Download - Controlling Rivers. Niagra Falls
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Controlling Rivers
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http://www.youtube.com/watch?v=IyBtnUZESk0
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Report of the World Commission on Dams
www.dams.org
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Purposes of large dams
• Hydropower
• Irrigation
• Water supply
• Flood control
• Multipurpose
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Irrigation: The Aral Sea
• Once the 4th largest inland body of water in the world
A series of dams was built to irrigate cotton.
• Aral Sea reduced to about 25% of its 1960 volume, quadrupled the salinity of the lake and wiped out the fishery. Pollutants became airborne as dust, causing significant local health problems.
• The environmental damage caused has been estimated at $1.25 -$2.5 billion a year.
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Dams and Development - Report of the World Commission on Dams
Dam Drawbacks to Human Communities
Human Displacement
Flooding of Cultural Sites(Archeological and Modern)
Cost overruns
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Dams and Development - Report of the World Commission on Dams
Dam Drawbacks to the Environment
Ecosystem Destruction
Fish Blockage and Wildlife Losses
Large-Scale Flooding Due to Dam Failures
Sedimentation and Salinity
Herbicide and Other Toxic Contamination
Evaporative Losses
Nutrient Flow Retardation
Release of greenhouse gasses
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Significant U.S. contribution…
• 19 percent of electricity from hydropower – more than 50% in 63 countries
• dams support 30-40% of irrigated area & 12-16% of global food production
• 12% of all dams have a water supply function
• 75 countries have dams for flood control
Dams and Development - Report of the World Commission on Dams
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Gravity Dams
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GRAVITY DAMS
Gravity dams are dams which resist the horizontal thrust of the water entirely by their own weight.
They use their weight to hold back the water in the reservoir.
Can be made of earth or rock fill or concrete.
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Arch Dam
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ARCH DAMS
Curved dam which is dependent upon arch action for its strength.
Transmits most of horizontal water thrust behind them to the abutments by the arch action.
Thinner and requires less material than any other type of dam.
Used only in narrow canyons.
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Buttress Dams
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BUTTRESS DAMS
Buttress dams are dams in which the face is held up by a series of supports.
Buttress dams can take many forms -- the face may be flat or curved.
Usually, buttress dams are made of concrete and may be reinforced with steel bars.
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Embankment Dams
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Embankment dams are massive dams made of earth or rock.
They rely on their weight to resist the flow of water, just like concrete gravity dams.
EMBANKMENT DAMS
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Components
FaceAbutmentsCrestToeOutletspillway
Upriver(reservoir)
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Components
Face – exposed surface of the structure
Abutments – sides of the dam
Crest – top of the dam
Toe – natural ground surface
Outlet – primary opening to discharge water
Spillway – chute to allow excess water flow
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Heel
Gallery
Toe
Spillway(inside dam)
Crest
NWLNormalwater level
MWLMax. level
Free boardSluice way
Upstream Down stream
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Hoover Dam
Concrete Gravity ArchCompleted 1935$175 millionBlack Creek Canyon
(Boulder Canyon Dam)
Border of Arizona and Nevada
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Hoover Dam
726 feet high
1244 ft length
660 feet thick at base
45 feet thick at crestBase
Crest
Concrete: 4.5 million yds3
Labor: 5,000 menCuring: trapezoidal columns
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The Reservoir
IrrigationMunicipal waterRecreationHydroelectric power
Lake Mead
10.5 trillion gallons581 feet deep110 miles long
2000 megawatts1 million people/day
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Hoover Dam: 180 m drop to turbine
Water flowing from Lake Mead through the gradually-narrowing penstocks to the powerhouse reaches a speed of about 85 miles per hour (137
km/h) by the time it reaches the turbines.
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Colorado River
CaliforniaArizonaColoradoNevadaUtahWyomingNew MexicoMexico
Nevada
California
Arizona
Utah
N.M
1,450 mi
9,000 ft = 6.2 ft/mi
Gradient
Diversion/allocation
Six major dams
17.5 million acre-feet
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Grand Cooley Dam
Concrete Gravity DamColumbia River in Central WashingtonConstructed 1933-1941
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Grand Cooley Dam
Largest concreteStructure in the U.S.
550 feet high5223 feet long500 feet wide at base30 feet wide at crest
largest single producer of electricity in the United States
There is enough concrete in theDam to build a highway across the United States.
Roosevelt Reservoir
130 square miles.
Cooling pipes
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Kingsley Dam
Largest Earthen Dam Ogallala NebraskaNorth Platte RiverConstructed 1936-41
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Kingsley Dam
Steel and Clay coreSand, gravel, soil
22 miles (35 km) long
Lake McConaughy
Width = 3.5 milesHeight = 162 feetBase thickness = 1100 feetCrest thickness = 28 feet
IrrigationElectricityRecreationHabitat
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Dates
Hoover Dam
Grand Cooley Dam
Kingsley Dam 1936-1941
1933-1941
1931-1935
Why?
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The Great Depression
1929 - 1941
Over 25% unemploymentManufacturing down 50%
United States Bureau of Reclamation
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The Three Gorges Dam Yangtze River
(The largest dam)
Concrete Gravity
Length = 1.2 miles
Height = 608 ft
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Yangtze River Watershed
Houses 1/3 China’s populationSupplies ½ China’s food
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The Reservoir
574 feet deep
373 miles long
Equal in length to Lake Superior
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Benefits
Hydroelectric Power
8.4 million kilowatts per year10% of future energy needsClean energy alternative
Flood Protection300,000 recorded deaths by flooding
NavigationCommercial shipping to central China