Water Resources
Chapter 13
13-1 Will We Have Enough Usable Water?
Concept 13-1A We are using available
freshwater unsustainably by wasting it, polluting
it, and charging too little for this irreplaceable
natural resource.
Concept 13-1B One of every six people does
not have sufficient access to clean water, and
this situation will almost certainly get worse.
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 is
available to us as liquid freshwater.
Girl Carrying Well Water over Dried Out
Earth during a Severe Drought in India
WATER’S IMPORTANCE, AVAILABILITY,
AND RENEWAL
Comparison of
population sizes and
shares of the world’s
freshwater among the
continents.
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
drainage basin.
Unconfined Aquifer Recharge Area
Precipitation Evaporation and transpiration Evaporation
Confined
Recharge
Area Runoff
Flowing Well
artesian well requiring
a pump Stream
Water
Infiltration Lake
table
Infiltration
Less permeable
material such as
clay
Fig. 13-3, p. 316
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%),
followed by industries (20%) and cities and
residences (10%).
Average Annual Precipitation and Major
Rivers, Water-Deficit Regions in U.S.
Fig 13-4
Water Hot Spots
Washington
North
Montana Dakota
Oregon
Idaho South
Dakota
Wyoming
Nevada Nebraska
Utah
Colorado
Kansas
California
Oklahoma
New
Arizona Mexico
Texas
Highly likely conflict potential
Substantial conflict potential
Moderate conflict potential
Unmet rural water needs
Fig. 13-5, p. 318
Europe Asia
North
America
Africa
South
America Australia
Stress
High None
Fig. 13-6, p. 319
Long-Term Severe Drought Is Increasing
Causes
• Extended period of below-normal rainfall
• Diminished groundwater
Harmful environmental effects
• Dries out soils
• Reduces stream flows
• Decreases tree growth and biomass
• Lowers net primary productivity and crop yields
• Shift in biomes
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 supplies.
13-2 Is Extracting Groundwater
the Answer?
Concept 13-2 Groundwater that is used to
supply cities and grow food is being pumped
from aquifers in some areas faster than it is
renewed by precipitation.
Other Effects of Groundwater Overpumping
Groundwater
overpumping can
cause land to sink,
and contaminate
freshwater aquifers
near coastal areas
with saltwater.
TRADE-OFFS
Withdrawing Groundwater
Advantages Disadvantages
Useful for drinking Aquifer depletion
and irrigation from overpumping
Sinking of land
Available year-round (subsidence) from
overpumping
Aquifers polluted for
Exists almost
decades or centuries
everywhere
Renewable if not Saltwater intrusion into
overpumped or drinking water supplies
contaminated near coastal areas
Reduced water flows
No evaporation into surface waters
losses
Increased cost and
Cheaper to extract contamination from
than most surface deeper wells
waters
Fig. 13-7, p. 321
Natural Capital Degradation: Irrigation in
Saudi Arabia Using an Aquifer
Natural Capital Degradation: Areas of
Greatest Aquifer Depletion in the U.S.
Fig 13-9
SOLUTIONS
Groundwater Depletion
Prevention Control
Waste less water Raise price of water
to discourage waste
Subsidize water Tax water pumped
conservation from wells near
surface waters
Limit number of wells Set and enforce
minimum stream flow
levels
Do not grow water- Divert surface water
intensive crops in in wet years to
dry areas recharge aquifers
Fig. 13-11, p. 324
13-3 Is Building More Dams the Answer?
Concept 13-3 Building dam and reservoir
systems has greatly increased water supplies in
some areas, but it has disrupted ecosystems
and displaced people.
Large Dams and Reservoirs Have
Advantages and Disadvantages (1)
Main goals of a dam and reservoir system
• Capture and store runoff
• Release runoff as needed to control:
• Floods
• Generate electricity
• Supply irrigation water
• Recreation (reservoirs)
Large Dams and Reservoirs Have
Advantages and Disadvantages (2)
Advantages
• Increase the reliable runoff available
• Reduce flooding
• Grow crops in arid regions
Large Dams and Reservoirs Have
Advantages and Disadvantages (3)
Disadvantages
• Displaces people
• Flooded regions
• Impaired ecological services of rivers
• Loss of plant and animal species
• Fill up with sediment within 50 years
Advantages and Disadvantages of Large
Dams and Reservoirs
Fig 13-12
Matilija Dam Removal Project
Click for report
The Colorado River Basin
Fig 13-14
Case Study: The Colorado River Basin—
An Overtapped Resource (3)
Four Major problems
• Colorado River basin has very dry lands
• Modest flow of water for its size
• Legal pacts allocated more water for human use
than it can supply
• Amount of water flowing to the mouth of the river
has dropped
Aerial View of Glen Canyon Dam Across
the Colorado River and Lake Powell
The Flow of the Colorado River Measured
at Its Mouth Has Dropped Sharply
Case Study: China’s Three
Gorges Dam (1)
World’s largest hydroelectric dam and reservoir
2 km long across the Yangtze River
Benefits
• Electricity-producing potential is huge (18 large
power plants)
• Holds back the Yangtze River floodwaters
• Allows cargo-carrying ships
Case Study: China’s Three
Gorges Dam (2)
Harmful effects
• Displaces about 5.4 million people
• Built over a seismic fault
• Significance?
• Rotting plant and animal matter producing CH4
• Worse than CO2 emissions
• Will the Yangtze River become a sewer?
13-4 Is Transferring Water from One
Place to Another the Answer?
Concept 13-4 Transferring water from one
place to another has greatly increased water
supplies in some areas, but it has also disrupted
ecosystems.
CALIFORNIA
Shasta Lake NEVADA
UTAH
Sacramento Oroville Dam and
River Reservoir
Feather
North Bay Lake Tahoe
River
Aqueduct
Sacramento
San Francisco
Hoover Dam
South Bay
and Reservoir
Aqueduct
Fresno (Lake Mead)
San Luis Dam
and Reservoir Colorado
Los Angeles River
Aqueduct
California Aqueduct ARIZONA
Colorado River
Santa Barbara Aqueduct Central Arizona
Los Angeles Project
Phoenix
Salton Sea
San Diego
Tucson
MEXICO
Fig. 13-17, p. 330
Natural Capital Degradation: The Aral
Sea, Shrinking Freshwater Lake
1976 2006
Oxnard water suppliers
United Water
Calleguas Municipal
City of Oxnard
13-5 Is Converting Salty Seawater to
Freshwater the Answer?
Concept 13-5 We can convert salty ocean
water to freshwater, but the cost is high, and the
resulting salty brine must be disposed of without
harming aquatic or terrestrial ecosystems.
Removing Salt from Seawater Seems
Promising but Is Costly (1)
Desalination
• Distillation
• Reverse osmosis, microfiltration
15,000 plants in 125 countries
• Saudi Arabia: highest number
Click for link to Desal Response Group
Removing Salt from Seawater Seems
Promising but Is Costly (2)
Problems
• High cost and energy footprint
• Keeps down algal growth and kills many marine
organisms
• Large quantity of brine wastes
Click for Oxnard’s GREAT RO plant info
13-6 How Can We Use Water More
Sustainably?
Concept 13-6 We can use water more
sustainably by cutting water waste, raising water
prices, slowing population growth, and
protecting aquifers, forests, and other
ecosystems that store and release water.
Reducing Water Waste Has Many
Benefits (1)
Water conservation
• Improves irrigation efficiency
• Improves collection efficiency
• Uses less in homes and businesses
Center pivot
(efficiency 80% with low-pressure
Drip irrigation sprinkler and 90–95% with LEPA
(efficiency 90–95%) sprinkler)
Gravity flow Above- or below-ground Water usually pumped from
(efficiency 60% and 80% with surge valves) pipes or tubes deliver water underground and sprayed
to individual plant roots. from mobile boom with
Water usually comes from an sprinklers. Stepped Art
aqueduct system or a nearby river.
Fig. 13-20, p. 335
Solutions: Reducing Irrigation
Water Waste
Fig 13-21
Solutions: Reducing Water Waste
Fig 13-22
SOLUTIONS
Sustainable Water Use
Waste less water and subsidize
water conservation
Do not deplete aquifers
Preserve water quality
Protect forests, wetlands,
mountain glaciers, watersheds,
and other natural systems that
store and release water
Get agreements among regions
and countries sharing surface
water resources
Raise water prices
Slow population growth
Fig. 13-23, p. 337
How can you save water at home?
Click for Family Water Audit
What Can You Do? Water Use and Waste
Fig 13-24
13-7 How Can We Reduce the Threat
of Flooding?
Concept 13-7 We can lessen the threat of
flooding by protecting more wetlands and natural
vegetation in watersheds and by not building in
areas subject to frequent flooding.
Some Areas Get Too Much Water from
Flooding (1)
Flood plains
• Highly productive wetlands
• Provide natural flood and erosion control
• Maintain high water quality
• Recharge groundwater
Benefits of floodplains
• Fertile soils
• Nearby rivers for use and recreation
• Flatlands for urbanization and farming
Some Areas Get Too Much Water from
Flooding (2)
Dangers of floodplains and floods
• Deadly and destructive
• Human activities worsen floods
• Failing dams and water diversion
• Hurricane Katrina and the Gulf Coast
• Removal of coastal wetlands
Natural Capital Degradation: Hillside
Before and After Deforestation
Fig 13-25
SOLUTIONS
Reducing Flood Damage
Prevention Control
Preserve forests on Straighten and
watersheds deepen streams
(channelization)
Preserve and restore
wetlands in floodplains
Build levees or
Tax development on
floodwalls along
floodplains
streams
Use floodplains primarily
for recharging aquifers,
sustainable agriculture
Build dams
and forestry
Fig. 13-26, p. 340