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  1. 1.  A dam is a hydraulic structure of impervious material built across a river or stream to create a reservoir on its upstream side for storing water for various purposes.  These purposes may be irrigation, hydro- power, water-supply, flood control, navigation, fishing and recreation.
  2. 2. Dams are classified on the basis of following types:  By structure  By material
  3. 3.  Arch dams  Gravity dams  Arch – Gravity dams  Embankment dams
  4. 4.  Situated at narrow canyon with steep side walls  Constant angle dams are more common than constant radius  Double curvature  Require good rock foundation
  5. 5.  Force that holds dam is earth’s gravity pulling down on mass of dam  Well suited for blocking rivers in wide valleys  Dam is made from concrete or masonry or both  Foundation must have high bearing strength
  6. 6.  It has characteristics of arch dam and gravity dam  They are made up of conventional concrete or RCC or masonry  It is thinner than pure gravity dams and require less internal fill
  7. 7.  Special kind of dam which consist of a line of large gates that can be opened or closed to control the amount of water  Built at mouth of rivers and often used to control water flow for irrigation system
  8. 8.  These are embankments of compact granular soil in combination with impervious areas  If clay is used then it is composite dam  These dams are resistant to damage from earthquakes
  9. 9.  They are generally made up of one type of material  Earthen dams can be constructed from materials found on site or nearby  They are cost effective
  11. 11. •Steel dam is a type of dam that is made of steel, rather than common masonry ,earthworks , concrete or construction material •Steel dams - an experiment which failed •Maintenance cost is high due to rust and corrosion
  12. 12.  Advantages and Disadvantages
  13. 13.  Timber dams were widely used in early part of industrial revolution and rarely used now  Suitable location for construction  In order to maintain water retension property they must be kept wet
  14. 14.  Cofferdam : a barrier usually temporary, constructed to exclude water from area that is normally submerged  Natural dams : created by natural geological forces. Volcanic dams are formed when erupted lava intercept path of a stream. Natural disasters like earthquake and landslides frequently create landslide dams in mountainous region. Eg. Usoi dam in Tajikistan
  15. 15. Hydroelectricity • Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. • It is the most widely used form of renewable energy, accounting for 16 percent of global electricity generation 3,427 terawatt-hours of electricity production in 2010. • Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global hydropower in 2010. China is the largest hydroelectricity producer.
  16. 16. • The theory is to build a dam on a large river that has a large drop in elevation . • The dam stores lots of water behind it in the reservoir. • Near the bottom of the dam wall there is the water intake. Gravity causes it to fall through the penstock inside the dam. • At the end of the penstock there is a turbine propeller, which is turned by the moving water. • The shaft from the turbine goes up into the generator, which produces the power. Power lines are connected to the generator that carry electricity to user . WORKING PRINCIPLE
  17. 17. Pumped storage: Reusing water for peak electricity demand Pumped storage is a method of keeping water in reserve for peak period power demands by pumping water that has already flowed through the turbines back up at storage pool above the powerplant.  An advantage of pumped storage is that hydroelectric generating units are able to start up quickly and make rapid adjustments in output.
  18. 18. Disadvantages of big Hydroelectricity plant • Ecosystem damage and loss of land • Siltation and flow shortage • Relocation of local people • Failure risks