Controlling Rivers

Niagra Falls

Report of the World Commission on Dams

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 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

Significant U.S. contribution… 19 percent of electricity from hydropower – more than 50% in 63 countries19 percent of electricity from hydropower – more than 50% in 63 countries dams support 30-40% of irrigated area & 12-16% of global food productiondams support 30-40% of irrigated area & 12-16% of global food production 12% of all dams have a water supply function12% of all dams have a water supply function 75 countries have dams for flood control75 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 Face Abutments Crest Toe Outlet spillway Upriver (reservoir)‏

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

Heel Gallery Toe Spillway (inside dam) Crest NWL Normal water level MWL Max. level Free board Sluice way Upstream Down stream

Hoover Dam Concrete Gravity Arch Completed 1935 $175 million Black 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 yds 3 Labor: 5,000 men Curing: trapezoidal columns

The Reservoir Irrigation Municipal water Recreation Hydroelectric power Lake Mead 10.5 trillion gallons 581 feet deep 110 miles long 2000 megawatts 1 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 River California Arizona Colorado Nevada Utah Wyoming New Mexico Mexico 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 Dam Columbia River in Central Washington Constructed

Grand Cooley Dam Largest concrete Structure in the U.S. 550 feet high 5223 feet long 500 feet wide at base 30 feet wide at crest largest single producer of electricity in the United States There is enough concrete in the Dam to build a highway across the United States. Roosevelt Reservoir 130 square miles. Cooling pipes

Kingsley Dam Largest Earthen Dam Ogallala Nebraska North Platte River Constructed

Kingsley Dam Steel and Clay core Sand, gravel, soil 22 miles (35 km) long Lake McConaughy Width = 3.5 miles Height = 162 feet Base thickness = 1100 feet Crest thickness = 28 feet Irrigation Electricity Recreation Habitat

Dates Hoover Dam Grand Cooley Dam Kingsley Dam Why?

The Great Depression  Over 25% unemployment  Manufacturing 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 population Supplies 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 year 10% of future energy needs Clean energy alternative Flood Protection 300,000 recorded deaths by flooding Navigation Commercial shipping to central China