environmental impact of reservoirs - wikipedia, the free encyclopedia.pdf

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The Wachusett Dam in Clinton,

Massachusetts.

From Wikipedia, the free encyclopedia

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.

Dams and reservoirs can be used to supply drinking water, generatehydroelectric power, increase the water supply for irrigation, provide

recreational opportunities, and improve certain aspects of the

environment.[citation needed] However, adverse environmental and

sociological impacts have been identified during and after many

reservoir constructions.[citation needed]

Whether reservoir projects are

ultimately beneficial or detrimental to either the environment or

surrounding human populations has been debated since the 1960s and

likely before then, as well.[citation needed] In 1960 the construction of

Llyn Celyn and the flooding of Capel Celyn provoked political uproar which continues to this day. More

recently, the construction of Three Gorges Dam and other similar projects throughout Asia, Africa and LatinAmerica have generated considerable environmental and political debate.

1 Upstream impacts

1.1 Creation of a reservoir

1.2 Fragmentation of river ecosystems

1.3 Reservoir sedimentation

2 Impact below dam2.1 Riverline and coastal erosion

2.2 Water temperature

3 Effects beyond the reservoir

3.1 Effects on humans

3.2 Effects on flood-dependent ecology and agriculture

3.3 Effects on the Earth itself

4 See also

5 References

6 External links

Creation of a reservoir

The damming of a river creates a reservoir upstream from the dam. The reservoir waters spill out into the

surrounding environments, flooding the natural habitats that existed before the dam's construction. To date, over

400,000 km2 of the earth have been flooded due to damming. The newly created reservoir has more surface

area than the river would have had, and therefore more evaporation occurs than previously. This can lead to a

onmental impact of reservoirs - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Environmental_impact_of_r

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Lake Nasser behind the Aswan dam,

Egypt, 5250 km, displaced 60,000

people[1]

loss of up to 2.1 meters in depth per year in some climates. Reservoirs

can also contribute to greenhouse gas emissions.[2]

The initial filling of a reservoir floods the existing plant material,

leading to the death and decomposition of the carbon-rich plants

and trees. The rotting organic matter releases large amounts of

carbon into the atmosphere. The decaying plant matter itself

settles to the non-oxygenated bottom of the reservoir, and the

decompositionunmitigated by a flow pattern that wouldoxygenate the waterproduces and eventually releases dissolved

methane.

[3]

Fragmentation of river ecosystems

A dam also acts as a barrier between the upstream and downstream movement of migratory river animals, such

as salmon and trout.[4]

Some communities have also begun the practice of transporting migratory fish upstream to spawn via a barge.[4]

Reservoir sedimentation

Rivers carry sediment down their riverbeds, allowing for the formation of depositional features such as river

deltas, alluvial fans, braided rivers, oxbow lakes, levees 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

storage space for sediment.[5] 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.[6]

Riverline and coastal erosion

As all dams result in reduced sediment load downstream, a dammed river is said to be "hungry" for sediment.

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 eats away at the river shores and riverbed, threatening shoreline

ecosystems, deepening the riverbed, and narrowing the river over time. This leads to a compromised water tablereduced 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.[6] This prompts coastal erosion,

as beaches are unable to replenish what waves erode without the sediment deposition of supporting river

systems. Channel erosion of rivers has its own set of consequences. 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.[7]

Water temperature


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Lake Manantali, 477 km, displaced

12,000 people.

The water of a deep reservoir in temperate climates typically stratifies with a large volume of cold, oxygen poor

water in the hypolimnion. If this water is released to maintain river flow, it can cause adverse impacts on the

downstream ecosystem including fish populations. [8]

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 (which are vectors for malaria) and snails (which are vectors for Schistosomiasis) can take

advantage of this slow flowing water.[9]

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 theThree Gorges dam 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 and

Dr. Thayer Scudder, a professor at the California Institute of

Technology.[1] As well, as resettlement of communities, care must also

be taken not to damage irreperable sites of historical or cultural value.

The Aswan Dam forced the movement of the Temple at Karnak to

prevent its destruction by the flooding of the reservoir.

Disaster

Main article: Dam_failure

Dams occasionally break causing catastrophic damage to communities downstream. Dams break due to

engineering errors, attack or natural disaster. The greatest dam break disaster happened in China killing 200,000

Chinese citizens. However, they have happened in California killing 600 people, Germany during World War II

and other countries.

Effects on flood-dependent ecology and agriculture

In many developing countries the savanna and forest ecology of the floodplains depend on seasonal floodingfrom rivers. Also, flood recession cropping is practiced extensively whereby the land is cultivated taking

advantage of the residual soil moisture after floods recede. Dams attenuate floods which may affect the ecology

and agriculture seriously.[citation needed]

Case studies

The Manatali reservoir formed by the Manantali dam in Mali intersects the migration routes of nomadic

pastoralists and destroyed 43000 ha of savannah, probably leading to overgrazing and soil erosion

elsewhere. Further, the reservoir destroyed 120 km of forest. The depletion of groundwater aquifers,


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Water becomes scarce for nomadic

pastoralist in Baluchistan due to newdam developments for irrigation.

[10]

which is caused by the suppression of the seasonal flood cycle, is

damaging the forests downstream of the dam.[11]

After the closure of the Kainji Dam in Nigeria, 50 to 70 percent of

the downstream area of flood-recession cropping was lost.[12]

Effects on the Earth itself

Reservoirs may contribute to changes in the Earth's climate. Warmclimate reservoirs generate methane, a greenhouse gas when the

reservoirs are stratified, in which the bottom layers are anoxic (i.e. they

lack oxygen), leading to degradation of biomass through anaerobic

processes.[13] In some cases, where flooded basins are wide and biomass volumes are high the amount of

biomass converted to methane results in pollution potential 3.5 times more than an oil-fired power plant would

for the same generation capacity.[2] Hydroelectric dams are the number one source of methane gas emissions

caused by humans.[14] Methane gas contributes much more to climate change then carbon dioxide.

Fish barrier

Fish ladder

Environmental impact of irrigation

^ abA comparative survey of dam-induced

resettlement in 50 cases by Thayer Scudder and

John Gray [1] (http://www.hss.caltech.edu/~tzs/50%20Dam%20Survey.pdf)

1.

^ ab Graham-Rowe, Duncan (2005). "Hydroelectric

Power's Dirty Secret Revealed

(http://www.newscientist.com/article.ns?id=dn7046)",

NewScientist.com.

2.

^ http://www.scirp.org/journal

/PaperDownload.aspx?paperID=3779 PDF

3.

^a

b

Mann, Charles C; Mark L. Plummer (August

2000). "Can Science Rescue Salmon?". Science,

New Series 289 (5480): 716719.

4.

^Silenced Rivers: The Ecology and Politics of

Large Dams, by Patrick McCully, Zed Books,London, 1996. ISBN 1-85649-902-2

5.

^a

b

Reservoir Sedimentation Handbook; Morris,

Gregory & Fan, Jiahua; McGraw-Hill Publishers;

1998.

6.

^ Sedimentation Engineering; American Society of

Civil Engineers Committee; American Society of

Civil Engineers Headquarters; 1975.

7.

^ Hurford, Clive.; Schneider, M; Cowx, Ian; West,

Richard (25 June 1997), "21" (http://crd.lbl.gov

/~dhbailey/...), Conservation Monitoring in

8.

Freshwater Habitats, Berlin: Springer Dordrecht,

pp. 219230, doi:10.1007/978-1-4020-9278-7

(http://dx.doi.org/10.1007%2F978-1-4020-9278-7),

ISBN 978-1-4020-9277-0, ISSN 0343-6993(//www.worldcat.org/issn/0343-6993)

^ William R. Jobin, 1999.Dams and Disease:

Ecological Design and Health Impacts of Large

Dams, Canals, and Irrigation Systems, Taylor &

Francis, ISBN 0-419-22360-6 [2]

(http://books.google.com

/books?vid=ISBN0419223606&

id=NH6WcjShY2oC&pg=PA239&lpg=PA239&

ots=TbZgPnlesk&dq=%22Bakoy+River%22&

ie=ISO-8859-1&output=html&

sig=ivNXJjX3GLZXNs6mZXEdNTHie6s)

9.

^ ILRI, 1982.Modern interferences in traditionalwater resources in Baluchistan. In: Annual Report

1982, pp. 23-34. ILRI, Wageningen, The Netherlands.

Reprinted in Water International 9 (1984), pp. 106-

111. Elsevier Sequoia, Amsterdam. Also reprinted in

Water Research Journal (1983) 139, pp. 53-60.

Download from : [3] (http://www.waterlog.info

/annrep.htm) , under nr. 10, or directly as PDF : [4]

(http://www.waterlog.info/pdf/baluchistan.pdf)

10.

^ A. deGeorges and B.K. Reilly, 2006. Dams and

large scale irrigation on the Senegal river: impacts

11.


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on man and the environment. UNDP Human

Development Report. On line: http://hdr.undp.org

/en/reports/global/hdr2006/papers

/DeGeorges%20Andre.pdf

^ C.A.Drijver and M.Marchand, 1985. Taming the

floods. Environmental aspects of the floodplain

developments of Africa. Centre of Environmental

12.

Studies, University of Leiden, The Netherlands.

^ Climate Change and Dams: An Analysis of the

Linkages Between the UNFCCC Legal Regime and

Dams.

13.

^ http://www.internationalrivers.org/resources

/greenhouse-gas-emissions-from-dams-faq-4064

14.

Rivers No More: The Environmental Effects of Large Dams (http://www.internationalrivers.org/en/node

/1636) at International Rivers (an excerpt forRivers No More: The Environmental Ef fects of Large

Dams)

World Commission on Dams (http://dams.org/)

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