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Water
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Water: A Vital Resource
Fresh Water 2.6% Oceans and saline lakes 97.4%
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Supply of Water Resources
Freshwater Readily accessible freshwater Biota 0.0001% Rivers Atmospheric water vapor 0.001% Lakes 0.007% Soil moisture 0.005% Groundwater 0.592% Ice caps and glaciers % 0.014%
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Surface Water Surface runoff Watershed (Drainage Basin)
Water flowing off the land into bodies of water Represents a stable source of water Watershed (Drainage Basin) Area of land drained by a single river or stream
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Groundwater
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Evaporation and transpiration
Ground Water Flowing artesian well Unconfined Aquifer Recharge Area Precipitation Evaporation and transpiration Well requiring a pump Evaporation Confined Recharge Area Runoff Aquifer Stream Infiltration Water table Lake Infiltration Unconfined aquifer Confined aquifer Less permeable material such as clay Confirming permeable rock layer
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Use of Water Resources Agriculture Industry Domestic Power Plants
Humans use about 50% of reliable runoff United States Industry 11% Public 10% Power cooling 38% Agriculture 41% Agriculture Industry Domestic Power Plants
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Water use (cubic kilometers per year)
5,500 5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 1900 1920 1940 1960 1980 2000 Water use (cubic kilometers per year) Total use Agricultural use Industrial use Domestic use Year
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Water in the United States
Average precipitation (top) in relation to water-deficit regions and their proximity to metropolitan areas (bottom).
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Too Little Water Dry climate Drought Desiccation Water stress
Air circulation patterns Drought 21 days+ Precipitation <70% Increased evaporation Desiccation Drying of the soil Water stress Low per capita availability Caused by increased population Limited runoff levels Acute shortage Adequate supply Shortage Metropolitan regions with population greater than 1 million
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Water scarcity – per capita availability below 1000 cu meter per year
Water stressed – reliable runoff per person below 1700 cu meters per year Water scarcity – per capita availability below 1000 cu meter per year 500 million people live in countries that are either water stressed or water scarce limited access (live far away) arrives during short periods hydrological poverty Collect water from unsafe sources Purchase from private vendor
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Increasing Fresh Water Supplies
Build dams and reservoirs to store runoff Bring surface water from another area Withdraw groundwater. Convert salt water to fresh water Waste less water Import food to reduce water use
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Using Dams and Reservoirs to Supply More Water (To Dam or Not To Dam)
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Provides water for year-round irrigation of cropland
Flooded land destroys forests or cropland and displaces people Large losses of water through evaporation Provides water for drinking Downstream cropland and estuaries are deprived of nutrient-rich silt Reservoir is useful for recreation and fishing Risk of failure and devastating downstream flooding Can produce cheap electricity (hydropower) Figure 14.13 Trade-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 reduced Migration and spawning of some fish are disrupted Fig a, p. 317
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Ecological Services of Rivers
• Deliver nutrients to the sea which helps to sustain coastal fisheries • Deposit silt that maintains deltas • Purify water • Renew and nourish wetlands • Provide habitats for aquatic life • Conserve species diversity
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Transferring Water from One Place to Another
Watershed transfer North Bay Aqueduct South Bay California Aqueduct CALIFORNIA NEVADA UTAH MEXICO Central Arizona Project Colorado River Los Angeles Shasta Lake Sacramento Fresno Phoenix Tucson ARIZONA Colorado River San Francisco San Diego California Water Project
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Increasing Fresh Water Supplies
Build dams and reservoirs to store runoff Bring surface water from another area Withdraw groundwater.
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Tapping Groundwater Advantages Potential Problems! Year-round use
No evaporation losses Often less expensive Potential Problems! Many
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Problems with Using Groundwater
Water Table Lowering Initial water table Cone of depression Original water table Lowered
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Problems with Using Groundwater
WYOMING SOUTH DAKOTA NEBRASKA COLORADO KANSAS OKLAHOMA NEW MEXICO TEXAS 100 Miles Kilometers Less than 61 meters (200 ft) meters ( ft) More than 183 meters (600 ft) (as much as 370 meters or 1,200 ft. in places) 160 Aquifer depletion Ogalala Aquifer
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Other Effects of Groundwater Overpumping
Sinkholes form when the roof of an underground cavern collapses after being drained of groundwater.
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Problems with Using Groundwater
Saltwater intrusion: when groundwater is depleted faster than it recharges Major irrigation well Well contaminated with saltwater Saltwater Intrusion Normal Interface Fresh groundwater aquifer Salt water Sea Level Water table
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Fresh groundwater aquifer
Major irrigation well Well contaminated with saltwater Water table Sea level Fresh groundwater aquifer Saltwater Figure 14.11 Natural capital degradation: saltwater intrusion along a coastal region. When the water table is lowered, the normal interface (dashed line) between fresh and saline groundwater moves inland, making groundwater drinking supplies unusable. QUESTION: What two things would you do to reduce the threat of saltwater intrusion? Seafloor Interface Saltwater intrusion Interface Normal interface Fig , p. 315
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Problems with Using Groundwater
Chemical contamination Reduced stream flow Tragedy of the commons
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Converting Salt Water to Fresh Water
Desalination – removing dissolved salts from ocean water or brackish water. Distillation desalination Heating salt water until it evaporates. Reverse osmosis desalination Salt water is pumped at high pressure through a thin membrane
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Converting Salt Water to Fresh Water
Desalination is very expensive Larger amounts of energy needed Desalination produces large quantities of wastewater waste disposal problem
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Making it Rain Cloud Seeding Limited Success Water condensation nuclei
Silver iodide particles Limited Success Not useful in dry areas Potential pollution from cloud seeding chemicals Legal disputes: ownership of clouds
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Using Water More Efficiently
Reduce losses due to leakage 60 to75% of water people use is lost! Causes of waste Water subsidy policy Artificially low cost of water False sense of abundance
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Using Water More Efficiently
Causes of waste cont. Water laws Doctrine of riparian rights (East) Anyone owning land adjoining stream has right to water Principle of prior appropriation (West) First-come, first-served Common law governs groundwater Subsurface water belongs to whoever owns the land above it Fragmented watershed management
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(efficiency 60% and 80% with surge valves)
Drip irrigation (efficiency 90–95%) Gravity flow (efficiency 60% and 80% with surge valves) Figure 14.18 Major 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
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Too Much Water: Floods Natural phenomena
heavy rain, melting snow Aggravated by human activities Renew and replenish Reservoir Dam Levee Flood wall Floodplain
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Solutions: Achieving a More Sustainable Water Future
Efficient irrigation Water-saving technologies Improving water management
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What Can You Do? Water Use and Waste
• Use water-saving toilets, showerheads, and faucet aerators. • Shower instead of taking baths, and take short showers. • Stop water leaks. • Turn off sink faucets while brushing teeth, shaving, or washing. • Flush toilets only when necessary. • Wash only full loads of clothes or use the lowest water-level for smaller loads. • Use recycled (gray) water for lawn, gardens, house plants, car washing. • Wash a car from a bucket of soapy water, and use the hose for rinsing only. Figure 14.25 Individuals matter: ways you can reduce your use and waste of water. Visit for an array of water-saving tips from the EPA and the California Urban Water Conservation Council that can be used anywhere. QUESTION: Which four of these actions do you think are the most important? • If you use a commercial car wash, try to find one that recycles its water. • Replace your lawn with native plants that need little if any watering and decorative gravel or rocks. • Water lawns and gardens in the early morning or evening. • Sweep or blow off driveways instead of hosing off with water. • Use drip irrigation and mulch for gardens and flowerbeds.
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