WATER

Supply

Use

management

What are the major uses of water in the U.S.?

• As of 2000:– Making electricity 48%

• (thermoelectric)

– Irrigation 34%– Public supply 11%– Industrial 5%– Domestic <1%– Aquaculture <1%– Mining <1%– Livestock <1%

Worldwide water use

70%

20%

10%

Agriculture

Industry

Residential/municipal

Thermoelectric

• Burning fossil fuels to make electricity.• Boils water to turn generator• Uses lots of water to condense the boiled

water• Much water lost to evaporation

(consumptive)• Still, much of the use is non-consumptive

– Water used in the plant is returned downstream

•

Irrigation

•

Main impacts of irrigation

• Dams• Waterlogging of soil• Salinization• Overdraft of groundwater

– Main source of drinking water for ½ the US– If withdrawal > replenishment mining

• Irrigation is mainly consumptive—water evaporates or transpirates and doesn’t return to source

Ogallala aquifer

• HUGE: water-bearing sands, gravels under about 400,000 km2 from SD to TX

• Use in some places is 20 times greater than rate of replenishment

Why are dams built?

• Usually, many advantages cited. WHY?– Appeal to as many constituents as possible

• Diversion of water for irrigation

• Flood control

• Recreation

• Stable water supply

Environmental impacts of dams

• Loss of land and cultural resources

• Sediment trapped behind dam. Why bad?– Reservoir fills up, reducing its life– Sediment would supply sand and nutrients

• River below dam is unnatural (flows irregular)

•

Three gorges of the Yangtze R.

•

Flooding of three gorges dam

• Rains in upper Yangtze basin so great the reservoir filled, threatening dam and towns.

• Releases of water so great that downstream towns threatened.

•

Dams destroy riparian habitat

•

Sedimentation problems with dams

• Problem that faces all dams

• Many trap nearly 100% of the sediment that washes down a river.

• As sediment accumulates, reservoir can hold less water but that was the point of the dam in the first

place—to hold water!

What happens to rivers?

• Colorado River near its source in Rocky Mt. Nat. Park.

•

Hoover dam

Clean Water Act

• Addresses surface water quality

• Not directly groundwater or quantity

• Tools to reduce pollutant discharges into waterways for "the protection and propagation of fish, shellfish, and wildlife and recreation in and on the water."

CWA

• Passed in 1972

• Point pollution was early emphasis

CWA

• Nonpoint source pollution now the big issue