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