Transcript Flowpaths of the Edwards Aquifer

Aquifers/Edwards Aquifer
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What is an Aquifer?
A body of rock, sediment, or soil that contains
drinkable water and can transmit this water to wells
or springs in economically usable quantities
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3 Major Types of Aquifers
1. Unconfined (most common)
2. Confined
3. Karst: a special type that occurs in
limestone rocks when a system of caves
is connected and water is flowing
through it. –Edwards Aquifer
Unconfined Aquifer
Water seeps through porous materials near the
surface, but is trapped by impermeable rock
below.
Confined Aquifer
Impermeable rock above and below. Rock strata must
bend and outcrop at surface for rain to recharge porous
material in between.
Water will pressurize if higher than well heads – artesian
system
Karst Aquifer
Develops in thick limestone formations, usually
in humid climates. Karst has both surface and
subsurface features.
http://www.watersheds.org/earth/Sinkholes.html
Karst Aquifer
Water naturally goes
underground through
sinkholes to caves
(solution caverns).
Rainwater is slightly
acidic and dissolves
limestone rock to
calcium carbonate &
carries it away
(dissolution).
Causes stalactite,
stalagmite, & pillar
formations in caverns
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Edwards Aquifer
Aquifer Region and Authority Boundaries
Drainage Area
Recharge Zone
Artesian Zone
Source: Edwards Aquifer Authority, 2002
Edwards Aquifer in Bexar County
Geologic History
About 17 million years ago, the aquifer rocks
were uplifted and faulted, forming the Balcones
Escarpment. They became subject to erosion and
dissolution.
http://www.watersheds.org/earth/karstmovie.htm
Edwards Aquifer
Cross Section
Recharge Zone
• Water enters the aquifer
through faults, fractures,
sinkholes, or percolation
through the soil. This
process is called recharge.
• The recharge
zone is the area
where water
enters the aquifer.
Caves Associated With the Edwards
Aquifer
Inner Space Cavern
Austin, TX
Devil’s Sinkhole
State Natural Area
Rocksprings, TX
Natural Bridge Caverns
Natural Bridge Caverns, TX
Kickapoo Caverns
State Park
Brackettville, TX
Flowpaths of the Edwards
Aquifer
Why does the water flow in the direction shown in the
figure?
Elevation
Flowpaths of the Edwards
Aquifer
The aquifer contains several
flow systems – One occurs
near Del Rio
Flowpaths of the Edwards
Aquifer
The largest flow system runs
from near Brackettville to near
Kyle…
Flowpaths of the Edwards
Aquifer
… and supplies the major springs at
San Marcos, New Braunfels, and
San Antonio.
Flowpaths of the Edwards
Aquifer
Smaller flow systems include the
Barton springs flow system…
Flowpaths of the Edwards
Aquifer
…and areas north of the
Colorado River .
How does the water come
out & who uses it?
Aquarina Springs
San Marcos, TX
1 Million gallons of water released from the ground
per day
Wells & Springs
Barton (main)
Spring
Austin, TX
Austin
San Marcos
Springs
San Marcos,
TX
San Marcos
San Felipe
Springs
Del Rio, TX
Del Rio
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Water Supply Problems
Water Supply Problems
http://www.watersheds.org/earth/karstmovie.htm
Environmental Impact
Eight species in the Edwards Aquifer, Comal Springs, and San
Marcos Springs ecosystems are currently listed by the U.S.
Department of Interior, Fish and Wildlife Service, as either
threatened or endangered species.
Endangered
Comal Springs Dryopid Beetle
Comal Springs Riffle Beetle
Fountain Darter
Peck’s Cave Amphipod
San Marcos Gambusia
Texas Blind Salamander
Texas wild-rice
Threatened
San Marcos Salamander