WATER

CHAPTER 14

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

• Importance of water:• Water keeps us alive • moderates climate • sculpts the land • removes and dilutes wastes and pollutants • moves continually through the hydrologic cycle

• Only about 0.02% of the earth’s water supply is available to us as liquid freshwater.

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

• Comparison of population sizes and shares of the world’s freshwater among the continents.

Figure 14-2Figure 14-2

WATER CONFLICTS IN THE MIDDLE EAST:

• Most water in this dry region comes from the Nile, Jordan or Tigris rivers.

• http://www.youtube.com/watch?v=7RZu4tTp_0U

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

• Some precipitation infiltrates the ground and is stored in soil and rock (groundwater).

• Water that does not sink into the ground or evaporate into the air runs off (surface runoff) into bodies of water.

• The land from which the surface water drains into a body of water is called its watershed or drainage basin.

Fig. 14-3, p. 308

Unconfined Aquifer Recharge Area

Precipitation Evaporation and transpiration Evaporation

Confined Recharge Area

Runoff

Flowing artesian well

Recharge Recharge Unconfined Unconfined AquiferAquifer

Stream Well requiring a pumpInfiltration Water

table LakeInfiltration

Unconfined aquifer

Confined aquiferConfining impermeable rock layer Confining impermeable rock layer

Less permeable Less permeable material such as claymaterial such as clay

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

• We currently use more than half of the world’s reliable runoff of surface water and could be using 70-90% by 2025.

• About 70% of the water we withdraw from rivers, lakes, and aquifers is not returned to these sources (consumptive use).

• Irrigation is the biggest user of water (70%), followed by industries (20%) and cities and residences (10%).

TOO LITTLE FRESHWATER

• About 41% of the world’s population lives in river basins that do not have enough freshwater.• Reasons

• Dry climate• Drought• Too many people use and waste water• Lack of money or gvmt stability to maintain water resources

• Many parts of the world are experiencing:• Rivers running dry.• Lakes and seas shrinking.• Falling water tables from overpumped aquifers.

STRESS ON THE WORLD’S RIVER BASINS

• Comparison of the amount of water available with the amount used by humans.

Figure 14-6Figure 14-6

OGALLALA

• http://www.youtube.com/watch?v=3gZWVIv8pB8

WHO SHOULD OWN AND MANAGE FRESHWATER RESOURCES?

• There is controversy over whether water supplies should be owned and managed by governments or by private corporations.

• European-based water companies aim to control 70% of the U.S. water supply by buying up water companies and entering into agreements with cities to manage water supplies.

• Read the Article: • How would you vote? Private or government

ownership of water?

TOO LITTLE FRESHWATER

• Cities are outbidding farmers for water supplies from rivers and aquifers.

• Countries are importing grain as a way to reduce their water use.

• BUT More crops are being used to produce biofuels.• Why import food but produce biofuel?

• Our water options are:• Get more water from aquifers and rivers,

desalinate ocean water, waste less water.

AQUIFERS- TAKE THE QUIZ HTTP://GA.WATER.USGS.GOV/EDU/QUIZGW.HTML

• Water entering an aquifer eventually is discharged from the aquifer from springs, seeps into streams, or is withdrawn from the ground by wells.

• Groundwater in aquifers is confined by poorly permeable clay or shale, and may be confined under pressure.

Fig. 14-7, p. 313

Trade-Offs

Withdrawing Groundwater

Advantages Disadvantages

Useful for drinking and irrigation

Aquifer depletion from overpumping

Available year-round

Sinking of land (subsidence) from overpumping

Exists almost everywhere

Polluted aquifers for decades or centuries

Renewable if not overpumped or contaminated

Saltwater intrusion into drinking water supplies near coastal areas

Reduced water flows into surface waters

No evaporation losses

Cheaper to extract than most surface waters

Increased cost and contamination from deeper wells

OTHER EFFECTS OF GROUNDWATER OVERPUMPING

• Groundwater overpumping can cause land to sink, and contaminate freshwater aquifers near coastal areas with saltwater.

Figure 14-11Figure 14-11

Fig. 14-12, p. 316

Solutions

Groundwater Depletion

Prevention Control

Waste less water Raise price of water to discourage waste

Subsidize water conservation

Ban new wells in aquifers near surface waters

Tax water pumped from wells near surface waters

Buy and retire groundwater withdrawal rights in critical areas

Do not grow water-intensive crops in dry areas

Set and enforce minimum stream flow levels

USING DAMS AND RESERVOIRS TO SUPPLY MORE WATER

• Large dams and reservoirs can produce cheap electricity, reduce downstream flooding, and provide year-round water for irrigating cropland, but they also displace people and disrupt aquatic systems.

• What happens to silt when a dam is built and how does that affect the ecosystem down stream?

Fig. 14-13a, p. 317

Provides water for year-round irrigation of cropland

Flooded land destroys forests or cropland and displaces people

Large losses of water through evaporation

Provides water for drinking Downstream

cropland and estuaries are deprived of nutrient-rich silt

Reservoir is useful for recreation and fishing

Risk of failure and devastating downstream flooding

Can produce cheap electricity (hydropower)

Downstream flooding is reduced

Migration and spawning of some fish are disrupted

CASE STUDY: THE COLORADO BASIN – AN OVERTAPPED RESOURCE

• The Colorado River has so many dams and withdrawals that it often does not reach the ocean.• 14 major dams and reservoirs, and canals.• Water is mostly used in desert area of the U.S.• Provides electricity from hydroelectric plants for 30 million

people (1/10th of the U.S. population).

• http://www.youtube.com/watch?v=FIPV-H9iCPA

THE COLORADO RIVER BASIN

• The area drained by this basin is equal to more than one-twelfth of the land area of the lower 48 states.

Figure 14-14Figure 14-14

CASE STUDY: CHINA’S THREE GORGES DAM

• There is a debate over whether the advantages of the world’s largest dam and reservoir will outweigh its disadvantages.• The dam will be 2 kilometers long.• The electric output will be that of 18 large coal-

burning or nuclear power plants.• It will facilitate ship travel reducing transportation costs.• Dam will displace 1.2 million people.• Dam is built over seismatic fault and already has small

cracks.

• http://www.youtube.com/watch?v=T2JMVxnMqxU

DAM REMOVAL

• Some dams are being removed for ecological reasons and because they have outlived their usefulness.• In 1998 the U.S. Army Corps of Engineers

announced that it would no longer build large dams and diversion projects in the U.S.

• The Federal Energy Regulatory Commission has approved the removal of nearly 500 dams.

• Removing dams can reestablish ecosystems, but can also re-release toxicants into the environment.

TRANSFERRING WATER FROM ONE PLACE TO ANOTHER

• Transferring water can make unproductive areas more productive but can cause environmental harm.• Promotes investment, jobs and strong economy.• It encourages unsustainable use of water in areas water

is not naturally supplied.

CASE STUDY: THE CALIFORNIA EXPERIENCE

• Should water be transferred from northern California to southern California?

Figure 14-16Figure 14-16

ARAL SEA

CASE STUDY: THE ARAL SEA DISASTER

• The Aral Sea was once the world’s fourth largest freshwater lake.

Figure 14-17Figure 14-17

THE ARAL SEA DISASTER

• Diverting water from the Aral Sea and its two feeder rivers mostly for irrigation has created a major ecological, economic, and health disaster.

• About 85% of the wetlands have been eliminated and roughly 50% of the local bird and mammal species have disappeared.

• Since 1961, the sea’s salinity has tripled and the water has dropped by 22 meters most likely causing 20 of the 24 native fish species to go extinct.

• Anthrax buried on island in Aral Sea

WAYS TO GET MORE FRESHWATER:

• DESALTING SEAWATER, SEEDING CLOUDS, AND TOWING ICEBERGS AND GIANT BAGGIES

• Distillation: heating saltwater until it evaporates, leaves behind water in solid form.

• Reverse osmosis: uses high pressure to force saltwater through a membrane filter.

• Both methods are expensive

CONT.

• Seeding clouds with tiny particles of chemicals to increase rainfall towing icebergs or huge bags filled with freshwater to dry coastal areas have all been proposed but are unlikely to provide significant amounts of freshwater.

• http://www.youtube.com/watch?v=Sn5g4Gt_EJw

INCREASING WATER SUPPLIES BY WASTING LESS WATER

• We waste about two-thirds of the water we use, but we could cut this waste to 15%.

• 65-70% of the water people use throughout the world is lost through evaporation, leaks, and other losses.

• Water is underpriced through government subsidies.

• The lack of government subsidies for improving the efficiency of water use contributes to water waste.

INCREASING WATER SUPPLIES BY WASTING LESS WATER

• Sixty percent of the world’s irrigation water is currently wasted, but improved irrigation techniques could cut this waste to 5-20%.

• Center-pivot, low pressure sprinklers sprays water directly onto crop.• It allows 80% of water to reach crop.• Has reduced depletion of Ogallala aquifer in Texas High Plains

by 30%.

• Low energy precision application sprinklers• 90% efficient

• Drip irrigation• 95% efficient

Fig. 14-18, p. 325

Center pivotCenter pivot

Drip irrigationDrip irrigation

Gravity flowGravity flow(efficiency 60% and

80% with surge valves)

Above- or below-ground pipes or tubes deliver water to individual plant roots.

Water usually comes from an aqueduct system or a nearby river.

(efficiency 90–95%)

(efficiency 80%–95%)

Water usually pumped from underground and sprayed from mobile boom with sprinklers.

Fig. 14-19, p. 326

Solutions

Reducing Irrigation Water Waste

• Line canals bringing water to irrigation ditches

• Level fields with lasers

• Irrigate at night to reduce evaporation

• Monitor soil moisture to add water only when necessary

• Polyculture

• Organic farming

• Don't grow water-thirsty crops in dry areas

• Grow water-efficient crops using drought resistant and salt-tolerant crop varieties

• Irrigate with treated urban waste water

• Import water-intensive crops and meat

Fig. 14-21, p. 327

Solutions

Reducing Water Waste

• Redesign manufacturing processes

• Repair leaking underground pipes

• Landscape yards with plants that require little water

• Use drip irrigation

• Fix water leaks

• Use water meters

• Raise water prices

• Use waterless composting toilets

• Require water conservation in water-short cities

• Use water-saving toilets, showerheads, and front loading clothes washers

• Collect and reuse household water to irrigate lawns and nonedible plants

• Purify and reuse water for houses, apartments, and office buildings

• Don't waste energy

RAISING THE PRICE OF WATER: A KEY TO WATER CONSERVATION

• We can reduce water use and waste by raising the price of water while providing low lifeline rates for the poor.

• What do you think about Tiered water pricing?• When Boulder, Colorado introduced water meters, water use

per person dropped by 40%.• A 10% increase in water prices cuts domestic water use by 3-

7%.

TOO MUCH WATER

• Human activities have contributed to flood deaths and damages.

Figure 14-23Figure 14-23

Fig. 14-24, p. 331

Solutions

Reducing Flood Damage

Prevention Control

Preserve forests on watersheds

Strengthen and deepen streams (channelization)

Preserve and restore wetlands in floodplains

Tax all development on floodplains

Build levees or floodwalls along streams

Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry, and recreation

Build dams

SOLUTIONS: USING WATER MORE SUSTAINABLY

• We can use water more sustainably by cutting waste, raising water prices, preserving forests and wetlands in water basins, and slowing population growth.

Figure 14-25Figure 14-25