1. Chapter 13 Water Resources

2. Case Study: The Colorado River Basin— An Overtapped Resource (1)
2,300 km through 7 U.S. states
14 Dams and reservoirs
Located in a desert area within the rain shadow of the Rocky Mountains
Water supplied mostly from snowmelt of the Rocky Mountains

3. Case Study: The Colorado River Basin— An Overtapped Resource (2)
Supplies water and electricity for about 30 million people
Las Vegas, Los Angeles, San Diego
Irrigation of crops that help feed America
Very little water reaches the Gulf of California
Southwest experiencing recent droughts

4. The Colorado River Basin
Figure 13.1: 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. Two large reservoirs—Lake Mead behind the Hoover Dam and Lake Powell behind the Glen Canyon Dam—store about 80% of the water in this basin.
Fig. 13-1, p. 317

5. Aerial View of Glen Canyon Dam Across the Colorado River and Lake Powell
Figure 13.2: The Glen Canyon Dam across the Colorado River was completed in Lake Powell behind the dam is the second largest reservoir in the United States.
Fig. 13-2, p. 317

6. 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.

7. Freshwater Is an Irreplaceable Resource That We Are Managing Poorly (1)
Why is water so important?
Earth as a watery world: 71% of surface
Poorly managed resource
Water waste
Water pollution

8. Freshwater Is an Irreplaceable Resource That We Are Managing Poorly (2)
Access to water is
A global health issue
An economic issue
A women’s and children’s issue
A national and global security issue

9. Girl Carrying Well Water over Dried Out Earth during a Severe Drought in India
Figure 13.3: Many areas of the world suffer from severe and long-lasting shortages of freshwater. This has a major impact on the poor in some areas of India, especially women and children such as this young girl carrying water to her home in a very dry area. According to the United Nations, over 1.2 billion people—about 4 times the entire U.S. population—do not have access to clean water where they live. Each day girls and women in this group typically walk an average of almost 6 kilometers (4 miles) and spend an average of 3 hours collecting water from distant sources.
Fig. 13-3, p. 319

10. Most of the Earth’s Freshwater Is Not Available to Us
Freshwater availability: 0.024%
Groundwater, lakes, rivers, streams
Hydrologic cycle
Movement of water in the seas, land, and air
Driven by solar energy and gravity
People divided into
Water haves
Water have-nots

11. Hydrologic Cycle Figure 3.16: Natural capital.
This diagram is a simplified model of the water cycle, or hydrologic cycle, in which water circulates in various physical forms within the biosphere. Major harmful impacts of human activities are shown by the red arrows and boxes. Question: What are three ways in which your lifestyle directly or indirectly affects the hydrologic cycle?
Fig. 3-16, p. 67

12. Groundwater and Surface Water Are Critical Resources (1)
Zone of saturation
Spaces in soil are filled with water
Water table
Top of zone of saturation
Aquifers
Natural recharge
Lateral recharge

13. Groundwater and Surface Water Are Critical Resources (2)
Surface runoff
Watershed (drainage) basin

14. We Use Much of the World’s Reliable Runoff
2/3 of the surface runoff: lost by seasonal floods
1/3 is reliable runoff = usable
World-wide averages
Domestic: 10%
Agriculture: 70%
Industrial use: 20%

15. Science Focus: Water Footprints and Virtual Water (1)
Volume of water we directly and indirectly
Average American uses 260 liters per day
Flushing toilets, 27%
Washing clothes, 22%
Taking showers, 17%
Running faucets, 16%
Wasted from leaks, 14%
World’s poorest use 19 liters per day

16. Science Focus: Water Footprints and Virtual Water (2)
More water is used indirectly = virtual water
Hamburger, 2400 liters
Virtual water often exported/imported
Grains and other foods

17. Virtual Water Use
Figure 13.A: Producing and delivering a single one of each of the products shown here requires the equivalent of at least one and usually many bathtubs full of water, called virtual water. A typical bathtub contains about 151 liters (40 gallons) of water. The average amount of water used to raise a single steer during its typical 3-year life from birth to slaughter and to market by an industrial producer would fill more than 20,000 bathtubs. This includes water used for providing the steer with food and drinking water and water used to clean up its wastes. It is not surprising that about 70% of the world’s water is used for irrigation, because it takes about 1,000 metric tons (900 tons) of water to produce 1 metric ton (0.9 ton) of grain. (Data from UNESCO-IHE Institute for Water Education, UN Food and Agriculture Organization, World Water Council, Water Footprint Network, and Coca Cola Company) [Photos from Shutterstock; Credits (top to bottom: Kirsty Pargeter, Aleksandra Nadeina, Alexander Kallina, Kelpfish, Wolfgang Amri, Skip Odonnell, Eky Chan, Rafal Olechowski)]
Fig. 13-A, p. 321

18. Case Study: Freshwater Resources in the United States
More than enough renewable freshwater, unevenly distributed and polluted
Effect of
Floods
Pollution
Drought
2007: U.S. Geological Survey projection
Water hotspots

19. Average Annual Precipitation and Major Rivers, Water-Deficit Regions in U.S.
Figure 13.4: The top map shows the average annual precipitation and major rivers in the continental United States. The bottom map shows water-deficit regions in the continental United States and their proximity to metropolitan areas having populations greater than 1 million (shaded areas). Question: Why do you think some areas with moderate precipitation still suffer from water shortages? (Data from U.S. Water Resources Council and U.S. Geological Survey)
Fig. 13-4, p. 322

20. Water Hotspots in 17 Western U.S. States
Figure 13.5: This map shows water scarcity hotspots in 17 western states that, by 2025, could face intense conflicts over scarce water needed for urban growth, irrigation, recreation, and wildlife. Some analysts suggest that this is a map of places not to live in the foreseeable future. Question: Which, if any, of these areas are found in the Colorado River basin (Figure 13-1)? (Data from U.S. Department of the Interior)
Fig. 13-5, p. 322

21. Water Shortages Will Grow (1)
Dry climates
Drought
Too many people using a normal supply of water
Wasteful use of water

22. Water Shortages Will Grow (2)
China and urbanization
30% earth’s land area experiences severe drought
Will rise to 45% by 2059 from climate change
Potential conflicts/wars over water
Refugees from arid lands
Increased mortality

23. Natural Capital Degradation: Stress on the World’s Major River Basins
Figure 13.6: Natural capital degradation.
The world’s major river basins differ in their degree of water scarcity stress, the measurement of which is based on a comparison of the amount of water available with the amount used by humans (Concept 13-1B). Questions: If you live in a water-stressed area, what signs of stress have you noticed? In what ways, if any, has it affected your life? (Data from World Commission on Water Use in the 21st Century)
Fig. 13-6, p. 323

24. 13-2 Is Extracting Groundwater the Answer?
Concept Groundwater used to supply cities and grow food is being pumped from aquifers in some areas faster than it is renewed by precipitation.

25. Groundwater is Being Withdrawn Faster Than It Is Replenished (1)
Most aquifers are renewable
Aquifers provide drinking water for half the world
Water tables are falling in many parts of the world, primarily from crop irrigation

26. Groundwater is Being Withdrawn Faster Than It Is Replenished (2)
India, China, and the United States
Three largest grain producers
Overpumping aquifers for irrigation of crops
India and China
Small farmers drilling tubewells
Effect on water table
Saudi Arabia
Aquifer depletion and irrigation

27. Trade-Offs: Withdrawing Groundwater, Advantages and Disadvantages
Figure 13.7: Withdrawing groundwater from aquifers has advantages and disadvantages. Questions: Which two advantages and which two disadvantages do you think are the most important? Why?
Fig. 13-7, p. 325

28. Natural Capital Degradation: Irrigation in Saudi Arabia Using an Aquifer
Figure 13.8: Natural capital degradation.
These satellite photos show farmland irrigated by groundwater pumped from an ancient and nonrenewable aquifer in a vast desert region of Saudi Arabia between 1986 (left) and 2004 (right). Irrigated areas appear as green dots (each representing a circular spray system) and brown dots show areas where wells have gone dry and the land has returned to desert. Hydrologists estimate that because of aquifer depletion, most irrigated agriculture in Saudi Arabia will disappear within the next 5 to 10 years.
Fig. 13-8, p. 325

29. Case Study: Aquifer Depletion in the United States
Ogallala aquifer: largest known aquifer
Irrigates the Great Plains
Very slow recharge
Water table dropping
Government subsidies to continue farming deplete the aquifer further
Biodiversity threatened in some areas
California Central Valley: serious water depletion

30. Natural Capital Degradation: Areas of Greatest Aquifer Depletion in the U.S.
Figure 13.9: Natural capital degradation.
This map shows areas of greatest aquifer depletion from groundwater overdraft in the continental United States. Aquifer depletion is also high in Hawaii and Puerto Rico (not shown on map). See an animation based on this figure at CengageNOW. Questions: Do you depend on any of these overdrawn aquifers for your drinking water? If so, what is the level of severity of overdraft where you live? (Data from U.S. Water Resources Council and U.S. Geological Survey)
Fig. 13-9, p. 326

31. Kansas Crops Irrigated by the Ogallala Aquifer
Figure 13.10: These crop fields in the state of Kansas are irrigated by groundwater pumped from the Ogallala. Green circles show irrigated areas and brown, gray, and white circles represent fields that have been recently harvested and plowed under or that have not been planted for a year.
Fig , p. 326

32. Overpumping Aquifers Has Several Harmful Effects
Limits future food production
Bigger gap between the rich and the poor
Land subsidence
Mexico City
San Joaquin Valley in California
Groundwater overdrafts near coastal regions
Contamination of groundwater with saltwater

33. Subsidence in the San Joaquin Valley
Figure 13.11: This pole shows subsidence from overpumping of an aquifer for irrigation in California’s San Joaquin Central Valley between 1925 and In 1925, the land surface in this area was near the top of this pole. Since 1977 this problem has gotten worse.
Fig , p. 327

34. Solutions: Groundwater Depletion, Prevention and Control
Figure 13.12: There are a number of ways to prevent or slow groundwater depletion by using water more sustainably. Questions: Which two of these solutions do you think are the most important? Why?
Fig , p. 327

35. Deep Aquifers Might Be Tapped
May contain enough water to provide for billions of people for centuries
Major concerns
Nonrenewable
Little is known about the geological and ecological impacts of pumping deep aquifers
Some flow beneath more than one country
Costs of tapping are unknown and could be high

36. 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.

37. Large Dams and Reservoirs Have Advantages and Disadvantages (1)
Main goal of a dam and reservoir system
Capture and store runoff
Release runoff as needed to control:
Floods
Generate electricity
Supply irrigation water
Recreation (reservoirs)

38. Large Dams and Reservoirs Have Advantages and Disadvantages (2)
Increase the reliable runoff available
Reduce flooding
Grow crops in arid regions

39. Large Dams and Reservoirs Have Advantages and Disadvantages (3)
Displaces people
Flooded regions
Impaired ecological services of rivers
Loss of plant and animal species
Fill up with sediment
Can cause other streams and lakes to dry up

40. Provides irrigation water above and below dam
Flooded land destroys forests or cropland and displaces people
Large losses of water through evaporation
Provides water for drinking
Deprives downstream cropland and estuaries of nutrient-rich silt
Reservoir useful for recreation and fishing
Risk of failure and devastating downstream flooding
Can produce cheap electricity (hydropower)
Figure 13.13: Trade-offs.
Large dams and reservoirs have advantages (green) and disadvantages (orange) (Concept 13-3). The world’s 45,000 large dams (15 meters (49 feet) or higher) capture and store about 14% of the world’s surface runoff, provide water for almost half of all irrigated cropland, and supply more than half the electricity used in 65 countries. The United States has more than 70,000 large and small dams, capable of capturing and storing half of the country’s entire river flow. Question: Which single advantage and which single disadvantage do you think are the most important?
Reduces down-stream flooding of cities and farms
Disrupts migration and spawning of some fish
Fig a, p. 328

41. Powerlines Reservoir Dam Powerhouse Intake Turbine
Figure 13.13: Trade-offs.
Large dams and reservoirs have advantages (green) and disadvantages (orange) (Concept 13-3). The world’s 45,000 large dams (15 meters (49 feet) or higher) capture and store about 14% of the world’s surface runoff, provide water for almost half of all irrigated cropland, and supply more than half the electricity used in 65 countries. The United States has more than 70,000 large and small dams, capable of capturing and storing half of the country’s entire river flow. Question: Which single advantage and which single disadvantage do you think are the most important?
Fig b, p. 328

42. A Closer Look at the Overtapped Colorado River Basin (1)
Only small amount of Colorado River water reaches Gulf of California
Threatens aquatic species in river and species that live in the estuary
Current rate of river withdrawal is not sustainable
Much water used for agriculture that is inefficient with water use: cotton, alfalfa, rice
Water use subsidized by government

43. A Closer Look at the Overtapped Colorado River Basin (2)
Reservoirs
Leak water into ground below
Lose much water through evaporation
Fill up with silt load of river, depriving delta
Could eventually lose ability to store water and create electricity
States must conserve water, control population, and slow urban development

44. The Flow of the Colorado River Measured at Its Mouth Has Dropped Sharply
Figure 13.14: The measured flow of the Colorado River at its mouth has dropped sharply since 1905 as a result of multiple dams, water withdrawals for agriculture and urban water supplies, and prolonged drought. Historical records and tree-ring analysis show that about once every century, the southwestern United States suffers from a mega-drought—a decades-long dry period. (Data from U.S. Geological Survey)
Fig , p. 329

45. 13-4 Is Transferring Water from One Place to Another the Answer?
Concept Transferring water from one place to another has greatly increased water supplies in some areas, but it has also disrupted ecosystems.

46. California Transfers Water from Water-Rich Areas to Water-Poor Areas
Water transferred from north to south by
Tunnels
Aqueducts
Underground pipes
California Water Project
Inefficient water use
Environmental damage to Sacramento River and San Francisco Bay

47. Southern California Lettuce Grown with Northern California Water
Figure 13.15: This lettuce crop is growing in the Imperial Valley of central California. This and other water-intensive crops are grown in this arid area mostly because of the availability of cheap, government-subsidized irrigation water brought in from northern California, but also because the weather allows for growing crops year round in this valley. Question: Have you ever checked to see where your lettuce and other produce that you eat come from?
Fig , p. 331

48. The California Water Project and the Central Arizona Project
Figure 13.16: The California Water Project and the Central Arizona Project transfer huge volumes of water from one watershed to another. The red arrows show the general direction of water flow. Questions: What effects might this system have on different areas on this map? How might it affect areas from which the water is taken?
Fig , p. 331

49. Case Study: The Aral Sea Disaster (1)
Large-scale water transfers in dry central Asia
Salinity
Wetland destruction and wildlife
Fish extinctions and fishing declines

50. Case Study: The Aral Sea Disaster (2)
Wind-blown salt
Water pollution
Restoration efforts
Cooperation of neighboring countries
More efficient irrigation
Dike built to raise lake level

51. Natural Capital Degradation: The Aral Sea, Shrinking Freshwater Lake
Figure 13.17: Natural capital degradation.
The Aral Sea was one of the world’s largest saline lakes. Since 1960, it has been shrinking and getting saltier because most of the water from the two rivers that replenish it has been diverted to grow cotton and food crops. These satellite photos show the sea in 1976 and in As the Southern Aral Sea shrank, it split into two lakes and left behind a salty desert, economic ruin, increasing health problems, and severe ecological disruption. By late 2009, the larger eastern part of the once huge Southern Aral Sea was gone (bottom-right part of each photo). The smaller Northern Aral Sea (top of each photo) has also shrunk, but not nearly as much as the Southern Aral Sea has. Question: What are three things that you think should be done to help prevent further shrinkage of the Aral Sea?
Fig , p. 332

52. 13-5 Is Converting Salty Seawater to Freshwater the Answer?
Concept 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.

53. Removing Salt from Seawater Is Costly, Kills Organisms, Creates Briny Wastewater (1)
Desalination
Removing dissolved salts
Distillation: evaporate water, leaving salts behind
Reverse osmosis, microfiltration: use high pressure to remove salts
14,450 plants in 125 countries
Saudi Arabia: highest number

54. Removing Salt from Seawater Is Costly, Kills Organisms, Creates Briny Wastewater (2)
Problems
High cost and energy footprint
Keeps down algal growth and kills many marine organisms
Large quantity of brine wastes

55. Science Focus: The Search for Improved Desalination Technology
Desalination on offshore ships
Solar or wind energy
Use ocean waves for power
Build desalination plants near electric power plants

56. 13-6 How Can We Use Water More Sustainably?
Concept 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.

57. Reducing Water Waste Has Many Benefits
One-half to two-thirds of water is wasted
Subsidies mask the true cost of water
Water conservation
Improves irrigation efficiency
Improves collection efficiency
Uses less in homes and businesses

58. We Can Cut Water Waste in Irrigation
Flood irrigation
Wasteful
Center pivot, low pressure sprinkler
Low-energy, precision application sprinklers
Drip or trickle irrigation, microirrigation
Costly; less water waste

59. Major Irrigation Systems
Figure 13.18: Several different systems are used to irrigate crops. The two most efficient systems are the low-energy, precision application (LEPA) center-pivot system and the drip irrigation system. Because of high initial costs, they are not widely used. The development of new, low-cost, drip-irrigation systems may change this situation.
Fig , p. 335

60. (efficiency 80% with low-pressure sprinkler and
Figure 13.18: Several different systems are used to irrigate crops. The two most efficient systems are the low-energy, precision application (LEPA) center-pivot system and the drip irrigation system. Because of high initial costs, they are not widely used. The development of new, low-cost, drip-irrigation systems may change this situation.
Center pivot
(efficiency 80% with low-pressure sprinkler and
90–95% with LEPA sprinkler)
Drip irrigation
(efficiency 90–95%)
Gravity flow
(efficiency 60% and 80% with surge valves)
Above- or below-ground pipes or tubes deliver water to individual plant roots.
Water usually pumped from underground and sprayed from mobile boom with sprinklers.
Water usually comes from an aqueduct system or a nearby river.
Fig , p. 335

61. Solutions: Reducing Irrigation Water Waste
Figure 13.19: There are a number of ways to reduce water waste in irrigation. Questions: Which two of these solutions do you think are the best ones? Why?
Fig , p. 336

62. We Can Cut Water Waste in Industry and Homes
Recycle water in industry
Fix leaks in the plumbing systems
Use water-thrifty landscaping: xeriscaping
Use gray water
Pay-as-you-go water use

63. Solutions: Reducing Water Waste
Figure 13.21: There are a number of ways to reduce water waste in industries, homes, and businesses (Concept 13-3). Questions: Which three of these solutions do you think are the best ones? Why?
Fig , p. 337

64. Xeriscaping in Southern California
Figure 13.22: This yard in Encinitas, a city in a dry area of southern California (USA), uses a diversity of plants that are native to the arid environment and require little watering.
Fig , p. 338

65. We Can Use Less Water to Remove Wastes
Can we mimic how nature deals with waste?
Use human sewage to create nutrient-rich sludge to apply to croplands
Waterless composting toilets

66. Solutions: Sustainable Water Use
Figure 13.23: A variety of methods can help us to use the earth’s water resources more sustainably (Concept 13-6). Questions: Which two of these solutions do you think are the most important? Why?
Fig , p. 339

67. What Can You Do? Water Use and Waste
Figure 13.24: Individuals matter.
You can reduce your use and waste of water. See for a number of tips, provided by the Environmental Protection Agency and the California Urban Water Conservation Council, that you can use anywhere for saving water. Questions: Which of these steps have you taken? Which of them would you like to take?
Fig , p. 339

68. 13-7 How Can We Reduce the Threat of Flooding?
Concept 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.

69. 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

70. Some Areas Get Too Much Water from Flooding (2)
Human activities make floods worse
Levees can break or be overtopped
Paving and development increase runoff
Removal of water-absorbing vegetation
Draining wetlands and building on them
Rising sea levels from global warming means more coastal flooding

71. Natural Capital Degradation: Hillside Before and After Deforestation
Figure 13.25: Natural capital degradation.
These diagrams show a hillside before and after deforestation. Once a hillside has been deforested for timber, fuelwood, livestock grazing, or unsustainable farming, water from precipitation rushes down the denuded slopes, erodes precious topsoil, and can increase flooding and pollution in local streams. Such deforestation can also increase landslides and mudflows. A 3,000-year-old Chinese proverb says, “To protect your rivers, protect your mountains.” See an animation based on this figure at CengageNOW. Question: How might a drought in this area make these effects even worse?
Fig , p. 340

72. Diverse ecological habitat Evapotranspiration
Trees reduce soil erosion from heavy rain and wind
Agricultural land
Figure 13.25: Natural capital degradation.
These diagrams show a hillside before and after deforestation. Once a hillside has been deforested for timber, fuelwood, livestock grazing, or unsustainable farming, water from precipitation rushes down the denuded slopes, erodes precious topsoil, and can increase flooding and pollution in local streams. Such deforestation can also increase landslides and mudflows. A 3,000-year-old Chinese proverb says, “To protect your rivers, protect your mountains.” See an animation based on this figure at CengageNOW. Question: How might a drought in this area make these effects even worse?
Tree roots stabilize soil
Vegetation releases water slowly and reduces flooding
Forested Hillside
Fig a, p. 340

73. Evapotranspiration decreases Roads destabilize hillsides
Tree plantation
Evapotranspiration decreases
Roads destabilize hillsides
Overgrazing accelerates soil erosion by water and wind
Winds remove fragile topsoil
Agricultural land is flooded and silted up
Gullies and landslides
Figure 13.25: Natural capital degradation.
These diagrams show a hillside before and after deforestation. Once a hillside has been deforested for timber, fuelwood, livestock grazing, or unsustainable farming, water from precipitation rushes down the denuded slopes, erodes precious topsoil, and can increase flooding and pollution in local streams. Such deforestation can also increase landslides and mudflows. A 3,000-year-old Chinese proverb says, “To protect your rivers, protect your mountains.” See an animation based on this figure at CengageNOW. Question: How might a drought in this area make these effects even worse?
Heavy rain erodes topsoil
Silt from erosion fills rivers and reservoirs
Rapid runoff causes flooding
After Deforestation
Fig b, p. 340

74. Forested Hillside After Deforestation Diverse ecological habitat
Evapotranspiration
Trees reduce soil erosion from heavy rain and wind
Tree roots stabilize soil
Vegetation releases water slowly and reduces flooding
Forested Hillside
Agricultural land
Stepped Art
Tree plantation
Roads destabilize hillsides
Overgrazing accelerates soil erosion by water and wind
Winds remove fragile topsoil
Agricultural land is flooded and silted up
Gullies and landslides
Heavy rain erodes topsoil
Silt from erosion fills rivers and reservoirs
Rapid runoff causes flooding
After Deforestation
Evapotranspiration decreases
Fig , p. 340

75. We Can Reduce Flood Risks
Rely more on nature’s systems
Wetlands
Natural vegetation in watersheds
Rely less on engineering devices
Dams
Levees
Channelized streams

76. Solutions: Reducing Flood Damage
Figure 13.27: These are some methods for reducing the harmful effects of flooding (Concept 13-4). Questions: Which two of these solutions do you think are the most important? Why?
Fig , p. 342

77. Three Big Ideas
One of the world’s major environmental problems is the growing shortage of freshwater in many parts of the world.
We can increase water supplies in water-short areas in a number of ways, but the most important way is to reduce overall water use and waste by using water more sustainably.

78. Three Big Ideas
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.