4/9 ERS102 - Withdrawal>recharge o Ogalla...

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Ground water flow: gravity and pressure o Flow in unsaturated zone is straight downward (gravity) o In the saturated zone, flow is more complicated. Governed by gravity and pressure o Infiltration=percolation Why does ground water flow follow a curved path? o Hydraulic head, potential energy driving flow, is due to… Elevation above sea-level (gravity) Pressure exerted by weight of overlying water o Recharge and discharge US Fresh Water Use (USGS, 2000) o 87 Billion Gallons/Day- groundwater o 273 Billion Gallons/Day- surface water Maine Water Use by Population o 50% of the state population relies on private wells Dug Wells Drilled Wells o Sand and gravel o Bedrock Pumped well Artesian Well Springs o Natural flow of water from the earth o Examples: Weeping hillside Perched spring Fracture spring Artesian spring o Pumping creates a cone of depression o Heavier use= larger cone of depression Ground water depletion o Pumping at a rate greater than recharge is mining the aquifer.
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Unformatted text preview: Withdrawal>recharge o Ogalla Aquifer 60-425 m thick Fossil water At present rate of withdrawal, by 2020, 25% of resource will be gone o Beneath coastal land, fresh water floats on salt water o Pumping causes the fresh/salt boundary to rise o Eventually, salt water may enter the pumping well o Salt water intrusion renders the water unpotable o Severe water table decline can alter surface water flow By capturing flow, wells may dewater streams and lakes Especially problematic in arid and semi-arid regions o Cones of depression are capable of reversing flow o An expanding cone may capture pollutants o There are many sources of groundwater contamination o Pollution is often not recognized until damaged occurs o Groundwater cleanup is slow, expensive and limited o Point source leaking gas tank...
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4/9 ERS102 - Withdrawal>recharge o Ogalla...

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