unti