PP

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