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.