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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