1. Groundwater

2. Groundwater and Surface Water Are Critical Resources
Zone of saturation
Spaces in soil are filled with water
Water table
Top of zone of saturation.
Aquifers
Permeable layers of rock and sediment that store and carry ground water in enough quantity to supply wells.

7. Aquifer Depletion in the United States
Ogallala aquifer: largest known aquifer. Covers portions of 8 states (174,000 square miles).
Irrigates the Great Plains. Provides approximately 30% of the nation’s groundwater for irrigation.
Also provides water to 82% of the people living with in the aquifer boundary.
Very slow recharge
Water table dropping
Government subsidies to continue farming deplete the aquifer further
Biodiversity threatened in some areas

9. Groundwater is Being Withdrawn Faster Than It Is Replenished
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

10. Groundwater is Being Withdrawn Faster Than It Is Replenished
India, China, and the United States
Three largest grain producers
Over pumping aquifers for irrigation of crops
India and China
Small farmers drilling tube wells
Effect on water table

11. Withdrawing Groundwater
Trade-Offs
Withdrawing Groundwater
Advantages
Disadvantages
Useful for drinking and irrigation
Aquifer depletion from overpumping
Sinking of land (subsidence) from overpumping
Exists almost everywhere
Renewable if not overpumped or contaminated
Pollution of aquifers lasts decades or centuries
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?
Cheaper to extract than most surface waters
Deeper wells are nonrenewable
Fig. 13-7, p. 325

12. 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

13. 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.

14. Groundwater Depletion
Solutions
Groundwater Depletion
Prevention
Control
Waste less water
Raise price of water to discourage waste
Subsidize water conservation
Tax water pumped from wells near surface waters
Limit number of wells
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?
Set and enforce minimum stream flow levels
Do not grow water-intensive crops in dry areas
Divert surface water in wet years to recharge aquifers
Fig , p. 327

15. 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