The classification of a reservoir by volume is not as straightforward as it may seem. As the name implies, water is held in reserve by a reservoir so it can serve a purpose. For example, in Thailand, reservoirs tend to store water from the wet season to prevent flooding, then release it during the dry season for farmers to grow rice. For this type of reservoir, almost the entire volume of the reservoir functions for the purpose it was built. Hydroelectric power generation, on the other hand, requires many dams to build up a large volume before operation can begin. For this type of reservoir only a small portion of the water held behind the dam is useful. Therefore, knowing the purpose for which a reservoir has been constructed, and knowing how much water can be used for that purpose, helps determine how much water is in possible reserve.
The following terms are used in connection with the volume of reservoirs:
The list below largely ignores many natural lakes that have been augmented with the addition of a relatively minor dam. For example, a small dam, two hydroelectric plants, and locks on the outlet of Lake Superior make it possible to artificially control the lake level. Certainly, the great majority of the lake is natural. However, the control of water that can be held in reserve means a portion of the vast lake functions as a reservoir.
Recognition of lakes like Lake Superior greatly changes the list below. For example, the Francis H. Clergue Generating Station and Saint Marys Falls Hydropower Plant, which are both on the lake's outlet, operate with just 5.9 meters total head. This is short compared to other dams. However, when viewed against the 81,200 km2 area of the lake, even a small range in Lake Superior's water level means its active volume is greater than the largest nominal in the table below.
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability. Hydropower is often used in conjunction with dams to generate electricity. A dam can also be used to collect or store water which can be evenly distributed between locations. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions.
Hydroelectricity, or hydroelectric power, is electricity generated from hydropower. Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and also more than nuclear power. Hydropower can provide large amounts of low-carbon electricity on demand, making it a key element for creating secure and clean electricity supply systems. A hydroelectric power station that has a dam and reservoir is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand. Once a hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably less greenhouse gas than fossil fuel-powered energy plants. However, when constructed in lowland rainforest areas, where part of the forest is inundated, substantial amounts of greenhouse gases may be emitted.
A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure that water does not damage parts of the structure not designed to convey water.
New Melones Dam is an earth and rock filled embankment dam on the Stanislaus River, about 5 miles (8.0 km) west of Jamestown, California, United States, on the border of Calaveras County and Tuolumne County. The water impounded by the 625-foot-tall (191 m) dam forms New Melones Lake, California's fourth-largest reservoir, in the foothills of the Sierra Nevada east of the San Joaquin Valley. The dam serves mainly for irrigation water supply, and also provides hydropower generation, flood control, and recreation benefits.
Dworshak Dam is a concrete gravity dam in the western United States, on the North Fork of the Clearwater River in north central Idaho. In Clearwater County, the dam is located approximately four miles (6 km) northwest of Orofino and impounds the Dworshak Reservoir for flood control and hydroelectricity generation.
A reservoir is an enlarged lake behind a dam. Such a dam may be either artificial, usually built to store fresh water, or it may be a natural formation.
Nagarjuna Sagar Dam is a masonry dam across the Krishna River at Nagarjuna Sagar which straddles the border between Palnadu district in Andhra Pradesh and Nalgonda district in Telangana. The dam provides irrigation water to the districts of Palnadu, Guntur, Nalgonda, Prakasam, Khammam, Krishna, and parts of West Godavari. It is also a source of electricity generation for the national grid.
Theodore Roosevelt Dam is a dam on the Salt River located northeast of Phoenix, Arizona. The dam is 357 feet (109 m) high and forms Theodore Roosevelt Lake as it impounds the Salt River. Originally built between 1905 and 1911, the dam was renovated and expanded in 1989–1996. The dam is named after President Theodore Roosevelt. Serving mainly for irrigation, water supply, and flood control, the dam also has a hydroelectric generating capacity of 36 megawatts.
The Lipno Reservoir is a dam and hydroelectric plant constructed along the Vltava River in the Czech Republic. It is the largest water area in the Czech Republic.
Lake Qaraoun is an artificial lake or reservoir located in the southern region of the Beqaa Valley, Lebanon. It was created near Qaraoun village in 1959 by building a 61 m-high (200 ft) concrete-faced rockfill dam in the middle reaches of the Litani River. The reservoir has been used for hydropower generation, domestic water supply, and for irrigation of 27,500 ha.
Ujjani Dam, also known as Bhima Dam or Bhima Irrigation Project, on the Bhima River, a tributary of the Krishna River, is an earthfill cum Masonry gravity dam located near Ujjani village of Madha Taluk in Solapur district of the state of Maharashtra in India.
Aliyar ( Reservoir is a 6.48 km2 reservoir located in Aliyar village near Pollachi town in Coimbatore District, Tamil Nadu, South India. The dam is located in the foothills of Valparai, in the Anaimalai Hills of the Western Ghats. It is about 65 kilometres from Coimbatore. The dam offers some ideal getaways including a park, garden, aquarium, play area and a mini Theme-Park maintained by Tamil Nadu Fisheries Corporation for visitors enjoyment. The scenery is beautiful, with mountains surrounding three quarters of the reservoir. Boating is also available.
The Gilgel Gibe III Dam is a 250m high roller-compacted concrete dam with an associated hydroelectric power plant on the Omo River in Ethiopia. It is located about 62 km (39 mi) west of Sodo in the Southern Nations, Nationalities, and Peoples' Region. Once fully commissioned, it will be the third largest hydroelectric plant in Africa with a power output of about 1,870 Megawatt (MW), thus more than doubling total installed capacity in Ethiopia from its 2007 level of 814 MW. The Gibe III dam is part of the Gibe cascade, a series of dams including the existing Gibe I dam and Gibe II power station as well as the planned Gibe IV and Gibe V dams. The existing dams are owned and operated by the state-owned Ethiopian Electric Power, which is also the client for the Gibe III Dam.
The Oker Dam is a dam in the Harz mountains in Lower Saxony, Germany. It is fed by the River Oker.
The Longyangxia Dam is a concrete arch-gravity dam at the entrance of the Longyangxia canyon on the Yellow River in Gonghe County, Qinghai Province, China. The dam is 178 metres (584 ft) tall and was built for the purposes of hydroelectric power generation, irrigation, ice control and flood control. The dam supports a 1,280 MW power station with 4 x 320 MW generators that can operate at a maximum capacity of 1400 MW. Controlling ice, the dam controls downstream releases to reservoirs lower in the river, allowing them to generate more power instead of mitigating ice. Water in the dam's 24.7 billion m3 reservoir provides irrigation water for up to 1,000,000 hectares of land.
Zengwen Dam, also spelled Tsengwen Dam, is a major earthen dam in Dapu Township, Chiayi County, Taiwan on the Zengwen River. It is the third tallest dam in Taiwan, and forms Zengwen Reservoir (曾文水庫), the biggest reservoir in Taiwan by volume. The dam stores water for irrigation of the Chianan Plain, Taiwan's most productive agricultural region, and provides flood control along the Zengwen River which flows through Tainan City. The dam supports a 50 megawatt hydroelectric power station.
The Shin-Takasegawa Pumped Storage Station (新高瀬川発電所) uses the Takase River to operate a pumped storage hydroelectric scheme about 12 kilometres (7.5 mi) west of Ōmachi in Nagano Prefecture, Japan. Part of the system is within Chūbu-Sangaku National Park.
The Koteshwar Dam is a gravity dam on the Bhagirathi River, located 22 km (14 mi) downstream of the Tehri Dam in Tehri District, Uttarakhand, India. The dam is part of the Tehri Hydropower Complex and serves to regulate the Tehri Dam's tailrace for irrigation and create the lower reservoir of the Tehri Pumped Storage Power Station. In addition, the dam has a 400 MW run-of-the-river power station. The project was approved in 2000 and its first generator was commissioned on 27 March 2011, the second on 30 March 2011. The construction site had been inundated in September 2010 by floods. The diversion tunnel was later blocked heaving/collapse of the hill in December 2010. The spillway was commissioned in Jan, 2011. The last two generators were made operational in March 2012.
The Kishanganga Hydroelectric Project is a run-of-the-river hydroelectric scheme in Jammu and Kashmir, India. Its dam diverts water from the Kishanganga River to a power plant in the Jhelum River basin. It is located near Dharmahama Village, 5 km (3 mi) north of Bandipore in the Kashmir valley and has an installed capacity of 330 MW.
