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DamsDams
Water News
Dams:costs/benefits
• economicgrowth• foodproduc8on• surfacewaterenhancement• recrea8onenhancement
• lossofwildlifehabitat• destruc8onofrivercorridors• displacedpeoples• methylmercury
Positive
Negative
PRINCIPALPARTSOFADAM
CLASSIFICATIONOFPRINCIPALSTORAGEZONESINACROSSSECTIONOFAMULTI-PURPOSERESERVOUR
Riverdams(locks,levees)formastaircaseofreservoirsthatstretchtheen6relengthoftheTennesseeRiver
Dambuildershavebeenbusybeavers
In2000therewereover45,000“largedams”worldwide.Halfoftheworld’sexis8nglargedamsarebuiltstrictlyforirriga8on,whiletheremainderarebuildforhydrogenera8on,watersupplyandfloodcontrol.
Ra8oofthepresentvalueofprojectbenefitstothepresentvalueofthecosts
• Benefitsandcostsassignedadollarvalue(yraccrued)
• Developara8o(i.e.2:1)• Ra8obe_erthan1:1meansposi8vera8o
Determinethepresentvalueofthefollowingcostsofdamconstruc8on.
ConsiderYear1asthepresentyear.
Allvaluesareinthethousands,andtheinterestis8%simpleinterestcompoundedannually.
Year1Year2Year3 TOTAL
$100,000 $150,000 $200,000 $450,000
ThepresentvaluecostofYear1=$100,000
ThepresentvaluecostofYear2=$150,000dividedby1.08%=$138,889($138889invested8%simpleinterestforoneyear=$150000)
ThepresentcostofYear3=$200,000dividedtwiceby1.08%=$171,468(Thismeansthat$171,468investedat8%simpleinterestwillbeworth$200000aiertwoyears)
Therefore,thepresentvaluecostof$450,000inthisexampleis$410,357
$100,000+$138,889+$171,468=$410357
ImpactsofDams
o Damschangebehaviourofrivers-sedimentloadse_lesbehindadam.o Downstream,waterreleasedthroughoutletpipescauseschannelerosion.
o Fartherdownstream,theoppositecanoccurwithsiltformingislandsandsandbars.
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