Download - Aquifers 101
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Aquifers 101
Robert E. MaceTexas Water Development Board
Groundwater 101November 10, 2010
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Outline
• Yay for aquifers!• Definitions• Flow through an aquifer• Pumping an aquifer
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World Water Balance
From Freeze and Cherry (1979)
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groundwater and Texas
• ~60 percent of the 16.6 million acre-feet of water used
• ~80 percent of groundwater is used for irrigation
• groundwater provides 39 percent of water to cities
• tastes good when yer thirsty
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Examples of Aquifers
• The following slides are examples of aquifers
• As we discuss them, try to think of how you would define AQUIFER
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catfish farm wellEdwards aquifer
• flowing well at 40,000 gpm• 1/4 of San Antonio’s use• 9% of Annual Recharge• world’s largest artesian well
National Geographic (1993)
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Major aquifers
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Minor aquifers
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Hickory Aquifer, sandstone
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Edwards-Trinity (Plateau) Aquifer, limestone
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Ogallala Aquifer, sand and gravel
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• an aquifer is geologic media that can yield economically usable amounts of water.
• Fill in the definition in your notes
what is an aquifer?Dirt and rocks
Depends onwho’s using it
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Aquifers have certain properties:
Limestone (especially karstified), sandstone, sand, gravel, fractured rocks
It must have spaces that water can fill up; These spaces are called pores. We call these
Materials porous. (The related noun is porosity)
It is measured by volume of space/total volume of material.
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Porosity is determined by:
1. Shape - Well rounded particles have greater porosity than angular.
ROUND ANGULAR
Porosity - The amount of space in between sediments.PO
RO
SITY
ROUNDNESS
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2. PACKING- The more closely packed the particles the lower the porosity.
UNPACKED PACKED
POR
OSI
TY
PACKING
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3. SORTING- - If all particles are the same size they are sorted. - If the particles are different sizes they are unsorted (poorly sorted) - The more sorted the higher the porosity
POR
OSI
TY
SORTING
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what is an aquifer?
For a layer to be a true aquifer, it mustAllow water to flow; if a layer lets water flow,We say its permeable. (The related noun is
Permeability.)
This is how interconnected the pores are.
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Permeability Ability of water to pass through Affected by: packing and particle size Tighter packing and Smaller particles =
less permeability Looser Packing and
Larger particles = more permeability
PER
MEA
BIL
ITY
PARTICLE SIZE
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Other things about Permeability
Permeability Rate – How fast a fluid can flow through a material
Impermeability (not permeable) is due to:
A. Tightly packing of particlesB. Cementing of particles by clayC. Cementing of particles by ice
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GRAVEL Rapid
drainage
FINE SANDModerate drainage
CLAYSlow
drainage
PERMEABILITY
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Clay is impermeable – water will not flow through easily
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• Another characteristic of most aquifers is the presence of layers that don’t let water flow easily.
• an aquitard is geologic media that can not yield economically usable amounts of water.
what is an aquitard?
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• clay, shale, unfractured dense rocks• Note: can still transmit water,
but s l o w l y
what is an aquitard?
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• A confining layer is an aquitard that bounds an aquifer.
what is a confining layer?
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• The vadose zone is the unsaturated geologic media between the water table and the land surface.
• Scientific side note: There is a saturated capillary zone between the vadose zone and the water table.
what is a vadose zone?
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the vadose zone
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• A water table is where the aquifer meets the vadose (unsaturated) zone.
• Scientific definition: surface on which the fluid pressure in the pores of a porous medium is exactly atmospheric.
what is a water table?
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the water table
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• Recharge is water that infiltrates to the water table of an aquifer.
what is recharge?
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recharge
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• A water level is the level at which water rests (or would rest) in a well.
what is a water level?
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the water level
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• water flows downhill (to lower potential energy)
• water flows uphill to money
2 rules of groundwater flow
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water flows downhill (to lower potential energy)
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Groundwater Flowpaths
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• An unconfined aquifer is an aquifer that is bounded by a confining layer at its bottom but not at its top.
what is an unconfined aquifer?
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an unconfined aquifer
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• A confined aquifer is an aquifer that is bounded by confining layers at its bottom and top and where the water level rises above the top of the aquifer.
• Scientific side note: This is also an artesian aquifer. “Artesian” does not require water to flow at land surface.
what is a confined aquifer?
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a confined aquifer
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confined or unconfined?
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confined or unconfined?
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confined or unconfined?
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same aquifer: unconfined and confined
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Major aquifers
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same location: confined and unconfined aquifers
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Outline
• Yay for aquifers!• Definitions• Flow through an aquifer• Pumping an aquifer
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Recharge
Aquifer
Pumping
Spring/baseflow
Your aquiferas a bathtub
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Edwards Group
Upper Trinity aquifer
Middle Trinity aquiferGuadalupe
River
CanyonLake
Edwards aquifer(BFZ)
SE model boundary
No flow
No flow
A
A’
2400
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
sea level
Spring flow
0 5 10 15 mi
Recharge
Cross-formational flow
Surface water-groundwater interaction
Groundwater flow
DrainPumping
cross-section - structure
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Recharge
Aquifer
Pumping
Spring/baseflow
Your aquiferas a bathtub
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recharge
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Graphic from Playa Lakes Joint Venture
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Attack of theKillerSalt Cedar!