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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. Unconfined Aquifer Recharge Area Evaporation and transpiration Evaporation Precipitation Confined Recharge Area Runoff Flowing artesian well Infiltration Water table Well requiring a pump Stream Lake Infiltration Less permeable material such as clay Fig. 13-3, p. 316 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 Water Hot Spots Washington Montana Oregon Idaho Wyoming Nevada North Dakota South Dakota Nebraska Utah Colorado California Arizona New Mexico Kansas Oklahoma Texas Highly likely conflict potential Substantial conflict potential Moderate conflict potential Unmet rural water needs Fig. 13-5, p. 318 Asia Europe North America Africa South America Australia Stress High None Fig. 13-6, p. 319 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. 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 Renewable if not overpumped or contaminated No evaporation losses Cheaper to extract than most surface waters Aquifers polluted for decades or centuries Saltwater intrusion into drinking water supplies near coastal areas Reduced water flows into surface waters Increased cost and contamination from deeper wells Fig. 13-7, p. 321 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 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 waterintensive crops in dry areas Divert surface water in wet years to recharge aquifers Fig. 13-11, p. 324 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. Sacramento River CALIFORNIA NEVADA Shasta Lake Oroville Dam and Reservoir UTAH Feather Lake Tahoe River North Bay Aqueduct San Francisco Sacramento South Bay Aqueduct San Luis Dam and Reservoir Fresno Hoover Dam and Reservoir (Lake Mead) Los Angeles Aqueduct California Aqueduct Colorado River Aqueduct Santa Barbara Los Angeles San Diego Salton Sea Colorado River ARIZONA Central Arizona Project Phoenix Tucson MEXICO Fig. 13-17, p. 330 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 Center pivot Drip irrigation (efficiency 90–95%) (efficiency 80% with low-pressure sprinkler and 90–95% with LEPA sprinkler) Above- or below-ground (efficiency 60% and 80% with surge valves) pipes or tubes deliver water to individual plant roots. Water usually comes from an aqueduct system or a nearby river. Gravity flow Water usually pumped from underground and sprayed from mobile boom with sprinklers. Stepped Art Fig. 13-20, p. 335 Solutions: Reducing Irrigation Water Waste Fig 13-21 Solutions: Reducing Water Waste Fig 13-22 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 Get agreements among regions and countries sharing surface water resources Raise water prices Slow population growth Fig. 13-23, p. 337 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 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 Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry Build levees or floodwalls along streams Build dams Fig. 13-26, p. 340