A dam is a barrier that stops or restricts the flow of water or underground streams. Reservoirs created by dams not only suppress floods but provide water for activities such as irrigation, human consumption, industrial use and navigability. Hydropower is used in conjunction with dams to generate electricity. A dam can be used to collect water or for storage of water which can be evenly distributed between locations. Dams serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions; the earliest known dam is the Jawa Dam in Jordan, dating to 3,000 BC. The word dam can be traced back to Middle English, before that, from Middle Dutch, as seen in the names of many old cities; the first known appearance of dam occurs in 1165. However, there is one village, mentioned in 1120; the word seems to be related to the Greek word taphos, meaning "grave" or "grave hill". So the word should be understood as "dike from dug out earth".
The names of more than 40 places from the Middle Dutch era such as Amsterdam and Rotterdam bear testimony to the use of the word in Middle Dutch at that time. Early dam building took place in the Middle East. Dams were used to control the water level, for Mesopotamia's weather affected the Tigris and Euphrates rivers; the earliest known dam is the Jawa Dam in Jordan, 100 kilometres northeast of the capital Amman. This gravity dam featured an 9-metre-high and 1 m-wide stone wall, supported by a 50 m-wide earth rampart; the structure is dated to 3000 BC. The Ancient Egyptian Sadd-el-Kafara Dam at Wadi Al-Garawi, located about 25 km south of Cairo, was 102 m long at its base and 87 m wide; the structure was built around 2800 or 2600 BC 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 16 km 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 release it to surrounding lands. The lake called "Mer-wer" or Lake Moeris is known today as Birket Qarun. By the mid-late third millennium BC, an intricate water-management system within Dholavira in modern-day India was built; the system included 16 reservoirs and various channels for collecting water and storing it. One of the engineering wonders of the ancient world was the Great Dam of Marib in Yemen. Initiated somewhere between 1750 and 1700 BC, it was made of packed earth – triangular in cross section, 580 m in length and 4 m 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 important around 750 BC, 250 years the dam height was increased to 7 m. After the end of the Kingdom of Saba, the dam fell under the control of the Ḥimyarites who undertook further improvements, creating a structure 14 m high, with five spillway channels, two masonry-reinforced sluices, a settling pond, a 1,000 m canal to a distribution tank.
These extensive works were not finalized until 325 AD and allowed the irrigation of 25,000 acres. Eflatun Pınar is a Hittite spring temple near Konya, Turkey, it is thought to be from the time of the Hittite empire between the 15th and 13th century BC. The Kallanai is constructed of unhewn stone, over 300 m long, 4.5 m high and 20 m 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-regulator structures in the world, 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, flooded a valley in modern-day northern Anhui province that created an enormous irrigation reservoir, a reservoir, still present today.
Roman dam construction was characterized by "the Romans' ability to plan and organize engineering construction on a grand scale." Roman planners introduced the then-novel concept of large reservoir dams which could secure a permanent water supply for urban settlements over the dry season. Their pioneering use of water-proof hydraulic mortar and Roman concrete allowed for much larger dam structures than built, such as the Lake Homs Dam the largest water barrier to that date, the Harbaqa Dam, both in Roman Syria; the highest Roman dam was the Subiaco Dam near Rome. 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, unknown until then; these include arch-gravity dams, arch dams, buttress dams and multiple arch buttress dams, all of which were known and employed by the 2nd century AD. Roman workforces were the first to build dam bridges, such as the Bridge of Valerian in Iran
A reservoir is, most an enlarged natural or artificial lake, pond or impoundment created using a dam or lock to store water. Reservoirs can be created in a number of ways, including controlling a watercourse that drains an existing body of water, interrupting a watercourse to form an embayment within it, through excavation, or building any number of retaining walls or levees. Defined as a storage space for fluids, reservoirs may hold gasses, including hydrocarbons. Tank reservoirs elevated, or buried tanks. Tank reservoirs for water are called cisterns. Most underground reservoirs are used to store liquids, principally either water or petroleum, below ground. Reservoir is most an enlarged natural or artificial lake. A dam constructed in a valley relies on the natural topography to provide most of the basin of the reservoir. Dams are located at a narrow part of a valley downstream of a natural basin; the valley sides act as natural walls, with the dam located at the narrowest practical point to provide strength and the lowest cost of construction.
In many reservoir construction projects, people have to be moved and re-housed, historical artifacts moved or rare environments relocated. Examples include the temples of Abu Simbel, the relocation of the village of Capel Celyn during the construction of Llyn Celyn, the relocation of Borgo San Pietro of Petrella Salto during the construction of Lake Salto. Construction of a reservoir in a valley will need the river to be diverted during part of the build through a temporary tunnel or by-pass channel. In hilly regions, reservoirs are constructed by enlarging existing lakes. Sometimes in such reservoirs, the new top water level exceeds the watershed height on one or more of the feeder streams such as at Llyn Clywedog in Mid Wales. In such cases additional side dams are required to contain the reservoir. Where the topography is poorly suited to a single large reservoir, a number of smaller reservoirs may be constructed in a chain, as in the River Taff valley where the Llwyn-on, Cantref and Beacons Reservoirs form a chain up the valley.
Coastal reservoirs are fresh water storage reservoirs located on the sea coast near the river mouth to store the flood water of a river. As the land based reservoir construction is fraught with substantial land submergence, coastal reservoir is preferred economically and technically since it does not use scarce land area. Many coastal reservoirs were constructed in Europe. Saemanguem in South Korea, Marina Barrage in Singapore and Plover Cove in China, etc are few existing coastal reservoirs. Where water is pumped or siphoned from a river of variable quality or size, bank-side reservoirs may be built to store the water; such reservoirs are formed by excavation and by building a complete encircling bund or embankment, which may exceed 6 km in circumference. Both the floor of the reservoir and the bund must have an impermeable lining or core: these were made of puddled clay, but this has been superseded by the modern use of rolled clay; the water stored in such reservoirs may stay there for several months, during which time normal biological processes may reduce many contaminants and eliminate any turbidity.
The use of bank-side reservoirs allows water abstraction to be stopped for some time, when the river is unacceptably polluted or when flow conditions are low due to drought. The London water supply system is one example of the use of bank-side storage: the water is taken from the River Thames and River Lee. Service reservoirs store treated potable water close to the point of distribution. Many service reservoirs are constructed as water towers as elevated structures on concrete pillars where the landscape is flat. Other service reservoirs can be entirely underground in more hilly or mountainous country. In the United Kingdom, Thames Water has many underground reservoirs, sometimes called cisterns, built in the 1800s, most of which are lined with brick. A good example is the Honor Oak Reservoir in London, constructed between 1901 and 1909; when it was completed it was said to be the largest brick built underground reservoir in the world and it is still one of the largest in Europe. This reservoir now forms part of the southern extension of the Thames Water Ring Main.
The top of the reservoir is now used by the Aquarius Golf Club. Service reservoirs perform several functions, including ensuring sufficient head of water in the water distribution system and providing water capacity to out peak demand from consumers, enabling the treatment plant to run at optimum efficiency. Large service reservoirs can be managed to reduce the cost of pumping, by refilling the reservoir at times of day when energy costs are low. Circa 3 000 BC, the craters of extinct volcanoes in Arabia were used as reservoirs by farmers for their irrigation water. Dry climate and water scarcity in India led to early development of stepwells and water resource management techniques, including the building of a reservoir at Girnar in 3000 BC. Artificial lakes dating to the 5th century BC have been found in ancient Greece; the artificial Bhojsagar lake in present-day Madhya Pradesh state of India, constructed in the 11th century, covered 650 square kilometres. In Sri Lanka large reservoirs were created by ancient Sinhalese kings in order to save the water for irrigation.
The famous Sri Lankan king Pa
A water turbine is a rotary machine that converts kinetic energy and potential energy of water into mechanical work. Water turbines were developed in the 19th century and were used for industrial power prior to electrical grids. Now they are used for electric power generation. Water turbines are found in dams to generate electric power from water kinetic energy. Water wheels have been used for hundreds of years for industrial power, their main shortcoming is size, which limits the flow head that can be harnessed. The migration from water wheels to modern turbines took about one hundred years. Development occurred during the Industrial revolution, using scientific methods, they made extensive use of new materials and manufacturing methods developed at the time. The word turbine was introduced by the French engineer Claude Burdin in the early 19th century and is derived from the Greek word "τύρβη" for "whirling" or a "vortex"; the main difference between early water turbines and water wheels is a swirl component of the water which passes energy to a spinning rotor.
This additional component of motion allowed the turbine to be smaller than a water wheel of the same power. They could harness much greater heads; the earliest known water turbines date to the Roman Empire. Two helix-turbine mill sites of identical design were found at Chemtou and Testour, modern-day Tunisia, dating to the late 3rd or early 4th century AD; the horizontal water wheel with angled blades was installed at the bottom of a water-filled, circular shaft. The water from the mill-race entered the pit tangentially, creating a swirling water column which made the submerged wheel act like a true turbine. Fausto Veranzio in his book Machinae Novae described a vertical axis mill with a rotor similar to that of a Francis turbine. Johann Segner developed a reactive water turbine in the mid-18th century in Kingdom of Hungary, it was a precursor to modern water turbines. It is a simple machine, still produced today for use in small hydro sites. Segner worked with Euler on some of the early mathematical theories of turbine design.
In the 18th century, a Dr. Robert Barker invented a similar reaction hydraulic turbine that became popular as a lecture-hall demonstration; the only known surviving example of this type of engine used in power production, dating from 1851, is found at Hacienda Buena Vista in Ponce, Puerto Rico. In 1820, Jean-Victor Poncelet developed an inward-flow turbine. In 1826, Benoît Fourneyron developed an outward-flow turbine; this was an efficient machine. The stationary outlet had curved guides. In 1844, Uriah A. Boyden developed an outward flow turbine that improved on the performance of the Fourneyron turbine, its runner shape was similar to that of a Francis turbine. In 1849, James B. Francis improved the inward flow reaction turbine to over 90% efficiency, he conducted sophisticated tests and developed engineering methods for water turbine design. The Francis turbine, named for him, is the first modern water turbine, it is still the most used water turbine in the world today. The Francis turbine is called a radial flow turbine, since water flows from the outer circumference towards the centre of runner.
Inward flow water turbines have a better mechanical arrangement and all modern reaction water turbines are of this design. As the water swirls inward, it accelerates, transfers energy to the runner. Water pressure decreases to atmospheric, or in some cases subatmospheric, as the water passes through the turbine blades and loses energy. Around 1890, the modern fluid bearing was invented, now universally used to support heavy water turbine spindles; as of 2002, fluid bearings appear to have a mean time between failures of more than 1300 years. Around 1913, Viktor Kaplan created a propeller-type machine, it was an evolution of the Francis turbine but revolutionized the ability to develop low-head hydro sites. All common water machines until the late 19th century were reaction machines. A reaction turbine needs to contain the water during energy transfer. In 1866, California millwright Samuel Knight invented a machine that took the impulse system to a new level. Inspired by the high pressure jet systems used in hydraulic mining in the gold fields, Knight developed a bucketed wheel which captured the energy of a free jet, which had converted a high head of water to kinetic energy.
This is called tangential turbine. The water's velocity twice the velocity of the bucket periphery, does a U-turn in the bucket and drops out of the runner at low velocity. In 1879, Lester Pelton, experimenting with a Knight Wheel, developed a Pelton wheel, which exhausted the water to the side, eliminating some energy loss of the Knight wheel which exhausted some water back against the center of the wheel. In about 1895, William Doble improved on Pelton's half-cylindrical bucket form with an elliptical bucket that included a cut in it to allow the jet a cleaner bucket entry; this is the modern form of the Pelton turbine. Pelton had been quite an effective promoter of his design and although Doble took over the Pelton company he did not change the name to Doble because it had brand name recognition. Turgo and cross-flow turbines were impulse designs. Flowing water is directed on to the blades of a turbine runner, creating a force on the
The wels catfish called sheatfish, is a large species of catfish native to wide areas of central and eastern Europe, in the basins of the Baltic and Caspian Seas. It has been introduced to Western Europe as a prized sport fish and is now found from the United Kingdom all the way east to Kazakhstan and China and south to Greece and Turkey, it is a scaleless freshwater fish wide mouth. Wels catfish can live for at least fifty years; the wels catfish lives in deep, slow-flowing rivers. It prefers to remain in sheltered locations such as holes in sunken trees, etc.. It consumes its food in the open water or in the deep, where it can be recognized by its large mouth. Wels catfish are kept in fish ponds as food fish. Like most freshwater bottom feeders, the wels catfish lives on annelid worms, insects and fish. Larger specimens have been observed to eat frogs, rats, aquatic birds such as ducks and can be cannibalistic. According to a study published by researchers at the University of Toulouse, France in 2012, individuals of this species in environments outside of their normal habitats have been observed lunging out of the water to feed on pigeons on land.
Out of all beaching behaviors observed and filmed in this study, 28% of them were successful in bird capture. Stable isotope analyses of catfish stomach contents using carbon 13 and nitrogen 15 revealed a variable dietary composition of terrestrial birds; this is the result of adapting their behavior to forage on novel prey in response to new environments upon its introduction to the Tarn River in 1983 since this type of behavior has not been reported before within the native range of this species. The wels catfish's mouth contains lines of numerous small teeth, two long barbels on the upper jaw and four shorter barbels on the lower jaw, it has a long anal fin that extends to the caudal fin, a small sharp dorsal fin far forward. It relies on hearing and smell for hunting prey, but its eyes have a tapetum lucidum, providing the advantage of night vision, contrary to popular belief that the wels has poor eyesight. With its sharp pectoral fins, it creates an eddy to disorient its victim, which the predator sucks into its mouth and swallows whole.
The skin is slimy. Skin colour varies with environment. Clear water will give the fish a black color, while muddy water will tend to produce green-brown specimens; the underside is always pale yellow to white in colour. Albinistic specimens are caught occasionally; the wels swims by undulating its muscular tail in a wave-like action, similar to crocodilians. They can swim backwards. With a possible total length up to 5 m and a maximum weight of over 300 kg, the wels catfish is the largest true freshwater fish in its region. However, such lengths are rare and were hard to prove during the last century, but there is a somewhat credible report from the 19th century of a wels catfish of this size. Brehms Tierleben cites Heckl's and Kner's old reports from the Danube about specimens 3 m long and 200–250 kg in weight, Vogt's 1894 report of a specimen caught in Lake Biel, 2.2 m long and weighed 68 kg. In 1856, K. T. Kessler wrote about specimens from the Dnieper River which were over 5 m long and weighed up to 400 kg.
Most wels catfish are about 1.3–1.6 m long. At 1.5 m they can weigh 15–20 kg and at 2.2 m they can weigh 65 kg. Only under exceptionally good living circumstances can the wels catfish reach lengths of more than 2 m, as with the record wels catfish of Kiebingen, 2.49 m long and weighed 89 kg. This giant was surpassed by some larger specimens from Poland, the former Soviet states, Spain and Greece, where this fish was released a few decades ago. Greek wels grow well thanks to the mild climate, lack of competition, good food supply. Wels have been observed thriving in the cooling pond of the damaged Chernobyl Nuclear Power Plant. Although believed by tourists to have mutated into large sizes as a result of radioactive fallout, in reality the fish are growing to such proportions due to the absence of humans and fishing having been outlawed in the exclusion zone following the accident. On 21 June 2018, a 2.4 m long and 117 kg heavy wels catfish was caught in the Gruža Lake in Serbia. It took 4 fishermen 3 hours to get it out of the water.
The largest accurate weight was 144 kg for a 2.78 m long specimen from the Po Delta in Italy. Exceptionally large specimens are rumored to attack humans in rare instances, a claim investigated by extreme angler Jeremy Wade in an episode of the Animal Planet television series River Monsters following his capture of three fish, two of about 66 kg and one of 74 kg, of which two attempted to attack him following their release. A report in the Austrian newspaper Der Standard on 5 August 2009, mentions a wels catfish dragging a fisherman near Győr, under water by his right leg after the man attempted to grab the fish in a hold; the man escaped with his life from the fish, which must have weighed over 100 kg, according to him. There are concerns about the ecological impact of introducing
Perca fluviatilis known as the European perch, redfin perch, big-scaled redfin, English perch, Eurasian perch, Eurasian river perch or common perch, is a predatory species of perch found in Europe and northern Asia. The species is a popular quarry for anglers, has been introduced beyond its native area, into Australia, New Zealand, South Africa, they have caused substantial damage to native fish populations in Australia and have been proclaimed a noxious species in New South Wales. European perch are greenish with red pelvic and caudal fins, they have five to eight dark vertical bars on their sides. When the perch grow larger, a hump grows between its dorsal fin. European perch can vary in size between bodies of water, they can live for up to 22 years, older perch are much larger than average. The British record is 2.8 kg. As of May 2016, the official all tackle world record recognised by the International Game Fish Association stands at 2.9 kg for a Finnish fish caught September 4, 2010. In January 2010 a perch with a weight of 3.75 kg has been caught in the River Meuse, Netherlands.
Due to the low salinity levels of the Baltic Sea around the Finnish archipelago and Bothnian Sea, many freshwater fish live and thrive there. Perch are in abundance and grow to a considerable size due to the diet of Baltic herring; the range of the European perch covers fresh water basins all over Europe, excluding the Iberian peninsula. Their range is known to reach the Kolyma River in Siberia to the east, it is common in some of the brackish waters of the Baltic Sea. European perch has been introduced, with reported adverse ecological impact after introduction; the European perch lives in deep lakes and ponds. It tends to avoid cold or fast-flowing waters but some specimens penetrate waters of these type, although they do not breed in this habitat; the perch is a predatory species. Juveniles feed on zooplankton, bottom invertebrate fauna and other perch fry, while adults feed on both invertebrates and fish sticklebacks, perch and minnows. Perch start eating other fish. Male perch become sexually mature at between two years of age, females between two and four.
In the northern hemisphere they spawn between February and July, depositing their eggs on water plants or the branches of trees or shrubs immersed in the water. There has been speculation, but only anecdotal evidence, that eggs stick to the legs of wading birds and are transferred to other waters; the first scientific description of the river perch was made by Peter Artedi in 1730. He defined the basic morphological signs of this species after studying perch from Swedish lakes. Artedi described its features, counting the fin rays vertebrae of the typical perch. In 1758, Carl Linnaeus named it Perca fluviatilis, his description was based on Artedi's research. Because of their similar appearance and ability to cross-breed, the yellow perch has sometimes been classified as a subspecies of the European perch, in which case its trinomial name would be Perca fluviatilis flavescens. European perch is fished for game fishing. According to FAO statistics 28,920 tonnes were caught in 2013. Largest perch fishing countries were Russia, Estonia and Kazakhstan.
Baits for perch include minnows, weather loaches, pieces of raw squid or pieces of raw fish, or brandling, red and lob worms, maggots and peeled crayfish tails. The tackle needed is strong. Artificial lures are effective for medium-sized perch, it is possible to fly fish for perch using artificial flies tied for the purpose. The flies required are "streamers" or bait-fish imitations and use flash and movement to entice a take from the perch. European perch is a frequent prey of many fish-eating predators like great cormorant or common kingfisher. Cucullanus elegans is a species of parasitic nematode, it is an endoparasite of the European perch. Juvenile perch are infected by Camallanus lacustris, Proteocephalus percae, Bothriocephalus claviceps, Glanitaenia osculata, Triaenophorus nodulosus and Acanthocephalus lucii The European perch is Finland’s national fish, it is pictured in emblems of several European towns and municipalities, such as Bad Buchau, Gröningen and Schönberg, Plön. Redfin Perch – Perca fluviatilis