Controlling Rivers

Niagra Falls

http://www.youtube.com/watch?v=IyBtnUZESk0

Report of the World Commission on Damswww.dams.org

Purposes of large dams

• Hydropower

• Irrigation

• Water supply

• Flood control

• Multipurpose

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.

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

Dams and Development - Report of the World Commission on Dams

Dam Drawbacks to the Environment

Ecosystem DestructionFish Blockage and Wildlife Losses

Large-Scale Flooding Due to Dam FailuresSedimentation and Salinity

Herbicide and Other Toxic ContaminationEvaporative Losses

Nutrient Flow RetardationRelease of greenhouse gasses

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

Gravity Dams

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.

Arch Dam

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.

Buttress Dams

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.

Embankment Dams

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

Components

FaceAbutmentsCrestToeOutletspillway

Upriver(reservoir)

Components

Face – exposed surface of the structureAbutments – sides of the damCrest – top of the damToe – natural ground surfaceOutlet – primary opening to discharge waterSpillway – chute to allow excess water flow

Heel

Gallery

Toe

Spillway(inside dam)

Crest

NWLNormalwater level

MWLMax. level

Free boardSluice way

Upstream Down stream

Hoover Dam

Concrete Gravity ArchCompleted 1935$175 millionBlack Creek Canyon

(Boulder Canyon Dam)

Border of Arizona and Nevada

Hoover Dam

726 feet high

1244 ft length

660 feet thick at base

45 feet thick at crest Base

Crest

Concrete: 4.5 million yds3

Labor: 5,000 menCuring: trapezoidal columns

The Reservoir

IrrigationMunicipal waterRecreationHydroelectric power

Lake Mead

10.5 trillion gallons581 feet deep110 miles long

2000 megawatts1 million people/day

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.

Colorado RiverCaliforniaArizonaColoradoNevadaUtahWyomingNew 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

Grand Cooley Dam

Concrete Gravity DamColumbia River in Central WashingtonConstructed 1933-1941

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

Kingsley DamLargest Earthen Dam Ogallala NebraskaNorth Platte RiverConstructed 1936-41

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

Dates

Hoover Dam

Grand Cooley Dam

Kingsley Dam 1936-1941

1933-1941

1931-1935

Why?

The Great Depression

1929 - 1941

Over 25% unemploymentManufacturing down 50%

United States Bureau of Reclamation

The Three Gorges Dam Yangtze River

(The largest dam)

Concrete Gravity

Length = 1.2 miles

Height = 608 ft

Yangtze River Watershed

Houses 1/3 China’s populationSupplies ½ China’s food

The Reservoir

574 feet deep

373 miles long

Equal in length to Lake Superior

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