Dam

This article is about structures for water impoundment. For other uses, see Dam (disambiguation).

A dam is a structure that impounds or restricts the flow of water. Dams are classified into four basic types: gravity dams are massive structures made of concrete or masonry that rely on their weight to resist the force of impounded water. Embankment dams are large earthworks consisting of rocks, clay, sand, soil, or gravel. Buttress dams consist of a sloped, concrete face supported on the downstream side by a series of triangular buttresses. Arch dams use a curved concrete wall to redirect the force of the water outwards into the surrounding valley walls.

Dams provide for irrigation, hydropower, water supply, flood management, recreation, inland navigation, and fish farming. Irrigation is a critical application of dams: about 20% of the world's arable land is irrigated by water that originated in reservoirs impounded by dams. Dams generate hydropower, providing a clean and renewable source of electricity, and also supply water for household and industrial needs. Dams that support flood management reduce downstream water levels to a safe limit.

An early dam was the Jawa Dam in modern Jordan, built around 3000 BCE. The Hittite Empire built several dams in modern Turkey between the 17th and 13th centuries BCE. By the first century CE, the Roman Empire began building masonry gravity dams – typically with vertical faces on both upstream and downstream sides. In medieval Europe, dams powered water wheels for milling and mining. The process of designing dams began to transform in the late 18th century from an informal practice to an engineering discipline rooted in science. In the 20th century, the widespread availability of concrete and heavy construction machinery led to the creation of many large-scale dam projects worldwide. Organized opposition to dam projects emerged in the modern era, including protests in the 1870s against the Thirlmere Dam in Britain.

Dams are often a component of a larger project. Many dams incorporate power plants that run water through generators to produce electricity. Spillways are often included to safely release excess reservoir water downstream and prevent catastrophic overflows. Dam outlets are structures which permit the reservoir to be partially drained to purge sediment, generate electricity, or increase water flow downstream. When a dam blocks a navigable river, locks may be incorporated into the project to allow ships to pass through.

Dams occasionally fail, resulting in flooding and loss of life. Many principles governing the design of safe dams have been developed based on lessons learned from dam failures. Dams can fail for many reasons: earthquakes, weak rocks at the abutments, water leaking within or under the dam, or the dam sliding over its foundation. Beyond structural issues, dams also present political challenges caused by water scarcity, population growth, and the impacts of climate change. Dams built in countries such as Turkey, India, Ethiopia, and China have led to international disputes with downstream nations.

Etymology

The English word "dam" is found in Middle English, and traces back to the word dam in the Germanic languages Middle Low German, Middle Dutch, and Old Norse. The word's roots include Gothic faur-dammjan ('to stop up'), and the Indo-European base *dhē- ('to set, put in place').

Types

Dams can be classified by their structural type: embankment, gravity, buttress, and arch. Other forms include composite dams and rockslide dams.

Embankment dam

Main article: Embankment dam

Embankment dams

Many embankment dams have a clay core and gradually sloping faces both upstream and downstream.

The Misogawa Dam is an embankment dam in Japan.

The most common type of dam is an embankment dam. These consist of a pile of earth (rocks, clay, sand, gravel, or soil) formed into the shape of a large levee with a broad trapezoidal cross-section. Embankment dams are categorized as rockfill or earthfill – depending on the primary material used in construction.

Embankment dams can be built from locally available materials, which tend to make them less expensive to build than concrete dams requiring imported rocks and cement. They can also be built on softer soils because their broad base spreads their weight over a greater area (as opposed to heavy gravity dams that require bedrock foundations).

The primary drawback to embankment dams is that they are inherently porous, so water can seep through or underneath the dam. Mitigation techniques to reduce seepage include placing a drainage system underneath the dam, injecting grout into the soil below the dam, and including a vertical layer of impervious material within the dam. If an impervious layer is included, it may be made of clay, cement, or asphalt. Failure to properly mitigate seepage can lead to dam failure caused by "piping" – water starts to flow through (or under) the dam in a small channel, which gradually enlarges until a large hole is pierced in the dam.

Early embankment dams were often built of a single type of earth, but starting in the mid-16th century, engineers began to use several types of material layered in zones. A typical zone pattern is a clay center (a vertical wall, extending from the riverbed to the crest of the dam), with gradually sloping banks of soil on both upstream and downstream sides, and both faces covered with large rocks. Large rocks on the upstream face protect the structure from wave action. The resistance to water seepage varies widely among the various materials: clay resists water seepage 10 times more than silt, 10,000 times more than sand, and 100 million times more than gravel. In the 1970s, the Concrete Face Rockfill Dam (CFRD) design was invented, which is a rock-filled embankment dam with concrete slabs on the upstream face, sealed with waterproof joints.

Gravity dam

Main article: Gravity dam

Gravity dams

A typical gravity dam has a nearly vertical upstream face, and a broad base.

The Grande Dixence Dam in Switzerland is one of the world's tallest gravity dams. The people atop the dam's crest illustrate its size.

Gravity dams rely on their weight to resist the force of upstream waters. Historically, gravity dams were built of masonry (stone, brick, or rubble) with mortar filling the joints but nearly all modern examples are made of concrete. The cost of concrete is much higher than dirt or rocks, so concrete gravity dams are generally more expensive than embankment or buttress dams. An approach to reduce cost is to incorporate large hollow chambers inside the dam – provided the dam's stability and strength is not compromised.

The crest (top) of a gravity dam is generally a straight line stretching between the walls of the valley it crosses. When the crest is curved (the convex side of the curve always faces upstream), it is called an arch-gravity dam (discussed below). The cross-section of gravity dams is roughly triangular, with a flat bottom resting on the valley floor, and two inclined faces (upstream and downstream) that meet at the crest. To ensure that the dam is stable and will not tip over, the profile must conform to the middle-third rule, which states that the forces acting on the dam (gravity, water pressure, etc) must produce a net force that is directed at the middle portion of the base (rather than directed near the downstream edge of the base). The thickness and inclination of a gravity dam must also be carefully designed to ensure stability. The thickness of the base should be 70 to 85% of the height. The inclination (steepness, measured as run/rise) of the downstream face is typically 0.75 to 0.8, and the upstream face should be more vertical than the downstream face.

Because gravity dams are so heavy, they must rest on bedrock; a gravity dam built over soil would compress the soil, cause the dam to settle, and perhaps crack and fail. If the bedrock has cracks or defects, it must be prepared by injecting grout or placing concrete plugs. A concern that designers must address is "uplift": if water seeps under the dam structure, the water pressure can apply extreme upward force on the dam structure, which may lead to leaks or even dam failure. This risk can be mitigated with the use of grout curtains under the dam (which prevent water from seeping under the dam) and drainage systems under the dam, which lead water away when pressure increases.

Buttress dam

Main article: Buttress dam

Buttress dams

A buttress dam has an inclined upstream face supported by multiple buttresses.

About 20 buttresses are visible in this photo of the Latyan buttress dam in Iran.

A buttress dam consists of a flat upstream face supported on the downstream side by numerous triangular buttresses. Most buttress dams are made of concrete. Unlike a gravity dam (where the upstream face is nearly vertical) the upstream face of a buttress dam is sloped, typically with an inclination between 0.3 and 1.0. The slant is required so the force of the upstream reservoir pushes downward onto the dam, forcing it into the ground and increasing its stability (in contrast to gravity dams, where the dam's weight alone is sufficient to remain immobile).

Buttress dams use much less concrete than comparable gravity dams, but the cost savings are offset by a more complex construction process. Buttress dams are not as strong as gravity dams, and are suited only for lower heights. Because buttress dams have a much smaller footprint (the area of ground the dam structure rests upon) than gravity dams, the risks associated with uplift forces (from water beneath the dam) are lower in buttress dams.

The individual buttresses may experience slight movements relative to each other. If the upstream face of the dam were a solid piece of concrete, the movements of the buttresses could introduce large stresses, resulting in cracking of the upstream dam face. To mitigate this, the upstream face is divided into multiple pieces, one per buttress, called the "buttress heads". Adjacent buttress heads are typically separated by a gap, and the gaps are filled with flexible seals.

Arch dam

Main article: Arch dam

Arch dams

Arch dams transmit the weight of impounded water into the valley walls.

This arch dam in Tasmania has a double curved shape, which is a recent innovation.

An arch dam is a curved dam that transfers the force of the impounded water to the valley walls (in contrast to gravity or buttress dams, which transfer the force to the foundation below the dam). Arch dams can only be built at built at a location where the valley is relatively narrow and has strong, steep rock walls. Arch dams are relatively thin: the thickness of their base is less than half their height. They are always made of concrete or masonry. The central angle subtended by an arch dam can be relatively shallow or nearly semicircular: arch dams exist with central angles from 46 degrees to 140 degrees.

All arch dams are curved, but there are a variety of shapes they may assume. Most older arch dams used a "constant radius" shape, which resembles a section of a vertical cylinder. A more complex shape is the "constant angle" shape, which gradually reduces radius from the crest to the base. Research into optimizing dam shapes for maximum strength led dam engineers to adopt the constant angle shape for many arch dams, beginning in 1914. Another shape is "double curved", which resembles a section of a dome and is defined by incorporating curvature in the vertical – as well as horizontal – direction.

Regardless of the shape of an arch dam's curvature, the dam must transfer the weight of the reservoir water into the valley walls. Tremendous forces are passed from the dam into the valley walls where they meet, so the valley walls must consist of strong rock. In some dams, concrete abutments must be constructed between the dam's arch and the valley walls to safely transfer the load.

Other dam structures

Composite dam structures

The Sayano-Shushenskaya Dam in Russia is an example of an arch-gravity dam.

Bartlett Dam in the US is a multiple-arch dam.

Some dams combine features from two of the basic dam structures. An arch-gravity dam combines features from arch dams and gravity dams: the overall shape is an arch, but it is not a true arch dam because the thickness of the dam's base is more than half of its height – giving it a weight and footprint that is characteristic of gravity dams.

A multiple-arch dam combines features of arch dams with buttress dams. It is similar to a buttress dam, but the upstream face is not flat – rather, the face consists of a number of small arch dams: each arch connects one pair of adjacent buttresses.

A barrage is a low dam that has a wide spillway integrated into dam structure, with multiple gates regulating the flow over the spillway. Dikes and levees – which share the same design as embankment dams – are not true dams because they generally line the banks of a river or sea, whereas dams are placed crosswise in a valley.

Rockslide dams

The Usoi Dam is a rockslide dam formed in 1911 by an earthquake. At 567 m (1,860 ft) high, it is one of the tallest dams in the world.

A rockslide dam is a natural dam formed by a rockslide that slides into a valley and blocks the flow of a river, forming a lake on the upstream side. There are thousands of rockslide dams around the world, including one created in 2010 in Pakistan that formed Attabad Lake. Rockslide dams have the potential to cause catastrophic loss of life, if they fail and create an outburst flood. In 1786 in China, an earthquake created a rockslide dam on the Dadu River, which failed ten days later, killing 100,000 people. Risks of outburst floods can be mitigated by building spillways on rockslide dams to lower the water level. Engineers have used rockslide dams as foundations upon which to build new dams. Rarely, engineers have used blasting on mountainsides to trigger a rockslide and create a crude embankment dam, called a "blast-fill" dam. Not all natural dams are created by rockslides: volcanic dams are the result of volcanic activity, which can create dams from lava flows, lahar deposits, pyroclastic flows, or other debris.

Uses

Primary purposes

Number of large dams, globally, by purpose.

The main purposes that dams serve include irrigation, hydropower, water supply, flood management, recreation, inland navigation, and fish farming. Many dams – called "multi-purpose dams" – support two or more of these primary purposes.

Irrigation is a critical application of dams: about 20% of the world's arable land is irrigated by water that originated in reservoirs impounded by dams (as of 2022). In addition to directly moving water from the reservoir to irrigation canals, dams can also support irrigation by "dry-season releases": the dam impounds water during the wet season, and releases it downstream into the river during the dry season, thus ensuring water in the river year-round.

Hydropower provides clean, renewable energy in the form of hydroelectricity. As of 2022, global hydropower capacity accounted for about 20% of the world's electricity supply. More than 80% of the world's reservoir water storage capacity is used to generate hydropower. Hydropower dams can act as an annual buffering system: the reservoir can be filled during the rainy season, then during the dry season (when it is typically hotter and electricity is needed to run air conditioning systems) the water can be released to generate electricity.

Some hydropower dams provide a pumped-storage capability: such dams can consume excess electricity (for example, from solar power on a sunny day) to drive pumps that lift water from a low reservoir to a higher reservoir. When the electrical grid needs more power (for example, on a cloudy day) the water can be released to power the dam's generators to create hydroelectricity. A pumped-storage capability can also be used in a 24-hour cycle: during the night, when community use of electricity is low, conventional power sources (nuclear, oil) can power pumps to lift water into reservoirs; then – during the peak consumption hours in daytime – the water can be released through the dam's generators to generate electricity.

In 2025, there were 3,394 large dams that supplied water for domestic or industrial use. Industrial usage is about twice domestic usage, but some of the water withdrawn from reservoirs (such as water used solely for cooling purposes) is returned to the river system.

Flood management is an important function of many dams. In 2025, there were 2,510 large dams in the world devoted to flood management. These dams do not try to prevent all floodwaters from reaching downstream, instead they try to reduce the peak flood level (height) to a safe limit. Since floods are so unpredictable, these goals are typically expressed as statistical margins based on lengthy return periods. For example, a dam may be designed with the goal of safely regulating 1-in-100 year floods.

Many dams are built on rivers for the purpose of keeping the water level sufficiently high to support transportation, including barges that carry freight. These dams are typically low, and are found in countries that have industries that require cargo to be transported on waterways.

Some dams are designed with the primary goal of supporting recreation or fish farming.

Other purposes

A cluster of tailings dams in England

The rusty steel panels are a temporary cofferdam which is keeping the worksite dry while a concrete bridge pier is being built in a river.

A weir in Spain

A tailings dam is a dam that impounds tailings – the waste from mining operations. Most tailings dams are embankment structures. Unlike a normal water-impound dam – which is almost always built in a valley – tailings dams may be built on flat ground, with the embankment constructed in a polygonal shape that encloses the tailings on all sides. Tailings dams are unique because they are often enlarged over time: as mine operations continue, the embankments are repeatedly raised. Tailings often include toxic by-products of mining, such as arsenic or lead. Therefore, tailings dams usually incorporate special protective measures to ensure that materials from the tailings do not contaminate the water supply outside the dam.

A cofferdam is a temporary dam built at a construction site to keep water out of the site until the job is completed. Cofferdams are commonly used when building bridge supports in lakes, rivers, and oceans. When building a dam in a river valley, cofferdams are often required upstream, where they divert the river into temporary tunnels or channels that carry the river around the construction site, and then release the water downstream.

A weir is a straight, flat, low structure built across a riverbed. Weirs are not designed to fully block a river, but rather to regulate the flow in a controlled way. Some weirs are used to create a segment of the river that has a fixed level; others are designed to minimize erosion of the river banks; some are for landscaping or recreation purposes; and other weirs are used as measuring gauges (the total water flow can be readily computed by measuring the depth of the water passing over the weir).

A saddle dam raises the height of a saddle (low point) in the ridge surrounding a reservoir. Saddle dams supplement a primary dam, and are built at the same time. They are only needed if the ridge surrounding the primary dam's reservoir contains a low point which is below the primary dam's water level. The saddle dam will prevent overflow when the reservoir is filled.

A diversion dam diverts a portion of a river's flow into a canal, which transports the water to another location where it is used for irrigation, hydropower, or other purposes. A detention dam does not create a permanent reservoir, but instead regulates the flow of water in a valley to minimize the risk of flooding downstream.

Underground dams are used to block the flow of groundwater and store it below the surface. Underground dams are small-scale structures constructed in arid regions where water is scarce. Some underground dams are built by digging a trench in the path of naturally flowing groundwater and placing a vertical, impervious barrier, then refilling the trench. Another design, used in sandy regions, is to build a low dam across a small valley so that occasional rainstorms will cause sand and water to accumulate behind the dam (the sand will inhibit evaporation of the groundwater). In both of these designs, a well or pipe is placed upstream of the barrier to withdraw the water.

History

Main article: History of dams

Antiquity

The Great Dam of Marib in Yemen was built around 500 BCE.

The Jawa Dam near Amman, Jordan, is the oldest known example, built around 3000 BCE. This embankment dam was part of an elaborate irrigation system, and was 28 m (92 ft) thick and 5.5 m (18 ft) high. Around 2600 BCE, the Egyptians built the Sadd el-Kafara embankment dam near Cairo, although it failed around the time its construction was completed. The Sabaean peoples built a series of dams across the Wadi Danah, located in modern Yemen, starting around 1500 BCE, culminating in the Great Dam of Marib (built around 500 BCE) which was 700 m (2,300 ft) long and 20 m (66 ft) high.

The Hittite Empire built several dams between the 17th and 13th centuries BCE, including the Eflatun Pınar dam and spring temple near modern Konya, Turkey. An early dam in China – built by engineer Sunshu Ao around 580 BCE – impounded the Afengtang Reservoir which still exists today. In Sri Lanka, several dams – including Tissa Wewa – were built around 370 BCE to create reservoirs. Some of the dams were several kilometers long.

Roman era

The Band-e Kaisar dam in Iran was built in the 3rd century CE.

The Roman Empire constructed major waterworks – including aqueducts and tunnels – starting in the 5th century BCE, but they did not begin building significant dams until the first century CE. Roman dams were typically masonry gravity dams with vertical faces on both upstream and downstream sides, although some were reinforced on the downstream side with buttresses or rock embankments. The Romans were the first to use cement as a construction material, which could be mixed with small rocks to form concrete, or mixed with sand to form mortar to join bricks or stones. Some Roman cements, particularly those containing volcanic ash, were waterproof.

One of the earliest dams built by the Romans was also their tallest: the Subiaco Dam, built around 60 CE, stood 40 m (130 ft) tall and 13.5 m (44 ft) thick. The Romans built about 80 dams in Hispania (modern Spain), including the Proserpina Dam, which impounded 6 million m³ of water. The dam was still operational in 2026. Roman dam technology was applied by neighboring countries: after Persian king Shapur I defeated Roman emperor Valerian, he put defeated Romans to work building the Band-e Kaisar dam, which also functioned as a 40-arch bridge spanning the Karun River.

Post-classical Asia and Middle Ages

The Kurit Dam was built around 1350 CE.

One of the earliest dams built in Japan was the Sayama embankment, built near Osaka in 380 CE, which was 8 m (26 ft) high and 300 m (980 ft) long. The Kurit Dam – the world's first large, thin arch dam – was built in Persia (modern-day Iran) around 1350 CE. It was 26 m (85 ft) high and was later raised to 64 m (210 ft); it remained the world’s tallest dam until the start of the 20th century. Dams in India were typically earthen dams with steep faces faced with stone. A notable example is the Veeranam Dam, built around 1020 CE in Tamil Nadu, which is 16 km (9.9 mi) long.

In Europe, dams were used to power water wheels for milling and mining. An early example was the Bazacle weir built around 1170 CE in France. Dams to create fish ponds were common in Europe, and hundreds were built in Bohemia during the 15th and 16th centuries, creating ponds covering a total of 1,800 km². Dams for irrigation included the Almansa Dam – a gravity/arch dam built in 1384 in Spain, and the Elche Dam (built in 1640 and still standing) – the first true arch dam built in Europe since Roman times. Several dams were built to supply Istanbul with water, including one in 1560 that brought water from Belgrad Forest. Another purpose of canals was transportation: the Saint-Ferréol Dam was built in France in 1675 to provide water for the Midi Canal. It remained the highest earthen dam in the world for over a century. Several books on the subject of dam design and construction were published in the 1600s and 1700s, by authors including Jacob Leupold, Albert Brahms, Johann Silberschlag, and Oliver Evans.

Industrial Revolution

In Australia the Parramatta Dam tested the limits of how thin a dam could be.

In the late 18th century, the process of designing dams began to transform from an informal practice – based on experience and trial and error – to an engineering discipline rooted in science. Important figures that contributed to this evolution included the French scientist Charles-Augustin de Coulomb who, in 1776, created a formula that described how soil reacts under stress, a theory that was later given practical application to dams by Alexandre Collin. Claude-Louis Navier developed the theory of elasticity in 1826. In 1847, François Zola became the first engineer to design an arch dam based on an analytical consideration of stresses. The French engineer J. Augustine DeSazilly established that the best cross-section for a gravity dam was a triangle, with a vertical face on the upstream side. The Scottish physicist William John Macquorn Rankine developed a theory governing retaining walls in the 1850s which was applicable to dams.

These scientific foundations led to safer, larger dams of all types. The Glencorse Dam in Britain (1824) was a 21 m (69 ft) high embankment dam that contained a clay core and had gently sloping faces. In France, the Gouffre d'Enfer masonry gravity dam (1866) was 60 m (200 ft) tall. The world's first large buttress dam was Mir Alam Dam (1804) in India. In Australia, an arch dam – the Parramatta Dam (1856) – tested the limits of how thin a dam could be.

Modern era

The Afsluitdijk embankment dam was built in the Netherlands in 1932 to enclose part of the North Sea and turn it into a freshwater lake.

In the first half of the 20th century, many large dams were built, particularly in Western Europe and the US. After WWII, the availability of heavy construction machinery such as bulldozers, dump trucks, and scrapers contributed to a large increase in the number of large dams. Famous dams of the modern era include massive concrete gravity dams like the Hoover Dam (US, 1936) and Three Gorges Dam (China, 2006). But some embankment dams are even larger, including the Tarbela Dam (Pakistan, 1976) and the Nurek Dam (Tajikistan, 1980).

The invention of grout curtain technologies enabled dams to be safely built on top of porous soils. This enabled the Aswan High Dam to be built in 1960 across the Nile River, which has a deep, sandy riverbed: grout was pumped 208 m (682 ft) deep into the riverbed (spanning 57,000 m²), preventing water from flowing underneath the dam.

The modern era also saw the emergence of arguments against dam construction, starting as early as the 1870s with objections to the Thirlmere Dam in Britain. In 1906, a fierce battle was fought over the construction of the Hetch Hetchy Dam in California, which was eventually built and flooded a valley in Yosemite National Park that dam opponents claimed was as scenic as the famed Yosemite Valley. After climate change became a global concern, debates emerged arguing whether the electricity produced by dams was as clean as solar power or wind generation. Although hydroelectricity itself is clean, dam opponents argue that adverse environmental impacts cancel any benefits.

Number of dams in the world

Number of large dams, globally, by structural type.

The number of large dams worldwide in 2025 was 62,362, according to the International Commission on Large Dams (ICOLD). The total number of reservoirs (large and small) in 2011 was estimated to be 16.7 million. These reservoirs store an estimated 8,070 km³ of water, which is about 10% of the volume of the Earth's natural freshwater lakes. The reservoirs cover about 305,000 km² of the planet's surface, which is about 7.3% of the area covered by natural lakes. About 7.6% of the world's rivers are significantly impacted by reservoirs and 46.7% of large rivers are affected. In 2015, the number of hydropower dams planned or under construction was 3,700, with most in China (highest total generation capacity), Brazil (highest number of planned dams), and India.

Design

Design process

The process of designing a dam can be undertaken in three stages: reconnaissance, feasibility, and project planning. In the reconnaissance stage, designers visit the site, study it carefully, and gather all available geological, seismic, and topographical data. In the feasibility stage, detailed technical investigations are performed to assess the geology, hydrology, and hydraulics of the site. Inquiries are made into land acquisition, public utility availability, and the location of construction materials (such as rocks and soil for landfill). Analysis of environmental and flood impacts is started. In the planning stage, detailed design plans are created, a construction schedule is established, and cost estimates are prepared.

Technical surveys and investigations

Dam engineers often use scale models to evaluate dam designs. This is a model of the Tellico Dam in the US.

During the planning process for a dam, a large number of surveys and technical investigations are typically conducted. These investigations may be categorized as topographic, geological, and hydrological. Topographic surveys are one of the first steps in planning a dam. Surveyors map the construction site and prepare detailed topographic maps of the region. The maps must be very precise, since virtually every aspect of the dam's construction will rely on the data.

The geological investigations study the rocks and soil of the dam site. The dam  – and the water it impounds – will exert very large forces on the ground beneath the dam structure, on the valley walls where the dam abuts them, and on the ground beneath the reservoir. An accurate understanding of the strength of the ground, and identifying any faults, is essential to minimizing seepage and reducing the risk of dam failure. The geological research must also assess the likelihood and magnitude of earthquakes and other seismic events.

The hydrological investigations examine all aspects of water flow in the vicinity of the dam. Data is produced which identifies the size of the upstream watershed and how much precipitation falls each year. Studies are performed to determine how much water flows through the dam site in an average year, how much it varies within a year, and how much it varies from year to year. These data are used to compute the frequency and magnitude of floods at the dam site, which are used to establish the capacity of the dam's spillway.

Impact assessment

The Three Gorges Dam in China displaced 1.4 million people.

Dams can provide significant benefits to a community in the form of irrigation, water supply, and hydroelectricity. However, many adverse impacts can follow from dam construction, leading some to oppose new dam construction. To evaluate these concerns, countries require developers of large dams to prepare an Environmental Impact Assessment (EIA) that documents the consequences the dam (and its reservoir) will have on communities and the environment. An EIA may address impacts in the following areas: air quality, climate change, water flow, reservoir, downstream region, socioeconomic, and infrastructure. The EIA enables the developer and government to assess the desirability of a dam, to mitigate its impacts, and to compensate people adversely affected. Mitigations include changing the dam's location, size, or design; compensating those impacted; or cancelling the project altogether.

Communities that live near the dam and its reservoir may be severely impacted. People who live within the reservoir boundaries must relocate to new homes, which can cause large-scale social disruption. The Aswan High Dam in Egypt displaced 50,000 Nubians and devastated the Nubian community. The Three Gorges Dam in China required the relocation of 1.4 million people. Land adjacent to the reservoir may become saturated with water, impacting agriculture and increasing soil salinity. The level of groundwater (underground water) surrounding the reservoir may rise, and the quality of groundwater that people pump from wells may degrade.

Some dam projects threaten to flood natural wonders or cultural heritage sites. Notable examples include the Aswan High Dam in Egypt that forced the relocation of the Philae and Abu Simbel temples; the Hetch Hetchy Dam in the US that flooded a scenic valley in Yosemite National Park; and the Itaipu Dam that submerged the spectacular Guaíra Falls.

Many dam projects require extensive modifications to the local infrastructure. New housing may be built for workers; electrical power transmission lines will be needed if the dam produced hydroelectricity; bridges and roads may need to be created or re-routed.

Environmental impact

Concrete dams contribute to global warming because the production of cement in kilns (shown) generates greenhouse gasses.

The Environmental Impact Assessment summarizes the effects a dam will have on the environment, including the atmosphere, rivers, fish, terrestrial animals, vegetation, forests, and biodiversity. Air quality may be impacted by dams in several ways: during construction, there may be large amounts of particulate matter in the air. After the dam is operating: the reservoir's water and associated humidity may have impacts on the microclimate near the dam site.

Although hydropower from dams is much cleaner than power from coal or oil plants, concrete dams are responsible for putting large amounts of greenhouse gases into the atmosphere, which contribute to climate change. To produce one cubic meter of concrete, roughly 200 kg of carbon dioxide (CO₂) is put into the atmosphere. For example, a dam the size of Three Gorges Dam – containing 28 million m³ concrete – would put roughly 5.6 billion kg of CO₂ into the atmosphere. CO₂ is also emitted from reservoir water as organic matter decomposes; the organic matter includes all plants and trees submerged by the reservoir, as well as plant life carried into the reservoir from upstream.

Dams impact the downstream water flow, which can have several adverse impacts. The flow of the river may be reduced, especially in the dry season. The quality of the downstream river water may also suffer. Many rivers normally carry sediment, which replenishes soil downstream of the dam site – but sediment flow is reduced after a dam is constructed, because sediment accumulates in the reservoir. Fish migration may be seriously impacted, since the dam may prevent fish from swimming upstream to spawn.

Reservoirs impounded by dams can impact the environment. Fish and plants that lived in or near the river will die, and perhaps become extinct in that locality. Terrestrial animals that lived in the valley will lose habitat. The reservoir may cause deforestation, if a large number of trees are submerged under the waters. There is evidence that the weight of the water in the reservoir can trigger landslides, seismic activity, and earthquakes.

Selection of location, structure, and material

Important steps in the design process are selecting the location, structure (arch, gravity, etc), and material (concrete, earth, etc). Factors that influence these decisions include topography (the shape of the valley), geology (especially as it relates to the strength of the ground below and to the side of the dam), the flow of water in the valley (hydrology), the availability of construction materials, and potential pathways for spillways. Designers must carefully assess all forces that that the dam structure must withstand, including water, ice, sediment, stresses from temperature gradients, uplift, floods, earthquakes, concrete shrinkage, and the dam's own weight.

The dam location should be chosen so the reservoir will be sufficiently large to meet project requirements. The location should also ensure that the ground is strong enough to support the forces that the dam structure and reservoir water will impose. The site selection must also consider seismic factors: when fault lines are discovered under or near the dam, designers must determine if they pose a risk.

If the dam is placed in a narrow valley, a gravity dam or arch dam may be most appropriate, especially if a tall dam is required. However, an arch dam can only be utilized if the walls of the valley are strong enough to support the large forces that the sides of the arch will impose. A gravity dam structure is only feasible if the ground under the dam is strong bedrock. Most gravity dams and arch dams are made of concrete, which is generally more expensive than earth or rock, and may influence the design choice.

If the dam must span a wide valley, an embankment dam structure is often the optimal choice. Rock fill embankment dams are appropriate if rock is plentiful near the site, and an earth fill embankment dam may be used when rocks are not available. For any embankment dam, an ideal site will be near impervious materials – such as clay – which can be used as a core layer within the dam.

The following table lists some factors that designers consider when selecting a dam structure.

Selection of dam structure

Dam type	Advantages	Characteristics and drawbacks
Embankment dam	• Dam can be built on sand or dirt because its weight is spread over a large area  • Little excavation required  • Low sensitivity to earthquakes  • Settlement of ground beneath dam is acceptable  • Materials for dam may be found locally	• Appropriate for: low-to-medium height dams in a wide, low valley without bedrock, with a modest budget  • Large amount of material required  • Separate spillway must be built
Gravity dam	• Minimal stress within concrete  • Integrated spillway possible  • Handles temperature fluctuations well	• Appropriate for: dams of any height, in a narrow or wide valley  • Requires bedrock foundation  • Lots of expensive concrete required  • Sensitive to earthquakes and ground settlement  • Refrigeration may be required while curing  • Large amount of excavation
Buttress dam	• Uses less concrete and has fewer cooling issues (vs gravity dams)  • Minimal ground settlement issues  • Integrated spillway possible	• Appropriate for: low-to-medium height dams on bedrock, with a modest budget  • High sensitivity to earthquakes  • Face of dam sensitive to temperature changes  • Large amount of excavation  • More formwork and labor (vs gravity dams)
Arch dam	• Little concrete required  • Less excavation needed  • Earthquake tolerant  • Few concerns with ground settlement	• Appropriate for: tall dams in a narrow valley that has strong, steep walls and can accommodate a separate spillway  • High stress within concrete  • Complex and risky abutment where dam meets valley walls  • Spillway placement may be difficult

Aesthetics

Khaju weir and bridge in Iran is noted for its beauty.

A dam's appearance can be a factor when evaluating potential designs, but it was not always so. An early advocate for aesthetically pleasing dams was British architect Charles Fowler, who gave a speech in 1929 which singled out the Roosevelt Dam and the O'Shaughnessy Dam as examples of beautiful dams. Fowler asserted that dams with some curvature, particularly arch dams, tend to be perceived as more attractive than those designed with entirely straight lines. The popularity of concrete after WWII as a material for building dams gave designers more flexibility to create pleasing dam shapes. The Swiss civil engineer Nicholas Schnitter noted that – although attractive dams are desirable – beauty is a matter of taste, making it difficult for designers to determine if a particular plan will improve the pre-dam landscape. In addition to aesthetics, dams can also serve as iconic monuments that provide a sense of pride and inspiration for the community; examples include the Hoover Dam and the Bratsk Dam.

Auxiliary structures

Power plant

Main article: Hydroelectricity

Hydropower dams

In this typical hydroelectricity installation of a dam, shown in cross-section, the water is flowing from left to right.

The generators of this dam are in the low, horizontal building lower-left. Five penstocks feed water from the reservoir into the generators.

Many dams include power plants that run water through a generator to produce electricity. The generator is typically located at a level near the bottom of the dam, enclosed in a powerhouse building. Some powerhouses are located inside the dam structure; this is typically encountered in hollow gravity dams, particularly when no area is available downstream to put a powerhouse.

Designing a hydropower facility for a particular dam requires analysis of the amount of electricity desired, the amount of water available to feed into the turbine, and the height of the upstream water level above the generator (this height is called the "head") Those factors will determine which turbine style is optimal; turbine styles commonly used in dams are Francis turbine, Pelton turbine, and Kaplan turbine.

Water is guided to the generator from upstream (often from a reservoir) via a passage – called the penstock – that feeds the water into the generator, which uses the force of the water to rotate a turbine and generate electricity.

Spillways and gates

Main articles: Spillway and Floodgate

The Oroville embankment dam in the US is the large rock structure on the right side of the image. Overflow water from the reservoir is cascading down the spillway on the left side.

The spillway of the Grand Coulee Dam is integrated into the main structure of the dam.

Many dam projects include spillways, which are structures that provide a controlled release of excess water from the reservoir into the river downstream, preventing the dam from overflowing and possibly failing.

Unusually heavy rainfall upstream may cause the reservoir to overflow. If the spillway is not large enough to safely transfer the overflow downstream, the water will spill over the dam structure, which could lead to significant damage or even total failure. Dam designers must perform a detailed analysis of the variability of the region's rainfall and flooding, And they use that data to design the spillway's capacity to handle a specific maximum flood. For small dams, spillways are typically designed to safely handle the largest flood expected to occur once in 100 or 500 years. Large dams are typically required to handle the largest flood expected to occur once in 10,000 years.

Spillways can be integrated into the dam project in a variety of ways. Concrete gravity dams may position the spillway directly on the dam structure (in the middle or at the side). Other dams locate the spillway at a low point (saddle) of the ridge surrounding the reservoir, these saddle spillways convey the water via a chute (channel) or through a tunnel to discharge downstream of the dam. One particularly interesting spillway design is the bell-mouth, which is a vertical shaft in the interior of the reservoir that leads to a tunnel that discharges downstream.

To operate effectively, the shape of the spillway must be carefully designed, usually adopting a parabolic shape at the top. The bottom of the spillway must use special technologies that dissipate the energy of the rapidly flowing water as it discharges into the river to minimize damage from erosion. Some spillways use an ogee shape: the spillway starts horizontally at the dam top, becomes steeply inclined in the middle, then curves horizontally at the bottom (ensuring that the water shoots away from the dam structure, to minimize damage).

Many dams include gates – usually positioned at the top of the spillway – to regulate the water level in the reservoir and control the rate at which overflow water is released downstream. Types of gates include vertical lift gates, drum gates, and radial gates.

Outlets

Dam outlets are structures – usually placed in the lower part of the dam structure – which permit the reservoir to be partially drained. Lowering the water level in a reservoir may be required for maintenance purposes, to purge sediment from the floor of the reservoir, to generate hydropower, to increase the water flow downstream in the dry season, or to reduce stress on the dam structure in an emergency situation. Some dam projects create tunnels early in the dam construction process to divert river water around the construction site while the dam is being constructed. Those tunnels are sometimes converted into outlet mechanisms after the dam is completed.

Locks and fish bypasses

Main articles: Lock and Fish bypass

Auxiliary structures

A tugboat is pushing barges into a lock integrated into this dam.

This fish ladder (diagonal steps) enables migratory fish to bypass this dam.

When a dam is placed in a river where it would prevent the movement of boats, locks may be incorporated into the dam project. Locks enable boats to pass the dam in both directions. Locks consist of one or more rectangular chambers with large doors at both ends, and piping that permits each chamber to be filled and emptied.

Some rivers are important migration paths for fish. If a dam is built on such a river, it could cause significant ecological damage. The impacts can be mitigated by including a fish bypass mechanism in the dam project. Designs for a fish bypass include fish ladders, fish lifts, or artificial creeks that mimic a natural river.

Construction

Constructing a dam requires a significant amount of planning and scheduling.

Cofferdams and diversion of river

A temporary cofferdam (bottom) is diverting river water around a dam construction site (top).

Many dams require more than one year to build, making it impossible to build them within a single dry season. For those dams, the flow of river water must be diverted around the dam construction site. Diversion can be accomplished by building a temporary tunnel or channel around the side of (or underneath) the dam, and building a temporary cofferdam to direct the river into the tunnel/channel. Cofferdams are typically removed after construction; but for some embankment dams, they are incorporated into the dam itself. Channels and tunnels are also typically plugged up or demolished; although some dam projects retain tunnels or channels as part of the permanent dam project, for example, as an outlet or a spillway.

Another diversion technique is to build a cofferdam which forces the river to one side of the valley, and build half the dam on the other side (within the cofferdam). After the first half of the dam is complete, the cofferdam is moved to direct the water to the first half-dam (which has passages to let the water through) while the second half of the dam is built within the cofferdam.

For some embankment dams, the cofferdam and diversion may be avoided by channeling the river into a narrow course in the center of the valley and building the dam inward from both sides of the valley, leaving a gap in the middle for the river to flow through. Then, in the dry season – when the flow of the river is small – the central portion of the dam is rapidly completed, as the water rises behind the dam.

Preparation, grouting, and drainage system

Workers are drilling holes in a dam site. Grout will be injected into the holes to strengthen the ground and reduce water seepage.

An early step in the construction process is preparing the foundation, which is the rock upon which the dam structure will rest. For heavy dams – gravity dams, arch dams, or buttress dams – the dam is very heavy and must rest on strong, solid, bedrock. Any soil, gravel, loose rock, or poor-quality rock must be removed to expose bedrock before building the dam. Tools used to expose and prepare the bedrock include high-power water jets and blasting. Embankment dams have wide bases, and do not subject the ground to as much pressure as heavy dams so – in some situations – they may be built on loose rocks or soil.

A major risk in any dam project is water seeping under the dam or around its sides. An important technique to mitigate that risk – performed before the dam is built – is to inject grout into the ground below the dam and into the valley walls on either side. Two types of grouting processes are utilized for dams: consolidation grouting locates rocks below and to the sides of the dam that may have cracks or defects, and injects grout under high pressure at those locations, thus filling any cracks or voids. The other technique is curtain grouting, which injects grout deep into the rock through boreholes drilled in a pattern calculated to create a solid wall of grout below and to the sides of the dam. The depth of the grout curtain is typically 30% to 70% of the planned depth of the water behind the dam.

Another approach to mitigate seepage is a drainage system, which aims to reduce the risk of "piping" (water inside the dam eroding the dam structure) or uplift (water under the dam pushing the dam upward). The drainage system collects water from inside or under the dam and carries it downstream. The drainage may consist of pipes, or a crushed rock "blanket" under the dam. Concrete dams may have passages inside the dam structure to collect water and carry it away; these passages are called "galleries" (horizontal) or "shafts" (vertical).

Building the dam

Concrete dams require a concrete plant which uses conveyor belts to move rocks and concrete.

The machine on the left is vibrating the roller compacted concrete of this dam in Turkey.

The process of building a dam structure depends on the dam material: embankment dams employ a different approach to construction than concrete dams. Embankment dams require vast amounts of soil and rock, and the material is usually excavated from "borrow areas" near the dam site. The soil and rocks are laid down in successive layers called "lifts". After laying down a layer, it is compacted with heavy machinery. The layers must be carefully monitored to ensure that they contain the correct materials, are not overly wet, and are sufficiently compacted. Instruments are embedded within the dam as it is built, and are continually monitored so any defects can be quickly corrected.

Concrete dams require a concrete plant to be built near the dam site. The plant combines aggregate (rocks), cement, fly ash, and water to produce concrete. The concrete is delivered from the concrete plant to the dam structure by means of conveyor belts, buckets, dump trucks or cranes. Formwork is built at the dam location to contain the concrete when it is placed. After it is placed into the dam structure, the concrete must be vibrated to eliminate any bubbles or air pockets.

Concrete components of dams are often very thick – much thicker than, for example, the wall of a building. Concrete of such thickness is called mass concrete, which contracts and generates a large amount of heat as it cures, which can lead to cracks. To mitigate this issue, expansion joints can be included within the dam to permit the concrete to shrink without cracking. After the heat dissipates, the expansion joints are filled with grout, and their upstream edge is sealed with strips of metal, rubber, or plastic. Additionally, refrigeration systems may be employed that circulate coolant through the concrete by means of pipes.

A recent innovation is roller compacted concrete (RCC) which has several benefits over conventional concrete. RCC uses less cement, permits use of aggregate up to 100 mm in size, and does not generate as much heat as conventional concrete. RCC also permits tracked bulldozers to immediately drive on top of it after it is placed, and it reduces construction costs because less formwork and labor is required.

Operation

Management processes

Control room of the Itaipu Dam on the border of Brazil and Paraguay

After a dam is completed and becomes operational, management processes are employed to ensure that it continues to fulfill its purposes (irrigation, hydropower, etc), avoids safety incidents, and achieves its intended lifespan. These management processes include activities such as:

• Prioritization and planning
• Operation
• Maintenance
• Testing
• Inspection, monitoring and surveillance
• Dam safety reviews
• Investigation and rectification of deficiencies
• Emergency planning and response
• External advice and management reviews
• Communication and records
• Continuous improvement

Inspection and monitoring

The interiors of some dam structures contain galleries (long, horizontal passages) where operators can inspect for leaks and check monitoring devices.

An essential task of dam operators is surveilling and inspecting the dam to identify potential safety issues. Dam operators must routinely monitor the dam for stresses that act on the dam, including:

• Force of the reservoir contents upon the dam: water, ice, sediment
• Waves in the reservoir striking the dam
• Earthquakes and minor seismic events
• Weight of the dam and water compressing the ground underneath the dam (and – for arch dams – on the abutments) causing the dam to settle or move
• Internal compression and tension stresses within the structure
• Expansion and contraction due to temperature fluctuations

These stresses have the potential to adversely impact a dam by bending, lifting, expanding, shrinking, or shifting the structure. To avoid these issues, stresses are monitored with permanent sensors placed within and around the dam. Sensors typically used in dams are tiltmeters, joint meters, strain meters, deflectometers, thermometers, deformation meters, and piezometers. Dam personnel monitor these sensors, and if irregular data are reported, they investigate the underlying cause, and – if needed – implement repairs or mitigations.

Sedimentation of reservoir

Most reservoirs gradually accumulate sediment, decreasing the amount of water that the reservoir can hold. When the water capacity is reduced, the dam's ability to perform its intended purposes (irrigation, hydropower, water supply, flood control, etc) is correspondingly reduced. Sediment enters a reservoir in the form of soil suspended in river water; as the river empties into the reservoir, the water velocity slows down, and the sediment settles to the bottom of the reservoir. Sediment can also enter a reservoir from wind-blown soil, landslides, construction work near the water, and erosion from irrigation or rainfall. Roughly half the sediment of the world's rivers is trapped by dams – about 8 to 16 km³ per year. To mitigate sedimentation, dam operators implement strategies to reduce the amount of sediment entering the reservoir. Some sedimentation can be reduced by planting plants and trees in the reservoir's drainage basin, or by building terraces.

Dam removal

Main article: Dam removal

A dam may be deliberately removed for various reasons: if it poses a safety hazard, if the dam no longer fulfills its original purpose, to restore fish migration routes, or to improve the health of downstream rivers by improving sediment flow. When a dam is removed, fisheries are restored, water and sediment flows are re-established, sediment in the reservoir gradually erodes and flows downstream, the river width increases and braiding is more pronounced, natural water temperatures are restored, and animal habitats are restored.

Removal of the Iron Gate Dam in the US

In 2009, before removal

In 2024, after removal

In the US, rivers and streams are obstructed by over 800,000 dams and barriers. Over 1,200 dams have been removed as of 2016, with over 600 removed between 1996 and 2016. Between 2014 and 2018, two dams – the Elwha Dam and the Glines Canyon Dam – were removed from the Elwha River in the US. Together, the two dams stored approximately 30 Mt of sediment. The dam removal restored delivery of sediment and wood to the downstream river, and the river delta was re-established. A group of four dams – including the Iron Gate Dam – were removed from the Klamath River in the US between 2020 and 2024. The removal was the result of a sustained campaign by Native Americans and environmentalists. One of the goals was to restore one of the largest salmon migration routes on the Pacific coast of North America.

In 2021, there were over 1,000,000 dams and barriers in Europe, and at least 150,000 of them were no longer required. Dams and the associated river fragmentation are a major cause of a 55% decline in migratory fish populations and an 80% decline in fish biodiversity. In 2024, the European Union passed the Nature Restoration Law which encourages the removal of unneeded dams. The Dam Removal Europe organization seeks to identify dams for removal and facilitate the process. In 2025, over 600 dams were removed in Europe, restoring 3,740 km (2,320 mi) of rivers and streams.

Dam failure

Main article: Dam failure

The concrete arch Malpasset Dam failed in 1959 in France.

The earthen embankment Teton Dam failed in the US in 1976.

Many principles governing the design of safe dams have been developed based on lessons learned from dam failures. Dams can fail for many reasons. Arch dam failures can result from rock weakness at the abutments (where the sides of the dam press into the valley walls), erosion of the foundation under the dam, or shearing (slipping) where the dam meets rock. Gravity dams and buttress dams can fail due to overturning, sliding, cracking, or earthquakes. A risk unique to earthen embankment dams is "piping": a small leak through or under the permeable dam structure gradually erodes the soil, until a small channel is formed, which – if unaddressed – may lead to dam failure.

A large number of dams failed during the 19th and early 20th centuries, particularly embankment dams. Increased emphasis on dam safety caused dam failure rates to decrease exponentially throughout the 20th century. Between 1900 and 1994, only 100 large dams (heights over 15m) failed. Although the failure rate is decreasing, the potential for downstream damage is higher due to increasing dam heights and reservoir capacities.

The earliest known dam failure occurred around 2600 BCE, when the Sadd el-Kafara dam in Egypt failed around the time it was completed, apparently due to a flood that severely damaged the dam structure.

The first modern arch dam to fail was the Malpasset Dam in France. The failure in 1959 was not due to the concrete dam's shape or strength, but rather the presence of an underground slip line which moved due to the combined weight of the dam and the reservoir water. The movement caused the dam to crack, and the resultant flood killed several hundred people downstream.

In some cases, it is not possible to determine the cause of the failure. The Baldwin Hills embankment dam in the US failed in 1963 but – despite extensive investigations – a definitive cause was not found. Potential factors included: weak foundation soil that subsided, irregular settling of the dam structure, fault lines under the dam, a nearby oil field that was depleted of oil then later re-pressurized, and the act of emptying and filling the reservoir.

An unusual dam failure was the Vajont Dam in Italy. This concrete arch dam was built in a valley that had steep sides which were prone to landslides. Designers failed to fully understand the geology of the valley, and built the dam in 1959 – then the tallest dam in the world at 267 m (876 ft). In 1963, a huge landslide slid down the hillside above the reservoir, displacing nearly all the water in the reservoir, and causing a 125 m (410 ft) tall wave to overtop the dam. The resulting flood killed over 2,000 people downstream. The dam structure itself suffered only minor damage.

Society and culture

International disputes

Further information: Water conflict

Ethiopia built the Grand Ethiopian Renaissance Dam on the Blue Nile River in 2020, over the objections of Egypt and Sudan.

World population increases and the impacts of climate change have led to water scarcity conditions which are responsible for international conflicts over sharing the water of transnational rivers. The United Nations and the International Law Association have recommended negotiation and collaboration to facilitate resolving water disputes, yet most countries believe they are entitled to unilaterally build dams within their borders without consulting downstream nations. Some authorities have predicted that water supply may be used as a weapon in future conflicts. Dams built in countries such as Turkey, India, Ethiopia, and China – without the consent of downstream nations – have led to notable international disputes.

Turkey's Southeastern Anatolia Project is a major water project which includes many dams, one of which is the large Karakaya Dam. Most of these dams are on the Euphrates and Tigris rivers, which flow downstream into neighboring nations Syria and Iraq. These downstream nations have protested to Turkey about potential water supply issues.

India and Bangladesh have a long-standing dispute about sharing the waters of the Ganges River, which focuses on the Farakka Barrage built in 1972. A treaty was signed in 1996, but tensions persist. The Indus River is the primary river of Pakistan, with headwaters in several countries, including India. The Indus Waters Treaty was signed between India and Pakistan in 1960, but India subsequently built large dams on the Indus over the opposition of Pakistan, including the Baglihar Dam and Kishanganga Dam.

The Nile River has been the source of tensions between the arid downstream nations (Egypt and Sudan) and the upstream nations where most of the Nile's water originates as rainfall. Throughout the 20th century and into the 21st, negotiations have led to various treaties and initiatives, including the Nile Basin Initiative. In 2020, Ethiopia built the Grand Ethiopian Renaissance Dam (GERD) on the Blue Nile, in spite of opposition from Sudan and Egypt.

The Mekong River traverses several countries. In 1995, Thailand, Cambodia, Laos, and Vietnam signed a treaty creating the Mekong River Commission to regulate the river's water supply. China did not participate in discussions leading to the treaty, and later built many dams on the river, including the Xiaowan Dam and Nuozhadu Dam.

Wartime targets

Dams have been targeted during wartime, with 20 documented attacks on dams between 1917 and 1993. The Geneva Conventions were amended in 1949 to prohibit attacks on dams if they would cause "severe losses among the civilian population".

Profession and regulation

Most countries with large dams have statutes or regulations governing dam construction and inspection practices. The regulations vary widely between countries. Some nations have a government agency responsible for inspecting dams, but many do not. Some countries regulate dams at a federal level, but others regulate at a province/state level. For example, Germany has no federal regulations; instead, each state has its own statutes. Dam owners are required to inspect their dams periodically with supervision by the government. The regulations of most nations typically do not specify particular dam design parameters, but instead require compliance with “recognized rules of technology” or “state of the art in science and technology”.

Art and culture

The Dnieper Dam is shown on this 1968 Soviet stamp.

Dams are featured in novels, movies, documentaries, songs, postage stamps, popular histories, and political posters. In the mid-20th century, Soviet artists such as Isaak Brodsky and Gustav Klutsis highlighted large dams in artworks intended to glorify workers and industry. Their works portrayed the Mingachevir Dam, Kayrakkum Dam, Bratsk Dam, and Dnieper Dam. Folk musician Woody Guthrie wrote the songs Grand Coulee Dam and Roll On, Columbia, Roll On (both 1941) as part of a series of songs he wrote about the Columbia Basin Project.

The docudrama war film The Dam Busters (1955) portrayed a WWII military operation in which the Allies successfully bombed a dam in Germany. Books about dams include The Johnstown Flood (1968) by David McCullough – a popular history of an 1889 dam failure and subsequent flood in the US. Edward Abbey wrote the novel The Monkey Wrench Gang (1975) about environmental activists who sought to destroy the Glen Canyon Dam. The Patagonia company produced the documentary movie DamNation (2014) which advocates for dam removal to restore ecosystems and fish populations.

References

Sources

Books

• Arnold, Arthur B.; et al. (1988). "Geology". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 106–152. ISBN 0442243979. Retrieved 20 April 2026.

• Berlow, L.H. (1998). Reference Guide to Famous Engineering Landmarks of the World. Bloomsbury Academic. ISBN 9780897749664. Retrieved 20 April 2026.

• Blight, Geoffrey E.; Jewell, Richard J.; et al. (1998). Case Studies on Tailings Management. United Nations Environment Programme – International Council on Metals and the Environment. ISBN 9781895720297. Retrieved 8 May 2026.

• Breeze, Paul (2014). Power Generation Technologies (2nd ed.). George Newnes Ltd. ISBN 9780080983363. Retrieved 20 May 2026.

• Bunbury, Judith; et al. (2023). "The Egyptian Nile". In Wantzen, Karl M. (ed.). River Culture. UNESCO. pp. 43–78. doi:10.54677/HHMI3947. ISBN 9789231005404. Retrieved 10 March 2026.

• Carpenter, Lynn R.; et al. (1988). "Instrumentation". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 751–776. ISBN 0442243979. Retrieved 20 April 2026.

• Cecilio, Catalino B.; et al. (1988). "Hydrology". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 60–105. ISBN 0442243979. Retrieved 20 April 2026.

• Chellaney, B. (2015). Water, Peace, and War: Confronting the Global Water Crisis. Bloomsbury Publishing. ISBN 9781442249288. Retrieved 16 May 2026.

• Collins, Robert (2002). The Nile. Yale University Press. ISBN 9780300097641. Retrieved 16 March 2026. The "Bibliographical Essay" (pp. 245–248) lists books about the Nile River.

• Cray, Ed (2004). Ramblin Man: The Life and Times of Woody Guthrie. W. W. Norton & Company. ISBN 9780393047592. Retrieved 19 May 2026.

• Creager, W.P. (1917). Engineering for Masonry Dams. J. Wiley & Sons. LCCN 17017759. Retrieved 20 April 2026.

• Denny, Mark (2010). Super Structures: The Science of Bridges, Buildings, Dams, and Other Feats of Engineering. Johns Hopkins University Press. ISBN 9780801894367. Retrieved 20 April 2026.

• Dolen, Timothy P.; et al. (1988). "Materials". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 172–218. ISBN 0442243979. Retrieved 20 April 2026.

• Duscha, Lloyd A.; et al. (1988). "Surveillance". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 777–797. ISBN 0442243979. Retrieved 20 April 2026.

• Evans, S.G.; et al., eds. (2011). Natural and Artificial Rockslide Dams. Springer. ISBN 9783642047633. Retrieved 20 April 2026.

• Fell, Robin; et al. (2014). Geotechnical Engineering of Dams (Second ed.). Taylor & Francis. ISBN 9781138000087. First edition (2005) online in Internet Archive.

• Fetzer, Claude A.; et al. (1988a). "Earthfill Dam Construction and Foundation Treatment". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 321–353. ISBN 0442243979. Retrieved 20 April 2026.

• Gerwick, Ben (2014). "Substructures of Major Overwater Bridges". In Chen, Wai-Fah; Duan, Lian (eds.). Bridge Engineering Handbook. Vol 5. Construction and Maintenance (Second ed.). CRC Press. pp. 137–174. ISBN 9781439852330. Retrieved 31 October 2025.

• James, Laurence (1988). "Reservoirs". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 722–750. ISBN 0442243979. Retrieved 20 April 2026.

• James, Laurence B.; et al. (1988a). "Lessons from Notable Events". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 8–59. ISBN 0442243979. Retrieved 20 April 2026.

• Jansen, Robert B. (1988). "Introduction". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 1–7. ISBN 0442243979. Retrieved 20 April 2026.

• Jansen, Robert B.; et al. (1988a). "Earthfill Dam Design and Analysis". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 256–320. ISBN 0442243979. Retrieved 20 April 2026.

• Jansen, Robert B.; et al. (1988b). "Outlet Design and Construction". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 686–703. ISBN 0442243979. Retrieved 20 April 2026.

• Kitchen, Amanda; et al. (2016). River Weirs: Design, Maintenance, Modification and Removal. Construction Industry Research and Information Association. ISBN 9780860177784. Retrieved 8 May 2026.

• Lemperiere, F.; et al. (2006). "The Role of Dams in the XXI Century to Achieve a Sustainable Development Target". In Berga, Luis; et al. (eds.). Dams and Reservoirs, Societies and Environment in the 21st Century. Vol. 2. Taylor & Francis. pp. 1065–1072. ISBN 9781134138500. Retrieved 20 April 2026.

• Leps, Thomas M. (1988). "Rockfill Dam Design and Analysis". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 368–387. ISBN 0442243979. Retrieved 20 April 2026.

• Leps, Thomas M. (1988a). "Rockfill Dam Construction and Foundation Treatment". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 388–408. ISBN 0442243979. Retrieved 20 April 2026.

• Leps, Thomas M. (1988b). "Rockfill Dam Performance and Remedial Measures". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 409–415. ISBN 0442243979. Retrieved 20 April 2026.

• Pelikan, B. (1997). "Fish Bypass Channels". In Broch, E. (ed.). Hydropower '97: Proceedings of the 3rd International Conference on Hydropower. A.A. Balkema. pp. 61–66. ISBN 9054108886. Retrieved 13 May 2026.

• Schleiss, A.J.; et al. (2022). Design, Safety and Operation of Dams. École Polytechnique Fédérale de Lausanne. ISBN 9782889149957. Retrieved 20 April 2026.

• Schnitter, N. (1994). A History of Dams: The Useful Pyramids. Balkema. ISBN 9789054101499. Retrieved 20 April 2026.

• Schrader, Ernest K.; et al. (1988). "Concrete Dam Construction and Foundation Treatment". In Jansen, R.B. (ed.). Advanced Dam Engineering for Design, Construction, and Rehabilitation. Van Nostrand Reinhold. pp. 540–577. ISBN 0442243979. Retrieved 20 April 2026.

• Siddiqui, I.H. (2009). Dams and Reservoirs: Planning and Engineering. Oxford University Press. ISBN 9780195475852. Retrieved 20 April 2026.

• Smith, Norman (1975). Man and Water: A History of Hydro-technology. Charles Scribner's Sons. ISBN 0684145227. Retrieved 13 May 2026.

• Turpin, Trevor (2008). Dam. Reaktion Books. ISBN 9781861893284. Retrieved 20 April 2026.

Journals, news, and websites

• Bellmore, J. R.; et al. (2017) [2016]. "Status and Trends of Dam Removal Research in the United States". WIREs Water. 4 (2) e1164. Wiley-Blackwell. doi:10.1002/wat2.1164. ISSN 2049-1948. Retrieved 22 May 2026.

• Boulange, Julien; et al. (2021). "Role of Dams in Reducing Global Flood Exposure Under Climate Change". Nature Communications. 12 (1) 417. Springer Nature. Bibcode:2021NatCo..12..417B. doi:10.1038/s41467-020-20704-0. ISSN 2041-1723. PMC 7814128. PMID 33462241.

• Brown, John Guthrie; et al. (2026). "Dam". Britannica. Retrieved 22 April 2026.

• Bulu, Atil. "Water Resources: Lecture Notes IV" (PDF). Istanbul Technical University. Retrieved 22 April 2026.

• El-Askary, Hesham; et al. (2026). "The World's Largest Saddle Dam at Risk". International Journal of Disaster Risk Reduction. 135 106045. Elsevier. doi:10.1016/j.ijdrr.2026.106045. ISSN 2212-4209.

• Fowkes, Maja; et al. (2025). "Mega-Dams In the Hydrologics of the Socialist Anthropocene". ARTMargins. 14 (2). The MIT Press: 11–38. doi:10.1162/artm_a_00411. ISSN 2162-2574. Retrieved 21 May 2026.

• Graves, Carl (29 August 2016). "Buhen: A Site Submerged". Egypt Exploration Society. Retrieved 29 May 2026.

• Horn, John (1 May 2014). "Patagonia's New Line of Activism Is Documentary 'DamNation'". Los Angeles Times. ISSN 2165-1736.

• Krol, Debra (2 September 2024). "Largest Dam Removal Project in US: Klamath River Flows Freely". USA TODAY. ISSN 0734-7456. Retrieved 22 May 2026.

• Lad, Rahul; et al. (2024). "India and the Ganga Waters Treaty: Analysis of the Water Sharing Mechanism". International Studies. 61 (2). SAGE Publications: 185–202. doi:10.1177/00208817241285256. ISSN 0020-8817. Retrieved 18 May 2026.

• Lehner, Bernhard; et al. (2011). "High-Resolution Mapping of the World's Reservoirs and Dams for Sustainable River-Flow Management". Frontiers in Ecology and the Environment. 9 (9). Ecological Society of America: 494–502. doi:10.1890/100125. ISSN 1540-9295. Retrieved 30 April 2026.

• Lichtenstein, Grace (20 January 1976). "Edward Abbey, Voice of Southwest Wilds". The New York Times. Retrieved 17 May 2026.

• Marchetti, Nicolò; et al. (2019). "A Multi-scalar Approach for Assessing the Impact of Dams on the Cultural Heritage in the Middle East and North Africa". Journal of Cultural Heritage. 37. Elsevier: 17–28. doi:10.1016/j.culher.2018.10.007. ISSN 1296-2074. Retrieved 26 May 2026.

• McSweeney, Catherine (1 September 2023). "Rewilding Europe's Rivers with Dam Removal Boosts Biodiversity, Economy". European Investment Bank. Retrieved 22 May 2026.

• Niranjan, Ajit (21 May 2026). "Record Number of Dams Dismantled in Europe in Effort to Help Wildlife Thrive". The Guardian. ISSN 1756-3224. Retrieved 22 May 2026.

• Onder, H.; Yilmaz, M. (2005). "Underground Dams: A Tool of Sustainable Development and Management of Ground Resources" (PDF). European Water. 11 (12). European Water Resources Association: 35–45. ISSN 1105-7580. Retrieved 9 May 2026. Author M. Yilmaz wrote a 2003 Masters thesis with additional detail and history on underground dams.

• Pearse-Smith, Scott W.D.; et al. (February 2014). "The Return of Large Dams to the Development Agenda: A Post-Development Critique". Consilience: The Journal of Sustainable Development. 11 (11). Columbia University Libraries: 123–131. ISSN 2333-9705. JSTOR 26188733.

• Ranjan, Amit (2024). "Grand Ethiopian Renaissance Dam Dispute: Implications, Negotiations, And Mediations". Journal of Contemporary African Studies. 42 (1). Routledge: 18–36. doi:10.1080/02589001.2023.2287425. ISSN 0258-9001.

• Ritchie, A. C.; et al. (2018). "Morphodynamic Evolution Following Sediment Release from the World's Largest Dam Removal". Scientific Reports. 8 (1) 13279. National Library of Medicine. doi:10.1038/s41598-018-30817-8. ISSN 2045-2322.

• Sutor, Dave (24 March 2018). "Johnstown Flood: McCullough's 'Lucky Break' Launched Career". AP News. Retrieved 16 May 2026.

• Villamayor-Tomas, Sergio; et al. (2026). "Challenges and Opportunities for the Governance of Hydropower". Nature Sustainability. 9 (5). Nature Portfolio: 653–663. doi:10.1038/s41893-026-01782-2. ISSN 2398-9629. Retrieved 25 April 2026.

• Watts, Jonathan (25 February 2019). "Concrete: the Most Destructive Material on Earth". The Guardian. ISSN 1756-3224. Retrieved 31 May 2026.

• Wieland, Martin (15 September 2023). "Comparing Vulnerabilities of CFRDs and ECRDs". International Water Power & Dam Construction. ISSN 0306-400X. Retrieved 31 May 2026.

Unknown author

• "Bombs Away". The Guardian. 6 May 2003. ISSN 1756-3224. Retrieved 15 May 2026.

• "China's Three Gorges Dam Faces Flood Test". BBC News. 20 July 2010. Retrieved 5 May 2026.

• "Concrete CO2 Fact Sheet" (PDF). National Ready Mixed Concrete Association. June 2008. Retrieved 20 May 2026.

• "Dam". Collins English Dictionary. HarperCollins. 2026. Retrieved 30 April 2026.

• "Dam Inspection and Plan Review (PH21-V-6)" (PDF). Mine Safety and Health Administration. MSHA Handbook Series. U.S. Department of Labor. 2021. Retrieved 30 April 2026.

• Dam Safety Management: Operational Phase of the Dam Life Cycle (PDF). International Commission on Large Dams. 2011. Retrieved 28 April 2026.

• "Geneva Conventions 1949 Protocol I" (PDF). International Committee of the Red Cross. Retrieved 28 May 2026.

• "Glossary". Reclamation Library. US Bureau of Reclamation. 2022. Retrieved 30 April 2026.

• "Grande Dixence". Grande Dixence SA. 2026. Retrieved 18 May 2026.

• "Hydraulic Design of Spillways". United States Army Corps of Engineers. 1965. Retrieved 20 April 2026.

• "Hydroelectric Power". Britannica. 2026. Retrieved 13 May 2026.

• "I-205 Abernethy Bridge" (PDF). Oregon Department of Transportation. Archived (PDF) from the original on 25 November 2025. Retrieved 2 October 2025.

• Instrumentation of Embankment Dams and Levees: Engineering and Design. United States Army Corps of Engineers. 1995. Retrieved 20 April 2026.

• Integrated Operation of Hydropower Stations and Reservoirs (PDF). International Commission on Large Dams. 2022. ISBN 9780367770051. Retrieved 28 April 2026.

• "Locks". Britannica. Retrieved 13 May 2026.

• Multipurpose Water Storage (PDF). International Commission on Large Dams. 2025. ISBN 9781003640035. Retrieved 28 April 2026.

• Observed Performance of Dams During Earthquakes: Volume III (PDF). United States Society on Dams. 2014. ISBN 978-1-884575-65-5.

• Regulation of Dam Safety (PDF). International Commission on Large Dams (ICOLD). 2025. ISBN 9781032456058. Retrieved 28 April 2026.

• "Research with GDW Data". Global Dam Watch. 2015. Retrieved 30 April 2026.

• "Three Gorges Dam". Britannica. 2026. Retrieved 15 May 2026.

• "Tracking Barriers and Their Impacts on European River Ecosystems". European Environment Agency. 8 February 2021. Retrieved 22 May 2026.

• "World Register of Dams: General Synthesis". International Commission on Large Dams (ICOLD). September 2025. Retrieved 30 April 2026.

• "Zuiderzee". Britannica. 2026. Retrieved 5 May 2026.