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Hydroelectric Hydroelectric powerpower

&&its impactsits impacts

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Outline

1. The global hydroelectric appetite.

2. Dams in the 20th century.

3. Benefits of dams.

4. Environmental impacts of big dams.

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1. The global hydroelectric appetite

Worldwide: represents _____% of the total energy generated (1999).

• _____% of world’s total commercial energy

Supplies 99% of electricity energy requirements in:

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World hydroelectric generating capacity - 1950-1991

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Hydroelectric power

There are various renewable ways of generating electric power using water:

• tidal power - bays, estuaries.• open ocean waves.• water temperature gradients.• saline solar ponds.• freshwater solar ponds.• run-of-the-river turbines.

The main method is through the use of large dams.

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Hydropower - Canada

1995 - the UN ranked Canada as the world's largest hydroelectric producer (_____% of global output).

Generated 340.3 billion kilowatt-hours (1999).

This constituted _____% of our electric power.• _____% of total commercial energy.

Canada ranks in the world's top 10 dam builders: _____ large dams (those higher than 10m).

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Major hydroelectric dams and transmission lines in Canada

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Hydropower - USA

The United States is second only to Canada in the amount of hydroelectric power produced.

Generated 305.6 billion kilowatt-hours in 1999.

This was only 8% of the electric power used in the USA.

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Potential and installed hydroelectric generating capacity

Constraints on development:

• political.

• economic.

• environmental

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2. Dams in the 20th century

Construction of dams to manage water resources dates back approx. 5000 years.

 Modern era of big dams (>15m in height) started in 1930s. Latter part of 20th century - global escalation in the rate and

scale of construction of big dams. This was due to advances in:

• concrete technology.• earth-moving machinery.

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Purpose of dams

Initially, big dams were solely for generating electricity but subsequent (and current) uses include:

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Dams on a global scaleGlobal stats*:

• most active phase of dam construction was 1950-1980’s; an average of 885 dams completed per year.

• 1961: 7408 large dams registered worldwide.

• by 1986: _____ large dams.

* Source: International Commission on Large Dams* Source: International Commission on Large Dams

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Construction of dams by decade (1900-2000)

Note: Note: excludes excludes dams in dams in China.China.

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Dams constructed by region(1900-2000)

Note: Information excludes the time-trend of dams in China.Note: Information excludes the time-trend of dams in China.

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Dams on a global scale

Of the large dams in place by 1986:• _____% were in Asia.• _____% of world total were located in

China.• _____% of dams are <30m in height.• _____% exceed 60m in height.• by early 1990’s reservoirs controlled ____

% of all land surface runoff.

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Regional distribution of large dams at the end of the 20th century

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Dams currently under construction

Country No. dams Purpose

India 695 – 960 * Irrigation, multipurpose

China 280 Flood control, irrigation, hydropower

Turkey 209 Irrigation, hydropower, water supply

South Korea 132 Irrigation, hydropower, flood management, water supply

Japan 90 Mainly flood control

Iran 48 (above 60m) Irrigation, multipurpose

* - depending on source of information* - depending on source of information

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3. Benefits of dams

The benefits of big dams include:• hydroelectricity is a renewable energy source,

cheap after the initial high costs of construction.• saves on money (and environmental effects)

required for purchase of fossil fuels.• allows management of river flow regimes, erasing

high flood and low flow periods, replacing them with a more constant annual flow.

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Benefits of dams

More benefits:• stability of river levels benefits navigation,

recreation and tourism.• reservoir provides irrigation water for croplands.• often seen as symbols of economic advantage and

national prestige for developing countries.• Lifespan is 2 – 10x greater than coal or nuclear

plants.• Emit no air pollution or GHG’s.

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4. Environmental impacts ofbig dams

Despite the success of big dams in achieving their economic aims, the construction of dams and their related reservoirs create significant environmental problems through:

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Areas affected by hydro projects

• catchment area contributing to the reservoir.

• river area below the dam, to the estuary, coastal zone and offshore.

• ancillary aspects such as power transmission corridors, pipelines, canals, tunnels, relocation and access roads, borrow pits, material disposal areas, construction camps.

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Areas affected by hydro projects

Cont’d:

• unplanned developments stimulated by the dam project, i.e., logging, shifting agriculture, hunting.

• off-site areas required for re-settlement.

• regional airshed surrounding the reservoir.

• migratory routes of humans, wildlife, fish.

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Columbia River

Example of intensively managed river.

Is the world’s largest generator of hydroelectricity with 19 major dams and 60 smaller dams.

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Temporal aspectsWhile the creation of the reservoir represents an immediate environmental change, many changes will require a long time period for the environment to adjust, if it can adjust.

Itaipu Dam, Brazil:• 196m high.• 7.8 km long.

Reservoir:• 170 km long.• 1350 km2.

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Range of impacts

The range of environmental and human impacts related to dam construction can be considered at three levels:• dam & reservoir.• upstream area.• downstream area.

Almendra Dam, Spain

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The dam & reservoir

Creation of a

reservoir results in

a loss of resources

in the inundated

land area.

Kenya

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Aswan High Dam - Egypt

Close-up of dam site

Lake Nasser

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Trees & vegetationTrees can be removed prior to inundation (for timber,

fuelwood). If the trees are not removed:• aerobic decomposition of woody material produces

hydrogen sulphide, which is toxic to fish.• organic matter decomposition produces mercury

(through methylation) which bioaccumulates in fish and renders them unsafe for consumption.

• dangers to boating and recreation (submerged trees floating to the surface)???

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Water quality

There are significant variations in water quality in the first decade of a reservoir’s life:

• initial impoundment: biological productivity is high due to initial flush of organic nutrients from flooded vegetation and soils.

• fish populations are high in the first few years.• organic nutrient levels decline after a few years,

followed by declines in aquatic organisms.

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Historical sitesReservoirs inundate areas with archeological sites.• Tucurui Dam in Brazil flooded 24 sites dating from 70-1000 AD

Temple of Isis moved to Philae Island when Lake Nasser was formed (Egypt).

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Population displacement

Land areas to be inundated are not always devoid of people.

• Sanmen Gorge project on the Huang Ho River required the resettlement of 300,000 people.

• Three Gorges Dam on the Yangtze River will require moving over 1.9 million people from 19 main cities by 2008.

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Population displacement

Human displacement results in:

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Longterm effects of reservoirs

There are various, longterm effects of reservoirs due to:

• their size – many reservoirs are very large, more so than natural regional waterbodies

• their composition – large bodies of water in anthropogenic settings.

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Longterm effects - diseases

Increases in diseases, due to alterations in the natural hydrological cycle.

Schistosomiasis – debilitating disease spread by parasitic larvae in some aquatic snail species.

Malaria – usually increases since mosquitoes breed in standing water.

Anopheles mosquito

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Longterm effects - invasive species

Spread of aquatic weed species, generally through eutrophication.

Lake Brokopondo reservoir (Suriname): water hyacinth covered 50% of the water surface within two years of the reservoir’s completion.

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Lake BrokopondoEffects of the Water Hyacinth:• decline in aquatic diversity and populations due to the toxicity of the weed.• absorbed much of the lake’s available nutrients.

• blocked the sun’s rays from penetrating to the depths of the lake.• turbines clogged by the weeds, necessitating periodic shut-downs.

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Longterm effects - local climate

Reservoirs alter the local climates in a variety of ways:

• huge quantities of water are lost through evaporation. This increases humidity and the incidence of fog.

• local winds increase (fetch over the water surface).

• temperature regime changes as the water body retains heat. Eg., the frost-free period in the region surrounding the Rybinsk reservoir (near Moscow) has been extended by 5-15 days.

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Longterm effects - global climateHydroelectric projects lessen the reliance on fossil fuels

and help decrease the emissions from the burning of coal/oil.

However…… decaying vegetation in reservoirs emit large quantities

of CO2 and methane.

Some research has suggested that GHG’s emitted via new hydro projects in Brazil will exceed the emissions that would be released by generating electricity through fossil-fuel burning.

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Longterm effects – waterlogged soils

Standing water seepage into surface soils impedes normal water drainage, especially in time of rainy seasons (increased surface erosion).

Kuban Reservoir (southern Russia) – reservoir filled to over-capacity to aid navigation and rice cultivation resulted in water damage to 130 communities, 27,000 homes, 150 km of roads, the Krasnodar airport and ruined 100,000 ha of crops.

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Longterm effects – waterlogged soils

Raised water tables lead to slope instability along the shore of the reservoir.

Vaiont Dam (Italy)• completed in 1961, was 262m high (6th

highest in the world at the time).• 1963 – large landslide (exacerbated by dam

project) into the reservoir displaced water which flowed over the dam.

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Vaiont Dam

Resulting downstream wave was 260m high.

Several villages were swept away; 2600 people died.

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Longterm effects – siltation

Build-up of sediments in reservoir:• decreases the water storage capacity.• shortens the life expectancy of the hydro-electric equipment.• requires big $$ to rectify.

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Sedimentation rates of Chinese reservoirs

Reservoir River Period of record (years)

Storage lost (%)

Sanmenxia Huang Ho 7.5 35

Qingtongxia Huang Ho 5 84

Yanguoxia Huang Ho 4 68

Liujiaxia Huang Ho 8 11

Xingqiao Hongliuhe 14 71

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Upstream effects

Hydro project infrastructure leads to better access to good quality timber.

Deforestation increases surface erosion which results in higher siltation rates into the reservoirs.

Ambukloo Project (Philippines) – deforestation above the reservoir has resulted in high sedimentation rates such that the useful life of the reservoir has decreased from 60 to 32 years.

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Downstream effects

The hydrological regime of the river is modified:

• discharge –

• velocity –

• thermal characteristics –

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Downstream effects - siltationSiltation loads decrease due to trapping of

sediment in the reservoir. This results in:

• altered ecosystems.

• coastal erosion (coastal currents remove material along deltas).

• decline in some fish species due to lack of nutrient “flush”.

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Downstream effects – flow regime

Decreased river flows allows saltwater intrusion into delta ecosystems.

Farakka Barrage (Ganges River) built in 1975 decreased dry-season discharge, allowing area in Bangladesh affected by salinity problems to increase from 350K ha to 890K ha.

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Downstream effects – wildlife

Dams are barriers to fish migration – unable to move from lakes/oceans upstream to spawning grounds.

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Three Gorges Dam

(China)

“cherished dream of Chinese leaders for several decades”.

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The Three Gorges Dam project

Purpose:

• to produce energy for burgeoning Chinese population.

• end disastrous floods along the Yangtze .

1998 Yangtze flood: 4,000 dead, 14 million left homeless and $24 billion in economic losses.

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The Three Gorges Dam projectAdvantages:

• improved navigability on the river.

• larger ships could sail as far as 2000 km upstream from the the sea, in the service of China's burgeoning domestic and export trade.

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The Three Gorges Dam project

The project will:• create a reservoir _____ km long, and 1.3

km wide (on average).• submerge _____cities, _____ towns and

over _____ villages.• require the resettlement of 1.9 million

people.• submerge _____ factories and mines.• cost approx $24 billion (US) by 2009

(completion date).

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The Three Gorges Dam project

It will inundate >1000 important archaeological sites.

About 74,000 ha of good agricultural land will be flooded.

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