Chapter 14 Water WATERS IMPORTANCE AVAILABILITY AND RENEWAL

Chapter 14 Water

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Ø Water keeps us alive, moderates climate, sculpts the land, removes and dilutes wastes and pollutants, and moves continually through the hydrologic cycle. Ø Only about 0. 02% of the earth’s water supply is available to us as liquid freshwater.

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Ø Comparison of population sizes and shares of the world’s freshwater among the continents. Figure 14 -2

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Ø Some precipitation infiltrates the ground and is stored in soil and rock (groundwater). Ø Water that does not sink into the ground or evaporate into the air runs off (surface runoff) into bodies of water. l 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 Recharge Unconfined Aquifer Infiltration Water table Less permeable material such as clay Infiltration Stream Well requiring a pump Lake Unconfined aquifer Confining impermea ble rock layer Fig. 14 -3, p. 308

WATER’S IMPORTANCE, AVAILABILITY, AND RENEWAL Ø We currently use more than half of the world’s reliable runoff of surface water and could be using 70 -90% by 2025. Ø About 70% of the water we withdraw from rivers, lakes, and aquifers is not returned to these sources. Ø Irrigation is the biggest user of water (70%), followed by industries (20%) and cities and residences (10%).

Water in the United States Ø Average precipitation (top) in relation to water -deficit regions and their proximity to metropolitan areas (bottom). Figure 14 -4

Case Study: Freshwater Resources in the United States Ø 17 western states by 2025 could face intense conflict over scarce water needed for urban growth, irrigation, recreation and wildlife. Figure 14 -5

TOO LITTLE FRESHWATER Ø About 41% of the world’s population lives in river basins that do not have enough freshwater. Ø Many parts of the world are experiencing: l l l Rivers running dry. Lakes and seas shrinking. Falling water tables from overpumped aquifers.

Stress on the World’s River Basins Ø Comparison of the amount of water available with the amount used by humans. Figure 14 -6

Case Study: Who Should Own and Manage Freshwater Resources Ø There is controversy over whether water supplies should be owned and managed by governments or by private corporations. Ø 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.

TOO LITTLE FRESHWATER Ø Cities are outbidding farmers for water supplies from rivers and aquifers. Ø Countries are importing grain as a way to reduce their water use. Ø More crops are being used to produce biofuels. Ø Our water options are: l Get more water from aquifers and rivers, desalinate ocean water, waste less water.

WITHDRAWING GROUNDWATER TO INCREASE SUPPLIES Ø Most aquifers are renewable resources unless water is removed faster than it is replenished or if they are contaminated. Ø Groundwater depletion is a growing problem mostly from irrigation. l At least one-fourth of the farms in India are being irrigated from overpumped aquifers.

Trade-Offs Withdrawing Groundwater Advantages Disadvantages Useful for drinking and irrigation Aquifer depletion from overpumping Available yearround 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 No evaporation losses Reduced water flows into surface waters Cheaper to extract than most surface waters Increased cost and contamination from deeper wells Fig. 14 -7, p. 313

Groundwater Depletion: A Growing Problem Ø Areas of greatest aquifer depletion from groundwater overdraft in the continental U. S. Ø The Ogallala, the world’s largest aquifer, is most of the red area in the center (Midwest). Figure 14 -8

Other Effects of Groundwater Overpumping Ø Groundwater overpumping can cause land to sink, and contaminate freshwater aquifers near coastal areas with saltwater. Figure 14 -11

Other Effects of Groundwater Overpumping Ø Sinkholes form when the roof of an underground cavern collapses after being drained of groundwater. Figure 14 -10

Groundwater Pumping in Saudi Arabia (1986 – 2004) Ø Irrigation systems from the nonrenewable aquifer appear as green dots. Brown dots are wells that have gone dry. Figure 14 -9

Solutions Groundwater Depletion Prevention Waste less water Control 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 waterintensive crops in dry areas Set and enforce minimum stream flow levels Fig. 14 -12, p. 316

USING DAMS AND RESERVOIRS TO SUPPLY MORE WATER Ø 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.

Provides water for year-round irrigation of cropland Provides water for drinking Reservoir is useful for recreation and fishing Can produce cheap electricity (hydropower) Downstream flooding is reduced Flooded land destroys forests or cropland displaces people Large losses of water through evaporation Downstream cropland estuaries are deprived of nutrient-rich silt Risk of failure and devastating downstream flooding Migration and spawning of some fish are disrupted Fig. 14 -13 a, p. 317

Powerlines Reservoir Dam Intake Powerhouse Turbine Fig. 14 -13 b, p. 317

Dam Removal Ø Some dams are being removed for ecological reasons and because they have outlived their usefulness. l l l 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 Ø Transferring water can make unproductive areas more productive but can cause environmental harm. l l Promotes investment, jobs and strong economy. It encourages unsustainable use of water in areas water is not naturally supplied.

Case Study: The Aral Sea Disaster Ø The Aral Sea was once the world’s fourth largest freshwater lake. Figure 14 -17

Case Study: The Aral Sea Disaster Ø Diverting water from the Aral Sea and its two feeder rivers mostly for irrigation has created a major ecological, economic, and health disaster. l l 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.

DESALTING SEAWATER, SEEDING CLOUDS, AND TOWING ICEBERGS AND GIANT BAGGIES Ø Removing salt from seawater by current methods is expensive and produces large amounts of salty wastewater that must be disposed of safely. l l Distillation: heating saltwater until it evaporates, leaves behind water in solid form. Reverse osmosis: uses high pressure to force saltwater through a membrane filter.

DESALTING SEAWATER, SEEDING CLOUDS, AND TOWING ICEBERGS AND GIANT BAGGIES Ø 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.

INCREASING WATER SUPPLIES BY WASTING LESS WATER Ø We waste about two-thirds of the water we use, but we could cut this waste to 15%. l l l 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 Ø Sixty percent of the world’s irrigation water is currently wasted, but improved irrigation techniques could cut this waste to 5 -20%. Ø Center-pivot, low pressure sprinklers sprays water directly onto crop. l l It allows 80% of water to reach crop. Has reduced depletion of Ogallala aquifer in Texas High Plains by 30%.

Drip irrigation (efficiency 90– 95%) Gravity flow (efficiency 60% and 80% with surge valves) Center pivot (efficiency 80%– 95%) Water usually comes from an aqueduct system or a nearby river. Above- or belowground pipes or tubes deliver water to individual plant roots. Water usually pumped from underground and sprayed from mobile boom with sprinklers. Fig. 14 -18, p. 325

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 -19, p. 326

Solutions: Getting More Water for Irrigation in Developing Countries – The Low-Tech Approach Ø Many poor farmers in developing countries use low-tech methods to pump groundwater and make more efficient use of rainfall. Figure 14 -20

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 watershort 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 Fig. 14 -21, p. 327

Raising the Price of Water: A Key to Water Conservation Ø We can reduce water use and waste by raising the price of water while providing low lifeline rates for the poor. l l When Boulder, Colorado introduced water meters, water use person dropped by 40%. A 10% increase in water prices cuts domestic water use by 3 -7%.

Solutions: Using Less Water to Remove Industrial and Household Wastes Ø We can mimic the way nature deals with wastes instead of using large amounts of high-quality water to wash away and dilute industrial and animal wastes. l l Use nutrients in wastewater before treatment as soil fertilizer. Use waterless and odorless composting toilets that convert human fecal matter into a small amount of soil material.

TOO MUCH WATER Ø Heavy rainfall, rapid snowmelt, removal of vegetation, and destruction of wetlands cause flooding. Ø Floodplains, which usually include highly productive wetlands, help provide natural flood and erosion control, maintain high water quality, and recharge groundwater. Ø To minimize floods, rivers have been narrowed with levees and walls, and dammed to store water.

TOO MUCH WATER Ø Comparison of St. Louis, Missouri under normal conditions (1988) and after severe flooding (1993). Figure 14 -22

TOO MUCH WATER Ø Human activities have contributed to flood deaths and damages. Figure 14 -23

Solutions Reducing Flood Damage Prevention Preserve forests on watersheds Control Strengthen and deepen streams (channelization) Preserve and restore wetlands in floodplains Tax all development on floodplains Use floodplains primarily for recharging aquifers, sustainable agriculture and forestry, and recreation Build levees or floodwalls along streams Build dams Fig. 14 -24, p. 331

SOLUTIONS: USING WATER MORE SUSTAINABLY Ø 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