Chapter 13: Water Resources

Will We Have Enough Usable Water?

Most of the Earth’s Freshwater Is Not Available to the Us

• Freshwater availability
  • 0.024%--Groundwater, lakes, rivers, streams
• Hydrologic cycle: Movement of water in the seas, land, and air. It is driven by solar energy and gravity

Groundwater and Surface Water Critical Resources

• Zone of saturation: Spaces in soil are filled with water
• Water table: Top of the zone of saturation
• Aquifers: Naturally recharge, lateral recharge
• Surface Run-off: Precipitation that does not infiltrate the ground or evaporate
• Water Shed: The region from which water drains into a body of water
• Groundwater: Precipitation that infiltrates the ground and percolates downwards through voids in soil and rocks

Water Footprints

• Water footprint: Volume of water we directly and indirectly
• The average American uses 260 L 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

Causes of Water Shortages

• Dry climates
• Drought
• Too many people using a normal supply of water
• Wasteful use of water
• 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

Is Extracting Groundwater the Answer?

Groundwater Depletion: Worldwide Problem

• India, China, and the United States: Three largest grain producers. Overpumping aquifers for the irrigation of crops
• India and China
  • Small farmers drilling tubewells. Effect on the water table
• Saudi Arabia
  • Aquifer depletion and irrigation

Aquifers

• Unconfined Aquifer: Aquifer with water table as top

• Confined Aquifer: Bounded above and below by semi-permeable beds of rock and clay

• 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

Groundwater Depletion

• Prevention
  • Waste less water
  • Subsidize water conservation
  • Limit the number of wells
  • Do not grow water-intensive crops in dry areas
• Control
  • Raise the price of water to discourage waste
  • Tax water pumped from wells near surface waters
  • Set and enforce minimum stream flow levels
  • Divert surface water in wet years to recharge aquifers

Is Building More Dams the Answer?

Large Dams and Reservoirs

• Dams/Reservoirs: They capture and store runoff as well as they release runoff as needed to control:

  • Floods
  • Generate electricity
  • Supply irrigation water
  • Recreation (reservoirs)

• Advantages

  • Increase the reliable runoff available
  • Reduce flooding
  • Grow crops in arid regions

• Disadvantages

  • Displaces people
  • Flooded regions
  • Impaired ecological services of rivers
  • Loss of plant and animal species
  • Fill up with sediment
  • This can cause other streams and lakes to dry up

Is Transferring Water from One Place to Another the Answer?

California Transfers Water from Water-Rich Areas to Water-Poor Areas

• Water is transferred from north to south by
  • Tunnels
  • Aqueducts
  • Underground pipes
• California Water Project: Inefficient water use. Environmental damage to the Sacramento River and San Francisco Bay

Is Converting Salty Seawater to Freshwater the Answer?

Desalination

• Desalination: Removing dissolved salts
• Distillation: evaporate water, leaving salts behind
• Reverse osmosis, microfiltration: use high pressure to remove salts

Removing Salt from Seawater Environmental Costs

• Problems
  • High cost and energy footprint
  • Keeps down algal growth and kills many marine organisms
  • Large quantity of brine wastes

How Can We Use Water More Sustainably?

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

We Can Cut Water Waste in Irrigation

• Flood irrigation
  • Wasteful
• Center pivot, low-pressure sprinkler
• Low-energy, precision application sprinklers
• Drip or trickle irrigation, micro irrigation
• Costly; less water waste

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
• Raise water prices
• Slow population growth

How Can We Reduce the Threat of Flooding?

Flood Plains: Too Much Water

• Flood plains: Highly productive wetlands, that provide natural flood and erosion control, maintain high water quality, and recharge groundwater
• Benefits of floodplains
  • Fertile soils
  • Nearby rivers for use and recreation
  • Flatlands for urbanization and farming

Human Activities Make Floods Worse

• Removal of water-absorbing vegetation
• Draining wetlands and building on them
• Rising sea levels from global warming mean more coastal flooding

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

Reducing Flood Damage

• Prevention
  • Preserve forests in watersheds
  • Preserve and restore wetlands in floodplains
  • Tax development on floodplains
  • Use floodplains primarily for recharging aquifers, sustainable agriculture, and forestry
• Control
  • Straighten and deepen streams (channelization)
  • Build levees or floodplains along streams
  • Build dams

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