Environmental Problems, Their Causes, and Sustainability 1

city’s water systems have been taken over by a foreignbasedcorporation, efforts to return the systems to publiccontrol can lead to severe economic penalties underthe rules of the World Trade Organization (WTO).In the Bolivian town of Cochabamba, 60% of thewater was being lost through leaky pipes. With nomoney to fix the pipes, the Bolivian government soldthe town’s water system to a subsidiary of the BechtelCorporation. Within 6 months, the company doubledwater rates. This led to a general strike and violentstreet clashes between protesters and governmenttroops that led to 10,000 injured people and 7 deaths.The Bolivian government ended up tearing up thecontract. But the town’s current government–privatecooperative water management system is in shamblesand most of the leaks have not been stopped.Some analysts point to two possible problems in afully privatized water system. First, since private companiesmake money by delivering water, they havemore incentive to sell as much water as they can ratherthan to conserve it. Second, because of lack of money topay water bills, the poor will continue to be left out.There are no easy answers for managing the water thateveryone needs.xHOW WOULD YOU VOTE? Should private companies ownand manage most of the world’s water resources? Cast yourvote online at http://biology.brookscole.com/miller14.15-4 USING DAMS AND RESERVOIRSTO SUPPLY MORE WATERWhat Are the Advantages and Disadvantagesof Large Dams and Reservoirs? MixedBlessingsLarge dams and reservoirs can produce cheapelectricity, reduce downstream flooding, andprovide year-round water for irrigating cropland,but they also displace people and disrupt aquaticsystems.An estimated 800,000 dams of all sizes now restrict theflow of the world’s rivers. Large dams and reservoirshave benefits and drawbacks (Figure 15-9). Their mainpurpose is to capture and store runoff and release it asneeded to control floods; to generate electricity; and tosupply water for irrigation and for towns and cities.Reservoirs also provide recreational activities such asswimming, fishing, and boating.The more than 45,000 large dams (22,000 of them inChina) built on the world’s 227 largest rivers have increasedthe annual reliable runoff available for humanuse by nearly one-third. But a series of dams on a river,especially in arid areas, can reduce downstream flow toa trickle and prevent it from reaching the sea as a part ofthe hydrologic cycle. According to the World Commissionon Water in the 21st Century, half of the world’sLarge lossesof water throughevaporationFlooded land destroysforests or cropland anddisplaces peopleMigration andspawning of somefish are disruptedDownstream cropland andestuaries are deprived ofnutrient-rich siltReservoir is usefulfor recreationand fishingCan producecheap electricity(hydropower)Downstreamflooding isreducedProvides water foryear-round irrigationof croplandFigure 15-9 Trade-offs: advantages (green) and disadvantages (orange) of large dams and reservoirs. The world’s 45,000large dams (higher than 15 meters or 50 feet) capture and store about 14% of the world’s runoff, provide water for about 45% ofirrigated cropland, and supply more than half the electricity used by 65 countries. The United States has more than 70,000 largeand small dams, capable of capturing and storing half of the country’s entire river flow. Pick the single advantage and disadvantagethat you think are the most important.http://biology.brookscole.com/miller14313