June 14, 2016

DRAFT
Explanatory Report for the Proposed Desired Future Conditionsof the Leona Gravel Aquifer
Groundwater Management Area 10

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

Groundwater Management Area 10 and the Leona Gravel Aquifer ............................1

2.

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

3.

Desired Future Conditions ...............................................................................................1

4.

Policy Justification ............................................................................................................2

5.

Technical Justification ......................................................................................................4

6.

Consideration of Designated Factors ...............................................................................7
6.1
Aquifer Uses or Conditions ..................................................................................8
6.1.1
Description of Factors in the Leona Gravel Aquiferin Uvalde County..................................................................................8
6.1.2
DFC Considerations.............................................................................9
6.2
Water-Supply Needs .............................................................................................9
6.2.1
Description of Factors in the Leona Gravel Aquiferin Uvalde County..................................................................................9
6.2.2
DFC Considerations.............................................................................9
6.3
Water-Management Strategies ..........................................................................10
6.3.1
Description of Factors in the Leona Gravel Aquiferin Uvalde County................................................................................10
6.3.2
DFC Considerations...........................................................................10
6.4
Hydrological Conditions ....................................................................................10
6.4.1
Description of Factors in the Leona Gravel Aquiferin Uvalde County................................................................................10
6.4.1.1
Total Estimated Recoverable Storage ..............................................10
6.4.1.2
Average Annual Recharge ................................................................126.4.1.3
Inflows .................................................................................................126.4.1.4
Discharge ............................................................................................126.4.1.5
Other Environmental Impacts Including Springflow and
Groundwater/Surface Water Interaction ........................................13
6.4.2
DFC Considerations...........................................................................13

7.

Subsidence Impacts .........................................................................................................13

8.

Socioeconomic Impacts Reasonably Expected to Occur .............................................13
ii

8.1
8.2

Description of Factors in the Leona Gravel Aquifer in Uvalde County .........13
DFC Considerations.............................................................................................14

9.

Private Property Impacts ...............................................................................................14
9.1
Description of Factors in the Leona Gravel Aquifer in Uvalde County .........14
9.2
DFC Considerations.............................................................................................14

10.

Feasibility of Achieving the DFCs .................................................................................14

11.

Discussion of Other DFCs Considered ..........................................................................15

12.

Discussion of Other Recommendations .........................................................................15
12.1 Advisory Committees ..........................................................................................15
12.2 Public Comments ............................................................................................15

13.

Any Other Information Relevant to the Specific DFCs ..............................................15

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 theManagement Area ............................................................................................................15

15.

References .........................................................................................................................16iii

List of Appendices
Appendix A—Proposed Desired Future Condition Resolution
Appendix B—TWDB GAM Task xxxx (Revised): Total Estimated Recoverable Storage for
Aquifers in GMA 10
Appendix C—Socioeconomic Impacts Analyses for Region L

iv

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

GCDs in GMA 10 (TWDB website) ...................................................................................22

Map of Uvalde County showing the delineated Leona Grave Aquifer and thepreviously delineated extent of the aquifer, GMAs, and rivers (From Bradley, 2012) .......33

Figure 3. Hydrographs of the J-27 Edwards (Balcones Fault Zone) Aquifer index
well and Leona Gravel Aquifer wells in Uvalde County (Bradley, 2012) ..........................64

Figure 4. Hydrographs showing maximum and minimum annual water levels for
the J-27 Edwards (Balcones Fault Zone) Aquifer index well and Leona Gravel
Aquifer wells in Uvalde County (Bradley, 2012) ................................................................6v

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

DFCs for the Leona Gravel Aquifer within Uvalde County in GMA 10 ............................4

2

Total estimated exempt use for the other aquifers in the Uvalde County UWCD for
decades from 2015 to 2070. Results are in acre-ft /yr. Estimated exempt use
calculated by TWDB and accepted by the district (TWDB, 2015) .....................................7

3

Estimated domestic exempt use for the other aquifers in the Uvalde County UWCD
for decades from 2015 to 2070. Results are in acre-ft /yr. Estimated exempt use
calculated by TWDB and accepted by the district (Thorkildsen and Backhouse, 2011;
TWDB, 2015) ......................................................................................................................7

4

Estimated livestock exempt use for the other aquifers in the Uvalde County UWCD
for decades from 2015 to 2070. Results are in acre-ft /yr. Estimated exempt use
calculated by TWDB and accepted by the district (TWDB, 2015) .....................................7

5

Use of the minor aquifers in Uvalde County for the years 2007–2010 (the Uvalde
County UWCD Groundwater Management Plan) (acre-ft) .................................................8

6

Aquifer use in Uvalde County divided between surface water and groundwaterand among industry sector (Uvalde County UWCD Groundwater Management Plan)(acre-ft) ................................................................................................................................97

Projected water supply and demand estimates for Uvalde County in the 2012 State
Water Plan ..........................................................................................................................11

8

Water-management strategies in Uvalde County in the 2012 State Water Plan
(acre-ft/yr) ..........................................................................................................................11

9

Total estimated recoverable storage for the Leona Gravel Aquifer within Uvalde
County UWCD in GMA10. Estimates are rounded within two significant numbers(Jones et al., 2013) .............................................................................................................12vi

Abbreviations
DFC

Desired Future Conditions

GCD

Groundwater Conservation District

GMA

Groundwater Management AreaMAG

Modeled Available Groundwater

TWDB

Texas Water Development Board

UWCD

Underground Water Conservation District

vii

1.

Groundwater Management Area 10 and the Leona Gravel Aquifer

Groundwater Management Areas (GMAs) were created by the Texas Legislature to provide forthe conservation, preservation, protection, recharging, and prevention of waste of thegroundwater, and of groundwater reservoirs or their subdivisions, and to control subsidence
caused by withdrawal of water from those groundwater reservoirs or their subdivisions. Each
GMA is charged with facilitating joint planning efforts in the GMAs within its jurisdiction.
GMA 10 was created to oversee the Edwards (Balcones Fault Zone) and Trinity aquifers. Other
aquifers 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) (Figure 1).
As mandated in Texas Water Code § 36.108, districts are required to submit Desired Future
Conditions (DFCs) of the groundwater resources in their GMA to the executive administrator of
the Texas Water Development Board (TWDB), unless that aquifer is deemed to be non-relevant.
According to Texas Water Code § 36.108 (d-3), the district representatives shall produce a DFC
Explanatory Report for the management area and submit to the TWDB a copy of the
Explanatory Report.
The Leona Gravel Aquifer is neither a major nor minor aquifer, but has been determined to belocally relevant in Uvalde County for joint planning purposes. The Leona Gravel Aquifer has
been determined to be not relevant in Medina County for joint planning purposes. This
document is the Explanatory Report for the Leona Gravel Aquifer where it is determined to be
relevant within GMA 10.
2.

Aquifer Description

For jurisdicational purposes, the Leona Gravel Aquifer is defined as Leona Gravels within
Uvalde County. The geographic extent of the Leona Gravel Aquifer is presented in Figure 2(Bradley, 2012). As illustrated, the jurisdiction is limited to Uvalde County. The Medina
County GCD declared the Leona Gravel Aquifer to be non-relevant in Medina County.
3.

Desired Future Conditions

The DFC for the Leona Gravel Aquifer in the Uvalde County part of GMA 10, as described in
Resolution No. 2010-11 and adopted August 23, 2010 by the GCDs in GMA 10, is a regional
average well drawdown of zero (0) feet (including exempt and non-exempt use) (Table 1). The
second round DFC was adopted at the GMA 10 meeting on March 14, 2016. Resolution No.
2016-xx is attached in Appendix A.

1

Figure 1. GCDs in GMA 10 (TWDB website)
4.

Policy Justification

The DFC for the Leona Gravel Aquifer in Uvalde County was adopted after considering thefollowing 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;
2

Figure 2. Map of Uvalde County showing the delineated Leona Grave Aquifer and thepreviously delineated extent of the aquifer, GMAs, and rivers (From Bradley, 2012)3

Table 1. DFCs for the Leona Gravel Aquifer within Uvalde County in GMA 10
Aquifer
DFC Summary
Date DFC Adopted
Leona Gravel
No drawdown (including exempt and non-exempt use)
8/23/2010
Leona Gravel
No drawdown (including exempt and non-exempt use)?/?/2015
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;

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; and9.

Any other information relevant to the specific DFCs.

These factors are discussed in detail in appropriate sections in this Explanatory Report.
5.

Technical Justification

Technical justification for selection of the DFC for the Leona Gravel Aquifer in Uvalde County
was provided using a Groundwater Availability Model simulation and alternative analyses. The
only Groundwater Availability Model simulation was an aquifer assessment to determine theeffects of various levels of pumping in the Edwards (Balcones Fault Zone) Aquifer on discharge
to the Leona Gravel Aquifer (Wade, 2008). Subsequent aquifer assessments were alternative
analyses to estimate the Managed {modeled} Available Groundwater (MAG) (George, 2010;
Wuerch and Backhouse, 2011; Bradley, 2012). The methodology used to estimate the Managed
MAG in analyses by George (2010) and Wuerch and Backhouse (2011) was distinct from themethodology used by Bradley (2013).
Wade (2008) used the GWSWIM-IV (Klemt et al., 1979; Thorkildsen and McElhaney, 1992)
version of the Groundwater Availability Model for the San Antonio Segment of the Edwards(Balcones Fault Zone) Aquifer to assess the effects of permitted pumping in the Edwards(Balcones Fault Zone) Aquifer on discharge from the Edwards (Balcones Fault Zone) Aquifer tothe Leona Gravel Aquifer. Wade (2008) noted that Leona Springs was poorly understood and
not well quantified; thus, model estimates of discharge to Leona Springs include uncertainty due
to model estimation and uncertainty about the hydrogeology.
Wuerch and Backhouse (2011) used the approach by George (2010) to evaluate the Managed
MAG associated with a DFC that specifies a regional average well drawdown in the Leona
Gravel Aquifer of zero (0) ft. Wuerch and Backhouse (2011) defined effective recharge as theamount of water that enters an aquifer and is available for development (Muller and Price, 1979).
4

Because the DFC is zero, no water can be taken out of storage. Thus, the Managed MAG can be
no greater than the effective recharge. Wuerch and Backhouse (2011) used the Atlas of Texas(US Geological Survey and Texas Water Development Board, 2006) to determine the boundaryof the Leona Gravel Aquifer.
The Leona Gravel Aquifer is defined as having three hydrostratigraphic units, the Leona
Formation (Qle), Quaternary alluvium (Qal), and terrace deposits (Qt) (Figure 2). Wuerch andBlackhouse (2011) calculated recharge by multiplying the outcrop area of each of the three units
by the average precipitation (1971-2000) and an effective recharge rate of 5.5 percent. Wuerch
and Blackhouse (2011) relied on an assessment by Lowry and Couch (2002) that included Qal
and Qt with the Leona Gravel Aquifer when determining aquifer area. Using this methodology
for the Leona Gravel Aquifer in Uvalde County, Wuerch and Blackhouse (2011) calculated theannual effective recharge at 30,772 acre-ft/yr, total pumping at 17,646 acre-ft/yr, and MAG at
rates that vary from 17,485 to 17,552 acre-ft/yr.
Managed MAG in analyses performed by Bradley (2013) are the most current analyses available
and are used as the basis for the Technical Justification. The following information is taken fromthe aquifer assessment for the Leona Gravel Aquifer within Uvalde County (Bradley, 2012).
Limited data for both historic water levels and pumpage estimates hinder an estimate of theMAG. However, there are four wells within Uvalde County that have short to long-term
measurements taken from the 1945s to 2001 (Figure 3). Based on historical water levels, theLeona Gravel Aquifer recharges in response to inflows from the Edwards (Balcones Fault Zone)
Aquifer (Green et al., 2008) and behaves in a similar manner as the Edwards (Balcones Fault
Zone) Aquifer. The hydrograph of Well 69-51-406 shows a highly variable water level trendthat mimics changes in the Edwards (Balcones Fault Zone) Aquifer J-27 Index Well (Bradley,2012), especially high and low water conditions. During the drought of the 1950s, extreme
water-level declines showed up in the other historic well measurements (69-51-801, 69-51-701)
that also mimic the J-27 water levels (Figure 3). Figure 4 shows annual minimum and maximum
measurements for the same wells to highlight that the Leona Gravel Aquifer reflects water levelsin the Edwards (Balcones Fault Zone) Aquifer.
Since exempt uses are not available for permitting, it is necessary to account for them when
determining the MAG. To do this, the TWDB developed a standardized method for estimating
exempt use for domestic and livestock purposes based on projected changes in population andthe ratio of domestic and livestock wells in an area to the total number of wells. Because otherexempt uses can vary significantly from district to district and there is much higher uncertainty
associated with estimating use due to oil and gas exploration, estimates of exempt pumping
outside domestic and livestock uses have not been included. If a district believes it has a more
appropriate estimate of exempt pumping, they may submit it, along with a description of how it
was developed, to the TWDB for consideration. Once established, the estimates of exempt
pumping are subtracted from the total pumping calculation to yield the estimated MAG for
permitting purposes. Exempt use of the Leona Gravel Aquifer in the Uvalde County UWCD has
not yet been independently estimated by the TWDB. Estimates for total, domestic, and livestockuse by aquifers other than the Trinity and Edwards Aquifers in Uvalde County are presented inTables 2–4 (TWDB, 2015). There is negligible exempt use due to oil and gas exploration in
Uvalde County.
5

Figure 3. Hydrographs of the J-27 Edwards (Balcones Fault Zone) Aquifer index well andLeona Gravel Aquifer wells in Uvalde County (Bradley, 2012).

Figure 4. Hydrographs showing maximum and minimum annual water levels for the J-27
Edwards (Balcones Fault Zone) Aquifer index well and Leona Gravel Aquifer wells in Uvalde
County (Bradley, 2012).
6

Table 2. Total estimated exempt use for the other aquifers in the Uvalde County UWCD for
decades from 2015 to 2070. Results are in acre-ft /yr. Estimated exempt use calculated by
TWDB and accepted by the district (TWDB, 2015).
Year
2015
2020
2030
2040
2050
2060
2070
537
473
522
544
566
587
607
Acre-ft
Table 3. Estimated domestic exempt use for the other aquifers in the Uvalde County UWCD for
decades from 2015 to 2070. Results are in acre-ft /yr. Estimated exempt use calculated by
TWDB and accepted by the district (Thorkildsen and Backhouse, 2011; TWDB, 2015).
Year
2015
2020
2030
2040
2050
2060
2070
171
233
282
304
326
347
367
Acre-ft
Table 4. Estimated livestock exempt use for the other aquifers in the Uvalde County UWCD for
decades from 2015 to 2070. Results are in acre-ft /yr. Estimated exempt use calculated by
TWDB and accepted by the district (TWDB, 2015).
Year
2015
2020
2030
2040
2050
2060
2070
366
240
240
240
240
240
240
Acre-ft
Without current water-level data to match with current groundwater pumpage estimates from theUvalde County UWCD, it is difficult to ascertain the MAG. However, J-27 hydrograph does
indicate a possible correlation between water-level conditions in the Edwards (Balcones Fault
Zone) Aquifer and water levels within the Leona Gravel Aquifer.
Analyses by Bradley (2013) relied on historical pumping to establish the MAG in response to a
DFC of zero drawdown. In response to requests by the Uvalde County UWCD, the TWDB first
reduced the extent of the Leona Gravel Aquifer to only include the Leona Formation. Secondly,
the TWDB restricted the extent of the Leona Formation to only the Leona River floodplain and
the Cooks Slough area. Bradley (2013) calculated that 84 percent of this area is in GMA 10 andthat 16 percent of the area is in GMA 13. Thus 57,474 acres of the total Leona Gravel Aquifer
acreage of 68,458 acres are in GMA 10. Bradley (2013) noted that if this restricted area wereused in the George (2010) calculation, the MAG would be about 6,600 acre-ft/yr.
Bradley (2013) assumed that the Edwards (Balcones Fault Zone) Aquifer index well in Uvalde
County, J-27, is an acceptable surrogate monitoring well for the Leona Gravel Aquifer. Using
2008 as a year in which no water was taken from storage, Bradley (2013) observed that
11,173 acre-ft were pumped from the Leona Gravel Aquifer without lowering the water tablemeasured by J-27. Eighty-four percent of this is assumed to have been pumped from the Leona
Gravel Aquifer in GMA 10. Using this reasoning, Bradley (2013) calculated the MAG from the
Leona Gravel Aquifer in Uvalde County to be constant at 9,385 acre-ft/yr.
6.

Consideration of Designated Factors

In accordance with Texas Water Code § 36.108 (d-3), the district representatives shall produce a
DFC Explanatory Report. The report must include documentation of how nine factors identified
in Texas Water Code §36.108 (d) were considered prior to proposing a DFC and how the7

proposed DFC impacts each factor. The following sections of the Explanatory Report summarize
the information that the GCDs used in its deliberations and discussions.
6.1

Aquifer Uses or Conditions

GMA 10 incorporated information from the Uvalde County UWCD Groundwater Management
Plan and analyses from the TWDB during development of the proposed DFCs.

6.1.1

Description of Factors in the Leona Gravel Aquifer in Uvalde County

Surface water in Uvalde County comes primarily from the Nueces River and its tributaries.
Groundwater is found in both major and local aquifers in Uvalde County. Major aquifers include
the Edwards (Balcones Fault Zone), Edwards-Trinity (Plateau), Carrizo-Wilcox and Trinity
Aquifers. Minor or local aquifers include the Leona Gravel, Buda Limestone, Anacacho, Austin
Chalk, and Glen Rose Formations. There is significant production from the Buda Limestone,
Austin Chalk, and Leona Formation Aquifers in areas of Uvalde County west of the Knippa Gap.
A report completed for the Uvalde County UWCD in 2009 concludes that the Edwards (Balcones
Fault Zone) Aquifer is in hydraulic communication with these minor aquifers and that index well
J-27, although completed in the Edwards (Balcones Fault Zone) Aquifer, can indicate declines ingroundwater levels in the Buda Limestone, Austin Chalk, and Leona Formation Aquifers thatadversely impact the water resource (Green et al., 2009). When the level in index well J-27
drops below 860 feet msl, recharge to the Leona Formation gravels and discharge to SoldiersCamp Springs to the Nueces River decline measurably.
Use of the minor aquifers in Uvalde County for the years 2007–2010, in terms of pumping, issummarized in Table 5. The significant increase in pumping between 2007 and 2008 is
attributed to improved reporting of pumping, not to a marked increase in aquifer use. Aquifer
use in Uvalde County divided between surface water and groundwater and among industry sector
for the years 2000–2004 is summarized in Table 6 (Uvalde County UWCD Groundwater
Management Plan).
Table 5. Use of the minor aquifers in Uvalde County for the years 2007–2010 (the Uvalde
County UWCD Groundwater Management Plan) (acre-ft)
Aquifer
2007
2008
2009
2010
Alluvium
190
199
669
143
Austin Chalk
1,443
2,816
3,238
1,626
Buda Limestone
110
1,637
2,059
734
Glen Rose
26
50
26
48
Leona Gravel287
11,173
7,780
7,176
Serpentine
0010Trinity/Glen Rose
79
61
53
435
Trinity
228
267
1,667
908
Total
2,362
16,236
15,508
11,070Source: Uvalde County UWCD Annual Water Use Report database8

Table 6. Aquifer use in Uvalde County divided by surface water and groundwater and amongindustry sector (Uvalde County UWCD Groundwater Management Plan) (acre-ft)
Year

SourceMunicipal

Manufacturing

Steam
Electric

Irrigation

MiningLivestock

7,846
378
0
56,967
250
642
0
0
0
1,094
0
642
Total
7,846
378
0
58,061
250
1,284
GW
5,472
1,110
0
83,276
250
592
2001
SW
67
13
0
1,700
0
592
Total
5,539
1,123
0
84,976
250
1,184
GW
4,777
751
0
88,392
717
579
2002
SW
59
9
0
1,804
0
579
Total
4,836
760
0
90,196
717
1,158
GW
5,207
152
0
67,820
239
557
2003
SW
64
2
0
425
0
557
Total
5,271
154
0
68,245
239
1,114
GW
4,083
3
0
66,399
239
522
2004
SW
50
0
0
377
0
522
Total
4,133
3
0
66,776239
1,044
GW = groundwater; SW = surface water
Source: Texas Water Development Board Water Use Survey Database 1/5/2010
2000

6.1.2

GW
SW

Total

66,083
1,736
67,81990,7002,372
93,072
95,216
2,451
97,66773,975
1,048
75,02371,246949
72,195DFC Considerations

The dominant use of the Leona Gravel Aquifer in Uvalde County by pumping is domestic use
and irrigation, 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 withsustainability of this groundwater supply is drought, notably extreme drought that stresses theaquifer. The DFC supports and is, in fact, the linchpin of a drought management program topromote long-term sustainability of water supplies.
6.2

Water-Supply Needs

6.2.1

Description of Factors in the Leona Gravel Aquifer in Uvalde County

Water use in Uvalde County is divided between surface water and groundwater and amongindustry sector (Uvalde County UWCD Groundwater Management Plan). Water use is notdelineated by aquifer in Table 5.
6.2.2

DFC Considerations

The population growth of Uvalde County is projected by the Office of the State Demographer forState of Texas, Texas State Data Center Texas A&M University System to grow from 28,616 in2010 to 35,650 in 2040, an increase of 24.6 percent (http://txsdc.tamu.edu/tpepp/2001_txpopprj_
method.php). The DFC maximizes the amount of water that can be provided during non-drought
9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 DFC indexes the amount of aquifer water available to meet the needs
with the severity of drought.
6.3

Water-Management Strategies

6.3.1

Description of Factors in the Leona Gravel Aquifer in Uvalde County

The following is from the 2011 Region L Water Planning Group Plan and the 2012 State Water
Plan, which relies on the Water Planning Group Plans. The projected water supply and demand
estimates for Uvalde County in the 2012 State Water Plan indicate that projected demands
exceed projected supplies (Table 7). To meet the needs of water-user groups in the Uvalde
County UWCD, Region L recommended water management strategies to address the identified
shortages. Water management strategies are projects or procedures that if implemented willproduce additional water to meet the identified needs of water-user groups. The total amount ofgroundwater and surface water resulting from implementation of the water-management
strategies recommended for Uvalde County in the 2007 State Water Plan is anticipated toprovide 4,487 acre-feet in 2010, increasing to 6,939 acre-feet in 2060. Transfers from the
Edwards (Balcones Fault Zone) Aquifer and municipal water conservation are the primarystrategies identified (Table 8). The Leona Gravel Aquifer is not identified as part of the water
mitigation strategy.
6.3.2

DFC Considerations

The DFC under consideration here is specific to the Leona Gravel Aquifer in Uvalde County.
The Edwards Aquifer in Uvalde County has a different DFC and is the subject of a separate
groundwater management zone, designed to promote protection of the downgradient springs in
the Edwards Aquifer and the endangered species impacted by spring discharge. The DFC for the
Leona Gravel Aquifer, as described above, underpin an aquifer-responsive drought management
program that encourages both full-time water conservation and further temporary curtailments inpumping during drought periods that increase with drought severity.
6.4

Hydrological Conditions

6.4.1

Description of Factors in the Leona Gravel Aquifer in Uvalde County

6.4.1.1 Total Estimated Recoverable Storage
Texas statute requires that the total estimated recoverable storage of relevant aquifers be
determined. Total estimated recoverable storage is a calculation provided by the TWDB. Texas
Administrative Code Rule §356.10 (Texas Administrative Code, 2011) defines the total
estimated recoverable storage as the estimated amount of groundwater within an aquifer that
accounts for recovery scenarios that range between 25 percent and 75 percent of theporosity-adjusted aquifer volume. As described in GAM Task 14-033 (Jones et al., 2013), thetotal recoverable storage was estimated for the portion of the aquifer within GMA 10 that lies
within the official lateral aquifer boundaries as delineated by George et al. (2011). Total
10

Table 7. Projected water supply and demand estimates for Uvalde County in the 2012 State
Water Plan
Supply/Shortage
Comment
Water User Group
2010
2060
(ac-ft/yr) (ac-ft/yr)
City of Sabinal
-127
-109
Projected shortage(2010 through 2060)
City of Uvalde-3,172-3,263
Projected shortage(2010 through 2060)
Rural Area Residential and Commercial
1,277
317
No projected shortage
Industrial
943
837
No projected shortage
Steam-Electric Power
00
No projected shortage
Mining105
0
No projected shortage
Irrigation
14,68024,768
No projected shortage
Livestock00
No projected shortage
Table 8. Water-management strategies in Uvalde County in the 2012 State Water Plan
(acre-ft/yr)
WUG

River
Basin

WaterManagement
Strategy

Source
Name

2010

2020

2030

2040

2050

2060

139

135

130

125

121

121

Sabinal

NuecesEdwards
Transfers

Edwards(Balcones
Fault Zone)
Aquifer

Sabinal

NuecesMunicipal
Water
Conservation

Conservation

34

65

92

116

139

145

UvaldeNuecesEdwards
Transfers

Edwards(Balcones
Fault Zone)
Aquifer

3,793

3,830

3,850

3,854

3,856

3,884

CountyOther

NuecesConservation

0

0

0

33

73

137

UvaldeNuecesConservation

521

1,017

1,471

1,882

2,269

2,652

4,487

5,047

5,543

6,010

6,458

6,939

Municipal
Water
Conservation
Municipal
Water
Conservation

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 water quality types. The
total estimated recoverable storage values do not take into account the effects of land surface
subsidence, degradation of water quality, or any changes to surface water-groundwaterinteraction that may occur due to pumping.
11Per an email from Robert G. Bradley, TWDB, dated February 17, 2015 “We [TWDB] have notcompleted the [total estimated recoverable] report yet. We still have the Leona, Buda, andAustin Chalk report to do, as well as the GMA 10 saline Edwards (Balcones Fault Zone) Aquifer.
Most of the Leona Gravel Aquifer is completed but we intend to write one report for Uvalde
County. However, we have been struggling with the numbers for the Austin Chalk and Buda.
Anyway some other projects had priority and we are now able to complete this report with some
information.” The TWDB Memorandum on Total Estimated Recoverable Storage in GMA 10 isattached in Appendix B. These data will be entered into Table 9 when available.
6.4.1.2 Average Annual Recharge
Using results from TWDB GAM Run 10-022 (Aschenbach, 2010), the estimated recharge fromthe Carrizo-Wilcox Aquifer in Uvalde County is 2,948 acre-ft/yr and the estimated recharge fromthe Edwards-Trinity Aquifer in Uvalde County is 28,213acre-ft/yr (Uvalde County UWCD
Groundwater Management Plan). The Uvalde County UWCD Groundwater Management Plandoes not include an estimate for average annual recharge from the Leona Gravel Aquifer.
6.4.1.3 Inflows
Analysis by Green et al. (2008) indicates that as much as 74,000 acre-ft/yr is recharged to the
Leona Gravel Aquifer as inflow where the gravels abut with Austin Chalk, Buda Limestone, andpossibly the Edwards (Balcones Fault Zone) Aquifer in the Leona River floodplain in the reachfrom Highway 90 in the north to Ft. Inge in the south. The quantity of recharge to the Leona
Gravel Aquifer is highly variable and is greatly affected by aquifer stage as measured at J-27.
6.4.1.4 Discharge
The Uvalde County UWCD has no estimate of discharge from the Leona Gravel Aquifer.
Discharge from the Leona Gravel Aquifer where it exits Uvalde County can be estimated bysubtracting the pumpage from the Leona Gravel Aquifer from the inflow to the Leona Gravel
Aquifer. The estimated inflow [74,000 acre-ft/yr] less the pumpage [7,176 acre-ft/yr reported in2010 by permittees] is estimated to be 66,824 acre-ft/yr if exempt pumping is not taken underconsideration. Discharge would be less than 66,824 acre-ft/yr if exempt pumping is included in
the calculation.
Table 9. Total estimated recoverable storage for the Leona Gravel Aquifer within Uvalde
County UWCD in GMA 10. Estimates are rounded within two significant numbers (Joneset al., 2013).
Total Storage
25 percent of Total Storage
75 percent of Total Storage(acre-ft)(acre-ft)(acre-ft)
Under development by the
Under development by the
Under development by the
TWDB
TWDB
TWDB

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6.4.1.5 Other Environmental Impacts Including Springflow and Groundwater/Surface
Water Interaction
Named springs in Uvalde County include Soldiers Camp Spring on the Nueces River and Leona
Springs on the Leona River. Leona Springs contributes to surface flow in the Leona River, but
not to the Leona Gravel Aquifer (Green et al., 2008). The source for the Leona Springs appears
to be the Uvalde Gravel and not the Leona Gravel Aquifer, thus discharge at the Leona Springs
should not be impacted by the conditions of or impact to the Leona Gravel Aquifer.
An aquifer pump test conducted on the Leona Gravel Aquifer approximately 6 miles south ofHighway 90 in the City of Uvalde indicated that the Leona Gravel Aquifer is not in hydrauliccommunication with the Leona River at that location (Green et al., 2008). The Leona Gravel
Aquifer may be in hydraulic communication with the Leona River at other locations; however,this communication has not been established.
6.4.2 DFC Considerations
The DFC is proposed on the basis that the Leona Gravel Aquifer in Uvalde County is in directhydrologic communication with the Edwards, Austin Chalk, and the Buda Limestone aquifers in
the vicinity of the headwaters of the Leona Gravel Aquifer. This hydraulic communication isthought to occur along a reach of the paleo-stream channel that encompasses the Leona Gravel
Aquifer starting from a point near Highway 90 in the City of Uvalde and continuing south tonear Ft Inge. The four aquifers are well-integrated hydrologically along this reach and have acommon potentiometric surface throughout this area. This hydrologic condition denotes that all
four aquifers are jointly vulnerable to drought. The Leona Gravel Aquifer in Uvalde County ismore vulnerable to drought than the Edwards Aquifer because it is above and has less saturated
thickness than the Edwards Aquifer.
7.

Subsidence Impacts

Subsidence has historically not been an issue with the Leona Gravel Aquifer in Uvalde County in
GMA 10.
8.

Socioeconomic Impacts Reasonably Expected to Occur

8.1

Description of Factors in the Leona Gravel Aquifer in Uvalde County

Administrative rules require that regional water planning groups evaluate the impacts of not
meeting water needs as part of the regional water planning process, and rules direct TWDB staff
to provide technical assistance [§357.7 (4)(A)]. 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). 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 support of the 2011 South Central Texas Regional Water Plan.

13

The report on socioeconomic impacts summarizes the results of the TWDB analysis anddiscusses the methodology used to generate the results for Region L. The report does not include
the socioeconomic impact associated with only the Leona Gravel Aquifer. The socioeconomic
impact report for Water Planning Group L is included in Appendix C.
8.2

DFC Considerations

Because none of the water management strategies involve changes in the current use of the
Leona Gravel Aquifer in Uvalde County, as described in Section 6.3, the proposed DFC does nothave a differential socioeconomic impact. They are supportive of the status quo in this regard,
which is considered positive.
9.

Private Property Impacts

9.1

Description of Factors in the Leona Gravel Aquifer in Uvalde County

The impact on the interests and rights in private property, including ownership and the rights of
GMA landowners and their lessees and assigns in groundwater is recognized under Texas Water
Code Section 36.002. The legislature recognizes that a landowner owns the groundwater below
the surface of the landowner's land as real property. Nothing in this code shall be construed as
granting the authority to deprive or divest a landowner, including a landowner's lessees, heirs, orassigns, of the groundwater ownership and rights described by this section.
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 Sections 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 DFC is designed to protect the sustained use of the aquifer as a water supply for all users inaggregate. The DFC does not prevent use of the groundwater by landowners either now or in the
future, although ultimately total use of the groundwater in the aquifer is restricted by the aquifer
condition, and that may affect the amount of water that any one landowner could use, either atparticular 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 Uvalde County UWCD tomanage the Leona Gravel Aquifer toward that goal. The Uvalde County UWCD is limited by thehydrogeology of the resource (e.g. how it responds to drought) and the authority of the Uvalde
County UWCD to regulate pumping (e.g. uses exempt from permitting and by virtue of the factthat the Edwards (Balcones Fault Zone) Aquifer, the principal aquifer within its jurisdictional
14

boundaries, is regulated by the Edwards Aquifer Authority, not the Uvalde County UWCD).
Because the Edwards (Balcones Fault Zone) Aquifer is the ultimate source of recharge to the
Leona Gravel Aquifer, the feasibility of achieving the DFC of the Leona Gravel Aquifer isdependent on the management and hydraulic condition of the Edwards (Balcones Fault
Zone) Aquifer.
11.

Discussion of Other DFCs ConsideredNo other DFC of the Leona Gravel Aquifer in Uvalde County was considered.
12.

Discussion of Other Recommendations

12.1

Advisory Committees

An Advisory Committee for GMA 10 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.
The GCDs have not yet approved their DFCs. The GCDs have not yet held public meetings togather public comment on the DFCs. No public comments have yet been offered regarding the
DFC for the Leona Gravel Aquifer in Uvalde County.
A draft of the Explanatory Report may be used as supporting documents to inform the public
before such hearings and meetings are held.
13.

Any Other Information Relevant to the Specific DFCs

No additional information relevant to the specific DFCs has been identified.
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
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. Participation by the project team at town hall meetings or with individual GCDs is
not included in the scope of this work. GCD management plans will be used to complete
this requirement.
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
15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.

References

Aschenbach, E. 2010. GAM Run 10-022. Texas Water Development Board. 8 p.
Bradley, R.G. 2012. Modeled available groundwater for the Leona Gravel Aquifer in Uvalde
County. AA10-28 MAG.
George, P.G. 2010. GTA Aquifer Assessment 09-01MAG, Groundwater Management Area 10,
Leona Gravel Aquifer, Evaluation of draft desired future conditions. 14 p.
George, P.G., R.E. Mace, and R. Petrossian. 2011. Aquifers of Texas, Texas Water
Development Board Report 380. http://www.twdb.texas.gov/groundwater/aquifer/index.asp
Green, R.T., J.R. Winterle, and J.D. Prikryl. 2008. Discharge from the Edwards Aquifer
through the Leona River Floodplain, Uvalde, Texas. J of American Water Resources
Association. 44(4):887-901. DOI: 10.1111/j.1752-1688.2008.00187.x.
Green, R.T., F. P. Bertetti, and R.N. McGinnis. 2009. Investigation of the Secondary Aquifers
in Uvalde County. Southwest Research Institute. Contract project conducted for the Uvalde
County Underground Water Conservation District. 74 p.
Jones, I.C., J Shi, and R Bradley. 2013. GAM Task 13-033: Total estimated recoverable
storage for aquifers in Groundwater Management Area 10.
Klemt, W. B., T.R. Knowles, G. Elder, and T. Sieh. 1979. Ground-water resources and model
applications for the Edwards (Balcones Fault Zone) aquifer in the San Antonio region, Texas: Texas
Department of Water Resources Report 239. 88 p.

Lowry, M.V. and B.E. Couch. 2002. Phase I Leona Gravel Aquifer Study: Prepared for theMedina County Groundwater Conservation District by Turner Collie & Braden Inc. 51 p.
Muller, D.A. and R.D. Price. 1979. Ground-water availability in Texas, estimates andprojections through 2030: Texas Department of Water Resources Report 238. 77 p.
Texas Administrative Code. 2011. http://info.sos.state.tx.us/pls/pub/readtac$ext.viewtac
Thorkildsen, D. and P.D. McElhaney. 1992. Model refinement and applications for the Edwards(Balcones Fault Zone) aquifer in the San Antonio region, Texas: Texas Water Development
Board Report 340. 33 p.
Thorkildsen, D. and S. Backhouse. 2011. GTA Aquifer Assessment 10-33 MAG: Texas Water
Development Board, GTA Aquifer Assessment 10-33 MAG Report, 11 p.
16

Texas Water Development Board (TWDB). 2015. Projected Exempt Groundwater Use
Estimates Groundwater Management Area 10. TWDB Final Estimates. December 2015.
U.S. Geological Survey and the Texas Water Development Board. 2006. Digital Geologic Atlasof Texas: U.S. Geological Survey and Texas Water Development Board, available through the
Texas natural Resources Information System.
Wade, S. 2008. Simulation of discharge to the Leona Gravel Aquifer from the Edwards(Balcones Fault Zone) Aquifer. GR06-030.
Wuerch, D. and S Backhouse. 2011. Modeled available groundwater for the Leona Gravel
Aquifer in Uvalde County. AA10-28 MAG.

17