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A dam is a barrier that stops or restricts the flow of surface water or underground streams. created by dams not only suppress floods but also provide water for activities such as irrigation, drinking water, Industrial water, aquaculture, and navigability. Hydropower is often used in conjunction with dams to generate electricity. A dam can also be used to collect or store water which can be evenly distributed between locations. Dams generally serve the primary purpose of retaining water, while other structures such as or (also known as dikes) are used to manage or prevent water flow into specific land regions.
The word dam can be traced back to Middle English,http://www.bartleby.com/ and before that, from Middle Dutch, as seen in the names of many old cities,Source: Tijdschrift voor Nederlandse Taal- en Letterkunde ( Magazine for Dutch Language and Literature), 1947 such as Amsterdam and Rotterdam.
Ancient dams were built in Mesopotamia and the Middle East for water control. The earliest known dam is the Jawa Dam in Jordan, dating to 3,000 BC. Egyptians also built dams, such as Sadd-el-Kafara Dam for flood control. In modern-day India, Dholavira had an intricate water-management system with 16 reservoirs and dams. The Great Dam of Marib in Yemen, built between 1750 and 1700 BC, was an engineering wonder, and Eflatun Pinar, a Hittite dam and spring temple in Turkey, dates to the 15th and 13th centuries BC. The Kallanai Dam in South India, built in the 2nd century AD, is one of the oldest water regulating structures still in use.
Roman engineers built dams with advanced techniques and materials, such as hydraulic mortar and Roman concrete, which allowed for larger structures. They introduced reservoir dams, arch-gravity dams, arch dams, buttress dams, and multiple arch buttress dams. In Iran, bridge dams were used for hydropower and water-raising mechanisms.
During the Middle Ages, dams were built in the Netherlands to regulate water levels and prevent sea intrusion. In the 19th century, large-scale arch dams were constructed around the British Empire, marking advances in dam engineering techniques. The era of large dams began with the construction of the Aswan Low Dam in Egypt in 1902. The Hoover Dam, a massive concrete arch-gravity dam, was built between 1931 and 1936 on the Colorado River. By 1997, there were an estimated 800,000 dams worldwide, with some 40,000 of them over 15 meters high.
The earliest known dam is the Jawa Dam in Jordan, northeast of the capital Amman. This gravity dam featured an originally and stone wall, supported by a earthen rampart. The structure is dated to 3000 BC.Günther Garbrecht: "Wasserspeicher (Talsperren) in der Antike", Antike Welt, 2nd special edition: Antiker Wasserbau (1986), pp.51–64 (52)S.W. Helms: "Jawa Excavations 1975. Third Preliminary Report", Levant 1977 However, the oldest continuously operational dam is Lake Homs Dam, built in Syria between 1319-1304 BC.
The Sadd-el-Kafara Dam at Wadi Al-Garawi, about south of Cairo, was long at its base and wide. The structure was built around 2800Günther Garbrecht: "Wasserspeicher (Talsperren) in der Antike", Antike Welt, 2nd special edition: Antiker Wasserbau (1986), pp.51–64 (52f.) or 2600 BChttp://www.fao.org/docrep/005/y4357e/y4357e14.htm as a diversion dam for flood control, but was destroyed by heavy rain during construction or shortly afterwards. During the Twelfth Dynasty in the 19th century BC, the Pharaohs Senosert III, Amenemhat III, and Amenemhat IV dug a canal long linking the Fayum Depression to the Nile in Middle Egypt. Two dams called Ha-Uar running east–west were built to retain water during the annual flood and then release it to surrounding lands. The lake called Mer-wer or Lake Moeris covered and is known today as Birket Qarun.
By the mid-late third millennium BC, an intricate water-management system in Dholavira in modern-day India was built. The system included 16 reservoirs, dams and various channels for collecting water and storing it.http://old.himalmag.com/component/content/article/1062-the-reservoirs-of-dholavira.html
One of the engineering wonders of the ancient world was the Marib Dam in Yemen. Initiated sometime between 1750 and 1700 BC, it was made of packed earth – triangular in cross-section, in length and originally high – running between two groups of rocks on either side, to which it was linked by substantial stonework. Repairs were carried out during various periods, most importantly around 750 BC, and 250 years later the dam height was increased to . After the end of the Sabaeans, the dam fell under the control of the Ḥimyarites (c. 115 BC) who undertook further improvements, creating a structure high, with five spillways, two masonry-reinforced sluices, a settling pond, and a canal to a distribution tank. These works were not finished until 325 AD when the dam permitted the irrigation of .
Eflatun Pınar is a Hittites dam and spring temple near Konya, Turkey. It is thought to date from the Hittite empire between the 15th and 13th centuries BC.
The Kallanai is constructed of unhewn stone, over long, high and wide, across the main stream of the Kaveri River in Tamil Nadu, South India. The basic structure dates to the 2nd century AD and is considered one of the oldest water diversion or water regulating structures still in use. The purpose of the dam was to divert the waters of the Kaveri across the fertile delta region for irrigation via canals.
Du Jiang Yan is the oldest surviving irrigation system in China that included a dam that directed waterflow. It was finished in 251 BC. A large earthen dam, made by Sunshu Ao, the prime minister of Chu (state), flooded a valley in modern-day northern Anhui Province that created an enormous irrigation reservoir ( in circumference), a reservoir that is still present today.Needham, Joseph (1986). Science and Civilization in China: Volume 4, Part 3. Taipei: Caves Books, Ltd.
Roman engineers made routine use of ancient standard designs like embankment dams and masonry gravity dams. Apart from that, they displayed a high degree of inventiveness, introducing most of the other basic dam designs which had been unknown until then. These include ,; ,; ; ; ; and multiple arch buttress dams,; ; ; all of which were known and employed by the 2nd century AD (see List of Roman dams). Roman workforces also were the first to build dam bridges, such as the Bridge of Valerian in Iran.
In Iran, bridge dams such as the Band-e Kaisar were used to provide hydropower through , which often powered water-raising mechanisms. One of the first was the Roman-built dam bridge in Dezful, which could raise water 50 (c. 23 m) to supply the town. Also were known.Donald Routledge Hill (1996), "Engineering", p. 759, in Milling dams were introduced which the Muslim engineers called the Pul-i-Bulaiti. The first was built at Shustar on the River Karun, Iran, and many of these were later built in other parts of the Islamic world. Water was conducted from the back of the dam through a large pipe to drive a water wheel and watermill.Adam Lucas (2006), Wind, Water, Work: Ancient and Medieval Milling Technology, p. 62. Brill, . In the 10th century, Al-Muqaddasi described several dams in Persia. He reported that one in Ahvaz was more than long, and that it had many water-wheels raising the water into aqueducts through which it flowed into reservoirs of the city. Another one, the Band-i-Amir Dam, provided irrigation for 300 villages.
In the Netherlands, a low-lying country, dams were often built to block rivers to regulate the water level and to prevent the sea from entering the marshlands. Such dams often marked the beginning of a town or city because it was easy to cross the river at such a place, and often influenced Dutch place names. The present Dutch capital, Amsterdam (old name Amstelredam), started with a dam on the river Amstel in the late 12th century, and Rotterdam began with a dam on the river Rotte, a minor tributary of the Nieuwe Maas. The central square of Amsterdam, covering the original site of the 800-year-old dam, still carries the name Dam Square.
Three pioneering arch dams were built around the British Empire in the early 19th century. Henry Russel of the Royal Engineers oversaw the construction of the Mir Alam dam in 1804 to supply water to the city of Hyderabad (it is still in use today). It had a height of and consisted of 21 arches of variable span.
In the 1820s and 30s, Lieutenant-Colonel John By supervised the construction of the Rideau Canal in Canada near modern-day Ottawa and built a series of curved masonry dams as part of the waterway system. In particular, the Jones Falls Dam, built by John Redpath, was completed in 1832 as the largest dam in North America and an engineering marvel. In order to keep the water in control during construction, two , artificial channels for conducting water, were kept open in the dam. The first was near the base of the dam on its east side. A second sluice was put in on the west side of the dam, about above the base. To make the switch from the lower to upper sluice, the outlet of Sand Lake was blocked off.
Hunts Creek near the city of Parramatta, Australia, was dammed in the 1850s, to cater to the demand for water from the growing population of the city. The masonry arch dam wall was designed by Lieutenant Percy Simpson who was influenced by the advances in dam engineering techniques made by the Royal Engineers in British India. The dam cost £17,000 and was completed in 1856 as the first engineered dam built in Australia, and the second arch dam in the world built to mathematical specifications.
The first such dam was opened two years earlier in France. It was the first French arch dam of the industrial era, and it was built by François Zola in the municipality of Aix-en-Provence to improve the supply of water after the 1832 cholera outbreak devastated the area. After royal approval was granted in 1844, the dam was constructed over the following decade. Its construction was carried out on the basis of the mathematical results of scientific stress analysis.
The 75-miles dam near Warwick, Australia, was possibly the world's first concrete arch dam. Designed by Henry Charles Stanley in 1880 with an overflow spillway and a special water outlet, it was eventually heightened to .
In the latter half of the nineteenth century, significant advances in the scientific theory of masonry dam design were made. This transformed dam design from an art based on empirical methodology to a profession based on a rigorously applied scientific theoretical framework. This new emphasis was centered around the engineering faculties of universities in France and in the United Kingdom. William John Macquorn Rankine at the University of Glasgow pioneered the theoretical understanding of dam structures in his 1857 paper On the Stability of Loose Earth. Rankine theory provided a good understanding of the principles behind dam design.Rankine, W. (1857) "On the stability of loose earth". Philosophical Transactions of the Royal Society of London, Vol. 147. In France, J. Augustin Tortene de Sazilly explained the mechanics of vertically faced masonry gravity dams, and Zola's dam was the first to be built on the basis of these principles.
The Hoover Dam is a massive concrete arch-gravity dam, constructed in the Black Canyon of the Colorado River, on the border between the US states of Arizona and Nevada between 1931 and 1936 during the Great Depression. In 1928, Congress authorized the project to build a dam that would control floods, provide irrigation water and produce hydroelectric power. The winning bid to build the dam was submitted by a consortium called Six Companies, Inc. Such a large concrete structure had never been built before, and some of the techniques were unproven. The torrid summer weather and the lack of facilities near the site also presented difficulties. Nevertheless, Six Companies turned over the dam to the federal government on 1 March 1936, more than two years ahead of schedule.
By 1997, there were an estimated 800,000 dams worldwide, some 40,000 of them over high. In 2014, scholars from the University of Oxford published a study of the cost of large dams – based on the largest existing dataset – documenting significant cost overruns for a majority of dams and questioning whether benefits typically offset costs for such dams.
Two types of single-arch dams are in use, namely the constant-angle and the constant-radius dam. The constant-radius type employs the same face radius at all elevations of the dam, which means that as the channel grows narrower towards the bottom of the dam the central angle subtended by the face of the dam becomes smaller. Jones Falls Dam, in Canada, is a constant radius dam. In a constant-angle dam, also known as a variable radius dam, this subtended angle is kept constant and the variation in distance between the abutments at various levels is taken care of by varying the radii. Constant-radius dams are much less common than constant-angle dams. Parker Dam on the Colorado River is a constant-angle arch dam.
A similar type is the double-curvature or thin-shell dam. Wildhorse Dam near Mountain City, Nevada, in the United States is an example of the type. This method of construction minimizes the amount of concrete necessary for construction but transmits large loads to the foundation and abutments. The appearance is similar to a single-arch dam but with a distinct vertical curvature to it as well lending it the vague appearance of a concave lens as viewed from downstream.
The multiple-arch dam consists of a number of single-arch dams with concrete buttresses as the supporting abutments, as for example the Daniel-Johnson Dam, Québec, Canada. The multiple-arch dam does not require as many buttresses as the hollow gravity type but requires a good rock foundation because the buttress loads are heavy.
For this type of dam, it is essential to have an impervious foundation with high bearing strength. Permeable foundations have a greater likelihood of generating uplift pressures under the dam. Uplift pressures are hydrostatic pressures caused by the water pressure of the reservoir pushing up against the bottom of the dam. If large enough uplift pressures are generated there is a risk of destabilizing the concrete gravity dam.
On a suitable site, a gravity dam can prove to be a better alternative to other types of dams. When built on a solid foundation, the gravity dam probably represents the best-developed example of dam building. Since the fear of flood is a strong motivator in many regions, gravity dams are built in some instances where an arch dam would have been more economical.
Gravity dams are classified as "solid" or "hollow" and are generally made of either concrete or masonry. The solid form is the more widely used of the two, though the hollow dam is frequently more economical to construct. Grand Coulee Dam is a solid gravity dam and Braddock Locks & Dam is a hollow gravity dam.
Barrages that are built at the mouths of rivers or lagoons to prevent tide or use the tidal flow for tidal power are known as .
, ICOLD's World Register of Dams contains 58,700 large dam records. (2025). 9789280861051, United Nations University Institute for Water, Environment and Health. . ISBN 9789280861051 The tallest dam in the world is the Jinping-I Dam in China.
Countries worldwide consider small hydropower plants (SHPs) important for their energy strategies, and there has been a notable increase in interest in SHPs. Couto and Olden (2018) conducted a global study and found 82,891 small hydropower plants (SHPs) operating or under construction. Technical definitions of SHPs, such as their maximum generation capacity, dam height, reservoir area, etc., vary by country.
Small dams incur risks similar to large dams. However, the absence of regulation (unlike more regulated large dams) and of an inventory of small dams (i.e., those that are non-jurisdictional) can lead to significant risks for both humans and ecosystems. For example, according to the US National Park Service (NPS), "Non-jurisdictional—means a structure which does not meet the minimum criteria, as listed in the Federal Guidelines for Dam Safety, to be included in dam safety programs. The non-jurisdictional structure does not receive a hazard classification and is not considered for any further requirements or activities under the NPS dam safety program." Small dams can be dangerous individually (i.e., they can fail), but also collectively, as an aggregation of small dams along a river or within a geographic area can multiply risks. Graham's 1999 study of US dam failures resulting in fatalities from 1960 to 1998 concluded that the failure of dams between 6.1 and 15 m high (typical height range of smaller dams) caused 86% of the deaths, and the failure of dams less than 6.1 m high caused 2% of the deaths. Non-jurisdictional dams may pose hazards because their design, construction, maintenance, and surveillance is unregulated. Scholars have noted that more research is needed to better understand the environmental impact of small dams (e.g., their potential to alter the flow, temperature, sediment and plant and animal diversity of a river).
There are two types of underground dams: "sub-surface" and a "sand-storage". A sub-surface dam is built across an aquifer or drainage route from an impervious layer (such as solid bedrock) up to just below the surface. They can be constructed of a variety of materials to include bricks, stones, concrete, steel or PVC. Once built, the water stored behind the dam raises the water table and is then extracted with wells. A sand-storage dam is a weir built in stages across a stream or wadi. It must be strong, as floods will wash over its crest. Over time, sand accumulates in layers behind the dam, which helps store water and, most importantly, prevent evaporation. The stored water can be extracted with a well, through the dam body, or by means of a drain pipe.
There are three raised tailings dam designs, the "upstream", "downstream", and "centerline", named according to the movement of the crest during raising. The specific design used is dependent upon topography, geology, climate, the type of tailings, and cost. An upstream tailings dam consists of embankments being constructed on top but toe to crest of another, moving the crest further upstream. This creates a relatively flat downstream side and a jagged upstream side which is supported by tailings slurry in the impoundment. The downstream design refers to the successive raising of the embankment that positions the fill and crest further downstream. A centerlined dam has sequential embankment dams constructed directly on top of another while fill is placed on the downstream side for support and slurry supports the upstream side.http://mining.ubc.ca/files/2013/03/Dirk-van-Zyl.pdf
Because tailings dams often store toxic chemicals from the mining process, modern designs incorporate an impervious geomembrane liner to prevent seepage. Water/slurry levels in the tailings pond must be managed for stability and environmental purposes as well.
Timber crib dams were erected of heavy timbers or dressed logs in the manner of a log house and the interior filled with earth or rubble. The heavy crib structure supported the dam's face and the weight of the water. were timber crib dams used to help float logging downstream in the late 19th and early 20th centuries.
"Timber plank dams" were more elegant structures that employed a variety of construction methods using heavy timbers to support a water retaining arrangement of planks.
Common uses for cofferdams include the construction and repair of offshore oil platforms. In such cases, the cofferdam is fabricated from sheet steel and welded into place under water. Air is pumped into the space, displacing the water and allowing a dry work environment below the surface.
Natural disasters such as earthquakes and landslides frequently create in mountainous regions with unstable local geology. Historical examples include the Usoi Dam in Tajikistan, which blocks the Murghab River to create Sarez Lake. At high, it is the tallest dam in the world, including both natural and man-made dams. A more recent example would be the creation of Attabad Lake by a landslide on Pakistan's Hunza River.
Natural dams often pose significant hazards to human settlements and infrastructure. The resulting lakes often flood inhabited areas, while a catastrophic failure of the dam could cause even greater damage, such as the failure of western Wyoming's Gros Ventre landslide in 1927, which wiped out the town of Kelly resulting in the deaths of six people.
Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator; to boost the power generation capabilities of a dam, the water may be run through a large pipe called a penstock before the turbine. A variant on this simple model uses pumped-storage hydroelectricity to produce electricity to match periods of high and low demand, by moving water between at different elevations. At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine. (For example, see Dinorwig Power Station.)
A spillway can be gradually erosion by water flow, including cavitation or turbulence of the water flowing over the spillway, leading to its failure. It was the inadequate design of the spillway and installation of fish screens that led to the 1889 over-topping of the South Fork Dam in Johnstown, Pennsylvania, resulting in the Johnstown Flood (the "great flood of 1889").
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.
Some of these purposes are conflicting, and the dam operator needs to make dynamic tradeoffs. For example, power generation and water supply would keep the reservoir high, whereas flood prevention would keep it low. Many dams in areas where precipitation fluctuates in an annual cycle will also see the reservoir fluctuate annually in an attempt to balance these different purposes. Dam management becomes a complex exercise amongst competing stakeholders.
Significant other engineering and engineering geology considerations when building a dam include:
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.Silva, S., Vieira-Lanero, R., Barca, S., & Cobo, F. (2017). Densities and biomass of larval sea lamprey populations (Petromyzon marinus Linnaeus, 1758) in north-western Spain and data comparisons with other European regions. Marine and Freshwater Research, 68(1), 116–122. Even fish ladders do not prevent a reduction in fish reaching the spawning grounds upstream.Tummers, J. S., Winter, E., Silva, S., O'Brien, P., Jang, M. H., & Lucas, M. C. (2016). Evaluating the effectiveness of a Larinier super active baffle fish pass for European river lamprey Lampetra fluviatilis before and after modification with wall-mounted studded tiles. Ecological Engineering, 91, 183–194. 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.Lansac-Tôha, Fernando Miranda (2019). 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). A study conducted by de Almeida, R. A., Steiner, M.T.A and others found that, while some species declined in population by more than 30% after the building of the dam, others increased their population by 28%.Almeida, Ricardo (2018). 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.
A large dam can cause the loss of entire ecology, including endangered and undiscovered species in the area, and the replacement of the original environment by a new inland lake. As a result, the construction of dams have been opposed in various countries with some, such as Tasmania's Franklin Dam project, being cancelled following environmentalist campaigns.
Large reservoirs formed behind dams have been indicated in the contribution of earthquake, 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. "However, a reservoir, at worst, can only advance an earthquake which would have occurred otherwise too. The magnitude of forces associated with an earthquake is several orders bigger compared to the additional load of water in the reservoir. The change in stresses due to water load is too small to cause fracture in the Earth's crust (Srivastava, 1993). Therefore, the presence of a reservoir 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.
The Three Gorges Dam on the Yangtze River in China is more than five times the size of the Hoover Dam (United States). 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.
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.
The world's largest dam removal occurred on the Elwha River in the U.S. state of Washington (see Restoration of the Elwha River). Two dams, the Elwha Dam and Glynes Canyon dams, were removed between 2011 and 2014 that together stored approximately 30 Megatonnes of sediment. As a result, the delivery of sediment and wood to the downstream river and River delta were re-established. Approximately 65% of the sediment stored in the eroded, of which ~10% was deposited in the Stream bed. The remaining ~90% was transported to the coast. In total, renewed sediment delivery caused approximately 60 ha of River delta growth, and also resulted in increased Braided river.
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.
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 Dam, Malpasset, Testalinden Creek dams), poor maintenance, especially of outlet pipes (Lawn Lake Dam, Val di Stava Dam collapse), extreme rainfall (Shakidor Dam), , and human, computer or design error (Buffalo Creek Flood, Dale Dike Reservoir, Taum Sauk pumped storage plant).
A notable case of deliberate dam failure (prior to the above ruling) 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.
Since 2007, the Dutch IJkdijk foundation is developing, with an open innovation model and 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.
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