Ecological Impacts of Dams

Grade 10 Lesson

http://users.owt.com/chubbard/gcdam/highres/dam08.jpg

Definition A barrier(wall) builtin a river in order torestrict orchange theflow of the water orto raise the water level in a certain area1

http://nrmsc.usgs.gov/files/norock/research/dam_base_flow_sm.jpg

Usage Provide reliable

water resource and flood control

Hydroelectric dams are used to produce electricity2

Drawbacks Negative impact on

fish life in the area Loss of sediment in

downstream areas People displacement Disease spread2, 3

Impact on Fish Dams are createdin order to change the currents of a river Changing the current has an immediate impact onthe ecosystem in the river3,4

http://www.vistapinas.com/images/48.jpg

The dam changes the water qualities to which organisms are used to

Many animal’s life cycles are synced with the annual floods that occur in an area; therefore, those cycles are interrupted when the floods stop because of the dam

The dam basically acts as a barrier stopping fish from going upstream or downstream; thus, lifecycles of migratory fish are deeply damaged, as they cannot go and spawn or interact with others4,5

Soil Erosion Before the

Dam The sediment that the

water carries is blocked by the dam; as time passes, it slowly builds up,adding additional pressure to the dam wall

In this way, serious accidents can occur: the dams are only built to withstand a certain amount of water pressure; with the pressure from the sediment in some time the wall either explodes or water is caused to go above the dam, creating a waterfall; in both cases, a lot of organisms, including humans are in great danger4,5

http://www.usbr.gov/pmts/sediment/projects/SavageRapids/images/Sedimentation.jpg

Soil ErosionAfter the Dam

As sediment coming from the upper parts is blocked, the water after the dam is essentially “cleared” of all particles

Once again, that interrupts the ecosystem present The nutrients are blocked along with the

sediment The organisms that used the mud to hide

themselves now have no protection from predators4,5

Disease Spread

When sediment builds up, along with algae and plants start developing; when they die, there is a huge amount of organic material left, which when decomposing, releases gases dangerous for animals and people2,4

The water that is blocked by the dam stays in one place, and, consequently, can get very dirty

It attracts mosquitoes and other disease-carrying insects, which contaminate it

People in less developedcountrieshave no access toclear water, so they usethe one fromthe reservoirs, which results in them being sickas well2

This photo is taken by Samuila; this is the dam on the Iskar river, creating the Pancharevo lake

People Displacement

When dams are built,the settlements and habitatsthat stand in their way aregenerally demolished This way, a lot of peopleare left without a home and a job, which is a bigeconomical problem2

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Three Gorges Dam, China

Located on theYangtze River The world’s largest hydropowerdam However, in orderfor the project to becompleted, more that 1.2 million people must be displaced3

http://en.citizendium.org/images/9/9c/Three_gorges_dam_map_2.gif

http://japanfocus.org/data/3gdam.jpg http://i.i.com.com/cnwk.1d/i/ne/p/2007/dam_china001_550x516.jpg

http://www.china-tourism.org/images/stories/articles/three-gorges-dam.jpg

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A lot of factories will be left under the resulting reservoir, which will seriously pollute the water

On the other hand, the already existing erosion and downstream sediment are cause landslides, which are a serious threat for the area

Scientists have proven that the weight of the water is influencing the seismicity of the area, resulting in more earthquakes than usual

Since the dam’s function is to control flooding, it has already changed the pre-existing natural cycle of the ecosystem in the river3,6

Aswan Dam, Egypt Located on theNile Creates Lake Nasser Actually two dams:

High Dam (1960) Low Dam (1902)

Displaced 60,000people7

http://www.quarryscapes.no/images/Egypt_sites/aswan_loc.jpg

During the controlled floods, the river goes to the farmlands, and problems are

caused by the soil erosion that follows When water is evaporated from the soil, salt is

left and the ground crystallizes The water is a breeding place for snails carrying theparasite bilharzia, which is the secondworst disease aftermalaria in Egypt7

http://www.mbarron.net/Nile/OWENFALL.JPG

Sources Cited1. “Dam.” The Free Dictionary. Farlex, Inc., n.d. Web. 16 Dec. 2010.

<http://www.thefreedictionary.com/ Dam>.2. Joyce, Stephanie. “Dams - the Advantages and Disadvantages.”

Environment, Health, and Safety Online. EHSO, Inc., n.d. Web. 16 Dec. 2010. <http://www.ehso.com/ ehshome/ energydams.htm>.

3. “Three Gorges Dam.” International Rivers. Creative Commons, n.d. Web. 16 Dec. 2010. <http://www.internationalrivers.org/ china/ three-gorges-dam>.

4. “The Ecology of Dams.” Stream Biology and Ecology. Cristi Cave, n.d. Web. 16 Dec. 2010. <http://chamisa.freeshell.org/ dam.htm>.

5. “Why Are Dams Potentially Harmful to Fish.” WiseGeek. Conjecture Corp., n.d. Web. 16 Dec. 2010. <http://www.wisegeek.com/ why-are-dams-potentially-harmful-to-fish.htm>.

6. “Three Gorges Dam.” Wikipedia. Wikipedia Foundation, Inc., n.d. Web. 16 Dec. 2010. <http://en.wikipedia.org/ wiki/ Three_Gorges_Dam>.

7. “Aswan Dam.” Wikipedia. Wikipedia Foundation, Inc., n.d. Web. 16 Dec. 2010. <http://en.wikipedia.org/ wiki/ Aswan_Dam#Displacement.2C_agriculture_and_health>.