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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

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

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

Karst Aquifer

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Recharge Zone

Drainage Area

Artesian Zone

Source: Edwards Aquifer Authority, 2002

Edwards AquiferAquifer Region and Authority Boundaries

Edwards Aquifer in Bexar County

Geologic HistoryAbout 17 million years ago, the aquifer rockswere uplifted and faulted, forming the BalconesEscarpment. They became subject to erosion anddissolution.

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

Devil’s Sinkhole State Natural Area

Rocksprings, TX

Natural Bridge CavernsNatural Bridge Caverns,

TX

Kickapoo Caverns State ParkBrackettville, TX

Inner Space CavernAustin, TX

Flowpaths of the Edwards Aquifer

Why does the water flow in the direction shown in the figure? Elevation

The aquifer contains severalflow systems – One occursnear Del Rio

Flowpaths of the Edwards Aquifer

Flowpaths of the Edwards Aquifer

The largest flow system runsfrom near Brackettville to nearKyle…

… and supplies the major springs at

San Marcos, New Braunfels, andSan Antonio.

Flowpaths of the Edwards Aquifer

Smaller flow systems include theBarton springs flow system…

Flowpaths of the Edwards Aquifer

Flowpaths of the Edwards Aquifer

…and areas north of the

Colorado River .

How does the water come out & who uses it?

Aquarina SpringsSan 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

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Del Rio

San Felipe

SpringsDel Rio,

TX

Water Supply Problems

Water Supply Problems

http://www.watersheds.org/earth/karstmovie.htm

EndangeredComal Springs Dryopid Beetle

Comal Springs Riffle Beetle

Fountain Darter

Peck’s Cave Amphipod

San Marcos Gambusia

Texas Blind Salamander

Texas wild-rice

ThreatenedSan Marcos Salamander

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.

Environmental Impact