GMA 13 Technical Memorandum 16-08
Draft 1

Sparta, Queen City, and Carrizo-Wilcox Aquifers:
Summary of Scenario 9 Drawdown and Outcrop Results

Prepared for:

Groundwater Management Area 13

Prepared by:William R. Hutchison, Ph.D., P.E., P.G.
Independent Groundwater Consultant
9305 Jamaica Beach
Jamaica Beach, TX 77554
512-745-0599
billhutch@texasgw.com

April 26, 2016

Table of Contents
1.0

Introduction and Objective ............................................................................................................ 1

2.0

Description of Simulations ............................................................................................................. 1

3.0

Predictive Simulation Results ........................................................................................................ 3

3.1
3.2
3.3

Pumping and Drawdown Results .............................................................................................. 3
Outcrop Area Saturated Thickness ........................................................................................... 5
Outcrop Area Classification ....................................................................................................... 8

List of Tables
Table 1. Summary of Pumping for Strategies ......................................................................................... 1
Table 2. Comparison of Strategies, 1999 Pumping, Current MAG, and Scenario 8 ........................... 2
Table 3. Scenario 9 Pumping (AF/yr)....................................................................................................... 3
Table 4. Scenario 9 Average Drawdown (ft) from 2011 to 2070 ............................................................ 4
Table 5. Summary of Outcrop Area Classification ................................................................................. 9Table 6. Summary of Outcrop Saturated Thickness Remaining in 2070 ............................................. 9

List of FiguresFigure 1. 2011 Saturated Thickness of the Outcrop Area of the Carrizo Aquifer ............................... 5
Figure 2. Simulated Saturated Thickness of the Outcrop Area of the Carrizo Aquifer in 2070
(Scenario 9) .................................................................................................................................................. 6Figure 3. 2011 Saturated Thickness of the Outcrop Area of the Wilcox Aquifer ................................ 7Figure 4. Simulated Saturated Thickness of the Outcrop Area of the Wilcox Aquifer in 2070
(Scenario 9) .................................................................................................................................................. 8

Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

1.0 Introduction and Objective
As a follow-up to the GMA 13 meeting of March 30, 2016, this technical memorandumsummarizes the results of Scenario 9 that are covered in Technical Memoranda 16-01, 16-02, and16-03. Technical Memorandum 16-01 included drawdown results of Scenarios 9 to 12, Technical
Memorandum 16-02 covered an analysis of the outcrop area of Scenarios 9 to 12, and Technical
Memorandum 16-03 covered a more detailed analysis of the outcrop areas of Scenarios 9, 13 and14. Thus, the results of Scenario 9 are covered in three separate tech memos. Because GMA 13
is considering proposed DFCs based on Scenario 9, it seemed reasonable to summarize all theresults in a single document to assist the districts during the public comment period. For moredetails, please refer to the original tech memos.
Scenario 9 was developed from Scenario 8, which was based on input from the groundwater
conservation districts, and added all recommended and alternative water management strategies inthe 2015 Region L plan.

2.0 Description of Simulations
Appendix A of Technical Memorandum 16-01 includes maps of the locations of the 12 strategies
that were taken from the Region L IPP. Table 1 summarizes the pumping amounts for all strategies
except the Local Carrizo strategy. Please note that nearly all require the same amount of pumping
in 2020 and in 2070. Only a few require increases in pumping during the planning period.
Table 1. Summary of Pumping for Strategies

1Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

Table 2 summarizes a comparison of groundwater pumping for Region L strategies, the calibrated
GAM (1999 pumping), the current MAG (GAM Run 09-34), and Scenarios 8 and 9.
Table 2. Comparison of Strategies, 1999 Pumping, Current MAG, and Scenario 8

Please note that within many of the areas of these strategies, Scenario 8 included substantial
pumping. These areas simply required adjustment to pumping input. Two strategy areas had nopumping in Scenario 8: Brackish Wilcox for SSWSC and SAWS Expanded Brackish Project(Strategies 4 and 9). New wells were included in these areas based on the locations as shown inAppendix A. Please note that Table 2 includes “Strategy 13” which is simply all the pumping in
the model that is not within the boundaries of the 12 strategies as noted in Appendix A.
For purposes of these simulations, strategy pumping was assumed to be equal for the entire
simulation period (2012 to 2070) and set based on the 2070 numbers in Table 2 (i.e. scheduledincreases were not simulated to avoid problems in MAG caps in future regional planning sessionsif there are changes in the timing of strategy implementation).
Scenario 9 includes all of Scenario 8 pumping plus all strategy pumping as presented in Table 2and discussed above. A summary of the pumping in Scenario 9 is also presented in Table 2. Please
note that pumping in Scenario 9 may be higher than listed by Region L to account for otherpumping that had already been included in Scenario 8.

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Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

3.0 Predictive Simulation Results
3.1

Pumping and Drawdown Results

Summary tables of pumping and average drawdown for each county and model layer for Scenario
9 are presented in Tables 3 and 4, respectively.
Table 3. Scenario 9 Pumping (AF/yr)

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Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

Table 4. Scenario 9 Average Drawdown (ft) from 2011 to 2070

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Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

3.2

Outcrop Area Saturated Thickness

Figure 1 presents the saturated thickness in 2011 of the outcrop area of the Carrizo Aquifer in
2011. Figure 2 presents the simulated saturated thickness of 2070 of the outcrop area of the Carrizo
Aquifer in 2070 under Scenario.

Figure 1. 2011 Saturated Thickness of the Outcrop Area of the Carrizo Aquifer

5Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

Figure 2. Simulated Saturated Thickness of the Outcrop Area of the Carrizo Aquifer in
2070 (Scenario 9)

Figure 3 presents the saturated thickness in 2011 of the outcrop area of the Wilcox Aquifer in
2011. Figure 4 presents the simulated saturated thickness of 2070 of the outcrop area of the Wilcox
Aquifer in 2070 under Scenario 9.

6Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

Figure 3. 2011 Saturated Thickness of the Outcrop Area of the Wilcox Aquifer

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Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

Figure 4. Simulated Saturated Thickness of the Outcrop Area of the Wilcox Aquifer in2070 (Scenario 9)

3.3

Outcrop Area Classification

The outcrop area of the Carrizo and Wilcox aquifers was subdivided based on estimated 2011
saturated thickness. Table 5 summarizes the classification and the number of cells within eachclass.

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Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

Table 5. Summary of Outcrop Area Classification
Aquifer

2011 Saturated
Thickness (ft)Number ofModel Cells in
GMA 13Carrizo
Carrizo
Carrizo
Carrizo
Carrizo
Wilcox
Wilcox
Wilcox
Wilcox
Wilcox0 to 50
50 to 100
100 to 250
250 to 500> 500
0 to 50
50 to 100
100 to 250
250 to 500
> 500

475
131
260
121
12860
168
291
177
62

Model output was processed to calculate the saturated thickness in 2070 for each of these classes.
The 2070 saturated thickness was then divided by the saturated thickness in 2011 (Table 5) andmultiplied by 100 to develop an estimate of the saturated thickness remaining in 2070 as apercentage of the saturated thickness in 2011 for each class.
Table 6 presents the saturated thickness in 2070 for Scenario 9, and compares these results toScenario 15 (a scenario where 2011 pumping is assumed from 2012 to 2070). Please note that insome western areas of GMA 13 (Dimmit, Maverick, Webb, and Zavala counties), Scenario 9
assumes pumping decreases that result in groundwater level recoveries. Thus, some of the results
for saturated thickness in Scenario 9 are greater than in Scenario 15.
Table 6. Summary of Outcrop Saturated Thickness Remaining in 2070

Please note that due to model limitations that have been documented in the Task 0 report anddiscussed by consultants for various stakeholders at previous GMA 13 meetings, the model9Sparta, Queen City, and Carrizo-Wilcox Aquifers: Summary of Scenario 9 Drawdown and Outcrop Results
GMA 13 Technical Memorandum 16-08, Draft 1

predicts drawdown in the outcrop area that is not always consistent with actual data. Note that
under Scenario 15, the model predicts that saturated thickness in 2070 would drop below 80
percent even if pumping remained at 2011 rates. This is not consistent with actual monitoring
data, and highlights the limitations of the model.
Therefore, a desired future condition of maintaining 75 percent of saturated thickness in theoutcrop areas under Scenario 9 is considered feasible despite model predictions to the contrary.
Improvements in the monitoring program in the outcrop area is needed. Also, the upcoming model
update needs to focus more attention on model calibration for the outcrop area. Presumably, thisupdate will be completed and the model will be available when the next proposed DFC is due in
2021.

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