Chapter 14
Chapter Overview Questions
Why is water so important, how much
freshwater is available to us, and how much of it are we using?
What causes freshwater shortages, and what
can be done about this problem?
What are the advantages and disadvantages
of withdrawing groundwater?
What are the advantages and disadvantages
Chapter Overview Questions (cont’d)
What are the advantages and disadvantages
of transferring large amounts of water from one place to another?
Can removing salt from seawater solve our
water supply problems?
How can we waste less water?
How can we use the earth’s water more
sustainably?
What causes flooding, and what can we do
Core Case Study: Water Conflicts in
the Middle East - A Preview
of the Future
Many countries in
the Middle East, which has one of the world’s highest population growth rates, face water shortages.
Water Conflicts in the Middle East: A
Preview of the Future
Most water in this dry region comes from the
Nile, Jordan or Tigris rivers.
Countries are in disagreement as to who has
water rights.
Currently, there are no cooperative
WATER’S IMPORTANCE,
AVAILABILITY, AND RENEWAL
Water keeps us alive, moderates climate,
sculpts the land, removes and dilutes wastes and pollutants, and moves continually
through the hydrologic cycle.
Only about 0.02% of the earth’s water supply
WATER’S IMPORTANCE,
AVAILABILITY, AND RENEWAL
Comparison of
population sizes and shares of the world’s freshwater among
the continents.
Fig. 14-2, p. 307
Continent Percent of world's water resources and population
Asia
60.5% 36%
Africa 10%
8% Europe
North and Central
America 7.3%
South America and
Caribbean 6.4%
26% 15%
5% Oceania
11.3%
0.5%
WATER’S IMPORTANCE,
AVAILABILITY, AND RENEWAL
Some precipitation infiltrates the ground and
is stored in soil and rock (groundwater).
Water that does not sink into the ground or
evaporate into the air runs off (surface runoff) into bodies of water.
The land from which the surface water drains into
a body of water is called its watershed or
Fig. 14-3, p. 308
Unconfined Aquifer Recharge Area
Precipitation Evaporation and transpiration Evaporation Confined Recharge Area Runoff Flowing artesian well Recharge Unconfined Aquifer Stream Well requiring a pump Infiltration Water table Lake Infiltration Unconfined aquifer Confined aquifer
Confining impermeable rock layer
Less permeable
Animation: Threats to the Aquifers
WATER’S IMPORTANCE,
AVAILABILITY, AND RENEWAL
We currently use more than half of the
world’s reliable runoff of surface water and could be using 70-90% by 2025.
About 70% of the water we withdraw from
rivers, lakes, and aquifers is not returned to these sources.
Irrigation is the biggest user of water (70%),
Water in the
United States
Average
precipitation (top) in relation to
water-deficit
regions and their proximity to
metropolitan areas (bottom).
Fig. 14-4a, p. 309
Average annual precipitation (centimeters)
More than 122
Less than 41 81–122
Fig. 14-4b, p. 309
Acute shortage
Metropolitan regions with population greater than 1 million
Shortage
Case Study: Freshwater Resources in
the United States
17 western states
by 2025 could face intense conflict over scarce water
needed for urban growth, irrigation, recreation and
wildlife.
Fig. 14-5, p. 310
Wash.
Montana Oregon
N.D. Idaho
Wyoming S.D.
Nevada Neb.
Utah
Colo. Kansas
California Oak.
N.M.
Texas Highly likely conflict potential
Moderate conflict potential Unmet rural water needs
TOO LITTLE FRESHWATER
About 41% of the world’s population lives in
river basins that do not have enough freshwater.
Many parts of the world are experiencing:
Rivers running dry.
Lakes and seas shrinking.
Stress on the World’s River Basins
Comparison of the amount of water available
with the amount used by humans.
Fig. 14-6, p. 311
Europe
North
America Asia
Africa South
America Australia
Stress
Case Study: Who Should Own and
Manage Freshwater Resources
There is controversy over whether water
supplies should be owned and managed by governments or by private corporations.
European-based water companies aim to
control 70% of the U.S. water supply by
buying up water companies and entering into agreements with cities to manage water
How Would You Vote?
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Should private companies own or manage most of the world's water resources?
a. No. Democratically elected governments, which are
accountable to the voters, should own and manage water resources.
b. Qualified yes. Governments should own the water, but
expert private companies should manage it.
c. Depends. Each case must be decided independently.
The record on private versus public ownership is mixed.
d. Yes. Private companies have more expertise and
TOO LITTLE FRESHWATER
Cities are outbidding farmers for water
supplies from rivers and aquifers.
Countries are importing grain as a way to
reduce their water use.
More crops are being used to produce
biofuels.
Our water options are:
Get more water from aquifers and rivers,
WITHDRAWING GROUNDWATER
TO INCREASE SUPPLIES
Most aquifers are renewable resources
unless water is removed faster than it is replenished or if they are contaminated.
Groundwater depletion is a growing problem
mostly from irrigation.
At least one-fourth of the farms in India are being
Fig. 14-7, p. 313
Trade-Offs
Withdrawing Groundwater
Advantages Disadvantages
Useful for drinking and irrigation
Aquifer depletion from overpumping
Available year-round
Sinking of land (subsidence) from overpumping
Exists almost
everywhere Polluted aquifers for decades or centuries Renewable if not
overpumped or contaminated
Saltwater intrusion into drinking water supplies near coastal areas
Reduced water flows into surface waters No evaporation
losses
Cheaper to extract than most surface waters
Groundwater Depletion:
A Growing Problem
The Ogallala, the world’s largest aquifer, is
most of the red area in the center (Midwest).
Areas of
greatest aquifer depletion from groundwater
overdraft in the continental U.S.
Fig. 14-8, p. 314
Groundwater Overdrafts: High
Moderate
Other Effects of Groundwater
Overpumping
Groundwater
overpumping can cause land to sink, and contaminate
freshwater aquifers near coastal areas with saltwater.
Other Effects of Groundwater
Overpumping
Sinkholes form when
the roof of an
underground cavern collapses after being drained of
groundwater.
Groundwater Pumping in Saudi
Arabia (1986 – 2004)
Irrigation systems from the nonrenewable
aquifer appear as green dots. Brown dots are wells that have gone dry.
Fig. 14-12, p. 316
Solutions
Groundwater Depletion
Prevention Control
Waste less water Raise price of water to discourage waste Subsidize water
conservation
Ban new wells in aquifers near surface waters
Tax water pumped from wells near surface waters Buy and retire
groundwater
withdrawal rights in critical areas
Do not grow water-intensive crops in dry areas
USING DAMS AND RESERVOIRS
TO SUPPLY MORE WATER
Large dams and reservoirs can produce
cheap electricity, reduce downstream
Fig. 14-13a, p. 317 Provides water for year-round irrigation of cropland Flooded land destroys forests or cropland and displaces people
Large losses of water through evaporation Provides water for drinking Downstream cropland and estuaries are deprived of nutrient-rich silt Reservoir is useful for recreation and fishing Risk of failure and devastating downstream flooding Can produce cheap electricity (hydropower) Downstream flooding is
reduced Migration and spawning of
Fig. 14-13b, p. 317
Powerlines
Reservoir
Dam
Powerhouse Intake
Case Study: The Colorado Basin – an
Overtapped Resource
The Colorado River has so many dams and
withdrawals that it often does not reach the ocean.
14 major dams and reservoirs, and canals.
Water is mostly used in desert area of the U.S.
Provides electricity from hydroelectric plants for
Case Study: The Colorado Basin – an
Overtapped Resource
Lake Powell, is
the second
largest reservoir in the U.S.
It hosts one of
the hydroelectric plants located on the Colorado
River.
The Colorado River Basin
The area
drained by this basin is equal to more than one-twelfth of the
land area of the lower 48 states.
Fig. 14-14, p. 318 Dam Aqueduct or canal Upper Basin LOWER BASIN
0 100 mi.
0 150 km
Lower Basin
UPPER BASIN IDAHO
WYOMING
Salt Lake City
Grand Junction Denver UTAH NEVADA COLORADO Lake Powell Las Vegas Grand Canyon Glen Canyon Dam Boulder City NEW MEXICO ARIZONA Los Angeles Albuquerque Phoenix San Diego Mexicali Yuma Tucson All-American
Canal Gulf of
How Would You Vote?
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Do the advantages of large dams outweigh
their disadvantages?
a. No. Large dams inflict extensive environmental
damage and humans must learn to meet their needs without them.
b. Yes. Dams are critical in providing water and
Case Study:
China’s Three Gorges Dam
There is a debate over whether the
advantages of the world’s largest dam and reservoir will outweigh its disadvantages.
The dam will be 2 kilometers long.
The electric output will be that of 18 large
coal-burning or nuclear power plants.
It will facilitate ship travel reducing transportation
costs.
Dam will displace 1.2 million people.
Dam is built over seismatic fault and already has
Dam Removal
Some dams are being removed for ecological
reasons and because they have outlived their usefulness.
In 1998 the U.S. Army Corps of Engineers
announced that it would no longer build large dams and diversion projects in the U.S.
The Federal Energy Regulatory Commission has
approved the removal of nearly 500 dams.
Removing dams can reestablish ecosystems, but
TRANSFERRING WATER FROM
ONE PLACE TO ANOTHER
Transferring water can make unproductive
areas more productive but can cause environmental harm.
Promotes investment, jobs and strong economy.
It encourages unsustainable use of water in
Case Study: The California Experience
A massive
transfer of water from water-rich northern
California to water-poor southern
California is controversial.
Fig. 14-16, p. 321
CALIFORNIA
Sacramento River
North Bay
Aqueduct Lake Tahoe
San Francisco Sacramento South Bay
Aqueduct
Hoover Dam and Reservoir (Lake Mead)
NEVADA
UTAH
Fresno
San Luis Dam
and Reservoir Los Angeles
Aqueduct Colorado River California Aqueduct Santa Barbara Colorado River
Aqueduct Central Arizona Project
ARIZONA
Los Angeles
Salton Sea Phoenix
San Diego Tucson MEXICO S an J oa qu in V alley Feather River Shasta Lake
Case Study: The Aral Sea Disaster
The Aral Sea was once the world’s fourth
largest freshwater lake.
Case Study: The Aral Sea Disaster
Diverting water from the Aral Sea and its two
feeder rivers mostly for irrigation has created a major ecological, economic, and health
disaster.
About 85% of the wetlands have been
eliminated and roughly 50% of the local bird and mammal species have disappeared.
Since 1961, the sea’s salinity has tripled and the
DESALTING SEAWATER, SEEDING
CLOUDS, AND TOWING ICEBERGS
AND GIANT BAGGIES
Removing salt from seawater by current
methods is expensive and produces large amounts of salty wastewater that must be disposed of safely.
Distillation: heating saltwater until it evaporates,
leaves behind water in solid form.
Reverse osmosis: uses high pressure to force
DESALTING SEAWATER, SEEDING
CLOUDS, AND TOWING ICEBERGS
AND GIANT BAGGIES
Seeding clouds with tiny particles of
chemicals to increase rainfall towing icebergs or huge bags filled with freshwater to dry
coastal areas have all been proposed but are unlikely to provide significant amounts of
INCREASING WATER SUPPLIES BY
WASTING LESS WATER
We waste about two-thirds of the water we
use, but we could cut this waste to 15%.
65-70% of the water people use throughout the
world is lost through evaporation, leaks, and other losses.
Water is underpriced through government
subsidies.
The lack of government subsidies for improving
How Would You Vote?
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Should water prices be raised sharply to help
reduce water waste?
a. No. Poor people, farmers, ranchers, and small
businesses would suffer from price increases.
b. Yes. People would be more likely to conserve
INCREASING WATER SUPPLIES BY
WASTING LESS WATER
Sixty percent of the world’s irrigation water is
currently wasted, but improved irrigation techniques could cut this waste to 5-20%.
Center-pivot, low pressure sprinklers sprays
water directly onto crop.
It allows 80% of water to reach crop.
Has reduced depletion of Ogallala aquifer in
Fig. 14-18, p. 325
Center pivot Drip irrigation
Gravity flow
(efficiency 60% and 80% with surge
valves)
Above- or
below-ground pipes or tubes deliver water to
individual plant roots. Water usually comes from
an aqueduct system or a nearby river.
(efficiency 90–95%)
Fig. 14-19, p. 326
Solutions
Reducing Irrigation Water Waste
• Line canals bringing water to irrigation ditches • Level fields with lasers
• Irrigate at night to reduce evaporation • Monitor soil moisture to add water only when necessary
• Polyculture
• Organic farming
Solutions: Getting More Water for
Irrigation in Developing Countries –
The Low-Tech Approach
Many poor farmers in
developing countries use low-tech methods to pump groundwater and make more
efficient use of rainfall.
Fig. 14-21, p. 327
Solutions
Reducing Water Waste
• Redesign manufacturing processes • Repair leaking underground pipes • Landscape yards with plants that
require little water • Use drip irrigation • Fix water leaks • Use water meters • Raise water prices
• Use waterless composting toilets • Require water conservation in
water-short cities
• Use water-saving toilets, showerheads, and front loading clothes washers
• Collect and reuse household water to irrigate lawns and nonedible plants • Purify and reuse water for houses,
Raising the Price of Water:
A Key to Water Conservation
We can reduce water use and waste by
raising the price of water while providing low lifeline rates for the poor.
When Boulder, Colorado introduced water
meters, water use per person dropped by 40%.
A 10% increase in water prices cuts domestic
Solutions: Using Less Water to Remove
Industrial and Household Wastes
We can mimic the way nature deals with
wastes instead of using large amounts of high-quality water to wash away and dilute industrial and animal wastes.
Use nutrients in wastewater before treatment as
soil fertilizer.
Use waterless and odorless composting toilets
TOO MUCH WATER
Heavy rainfall, rapid snowmelt, removal of
vegetation, and destruction of wetlands cause flooding.
Floodplains, which usually include highly
productive wetlands, help provide natural
flood and erosion control, maintain high water quality, and recharge groundwater.
To minimize floods, rivers have been
TOO MUCH WATER
Comparison of St. Louis, Missouri under
normal conditions (1988) and after severe flooding (1993).
TOO MUCH WATER
Human activities have contributed to flood
deaths and damages.
Fig. 14-23a, p. 330 Oxygen released by vegetation Diverse ecological habitat Evapotranspiration
Trees reduce soil erosion from heavy rain and wind
Agricultural land Steady river flow Leaf litter improves soil fertility
Tree roots stabilize soil and aid water flow
Fig. 14-23b, p. 330 Tree plantation Roads destabilize hillsides Evapotranspiration decreases Ranching accelerates
soil erosion by water and wind
Winds remove fragile topsoil
Agricultural land is flooded and silted up Gullies and
landslides
Heavy rain leaches nutrients from soil and erodes topsoil
Silt from erosion blocks rivers and reservoirs and causes flooding downstream
Animation: Effects of Deforestation
Fig. 14-24, p. 331
Solutions
Reducing Flood Damage
Prevention Control
Preserve forests on watersheds Strengthen and deepen streams (channelization) Preserve and restore wetlands in floodplains
Tax all development on floodplains
SOLUTIONS: USING
WATER MORE
SUSTAINABLY
We can use water more
sustainably by cutting waste, raising water prices, preserving
forests and wetlands in water basins, and
slowing population growth.
Fig. 14-25, p. 333
What Can You Do?
Water Use and Waste
• Use water-saving toilets, showerheads, and faucet aerators. • Shower instead of taking baths, and take short showers. • Stop water leaks.
• Turn off sink faucets while brushing teeth, shaving, or washing. • Flush toilets only when necessary.
• Wash only full loads of clothes or use the lowest water-level for smaller loads.
• Use recycled (gray) water for lawn, gardens, house plants, car washing.
• Wash a car from a bucket of soapy water, and use the hose for rinsing only.
• If you use a commercial car wash, try to find one that recycles its water.
• Replace your lawn with native plants that need little if any watering and decorative gravel or rocks.
