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102-718: Lake Mead is a reservoir formed by the Hoover Dam on the Colorado River in the Southwestern United States . It is located in the states of Nevada and Arizona , 24 mi (39 km) east of Las Vegas . It is the largest reservoir in the US in terms of water capacity. Lake Mead provides water to the states of Arizona, California , and Nevada as well as some of Mexico , providing sustenance to nearly 20 million people and large areas of farmland. At maximum capacity, Lake Mead

204-537: A block for migrating fish, trapping them in one area, producing food and a habitat for various water-birds. They can also flood various ecosystems on land and may cause extinctions. Creating reservoirs can alter the natural biogeochemical cycle of mercury . After a reservoir's initial formation, there is a large increase in the production of toxic methylmercury (MeHg) via microbial methylation in flooded soils and peat. MeHg levels have also been found to increase in zooplankton and in fish. Dams can severely reduce

306-791: A chain up the valley. Coastal reservoirs are fresh water storage reservoirs located on the sea coast near a river mouth to store the flood water of a river. As the land-based reservoir construction is fraught with substantial land submergence, coastal reservoirs are preferred economically and technically since they do not use scarce land area. Many coastal reservoirs were constructed in Asia and Europe. Saemanguem in South Korea, Marina Barrage in Singapore, Qingcaosha in China, and Plover Cove in Hong Kong are

408-636: A conventional oil-fired thermal generation plant. For instance, In 1990, the impoundment behind the Balbina Dam in Brazil (inaugurated in 1987) had over 20 times the impact on global warming than would generating the same power from fossil fuels, due to the large area flooded per unit of electricity generated. Another study published in the Global Biogeochemical Cycles also found that newly flooded reservoirs released more carbon dioxide and methane than

510-529: A drop of water seep into the ocean without benefiting mankind." He created the reservoir named Parakrama Samudra ("sea of King Parakrama"). Vast artificial reservoirs were also built by various ancient kingdoms in Bengal, Assam, and Cambodia. Many dammed river reservoirs and most bank-side reservoirs are used to provide the raw water feed to a water treatment plant which delivers drinking water through water mains. The reservoir does not merely hold water until it

612-538: A few feet by October 2015 and avoided triggering the drought restrictions. The water level started falling in Spring 2016 and fell below the drought trigger level of 1,075 feet again in May 2016. It fell to a new record low of 1,071.60 feet (326.62 m) on July 1, 2016, before beginning to rebound slowly. Drought restrictions were narrowly avoided again when the lake level rose above 1,075 feet on September 28, 2016, three days before

714-525: A few such coastal reservoirs. Where water is pumped or siphoned from a river of variable quality or size, bank-side reservoirs may be built to store the water. Such reservoirs are usually formed partly by excavation and partly by building a complete encircling bund or embankment , which may exceed 6 km (4 miles) in circumference. Both the floor of the reservoir and the bund must have an impermeable lining or core: initially these were often made of puddled clay , but this has generally been superseded by

816-455: A high-level reservoir is filled with water using high-performance electric pumps at times when electricity demand is low, and then uses this stored water to generate electricity by releasing the stored water into a low-level reservoir when electricity demand is high. Such systems are called pump-storage schemes. Reservoirs can be used in a number of ways to control how water flows through downstream waterways: Reservoirs can be used to balance

918-604: A high-water mark is visible in photos that show the shoreline of Lake Mead. The high-water mark is white because of the deposition of minerals on previously submerged surfaces. Nine main access points to the lake are available. On the west are three roads from the Las Vegas metropolitan area . Access from the north-west from Interstate 15 is through the Valley of Fire State Park and the Moapa River Indian Reservation to

1020-570: A loss in both quantity and quality of water necessary for maintaining ecological balance and pose a risk of increasing severity and duration of droughts due to climate change. In summary, they consider it a misadaptation to climate change. Proponents of reservoirs or substitution reserves, on the other hand, see them as a solution for sustainable agriculture while waiting for a truly durable agricultural model. Without such reserves, they fear that unsustainable imported irrigation will be inevitable. They believe that these reservoirs should be accompanied by

1122-529: A low Glen Canyon release in 2014 – the lowest since 1963, during the initial filling of Lake Powell – in the interest of recovering the level of the upstream reservoir, which had fallen to less than 40% capacity as a result of the drought. Consequently, Lake Mead's level fell significantly, reaching a new record low in 2014, 2015 and 2016. In 2014, its record low was 1,081.82 feet (329.74 m) on July 10, 2014. On June 26, 2015, Lake Mead reached another new record low when it fell to 1,074.71 feet (327.57 m) for

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1224-682: A miniature trout. This silvery minnow gets its name from the sharp spiny rays in its dorsal fin. Virgin spinedace are found only in the Virgin River Basin. Unlike the woundfin and chub, which live only in the Virgin River, spinedace are also found throughout many tributary streams. Virgin Spinedace prefer deep pools and runs and are at home in both clear and turbid water. Flannelmouth sucker ( Catostomus latipinnis ) State conservation species Size: 2.13 ft (64.8 cm) The flannelmouth sucker

1326-419: A narrow valley or canyon may cover relatively little vegetation, while one situated on a plain may flood a great deal of vegetation. The site may be cleared of vegetation first or simply flooded. Tropical flooding can produce far more greenhouse gases than in temperate regions. The following table indicates reservoir emissions in milligrams per square meter per day for different bodies of water. Depending upon

1428-544: A new record monthly low. From mid-May 2011 to January 22, 2012, Lake Mead's water elevation increased from 1,095.5 to 1,134.52 feet (333.91 to 345.80 m) after a heavy snowmelt in the Rocky Mountains prompted the release of an extra 3.3 million acre-feet (4,100,000 ML) from Glen Canyon into Lake Mead. In 2012 and 2013, the Colorado River basin experienced its worst consecutive water years on record, prompting

1530-401: A projected 4.44% curtailment in downstream water delivery. In the area that was chosen to become Lake Mead, native Americans referred to as Ancestral Puebloans settled in the area. Many archaeological sites were submerged by the creation of Lake Mead, including the most representative, which is referred to as the "Lost City". The lake was named after Elwood Mead , who was the commissioner of

1632-592: A reservoir is called the "conservation pool". In the United Kingdom, "top water level" describes the reservoir full state, while "fully drawn down" describes the minimum retained volume. There is a wide variety of software for modelling reservoirs, from the specialist Dam Safety Program Management Tools (DSPMT) to the relatively simple WAFLEX , to integrated models like the Water Evaluation And Planning system (WEAP) that place reservoir operations in

1734-720: A river valley, with the potential to wash away towns and villages and cause considerable loss of life, such as the devastation following the failure of containment at Llyn Eigiau which killed 17 people. (see also List of dam failures ) A notable case of reservoirs being used as an instrument of war involved the British Royal Air Force Dambusters raid on Germany in World War II (codenamed " Operation Chastise " ), in which three German reservoir dams were selected to be breached in order to damage German infrastructure and manufacturing and power capabilities deriving from

1836-574: A territorial project that unites all water stakeholders with the goal of preserving and enhancing natural environments. Two main types of reservoirs can be distinguished based on their mode of supply. Circa 3000 BC, the craters of extinct volcanoes in Arabia were used as reservoirs by farmers for their irrigation water. Dry climate and water scarcity in India led to early development of stepwells and other water resource management techniques, including

1938-566: Is 112 miles (180 km) long, 532 feet (162 m) at its greatest depth, has a surface elevation of 1,229 feet (375 m) above sea level, has a surface area of 247 square miles (640 km), and contains 28.23 million acre-feet (34.82 km) of water. The lake has remained below full capacity since 1983 owing to drought and increased water demand . As of May 31, 2022, Lake Mead held 26.63% of full capacity at 7.517 million acre-feet (9,272,000 megaliters), having dropped in June 2021 below

2040-449: Is a migratory bird that winters in Mexico, Central America, and northern South America. Currently, the breeding range for the flycatcher is similar to the historic range, though much of the riparian habitat in the southwest has been degraded by agricultural practices, invasion of non-native vegetation and urban development. The Southwestern Willow Flycatcher is an insectivore, taking insects from

2142-471: Is a natural lake whose level was raised by a low dam and into which the River Dee flows or discharges depending upon flow conditions, as part of the River Dee regulation system . This mode of operation is a form of hydraulic capacitance in the river system. Many reservoirs often allow some recreational uses, such as fishing and boating . Special rules may apply for the safety of the public and to protect

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2244-545: Is a three-level paddle wheeler certified by the U.S. Coast Guard to carry 275 passengers. It cruises to the Hoover Dam five days a week. At the bottom of the lake is a Boeing B-29 Superfortress that crashed in 1948 while testing a prototype missile guidance system known as "suntracker" . The wreckages of at least two smaller airplanes are submerged in Lake Mead. The 2018 novel Lords of St. Thomas , by Jackson Ellis, tells

2346-480: Is a water reservoir for agricultural use. They are filled using pumped groundwater , pumped river water or water runoff and are typically used during the local dry season. This type of infrastructure has sparked an opposition movement in France, with numerous disputes and, for some projects, protests, especially in the former Poitou-Charentes region where violent demonstrations took place in 2022 and 2023. In Spain, there

2448-437: Is also used technically to refer to certain forms of liquid storage, such the "coolant reservoir" that captures overflow of coolant in an automobile's cooling system. Dammed reservoirs are artificial lakes created and controlled by a dam constructed across a valley and rely on the natural topography to provide most of the basin of the reservoir. These reservoirs can either be on-stream reservoirs , which are located on

2550-399: Is an enlarged lake behind a dam , usually built to store fresh water , often doubling for hydroelectric power generation . Reservoirs are created by controlling a watercourse that drains an existing body of water, interrupting a watercourse to form an embayment within it, excavating, or building any number of retaining walls or levees to enclose any area to store water. The term

2652-424: Is comparable to the capacity of Hoover Dam, and would reduce water lost to evaporation in the covered area by as much as 90%. A 2021 estimate stated that covering 10% of the lake's surface with foam-backed floating photovoltaics could result in "enough water conserved and electricity generated to service Las Vegas and Reno combined." In December 2021, with Lake Mead at 35% of capacity, Arizona, California, Nevada, and

2754-418: Is generally in the range of 9.5 to 9.7 million acre-feet (11,700,000 to 12,000,000 megaliters), resulting in a net annual deficit of about 1.2 million acre-feet (1,500,000 ML). Before the filling of Lake Powell (a reservoir of similar size to Lake Mead) behind Glen Canyon Dam, the Colorado River flowed largely unregulated into Lake Mead, making Mead more vulnerable to drought. From 1953 to 1956,

2856-501: Is greater acceptance because all beneficiary users are involved in the implementation of the system. The specific debate about substitution reservoirs is part of a broader discussion related to reservoirs used for agricultural irrigation, regardless of their type, and a certain model of intensive agriculture. Opponents view these reservoirs as a monopolization of resources benefiting only a few, representing an outdated model of productive agriculture. They argue that these reservoirs lead to

2958-855: Is located at the intersection of three physiographic regions: the Colorado Plateau , the Great Basin , and the Mojave Desert . The exceptional landscapes and habitats of this region harbor unique plant and animal communities and species found nowhere else in the world. Without the water of the Virgin River system, these species could not exist. The Virgin River directly supports hundreds of wildlife species, including woundfin , Virgin River chub, Virgin spinedace, flannelmouth sucker, desert sucker, speckled dace, and Southwestern Willow Flycatcher. Many of these species are endangered or are considered sensitive species within

3060-466: Is needed: it can also be the first part of the water treatment process. The time the water is held before it is released is known as the retention time . This is a design feature that allows particles and silts to settle out, as well as time for natural biological treatment using algae , bacteria and zooplankton that naturally live in the water. However natural limnological processes in temperate climate lakes produce temperature stratification in

3162-528: Is now used by the Aquarius Golf Club. Service reservoirs perform several functions, including ensuring sufficient head of water in the water distribution system and providing water capacity to even-out peak demand from consumers, enabling the treatment plant to run at optimum efficiency. Large service reservoirs can also be managed to reduce the cost of pumping by refilling the reservoir at times of day when energy costs are low. An irrigation reservoir

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3264-418: Is shark-like in both appearance and action as it feeds on small insects in shallow areas along the river. Woundfin live only one to two years, and their survival depends upon sufficient flow within the river, especially during hot summer months. Virgin River chub ( Gila seminuda ) Federally listed endangered species Size: 18 in (46.4 cm) Rare and beautiful, this fish is the top native predator in

3366-541: Is significant. It is nearly usually the case that standing or slowly moving water is present in preferred environments. The destruction of riparian habitats has caused a severe decline in the populations of the southwestern willow flycatcher. Currently, this sub-species exists only in fragmented and scattered locations throughout its range. Historically, the breeding range reached from southern California, southern Nevada, southern Utah, Arizona, New Mexico, western Texas, southwestern Colorado, and northwestern Mexico. The flycatcher

3468-419: Is stored in the reservoir. Any excess water can be spilled via a specifically designed spillway. Stored water may be piped by gravity for use as drinking water , to generate hydro-electricity or to maintain river flows to support downstream uses. Occasionally reservoirs can be managed to retain water during high rainfall events to prevent or reduce downstream flooding. Some reservoirs support several uses, and

3570-427: Is the largest native fish in the Virgin River, growing over two feet in length and weighing over six pounds. The flannelmouth's thick fleshy lips contain taste buds that help it find food along the bottom of the River, including aquatic invertebrates, organic debris and algae. Flannelmouth suckers are usually found in deep sandy areas of the Virgin River, but large numbers congregate in shallow gravel areas for spawning in

3672-466: Is the portion of the reservoir that can be used for flood control, power production, navigation , and downstream releases. In addition, a reservoir's "flood control capacity" is the amount of water it can regulate during flooding. The "surcharge capacity" is the capacity of the reservoir above the spillway crest that cannot be regulated. In the United States, the water below the normal maximum level of

3774-607: The Gila River Indian Community and the Colorado River Indian Tribes which is expected to save an estimated 11 vertical feet of reservoir water. Severe drought lowers the level of the lake, affording social anthropologists opportunities to study indigenous dwellings that were previously submerged. Meanwhile, their forensic colleagues are routinely called in whenever relatively contemporary remains of people are revealed, to investigate scientifically who

3876-457: The Mojave Desert . The Grand Wash is a recreational area located in the north side of the lake. On October 28, 1971, Lake Mead hosted the 1st ever B.A.S.S Bassmaster Classic . This fishing site was a "mystery lake" and the 24 anglers were not told of the location of the tournament until their plane was in the air. The "winner take all" payout of $ 10,000 was won by Bobby Murray of Arkansas. The Desert Princess , operated by Lake Mead Cruises,

3978-610: The National Park Service . The name was changed to the Lake Mead National Recreation Area in 1947, and Lake Mohave and the Shivwits Plateau were later added to its jurisdiction. Both lakes and the surrounding area offer year-round recreation options. The accumulated water from Hoover Dam forced the evacuation of several communities, most notably St. Thomas, Nevada , the last resident of which left

4080-582: The Overton Arm of the lake. The lake is divided into several bodies. The large body closest to the Hoover Dam is Boulder Basin . The narrow channel, which was once known as Boulder Canyon and is now known as The Narrows, connects Boulder Basin to Virgin Basin to the east. The Virgin River and Muddy River empty into the Overton Arm , which is connected to the northern part of the Virgin Basin. The next basin to

4182-448: The Ruhr and Eder rivers. The economic and social impact was derived from the enormous volumes of previously stored water that swept down the valleys, wreaking destruction. This raid later became the basis for several films. All reservoirs will have a monetary cost/benefit assessment made before construction to see if the project is worth proceeding with. However, such analysis can often omit

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4284-636: The U.S. Bureau of Reclamation from 1924 to 1936, during the planning and construction of the Boulder Canyon Project that created the dam and lake. Lloyd Joseph Hudlow, an engineer with the Bureau of Reclamation, came to Boulder City in March 1933 to assist in the survey, and ended up as the project manager. Lake Mead was established as the Boulder Dam Recreation Area in 1936, administered by

4386-464: The U.S. Department of the Interior signed an agreement to spend $ 200 million for 2022 and 2023 to subsidize water users who voluntarily reduce their usage or undertake capital projects to improve efficiency. Along with a variety of state and local regulations, this "500+ Plan" aims to retain an additional 500,000 acre-feet (620,000,000 m) in the reservoir. At the same time an agreement was reached with

4488-646: The 1800s, most of which are lined with brick. A good example is the Honor Oak Reservoir in London, constructed between 1901 and 1909. When it was completed it was said to be the largest brick built underground reservoir in the world and it is still one of the largest in Europe. This reservoir now forms part of the southern extension of the Thames Water Ring Main . The top of the reservoir has been grassed over and

4590-753: The Boulder Basin, the River Mountains , oriented northwest to southeast and the Muddy Mountains , oriented west to northeast. Bonelli Peak lies to the east of the Virgin Basin. Las Vegas Bay is the terminus for the Las Vegas Wash which is the sole outflow from the Las Vegas Valley . Lake Mead receives the majority of its water from snow melt in the Colorado, Wyoming, and Utah Rocky Mountains. Inflows to

4692-512: The Bureau of Reclamation to declare a water shortage in August 2021. On July 28, 2022, the level was 1,040.58 feet (317.17 m), the lowest level since 1937 when the reservoir was initially filled. The lake has rebounded somewhat from its low point in 2022, but its level still remains below the drought threshold as of June 2024. As a result of the decreasing water level, marinas and boat launch ramps have either had to be relocated to another area of

4794-635: The Gripentogs, and Callville Bay (in Callville Bay, NV) and Temple Bar (in Arizona.) The area has many coves with rocky cliffs and sandy beaches. Several small to medium-sized islands occur in the lake area depending on the water level, the largest of which is Oberlink Island. The Alan Bible Visitor Center hosts the Alan Bible Botanical Garden , a small garden of cactus and other plants native to

4896-600: The Lake Mead Marina) and the South Cove launch ramp. Changing rainfall patterns, climate variability, high levels of evaporation, reduced snow melt runoff, and current water use patterns are putting pressure on water management resources at Lake Mead as the population relying on it for water, and the Hoover Dam for electricity, continues to increase. To lower the minimum lake level necessary to generate electricity from 1,050 feet (320 m) to 950 feet (290 m), Hoover Dam

4998-710: The Meroitic town of Butana . The Hafirs catch the water during rainy seasons in order to ensure water is available for several months during dry seasons to supply drinking water, irrigate fields and water cattle. The Great Reservoir near the Lion Temple in Musawwarat es-Sufra is a notable hafir in Kush. In Sri Lanka , large reservoirs were created by ancient Sinhalese kings in order to store water for irrigation. The famous Sri Lankan king Parākramabāhu I of Sri Lanka said "Do not let

5100-825: The North Fork Virgin River, that flows from Navajo Lake through Zion Canyon in Zion National Park. The river flows in a southwesterly direction, passing south of the old townsite of St. George where the Fort Pearce Wash and the Santa Clara River both join the Virgin at a place the Paiutes called Tonaquint. The river then flows across the northwestern corner of Arizona through the Virgin River Gorge and past

5202-476: The Southwest In thick riparian environments around streams, rivers, and other wetlands, flycatchers can be found. The flycatcher breeds in dense, patchy environments made up of medium-sized to towering trees and shrubs at low elevations. It grows in dense populations of riparian bushes that range in height from low to moderate at higher elevations. In particular, the density of vegetation inside 4 m (13 ft)

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5304-589: The State of Utah. The Virgin River Program was established to balance increasing human demand and maintain this unique system. Woundfin ( Plagopterus argentissimus ) Federally listed endangered species Size: 4 in (10.2 cm) One of the rarest species on earth, the endangered woundfin is found only in a small section of the Virgin River. Woundfin have large fins and scale-less, streamlined bodies that help them survive in swift, silty conditions. Although small, it

5406-440: The US. The capacity, volume, or storage of a reservoir is usually divided into distinguishable areas. Dead or inactive storage refers to water in a reservoir that cannot be drained by gravity through a dam's outlet works , spillway, or power plant intake and can only be pumped out. Dead storage allows sediments to settle, which improves water quality and also creates an area for fish during low levels. Active or live storage

5508-801: The Virgin River for part of its length from near St. George to the point it ascended the Mormon Plateau to cross to the Muddy River in present-day Nevada . Its origin is in Southwestern Utah, at the Navajo Reservoir in the Dixie National Forest , north of Zion National Park, and is formed by the confluence of the East Fork Virgin , that flows through Mount Carmel Junction on the east side of Zion National Park and Parunaweap Canyon, with

5610-620: The Virgin River. Chub is a fast, streamlined fish with a sloped forehead, humped back, and thin, rounded tail. The Virgin River chub feeds on small fish, insects, and plant matter. Chub prefer deep pools and runs with boulders and debris for cover. Virgin River chub were once an important food source for Native Americans and early pioneers. Listed as an endangered species, the Virgin River chub is found from Pah Tempe Hot Springs down to Halfway Wash, Nevada. Desert sucker ( Catostomus clarkii ) State of Utah wildlife species of concern Size: 18 in (46.4 cm) The desert sucker gets its name from

5712-438: The air, or picking them from the foliage. The Southwestern Willow Flycatcher is present on breeding grounds by mid-May. By late May, nests are built, usually in a branched tree fork near the water. Typically, three eggs are laid and then incubated for 12–13 days. Virgin spinedace ( Lepidomeda mollispinis mollispinis ) State conservation species Size: 5 in (12.7 cm) The Virgin spinedace looks, feeds, and behaves like

5814-578: The amount of water reaching countries downstream of them, causing water stress between the countries, e.g. the Sudan and Egypt , which damages farming businesses in the downstream countries, and reduces drinking water. Virgin River The first known Euro-American party to encounter the Virgin was led by Jedediah Smith in 1826. Smith named it "Adams River", after then-president John Quincy Adams . Later explorer and mapmaker John C. Fremont reported that it

5916-523: The area flooded versus power produced, a reservoir built for hydro- electricity generation can either reduce or increase the net production of greenhouse gases when compared to other sources of power. A study for the National Institute for Research in the Amazon found that hydroelectric reservoirs release a large pulse of carbon dioxide from decay of trees left standing in the reservoirs, especially during

6018-428: The base of the dam or some distance away. In a flat river valley a reservoir needs to be deep enough to create a head of water at the turbines; and if there are periods of drought the reservoir needs to hold enough water to average out the river's flow throughout the year(s). Run-of-the-river hydro in a steep valley with constant flow needs no reservoir. Some reservoirs generating hydroelectricity use pumped recharge:

6120-547: The building of a reservoir at Girnar in 3000 BC. Artificial lakes dating to the 5th century BC have been found in ancient Greece. The artificial Bhojsagar lake in present-day Madhya Pradesh state of India, constructed in the 11th century, covered 650 square kilometres (250 sq mi). The Kingdom of Kush invented the Hafir , a type of reservoir, during the Meroitic period . 800 ancient and modern hafirs have been registered in

6222-442: The context of system-wide demands and supplies. In many countries large reservoirs are closely regulated to try to prevent or minimize failures of containment. While much of the effort is directed at the dam and its associated structures as the weakest part of the overall structure, the aim of such controls is to prevent an uncontrolled release of water from the reservoir. Reservoir failures can generate huge increases in flow down

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6324-548: The dam located at the narrowest practical point to provide strength and the lowest cost of construction. In many reservoir construction projects, people have to be moved and re-housed, historical artifacts moved or rare environments relocated. Examples include the temples of Abu Simbel (which were moved before the construction of the Aswan Dam to create Lake Nasser from the Nile in Egypt ),

6426-449: The deadline, and the Bureau of Land Reclamation did not issue a shortage declaration. A reprieve from the steady annual decline occurred in 2017, when lake levels rose throughout the year due to heavier than normal snowfall in the Rocky Mountains. As a result of the large snowmelt, the lake regained the water levels it had in 2015 with a seasonal high of 1,089.77 feet (332.16 m). The seasonal low of 1,078.96 feet (328.87 m) in 2017

6528-628: The deceased might have been in life, how they died, and how their bodies got to the lake. For example, the 2020–2023 North American drought caused a series of unexplained human remains to be revealed, prompting speculation about how many more will be discovered as the water level recedes. However, this is not the first time such mysteries have surfaced at Lake Mead: Lake Mead provides many types of recreation to locals and visitors, including boating, fishing, swimming, sunbathing, and water skiing. Four marinas are located on Lake Mead: Las Vegas Boat Harbor and Lake Mead Marina (in Hemenway Harbor, NV) operated by

6630-460: The developed world Naturally occurring lakes receive organic sediments which decay in an anaerobic environment releasing methane and carbon dioxide . The methane released is approximately 8 times more potent as a greenhouse gas than carbon dioxide. As a human-made reservoir fills, existing plants are submerged and during the years it takes for this matter to decay, will give off considerably more greenhouse gases than lakes do. A reservoir in

6732-507: The downstream river to maintain river quality, support fisheries, to maintain downstream industrial and recreational uses or for a range of other purposes. Such releases are known as compensation water . The units used for measuring reservoir areas and volumes vary from country to country. In most of the world, reservoir areas are expressed in square kilometers; in the United States, acres are commonly used. For volume, either cubic meters or cubic kilometers are widely used, with acre-feet used in

6834-400: The east is Temple Basin, and following that is Gregg Basin, which is connected to the Temple Basin by the Virgin Canyon. When the lake levels are high enough, a section of the lake farther upstream from the Gregg Basin is flooded, which includes Grand Wash Bay, the Pearce Ferry Bay and launch ramp, and about 55 miles (89 km) of the Colorado River within the lower Grand Canyon, extending to

6936-440: The environmental impacts of dams and the reservoirs that they contain. Some impacts, such as the greenhouse gas production associated with concrete manufacture, are relatively easy to estimate. Other impacts on the natural environment and social and cultural effects can be more difficult to assess and to weigh in the balance but identification and quantification of these issues is now commonly required in major construction projects in

7038-501: The first 16 years of the 21st century. Of any 16-year period in the last 60 years, 2000-2015 had the lowest water availability. Although Glen Canyon was able to meet its required minimum release until 2014, the water level in Lake Mead has steadily declined. The decreasing water level is due to the loss of the surplus water that once made up for the annual overdraft. In June 2010, the lake was at 39% of its capacity, and on November 30, 2010, it reached 1,081.94 feet (329.78 m), setting

7140-433: The first decade after flooding. This elevates the global warming impact of the dams to levels much higher than would occur by generating the same power from fossil fuels . According to the World Commission on Dams report (Dams And Development), when the reservoir is relatively large and no prior clearing of forest in the flooded area was undertaken, greenhouse gas emissions from the reservoir could be higher than those of

7242-456: The first time since the lake was filled, which risked triggering drought restrictions. If the lake is below the elevation of 1,075 feet at the beginning of the water year, an official shortage declaration by the Bureau of Reclamation will enforce water rationing in Arizona and Nevada. The water year begins October 1 to coincide with seasonal Rocky Mountain snowfall, which produces most of the Colorado River's flow. Lake Mead's water level rebounded

7344-413: The flow in highly managed systems, taking in water during high flows and releasing it again during low flows. In order for this to work without pumping requires careful control of water levels using spillways . When a major storm approaches, the dam operators calculate the volume of water that the storm will add to the reservoir. If forecast storm water will overfill the reservoir, water is slowly let out of

7446-468: The foot of 240 Mile Rapids (north of Peach Springs, Arizona ). In addition, two small basins, the Muddy River Inlet and the Virgin River Basin, are flooded when the lake is high enough where these two rivers flow into the lake. As of February 2015, these basins remain dry. Jagged mountain ranges surround the lake, offering a scenic backdrop, especially at sunset. Two mountain ranges are within view of

7548-580: The hydroelectric reservoirs there do emit greenhouse gases, it is on a much smaller scale than thermal power plants of similar capacity. Hydropower typically emits 35 to 70 times less greenhouse gases per TWh of electricity than thermal power plants. A decrease in air pollution occurs when a dam is used in place of thermal power generation, since electricity produced from hydroelectric generation does not give rise to any flue gas emissions from fossil fuel combustion (including sulfur dioxide , nitric oxide and carbon monoxide from coal ). Dams can produce

7650-556: The lake are largely moderated by the upstream Glen Canyon Dam , which is required to release around 8.23 million acre-feet (10,150,000 Ml) of water each year to Lake Mead under the Colorado River Compact . Releases from Hoover Dam have been over 9 million acre-feet (11,000,000 Ml) of water each year, which has led to declining levels in Lake Mead since 2000. Outflow, which includes evaporation and delivery to Arizona, California, Nevada, and Mexico from Lake Mead

7752-723: The lake or have closed down permanently. The Las Vegas Bay Marina was relocated in 2002 and the Lake Mead Marina was relocated in 2008 to Hemenway Harbor. Overton Marina and Echo Bay Marina have been closed due to low levels in the northern part of the Overton Arm. Government Wash, Las Vegas Bay, and Pearce Ferry boat launch ramps have been closed. Las Vegas Boat Harbor and Lake Mead Marina in Hemenway Harbor/Horsepower Cove remain open, along with Callville Bay Marina, Temple Bar Marina , Boulder Launch Area (former location of

7854-432: The landscape is relatively flat. Other service reservoirs can be storage pools, water tanks or sometimes entirely underground cisterns , especially in more hilly or mountainous country. Modern reserviors will often use geomembrane liners on their base to limit seepage and/or as floating covers to limit evaporation, particularly in arid climates. In the United Kingdom, Thames Water has many underground reservoirs built in

7956-470: The modern use of rolled clay. The water stored in such reservoirs may stay there for several months, during which time normal biological processes may substantially reduce many contaminants and reduce turbidity . The use of bank-side reservoirs also allows water abstraction to be stopped for some time, for instance when the river is unacceptably polluted or when flow conditions are very low due to drought . The London water supply system exhibits one example of

8058-532: The most widespread species in western North America, the speckled dace is found in large numbers throughout the Virgin River and its tributaries. Speckled dace prefer rocky areas but are comfortable living in all habitats and stream sizes. Speckled dace exhibit a kaleidoscope of shapes and colors across their range. Males display bright red "lipstick" and red fins to attract mates during the breeding season. Southwestern Willow Flycatcher ( Empidonax traillii extimus ) Federally listed endangered species The Willow in

8160-593: The new top water level exceeds the watershed height on one or more of the feeder streams such as at Llyn Clywedog in Mid Wales . In such cases additional side dams are required to contain the reservoir. Where the topography is poorly suited to forming a single large reservoir, a number of smaller reservoirs may be constructed in a chain, as in the River Taff valley where the Llwyn-on , Cantref and Beacons Reservoirs form

8262-415: The operating rules may be complex. Most modern reservoirs have a specially designed draw-off tower that can discharge water from the reservoir at different levels, both to access water as the water level falls, and to allow water of a specific quality to be discharged into the downstream river as "compensation water": the operators of many upland or in-river reservoirs have obligations to release water into

8364-428: The original streambed of the downstream river and are filled by creeks , rivers or rainwater that runs off the surrounding forested catchments, or off-stream reservoirs , which receive diverted water from a nearby stream or aqueduct or pipeline water from other on-stream reservoirs. Dams are typically located at a narrow part of a downstream of a natural basin. The valley sides act as natural walls, with

8466-477: The pre-flooded landscape, noting that forest lands, wetlands, and preexisting water features all released differing amounts of carbon dioxide and methane both pre- and post-flooding. The Tucuruí Dam in Brazil (completed in 1984) had only 0.4 times the impact on global warming than would generating the same power from fossil fuels. A two-year study of carbon dioxide and methane releases in Canada concluded that while

8568-437: The quality of the water and the ecology of the surrounding area. Many reservoirs now support and encourage less formal and less structured recreation such as natural history , bird watching , landscape painting , walking and hiking , and often provide information boards and interpretation material to encourage responsible use. Water falling as rain upstream of the reservoir, together with any groundwater emerging as springs,

8670-464: The relocation of the village of Capel Celyn during the construction of Llyn Celyn , and the relocation of Borgo San Pietro of Petrella Salto during the construction of Lake Salto . Construction of a dammed reservoir will usually require the river to be diverted during part of the build, often through a temporary tunnel or by-pass channel. In hilly regions, reservoirs are often constructed by enlarging existing lakes. Sometimes in such reservoirs,

8772-409: The required 8.23 million acre-feet (10,150,000 ML) to Lake Mead each year. That allowed Lake Mead to maintain a high water level despite releasing significantly more water than it is contracted for. Since 2000, the Colorado River has experienced the southwestern North American megadrought , with average or above-average conditions occurring in only five years (2005, 2008–2009, 2011 and 2014) in

8874-627: The reservoir prior to, and during, the storm. If done with sufficient lead time, the major storm will not fill the reservoir and areas downstream will not experience damaging flows. Accurate weather forecasts are essential so that dam operators can correctly plan drawdowns prior to a high rainfall event. Dam operators blamed a faulty weather forecast on the 2010–2011 Queensland floods . Examples of highly managed reservoirs are Burrendong Dam in Australia and Bala Lake ( Llyn Tegid ) in North Wales . Bala Lake

8976-451: The reservoir's previous all-time low of 9.328 million acre-feet (11,506,000 megaliters) recorded in July 2016, and never returning to that level. In a draft 2022 Colorado River annual operating plan, released by the U.S. Bureau of Reclamation , a "Shortage Condition" was expected to be declared for 2022, due to the lake level falling below 1,075 feet (327.7 m), which would have resulted in

9078-530: The spring. Water in the river's lower valley provides irrigation for the cultivation of cotton , pomegranates , and figs . The Nevada river valley's significance is commemorated by Nevada Historical Marker 56. The scenic Virgin River Gorge is in northwest Arizona just south of the Utah state line. It is a popular winter rock climbing area noted for its steep and overhanging limestone walls. Interstate 15 follows

9180-414: The story of the last family to vacate the flooded town of St. Thomas in 1938, following construction of the Hoover Dam and creation of Lake Mead. Lake Mead, Hoover Dam, and the wrecked B-29 play a large role in the setting of the video game Fallout: New Vegas . Reservoir A reservoir ( / ˈ r ɛ z ər v w ɑːr / ; from French réservoir [ʁezɛʁvwaʁ] )

9282-439: The town in 1938. The ruins of St. Thomas are currently visible (as of May 23, 2022) via dirt road and hiking trail, due to Lake Mead's low water level. Lake Mead also covered the sites of the Colorado River landings of Callville and Rioville, Nevada , and the river crossing of Bonelli's Ferry , between Arizona and Nevada. Six years after the dam's construction, the lake filled to an elevation of 1200 feet. At lower water levels,

9384-491: The towns of Beaver Dam and Littlefield . It enters southern Nevada near the town of Mesquite and empties into the Colorado at the Lake Mead reservoir, approximately 40 miles (64 km) east of Las Vegas . The last 30 miles (48 km) of the Virgin River forms the north arm of Lake Mead. Despite flowing through an arid region, the Virgin River is home to a surprisingly diverse array of plants and animals. Southwestern Utah

9486-493: The use of bank-side storage: here water is taken from the River Thames and River Lee into several large Thames-side reservoirs, such as Queen Mary Reservoir that can be seen along the approach to London Heathrow Airport . Service reservoirs store fully treated potable water close to the point of distribution. Many service reservoirs are constructed as water towers , often as elevated structures on concrete pillars where

9588-413: The water level fell from 1,200 to 1,085 feet (366 to 331 m). During the filling of Lake Powell from 1963 to 1965, the water level fell from 1,205 to 1,090 feet (367 to 332 m). Many wet years from the 1970s to the 1990s filled both lakes to capacity, reaching a record high of 1,225 feet (373 m) in the summer of 1983. In these decades prior to 2000, Glen Canyon Dam frequently released more than

9690-399: The water level stood at 1,096.39 feet (334.18 m), again benefiting from above average mountain snowpack (107% of average). From 2018 to early-2021, Lake Mead water levels remained well above the 1,075-foot (328 m) level that would trigger a shortage determination. However, by mid-2021 its level fell below the trigger elevation and was projected to keep falling through 2022, which led

9792-412: The water, which tends to partition some elements such as manganese and phosphorus into deep, cold anoxic water during the summer months. In the autumn and winter the lake becomes fully mixed again. During drought conditions, it is sometimes necessary to draw down the cold bottom water, and the elevated levels of manganese in particular can cause problems in water treatment plants. In 2005, about 25% of

9894-516: The way it feeds on aquatic vegetation and insects. It uses its thick cartilaginous lips to scrape and suck food from rocks and boulders along the bottom of the river. Desert Suckers are very colorful during the spring spawning season, developing bright orange and black 'racing stripes' along their sides. Desert suckers are considered a sensitive species in Utah, where they are only found in the Virgin River and its tributaries. Speckled dace ( Rhinichthys osculus ) Size: 4 in (10.2 cm) One of

9996-476: The world's 33,105 large dams (over 15 metres in height) were used for hydroelectricity. The U.S. produces 3% of its electricity from 80,000 dams of all sizes. An initiative is underway to retrofit more dams as a good use of existing infrastructure to provide many smaller communities with a reliable source of energy. A reservoir generating hydroelectricity includes turbines connected to the retained water body by large-diameter pipes. These generating sets may be at

10098-444: Was called "Rio Virgen" but did not state the origin of the name. Hiram Chittenden speculated that Smith had later renamed the river after Thomas Virgin, who was badly wounded in an 1827 attack by Mohave people during the crossing of the Mojave Desert . Virgin recovered from his wounds but was later killed, along with most of Smith's companions, in an attack by Umpqua people (in present-day Oregon). The Old Spanish Trail followed

10200-717: Was close to that experienced in 2014, safely above the drought trigger. That level was still 36 feet (11 m) below the seasonal low experienced in 2012, and the lake was projected to begin falling again in 2018. Despite those and other predictions of an impending shortage determination by 2020, snowpack of 140% of average in the Upper Colorado River basin as of April 2019 resulted in 128% above average inflow into Lake Powell, resulting in 1,090.20-foot (332.29 m) water level on Lake Mead. In December 2019, Lake Mead water level reached 1,090.47 feet (332.38 m), about ten feet (three meters) above projections. As of April, 2020,

10302-500: Was retrofitted with wide-head turbines, designed to work efficiently with less flow in 2015 and 2016. If water levels continue to drop, Hoover Dam would cease generating electricity when the water level falls below 950 feet (290 m) and the lake would stabilize at a level of 895 feet (273 m) when the water reaches the lowest water outlet of the dam. In order to ensure that the city of Las Vegas will continue to be able to draw its drinking water from Lake Mead, nearly $ 1.5 billion

10404-438: Was spent on building a new water intake tunnel in the middle of the lake at the elevation of 860 feet (260 m). The 3-mile (4.8 km) tunnel took seven years to build under the lake and was put into operation in late 2015. According to a 2016 estimate, about 6% of Lake Mead's water evaporates annually. Covering 6 percent of Lake Mead with floating photovoltaics has a potential generating capacity of 3,400 megawatts, which

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