17-Groundwater-F08

17-Groundwater-F08 - The Hydrologic Cycle and Groundwater...

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The Hydrologic Cycle and Groundwater Chapter 17
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Summary Water – resource and agent How much water do we have? Storage and circulation of Earth’s water Water as a mined quantity?
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How much water is there? Models for the global hydrologic cycle, consider water in several reservoirs” . Over moderate time periods (years), inflow is assumed to equal outflow, and the size of each reservoir remains ~constant. Over longer times, the amount of water in reservoirs may vary according to global climate changes. Total Water: USA covered by 145 km deep
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Groundwater withdrawals in the US
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The Hydrologic Cycle The hydrologic cycle models the movement of water from one reservoir to another (means and amount). Knowing flux and reservoir size, a residence time can be calculated - the time that a water molecule spends in each reservoir. km 3 yr -1
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Reservoirs 1. Precipitation (Inflow) Rain, Snow, Condensation 420,000 km 3 /yr 2. Storage World Oceans 1,320,000,000 km 3 Ice caps and glaciers 29,200,000 km 3 (2.2% of oceans) Soil moisture, Ground water 8,350,000 km 3 Freshwater Lakes 25,000 km 3 Atmosphere 13,000 km 3 Rivers (instantaneous storage) 1,250 km 3 3. Runoff (Outflow) Interflow and Rivers 38,000 km 3 /yr Infiltration and Ground Water 1,600 km 3 /yr 4. Evapotranspiration (Outflow) Ocean evaporation 350,000 km 3 /yr Evapotranspiration 70,000 km 3 /yr
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Energy consumed by the cycle Energy released by the cycle Energy consumed and released
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Phase Equilibria The hydrologic cycle is driven by solar energy - each transition from one form of water (ice, liquid, vapor) results in loss or gain of energy of the hydrologic system Eg. evaporation occurs as water absorbs sufficient heat to overcome the “ latent heat of vaporization” (590 cal/gm) to convert liquid water to vapor. Condensation of water from vapor releases the same amount of heat back to the environment The hydrologic cycle is the primary mechanism for the redistribution of solar energy at the Earth’s surface.
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At any temperature, the maximum amount of water in the atmosphere is assigned a value of 100% relative humidity . That amount of water vapor ( absolute humidity ) increases with air temperature. Evaporation can continue until the atmosphere is saturated with water vapor. The temperature at which the absolute amount of water in a body of air equals 100% relative humidity is the dew point If a water saturated air mass is cooled, it becomes supersaturated, and condensation (clouds, rain or snow) will occur. Thermal Lapse Rate
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17-Groundwater-F08 - The Hydrologic Cycle and Groundwater...

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