Reservoir Cauquenes
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A reservoir (; from
French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
or it may be a natural formation. 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
levee A levee (), dike (American English), dyke (English in the Commonwealth of Nations, Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually soil, earthen and that often runs parallel (geometry), parallel to ...
s. In other contexts, "reservoirs" may refer to storage spaces for various fluids; they may hold liquids or gasses, including hydrocarbons. ''Tank reservoirs'' store these in ground-level, elevated, or buried tanks. Tank reservoirs for water are also called
cistern A cistern (Middle English ', from Latin ', from ', "box", from Greek ', "basket") is a waterproof receptacle for holding liquids, usually water. Cisterns are often built to catch and store rainwater. Cisterns are distinguished from wells by t ...
s. Most underground reservoirs are used to store liquids, principally either water or petroleum.


Types


Dammed valleys

Dammed reservoirs are artificial lakes created and controlled by a dam constructed across a valley, and rely on the natural topography to provide most of the basin of the reservoir. These reservoirs can either be ''on-stream reservoirs'', which are located on the original
streambed A stream bed or streambed is the bottom of a stream or river (bathymetry) or the physical confine of the normal water flow (channel). The lateral confines or channel margins are known as the stream banks or river banks, during all but flood st ...
of the downstream river and are filled by
creek A creek in North America and elsewhere, such as Australia, is a stream that is usually smaller than a river. In the British Isles it is a small tidal inlet. Creek may also refer to: People * Creek people, also known as Muscogee, Native Americans ...
s, rivers or rainwater that runs off the surrounding forested catchments; or '' off-stream reservoirs'', which receive diverted water from a nearby stream or aqueduct/ pipelined water from other on-stream reservoirs. Dams are typically located at a narrow part of a 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 by Roman peoples Examples include the temples of Abu Simbel (which were moved before the construction of the Aswan Dam to create
Lake Nasser Lake Nasser ( ar, بحيرة ناصر ', ) is a vast reservoir in Southern Egypt and northern Sudan. It is one of the largest man-made lakes in the world. Before construction, Sudan was against the building of Lake Nasser because it would encro ...
from the Nile in Egypt), the relocation of the village of Capel Celyn during the construction of
Llyn Celyn Llyn Celyn () is a reservoir constructed between 1960 and 1965 in the valley of the River Tryweryn in Gwynedd, Wales. It measures roughly long by wide, and has a maximum depth of . It has the capacity to hold of water. It was originally ...
, and the relocation of Borgo San Pietro of Petrella Salto during the construction of
Lake Salto Lago del Salto is a reservoir lake in the Province of Rieti, Lazio, Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranea ...
. Construction of a dammed reservoir will usually need the river to be diverted during part of the build, often through a temporary tunnel or by-pass channel. In hilly regions, reservoirs are often constructed by enlarging existing lakes. Sometimes in such reservoirs, the new top water level exceeds the
watershed Watershed is a hydrological term, which has been adopted in other fields in a more or less figurative sense. It may refer to: Hydrology * Drainage divide, the line that separates neighbouring drainage basins * Drainage basin, called a "watershe ...
height on one or more of the feeder streams such as at
Llyn Clywedog The Clywedog Reservoir ( cy, Llyn Clywedog) is a reservoir near Llanidloes, Wales on the head-waters of the River Severn. The construction of the reservoir was enabled by an Act of Parliament which asserted that ''"At certain times the flow of w ...
in
Mid Wales Mid Wales ( cy, Canolbarth Cymru or simply ''Y Canolbarth'', meaning "the midlands") or Central Wales refers to a region of Wales, encompassing its midlands, in-between North Wales and South Wales. The Mid Wales Regional Committee of the Senedd ...
. 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 A cantref ( ; ; plural cantrefi or cantrefs; also rendered as ''cantred'') was a medieval Welsh land division, particularly important in the administration of Welsh law. Description Land in medieval Wales was divided into ''cantrefi'', which were ...
and
Beacons Reservoir Beacons Reservoir () is the northernmost of the three reservoirs in the Taff Fawr valley in South Wales. It was built by Cardiff Corporation Waterworks between 1893 and 1897, and the water is impounded by an earth dam with a clay core. Since 1 ...
s form a chain up the valley.


Coastal

Coastal reservoirs are
fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
storage reservoirs located on the sea coast near the
river mouth A river mouth is where a river flows into a larger body of water, such as another river, a lake/reservoir, a bay/gulf, a sea, or an ocean. At the river mouth, sediments are often deposited due to the slowing of the current reducing the carrying ...
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 Asia and Europe. Saemanguem in South Korea, Marina Barrage in Singapore, Qingcaosha in China, and Plover Cove in Hong Kong, are a few existing coastal reservoirs.


Bank-side

Where water is pumped or
siphon A siphon (from grc, σίφων, síphōn, "pipe, tube", also spelled nonetymologically syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in a ...
ed from a river of variable quality or size, bank-side reservoirs may be built to store the water. Such reservoirs are usually formed partly by excavation and partly by building a complete encircling bund or embankment, which may exceed 6 km (4 miles) in circumference. Both the floor of the reservoir and the bund must have an impermeable lining or core: initially these were often made of puddled clay, but this has generally 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 substantially reduce many contaminants and almost eliminate any turbidity. The use of bank-side reservoirs also allows water abstraction to be stopped for some time, when the river is unacceptably polluted or when flow conditions are very 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; several large Thames-side reservoirs such as Queen Mary Reservoir can be seen along the approach to London Heathrow Airport.


Service

Service reservoirs store fully treated potable water close to the point of distribution. Many service reservoirs are constructed as water towers, often as elevated structures on concrete pillars where the landscape is relatively flat. Other service reservoirs can be storage pools, water tanks or sometimes entirely underground
cistern A cistern (Middle English ', from Latin ', from ', "box", from Greek ', "basket") is a waterproof receptacle for holding liquids, usually water. Cisterns are often built to catch and store rainwater. Cisterns are distinguished from wells by t ...
s, especially in more hilly or mountainous country. In the United Kingdom, Thames Water has many underground reservoirs 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 has been grassed over and 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 even out peak demand from consumers, enabling the treatment plant to run at optimum efficiency. Large service reservoirs can also be managed to reduce the cost of pumping, by refilling the reservoir at times of day when energy costs are low.


History

Circa 3000 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 . Kush invented the
Hafir A hafir is an artificially constructed water catchment basin with a circular earthen wall and diameters of between 70-250 m and heights of up to 7 m. Adapted to semi-desert conditions, the hafirs catch the water during the rainy season to ...
, which is a type of reservoir, during the
Meroitic period Meroitic may refer to: * things related to the city and kingdom of Meroë in pre-Islamic Sudan * Meroitic alphabet * Meroitic language The Meroitic language () was spoken in Meroë (in present-day Sudan) during the Meroitic period (attested fro ...
. 800 ancient and modern hafirs have been registered in the Meroitic town of
Butana The Butana (Arabic: البطانة, ''Buṭāna''), historically called the Island of Meroë, is the region between the Atbara and the Nile in the Sudan. South of Khartoum it is bordered by the Blue Nile and in the east by Lake Tana in Ethiopia. ...
.Fritz Hintze, Kush XI; pp.222-224. The Hafirs catch the water during raining season in order to ensure water is available for several months during the dry season to supply drinking water, irrigate fields and water cattle. The Great Reservoir near the Lion Temple in Musawwarat es-Sufra is a notable hafir in Kush. In
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
, large reservoirs were created by ancient Sinhalese kings in order to save the water for irrigation. The famous Sri Lankan king
Parākramabāhu I of Sri Lanka Parākramabāhu I ( Sinhala: මහා පරාක්‍රමබාහු, 1123–1186), or Parakramabahu the Great, was the king of Polonnaruwa from 1153 to 1186. He oversaw the expansion and beautification of his capital, constructed extensiv ...
said "Do not let a drop of water seep into the ocean without benefiting mankind". He created the reservoir named Parakrama Samudra (sea of King Parakrama). Vast artificial reservoirs were also built by various ancient kingdoms in Bengal, Assam and Cambodia.


Uses


Direct water supply

Many dammed river reservoirs and most bank-side reservoirs are used to provide the
raw water Raw water is water found in the environment that has not been treated and does not have any of its minerals, ions, particles, bacteria, or parasites removed. Raw water includes rainwater, ground water, water from infiltration wells, and water from ...
feed to a water treatment plant which delivers drinking water through water mains. The reservoir does not merely hold water until it is needed: it can also be the first part of the water treatment process. The time the water is held before it is released is known as the ''retention time''. This is a design feature that allows particles and silts to settle out, as well as time for natural biological treatment using
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
, bacteria and zooplankton that naturally live in the water. However natural limnological processes in temperate climate lakes produce temperature stratification in the water, which tends to partition some elements such as manganese and phosphorus into deep, cold anoxic water during the summer months. In the autumn and winter the lake becomes fully mixed again. During drought conditions, it is sometimes necessary to draw down the cold bottom water, and the elevated levels of manganese in particular can cause problems in water treatment plants.


Hydroelectricity

In 2005, about 25% of the world's 33,105 large dams (over 15 metres in height) were used for hydroelectricity. The U.S. produces 3% of its electricity from 80,000 dams of all sizes. An initiative is underway to retrofit more dams as a good use of existing infrastructure to provide many smaller communities with a reliable source of energy. A reservoir generating hydroelectricity includes turbines connected to the retained water body by large-diameter pipes. These generating sets may be at the base of the dam or some distance away. In a flat river valley a reservoir needs to be deep enough to create a
head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may ...
of water at the turbines; and if there are periods of drought the reservoir needs to hold enough water to average out the river's flow throughout the year(s). Run-of-the-river hydro in a steep valley with constant flow needs no reservoir. Some reservoirs generating hydroelectricity use pumped recharge: a high-level reservoir is filled with water using high-performance electric pumps at times when electricity demand is low, and then uses this stored water to generate electricity by releasing the stored water into a low-level reservoir when electricity demand is high. Such systems are called pump-storage schemes.


Controlling watersources

Reservoirs can be used in a number of ways to control how water flows through downstream waterways: :Downstream water supply – water may be released from an upland reservoir so that it can be abstracted for drinking water lower down the system, sometimes hundreds of miles further downstream. :Irrigation – water in an irrigation reservoir may be released into networks of canals for use in farmlands or secondary water systems. Irrigation may also be supported by reservoirs which maintain river flows, allowing water to be abstracted for irrigation lower down the river. :Flood control – also known as an "attenuation" or "balancing" reservoirs, flood control reservoirs collect water at times of very high rainfall, then release it slowly during the following weeks or months. Some of these reservoirs are constructed across the river line, with the onward flow controlled by an orifice plate. When river flow exceeds the capacity of the orifice plate, water builds up behind the dam; but as soon as the flow rate reduces, the water behind the dam is slowly released until the reservoir is empty again. In some cases, such reservoirs only function a few times in a decade, and the land behind the reservoir may be developed as community or recreational land. A new generation of balancing dams are being developed to combat the possible consequences of climate change. They are called "Flood Detention Reservoirs". Because these reservoirs will remain dry for long periods, there may be a risk of the clay core drying out, reducing its structural stability. Recent developments include the use of composite core fill made from recycled materials as an alternative to clay. :Canals – Where a natural watercourse's water is not available to be diverted into a canal, a reservoir may be built to guarantee the water level in the canal: for example, where a canal climbs through locks to cross a range of hills. Another use is to reduce costs or construction time when the canal must be dug through rock, as used on the
Rideau Canal The Rideau Canal, also known unofficially as the Rideau Waterway, connects Canada's capital city of Ottawa, Ontario, to Lake Ontario and the Saint Lawrence River at Kingston. It is 202 kilometres long. The name ''Rideau'', French for "curtain", ...
with The Narrows locks dividing the two Rideau's and essentially turning the upper Rideau into an enlarged reservoir, albeit only by two or three feet. :Recreation – water may be released from a reservoir to create or supplement white water conditions for
kayak A kayak is a small, narrow watercraft which is typically propelled by means of a double-bladed paddle. The word kayak originates from the Greenlandic word ''qajaq'' (). The traditional kayak has a covered deck and one or more cockpits, each se ...
ing and other white-water sports. On salmonid rivers special releases (in Britain called '' freshets'') are made to encourage natural migration behaviours in fish and to provide a variety of fishing conditions for anglers.


Flow balancing

Reservoirs can be used to balance the flow in highly managed systems, taking in water during high flows and releasing it again during low flows. In order for this to work without pumping requires careful control of water levels using spillways. When a major storm approaches, the dam operators calculate the volume of water that the storm will add to the reservoir. If forecast storm water will overfill the reservoir, water is slowly let out of the reservoir prior to, and during, the storm. If done with sufficient lead time, the major storm will not fill the reservoir and areas downstream will not experience damaging flows. Accurate weather forecasts are essential so that dam operators can correctly plan drawdowns prior to a high rainfall event. Dam operators blamed a faulty weather forecast on the
2010–2011 Queensland floods A series of floods hit Queensland, Australia, beginning in November 2010. The floods forced the evacuation of thousands of people from towns and cities. At least 90 towns and over 200,000 people were affected. Damage initially was estimated at ...
. Examples of highly managed reservoirs are Burrendong Dam in Australia and Bala Lake (''Llyn Tegid'') in North Wales. Bala Lake is a natural lake whose level was raised by a low dam and into which the River Dee flows or discharges depending upon flow conditions, as part of the
River Dee regulation system The Dee regulation scheme is a system of flow balancing and quality management along the River Dee, Wales, River Dee managed by a consortium of the three largest water companies licensed to take water from the river, United Utilities, Welsh Wate ...
. This mode of operation is a form of hydraulic capacitance in the river system.


Recreation

Many reservoirs often allow some
recreation Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasur ...
al uses, such as fishing and
boating Boating is the leisurely activity of travelling by boat, or the recreational use of a boat whether Motorboat, powerboats, Sailing, sailboats, or man-powered vessels (such as rowing and paddle boats), focused on the travel itself, as well as sp ...
. Special rules may apply for the safety of the public and to protect the quality of the water and the ecology of the surrounding area. Many reservoirs now support and encourage less formal and less structured recreation such as natural history, bird watching, landscape painting, walking and hiking, and often provide information boards and interpretation material to encourage responsible use.


Operation

Water falling as rain upstream of the reservoir, together with any groundwater emerging as springs, is stored in the reservoir. Any excess water can be spilled via a specifically designed spillway. Stored water may be piped by gravity for use as drinking water, to generate hydro-electricity or to maintain river flows to support downstream uses. Occasionally reservoirs can be managed to retain water during high rainfall events to prevent or reduce downstream flooding. Some reservoirs support several uses, and the operating rules may be complex. Most modern reservoirs have a specially designed draw-off tower that can discharge water from the reservoir at different levels, both to access water as the water level falls, and to allow water of a specific quality to be discharged into the downstream river as "compensation water": the operators of many upland or in-river reservoirs have obligations to release water into the downstream river to maintain river quality, support fisheries, to maintain downstream industrial and recreational uses or for a range of other purposes. Such releases are known as ''compensation water''.


Terminology

The units used for measuring reservoir areas and volumes vary from country to country. In most of the world, reservoir areas are expressed in square kilometres; in the United States, acres are commonly used. For volume, either cubic metres or cubic kilometres are widely used, with acre-feet used in the US. The capacity, volume, or storage of a reservoir is usually divided into distinguishable areas. ''Dead'' or ''inactive'' storage refers to water in a reservoir that cannot be drained by gravity through a dam's outlet works, spillway, or power plant intake and can only be pumped out. Dead storage allows sediments to settle, which improves water quality and also creates an area for fish during low levels. ''Active'' or ''live'' storage is the portion of the reservoir that can be used for flood control, power production, navigation, and downstream releases. In addition, a reservoir's "flood control capacity" is the amount of water it can regulate during flooding. The "surcharge capacity" is the capacity of the reservoir above the spillway crest that cannot be regulated. In the United States, the water below the normal maximum level of a reservoir is called the "conservation pool". In the United Kingdom, "top water level" describes the reservoir full state, while "fully drawn down" describes the minimum retained volume.


Modelling reservoir management

There is a wide variety of software for modelling reservoirs, from the specialist Dam Safety Program Management Tools (DSPMT) to the relatively simple
WAFLEX WAFLEX is a spreadsheet-based model. It can be used to analyse upstream-downstream interactions, dam management options and water allocation and development options. Structure of the Model WAFLEX is set up as a network, where each cell is rive ...
, to integrated models like the Water Evaluation And Planning system (WEAP) that place reservoir operations in the context of system-wide demands and supplies.


Safety

In many countries large reservoirs are closely regulated to try to prevent or minimise failures of containment. While much of the effort is directed at the dam and its associated structures as the weakest part of the overall structure, the aim of such controls is to prevent an uncontrolled release of water from the reservoir. Reservoir failures can generate huge increases in flow down a river valley, with the potential to wash away towns and villages and cause considerable loss of life, such as the devastation following the failure of containment at Llyn Eigiau which killed 17 people.(see also
List of dam failures A dam failure or dam burst is a catastrophic type of structural failure characterized by the sudden, rapid, and uncontrolled release of impounded water or the likelihood of such an uncontrolled release. Between the years 2000 and 2009 more than ...
) A notable case of reservoirs being used as an instrument of war involved the British Royal Air Force Dambusters raid on Germany in World War II (codenamed " Operation Chastise"), in which three German reservoir dams were selected to be breached in order to damage German infrastructure and manufacturing and power capabilities deriving from the
Ruhr The Ruhr ( ; german: Ruhrgebiet , also ''Ruhrpott'' ), also referred to as the Ruhr area, sometimes Ruhr district, Ruhr region, or Ruhr valley, is a polycentric urban area in North Rhine-Westphalia, Germany. With a population density of 2,800/km ...
and
Eder Eder may refer to: People * Eder (surname) * Éder (given name), a Portuguese or Spanish given name *Éder (footballer, born 1986), Brazilian footballer Éder Citadin Martins *Eder (footballer, born 1987), Portuguese footballer from Guinea-Bissau E ...
rivers. The economic and social impact was derived from the enormous volumes of previously stored water that swept down the valleys, wreaking destruction. This raid later became the basis for several films.


Environmental impact


Whole life environmental impact

All reservoirs will have a monetary cost/benefit assessment made before construction to see if the project is worth proceeding with. However, such analysis can often omit the environmental impacts of dams and the reservoirs that they contain. Some impacts, such as the greenhouse gas production associated with concrete manufacture, are relatively easy to estimate. Other impact on the natural environment and social and cultural effects can be more difficult to assess and to weigh in the balance but identification and quantification of these issues are now commonly required in major construction projects in the developed world


Climate change


Reservoir greenhouse gas emissions

Naturally occurring lakes receive organic sediments which decay in an anaerobic environment releasing methane and carbon dioxide. The methane released is approximately 8 times more potent as a
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
than carbon dioxide. As a man-made reservoir fills, existing plants are submerged and during the years it takes for this matter to decay, will give off considerably more greenhouse gases than lakes do. A reservoir in a narrow valley or canyon may cover relatively little vegetation, while one situated on a plain may flood a great deal of vegetation. The site may be cleared of vegetation first or simply flooded. Tropical flooding can produce far more greenhouse gases than in temperate regions. The following table indicates reservoir emissions in milligrams per square meter per day for different bodies of water.


Hydroelectricity and climate change

Depending upon the area flooded versus power produced, a reservoir built for hydro-electricity generation can either reduce or increase the net production of greenhouse gases when compared to other sources of power. A study for the National Institute for Research in the Amazon found that hydroelectric reservoirs release a large pulse of carbon dioxide from decay of trees left standing in the reservoirs, especially during the first decade after flooding. This elevates the global warming impact of the dams to levels much higher than would occur by generating the same power from fossil fuels. According to the World Commission on Dams report (Dams And Development), when the reservoir is relatively large and no prior clearing of forest in the flooded area was undertaken, greenhouse gas emissions from the reservoir could be higher than those of a conventional oil-fired thermal generation plant. For instance, In 1990, the impoundment behind the
Balbina Dam The Balbina Dam ( pt, Usina Hidrelétrica de Balbina) is a hydroelectric dam and power station on the Uatumã River in the Amazon Rainforest, Brazil. The location is under the municipality of Presidente Figueiredo jurisdiction, in the state of A ...
in Brazil (inaugurated in 1987) had over 20 times the impact on global warming than would generating the same power from fossil fuels, due to the large area flooded per unit of electricity generated. Another study published in the Global Biogeochemical Cycles also found that newly-flooded reservoirs released more carbon dioxide and methane than the pre-flooded landscape, noting that forest lands, wetlands, and preexisting water features all released differing amounts of carbon dioxide and methane both pre- and post-flooding. The Tucuruí Dam in Brazil (completed in 1984) had only 0.4 times the impact on global warming than would generating the same power from fossil fuels. A two-year study of carbon dioxide and methane releases in Canada concluded that while the hydroelectric reservoirs there do emit greenhouse gases, it is on a much smaller scale than thermal power plants of similar capacity. Hydropower typically emits 35 to 70 times less greenhouse gases per TWh of electricity than thermal power plants. A decrease in air pollution occurs when a dam is used in place of
thermal power A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a s ...
generation, since electricity produced from hydroelectric generation does not give rise to any
flue gas emissions from fossil fuel combustion Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced a ...
(including
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
,
nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...
and carbon monoxide from coal).


Biology

Dams can produce a block for migrating fish, trapping them in one area, producing food and a habitat for various water-birds. They can also flood various ecosystems on land and may cause extinctions. Creating reservoirs can alter the natural
biogeochemical cycle A biogeochemical cycle (or more generally a cycle of matter) is the pathway by which a chemical substance cycles (is turned over or moves through) the biotic and the abiotic compartments of Earth. The biotic compartment is the biosphere and the ...
of
mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...
. After a reservoir's initial formation, there is a large increase in the production of toxic
methylmercury Methylmercury (sometimes methyl mercury) is an organometallic cation with the formula . It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It is a ...
(MeHg) via microbial methylation in flooded soils and peat. MeHg levels have also been found to increase in zooplankton and in fish.


Human impact

Dams can severely reduce the amount of water reaching countries downstream of them, causing water stress between the countries, e.g. the
Sudan Sudan ( or ; ar, السودان, as-Sūdān, officially the Republic of the Sudan ( ar, جمهورية السودان, link=no, Jumhūriyyat as-Sūdān), is a country in Northeast Africa. It shares borders with the Central African Republic t ...
and Egypt, which damages farming businesses in the downstream countries, and reduces drinking water. Farms and villages, e.g. Ashopton can be flooded by the creation of reservoirs, ruining many livelihoods. For this very reason, worldwide 80 million people (figure is as of 2009, from the Edexcel GCSE Geography textbook) have had to be forcibly relocated due to dam construction.


Limnology

The limnology of reservoirs has many similarities to that of lakes of equivalent size. There are however significant differences. Many reservoirs experience considerable variations in level producing significant areas that are intermittently underwater or dried out. This greatly limits the productivity or the water margins and also limits the number of species able to survive in these conditions. Upland reservoirs tend to have a much shorter residence time than natural lakes and this can lead to more rapid cycling of
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
s through the water body so that they are more quickly lost to the system. This may be seen as a mismatch between water chemistry and water biology with a tendency for the biological component to be more oligotrophic than the chemistry would suggest. Conversely, lowland reservoirs drawing water from nutrient rich rivers, may show exaggerated eutrophic characteristics because the residence time in the reservoir is much greater than in the river and the biological systems have a much greater opportunity to utilise the available nutrients. Deep reservoirs with multiple level draw off towers can discharge deep cold water into the downstream river greatly reducing the size of any hypolimnion. This in turn can reduce the concentrations of phosphorus released during any annual mixing event and may therefore reduce
productivity Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proces ...
. The dams in front of reservoirs act as knickpoints-the energy of the water falling from them reduces and deposition is a result below the dams.


Seismicity

The filling (impounding) of reservoirs has often been attributed to reservoir-triggered seismicity (RTS) as seismic events have occurred near large dams or within their reservoirs in the past. These events may have been triggered by the filling or operation of the reservoir and are on a small scale when compared to the amount of reservoirs worldwide. Of over 100 recorded events, some early examples include the tall
Marathon Dam The marathon is a long-distance foot race with a distance of , usually run as a road running, road race, but the distance can be covered on trail routes. The marathon can be completed by running or with a run/walk strategy. There are also w ...
in Greece (1929), the tall
Hoover Dam Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on Se ...
in the U.S. (1935). Most events involve large dams and small amounts of seismicity. The only four recorded events above a 6.0- magnitude (Mw) are the tall Koyna Dam in India and the Kremasta Dam in Greece which both registered 6.3-Mw, the high
Kariba Dam The Kariba Dam is a double curvature concrete arch dam in the Kariba Gorge of the Zambezi river basin between Zambia and Zimbabwe. The dam stands tall and long. The dam forms Lake Kariba, which extends for and holds of water. Construction Th ...
in Zambia at 6.25-Mw and the
Xinfengjiang Dam The Xinfengjiang Dam (''also known as the'' Xinfeng Dam) is a gravity dam on the Xinfeng River, upstream of its confluence with the Dong River, and just west of Heyuan City in Guangdong Province, China. The dam's power station has a 292.5 MW ins ...
in China at 6.1-Mw. Disputes have occurred regarding when RTS has occurred due to a lack of hydrogeological knowledge at the time of the event. It is accepted, though, that the infiltration of water into pores and the weight of the reservoir do contribute to RTS patterns. For RTS to occur, there must be a seismic structure near the dam or its reservoir and the seismic structure must be close to failure. Additionally, water must be able to infiltrate the deep rock
stratum In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...
as the weight of a deep reservoir will have little impact when compared the deadweight of rock on a crustal stress field, which may be located at a depth of or more.


Microclimate

Reservoirs may change the local micro-climate increasing humidity and reducing extremes of temperature, especially in dry areas. Such effects are claimed also by some South Australian wineries as increasing the quality of the wine production.


List of reservoirs

In 2005 there were 33,105 large dams (≥15 m height) listed by the International Commission on Large Dams (ICOLD).


List of reservoirs by area


List of reservoirs by volume


See also

* Ab Anbar * Coastal sediment supply * Colourful lakelets (in Poland) * Dam failure * Drainage basin * Forebay *
Head of the reservoir In hydrology, the head is the point on a watercourse up to which it has been artificially broadened and/or raised by an impoundment. Above the head of the reservoir natural conditions prevail; below it the water level above the riverbed has be ...
* Mill pond * Quarry lake *
Reservoir safety Reservoirs storing large volumes of water have the capability of causing considerable damage and loss of life if they fail. Reservoirs are considered "installations containing dangerous forces" under international humanitarian law because of their ...
* Shade balls


References


External links

* * {{authority control Lakes by type Bodies of water