© 2011 Pearson Education, Inc. How We Use Water Discuss how we use and later freshwater systems

© 2011 Pearson Education, Inc.

How We Use Water

• Discuss how we use and later freshwater systems


Climate change may bring shortages

• Climate change will cause - Altered precipitation

patterns- Melting glaciers- Early season runoff- Intensified droughts- Flooding

Lake Mead is already hurting from drought


How we use water

• We have achieved impressive engineering accomplishments to harness fresh water- 60% of the world’s largest 227 rivers have been

strongly or moderately affected - Dams, dikes, and diversions

• Consumption of water in most of the world is unsustainable- We are depleting many sources of surface water and

groundwater


There are more than 1,000 dams in the Connecticut River watershed. The States of Vermont, New Hampshire, Massachusetts and Connecticut are included in the watershed.


Water supplies houses, agriculture, and industry

• Proportions of these three types of use vary dramatically among nations- Arid countries use water for agriculture- Developed countries use water for industry

• Consumptive use = water is removed from an aquifer or surface water body and is not returned - Irrigation = the provision of water to crops

• Nonconsumptive use = does not remove, or only temporarily removes, water- Electricity generation at hydroelectric dams


Why does agriculture use so much water?

• Rapid population growth requires more food and clothes• The Green Revolution uses irrigation

- We use 70% more irrigation water than 50 years ago• Irrigation can double crop yields

- 18% of land is irrigated but produces 40% of our crops• Irrigation is highly inefficient

- Water evaporates in “flood and furrow” irrigation• Overirrigation leads to waterlogging and salinization

- Reducing world farm income by $11 billion


Governments subsidize irrigation

• Irrigation subsidies promote food self-sufficiency- But irrigation uses up huge amounts of groundwater

for little gain• Water in the Colorado River Valley is diverted for

cotton and other crops grown in the desert

Farmers in California’s Imperial Valley pay only 1 penny for 220 gallons of water


We divert surface water for our needs

• People divert water to farm fields, homes, and cities

The once mighty Colorado River has been extensively diverted and used


Water-poor regions take water from others

• Politically strong, water-poor areas forcibly take water from weaker communities

• Los Angeles commandeered water from rural areas- Turning the environment into desert, creating

dustbowls, and destroying the economy• In 1941, L.A. diverted streams that fed Lake Mono

- Lake levels fell, salt concentrations doubled• Las Vegas wants to import water from sparsely

populated eastern Nevada- An ecologically sensitive area


We build dikes and levees to control floods

• Flooding = a normal, natural process where water spills over a river’s banks- Spreading nutrient-rich sediments over large areas

• In the short term, floods damage property• Dikes and levees (long, raised mounds of earth) along

the banks of rivers hold water in channels- Levees make floods worse by forcing water to stay

in channels and then overflow• Dams prevent flooding and change a river’s nature

- Releasing water periodically simulates flooding


Levees increase flooding

• A major levee along the Mississippi River failed after Hurricane Katrina, allowing parts of New Orleans to be flooded


We have erected thousands of dams

• Dam = any obstruction placed in a river or stream to block the flow of water to prevent floods, provide drinking water, allow irrigation, and generate electricity- 45,000 large dams have been erected in more than

140 nations• Only a few major rivers remain undammed

- In remote regions of Canada, Alaska, and Russia• Dams are great engineering feats

- Many stand hundreds of feet tall


A typical dam


China’s Three Gorges Dam

• The dam, on the Yangtze River, is the largest in the world- 186 m (610 feet) high, 2.3

km (1.4 mi) wide- Its reservoir stretches for

616 km (385 mi)- Provides flood control,

passage for boats, and electricity


Drawbacks of the Three Gorges Dam

• Cost $39 billion to build• Flooded 22 cities and the

homes of 1.24 million people• Submerged 10,000-year-old

archaeological sites• Drowned farmland and

wildlife habitat• Tidal marshes at the Yangtze’s

mouth are eroding• Pollutants will be trapped

It will cost $5 billion to build sewage treatment plants to treat water


Some dams are being removed

• Some people feel that the costs of dams outweigh their benefits- They are pushing to dismantle dams

• The Federal Energy Regulatory Commission (FERC) renews licenses for dams- If dam costs exceed benefits, the license may not be

renewed• 400 dams have been removed in the U.S.

- Property owners who opposed the removal change their minds once they see the healthy river


We are depleting surface water

• In many places, we are withdrawing water at unsustainable rates- Reduced flow drastically changes the river’s ecology,

plant community, and destroys fish and invertebrates

The Colorado River often does not reach the Gulf of California


The Aral Sea

• Once the fourth-largest lake on Earth- It lost 80% of its volume in 45

years • The two rivers leading into the Aral

Sea were diverted to irrigate cotton fields

• 60,000 fishing jobs are gone• Pesticide-laden dust from the lake

bed is blown into the air• Cotton cannot save the region’s

economy


Can the Aral Sea be saved?

People have begun saving the northern part of the Aral Sea


Irrigation wastes water

• 15–35% of water withdrawals for irrigation are unsustainable

• Water mining = withdraws water faster than it can be replenished


The world is losing wetlands

• Wetlands are being lost as we divert and withdraw water- Channelize rivers, build dams, etc.

• As wetlands disappear, we lose ecosystem services- Filtering pollutants, wildlife habitat, flood control, etc.

• Many are trying to protect and restore them• The Ramsar Convention on Wetlands of International

Importance (1971)- Seeks the conservation and wise use of wetlands in the

context of sustainable development- 1,900 sites covering 185 million ha are protected


We are depleting groundwater

• Groundwater is easily depleted - Aquifers recharge slowly- Used by one-third of all people

• As aquifers are mined, water tables drop- Salt water intrudes in coastal areas

• Sinkholes = areas where ground gives way unexpectedly- Aquifers can’t recharge

• Wetlands dry up


Salt water intrustion

Saline water flows upward through the nearly vertical structural features in response to ground-water pumping from the uppermost aquifer.


Can we quench our thirst for bottled water?

• Groundwater is being withdrawn for bottled water- An average American drinks 29 gallons/year

• People drink bottled water for portability, convenience- They think it tastes better or is healthier

• Bottled water is no better than tap water- It is heavily packaged and travels long distances using

fossil fuels- Bottles are not recycled- Corporations move in, deplete water, and move away

http://geology.com/articles/bottled-water.shtml


Bottled water is popular but problematic

• Bottled water is popular but it has several problems

Energy costs of bottled water are 1,000–2,000 times greater than those of tap water


Will we see a future of water wars?

• Freshwater depletion leads to shortages, which can lead to conflict- 261 major rivers cross national borders

• Water is a key element in hostilities among Israel, Palestinians, and neighboring countries

• Many nations have cooperated with neighbors to resolve disputes- They sign water-sharing treaties


QUESTION: Review

Why do governments subsidize irrigation?

a) It promotes food self-sufficiency.

b) Governments have to or food could not be grown.

c) Governments want to lower water tables.

d) Governments do not subsidize irrigation.


QUESTION: Review

Which of the following statements is NOT true about dams?

a) They change habitat.

b) They generate electrical power.

c) They have created more farmland upstream.

d) Pollutants are trapped in reservoirs.

Documents

© 2011 Pearson Education, Inc. How We Use Water Discuss how we use and later freshwater systems