Water Resources
12
Water
Resources
12.1 Water Supply and Demand
• Withdrawal – any process that uses water and returns it locally
• Consumption – processes that use water and return it far from its source
• Together make up the three usage categories:
– Domestic, industrial, and agricultural
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Water Supply and Demand
• Domestic water use – 10%
– Flushing, bathing, drinking
• Industrial – 49%
– ¾ goes to cooling of electrical power plants
– ¼ to all other industry
• Agriculture – 41%
– Irrigation feeds most of the world
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12.2 Dams and Diversion
• Diversion systems – pipes or canals to transport water
• Dams – to trap and store seasonal precipitation
– Often coupled with energy production
– Represent ~5% of global electric production
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Dams and Diversion
• Water loss
– Water in reservoirs evaporates and infiltrates
• Less water flows through the river system
• Salinization
– Occurs with long-term irrigation in dry climates
– Dissolved load (salts) in water builds up in soil
– Saline soil lowers crop yield
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Dams and Diversion
• Silting – sediment deposits in reservoirs
• Erosion – lack of sediment in water leaving dam erodes downstream
• Risk – dams can fail
• Recreational and aesthetic loss
– Dams flood the landscape
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Dams and Diversion
• Ecological disruption – changing a river valley to a lake alters biota
• Human cost
– People often have to move to accommodate dam projects
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Dams and Diversion
• Ground water diversion – ground water is a valuable resource
– Provides much water
– Is usually available when surface water is not
• Ground water depletion – use of water faster than it is replenished
– Cone of depression – deflection of water table caused by over-pumping
– Many aquifers are over-pumped (Ogallala)
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Dams and Diversion
• Subsidence
– Sinking of Earth’s surface
– Caused by loss of aquifer porosity
• Saltwater intrusion
– Depletion of fresh ground water in coastal zones allows saline water to intrude
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12.3 The Great American Desert
• Between western mountains and 100° meridian
– Mostly arid or semiarid
– Still popular settlement, despite lack of precipitation
• Billions spent on water diversion
– Example: California
• 1,200 dams
• Two of the world’s largest irrigation projects
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The Great American Desert
• Colorado River
– Apportioned to states
– Water does not reach the sea
– Very salty
– Declining rainfall and reservoir levels
• Minor drought → severe consequences
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12.4 Water and International Politics
• Jordan River – amid enemy countries
– Dams planned by Syria
• Diverts water from Jordan (threats from Israel)
– Over pumped aquifer in Israel
• Upstream nations tend to assert domain
• Currently no international code for water usage
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12.5 Water Pollution
• Pollution – reduction in water quality
– Significant during Industrial Revolution
• Clean Water Act
– 1972 policy to clean water sources and keep them clean by mid-1980s
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Water Pollution
• Biodegradable pollutants – decay naturally
(food/human waste, soap)
• Nonbiodegradable pollutants – not decomposed naturally (some pesticides, mine waste, sediment)
– PBTs – nonbiodegradable poisons
• Radioactive materials – mining radioactive ores, nuclear power plants
– Heat is also a pollutant
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Water Pollution
• Point source pollution – stems from specific site (septic tank, gas spill)
• Nonpoint source pollution – stems from a broader area (fertilizer, pesticide runoff from lawns/farms)
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12.6 How Sewage, Detergent, and
Fertilizers Pollute Waterways
• Pollutants are nutrients
– Increase O
2 consumption by organisms
• All O
2 consumed by anaerobic bacteria
– Release hydrogen sulfide
• Decay organisms die once all pollutants are consumed
• Natural turbulence eventually replenishes
O
2
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Toxic Pollutants, Risk Assessments, and
Cost Benefit Analysis
• Some compounds persist in the environment
• Effects by dose unknown
– Difficult to test, especially long-term
– Epidemiological studies used
• Both pollution and pollution control are expensive
– Externalities – additional/unintentional consequences to an original activity
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12.8 Groundwater Pollution
• Many sources of contamination
• Very hard to clean tainted aquifer
• Plume of contamination – zone within aquifer affected by pollutant
• Contaminants persist longer than in lakes and streams due to slower flow
• O
2 less abundant in ground water
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Groundwater Pollution
• Treating a contaminated aquifer
– Eliminate source of pollution
– Monitor to determine rates
– Model to help predict impact
– Clean it up
• Bioremediation – use of microorganisms
• Chemical remediation – reacts with pollutant to create harmless product
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12.9 Nuclear Waste Disposal
• 2,000 tons high-level radioactive waste generated every year in the U.S.
• Disposal: store in safe place
– Defined by isolation for minimum 10,000 years
– Waste remains harmful for 1 million years
– Must be safe from geologic hazards
(earthquakes, landslides, floods)
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12.10 The Clean Water Act: A Modern
Perspective
• Municipalities no longer dump
– Many still don’t meet Act’s standards
• 40% unsafe for human consumption
• 2009 New York Times study
– Over half a million violations occurred in the prior five years
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