![Wachusett-dam](https://upload.wikimedia.org/wikipedia/commons/e/eb/Wachusett-dam.jpg)
The environmental impact of reservoirs comes under ever-increasing scrutiny as the global demand for water and energy increases and the number and size of reservoirs increases.
Dam
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
s and
reservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including contro ...
s can be used to supply
drinking water
Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...
, generate
hydroelectric power
Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined an ...
, increase the water supply for
irrigation
Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been devel ...
, provide recreational opportunities, and
flood control
Flood control methods are used to reduce or prevent the detrimental effects of flood waters."Flood Control", MSN Encarta, 2008 (see below: Further reading). Flood relief methods are used to reduce the effects of flood waters or high water level ...
. In 1960 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 flooding of
Capel Celyn
Capel Celyn was a rural community to the northwest of Bala in Gwynedd, Wales, in the Afon Tryweryn valley. The village and other parts of the valley were flooded in 1965 to create a reservoir, Llyn Celyn, in order to supply Liverpool and Wirra ...
provoked political uproar which continues to this day. More recently, the construction of
Three Gorges Dam
The Three Gorges Dam is a hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The Three Gorges Dam has been the world' ...
and other similar projects throughout
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
,
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
and
Latin America
Latin America or
* french: Amérique Latine, link=no
* ht, Amerik Latin, link=no
* pt, América Latina, link=no, name=a, sometimes referred to as LatAm is a large cultural region in the Americas where Romance languages — languages derived f ...
have generated considerable environmental and political debate. Currently, 48 percent of rivers and their
hydro-ecological systems are affected by reservoirs and dams.
Upstream impacts
Fragmentation of river ecosystems
A dam acts as a barrier between the upstream and downstream movement of migratory river animals, such as
salmon
Salmon () is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic (genus ''Salmo'') and North Pacific (genus '' Oncorhy ...
and
trout
Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', '' Salmo'' and '' Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salm ...
.
Some communities have also begun the practice of transporting migratory fish upstream to spawn via a barge.
Reservoir sedimentation
Rivers carry sediment down their riverbeds, allowing for the formation of depositional features such as
river delta
A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more ra ...
s,
alluvial fan
An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...
s,
braided rivers,
oxbow lakes,
levees
A levee (), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually earthen and that often runs parallel to the course of a river in its floodplain or along low-lying coastli ...
and
coastal shores. The construction of a dam blocks the flow of sediment downstream, leading to downstream erosion of these sedimentary depositional environments, and increased sediment build-up in the reservoir. While the rate of sedimentation varies for each dam and each river, eventually all reservoirs develop a reduced water-storage capacity due to the exchange of "live storage" space for sediment.
[''Silenced Rivers: The Ecology and Politics of Large Dams'', by Patrick McCully, Zed Books, London, 1996. ] Diminished storage capacity results in decreased ability to produce hydroelectric power, reduced availability of water for irrigation, and if left unaddressed, may ultimately result in the expiration of the dam and river.
[Reservoir Sedimentation Handbook; Morris, Gregory & Fan, Jiahua; McGraw-Hill Publishers; 1998.]
The trapping of
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
in reservoirs reduce sediment delivery downstream, which negatively impacts channel morphology,
aquatic habitats
Marine biology is the scientific study of the biology of marine life, organisms in the sea. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies s ...
and
land elevation
Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound a ...
maintenance of
deltas
A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rarel ...
.
Apart from
dam removal
Dam removal is the process of demolishing a dam, returning water flow to the river. Arguments for dam removal consider whether their negative effects outweigh their benefits. The benefits of dams include hydropower production, flood control, i ...
, there are other strategies to mitigate reservoir sedimentation.
Flushing flow method
The flushing flow method involves partially or completely emptying the
reservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including contro ...
behind a
dam
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
to
erode
Erode () is a city in the Indian state of Tamil Nadu. Erode is the seventh largest urban agglomeration in the state, after Chennai, Coimbatore, Madurai, Tiruchirapalli, Tiruppur and Salem. It is also the administrative headquarters of the ...
the
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
stored on the bottom and
transport
Transport (in British English), or transportation (in American English), is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land ( rail and road), water, cable, pipelin ...
it downstream.
Flushing flows aim to restore natural water and sediment fluxes in the river downstream of the dam, however the flushing flow method is less costly compared to removing dams or constructing bypass tunnels.
Flushing flows have been implemented in the
Ebro river
, name_etymology =
, image = Zaragoza shel.JPG
, image_size =
, image_caption = The Ebro River in Zaragoza
, map = SpainEbroBasin.png
, map_size =
, map_caption = The Ebro ...
twice a year in autumn and spring since 2003, except for two dry years in 2004 and 2005.
The construction of multiple
dam
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
s on the Ebro river disrupted the
delivery of sediments downstream and as a result, the Ebro delta faces a
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
deficit. The
river channel also narrowed and
bank erosion
Bank erosion is the wearing away of the banks of a stream or river. This is distinguished from erosion of the bed of the watercourse, which is referred to as ''scour''.
The roots of trees growing by a stream are undercut by such erosion. As the ...
increased.
During experiments, it was found that
suspended sediment concentration during flushing flows is double that of natural
flood
A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...
s, although the total
water discharge
In hydrology, discharge is the volumetric flow rate of water that is transported through a given cross-sectional area. It includes any suspended solids (e.g. sediment), dissolved chemicals (e.g. CaCO3(aq)), or biologic material (e.g. diatoms) in ad ...
is lower. This means that flushing flows have a relatively high
sediment transport capacity,
which in turn suggests that flushing flows positively impact downstream
river ecosystem
River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts.Angelier ...
s, maximising sediment delivery to the lowest reaches of the river. A total of 340,000 t/year of sediment could be delivered to the Ebro delta, which could result in a net
accretion rate of 1 mm per year.
Sediment bypasses
Sediment bypass tunnels can partially restore
sediment dynamics in rivers downstream of
dam
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
s, and are primarily used in
Japan and
Switzerland. Bypass tunnels divert part of the incoming
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
and
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...
s during
flood
A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...
s into a tunnel around a
reservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including contro ...
and
dam
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
. The water and sediment thus never enter the reservoir but join the river again below the dam. Bypass tunnels reduce
riverbed
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 ...
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...
and increase morphological variability below the dam.
Impact below dam
River line and coastal erosion
As all dams result in reduced sediment load downstream, a dammed river is greatly demanding for sediment as it will not have enough sediment. This is because the rate of deposition of sediment is greatly reduced since there is less to deposit but the rate of erosion remains nearly constant, the water flow erodes the river shores and riverbed, threatening shoreline ecosystems, deepening the riverbed, and narrowing the river over time. This leads to a compromised water table, reduced water levels, homogenization of the river flow and thus reduced ecosystem variability, reduced support for wildlife, and reduced amount of sediment reaching coastal plains and deltas.
This prompts
coastal erosion
Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landwa ...
, as beaches are unable to replenish what waves erode without the sediment deposition of supporting river systems. Downstream channel erosion of dammed rivers is related to the morphology of the riverbed, which is different from directly studying the amounts of sedimentation because it is subject to specific long term conditions for each river system. For example, the eroded channel could create a lower water table level in the affected area, impacting bottomland crops such as
alfalfa or
corn, and resulting in a smaller supply.
[Sedimentation Engineering; American Society of Civil Engineers Committee; American Society of Civil Engineers Headquarters; 1975.]
In the case of the Three Gorges Dam in China the changes described above now appears to have arrived at a new balance of erosion and sedimentation over a 10-year period in the lower reaches of the river. The impacts on the tidal region have also been linked to the upstream effects of the dam.
Nutrients sequestration
Once a dam is put in place represents an obstacle to the flux of nutrients such as carbon (C), nitrogen (N), phosphorus (P), and silicon (Si) on downstream river, floodplains and delta. The increased
residence time
The residence time of a fluid parcel is the total time that the parcel has spent inside a control volume (e.g.: a chemical reactor, a lake, a human body). The residence time of a set of parcels is quantified in terms of the frequency distributi ...
of these elements in the
lentic system of a reservoir, compared to the
lotic system of a river, promotes their sedimentation or elimination which can be up to 40%, 50%, and 60% for nitrogen, phosphorus and silica respectively and this ultimately changes nutrients
stoichiometry in the aquatic ecosystem downstream a dam. The stochiometric imbalance of nitrogen, phosphorus, and silicon of the outflow can have repercussion on downstream ecosystems by shifting the phytoplankton community at the base of the food web with consequences to the whole aquatic population. An example is the effect of the construction of the Aswan High dam in Egypt, where the drop in nutrient concentration to the Nile delta impeded the diatom blooms causing a substantial decrease the fish population of ''Sardinella aurita'' and ''Sardinella eba'', while the reduced load of mud and silt affected the micro-
benthic fauna leading to the decline of shrimp population. The change in nutrients stoichiometry and silicon depletion at a
river delta
A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more ra ...
can also cause harmful algal and bacterial blooms to the detriment of
diatoms' growth for whom silicon availability represents a milestone for shells' formation.
Since dammed rivers store nutrients during their lifespan, it can be expected that when a dam is removed, these legacy nutrients are remobilized causing downstream ecosystems' eutrophication and probable
loss of biodiversity
Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...
, thereby achieving the opposite effect desired by the river restoration action at dam dismissal.
Water temperature
The water of a deep reservoir in temperate climates typically stratifies with a large volume of cold, oxygen poor water in the hypolimnion. Analysis of temperature profiles from 11 large dams in the Murray Darling Basin (Australia) indicated differences between surface water and bottom water temperatures up to 16.7 degrees Celsius.
If this water is released to maintain river flow, it can cause adverse impacts on the downstream ecosystem including fish populations. Under worse case conditions (such as when the reservoir is full or near full), the stored water is strongly stratified and large volumes of water are being released to the downstream river channel via bottom level outlets, depressed temperatures can be detected 250 - 350 kilometres downstream.
The operators of Burrendong Dam on the Macquarie River (eastern Australia) are attempting to address thermal suppression by hanging a geotextile curtain around the existing outlet tower to force the selective release of surface water.
Natural ecosystems destroyed by agriculture
Many dams are built for irrigation and although there is an existing dry ecosystem downstream, it is deliberately destroyed in favor of irrigated farming. After the
Aswan Dam
The Aswan Dam, or more specifically since the 1960s, the Aswan High Dam, is one of the world's largest embankment dams, which was built across the Nile in Aswan, Egypt, between 1960 and 1970. Its significance largely eclipsed the previous Aswan L ...
was constructed in Egypt it protected Egypt from the droughts in 1972–73 and 1983–87 that devastated East and West Africa. The dam allowed Egypt to reclaim about 840,000 hectares in the
Nile Delta and along the Nile Valley, increasing
the country's irrigated area by a third. The increase was brought about both by irrigating what used to be desert and by bringing under cultivation 385,000 hectares that were natural flood retention basins. About half a million families were settled on these new lands.
Effects on flood-dependent ecology and agriculture
In many low lying developing countries the
savanna
A savanna or savannah is a mixed woodland- grassland (i.e. grassy woodland) ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to ...
and
forest
A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...
ecology adjacent to
floodplain
A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
s and
river delta
A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more ra ...
s are irrigated by wet season annual floods. Farmers annually plant flood recession crops, where the land is cultivated after floods recede to take advantage of the moist soil. Dams generally discourage this cultivation and prevent annual flooding, creating a dryer downstream ecology while providing a constant water supply for irrigation.
![BaluchNomads](https://upload.wikimedia.org/wikipedia/commons/e/ed/BaluchNomads.jpg)
''Case studies''
*The Lake Manatali reservoir formed by the
Manantali dam in
Mali
Mali (; ), officially the Republic of Mali,, , ff, 𞤈𞤫𞤲𞥆𞤣𞤢𞥄𞤲𞤣𞤭 𞤃𞤢𞥄𞤤𞤭, Renndaandi Maali, italics=no, ar, جمهورية مالي, Jumhūriyyāt Mālī is a landlocked country in West Africa. Mal ...
, West Africa intersects the migration routes of nomadic
pastoralists
Pastoralism is a form of animal husbandry where domesticated animals (known as "livestock") are released onto large vegetated outdoor lands (pastures) for grazing, historically by nomadic people who moved around with their herds. The animal s ...
and withholds water from the downstream savanna. The absence of the seasonal flood cycle causes
depletion of grazing land, and is also drying the forests on the floodplain downstream of the dam.
*After the construction of the
Kainji Dam
Kainji Dam is a dam across the Niger River in Niger State of Central Nigeria. Construction of the dam was carried out by Impregilo (a consortium of Italian Civil Engineering Contractors) to designs by Joint Consultants, Balfour Beatty and Nedeco, ...
in
Nigeria
Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg, Naijeriya officially the Federal Republic of Nigeria, is a country in West Africa. It is situated between the Sahel to the north and the Gulf o ...
, 50 to 70 percent of the downstream area of flood-recession cropping stopped.
Potential for disaster
Dams occasionally break causing catastrophic damage to communities downstream. Dams break due to engineering errors, attack or natural disaster. The greatest dam break disaster to date happened
in China in 1975 killing 200,000 Chinese citizens. Other major failures during the 20th century were
at Morbi, India (5,000 fatalities),
at Vajont, Italy (2000 dead), while
three other dam failures have each caused at least 1000 fatalities.
Flood control
The controversial
Three Gorges Dam
The Three Gorges Dam is a hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The Three Gorges Dam has been the world' ...
in China is able to store 22 cubic kilometres of floodwaters on the Yangtze River. The
1954 Yangtze River floods
From June to September 1954, the Yangtze River Floods were a series of catastrophic floodings that occurred mostly in Hubei Province. Due to unusually high volume of precipitation as well as an extraordinarily long rainy season in the middle stret ...
killed 33,000 people and displaced 18 million people from their homes. In
1998 a flood killed 4000 people and 180 million people were affected. The flooding of the reservoir caused over a million people to relocate, then a flood in August 2009 was completely captured by the new reservoir, protecting hundreds of millions of people downstream.
Mercury cycling and methylmercury production
The creation of reservoirs can alter the natural
biogeochemical cycle of
mercury. Studies conducted on the formation of an experimental reservoir by the flooding of a boreal wetland showed a 39-fold increase in the production of toxic
methylmercury (MeHg) following the flooding.
The increase in MeHg production only lasted about 2–3 years before returning to near normal levels. However, MeHg concentration in lower food chain organisms remained high and showed no signs of returning to pre-flood levels. The fate of MeHg during this time period is important when considering its potential to bioaccumulate in predatory fish.
Effects beyond the reservoir
Effects on humans
Diseases
Whilst reservoirs are helpful to humans, they can also be harmful as well. One negative effect is that the reservoirs can become breeding grounds for disease vectors. This holds true especially in tropical areas where
mosquitoes
Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small Diptera, flies within the family Culicidae (from the Latin ''culex'' meaning "gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish ...
(which are
vectors for
malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
) and
snails
A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastro ...
(which are vectors for
Schistosomiasis) can take advantage of this slow flowing water.
![10](https://upload.wikimedia.org/wikipedia/commons/9/9b/10.34748W_13.10430N.png)
Resettlement
Dams and the creation of reservoirs also require relocation of potentially large human populations if they are constructed close to residential areas. The record for the largest population relocated belongs to the
Three Gorges dam
The Three Gorges Dam is a hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The Three Gorges Dam has been the world' ...
built in
China. Its reservoir submerged a large area of land, forcing over a million people to relocate. "Dam related relocation affects society in three ways: an economic disaster, human trauma, and social catastrophe", states Dr. Michael Cernea of the
World Bank
The World Bank is an international financial institution that provides loans and grants to the governments of low- and middle-income countries for the purpose of pursuing capital projects. The World Bank is the collective name for the Inte ...
and Dr. Thayer Scudder, a professor at the
California Institute of Technology
The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...
.
As well, as resettlement of communities, care must also be taken not to irreparably damage sites of historical or cultural value. The Aswan Dam forced the movement of the Temple at Aswan to prevent its destruction by the flooding of the reservoir.
Greenhouse gases
Reservoirs may contribute to changes in the Earth's climate. Warm climate reservoirs generate
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...
, a
greenhouse gas when the reservoirs are stratified, in which the bottom layers are
anoxic
The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts:
* Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...
(i.e. they lack oxygen), leading to degradation of
biomass through anaerobic processes.
[Climate Change and Dams: An Analysis of the Linkages Between the UNFCCC Legal Regime and Dams.] At a dam in Brazil, where the flooded basin is wide and the biomass volume is high the methane produced results in a pollution potential 3.5 times more than an oil-fired power plant would be.
[Graham-Rowe, Duncan (2005).]
Hydroelectric Power's Dirty Secret Revealed
, ''NewScientist.com''. A theoretical study has indicated that globally hydroelectric reservoirs may emit 104 million metric tonnes of methane gas annually. Methane gas is a
significant contributor to global climate change. This isn't an isolated case, and it appears that especially hydroelectric dams constructed in lowland
rainforest areas (where inundation of a part of the forest is necessary) produce large amounts of methane. Bruce Forsberg and Alexandre Kemenes have demonstrated that the
Balbina Dam for instance emits 39,000 tonnes of methane each year and three other dams in the Amazon produce at least 3 to 4× as much as an equivalent coal-fired power plant. Reasons for this being that lowland rainforests are extremely productive and thus stores far more carbon than other forests. Also, microbes that digest rotting material grow better in hot climates, thus producing more greenhouse gases. Despite this, as of 2020, another 150 hydroelectric dams are planned to be constructed in the Amazon basin. There is some indication that
greenhouse gas emissions
Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and ...
decline over the lifetime of the dam. "But even including
methane emissions
Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% (360 million tons) of methane r ...
, total GHG
reen-House Gasper KWh generated from hydropower is still at least half that from the least polluting thermal alternatives.Thus, from the perspective of global warming mitigation, dams are the most attractive alternative to fossil fuel based energy sources."
Research conducted at the
Experimental Lakes Area
IISD Experimental Lakes Area (IISD-ELA, known as ELA before 2014) is an internationally unique research station encompassing 58 formerly pristine freshwater lakes in Kenora District Ontario, Canada. Previously run by Fisheries and Oceans Canada, ...
indicates that creating reservoirs through the flooding of boreal wetlands, which are sinks for , converts the wetlands into sources of atmospheric carbon.
In these ecosystems, variation in organic carbon content has been found to have little effect on the rates of greenhouse gas emission. This means that other factors such as the lability of carbon compounds and temperature of the flooded soil are important to consider.
The following table indicates reservoir emissions in milligrams per square meter per day for different bodies of water.
See also
*
Akosombo Dam Impact
*
Alta controversy
The Alta conflict or Alta controversy refers to a series of massive protests in Norway in the late 1970s and early 1980s concerning the construction of a hydroelectric power plant in the Alta River in Finnmark, Northern Norway.
Timeline
*Inhabitan ...
*
Environmental impact of irrigation
The environmental effects of irrigation relate to the changes in quantity and quality of soil and water as a result of irrigation and the subsequent effects on natural and social conditions in river basins and downstream of an irrigation scheme ...
*
Environmental racism
Environmental racism or ecological apartheid is a form of institutional racism leading to landfills, incinerators, and hazardous waste disposal being disproportionally placed in communities of colour. Internationally, it is also associated with ...
*
Fish barrier
*
Fish ladder
A fish ladder, also known as a fishway, fish pass, fish steps, or fish cannon is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes' natural migration as well as move ...
*
Renewable energy debate – Hydroelectricity
References
External links
''Rivers No More: The Environmental Effects of Large Dams''at International Rivers (an excerpt for ''Rivers No More: The Environmental Effects of Large Dams'')
''World Commission on Dams''
{{DEFAULTSORT:Environmental Impacts Of Reservoirs
Reservoirs
Reservoirs
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including control ...
Reservoirs
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including control ...