Ecological impacts of dams and water diversions


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  • Ecological impacts of dams and water diversions

    1. 1. Ecological impacts of dams and water diversions
    2. 2. Definition and effects of dams <ul><li>A dam is an artificial barrier put into flowing water in order to create a reservoir or a lake </li></ul><ul><li>Every river has its unique flow, flora and fauna and environment around it (landscapes) </li></ul><ul><li>Thus each dam is constructed with regard to the specific river </li></ul><ul><li>That is why all dams have different impacts on the rivers </li></ul>
    3. 3. Impact on fish <ul><li>Migratory fish (born in rivers, migrate to the sea or ocean to mature and go back to rivers to reproduce and in most cases die after that) </li></ul><ul><li>Some dams do not have the so called fish ladders (or other constructions) which allow migratory fish, for example salmon, to reach the upstream of the river and the ocean </li></ul><ul><ul><li>Grand Coulee Dam on the Columbia River in Washington has no fish passage facilities and thus it kills salmon worth 250 000 $ a year </li></ul></ul><ul><li>But even if there are fish ladders in most cases only adult fish can pass through them, while their offspring finds it very difficult and it costs them time </li></ul><ul><li>The time is extremely important, because when the migration is delayed, the whole life cycle of the fish is behind schedule and fish can lose their ability to switch from fresh to salt water or to swim downstream </li></ul><ul><ul><li>Example: It took salmon from the Snake River in Idaho less than 3 days to get to the sea before the dams were built compared to the 39 days it needs now </li></ul></ul>
    4. 4. Impact on fish <ul><li>Many predator fish gather around dams and they are a potential threat to the smolts </li></ul><ul><li>Birds enjoy a rich feast, because the water around dams is not so deep </li></ul><ul><li>In a reservoir, water on top is too warm, and at the bottom it is cooler and deeper, but with lack of oxygen </li></ul><ul><li>Water in reservoir contains high level of pollutants, lethal to any fish or organism </li></ul><ul><li>Dams twirl water and fish, even these which are adapted to fast current may get pulled into the intakes of the dams and killed </li></ul><ul><li>Habitats of organisms get changed, e.g. new species invade slow current areas thus increasing competition for resources and causing extinction </li></ul><ul><li> More than 95% of the smolts in Snake River may die before getting to the ocean </li></ul>
    5. 5.
    6. 6. Impact on sediment flow <ul><li>Sediment is usually picked up along banks and stream beds, then carried downstream </li></ul><ul><li>Sediment provides nutrients for the fish and other organisms which live in rivers </li></ul><ul><li>When a dam is built the sediment is collected behind it and the water bed below the dam becomes rocky and with no sediment </li></ul><ul><li>Thus organisms have no food and aquatic plants can’t tackle to the water bed </li></ul><ul><li>Thus, the lack of sediment leads to extinction of large numbers of organisms </li></ul>
    7. 7. Impact on water quality <ul><li>Dams tend to collect pollutants and toxins with the sediment and water behind dams is extremely dangerous for any species downstream </li></ul><ul><li>Deeper dams do not allow the current to mix the water and the water near the surface is hotter than it should be, and the deeper water is vey cold, but with almost no oxygen circulation </li></ul><ul><li>During the warm season, great amounts of water evaporate, because dams increase the water surface directly exposed to sun rays </li></ul><ul><li>170 cubic kilometers water evaporates every year, which is more than 7% of the all used by humans freshwater (all activities) </li></ul><ul><ul><li>Example: 10% of the storing capacity of the High Aswan Dam in Africa evaporates every year and these 11.2 cubic kilometers are roughly the same amount of water as that used for both residential and commercial use on the continent </li></ul></ul><ul><li>The high level of evaporation (e.g. 1/3 of the Colorado River!!) leads to increase in salinity which is poisonous to all aquatic organisms and causes great damages to the machinery and pipes (corrosion) </li></ul><ul><ul><li>Example: Millions of dollars per year is the cost of the increased salinity in Colorado River </li></ul></ul>
    8. 8. The Mahaweli mega scheme <ul><li>A five-dam mega scheme in Sri Lanka </li></ul><ul><li>Has the purpose to irrigate previously forested areas </li></ul><ul><li>Due to its building the habitat of seven endangered and two threatened animals was turned into agricultural land </li></ul><ul><li>The two threatened species are the purple-faced langur and the toque macaque (both monkeys) live only on the island Sri Lanka </li></ul><ul><li>800 elephants live in this area and this specie is endangered. They migrate and the reservoirs and canals are an obstacle in on of their migratory routes. That is why they go through the farmland causing much trouble to the farmers and to other animals in the area. </li></ul>
    9. 9. The Victoria Dam, part of the Mahaweli mega scheme
    10. 10. Parana River, Itaipu Reservoir
    11. 11. Sete Quedas Waterfall <ul><li>Dams not only affect life and environment, they also destroy beautiful scenery </li></ul><ul><li>At the Brazilian-Paraguayan border the Paran á River suddenly narrows to only 60 meters width and then divides to 18 waterfalls (each more than 30 meters high) </li></ul><ul><li>A French traveler from the 19 th century commented on this spectacular view: “ A more imposing spectacle can scarcely be conceived .” </li></ul><ul><li>One of these waterfalls, Sete Quedas, was flooded by the Itaipú Reservoir , and is now only a rock formation below the reservoir </li></ul><ul><li>A great loss to Earth’s heritage </li></ul>
    12. 12.
    13. 13. Works Cited <ul><li>&quot;Impacts of Dams on Rivers.&quot; FAO Corporate Document Repository . Food and      Agriculture Organization of the United Nations, n.d. Web. 5 June 2010.      <>. </li></ul><ul><li>McCully, Patrick. &quot;Dams and Migratory Fish.&quot; International Rivers . Creative      Commons, 1 Jan. 2001. Web. 5 June 2010.      <>. </li></ul><ul><li>McCully, Patrick . &quot;Dams and Water Quality.&quot; International Rivers . Creative Commons, 1 Jan.      2001. Web. 5 June 2010. <      1638>. </li></ul><ul><li>McCully, Patrick. &quot;Rivers No More: The Environmental Effects of Large Dams.&quot;       International Rivers . Creative Commons, 1 Jan. 2001. Web. 5 June 2010.      <>. </li></ul><ul><li>Smith, S. E. &quot;Why are Dams Potentially Harmful to Fish?&quot; Wise Geek . N.p., 12      Apr. 2010. Web. 5 June 2010. <      why-are-dams-potentially-harmful-to-fish.htm>. </li></ul>