Hydroelectric in the context of "Dam failure"

A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ventilation openings at various points along the length. A pipeline differs significantly from a tunnel, though some recent tunnels have used immersed tube construction techniques rather than traditional tunnel boring methods.

A tunnel may be for foot or vehicular road traffic, for rail traffic, or for a canal. The central portions of a rapid transit network are usually in the tunnel. Some tunnels are used as sewers or aqueducts to supply water for consumption or for hydroelectric stations. Utility tunnels are used for routing steam, chilled water, electrical power or telecommunication cables, as well as connecting buildings for convenient passage of people and equipment.

The Kura, also known in Georgian as Mtkvari (Georgian: მტკვარი, romanized: mt'k'vari [ˈmt'k'ʷäɾi]), is an east-flowing transboundary river south of the Greater Caucasus Mountains which drains the southern slopes of the Greater Caucasus east into the Caspian Sea. It also drains the north side of the Lesser Caucasus, while its main tributary, the Aras, drains the south side of those mountains. Starting in northeastern Turkey, the Kura flows through to Georgia, then into Azerbaijan, where it receives the Aras as a right tributary, and finally enters the Caspian Sea. The total length of the river is 1,515 kilometres (941 mi).

People have inhabited the Caucasus region for thousands of years and first established agriculture in the Kura Valley over 4,500 years ago. Large, complex civilizations eventually grew on the river, but by 1200 CE most were reduced to ruin by natural disasters and foreign invaders. The increasing human use, and eventual damage, of the watershed's forests and grasslands, contributed to a rising intensity of floods through the 20th century. In the 1950s, the Soviet Union started building many dams and canals on the river. Previously navigable up to Tbilisi in Georgia, the Kura is now much slower and shallower, having been harnessed by irrigation projects and hydroelectric power stations. The river is now moderately polluted by major industrial centers like Tbilisi and Rustavi in Georgia.

The Three Gorges Dam, officially known as Yangtze River Three Gorges Water Conservancy Project is a hydroelectric gravity dam that spans the Yangtze River near Sandouping in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The world's largest power station by installed capacity (22,500 MW), the Three Gorges Dam generates 95±20 TWh of electricity per year on average, depending on the amount of precipitation in the river basin. After the monsoons of 2020, the dam produced nearly 112 TWh in a year, breaking the record of 103 TWh set by the Itaipu Dam in 2016.

The dam's body, 185 meters high and 2,309 meters wide, was completed in 2006. The power plant became fully operational in 2012, when the last of the 32 main water turbines in the underground plant began production. The last major component of the project, the ship lift, was completed in 2015.

This article provides a list of the largest hydroelectric power stations by generating capacity. Only plants with capacity larger than 3,000 MW are listed.

The Three Gorges Dam in Hubei, China, has the world's largest instantaneous generating capacity at 22,500 MW of power. In second place is the Baihetan Dam, also in China, with a capacity of 16,000 MW. The Itaipu Dam in Paraguay and Brazil is the third largest with 14,000 MW of power. Despite the large difference in installed capacity between Three Gorges Dam and Itaipu Dam, they generate nearly equal amounts of electrical energy during the course of an entire year – Itaipu 103 terawatt-hours (370 PJ) in 2016 and Three Gorges 111.8 TWh (402 PJ) in 2020, because the Three Gorges experiences six months per year when there is very little water available to generate power, while the Paraná River continuously feeds the Itaipu with an ample supply of water year-round.

Pumped-storage hydroelectricity (PSH), or pumped hydroelectric energy storage (PHES), is a type of hydroelectric energy storage used by electric power systems for load balancing. A PSH system stores energy in the form of gravitational potential energy of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost surplus off-peak electric power is typically used to run the pumps. During periods of high electrical demand, the stored water is released through turbines to produce electric power.

Pumped-storage hydroelectricity allows energy from intermittent sources (such as solar, wind, and other renewables) or excess electricity from continuous base-load sources (such as coal or nuclear) to be saved for periods of higher demand.The reservoirs used with pumped storage can be quite small, when contrasted with the lakes of conventional hydroelectric plants of similar power capacity, and generating periods are often less than half a day.

The Arda (Bulgarian: Арда [ˈardɐ], Greek: Άρδας [ˈarðas], Turkish: Arda [ˈaɾda]) is a 290-kilometre-long (180 mi) river in Bulgaria and Greece. It is a tributary of the Maritsa (or Evros). Its source lies in the Bulgarian Rhodope Mountains near the village Arda, part of the municipality of Smolyan. It flows eastward past Rudozem, Kardzhali and Ivaylovgrad and enters Greece in the northern part of the Evros regional unit. It flows into the Maritsa on the border of Greece and Turkey, between the Greek village Kastanies and the Turkish city Edirne. In the Bulgarian section, there are three hydroelectric and irrigation dams, Kardzhali Dam, Studen Kladenets and Ivaylovgrad Dam. The Bulgarian section is 229 kilometres (142 mi) long, making the Arda the longest river in the Rhodopes. The medieval Dyavolski most arch bridge crosses the river 10 kilometres (6 mi) from Ardino.

The three floods of February 18, 2005, when the water level was at 4.8 metres (16 ft), March 1 and March 7, 2005, flooded the low-lying areas, especially the Kastanies area which turned into a lagoon. The merging of the waters of the Maritsa (Evros/Meriç) caused streets and buildings including homes to be flooded, leaving people stranded in their homes.

Grand Coulee Dam is a concrete gravity dam on the Columbia River in the U.S. state of Washington, built to produce hydroelectric power and provide irrigation water. Constructed between 1933 and 1942, Grand Coulee originally had two powerhouses. The third powerhouse ("Nat"), completed in 1974 to increase energy production, makes Grand Coulee the largest power station in the United States by nameplate capacity at 6,809 MW.

The proposal to build the dam was the focus of a bitter debate during the 1920s between two groups. One group wanted to irrigate the ancient Grand Coulee with a gravity canal while the other pursued a high dam and pumping scheme. The dam supporters won in 1933, but, although they fully intended otherwise, the initial proposal by the Bureau of Reclamation was for a "low dam" 290 feet (88 m) tall which would generate electricity without supporting irrigation. That year, the U.S. Bureau of Reclamation and a consortium of three companies called MWAK (Mason-Walsh-Atkinson Kier Company) began construction on a high dam, although they had received approval for a low dam. After visiting the construction site in August 1934, President Franklin Delano Roosevelt endorsed the "high dam" design, which at 550 ft (168 m) high would provide enough electricity to pump water into the Columbia basin for irrigation. Congress approved the high dam in 1935, and it was completed in 1942. The first waters overtopped Grand Coulee's spillway on June 1 of that year.

Distributed generation, also distributed energy, on-site generation (OSG), or district/decentralized energy, is electrical generation and storage performed by a variety of small, grid-connected or distribution system-connected devices referred to as distributed energy resources (DER).

Conventional power stations, such as coal-fired, gas, and nuclear powered plants, as well as hydroelectric dams and large-scale solar power stations, are centralized and often require electric energy to be transmitted over long distances. By contrast, DER systems are decentralized, modular, and more flexible technologies that are located close to the load they serve, albeit having capacities of only 10 megawatts (MW) or less. These systems can comprise multiple generation and storage components; in this instance, they are referred to as hybrid power systems.