Chapter 9 Water Resources

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Chapter 9Water Resources

• Geosystems 6e
• An Introduction to Physical Geography

Robert W. Christopherson Charles E. Thomsen
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Water

• Constantly cycling through the environment
• Water spends time in the ocean, the air, on the
  surface, and underground.
• Hydrologic Cycle the circulation and
  transformation of water through Earths
  atmosphere, hydrosphere, lithosphere, and
  biosphere.
• Water-resource management
• Wells, reservoirs, dams

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• 97 of Earths water in the ocean, so most
  precipitation and evaporation takes place there
• The bulk of global precipitation comes from ocean
  water

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• 86 of all evaporation traced to ocean
• 14 of all evaporation traced to the land

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Surface Water
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Transpiration

• The movement of water vapor through the pores of
  leaves and into plants through roots from soil
  moisture.
• People perspire, plants transpire.

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Evaporation

• The movement of free water molecules away from a
  wet surface into the air that is less saturated.

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Evapotranspiration

• The combined loss of water to the atmosphere
  through evaporation and transpiration

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• Water spends 10 days (on average) in the
  atmosphere
• Water spends 3000-10000 years in deep-ocean
  circulation, groundwater aquifers, glacial ice

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Water Budget
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Water Resources

• The purpose of water resource management is to
  minimize deficits
• Areas of highest runoff are those influenced by
  ITCZ, monsoons, and orographic precipitation
• Areas of lowest runoff subtropical deserts,
  rainshadows, and continental interiors

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Water Management

• Tennessee Valley Authority
• Hydroelectric power, recreation, flood control
• Migratory birds
• Pollution storage

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Groundwater

• Important source of freshwater
• Threatened by overconsumption and pollution
• Recharged by surface water
• More reliable than surface water systems that
  depend on runoff
• 50 0f US population depends on groundwater

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Water Resources

• Water table the upper limits of water that
  collect in the zone of saturation
• Aquifer an underground layer of permeable rock
• Springs where the water table intersects with
  the surface

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Water Resources

• Effluent streams receive recharge from the
  ground
• Mississippi River
• Influent streams recharges the ground
• Rio Grande and Colorado River

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Groundwater Overuse

• Drawdown when pumping rate exceeds the
  replenishment flow of water
• Aquifer collapse
• Desert regions
• Strip mining
• Oil exploitation
• Subsidence

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Anthropogenic Factors

• Salt-water intrusion
• When fresh water is withdrawn at a faster rate
  than it can be replenished, a draw down of the
  water table occurs with a a resulting decrease in
  the overall hydrostatic pressure.
• When this happens near an ocean coastal area,
  salt water from the ocean intrudes into the fresh
  water aquifer.

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Anthropogenic Factors

• Increases in water usage mean increases in
  wastewater discharge
• Introduction of agricultural, industrial, and
  domestic bacteria and chemicals into water supply
• Oil
• Pesticides
• Sink holes

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Groundwater Pollution

• Once polluted, always polluted
• Point-source pollution
• Gasoline tank
• Septic tank
• Nonpoint-source pollution
• Agriculture
• Urban runoff