Brian A. Smith, Ph. D., P.G.

Brian B. Hunt, P.G.

Barton Springs/Edwards Aquifer Conservation District

Texas Groundwater 2004: Towards Sustainability

November 18-19

Austin, Texas

GROUNDWATER AVAILABILITY MODELING OF THE BARTON SPRINGS SEGMENT OF THE

EDWARDS AQUIFER, CENTRAL TEXAS

FUNDAMENTAL PROBLEM

What are the impacts to discharge from Barton Springs and water levels under a recurrence of 1950’s drought conditions and increasing pumping?

1950’s drought

(7-year drought)

+Pumping

IMPACTS?=

OUTLINE• Hydrogeologic Setting• 2000 and 2001 Groundwater

Availability Models (GAM)• Recalibration of GAM to 1950’s

Drought Conditions• Impacts to Barton Springs

Discharge• Impacts to Water Levels and Wells• Conclusions• Future Studies

Barton Springs Aquifer

Conceptual Aquifer Model

Trinity

Edwards

•Most of the recharge to the aquifer occurs via surface streams in discrete (karst) recharge features.

•Limited contribution from the Trinity Aquifer and saline-water zone.

Contributing zone

Barton Springs Aquifer

• Sole source of drinking water to more than 50,000 people

• Home to endangered species at springs

• Important source of recreation for Austin

Barton Springs Aquifer

• Sole source of drinking water to more than 50,000 people

• Home to endangered species at springs

• Important source of recreation for Austin

Barton Springs Aquifer

• Sole source of drinking water for more than 50,000 people

• Home to endangered species

• Important source of recreation for Austin

Permitted and Actual Pumpage

Note: 1 cfs = 448 gal/min = 235,889,000 gal/yr = 723 acre-ft/yr

Drought of Record: Rainfall

0

10

20

30

40

50

60

70

1856

1866

1876

1886

1896

1906

1916

1926

1936

1946

1956

1966

1976

1986

1996

An

nu

al R

ain

fall

(in

)

1950-1956

33.0 inches, average annual

Camp Mabry, Austin, Texas

Drought of record: Springflow

Barton Springs

Drought of record potentiometric map (feet above msl)

Drought of record saturated thickness map (feet)

Drought of Record: Water Levels

GAM is an initiative by TWDBto develop state of the art, publicly available, numerical groundwater flow models to provide reliable information of groundwater availability in Texas.

Barton Springs GAM:•Scanlon et al., 2000 and 2001•Recalibrated to better-match 1950’s drought conditions

Groundwater Availability Model

• Raymond Slade- Retired, USGS• Rene Barker- Retired, USGS• Nico Hauwert- City of Austin• David Johns- City of Austin• Jack Sharp- UT Dept. of Geosciences• Bridget Scanlon- UT BEG• Robert Mace- TWDB• Eric Strom- USGS

Groundwater Model Advisory Team

Zones of Hydraulic Conductivity

GAM SimulatedSpring Flow

Simulated spring flow under 1950’s drought andvarious pumping rates

Drawdown Due to Drought

•Stratigraphy and geologic structures

•Measured water levels

•Specific capacity and pumping test data

•Well construction data

•Simulated pumping drawdown from GAM

Evaluation of Hydrogeologic Data to Quantify Impacts to Wells

Cross Section

RESULTS: impacts to wells

• 7% of wells may be negatively impacted under 1950’s drought conditions alone.

Current permitted pumpage

• 19% of the wells in the District may be negatively impacted under 1950’s drought and 10 cfs pumping.

• For each 1 cfs of groundwater pumped from the aquifer under 1950’s drought conditions, discharge from Barton Springs will diminish by about the same rate.

• At current permitted pumping levels (10 cfs), Barton Springs discharge is predicted to decrease to about 1 cfs on a monthly average, although may temporarily cease at times.

CONCLUSIONS:Spring Flow

CONCLUSIONS:Impacts to Wells

• At current permitted pumping levels (10 cfs), as many as 19% of wells in the District may be negatively impacted. Most of the impacts are to wells that only partially penetrate the aquifer.

• The southwestern portion of the aquifer is most threatened from low water levels and increased pumping rates during a recurrence of 1950’s drought conditions.

Future Studies

Next Generation of Model

• Conduit/diffuse-flow model

• Variable hydraulic conductivities

Aquifer Characterization

• Saline-water zone studies

• Dye-trace studies

• Edwards-Trinity hydraulic connection

• Southern groundwater divide

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