Dam

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

in Spain was built by the Romans, and has been in use for almost two millennia. dam in Iran was built in the 3rd century CE. was built around 1350 CE. in Spain was the first true arch dam built in Europe since Roman times. tested the limits of how thin a dam could be. Antiquity The earliest known dam is the Jawa Dam near Amman Jordan, built around 3000 BCE. This embankment dam was part of an elaborate irrigation system, and was wide and high. Around 2600 BCE, Egyptians built the Sadd el-Kafara embankment dam near Cairo, although it failed about the time its construction completed. Some of the stone blocks weighed . 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 dam (built around 500 BCE) which was long and 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 Chinabuilt by engineer Sunshu Ao around 580 BCEimpounded the Afengtang Reservoir which is still in existence today. In Sri Lanka, several damsincluding Tissa Wewawere build around 370 BCE to create reservoirs; some of the dams were several kilometers long. Roman era The Roman empire constructed major water worksincluding aqueducts and tunnelsstarting 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 the tallest they built: the Subiaco dam, built around 60 CE, stood tall and wide. The Romans built about 80 dams in Hispania (modern Spain), including the Proserpina Dam, which impounded 6 million m 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 One of the earliest dams built in Japan was the Sayama embankment, built near Osaka in 380 CE, and long. The Kurit Damthe world's first large, thin arch damwas built in Persia (modern-day Iran) around 1350 CE. Its height was initially and was later raised to ; 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 in stone. A notable example is the Veeranam Dam built around 1020 CE in Tamil Nadu, 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 km. Dams for irrigation included the Almansa Dama 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 designed by Mimar Sinan in 1560 to bring water from Belgrad Forest. Another purpose for 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 the late 18th century, the process of designing dams began to transform from an informal practice based on experience, to an engineering discipline rooted in science. Important figures that contributed to this evolution included 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. 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. 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 high embankment dam that contained a clay core and had gently sloping faces. In France, the Gouffre d'Enfer masonry gravity dam (1866) was tall. The world's first large buttress dam was Mir Alam Dam (1804) in India. In Australia, an arch damthe Parramatta Dam (1856)tested the limits of how thin a dam could be. Modern era in China In the first half of the 20th century, many large dams were built, particularly in western Europe and the US. After WW II, the availability of power construction machinery such as bulldozers, dump trucks, and scrapers contributed to an explosion in the number of large dams. The 1933 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 across the Nile river, which has a deep, sandy riverbed: grout was pumped deep into the riverbed (spanning 57,000 m), preventing water from flowing underneath the dam. Notable dams built in the modern era include: • Afsluitdijk (Netherlands, 1932) A 32 km long causeway that reclaimed 1,620 km of land. • Hoover Dam (US 1936) Enabled the development of the US Southwest. • Grand Coulee Dam (US, 1942) Provided irrigation for a large portion of northwest US. • Aswan High Dam (Egypt, 1970) Revolutionized Egyptian society by providing a reliable water supply. • Tarbela Dam (Pakistan, 1976) One of the largest earth-filled dams in the world. • Nurek Dam (Tajikistan, 1980) One of the tallest dams in the world. • Itaipu Dam (Brazil/Paraguay, 1984) An example of international cooperation. • Three Gorges Dam (China 2006). The reservoir it created displaced 1.4 million people. • Grand Ethiopian Renaissance Dam (Ethiopia, 2025) Sparked a major political conflict between Ethiopia and Egypt. 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 seven-year 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 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 The number of large dams in the world 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 km of water, which is about 10% of the volume of the earth's natural freshwater lakes. The reservoirs cover about 305,000 km 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. == Types==

Dams can be classified by their structure. The major structural types are embankment, gravity, buttress, and arch. Other forms include hybrid dams and non-humanmade dams. Embankment dam Embankment dams are the most common type of dams in the world. An embankment dam consists of a pile of earth (rocks, clay, sand, gravel, soil, etc) placed in such a way to impound a reservoir or block the flow of water. Embankment dams are the only type of modern dam not made of concrete. There are several advantages of embankment dams. First, they can be built from locally available dirt and rocks, as opposed to importing rocks and cement required for concrete dams. Second, they tend to be less expensive to build. Finally, they can 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 the dam or underneath the dam. Mitigation techniques to reduce seepage include the use of a clay wall within the dam, placing a drainage system underneath the dam, and injecting grout into the soil below the dam. Failure to properly mitigate seepage can lead to dam failure caused by "piping": when water starts to flow thru (or under) the dam in a small channel, which gradually enlarges until a large hole is pierced through the dam. Early embankment dams were often built of a single type of earth, but starting in mid-16th century, dam engineers began to use several types of material, carefully layered in zones. A typical zone pattern for embankment dams is a clay center (a vertical wall, extending from the riverbed to the crest of the dam), with gradually sloped banks of soil on both upstream and downstream sides, and both faces covered with large rocks. The resistance to water seepage varies widely between the various materials: clay resists water seepage 10x more than silt, 10,000x more than sand, and 100,000,000x more than gravel.. Gravity dam Gravity dams are dams that rely on their weight to remain immobile and resist the forces exerted by the upstream waters. In the past, gravity dams were built of masonry (stone, brick, or rubble) with mortar filling the joints; in the modern era, most gravity dams are made of concrete. Concrete gravity dams can be solid or hollow. The crest (top) of most gravity dams is a straight line, perpendicular to the walls of the valley it crosses. When the crest of a gravity dam is curved (the convex side of the curve always faces upstream) it is called an arch-gravity dam (described below). The cross-section of gravity dams is typically triangular, with a flat bottom resting on bedrock, and two slightly inclined faces (upstream and downstream) that meet at the crest. The upstream face is typically more vertical than the downstream face, to ensure stability. 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 is permeable in any way, grout must be injected into the bedrock (before the dam is constructed) to seal the cracks and ensure that no water will seep under the dam. 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 result in 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. When concrete cures, it generates heat. For large dams this excess heat in the interior of the dam can cause the concrete to crack. 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. Buttress dam 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 dams slant, typically with inclinations between 0.7 and 1.67. 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 (contrasted with gravity dams, where the dam's weight alone is sufficient to remain immobile). Buttress dams use much less concrete than a comparable gravity dam, but have a more complex construction process, and are not as strong. Because buttress dams have a much smaller footprint (the area of ground the dam covers) than gravity dams, the risks associated with uplift forces (from water under 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 An arch dam is a curved dam that transfers the force of the impounded waters 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 a location in a valley where the valley is relatively narrow and has strong, steep rock walls. Arch dams are always made of concrete or masonry, and are relatively thin: the width of their base (measured in the upstream-downstream direction) is less than half their height. The angle subtended by the arc of an arch dam can be relatively shallow or nearly semicircular: arch dams exist with arcs 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. Research into optimizing dam shapes for maximum strenght led many dam engineers to adopt the constant angle shape for arch dams, with the first example built in 1914. Another shape is the "double curved" or "cupola" which resembles a section of a dome, and is defined by incorporating curvature in the vertical direction, as well as the 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, special concrete abutments must be constructed between the dam's arch and the valley walls to safely transfer the load. 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 flatrather, the face consists of a number of small arch dams: one arch connecting each pair of adjacent buttresses. Rockslide dams is a rockslide dam formed in 1911 by an earthquake. At high, it is the tallest dam 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: many are the result of volcanic activity, which can create dams from lava flows, lahar deposits, pyroclastic flows, or other debris. == Uses ==

Primary purposes The main purposes that dams serve are hydropower, water supply, irrigation, flood management, land reclamation, and inland navigation. Other purposes Not all dams are created to support the primary purposes listed above: some dams support other purposes (often in addition to primary purposes). Dams that support other purposes include tailings dams, saddle dams, weirs, cofferdams, check dams, dry dams, diversionary dams, and underground dams. surrounds a pit used to store waste from mining activity. A tailings dam is typically an earth-fill embankment dam used to store tailings, which are produced during mining operations after separating the valuable fraction from the uneconomic fraction of an ore. Conventional water retention dams can serve this purpose, but due to cost, a tailings dam is more viable. Unlike water retention dams, a tailings dam is raised in succession throughout the life of the particular mine. Typically, a base or starter dam is constructed, and as it fills with a mixture of tailings and water, it is raised. Material used to raise the dam can include the tailings (depending on their size) along with soil. A saddle dam is an auxiliary dam constructed to confine the reservoir created by a primary dam either to permit a higher water elevation and storage or to limit the extent of a reservoir for increased efficiency. An auxiliary dam is constructed in a low spot or "saddle" through which the reservoir would otherwise escape. On occasion, a reservoir is contained by a similar structure called a dike to prevent inundation of nearby land. Dikes are commonly used for reclamation of arable land from a shallow lake, similar to a levee, which is a wall or embankment built along a river or stream to protect adjacent land from flooding. A weir is a low dam placed in a river channel. Other names (sometimes associated with specific purpose) include overflow dam, low head dam, and fixed-crest dam. Weirs are typically a straight, level and made of concrete. Some weirs are designed to maintain depth in the upstream channel to supportc navigation. They can pose risks to boaters who may travel over them, as they may be difficult to see and may create induced currents that are difficult to escape. A barrage dam is a special kind of dam that consists of a line of large gates that can be opened or closed to control the amount of water passing the dam. The gates are set between flanking piers which are responsible for supporting the water load, and are often used to control and stabilize water flow for irrigation systems. Barrages that are built at the mouths of rivers or lagoons to prevent tidal incursions or use the tidal flow for tidal power are known as tidal barrages. during the construction of locks at the Montgomery Point Lock and Dam A cofferdam is a barrier, usually temporary, constructed to exclude water from an area that is normally submerged. Made commonly of wood, concrete, or steel sheet piling, cofferdams are used to allow construction on the foundation of permanent dams, bridges, and similar structures. When the project is completed, the cofferdam will usually be demolished or removed unless the area requires continuous maintenance. A check dam is a small dam designed to reduce flow velocity and control soil erosion. Conversely, a wing dam is a structure that only partly restricts a waterway, creating a faster channel that resists the accumulation of sediment. A dry dam, also known as a flood retarding structure, is designed to control flooding. It normally holds back no water and allows the channel to flow freely, except during periods of intense flow that would otherwise cause flooding downstream. A diversionary dam is designed to divert all or a portion of the flow of a river from its natural course. The water may be redirected into a canal or tunnel for irrigation and/or hydroelectric power production. Underground dams are used to trap groundwater and store all or most of it below the surface for extended use in a localized area. In some cases, they are also built to prevent saltwater from intruding into a freshwater aquifer. Underground dams are typically constructed in areas where water resources are minimal and need to be efficiently stored, such as in deserts and on islands like the Fukuzato Dam in Okinawa, Japan. They are most common in northeastern Africa and the arid areas of Brazil while also being used in the southwestern United States, Mexico, India, Germany, Italy, Greece, France and Japan. ==Design==

Design process Geological assessment and site selection Specifications and Standards Aesthetics A dam's appearance can be a factor when evaluating potential designs. Bridges with some curvature, such as arch dams, tend to be perceived as more attractive than those designed with entirely straight lines. The advent of concrete after WWII as material for building bridges gave designers more flexibility to create pleasing bridge designs. Some dams such as the Hoover Dam and the Bratsk Damserve as objects that inspire admiration and pride, and can act as a symbol or icon of a community. Swiss dam engineer Niklaus Schnitter maintains that it is impossible to objectively determine if a dam and its reservoir will improve or detract from the pre-dam landscape, maintaining that it is a matter of taste. Materials Earthen Concrete and masonry Other Some dams are made of steel. Others are made of timber. Impact assessment Impact is assessed in several ways: the benefits to human society arising from the dam (agriculture, water, damage prevention and power), harm or benefit to nature and wildlife, impact on the geology of an area (whether the change to water flow and levels will increase or decrease stability), and the disruption to human lives (relocation, loss of archeological or cultural matters underwater). Environmental impact Reservoirs held behind dams affect many ecological aspects of a river. Rivers topography and dynamics depend on a wide range of flows, whilst rivers below dams often experience long periods of very stable flow conditions or sawtooth flow patterns caused by releases followed by no releases. Water releases from a reservoir including that exiting a turbine usually contain very little suspended sediment, and this, in turn, can lead to scouring of river beds and loss of riverbanks; for example, the daily cyclic flow variation caused by the Glen Canyon Dam was a contributor to sand bar erosion. Older dams often lack a fish ladder, which keeps many fish from moving upstream to their natural breeding grounds, causing failure of breeding cycles or blocking of migration paths. Even fish ladders do not prevent a reduction in fish reaching the spawning grounds upstream. In some areas, young fish ("smolt") are transported downstream by barge during parts of the year. Turbine and power-plant designs that have a lower impact upon aquatic life are an active area of research. At the same time, however, some particular dams may contribute to the establishment of better conditions for some kinds of fish and other aquatic organisms. Studies have demonstrated the key role played by tributaries in the downstream direction from the main river impoundment, which influenced local environmental conditions and beta diversity patterns of each biological group. Both replacement and richness differences contributed to high values of total beta diversity for fish (average = 0.77) and phytoplankton (average = 0.79), but their relative importance was more associated with the replacement component for both biological groups (average = 0.45 and 0.52, respectively). Such changes may be explained by the fact that the fish obtained "different feeding habits, with almost all species being found in more than one group. Large reservoirs formed behind dams have been indicated in the contribution of seismic activity, due to changes in water load and/or the height of the water table. However, this is a mistaken assumption, because the relatively marginal stress attributed to the water load is orders of magnitude lesser than the force of an earthquake. The increased stress from the water load is insufficient to fracture the Earth's crust, and thus does not increase the severity of an earthquake. Dams are also found to influence global warming. The changing water levels in reservoirs are a source for greenhouse gases like methane. While dams and the water behind them cover only a small portion of earth's surface, they harbour biological activity that can produce large quantities of greenhouse gases. Social impact Dams' impact on human society is significant. Nick Cullather argues in ''Hungry World: America's Cold War Battle Against Poverty in Asia'' that dam construction requires the state to displace people in the name of the common good, and that it often leads to abuses of the masses by planners. He cites Morarji Desai, Interior Minister of India, in 1960 speaking to villagers upset about the Pong Dam, who threatened to "release the waters" and drown the villagers if they did not cooperate. The Three Gorges Dam on the Yangtze River in China is more than five times the size of the Hoover Dam (U.S.). It creates a reservoir long to be used for flood control and hydropower generation. Its construction required the loss of over a million people's homes and their mass relocation, the loss of many valuable archaeological and cultural sites, and significant ecological change. During the 2010 China floods, the dam held back a what would have been a disastrous flood and the huge reservoir rose by 4 m (13 ft) overnight. In 2008, it was estimated that 40–80 million people worldwide have been displaced from their homes as a result of dam construction. Economic impact Construction of a hydroelectric plant requires a long lead time for site studies, hydrological studies, and environmental impact assessments, and are large-scale projects in comparison to carbon-based power generation. The number of sites that can be economically developed for hydroelectric production is limited; new sites tend to be far from population centers and usually require extensive power transmission lines. Hydroelectric generation can be vulnerable to major changes in the climate, including variations in rainfall, ground and surface water levels, and glacial melt, causing additional expenditure for the extra capacity to ensure sufficient power is available in low-water years. Once completed, if it is well designed and maintained, a hydroelectric power source is usually comparatively cheap and reliable. It has no fuel and low escape risk, and as a clean energy source it is cheaper than both nuclear and wind power. It is more easily regulated to store water as needed and generate high power levels on demand compared to wind power. == Auxiliary structures ==

Hydropower and electric generator , hydroelectric power, mostly from dams, supplies some 19% of the world's electricity, and over 63% of renewable energy. Much of this is generated by large dams, although China uses small-scale hydro generation on a wide scale and is responsible for about 50% of world use of this type of power. Erosion rates are often monitored, and the risk is ordinarily minimized, by shaping the downstream face of the spillway into a curve that minimizes turbulent flow, such as an ogee curve. Gates Locks Penstocks, inlets, and outlets Fish ladders ==Construction ==

Cofferdams and diversion of river Preparation, grouting, and foundations Building the dam Filling Hydropower facilities ==Operation and maintenance==

Management procedures Maintenance, leaks, and repairs Inspection and monitoring Sedimentation of reservoir Dam removal Water and sediment flows can be re-established by removing dams from a river. Dam removal is considered appropriate when the dam is old and maintenance costs exceed the expense of its removal. Some effects of dam removal include erosion of sediment in the reservoir, increased sediment supply downstream, increased river width and braiding, re-establishment of natural water temperatures and recolonisation of habitats that were previously unavailable due to dams. As a result, the delivery of sediment and wood to the downstream river and delta were re-established. Approximately 65% of the sediment stored in the reservoirs eroded, of which ~10% was deposited in the riverbed. The remaining ~90% was transported to the coast. In total, renewed sediment delivery caused approximately 60 ha of delta growth, and also resulted in increased river braiding. == Safety and Failures==

Risk analysis and mitigation methods Failures failed in 1976 in the US. failed in 1959 in France. Dam failures are generally catastrophic if the structure is breached or significantly damaged. Routine deformation monitoring and monitoring of seepage from drains in and around larger dams is useful to anticipate any problems and permit remedial action to be taken before structural failure occurs. Most dams incorporate mechanisms to permit the reservoir to be lowered or even drained in the event of such problems. Another solution can be rock grouting – pressure pumping Portland cement slurry into weak fractured rock. The main causes of dam failure include inadequate spillway capacity, piping through the embankment, foundation or abutments, spillway design error (South Fork Dam), geological instability caused by changes to water levels during filling or poor surveying (Vajont, Malpasset, Testalinden Creek dams), poor maintenance, especially of outlet pipes (Lawn Lake Dam, Val di Stava Dam collapse), extreme rainfall (Shakidor Dam), earthquakes, and human, computer or design error (Buffalo Creek Flood, Dale Dike Reservoir, Taum Sauk pumped storage plant). Since 2007, the Dutch IJkdijk foundation is developing, with an open innovation model, an early warning system for levee/dike failures. As a part of the development effort, full-scale dikes are destroyed in the IJkdijk fieldlab. The destruction process is monitored by sensor networks from an international group of companies and scientific institutions. == Society and culture ==

International geopolitics Profession and regulation Most countries with large dams have statutes or regulations regulating dam construction and inspection practices. The regulations vary widely across the countries. Some nations have an 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 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 Wartime During an armed conflict, a dam is to be considered as an "installation containing dangerous forces" due to the massive impact of possible destruction on the civilian population and the environment. As such, it is protected by the rules of international humanitarian law (IHL) and shall not be made the object of attack if that may cause severe losses among the civilian population. To facilitate the identification, a protective sign consisting of three bright orange circles placed on the same axis is defined by the rules of IHL. A notable case of deliberate destruction of a dam was the Royal Air Force 'Dambusters' raid on Germany in World War II (codenamed "Operation Chastise"), in which three German dams were selected to be breached in order to damage German infrastructure and manufacturing and power capabilities deriving from the Ruhr and Eder rivers. This raid later became the basis for several films. == References==