Chapter 11 – WATER UNDER THE GROUND
Freshwater Underground• Ground water
– Subsurface water contained in pore spaces in regolith & bedrock
Freshwater Underground• Zone of aeration
– Mix of air & water
• Zone of saturation– Saturated with
water• Water table
– Top of saturated zone
• How groundwater moves– Porosity
• % of total volume of rock body or regolith made of open spaces (pores)
– Permeability• Measure of how easily a solid
allows fluids to pass through it
Freshwater Underground
• How groundwater moves– Hydraulic gradient
• Change in elevation divided by distance• Used to
determine rate of groundwater flow
Freshwater Underground
• How groundwater moves (continued)– Percolation
• Groundwater seeps downward
– Recharge• Replenishment of
groundwater– Discharge
• Subsurface water leaves saturated zone
• Becomes surface water– Spring
• Occurs where water table intersects land surface
Freshwater Underground
• How groundwater moves (continued)– Other methods of discharge
• Hot springs• Geysers
Freshwater Underground
• Where groundwater is stored– Aquifer
• Rock body or regolith that is water saturated, porous, & permeable
– Aquiclude• Layer of
impermeable rock
Freshwater Underground
• Where groundwater is stored– Aquifer
• Unconfined• Confined• Potentiometric
surface– Artesian well
Freshwater Underground
• Groundwater depletion– Cone of depression
• Cone-shaped dip in water table due to pumping
– Groundwater mining• Rates of groundwater withdrawal
continuously exceed rate of recharge
Freshwater Underground
• Groundwater depletion (continued)– Land subsidence
• Compaction– Salt water intrusion
Freshwater Underground
• Groundwater contamination– Contamination
Freshwater Underground
• Dealing with groundwater issues– Enhanced recharge– Conservation– Other sources
• Desalination (i.e. distillation; reverse osmosis; electrolysis)
• Icebergs
Freshwater Underground
• Natural methods– Filtration– Decomposition– Bacterial action
• Human methods– Exterior treatments– Dilution– Chemical
treatments
Freshwater Underground
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Groundwater in the U.S.
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• Groundwater Mining– Recharge rate vs. consumption rate
• Ogallala Aquifer: largest aquifer in U.S. – 225,000 sq miles– Found in 8 states– 30,000 years of
water accumulation
Groundwater in the U.S.
Ogallala Aquifer
Groundwater in Nebraska
Groundwater in Nebraska
What areas seem best suited for groundwater withdrawal? Why do you think these areas are not utilized?Answer: The Nebraska Sandhills However, Crops do not grow well in sand, so the area is primarily used for ranching.
Groundwater in Nebraska
• When groundwater dissolves rock– Carbon dioxide + water =
carbonic acid• Adds acid to water in atmosphere
& underground– Calcite + carbonic acid =
dissolution• Calcite dissolves
Freshwater Underground
• Factors of dissolution– Rock composition– Extent of rock fracturing,
jointing, & bedding– Acidity of water– Climate
Freshwater Underground
• When groundwater dissolves rock– Karst topography– Sinkholes– Disappearing streams
Freshwater Underground
• When groundwater dissolves rock– Cave
• Underground open space• Cavern = system of connected
caves • Stalactites• Stalagmites• Columns (pillars)
Freshwater Underground