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Coupled Surface-Water/Groundwater Evaluation in the Edwards Plateau
Groundwater Management Area 7 October 19, 2017
Ronald T. Green, Ph.D., P.G., Beth Fratesi, Ph.D.,
Nathaniel Toll, and Rebecca Nunu
Southwest Research Institute®
Photo: Texas Parks and Wildlife Department
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Edwards-Trinity Aquifer
Edwards-Trinity Aquifer GAM (Anaya and Jones, 2009)
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Edwards-Trinity Aquifer
Edwards-Trinity Aquifer GAM (Anaya and Jones, 2009)
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Page 4 Edwards-Trinity Aquifer GAM (Jones et al., 2009)
Edwards-Trinity Aquifer Regional-Scale Groundwater
Availability Model
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The Problem
Regional-scale models not capable of replicating local-
scale hydraulic features
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Related Studies Provide Insight on Modeling Watersheds Independently
Edwards Aquifer
Refined Model Distinct Watersheds
Refined Grid
Edwards Aquifer FEM (Fratesi et al., 2014)
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Edwards-Trinity Aquifer Major Watersheds Act Separately
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Challenge: Adjoining Basins Merge at Downdip Boundaries
8
Edwards Plateau
Schleicher
County
Sutton
County
Val Verde
County
Unconfined Partially Confined Confined
No Communication Communication
Between Watersheds Between Watersheds
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What is the nature of river and groundwater flow in the headwater areas of the Edwards Plateau?
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Rain Water Is Focused into River Beds and Acts as a Mild Acid That Dissolves the Limestone
The preferential flow paths that are formed may be a “pipe”, but it is more likely the flow paths are simply
zones of enhanced permeability
Incised River Channels
Preferential Flow Paths
Woodruff and Abbott, 1970s, 1980s
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Groundwater Chemistry Indication of Conduit Location
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Pipes in a sponge
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Hydraulic couplings are more complex than just SW ↔GW
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Headwater Streams are Mostly Gaining
2006 – TCEQ 2013 – Jeff Bennett/NPS; Marcus
Gary/EAA; Ron Green/SwRI; Kevin Urbanczyk/Sul Ross;
students
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Watershed-Scale Studies
Lower Pecos River
Watershed
Devils River
Watershed
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Parsing Out the Lower Pecos River Watershed
Independence Creek
Live Oak Creek
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Devils River Watershed
Devils River watershed has
features that make it difficult
or impossible to model with
just any SW-GW software.
Drains southward off
Edwards Plateau
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The Problem
• Accurately predicting impact of groundwater
pumping on surface flow or depletion of surface
water on groundwater recharge requires modeling
interdependent surface and subsurface processes.
• Integrated models are available, but not well
developed, particularly for challenging environments
such as semi-arid karstic watersheds.
• TCEQ WAM is not coupled with TWDB GAM
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Surface Water
Owned by the State
Governed by TCEQ
Administered using WAMs
Groundwater
Owned by Land Owners
Governed by
TWDB/GMAs/GCDs
Administered using GAMs
(Winter et al., 1998)
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Surface-Water Model
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Long-Term Calibration 2000-2015
0
1
2
3
4
5
60
5000
10000
15000
20000
25000
30000
35000
40000
45000
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015
Pre
cip
itation (
in)
Direct
Dis
charg
e (
cfs
)
Year
2000-2015
Actual Discharge Model Discharge Precipitation
Storm absent in PRISM data
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Percolation is Calculated by Surface-Water Model and Imported into the Groundwater Model
(A)
Infiltration
2.4”
February 4, 2004 March 12, 2004
1
Saturated Fraction
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Groundwater Model Refinement
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Groundwater Model Mesh Refinement
Mesh refinement at areas where the surface-water flow
accumulation has selected stream channels
Sycamore Creek
Watershed
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Groundwater Model Mesh Refinement
Quad-Tree mesh
refined along stream
centerlines
Significantly reduces
mesh density while
preserving complexity
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Groundwater Model Performance
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Groundwater Model River Discharge: Pafford Crossing
100,000
300,000
500,000
700,000
900,000
1,100,000
1,300,000
1,500,000
1,700,000
1,900,000
2,100,000
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Flo
w C
ub
ic M
ete
rs/d
ay
Date
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Groundwater Pumping Scenario
• Well field located near Juno
• Cumulative pumping of 8,000 gpm
(12,800 acre-ft/yr)
• What is the effect on baseflow to the
Devils River?
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Groundwater Pumping Scenario 8,000 gpm at Juno
200,000
300,000
400,000
500,000
600,000
700,000
800,000
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Flo
w C
ub
ic M
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rs/d
ay
Date
With pumping
Without pumping
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Self Selecting Spring Locations
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Self Selecting Spring Locations
Pre-Development Current Conditions With Juno Wellfield
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• Improved insight on water resources provided when evaluating coupled surface water and groundwater.
• Individual watersheds in the Edwards Plateau can be evaluated and modeled separately.
• Groundwater flow controlled by the morphology of the area more than the hydraulic properties of the rocks. Model is relatively insensitive to assignment of hydraulic properties.
• Recharge in the Edwards Plateau is modest. • Pumping of groundwater in basin will result in proportional reduction
of flow in the Devils River. Impact is most pronounced during low flow conditions.
• Relatively modest pumping in upper Devils River watershed has shifted live water ~10 miles south.
Major Observations
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Acknowledgements
Regional reconnaissance water-resource evaluation – Six
Edwards Plateau counties & Del Rio: (2009-2010)
Devils River Watershed
Field studies – Coypu Foundation: (2012-2013)
Groundwater Model – Nueces River Authority: (2014-2015)
Surface-Water Model – Devils River Conservancy: (2016-2017)
Lower Pecos River/Devils River Watersheds
Field studies – Coypu Foundation: (2015-2016)
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Contact Information
Ronald T. Green, Ph.D., P.G.
Institute Scientist
Earth Science Section
Space Science and Engineering Division
Southwest Research Institute
6220 Culebra
San Antonio, Texas 78238
1.210.522.5305 (office)
1.210.316.9242 (cell)