Hydro Lecture 1

Although I missed this class, I'm gonna attempt to read our professor's mind and pull the most important info. See [/wiki:hydrogeology-notes] for introductory material about the class.

Water on Earth

  • It is the only known substance that exists as a gas, liquid and solid at surface temperatures
  • Approx 75% of Earth's surface is covered in water
    • Of ALL the water contained within Earth:
      • 97% is found in the ocean
      • < 3% is considered fresh water
      • There is more groundwater than fresh surface water
      • There is more soil moisture than atmospheric moisture
      • 98% of available freshwater is groundwater, <2% is surface water

The Hydrologic Cycle

The constant flux of water moving throughout the earth's interior and exterior. It interacts directly with almost every natural system on Earth.

Processes in the Hydrologic Cycle

  • Precipitation (rain & stuff)
  • Evaporation (gas-phase water)
  • Transpiration (plants drink up water from soil and sweat it out into the atmosphere)
  • Infiltration (water moves into subsurface)
  • Runoff
    • Overland flow (land surface drainage; moving water)
    • Interflow (lateral flow of water through subsurface: unsaturated zone/ vadose zone)
    • Baseflow (lateral flow of water through the subsurface: saturated zone; water that flows from an aquifer to a surface body of water)
    • Underflow (lateral flow of water through deep subsurface; does not interact with surface water)

Hydrologic Cycle Components

  • Land
    • groundwater (interflow, baseflow, underflow)
    • surface water (lakes, rivers, etc.)
      • depression storage (aka puddle-like stuff)
  • Air
    • water to water vapor: transpiration & evaporation
    • water vapor to water: precipitation

Water Use

Above taken from USGS 2004
  • People use LOTS of water!!!
  • A vast majority of freshwater is used in industry and agriculture.
  • Globally, about 70% of freshwater withdrawn goes to just agriculture.
    • 23% goes to industry
    • 7% goes to civilians
  • The average person needs a minimum of five liters (1.3 gallons) of water per day to survive in a moderate climate at an average activity level, according to UN figures.
  • The minimum amount of water needed for drinking and cooking, bathing and sanitation is 50 liters (13 gallons).
  • International Use Comparison:
    • The average person in the United States uses between 250 to 300 litres of water (65-78 gallons) per day for drinking, cooking bathing, and watering their yard.
    • The average person in the Netherlands uses 104 litres per day (27 gallons).
    • The average person in the African nation of Gambia uses 4.5 litres per day (1.2 gallons of water).

Water Trends

  • There is too little water for everyone
    • Causes include dry climate, drought, desiccation (drying of soil because of such activities as deforestation and overgrazing), and water stress (low per capita availability of water caused by overpopulation).
  • Surface water withdrawals exceed groundwater withdrawals
  • Irrigation wastes a lot of water, not very efficient
  • Increase in uses of gray water or saline water as alternative to freshwater

Attempts to Increase Water Supplies

  1. Build bigger dams
    • Collect and store water from rain and snow
    • Produce electricity
    • Irrigate land below the dam
    • Control flooding
    • Provide recreational activities
    • Numerous negative environmental side-effects
  2. Withdrawal of more groundwater
    • About half the freshwater used in the U.S. is pumped from aquifers
    • About 40% of surface water is groundwater
  3. Rerouting rivers
  4. Desalinization
  5. Improved efficiency in use of water

Excessive groundwater pumping can lead to:

  • aquifer depletion (the pumping rate is higher than the recharge rate)
  • aquifer subsidence (so much water is removed from the subsurface that it compacts in on itself, decreasing elevation of the land)
  • Saltwater intrusion (when coastal freshwater aquifers lose so much water that the saline coastal water begins to replace the freshwater)
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