Water Resources

Chapter 13

13-1 Will We Have Enough Usable Water?

Concept 13-1A We are using available freshwater unsustainably by wasting it, polluting it, and charging too little for this irreplaceable natural resource.

Concept 13-1B One of every six people does not have sufficient access to clean water, and this situation will almost certainly get worse.

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

Water keeps us alive, moderates climate, sculpts the land, removes and dilutes wastes and pollutants, and moves continually through the hydrologic cycle.

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

Girl Carrying Well Water over Dried Out Earth during a Severe Drought in India

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL

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

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. 13-3, p. 316

Unconfined Aquifer Recharge Area

Precipitation Evaporation and transpiration Evaporation

Confined Recharge Area Runoff

Flowing artesian well

Well requiring a pump Stream

InfiltrationWater table Lake

InfiltrationUnconfined aquiferLess permeable

material such as clay

Confined aquiferConfining impermeable rock layer

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.

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

Average Annual Precipitation and Major Rivers, Water-Deficit Regions in U.S.

Fig 13-4

Fig. 13-5, p. 318

Substantial conflict potential

Highly likely conflict potential

Unmet rural water needs

Moderate conflict potential

Washington

Oregon

MontanaNorth Dakota

Idaho South DakotaWyoming

Nevada NebraskaUtah

ColoradoKansas

CaliforniaOklahoma

New Mexico

Texas

Arizona

Water Hot Spots

Fig. 13-6, p. 319

Europe Asia

North America

Africa

South America Australia

Stress

High None

Long-Term Severe Drought Is Increasing

Causes• Extended period of below-normal rainfall• Diminished groundwater

Harmful environmental effects• Dries out soils• Reduces stream flows• Decreases tree growth and biomass• Lowers net primary productivity and crop yields• Shift in biomes

Case Study: 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.

13-2 Is Extracting Groundwater the Answer?

Concept 13-2 Groundwater that is used to supply cities and grow food is being pumped from aquifers in some areas faster than it is renewed by precipitation.

Other Effects of Groundwater Overpumping

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

Fig. 13-7, p. 321

TRADE-OFFS

Withdrawing Groundwater

Advantages DisadvantagesUseful for drinking and irrigation

Aquifer depletion from overpumping

Available year-roundSinking of land (subsidence) from overpumping

Exists almost everywhere

Aquifers polluted for decades or centuries

Renewable if not overpumped or contaminated

Saltwater intrusion into drinking water supplies near coastal areas

No evaporation losses

Reduced water flows into surface waters

Cheaper to extract than most surface waters

Increased cost and contamination from deeper wells

Natural Capital Degradation: Irrigation in Saudi Arabia Using an Aquifer

Natural Capital Degradation: Areas of Greatest Aquifer Depletion in the U.S.

Fig 13-9

Fig. 13-11, p. 324

SOLUTIONS

Groundwater Depletion

Prevention Control

Waste less water Raise price of water to discourage waste

Subsidize water conservation

Tax water pumped from wells near surface waters

Limit number of wells Set and enforce minimum stream flow levels

Do not grow water-intensive crops in dry areas

Divert surface water in wet years to recharge aquifers

13-3 Is Building More Dams the Answer?

Concept 13-3 Building dam and reservoir systems has greatly increased water supplies in some areas, but it has disrupted ecosystems and displaced people.

Large Dams and Reservoirs Have Advantages and Disadvantages (1)

Main goals of a dam and reservoir system• Capture and store runoff

• Release runoff as needed to control:• Floods• Generate electricity• Supply irrigation water• Recreation (reservoirs)

Large Dams and Reservoirs Have Advantages and Disadvantages (2)

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

Large Dams and Reservoirs Have Advantages and Disadvantages (3)

Disadvantages• Displaces people• Flooded regions• Impaired ecological services of rivers• Loss of plant and animal species• Fill up with sediment within 50 years

Advantages and Disadvantages of Large Dams and Reservoirs

Fig 13-12

Matilija Dam Removal Project

Click for report

The Colorado River Basin

Fig 13-14

Case Study: The Colorado River Basin— An Overtapped Resource (3)

Four Major problems• Colorado River basin has very dry lands• Modest flow of water for its size• Legal pacts allocated more water for human use

than it can supply• Amount of water flowing to the mouth of the river

has dropped

Aerial View of Glen Canyon Dam Across the Colorado River and Lake Powell

The Flow of the Colorado River Measured at Its Mouth Has Dropped Sharply

Case Study: China’s Three Gorges Dam (1)

World’s largest hydroelectric dam and reservoir

2 km long across the Yangtze River

Benefits• Electricity-producing potential is huge (18 large

power plants)• Holds back the Yangtze River floodwaters• Allows cargo-carrying ships

Case Study: China’s Three Gorges Dam (2)

Harmful effects• Displaces about 5.4 million people• Built over a seismic fault• Significance?

• Rotting plant and animal matter producing CH4

• Worse than CO2 emissions

• Will the Yangtze River become a sewer?

13-4 Is Transferring Water from One Place to Another the Answer?

Concept 13-4 Transferring water from one place to another has greatly increased water supplies in some areas, but it has also disrupted ecosystems.

Fig. 13-17, p. 330

CALIFORNIAShasta Lake NEVADA

Sacramento River

UTAH

North Bay Aqueduct

Feather River

Lake Tahoe

San FranciscoSacramento

South Bay Aqueduct

Hoover Dam and Reservoir (Lake Mead)

Los Angeles Aqueduct

Colorado River

California AqueductColorado River

Aqueduct Central Arizona Project

ARIZONA

Fresno

Santa Barbara

Los Angeles

San DiegoSalton Sea

Phoenix

Tucson

MEXICO

San Luis Dam and Reservoir

San Joaquin V

alley

Oroville Dam and Reservoir

Natural Capital Degradation: The Aral Sea, Shrinking Freshwater Lake

1976 2006

Oxnard water suppliers

United Water

Calleguas Municipal

City of Oxnard

13-5 Is Converting Salty Seawater to Freshwater the Answer?

Concept 13-5 We can convert salty ocean water to freshwater, but the cost is high, and the resulting salty brine must be disposed of without harming aquatic or terrestrial ecosystems.

Removing Salt from Seawater Seems Promising but Is Costly (1)

Desalination• Distillation• Reverse osmosis, microfiltration

15,000 plants in 125 countries• Saudi Arabia: highest number

Click for link to Desal Response Group

Removing Salt from Seawater Seems Promising but Is Costly (2)

Problems• High cost and energy footprint• Keeps down algal growth and kills many marine

organisms• Large quantity of brine wastes

Click for Oxnard’s GREAT RO plant info

13-6 How Can We Use Water More Sustainably?

Concept 13-6 We can use water more sustainably by cutting water waste, raising water prices, slowing population growth, and protecting aquifers, forests, and other ecosystems that store and release water.

Reducing Water Waste Has Many Benefits (1)

Water conservation• Improves irrigation efficiency• Improves collection efficiency• Uses less in homes and businesses

Fig. 13-20, p. 335

Stepped Art

Gravity flow (efficiency 60% and 80% with surge valves)

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

Drip irrigation (efficiency 90–95%)

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

Center pivot (efficiency 80% with low-pressure sprinkler and 90–95% with LEPA

sprinkler)

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

Solutions: Reducing Irrigation Water Waste

Fig 13-21

Solutions: Reducing Water Waste

Fig 13-22

Fig. 13-23, p. 337

SOLUTIONS

Sustainable Water Use

Waste less water and subsidize water conservation

Preserve water quality

Protect forests, wetlands, mountain glaciers, watersheds, and other natural systems that store and release water

Get agreements among regions and countries sharing surface water resources

Raise water prices

Do not deplete aquifers

Slow population growth

How can you save water at home?

Click for Family Water Audit

What Can You Do? Water Use and Waste

Fig 13-24

13-7 How Can We Reduce the Threat of Flooding?

Concept 13-7 We can lessen the threat of flooding by protecting more wetlands and natural vegetation in watersheds and by not building in areas subject to frequent flooding.

Some Areas Get Too Much Water from Flooding (1)

Flood plains • Highly productive wetlands• Provide natural flood and erosion control• Maintain high water quality• Recharge groundwater

Benefits of floodplains• Fertile soils• Nearby rivers for use and recreation• Flatlands for urbanization and farming

Some Areas Get Too Much Water from Flooding (2)

Dangers of floodplains and floods• Deadly and destructive• Human activities worsen floods• Failing dams and water diversion• Hurricane Katrina and the Gulf Coast• Removal of coastal wetlands

Natural Capital Degradation: Hillside Before and After Deforestation

Fig 13-25

Fig. 13-26, p. 340

SOLUTIONS

Reducing Flood Damage

Prevention Control

Preserve forests on watersheds

Straighten and deepen streams (channelization)

Preserve and restore wetlands in floodplains

Tax development on floodplains

Build levees or floodwalls along streams

Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry

Build dams