brian a. smith, ph. d., p.g. brian b. hunt, p.g. barton springs/edwards aquifer conservation...
TRANSCRIPT
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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
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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?=
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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
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Barton Springs Aquifer
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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
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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
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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
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Barton Springs Aquifer
• Sole source of drinking water for more than 50,000 people
• Home to endangered species
• Important source of recreation for Austin
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Permitted and Actual Pumpage
Note: 1 cfs = 448 gal/min = 235,889,000 gal/yr = 723 acre-ft/yr
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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
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Drought of record: Springflow
Barton Springs
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Drought of record potentiometric map (feet above msl)
Drought of record saturated thickness map (feet)
Drought of Record: Water Levels
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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
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• 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
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Zones of Hydraulic Conductivity
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GAM SimulatedSpring Flow
Simulated spring flow under 1950’s drought andvarious pumping rates
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Drawdown Due to Drought
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•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
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Cross Section
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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.
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• 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
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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.
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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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