2WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Importance of water:Water keeps us alivemoderates climatesculpts the landremoves and dilutes wastes and pollutantsmoves continually through the hydrologic cycleOnly about 0.02% of the earth’s water supply is available to us as liquid freshwater.
3WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Comparison of population sizes and shares of the world’s freshwater among the continents.Figure 14-2
4Water Conflicts in the Middle East: Most water in this dry region comes from the Nile, Jordan or Tigris rivers.
5WATER’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.
6Unconfined Aquifer Recharge Area Evaporation and transpiration PrecipitationEvaporation and transpirationEvaporationConfined Recharge AreaRunoffFlowing artesian wellRecharge Unconfined AquiferStream Well requiring a pumpFigure 14.3Natural capital: groundwater system. An unconfined aquifer is an aquifer with a permeable water table. A confined aquifer is bounded above and below by less permeable beds of rock where the water is confined under pressure. Some aquifers are replenished by precipitation; others are not.InfiltrationWater tableLakeInfiltrationUnconfined aquiferLess permeable material such as clayConfined aquiferConfining impermeable rock layerFig. 14-3, p. 308
7WATER’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%).
8TOO LITTLE FRESHWATERAbout 41% of the world’s population lives in river basins that do not have enough freshwater.ReasonsDry climateDroughtToo many people use and waste waterLack of money or gvmt stability to maintain water resourcesMany parts of the world are experiencing:Rivers running dry.Lakes and seas shrinking.Falling water tables from overpumped aquifers.
9Stress on the World’s River Basins Comparison of the amount of water available with the amount used by humans.Figure 14-6
11Who 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?
12TOO LITTLE FRESHWATERCities 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.
13Aquifers- 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.
14Withdrawing Groundwater Trade-OffsWithdrawing GroundwaterAdvantagesDisadvantagesUseful for drinking and irrigationAquifer depletion from overpumpingSinking of land (subsidence) from overpumpingAvailable year-roundExists almost everywherePolluted aquifers for decades or centuriesRenewable if not overpumped or contaminatedSaltwater intrusion into drinking water supplies near coastal areasFigure 14.7Trade-offs: advantages and disadvantages of withdrawing groundwater. QUESTION: Which two advantages and which two disadvantages do you think are the most important?No evaporation lossesReduced water flows into surface watersIncreased cost and contamination from deeper wellsCheaper to extract than most surface watersFig. 14-7, p. 313
15Other Effects of Groundwater Overpumping Groundwater overpumping can cause land to sink, and contaminate freshwater aquifers near coastal areas with saltwater.Figure 14-11
16Groundwater Depletion SolutionsGroundwater DepletionPreventionControlWaste less waterRaise price of water to discourage wasteSubsidize water conservationBan new wells in aquifers near surface watersTax water pumped from wells near surface watersBuy and retire groundwater withdrawal rights in critical areasFigure 14.12Solutions: ways to prevent or slow groundwater depletion by using water more sustainably. QUESTION: Which two of these solutions do you think are the most important?Set and enforce minimum stream flow levelsDo not grow water-intensive crops in dry areasFig , p. 316
17USING 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?
18Provides water for year-round irrigation of cropland Flooded land destroys forests or cropland and displaces peopleLarge losses of water through evaporationProvides water for drinkingDownstream cropland and estuaries are deprived of nutrient-rich siltReservoir is useful for recreation and fishingRisk of failure and devastating downstream floodingCan produce cheap electricity (hydropower)Figure 14.13Trade-offs: advantages (green) and disadvantages (orange) of large dams and reservoirs. The world’s 45,000 large dams (higher than 15 meters or 50 feet) capture and store 14% of the world’s runoff, provide water for almost half of all irrigated cropland, and supply more than half the electricity used by 65 countries. The United States has more than 70,000 large and small dams, capable of capturing and storing half of the country’s entire river flow. QUESTION: Which single advantage and which single disadvantage do you think are the most important?Downstream flooding is reducedMigration and spawning of some fish are disruptedFig a, p. 317
19Case 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).
20The 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 14-14
21Case 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.
22Dam RemovalSome 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.
23TRANSFERRING 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.
24Case Study: The California Experience Should water be transferred from northern California to southern California?Figure 14-16
26Case Study: The Aral Sea Disaster The Aral Sea was once the world’s fourth largest freshwater lake.Figure 14-17
27The Aral Sea DisasterDiverting 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
28Ways to get more freshwater: DESALTING SEAWATER, SEEDING CLOUDS, AND TOWING ICEBERGS AND GIANT BAGGIESDistillation: 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
29Cont.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.
30INCREASING 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.
31INCREASING 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 sprinklers90% efficientDrip irrigation95% efficient
32(efficiency 60% and 80% with surge valves) Drip irrigation(efficiency 90–95%)Gravity flow(efficiency 60% and 80% with surge valves)Figure 14.18Major irrigation systems: because of high initial costs, center-pivot irrigation and drip irrigation are not widely used. The development of new low-cost drip-irrigation systems may change this situation.Center pivot(efficiency 80%–95%)Water usually pumped from underground and sprayed from mobile boom with sprinklers.Above- or below-ground pipes or tubes deliver water to individual plant roots.Water usually comes from an aqueduct system or a nearby river.Fig , p. 325
33Reducing Irrigation Water Waste SolutionsReducing 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 farmingFigure 14.19Solutions: methods for reducing water waste in irrigation. QUESTION: Which two of these solutions do you think are the most important?• 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 meatFig , p. 326
34Solutions 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 citiesFigure 14.21Solutions: methods of reducing water waste in industries, homes, and businesses. QUESTION: Which three of these solutions do you think are the most important?• 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 energyFig , p. 327
35Raising 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%.
36TOO MUCH WATERHuman activities have contributed to flood deaths and damages.Figure 14-23
37Preserve forests on watersheds SolutionsReducing Flood DamagePreventionControlPreserve forests on watershedsStrengthen and deepen streams (channelization)Preserve and restore wetlands in floodplainsBuild levees or floodwalls along streamsTax all development on floodplainsFigure 14.24Solutions: methods for reducing the harmful effects of flooding. QUESTION: Which two of these solutions do you think are the most important?Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry, and recreationBuild damsFig , p. 331
38SOLUTIONS: 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 14-25