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
5. Aerial View of Glen Canyon Dam Across the Colorado
River and Lake Powell
Fig. 13-2, p. 317
6. 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
7. 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
8. Girl Carrying Well Water over Dried Out Earth during
a Severe Drought in India
Fig. 13-3, p. 319
9. 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. 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
• Surface Water
• Surface runoff
• Watershed (drainage) basin
12. 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%
13. Science Focus: Water Footprints and
Virtual Water (1)
• Water footprint
• 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
14. 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
17. Water Shortages Will Grow (1)
• Dry climates
• Drought
• Too many people using a normal supply of water
• Wasteful use of water
18. 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
20. 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
23. 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
27. Overpumping Aquifers Has Several
Harmful Effects
• Limits future food production
• Bigger gap between the rich and the poor
• Land subsidence (sinking)
• Mexico City
• San Joaquin Valley in California
• Groundwater overdrafts near coastal regions
• Contamination of groundwater with saltwater
29. Deep Aquifers Might Be Tapped
• May contain enough water to provide for billions of
people for centuries
• Major concerns
1. Nonre
newab
le
2. Little is
known
about
the
geolog
30. 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)
31. Large Dams and Reservoirs Have
Advantages and Disadvantages (2)
• Advantages
• Increase the reliable runoff available
• Reduce flooding
• Grow crops in arid regions
32. 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
• Can cause other streams and lakes to dry up
34. 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
35. 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
36. The Flow of the Colorado River Measured at Its
Mouth Has Dropped Sharply
Fig. 13-14, p. 329
37. 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
38. 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
40. 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
41. Removing Salt from Seawater Is Costly, Kills
Organisms, Creates Briny Wastewater (2)
• Problems
1. High cost and energy footprint
2. Keeps down algal growth and kills many marine
organisms
3. Large quantity of brine wastes
42. 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
43. 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
44. 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
46. Less-Developed Countries Use Low-
Tech Methods for Irrigation
• Human-powered treadle pumps
• Harvest and store rainwater
• Create a polyculture canopy over crops: reduces
evaporation
48. 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
50. 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
51. 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
52. 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
55. Case Study: Living Dangerously on
Floodplains in Bangladesh
• Dense population on coastal floodplain
• Moderate floods maintain fertile soil
• Increased frequency of large floods
• Effects of development in the Himalayan foothills
• Destruction of coastal wetlands: mangrove forests
56. 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
57. Three Big Ideas
1. One of the world’s major environmental problems
is the growing shortage of freshwater in many parts
of the world.
2. 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.
3. 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.
Editor's Notes
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.
Figure 13.2: The Glen Canyon Dam across the Colorado River was completed in 1963. Lake Powell behind the dam is the second largest reservoir in the United States.
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 .
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?
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 Surve y)
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 )
Figure 13.6: N atural 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)
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?
Figure 13.8: N atural 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.
Figure 13.9: N atural 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 Surve y)
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.
Figure 13.11: This pole shows subsidence from overpumping of an aquifer for irrigation in California’s San Joaquin Central Valley between 1925 and 1977. In 1925, the land surface in this area was near the top of this pole. Since 1977 this problem has gotten worse.
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?
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 )
Figure 13.17: N atural 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 2009. 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?
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.
Figure 13.20: S olutions. In areas of Bangladesh and India, where water tables are high, many small-scale farmers use treadle pumps to supply irrigation water to their fields.
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.
Figure 13.25: N atural 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?
Figure 13.26: Deforestation of hills and mountains in China’s Yangtze River Basin contributed to increased flooding, topsoil erosion, and the flow of eroded sediment into the Yangtze River. Because of these harmful effects, China stopped the deforestation and established a massive tree-planting program to reforest the degraded land.
