June 14, 2016

DRAFT
Explanatory Report for Proposed Desired Future Conditions of
the Fresh Edwards (Balcones Fault Zone) Aquifer
in Northern Subdivision, Groundwater Management Area 10

Table of Contents
Section ...................................................................................................................................... Page
APPENDICES .............................................................................................................................. iv
FIGURES ........................................................................................................................................v
TABLES ........................................................................................................................................ vi
ABBREVIATIONS ..................................................................................................................... vii
1.

Description of Groundwater Management Area 10 and its Northern Subdivision .....1

2.

Aquifer Description ...........................................................................................................1

3.

Desired Future Conditions ...............................................................................................2

4.

Policy Justification ............................................................................................................4

5.

Technical Justification ......................................................................................................5

6.

Consideration of Designated Factors ...............................................................................8
6.1
Aquifer Uses or Conditions ..................................................................................8
6.1.1
Description of Factors in the Northern Subdivision, GMA 10 ........8
6.1.2
DFC Considerations...........................................................................10
6.2
Water-Supply Needs ...........................................................................................11
6.2.1
Description of Factors in the Northern Subdivision, GMA 10 ......11
6.2.2
DFC Considerations...........................................................................12
6.3
Water-Management Strategies ..............................................................................12
6.3.1
Description of Factors in the Northern Subdivision, GMA 10 ......12
6.3.2
DFC Considerations...........................................................................12
6.4
Hydrological Conditions ....................................................................................13
6.4.1
Description of Factors in the Northern Subdivision, GMA 10 ......13
6.4.1.1
Total Estimated Recoverable Storage ..............................................13
6.4.1.2
Average Annual Recharge ................................................................14
6.4.1.3
Inflows .................................................................................................16
6.4.1.4
Discharge ............................................................................................17
6.4.1.5
Other Environmental Impacts Including Springflow and
Groundwater/Surface Water Interaction ........................................18
6.4.2
DFC Considerations...........................................................................19

7.

Subsidence Impacts .........................................................................................................20

8.

Socioeconomic Impacts Reasonably Expected to Occur .............................................20
8.1
Description of Factors in Northern Subdivision, GMA 10 ..............................20
8.2
DFC Considerations.............................................................................................20

9.

Private Property Impacts ...............................................................................................20
ii

9.1
9.2

Description of Factors in Northern Subdivision, GMA 10 ..............................21
DFC Considerations.............................................................................................21

10.

Feasibility of Achieving the DFCs .................................................................................21

11.

Discussion of Other DFCs Considered ..........................................................................22

12.

Discussion of Other Recommendations .........................................................................2212.1 Advisory Committees ..........................................................................................2212.2 Public Comments ............................................................................................22

13.

Any Other Information Relevant to the Specific DFCs ..............................................22

14.

Provide a Balance Between the Highest Practicable Level of Groundwater
Production and the Conservation, Preservation, Protection, Recharging, andPrevention of Waste of Groundwater and Control of Subsidence in the Management
Area ...................................................................................................................................23

15.

References .........................................................................................................................23iii

List of Appendices
Appendix A—Proposed Desired Future Condition Resolution
Appendix B—Texas Water Development Board GAM Task xxxx (Revised): Total
Estimated Recoverable Storage for Aquifers in Groundwater Management Area 10
Appendix C—Socioeconomic Impacts Analyses for Regions K, L, and M

iv

FIGURES
Figure ....................................................................................................................................... Page
1

Map of the administrative boundaries of GMA10 designated for joint-planning purposes
and the GCDs in the GMA (From Texas Water Development Board website) ..................22

Map showing the extent and hydrologic zones of the Edwards (Balcones Fault Zone)
Aquifer in the Barton Springs segment in Hays and Travis counties in Groundwater
Management Area 10 (from Barton Springs/Edwards Aquifer Conservation District) ......3

3

Hydrograph of simulated springflow during the drought of record conditions withvariable pumping rates (0.7, 10, and 15 cfs). An increase of pumping from 0.7 to 10 cfs
results in a decline in springflow of the same amount. Figure from Hunt et al. (2011) ......7

4

Hydrograph of springflow from two simulations in which pumping that differs by 4 cfs
results in spring discharge that differs by 4 cfs (Hunt el al., 2011) .....................................7v

TABLES
Table ....................................................................................................................................... Page
1

Desired Future Conditions for the fresh Edwards (Balcones Fault Zone) Aquifer innorthern subdivision, Groundwater Management Area 10 ..................................................42

Calculations of drought Modeled Available Groundwater (MAG) by decade using waterbudget approach (Hunt et al., 2011).....................................................................................8

3

Type of use of the Edwards (Balcones Fault Zone) Aquifer in the Barton
Springs/Edwards Aquifer Conservation District for the years 2007–2010 (the Barton
Springs/Edwards Aquifer Conservation District Management Plan) (in gallons andacre-ft) ..................................................................................................................................94

Use of the Edwards (Balcones Fault Zone) Aquifer in the Barton Springs/Edwards
Aquifer Conservation District for the years 2007–2010 by county and aquifer
management zone (the Barton Springs/Edwards Aquifer Conservation District
Management Plan) (in gallons and acre-ft) ........................................................................10

5

Projected water-supply needs in the Barton Springs/Edwards Aquifer Conservation
District for the State Water Plan planning period 2010-2060............................................11

6

Total estimated recoverable storage for the Edwards (Balcones Fault Zone) Aquifer
within Barton Springs/Edwards Aquifer Conservation District in Groundwater
Management Area 10. Estimates are rounded within two significant numbers (Jones etal., 2013) ............................................................................................................................13

7

Total estimated recoverable storage for the Edwards (Balcones Fault Zone) Aquifer
within Hays and Travis counties in Groundwater Management Area 10. Estimates arerounded within two significant numbers (Jones et al., 2013) ............................................13

8

Summarized information needed for the Barton Springs/Edwards Aquifer Conservation
District’s groundwater management plan. All values are reported in acre-ft/yr. All
numbers are rounded to the nearest 1 acre-ft. Negative values indicate water isleaving the aquifer system using the parameters or boundaries listed in the table (Oliver,2008) ..................................................................................................................................15

9

Areal distribution of Barton Springs/Edwards Aquifer Conservation District by County.
Most of the Barton Springs/Edwards Aquifer Conservation District is in Travis and Hays
Counties, in sub-equal amounts; the Barton Springs/Edwards Aquifer Conservation
District comprises only a small part of any one county (Barton Springs/Edwards Aquifer
Conservation District Management Plan) (acre-ft/yr). ......................................................18

10

Projected annual surface-water supplies provided by county (Barton Springs/Edwards
Aquifer Conservation District Management Plan) (acre-ft/yr) ..........................................19vi

Abbreviations
DFC

Desired Future Conditions

GCD

Groundwater Conservation District

GMA

Groundwater Management AreaMAG

Modeled Available Groundwater

TWDB

Texas Water Development Board

vii

1.

Description of Groundwater Management Area 10 and its Northern Subdivision

Groundwater Conservation Districts (GCDs, or districts) were created, typically by legislative
action, to provide for the conservation, preservation, protection, recharging, and prevention ofwaste of the groundwater, and of groundwater reservoirs or their subdivisions, and to control
subsidence caused by withdrawal of water from those groundwater reservoirs or theirsubdivisions. The individual GCDs overlying each of the major aquifers or, for some aquifers,
their geographic subdivisions were aggregated by the Texas Water Development Board (TWDB)
acting under legislative mandate to form Groundwater Management Areas (GMAs). Each GMA
is charged with facilitating joint planning efforts for all aquifers wholly or partially within its
GMA boundaries that are considered relevant to joint regional planning. .
GMA 10 was created to coordinate planning primarily for the San Antonio and Barton Springs
segments of the Fresh Edwards (Balcones Fault Zone) Aquifer, but it also includes theunderlying down-dip Trinity Aquifer. Other aquifers in GMA 10 include the Leona Gravel, Buda
Limestone, Austin Chalk, and the Saline Edwards (Balcones Fault Zone) aquifers. The
jurisdiction of GMA 10 includes all or parts of Bexar, Caldwell, Comal, Guadalupe, Hays,
Kinney, Medina, Travis, and Uvalde counties (Figure 1). Groundwater Conservation Districts(GCD) in GMA 10 include Barton Springs/Edwards Aquifer Conservation District, Comal
Trinity GCD, Edwards Aquifer Authority, Kinney County GCD, Medina County GCD, Plum
Creek Conservation District, and Uvalde County Underground Water Conservation District(UWCD).
As mandated in Texas Water Code § 36.108, districts in a GMA are required to submit Desired
Future Conditions (DFCs) of the groundwater resources in their GMA to the executive
administrator of the TWDB, unless that aquifer is deemed to be non-relevant for the purposes ofjoint planning. According to Texas Water Code § 36.108 (d-3), the district representatives shallproduce a Desired Future Conditions Explanatory Report for the management area and submit to
the TWDB Board a copy of the Explanatory Report.
GMA 10 has designated the fresh Edwards (Balcones Fault Zone) Aquifer in the northern
subdivision of the GMA as a major aquifer for purposes of joint planning of. The extent of thisaquifer-based subdivision corresponds to the Barton Springs segment of the fresh Edwards(Balcones Fault Zone) Aquifer, a TWDB-designated major aquifer system in Texas. This
document is the Explanatory Report for the fresh Edwards (Balcones Fault Zone) Aquifer in thenorthern subdivision within GMA 10.
2.

Aquifer Description

For jurisdictional purposes, the northern subdivision of GMA 10 for the fresh Edwards (Balcones
Fault Zone) Aquifer is coincident with the Barton Springs segment of the Edwards (Balcones
Fault Zone) Aquifer (Figure 2). The boundaries of the northern subdivision, fresh Edwards(Balcones Fault Zone) Aquifer were determined using the Digital Geologic Atlas of Texas (U.S.
Geological Survey and Texas Water Development Board, 2006) and the GMA 10 boundary. The
northern subdivision of GMA 10 for the Edwards (Balcones Fault Zone) Aquifer is locatedwithin the Regional Water Planning Areas K and L, and is almost entirely within the Barton
1

Springs/Edwards Aquifer Conservation District. The geographic extent of the northern fresh
Edwards (Balcones Fault Zone) Aquifer in the Barton Springs/Edwards Aquifer Conservation
District is presented in Figure 3 (Barton Springs/Edwards Aquifer Conservation Districtwebsite). As illustrated, the jurisdictional area for this aquifer subdivision includes substantial
portions of Hays and Travis Counties and a small portion of Caldwell County.

Figure 1. Map of the administrative boundaries of GMA10 designated for joint-planningpurposes and the GCDs in the GMA (From Texas Water Development Board website)
3.

Desired Future Conditions

GMA10 incorporated information from the Barton Springs/Edwards Aquifer Conservation
District Management Plan and analyses from the TWDB during development of the proposed
DFCs. The DFCs in the first round of joint planning for the northern fresh Edwards (Balcones
Fault Zone) Aquifer in Hays and Travis counties in GMA10, were described in Resolution No.
2010-11 and adopted August 23, 2010, by the GCDs in GMA 10.
This subdivision of the aquifer had two DFCs in the first round:2(1) springflow at Barton Springs during average recharge conditions shall be no less than 49.7
cfs averaged over an 84 month (7-year) period; and(2) springflow of Barton Springs during extreme drought conditions, including those as severe asa recurrence of the 1950s drought of record, shall be no less than 6.5 cfs averaged on a monthly
basis.
The expression of the All Conditions DFC was initially adopted with the intent of providing alimit on the acceleration of the change from non-drought to drought conditions in the aquifer by
no more than one month. The expression of the Extreme Drought DFC was initially adopted topreserve a minimum amount of springflow during a recurrence of drought of record conditions.
The second round of DFCs was adopted at the GMA10 meeting on March 14, 2016. Resolution
No. 2016-xx is attached in Appendix A. GMA 10 has resolved to maintain the same DFCs in thesecond round as in the first round for this aquifer, and to continue to have two DFCs, related todifferent water level conditions in the aquifer (Table 1).

Figure 2. Map showing the extent and hydrologic zones of the Edwards (Balcones Fault Zone)
Aquifer in the Barton Springs segment in Hays and Travis counties in Groundwater Management
Area 10 (from Barton Springs/Edwards Aquifer Conservation District)3

Table 1. Desired Future Conditions for the fresh Edwards (Balcones Fault Zone) Aquifer innorthern subdivision, Groundwater Management Area 10
Date Desired Future
AquiferDesired Future Condition Summary
Condition Adopted
Springflow at Barton Springs during average
recharge conditions shall be no less than 49.7
cfs averaged over an 84 month (7-year)
Northern subdivision’s
fresh Edwards
period; and during extreme droughtFirst Round: 8/4/2010
conditions, including those as severe as a
(Balcones Fault Zone)
Aquiferrecurrence of the 1950s drought of record,
springflow of Barton Springs shall be no lessthan 6.5 cfs average on a monthly basis.
Springflow at Barton Springs during average
recharge conditions shall be no less than 49.7
Northern subdivision’s
cfs averaged over an 84 month (7-year)
Second Round:fresh Edwards
period; and springflow of Barton Springs
3/14/2016(Balcones Fault Zone) during extreme drought conditions, including
Aquiferthose as severe as a recurrence of the 1950s
drought of record, shall be no less than 6.5
cfs average on a monthly basis.
4.

Policy Justification

The DFCs in the northern subdivision of GMA 10 for the fresh Edwards (Balcones Fault Zone)
Aquifer in Hays and Travis Counties were adopted after considering the following factors
specified in Texas Water Code §36.108 (d):1.

Aquifer uses or conditions within the management area, including conditions that differ
substantially from one geographic area to another;a.
for each aquifer, subdivision of an aquifer, or geologic strata; andb.
for each geographic area overlying an aquifer

2.

The water supply needs and water management strategies included in the state water
plan;

3.

Hydrological conditions, including for each aquifer in the management area the total
estimated recoverable storage as provided by the executive administrator, and the averageannual recharge, inflows, and discharge;

4.

Other environmental impacts, including impacts on spring flow and other interactions
between groundwater and surface water;

5.

The impact on subsidence;

6.

Socioeconomic impacts reasonably expected to occur;

4

7.

The impact on the interests and rights in private property, including ownership and therights of management area landowners and their lessees and assigns in groundwater asrecognized under Section 36.002;

8.

The feasibility of achieving the DFC; and,9.

Any other information relevant to the specific DFCs.

GCDs are required to comply with all federal and state statutes and laws as a matter of law andpolicy. Two endangered species of salamander have habitat at the Barton Springs outlets of theaquifer; the preservation and health of that habitat depends on maintaining a certain amount ofspringflow, which is demonstrably affected by groundwater withdrawals by wells. Federal law
requires that positive steps be taken to have an approved habitat conservation plan that avoids
jeopardy (inability for the endangered species populations to recover) and to minimize take(harm to individuals in the population). The Barton Springs/Edwards Aquifer Conservation
District is in the process of finalizing a habitat conservation plan and acquiring a federal
Incidental Take Permit that, once issued, will legally allow District-permitted pumping from thefederal prohibition on take on an exception basis.
These factors and their relevance to establishing the DFCs are discussed in appropriate detail incorresponding subsections within Section 6 of this Explanatory Report.
5.

Technical Justification

Technical justification for the DFCsand the subsequent Modeled Available Groundwater in boththe first and second rounds of DFCs is summarized in a technical note by Hunt et al. (2011).
There are several numerical models of the Barton Springs segment of the Edwards Aquifer
available for simulating aquifer performance and spring discharge. The TWDB-approved
Groundwater Availability Model (GAM) for the Barton Springs segment of the Edwards(Balcones Fault Zone) Aquifer was developed by Scanlon et al. in 2001, which incorporated
concepts and modeling approaches by earlier researchers (Slade et al., 1986; Barrett andCharbeneau, 1996). This model was calibrated on data from 1989 to 1998 and did not include thehistoric drought-of-record that lasted from 1950 through 1956, when the estimated minimum
monthly discharge of 11 cfs occurred at Barton Springs. Since 2001, there have been several
modeling studies to re-calibrate the model to include the drought of record (Smith and Hunt,
2004; Winterle et al., 2009; Hutchison and Hill, 2011) for more confident use in aquifer
management and as a Groundwater Availability Model in joint planning. Each of these isdescribed below.
The first Groundwater Availability Model developed for the Barton Springs segment of the
Edwards (Balcones Fault Zone) Aquifer (Scanlon et al., 2001) was constructed to match waterlevels and spring flow from a period wetter than that of the 1950’s drought. Because the model
was calibrated to a relatively wet period, it overestimates spring flow and under-predicts waterlevel elevations compared with measurements when simulating the 1950s drought of record. The
model was recalibrated by Smith and Hunt (2004) so that simulated and measured spring-flow
and water-level data from the 1950s drought matched better. This recalibrated model was the5model that was used as the basis to determine the Modeled Available Groundwater during joint
planning in 2010 and during the current cycle of joint planning.
In 2008, the TWDB, in collaboration with the Barton Springs/Edwards Aquifer Conservation
District, contracted with Southwest Research Institute® to develop a groundwater flow model for
the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer utilizing the
MODFLOW-DCM code (Winterle et al., 2009). This model was calibrated based on data from1989 to 1998. This model is referred to as the Barton Springs segment of the Edwards (Balcones
Fault Zone) Aquifer MODFLOW-DCM model and is considered an alternative Groundwater
Availability Model for the Barton Springs segment of the Edwards (Balcones Fault Zone)
Aquifer. The 2001 Groundwater Availability Model (Scanlon et al., 2001) was more recently
recalibrated by Hutchison and Hill (2011) for the period January 1943 to December 2004. This
Groundwater Availability Model is also considered an alternative Groundwater Availability
Model.
Evaluation of the various model results during the drought of record indicated that water levels
and spring discharge are significantly impacted by 1950s drought conditions and increasinglevels of pumping. The models show nearly a one-to-one relationship between pumping
increases and spring discharge decreases during low-flow conditions. Hunt et al. (2011)
determined that for a total water budget of 11.7 cfs, springflow is simulated at 11 cfs forpumping of 0.7 cfs. This relationship, which has become a key tenet of this aquifer’s conceptualmodel and extreme-drought management, is graphically illustrated in Figures 3 and 4 (Hunt etal., 2011).
Since exempt uses are not metered, unlike permitted (non-exempt) uses, pumping data for
exempt wells are not available. It is necessary to account for pumping by exempt wells byalternate means when using the Modeled Available Groundwater to determine non-exempt
groundwater availability. To do this, the TWDB developed a standardized method for estimating
exempt use for domestic and livestock purposes in an area based on projected changes in
population and the ratio of domestic and livestock wells to the total number of wells. If a district
believes it has a more appropriate estimate of exempt pumping, it may submit the estimate, alongwith a description of how it was developed, to the TWDB for consideration. The Barton
Springs/Edwards Aquifer Conservation District developed a GIS-based analysis of exempt use
for its relatively small geographic area, for which the TWDB method was not readily applicable.
The TWDB accepted the District’s estimate of exempt use for this aquifer subdivision. Pumping
for exempt uses was estimated using the District’s alternative method to be 0.5 cfs (361 acreft/yr) in the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer (Hunt et al.
2011). Once established, the estimates of exempt pumping were subtracted from the total
pumping calculation to yield the portion of the estimated Modeled Available Groundwater foruses under permits.
Although the official and alternate Groundwater Availability Models (Scanlon et al., 2001; Smithand Hunt, 2004; Hutchison and Hill, 2011) were used to confirm a reasonable water budget for
the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer for the 1950s droughtof record, the Modeled Available Groundwater was actually based on this water budget rather
than model simulations.
6Figure 3. Hydrograph of simulated springflow during the drought of record conditions withvariable pumping rates (0.7, 10, and 15 cfs). An increase of pumping from 0.7 to 10 cfs results ina decline in springflow of the same amount. Figure from Hunt et al. (2011).

Figure 4. Hydrograph of springflow from two simulations in which pumping that differs by 4 cfs
results in spring discharge that differs by 4 cfs (Hunt el al., 2011)7

The water budget for the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer
for the 1950s drought of record is calculated by adding the lowest springflow during the droughtof record (11 cfs) to the estimated pumping during the drought of record (0.7 cfs) to provide thetotal discharge from the aquifer at that time (11.7 cfs). To arrive at the estimated Modeled
Available Groundwater, the one-to-one correspondence between pumping and spring discharge
is used to justify subtracting DFCs pring discharge from the water budget of 11.7 cfs, as shownin in Table 2. The DFC of 6.5 cfs of minimum spring discharge plus the estimated amount of
current exempt use of 0.5 cfs are subtracted from the total water budget calculated above to yield
an amount of 4.7 cfs available for non-exempt withdrawals during a recurrence of the droughtof-record (Hunt el al., 2011). Hunt et al. (2011) noted that the water-budget approach reflected inTable 2 is conservative, but prudent given current available data. The water budget, and hence
the Modeled Available Groundwater estimates, may be revisited should the influences of urban
recharge, the dynamic southern boundary, and climate change be better understood andquantified.
Table 2. Calculations of drought Modeled Available Groundwater (MAG) by decade using
water-budget approach (Hunt et al., 2011)
2010
2020
2030
2040
2050
2060
Total Water Budget in cfs
11.7
11.7
11.7
11.7
11.7
11.7
(acre-ft/yr)(8,470)(8,470)(8,470)(8,470) (8,470) (8,470)
Desired Future Condition
6.5
6.5
6.5
6.5
6.5
6.5
in cfs (acre-ft/yr)(4,705)(4,705)(4,705)(4,705) (4,705) (4,705)
Modeled Available
5.2
5.2
5.2
5.2
5.2
5.2
Groundwater in cfs (acre(3,765)(3,765)(3,765)(3,765) (3,765) (3,765)
ft/year)
Exempt Pumping in cfs
0.5
0.5
0.5
0.5
0.5
0.5
(acre-ft/yr)
(361)
(361)
(361)
(361)
(361)
(361)
Non-Exempt Pumping cfs
4.7
4.7
4.7
4.7
4.7
4.7
(acre-ft/yr)(3,402)(3,402)(3,402)(3,402) (3,402) (3,402)
6.

Consideration of Designated Factors

In accordance with Texas Water Code § 36.108 (d-3), the district representatives shall produce a
Desired Future Condition Explanatory Report. The report must include documentation of hownine factors identified in Texas Water Code §36.108(d) were considered prior to proposing a
DFC, and how the proposed DFC impacts each factor. The following sections of the Explanatory
Report summarize the information that the GCDs used in their deliberations and discussions.
6.1

Aquifer Uses or Conditions

6.1.1

Description of Factors in the Northern Subdivision, GMA 10

The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013).
Groundwater use within the Barton Springs/Edwards Aquifer Conservation District is comprised
primarily of pumpage from the freshwater Edwards (Balcones Fault Zone) Aquifer with a small
8but increasing component of pumpage from the Trinity Aquifer. An incidental amount ofgroundwater is derived from the Taylor and Austin Groups and more geologically recent alluvial
deposits. These withdrawals, however, are largely from exempt wells and are not permitted.
Given the current Barton Springs/Edwards Aquifer Conservation District management scheme of
conditional permitting and the drought restrictions and curtailment requirements associated withmandatory interruptible-supply for new pumpage authorizations for the freshwater Edwards(Balcones Fault Zone) Aquifer, it is likely that future groundwater production will trend more
towards pumpage from the Middle and Lower Trinity Aquifers and, eventually, the Saline
Edwards (Balcones Fault Zone) Aquifer.
Data presented in Table 3 are a compilation of the Barton Springs/Edwards Aquifer
Conservation District monthly meter readings reported by the Barton Springs/Edwards Aquifer
Conservation District permittees and are therefore, a more accurate representation of actual
District groundwater use than estimates provided by the TWDB
(http://www.twdb.texas.gov/waterplanning/waterusesurvey/historical-pumpage.asp). The reported use
data are organized by Major Aquifer and Water Use Type (using the Barton Springs/Edwards
Aquifer Conservation District’s water-use type designations) in Table 3 and by County andManagement Zone in Table 4. These data include neither Exempt Use, which is primarily fromthe Edwards (Balcones Fault Zone) Aquifer and is estimated to be about 105,000,000 gallons(322.2 acre-ft) annually, nor Non-exempt Domestic Use under the District’s Non-exempt
Domestic Use general permit, which is also primarily from the Edwards (Balcones Fault Zone)
Aquifer and is estimated to be about 20,600,000 gallons (63.2 acre-ft) annually.
Table 3. Type of use of the Edwards (Balcones Fault Zone) Aquifer in the Barton
Springs/Edwards Aquifer Conservation District for the years 2007–2010 (the Barton
Springs/Edwards Aquifer Conservation District Management Plan) (in gallons and acre-ft)
Public Water System Commercial
Irrigation
Industrial
Totals1,237,098,520
9,157,492
90,327,219
145,977,492
1,482,560,723
2007
3,797
28
277
448
4,550
1,635,001,051
8,129,101
95,486,300
223,125,231
1,961,741,683
2008
5,018
25
293
685
6,020
1,334,838,604
6,858,106
81,294,200
174,509,965
1,597,500,875
2009
4,096
21
249
536
4,903
1,398,211,160
8,565,229
91,338,590
240,230,719
1,738,345,698
2010
4,291
26
280
737
5,335
1,647,368,453
8,791,848
104,405,640
261,507,704
2,022,073,645
2011
5,056
27
320
803
6,206

9

Table 4. Use of the Edwards (Balcones Fault Zone) Aquifer in the Barton Springs/Edwards
Aquifer Conservation District for the years 2007–2010 by county and aquifer management zone
(the Barton Springs/Edwards Aquifer Conservation District Management Plan) (in gallons andacre-ft)
Trinity Aquifers
Edwards (Balcones Fault Zone)
Aquifer
TotalsFreshwater
SalineMiddle
Lower
Zones
Zone
Trinity
Trinity
Hays County
862,705,785
00
2007
862,705,785
2,648
0
0
2,648
1,130,608,005
00
2008
1,130,608,005
3,470
0
0
3,470
892,759,134
00
2009
892,759,134
2,740
0
0
2,740
1,079,339,042
0
0
2010
1,079,339,042
3,312
0
0
3,312
1,171,615,241
0
8,937,000
2011
1,180,552,241
3,596
0
27
3,623
Travis County
619,854,938
0
129,680
3,508,300
2007
623,492,918
1,902
0
0.4
11
1,913
831,133,678
0
111,640
9,107,100
2008
840,352,418
2,551
0
0.3
28
2,579
704,741,741
0
139,5105,801,300
2009
710,682,551
2,163
0
0.4
18
2,181
659,006,656
0
81,5206,449,900
2010
665,538,076
2,022
0
0.3
20
2,042
850,458,404
0
1,502,910
5,694,600
2011
857,655,914
2,610
0
5
17
2,632
6.1.2

DFC Considerations

The dominant use of the aquifer by pumping is public water supply, and the sustainability of that
supply, especially for users who have no alternative supply physically or economically available
and/or who are in vulnerable locations, must be protected to the extent feasible (Texas Water
Code §36). The primary concern with sustainability of this karst aquifer groundwater supply isdrought, notably extreme drought that stresses the entire aquifer, but especially the western
portion of the northern subdivision. Both DFCs support and are, in fact, linchpins of a droughtmanagement program to promote long-term sustainability of both springflow and water supplies.
Additional firm-yield water supplies must be provided from other sources, while conditionalpermitted withdrawals from the aquifer are only available on an interruptible basis.
The All Conditions DFC is expressly designed to postpone as long as possible permitted
pumping curtailments that would be triggered by a District-declared drought. Postponement
would be effected by delaying, to an acceptable degree, the elevation of a designation of droughtfrom a non-drought designation that is attendant with pumping. The Extreme Drought DFC is10designed to serve the mutual management objectives of: 1) preserving water supplies, especiallyin the more vulnerable western portions of the District and 2) minimizing the amount of take andavoiding jeopardy of the two endangered species that have the natural outlets of the aquifer assole habitat. The DFC allows an amount of groundwater use that would produce a lower
springflow than the historically low springflow during the 1950s drought of record, but still
maintain acceptable minimum spring discharge levels.
6.2

Water-Supply Needs

6.2.1

Description of Factors in the Northern Subdivision, GMA 10

The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013). For
estimating projected water supply needs (i.e., water demand vs. supply) the Barton
Springs/Edwards Aquifer Conservation District used data extracted from the State Water Planand provided by the TWDB. The TWDB provides water-supply needs estimates by decade as well
as by county. The decadal estimates for 2020 are used to approximate demand for the year 2022,
the final year of the Barton Springs/Edwards Aquifer Conservation District Management Plan
(Barton Springs/Edwards Aquifer Conservation District, 2013). A summary of the projectedwater-supply needs is provided in the Table 5 by decade in acre-ft/yr.
Table 5. Projected water-supply needs in the Barton Springs/Edwards Aquifer Conservation
District for the State Water Plan planning period 2010-2060
2010
2020
2030
2040
2050
2060
Travis-3,538-11,053-14,067-18,134-55,470-92,045
Hays-1,674-5,738-11,146-18,871-28,549-36,273
Caldwell-210-892-1,910-3,054-4,300-5,694
Totals-5,422-17,683-27,123-40,059-88,319-134,012
The projections in Table 5 show that for the State Water Plan planning period (2010-2060), there
is a progressively increasing water-supply deficit, increasing from 5,422 acre-ft in 2020 up to134,012 acre-ft in 2060. These water-supply needs in the Barton Springs/Edwards Aquifer
Conservation District arise primarily from and are dominated by the burgeoning growth on thesouthern fringe of the Austin metropolitan area, and also in the gradual diminution of thesurface-water supplies, as reservoir capacity decreases with time. As in prior plans, some of thewater-demand deficits in the Barton Springs/Edwards Aquifer Conservation District area in theout-years (the later years in the planning period) include numerous contractual shortages. These
contractual shortages will be addressed on an ad-hoc basis, through the renewal and expansion ofcontracts with wholesale water suppliers and the contractual reallocation of existing supplies inorder to address the projected water demands for these and other area water-user groups. But
even so, it is projected that there will be unmet needs in the Barton Springs/Edwards Aquifer
Conservation District, especially under drought-of-record conditions and in the out-years.

116.2.2DFC Considerations

The population growth of the Austin-San Marcos metropolitan area is creating demand for
additional water supplies from all sources, both within and outside of the northern subdivision.
The DFCs maximize the amount of water that can be provided during non-drought periods that is
consistent with the implementation of a drought management program that protects the supply
for existing uses during drought, especially extreme drought. The drought program response to
the DFCs indexes the amount of aquifer water available to meet the needs with the severity ofdrought.
6.3

Water-Management Strategies

6.3.1

Description of Factors in Northern Subdivision, GMA 10

The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013), the2011 Regions K and L Water Planning Group Plans, and the 2012 State Water Plan, which relieson the Water Planning Group Plans.
Water management strategies for the northern subdivision included in the regional and statewater plans are diverse, arising from the increasing deficit in supply relative to the burgeoning
demand in the northern subdivision. Strategies include increased public/municipal water
conservation, drought management, use/transfer of available or re-allocated surface watersupplies, purchase of water from wholesale water providers, purchase of Carrizo-Wilcox water,development of the saline zone of the Edwards (Balcones Fault Zone) water, development of the
Trinity Aquifer, Edwards/Middle Trinity aquifer storage and recovery, and saline Edwards
aquifer storage and recovery. Perhaps even more on point here is that increased use of the fresh
Edwards (Balcones Fault Zone) Aquifer water is not included as a strategy, as it is widely
recognized as fully subscribed. None of the Water User Groups in the northern subdivision
include allocation or transfer of their existing supplies.
6.3.2

DFC Considerations

The DFCs under consideration here are specific to the freshwater portion of the Edwards(Balcones Fault Zone) Aquifer in the northern subdivision of GMA 10. The saline portion ofthat aquifer has a different DFC and is the subject of a separate groundwater management zone,
designed to promote utilization of the saline resource via desalination and/or as host for aquifer
storage and recovery facilities. The All-Conditions DFC, by design, accommodates a certain
amount of use for Aquifer Storage and Recovery (ASR) during non-drought periods. Both
DFCs, as described above, underpin an aquifer-responsive drought management program thatencourages both full-time water conservation and further temporary curtailments in pumping
during drought periods that increase with drought severity. These curtailments in pumping also
promote the use of alternative water supplies consistent with the water management strategies.

12

6.4

Hydrological Conditions

6.4.1

Description of Factors in Northern Subdivision, GMA 10

6.4.1.1 Total Estimated Recoverable Storage
Texas statute requires that the total estimated recoverable storage of relevant aquifers be
determined (Texas Water Code § 36.108) by the TWDB. Texas Administrative Code Rule§356.10 (Texas Administrative Code, 2011) defines the total estimated recoverable storage as theestimated amount of groundwater within an aquifer that accounts for recovery scenarios that
range between 25 percent and 75 percent of the porosity-adjusted aquifer volume.
Total estimated recoverable storage values may include a mixture of water-quality types,
including fresh, brackish, and saline groundwater, because the available data and the existing
Groundwater Availability Models do not permit the differentiation between different waterquality types. The total estimated recoverable storage values do not take into account the effectsof land surface subsidence, degradation of water quality, or any changes to surfacewater/groundwater interaction that may occur due to pumping.
The total recoverable storage estimated for the Edwards (Balcones Fault Zone) Aquifer within
the Barton Springs/Edwards Aquifer Conservation District in Groundwater Management Area 10
is listed in Table 6 (Jones et al., 2013). The total recoverable storage estimated for the Edwards(Balcones Fault Zone) Aquifer within Hays and Travis counties in GMA 10 is listed in Table 7(Jones et al., 2013). The total recoverable storage estimated for Hays County includes
groundwater in the San Antonio segment as well as the Barton Springs segment of the Edwards
Aquifer, so not all of the water shown in Table 7 is in the northern subdivision of GMA 10.
Table 6. Total estimated recoverable storage for the Edwards (Balcones Fault Zone) Aquifer
within Barton Springs/Edwards Aquifer Conservation District in Groundwater Management
Area 10. Estimates are rounded within two significant numbers (Jones et al., 2013).
Total Storage
25 percent of Total Storage
75 percent of Total Storage(acre-ft)(acre-ft)(acre-ft)
130,000
32,50097,500
Table 7. Total estimated recoverable storage for the Edwards (Balcones Fault Zone) Aquifer
within Hays and Travis counties in Groundwater Management Area 10. Estimates are roundedwithin two significant numbers (Jones et al., 2013).
25 percent of
Total Storage
75 percent of Total Storage
CountyTotal Storage(acre-ft)(acre-ft)(acre-ft)
Hays200,000
50,000150,000
Travis69,00017,25051,75013

6.4.1.2 Average Annual Recharge
The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013). For
the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer, the long-term meansurface recharge should approximately equal the mean natural (i.e., with no well withdrawals)
spring discharge, which is reported to be about 53 cfs at Barton Springs (Slade et al., 1986;
Scanlon et al., 2001). Since the 1950s drought, the mean natural springflow at Barton Springs
has been higher, about 62 cfs (Hunt et al., 2012; Johns, 2016). The distribution and volume ofthis recharge have been modeled multiple times. Scanlon et al. (2001) estimated average
recharge at 55 cfs (39,844 acre-ft/yr) in the initial groundwater availability model of the Barton
Springs segment for the TWDB. A later report by the TWDB, GAM Run 08-37 (Oliver, 2008),
summarized the estimated amount of recharge from precipitation, the amount of springdischarge, and the amount of flow into and out of the Barton Springs/Edwards Aquifer
Conservation District for steady-state conditions in 1989 (Table 8). As illustrated in Table 7,
annual recharge from precipitation for the modeling was 42,858 acre-ft.
The majority (as much as 85 percent) of recharge to the aquifer is derived from streams
originating on the contributing zone, located up gradient and to the west of the recharge zone.
Water flowing onto the recharge zone sinks into numerous caves, sinkholes, and fractures along
its six major, ephemeral losing streams. The remaining recharge (15 percent) occurs in the
upland areas of the recharge zone (Slade et al., 1986). Current studies indicate that uplandrecharge may constitute a larger fraction (up to 30 percent) of recharge (Hauwert, 2009;
Hauwert, 2011); Slade (2014) more recently calculated the upland recharge at 25 percent of thetotal. Studies have shown that recharge is highly variable in space and time and is focused within
discrete features (Smith et al., 2011). For example, Onion Creek is the largest contributor ofrecharge (34 percent) with maximum recharge rates up to 160 cfs (Slade et al., 1986; Fieseler,
1998). Antioch Cave is located within Onion Creek and is the largest-capacity recharge feature
with an average recharge of 46 cfs and a maximum of 95 cfs during one 100-day study (Fieseler,
1998). Recent work at Antioch Cave has also documented greater than 100 cfs of recharge
entering the aquifer through the entrance to Antioch Cave (Smith et al., 2011). Dye-tracing
studies have shown that some of this water flows directly and very rapidly to Barton Springs
with an unknown percentage contributing to storage.

14

Table 8. Summarized information needed for the Barton Springs/Edwards Aquifer Conservation
District’s groundwater management plan. All values are reported in acre-ft/yr. All numbers arerounded to the nearest 1 acre-ft. Negative values indicate water is leaving the aquifer systemusing the parameters or boundaries listed in the table (Oliver, 2008).
Barton Springs/Edwards Aquifer Conservation
Aquifer or confining
Results
District Management Plan Requirement
unit
Estimated annual amount of recharge from
Edwards and associated42,858a
precipitation to the district
limestones
Estimated annual volume of water that discharges
Edwards and associated-39,723from the aquifer to springs and any surface water bodylimestones
including lakes, streams, and rivers
Estimated annual volume of flow into the district
Edwards and associated
3,191bwithin each aquifer in the district
limestones
Estimated annual volume of flow out of the district
Edwards and associated-2,651b
within each aquifer in the district
limestones
Estimated net annual volume of flow between each
Edwards into Trinity0caquifer in the districtaRecharge value includes concentrated infiltration of water from stream channels. Scanlon and
et al. (2001) estimated that approximately 15 percent of recharge in the model was due to diffuse
inter-stream recharge, or direct infiltration of precipitation, which equates to approximately
6,429 acre-ft/yr.
b
The orientation of the model cells and the political jurisdictional boundaries of the district do
not align perfectly, therefore even though the district is larger than the model boundaries, someflow into and out of the district is reported due to the method of data extraction from the model.
c
The Groundwater Availability Model (cite model) does not consider flow into or out of the
Edwards (Balcones Fault Zone) Aquifer from other formations.
Groundwater divides delineate the boundaries of aquifer systems and influence not only the local
aquifer hydrodynamics, but also the groundwater budget (recharge and discharge). The
groundwater divide separating the San Antonio and Barton Springs segments of the Edwards(Balcones Fault Zone) Aquifer has historically been drawn along topographic or surface water
divides between the Blanco River and Onion Creek in the recharge zone, and alongpotentiometric highs in the confined zone between the cities of Kyle and Buda in Hays County.
Recent studies reveal that during wet conditions the groundwater divide is located generally
along Onion Creek in the recharge zone, extending easterly along a potentiometric ridge between
the cities of Kyle and Buda toward the saline-zone boundary (Hunt et al. 2006). During dry
conditions, Hunt et al. (2006) posit that the hydrologic divide migrates south and is located along
the Blanco River in the recharge zone, extending southeasterly to San Marcos Springs (Johnson
et al., 2011). Thus, the groundwater divide is a hydrodynamic feature dependent upon thehydrologic conditions (wet versus dry) and the resulting hydraulic heads between Onion Creek
and the Blanco River. Under extreme drought conditions, some groundwater flow from the west
may bypass San Marcos Springs and continue toward Barton Springs (Land et al., 2011) andsome surface water from the Blanco River may recharge the Barton Springs segment rather thanthe San Antonio segment (Smith et al., 2012).

15

6.4.1.3 Inflows
The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013). The
amount of cross-formational inflow (subsurface recharge) occurring through adjacent aquifers
into the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer is unknown,
although it is thought to be relatively small on the basis of water-budget analysis for surface
recharge and discharge (Slade et al., 1985). Recent studies by the Barton Springs/Edwards
Aquifer Conservation District and others have shown the potential for cross-formational flow
both to and from the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer.
Sources of cross-formational flow are discussed below and include the saline-water zone, San
Antonio segment of the Edwards (Balcones Fault Zone) Aquifer, the Trinity Aquifer, and urban
recharge.
Leakage from the saline-water zone into the freshwater zone is probably minimal, althoughleakage appears to influence water chemistry at Barton Springs during low-flow conditions(Senger and Kreitler, 1984; Slade et al., 1986). Recent studies indicate that the fresh-saline zone
interface may be relatively stable over time (Lambert et al., 2010; Brakefield, 2015). On thebasis of a geochemical evaluation, Hauwert et al. (2004) state that the saline-water zone
contribution could be as high as 3 percent for Old Mill Spring and 0.5 percent for Main and Eliza
Springs under low-flow conditions of 17cfs (combined) Barton Springs flow. These estimates
were independently recalculated and corroborated by Johns (2006) and are similar to the resultsof Garner and Mahler (2007). Under normal flow conditions contribution from the saline-waterzone would be smaller. Massei et al. (2007) noted that specific conductance of Barton Springs
increased 20 percent under the 2000 drought condition, probably from saline-water zone
contribution.
Subsurface flow into the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer
from the adjacent San Antonio segment located to the southwest is limited when compared withsurface recharge (Slade et al., 1985). Hauwert et al. (2004) indicated that flow across thesouthern boundary of the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer
is probably insignificant under normal conditions. Recent studies have documented that thesouthern boundary of the Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer
is hydrodynamic in nature and fluctuates between Onion Creek and the Blanco River.
Accordingly, groundwater from the recharge zone of the San Antonio segment of the Edwards(Balcones Fault Zone) Aquifer is flowing into the Barton Springs segment during drought
conditions (Smith et al,, 2012). Results of recent dye-trace studies indicate that under certain
high-flow conditions water recharging along Onion Creek flows from the Barton Springs
segment of the Edwards (Balcones Fault Zone) Aquifer to San Marcos Springs (Hunt et al.,2006).Under moderate drought conditions, water recharged along the Blanco River can flow toboth San Marcos and Barton springs (Smith et al., 2012). Under extreme drought conditions, it
has been estimated that up to 5 cfs of groundwater flow bypasses (underflows) San Marcos
Springs and flows toward Barton Springs (Land et al., 2011).
Changes in land use influence the inflows of aquifers systems. Recent studies have shown thaturbanization may increase recharge to the Edwards (Balcones Fault Zone) Aquifer (Sharp, 2010;16

Sharp et al., 2009). Sources of the increase in recharge include leaking infrastructure such aspressurized potable water lines, wastewater from both collector lines and septic tank drainfields,
and stormwater in infiltration basins in the recharge zone. Recharge in urban environments isincreased from the return flows of irrigation practices (e.g. lawn watering) and when impervious
cover decreases evapotranspiration (Sharp, 2010; Sharp et al., 2009).
6.4.1.4 Discharge
The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013). The
largest natural discharge point of the Barton Springs segment of the Edwards (Balcones Fault
Zone) Aquifer is Barton Springs, the fourth largest spring in Texas. Barton Springs consist offour major outlets: Main, Eliza, Old Mill, and Upper. Main Spring is the largest and discharges
directly into Barton Springs Pool. Springflow at Barton Springs is determined and reported by
the U.S. Geological Survey. Discharge reported for Barton Springs is based on a rating-curve
correlation between water levels in the Barton Well (State Well Number 5842903) and physicalflow measurements from Main, Eliza, and Old Mill. Flow from Upper Barton Springs, which islocated about 400 feet upstream of the pool, is not included in the reported discharge, andbypasses the pool. Upper Barton Springs is characterized as an “overflow” spring and only flows
when the total discharge at Barton Springs exceeds about 40 cfs (Hauwert et al., 2004).
Barton Springs has a long record of continuous discharge data beginning in 1917. Monthly meandata are available from 1917 to 1978 (Slade et al., 1986), and daily mean discharge data are
available thereafter. The long-term average springflow at Barton Springs is 53 cfs based on datafrom 1917 to 1995 and is a widely reported value (Slade et al., 1986; Scanlon et al., 2001;
Hauwert et al., 2004). More recent studies indicate that average springflows after the 1950s
drought are higher, about 62 cfs (Hunt et al., 2012; Johns, 2016). The maximum and minimum
measured discharges are 166 and 9.6 cfs, respectively. The lowest measured spring discharge
value occurred on March 26, 1956 during the 1950s drought (Slade et al., 1986). Low-flow
periods are defined as discharge below 35 cfs, moderate-flow conditions occur between 35 and70 cfs, and high-flow conditions correspond to flows greater than 70 cfs (Hauwert et al., 2004).
Mahler et al. (2006) define low flow as below 40 cfs. A peak in the daily average flow occurs inJune following the average peak rainfall in May.
Barton Springs discharge is typical of a spring in a karst system that responds dynamically torecharge events and integrates conduit, fracture, and matrix flow. Springflow recessions anddischarge rates are in large part determined by pre-existing conditions, the magnitude ofrecharge, and location of recharge. Massei et al. (2007) identify several source-water types
contributing to the specific conductivity measured in Barton Springs. Sources include matrix,
surface water, saline water, and other unidentified sources. Their relative contributions are
dependent upon aquifer response to climatic and hydrologic conditions. Generally speaking;however, base springflow during periods of drought is sustained by the discharge of the matrixflow system into the conduit system (White, 1988; Mahler et al., 2006).
The Barton Springs segment of the Edwards (Balcones Fault Zone) Aquifer contains othersmaller springs. Cold Springs discharges directly into the Colorado River and is partially17

submerged by Lady Bird Lake. There are very few discharge data for Cold Springs, but its
discharge is estimated to be about 5 percent of Barton Springs discharge (Scanlon et al., 2001).
Similarly, Slade (2014) indicates the long-term average discharge of Cold Springs is about 5.5
cfs. A small spring named Rollingwood Spring, near Cold Springs, discharges into the Colorado
River at a rate of about 0.02 to 0.06 cfs. Backdoor Spring is a small, perched spring located on
Barton Creek and has discharge of about 0.02 cfs. Bee Springs is a small, perched spring andseep horizon discharging along Bee Creek and into Lake Austin and discharges about 0.2 to 0.6
cfs (Hauwert et al., 2004).
GAM Run 08-37 (Oliver, 2008) states that discharge from Barton and Cold springs was 39,723
acre-ft/yr (54.9 cfs) under steady-state conditions in 1989. The amount of water withdrawn fromwells was 3,135 acre-ft (4.3 cfs) at that time (Table 7).
6.4.1.5 Other Environmental Impacts Including Springflow and Groundwater/Surface-Water
Interaction
The discussion in this section is taken from the Barton Springs/Edwards Aquifer Conservation
District Management Plan (Barton Springs/Edwards Aquifer Conservation District, 2013). The
surface-water supply in the Barton Springs/Edwards Aquifer Conservation District is provided
primarily by run-of-river diversions and especially by reservoirs in the Colorado River basin.
The southeastern-most part of the Barton Springs/Edwards Aquifer Conservation District inHays County and Caldwell County is supplied by the Guadalupe-Blanco River system,
especially water from main-stem reservoirs like Canyon Lake. Most of this Guadalupe-Blancowater is conveyed to some users in the Barton Springs/Edwards Aquifer Conservation District by
the Hays County Pipeline.
Projected water-supply data have been extracted from the 2012 State Water Plan database andprovided by the TWDB at the county level. The projections are estimated using an apportioning
multiplier derived from the ratio of the land area of Barton Springs/Edwards Aquifer
Conservation District in the county relative to the entire county area. The apportioning multiplier
was used for all water-user groups except for public-water supplies (i.e. municipalities, watersupply corporations, and utility districts). The derivation of these apportioning multipliers isshown in Table 9.
Table 9. Areal distribution of Barton Springs/Edwards Aquifer Conservation District by County.
Most of the Barton Springs/Edwards Aquifer Conservation District is in Travis and Hays
Counties, in sub-equal amounts; the Barton Springs/Edwards Aquifer Conservation District
comprises only a small part of any one county (Barton Springs/Edwards Aquifer Conservation
District Management Plan) (acre-ft/yr).
CountyTotal Acres inAcres in
Percent in Co.
Apportioning
CountyDistrict
Multiplier
Travis656,348
75,377
48%
11.5%
Hays
433,248
66,74842%
15.4%
Caldwell
350,498
15,82310%
4.5%
Totals1,440,094
157,948
100%
100%

18

The total annual projected surface-water supply in the counties of the Barton Springs/Edwards
Aquifer Conservation District is estimated to be 293,027acre-ft in 2020 (2020 is the closest
decadal estimate to 2022, the final year of the Barton Springs/Edwards Aquifer Conservation
District Management Plan). These supplies refer to the firm-yield supplies from surface-water
sources during a recurrence of the drought of record. For comparison purposes, the projectedsurface-water supplies from the three primary counties comprising the Barton Springs/Edwards
Aquifer Conservation District (Bastrop was excluded because its area has been de-annexed since
the previous management plan was approved) are provided in Table 10 by decade in acre-ft.
Table 10. Projected annual surface-water supplies provided by county (Barton Springs/Edwards
Aquifer Conservation District Management Plan) (acre-ft/yr)
2010
2020
2030
2040
2050
2060
Travis287,687
286,132
277,118
263,891
254,337
244,503
Hays
4,120
4,680
4,680
4,680
4,680
4,680
Caldwell
195
195
195
195
195
195
Total
294,012
293,027
284,023
270,806
261,262
251,438
6.4.2

DFC Considerations

The DFCs are proposed on the basis that the aquifer is hydrologically a classic karst aquifer, withtemporally variable inflows from various recharge sources and a major natural discharge point at
Barton Springs that is also temporally variable with aquifer conditions. This hydrologic
condition denotes that it is highly vulnerable to drought, and water supplies are substantiallyadversely affected by drought. Additionally, the geologic strata that form the aquifer dip
regionally to the southeast, such that both the saturated thickness in the unconfined zone and theartesian pressure head in the confined zone are larger to the southeast. However, while faulted,
the aquifer is well-integrated hydrologically and has a common potentiometric surface
throughout the subdivision.
The springflow at Barton Springs is directly and essentially solely related to the elevation of thepotentiometric surface, regardless of the different thickness and depth of groundwater that exists
in various parts of the subdivision or other hydrologic conditions, except as they affect thepotentiometric surface. So the proposed DFCs relate to the elevations of the potentiometricsurface corresponding to two different conditions, regardless of the volumes of water in storageat any one location. The elevation of water near the drought/non-drought boundary combineswith the geometric configuration of the aquifer host at that elevation and the rate of aquifer
discharge, including the amount of pumping, to control the rate of acceleration into drought from
non-drought conditions.
Preservation of a minimal springflow at Barton Springs and a related dissolved oxygen
concentration that will sustain the endangered species at the spring outlets is mandated by federallaw. The Extreme Drought DFC is expressly designed to provide that level of environmental andecological protection.

19

7.

Subsidence Impacts

Subsidence has historically not been an issue with the Edwards (Balcones Fault Zone) Aquifer in
GMA10. The aquifer matrix in the northern subdivision is well-indurated and the amount ofpumping does not create compaction of the host rock and/or subsidence of the land surface.
Similarly, when the aquifer recharges the same volume of water is able to be stored as existed
before an equivalent volume was withdrawn. Hence, the proposed DFCs are not affected by anddo not affect land-surface subsidence or compaction of any aquifer.
8.

Socioeconomic Impacts Reasonably Expected to Occur

8.1

Description of Factors in Northern Subdivision, GMA 10

Administrative rules require that regional water planning groups evaluate the impacts of not
meeting water needs as part of the regional water planning process. The executive administrator
shall provide available technical assistance to the regional water planning groups, upon request,
on water supply and demand analysis, including methods to evaluate the social and economic
impacts of not meeting needs [§357.7 (4)]. Staff of the TWDB’s Water Resources Planning
Division designed and conducted a report in support of the South Central Texas Regional Water
Planning Group (Region L) and also the Lower Colorado Regional Water Planning Group(Region K). The report “Socioeconomic Impacts of Projected Water Shortages for the South
Central Texas Regional Water Planning Area (Region L)” was prepared by the TWDB in supportof the 2011 South Central Texas Regional Water Plan and is illustrative of these types ofanalyses.
The report on socioeconomic impacts summarizes the results of the TWDB analysis anddiscusses the methodology used to generate the results for Region L. The socioeconomic impact
report for Water Planning Group L is included in Appendix C as an example. These reports aresupportive of a cost-benefit assessment of the water management strategies and thesocioeconomic impact of not promulgating those strategies.
The maintenance of the natural discharge of the Aquifer at iconic Barton Springs supports
recreation and tourism that is a recognized socioeconomic engine for central Austin.
8.2

DFC Considerations

Because none of the water management strategies involve changes in the current use of the
freshwater portion of the Edwards (Balcones Fault Zone) Aquifer in the northern subdivision of
GMA 10, as described in Section 6.3, the proposed DFCs do not have a differentialsocioeconomic impact. They are supportive of the status quo in this regard, which is considered
positive.
9.

Private Property Impacts

20

9.1

Description of Factors in Northern Subdivision, GMA 10

The interests and rights in private property, including ownership and the rights of GMA10
landowners and their lessees and assigns in groundwater, are recognized under Texas Water
Code Section 36.002. The legislature recognized that a landowner owns the groundwater below
the surface of the landowner's land as real property. Joint planning must take into account the
impacts on those rights in the process of establishing DFCs, including the property rights of both
existing and future groundwater users. Nothing should be construed as granting the authority todeprive or divest a landowner, including a landowner's lessees, heirs, or assigns, of thegroundwater ownership and rights described by this section. At the same time, the law holds thatno landowner is guaranteed a certain amount of such groundwater below the surface of his/herland.
Texas Water Code Section 36.002 does not: (1) prohibit a district from limiting or prohibiting
the drilling of a well by a landowner for failure or inability to comply with minimum wellspacing or tract size requirements adopted by the district; (2) affect the ability of a district toregulate groundwater production as authorized under Section 36.113, 36.116, or 36.122 orotherwise under this chapter or a special law governing a district; or (3) require that a rule
adopted by a district allocate to each landowner a proportionate share of available groundwaterfor production from the aquifer based on the number of acres owned by the landowner.
9.2

DFC Considerations

The DFCs are designed to protect the sustained use of the aquifer as a water supply for all users
in aggregate and as ecological habitat for protected species. Neither DFC prevents use of thegroundwater by landowners either now or in the future, although ultimately total use of thegroundwater in the aquifer is restricted by the aquifer condition, and that may affect the amountof water that any one landowner could use, either at particular times or all of the time.
10.

Feasibility of Achieving the DFCs

The feasibility of achieving a DFC directly relates to the ability of the Barton Springs/Edwards
Aquifer Conservation District to manage the Barton Springs segment of the Edwards (Balcones
Fault Zone) Aquifer to achieve the DFCs, including promulgating and enforcing rules and otherboard actions that support the DFCs. The feasibility of achieving this goal is limited by (1) the
finite nature of the resource and how it responds to drought; (2) the pressures placed on thisresource by the high level of economic and population growth within the area served by thisresource; and (3) how the endangered species habitat at Barton Springs is protected in response
to federal statute. Texas State law provides Groundwater Conservation Districts with the
responsibility and authority to conserve, preserve, and protect these resources and to ensure forthe recharge and prevention of waste of groundwater and control of subsidence in the
management area; State law also provides that GMAs assist in that endeavor by joint regional
planning that balances aquifer protection and highest practicable production of groundwater. The
feasibility of achieving these goals could be altered if state law is revised or interpreted
differently than is currently the case.

21

The caveats above notwithstanding, the current regulatory program of the Barton
Springs/Edwards Aquifer Conservation District is designed to achieve the proposed DFCs, andthere is no reason to consider that it is not feasible to achieve the DFCs.
11.

Discussion of Other DFCs ConsideredNo other DFCof the fresh Edwards (Balcones Fault Zone) Aquifer in the GMA’s northern
subdivision was considered.
12.

Discussion of Other Recommendations

12.1

Advisory Committees

An Advisory Committee for GMA10 has not been established.
12.2

Public Comments

Each GCD must hold a public meeting within 90 days after the GMA approves its DFCs. During
this meeting, the GCD needs to document stakeholder input. This input is to be submitted by areport from the GCD to the GMA within 90 days after the GMA approves its DFC.
GCD sin GMA 10 have not yet approved its second round of DFCs. The GCD shave not yet held
public meetings to gather public comment on the DFCs. No public comments have yet beenoffered regarding the the northern fresh Edwards (Balcones Fault Zone) Aquifer.
13.

Any Other Information Relevant to the Specific DFCs

As the down-dip Trinity Aquifer is increasingly used as a water supply in GMA 10 in lieu of themore restricted Edwards (Balcones Fault Zone) Aquifer, additional information on how its
groundwater relates to the Edwards (Balcones Fault Zone) Aquifer is being elucidated. This new
information may ultimately change what DFC for the northern subdivision of the fresh Edwards
is and isn’t feasible, and therefore what MAG is consistent with that DFC.
In the northern subdivision of GMA 10, there is no evidence that the Edwards and the Middle
Trinity (and by inference, the Lower Trinity) aquifers are significantly hydrologically connected(Wong et al., 2014). So pumpage from one is not likely to appreciably affect the water available
in the other. On the other hand, there is a demonstrable hydrologic connection between theUpper Trinity Aquifer and the Edwards Aquifer where the Upper Trinity Aquifer underlies the
Edwards Aquifer; in fact, from a hydrostratigraphic standpoint, the top 100 feet or so of theUpper Glen Rose (i.e., traditionally, the uppermost Upper Trinity Aquifer) is more correctly
considered part of the Edwards Aquifer (Wong et al., 2014). Pumping in the Edwards Aquifer
near its western boundary can induce flow from the Upper Trinity Aquifer, and that induced
water flow may be of considerably poorer quality that could affect the existing use of the
Edwards Aquifer wells.

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In addition, as noted earlier, the Blanco River, which has base flow largely determined bydischarges from the Middle and Upper Trinity Aquifers, now appears to be a substantial sourcefor part of the springflows at Barton Springs during extreme drought conditions. Increased
pumping of the Trinity Aquifer, especially the Middle Trinity Aquifer, in the watersheds above
the recharge zone of the Edwards Aquifer may reduce the amount of recharge available to the
Edwards Aquifer and therefore the springflows at Barton Springs during extreme droughts (Huntet al., 2012). While this pumping would occur in GMA 9, its adverse impacts would be felt in thenorthern subdivision of GMA 10.
14.
Provide a Balance Between the Highest Practicable Level of Groundwater
Production and the Conservation, Preservation, Protection, Recharging, and Prevention ofWaste of Groundwater and Control of Subsidence in the Management Area
The TWDB has not developed guidance on how to approach this factor. It is up to the wishes of
the GCDs on how they wish to approach it, whether in a qualitative, quantitative, or combinationmanner. But, the GCDs need to include stakeholder input so that this factor can be satisfactorily
addressed. GCD management plans will be used to complete this requirement.
That said, it is relevant here that Barton Springs/Edwards Aquifer Conservation District hasestablished a conditional permitting program that promotes responsible use of the resources ofthis particular aquifer while the necessary restrictions during extreme drought conditions cancontinue to be effective. The Extreme Drought DFC, among other things, will become a
specified part of the District’s planned response to comply with federal law concerning
endangered species once the now-pending federal Incidental Take Permit has been received,
which will allow a curtailed amount of pumping to take place even during extreme drought. And
in addition, the primary objective of the All Conditions DFC is to delay the onset of conditions
triggering district-declared drought and minimize the length of time that all Barton
Springs/Edwards Aquifer Conservation District permittees are required to curtail all or part oftheir authorized groundwater use during drought.
Each GCD must hold a public meeting within 90 days after the GMA approves its DFCs. During
this meeting, the GCD needs to document stakeholder input regarding whether the DFCs provide
a balance between the highest practicable level of groundwater production and the conservation,
preservation, protection, recharging, and prevention of waste of groundwater and control ofsubsidence in the management area. This input is to be submitted by a report from the GCD to
the GMA within 90 days after the GMA approves its DFCs.
15.

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Conservation District Management Plan. 94 p + appendices.

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Brakefield, L.K., White, J.T., Houston, N.A., and Thomas, J.V., 2015, Updated numerical modelwith uncertainty assessment of 1950–56 drought conditions on brackish-water movement within
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