GMA 13 Technical Memorandum 16-01
Draft 1

Sparta, Queen City, and Carrizo-Wilcox Aquifers
GAM Predictive Scenarios 9 to 12
Region L Strategies

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

January 18, 2016

Table of Contents
1.0
1.1
1.2

Introduction and Objective ............................................................................................................ 1
Review of Scenarios 1 to 8 .......................................................................................................... 1
Regional Planning Strategies ..................................................................................................... 1

2.0

Description of Simulations ............................................................................................................. 3

3.0

Predictive Simulation Results ........................................................................................................ 53.1
3.2
3.3

Overall Pumping and Drawdown Results................................................................................. 5County Level Pumping and Drawdown Results ...................................................................... 6
Wilcox Aquifer Water Budget ................................................................................................... 9

List of Tables
Table 1. Summary of Pumping for Strategies ......................................................................................... 3
Table 2. Comparison of Strategies, 1999 Pumping, Current MAG, and Scenario 8 ........................... 3
Table 3. Summary of Pumping in Scenarios 9 to 12 ............................................................................... 4Table 4. Groundwater Budgets for the Wilcox Aquifer in GMA 13 – Scenario 9 ............................. 10Table 5. Groundwater Budgets for the Wilcox Aquifer in GMA 13 – Scenario 13 ........................... 11

List of Figures
Figure 1. GMA 13 Average Drawdown Time Series .............................................................................. 5Figure 2. GMA 13 Pumping versus Drawdown for all Scenarios.......................................................... 6Figure 3. Bexar County Drawdown in Carrizo and Wilcox................................................................... 7Figure 4. Gonzales County Drawdown in Carrizo and Wilcox ............................................................. 7Figure 5. Guadalupe County Drawdown in Carrizo and Wilcox .......................................................... 8Figure 6. Wilson County Drawdown in Carrizo and Wilcox ................................................................. 8AppendicesA – Location Maps of 12 Water Management Strategies Contained in Region L IPP
B – Tabluar Summaries of Pumping and Drawdown for Scenarios 9 to 12

Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

1.0 Introduction and Objective
1.1

Review of Scenarios 1 to 8

As part of this round of joint planning, GMA 13 has been reviewing GAM predictive simulations.
Scenarios 1 to 7 were completed and reviewed at the GMA 13 meeting on October 13, 2013. Abase case (Scenario 4) was developed based on input from the groundwater conservation districtsin GMA 13 as follows:

Pumping in the Carrizo Aquifer in Bexar County was increased as compared to the MAG
that was developed from the DFC that was adopted in 2010 in response to a request fromSAWS
Pumping in the Carrizo Aquifer in Gonzales County was increased as compared to theMAG that was developed from the DFC that was adopted in 2010 in response to a requestfrom Gonzales County UWCD
Pumping the Wilcox Aquifer in Gonzales County was decreased as compared to the MAG
that was developed from the DFC that was adopted in 2010 in response to a request fromGonzales County UWCD
Pumping in the Carrizo Aquifer in McMullen County was increased as compared to theMAG that was developed from the DFC that was adopted in 2010 in response to a requestfrom McMullen GCD

Scenarios 1 to 3 represented incremental reductions of Scenario 4, and Scenarios 4 to 7 represented
incremental increases of Scenario 4.
After reviewing the results, Scenario 8 was completed which represented the following changes toScenario 4:
Gonzales County UWCD requested that pumping be revised to match the current MAG
Guadalupe County GCD requested increases in both the Carrizo and Wilcox aquifers

Results of Scenario 8 were completed and reviewed at the GMA 13 meeting of March 13, 2014.
As a result of the comments received at the March 13, 2014 meeting, additional pumping was tobe included in the next simulation that reflected additional pumping by SAWS. However, due tochanges in the administration in GMA 13, the work was left pending.

1.2

Regional Planning Strategies

In considering the request of SAWS to simulate additional pumping, and the potential incremental
effect of each entity in GMA 13 requesting similar simulations in the future, a more comprehensive
approach was taken to consider all recommended and alternative water management strategies
from the Region L plan. Sam Vaugh of HDR provided the initial data on August 22, 2014.
However, due to the imminent release of the Region L IPP, it was decided to wait until the IPP
was released to ensure that all strategies were current.

1Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

A meeting with HDR was held on May 27, 2015 to clarify the strategies and the data contained inthe IPP. The IPP contained 12 strategies that were relevant to GMA 13. One of these was acollective strategy called “Local Carrizo Wells” that covered several areas in GMA 13. The
pumping for all other strategies totaled 116,000 AF/yr in 2020, and 222,000 AF/yr in 2070.
The IPP distinguished between recommended and alternative strategies in areas where future
pumping exceeded the MAG that was set in 2010 on the basis of the DFC that was established by
GMA 13. Water management strategies are developed to meet deficits between current supply
and future demand as part of the regional planning process. TWDB considers the MAG to be ahard limit, and recommended water management strategies cannot result in pumping that exceeds
the MAG. Thus, Region L has included strategies that exceed the MAG as alternative strategies.
The heavy-handed approach of TWDB to the interaction between the joint planning process andthe regional planning discounts the fact that DFCs and MAGs are updated every five years. If astrategy is identified that requires groundwater in excess of the MAG in 30 to 50 years, it should
be a recommended strategy, which would then provide a signal to the joint planning process toconsider revising the DFC to accommodate such a strategy in the next round of joint planning.
This technical memorandum documents four simulations that focus on simulating therecommended and alternative water management strategies in the 2015 Region L plan. Scenario
9 includes all pumping from Scenario 8 described above, and all recommended and alternative
water management strategies. Scenarios 10 to 12 simulate reductions in all Wilcox Aquifer
strategies in order to understand the interaction between the Wilcox and the overlying Carrizo
Aquifer.

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Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 12.0 Description of Simulations
Appendix A includes maps of the locations of the 12 strategies that were taken from the Region LIPP. 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

Table 2 summarizes a comparison of Region L strategies, the calibrated GAM (1999 pumping),
the current MAG (GAM Run 09-34), and Scenario 8 described above.
Table 2. Comparison of Strategies, 1999 Pumping, Current MAG, and Scenario 8Please note that within many of the areas of these strategies, Scenario 8 included substantialpumping. 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 inthe model that is not within the boundaries of the 12 strategies as noted in Appendix A.
3

Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

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 sessions
if there are changes in the timing of strategy implementation).
Scenarios 9 to 12 were developed as follows:
Scenario 9 includes all of Scenario 8 pumping plus all strategy pumping as presented inTable 2 and discussed above.
Scenario 10 includes all of Scenario 8 pumping, all Carrizo Aquifer strategy pumping, and67 percent of Wilcox Aquifer strategy pumping.
Scenario 11 includes all of Scenario 8 pumping, all Carrizo Aquifer strategy pumping, and33 percent of Wilcox Aquifer strategy pumping.
Scenario 12 includes all of Scenario 8 pumping, all Carrizo Aquifer strategy pumping, andno Wilcox Aquifer strategies.

Scenarios 10 to 12 were designed to understand the drawdown and water budget impacts of Wilcox
Aquifer pumping on the overlying Carrizo Aquifer.
A summary of the pumping in Scenarios 9 to 12 by strategy is presented in Table 3. Please notethat pumping in a strategy area in Table 3 may be higher than listed in Table 2 to account for otherpumping that had already been included in Scenario 8.
Table 3. Summary of Pumping in Scenarios 9 to 12

4

Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

3.0 Predictive Simulation Results
3.1

Overall Pumping and Drawdown Results

Summary drawdown and pumping results on a county scale and at the GMA 13 scale wereextracted from the simulation output files. Additional detailed results for outcrop, downdip, andGCD areas were not extracted for this draft, but will be included once a proposed DFC is agreedupon.
Figure 1 is a time-series plot of average drawdown from 2012 to 2070 for GMA 13. This plotshows that after 59 years of pumping, drawdown is not flattening in any of the scenarios, whichsuggests that storage depletion is a dominant supply of the pumped water (i.e. pumping induced
inflows and decreased outflows are not sufficient to supply the increased pumping).

Figure 1. GMA 13 Average Drawdown Time Series

Figure 2 is an update of the pumping versus drawdown relationship of the current DFC and MAG
and all 12 scenarios completed to date at the scale of GMA 13. Pumping is for all of GMA 13 (alllayers), and the drawdown is the average drawdown for all layers over the entirety of GMA 13.
This is a summary graph intended to provide regional perspective.

5

Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

Figure 2. GMA 13 Pumping versus Drawdown for all Scenarios

3.2

County Level Pumping and Drawdown Results

Summary tables of pumping and drawdown for each county are presented in Appendix B.
Of note is the drawdown impact in the Carrizo Aquifer (Layer 5) as a result of changes in Wilcox
Aquifer pumping. Recall that Scenario 9 included all Wilcox Aquifer strategies, and Scenarios 10and 11 represented reductions in Wilcox Aquifer strategy pumping, and Scenario 12 included noWilcox Aquifer strategies.
Bexar, Gonzales, Guadalupe, and Wilson counties are the locations of these Wilcox Aquifer
strategies, and Figures 3 to 6 summarize the drawdown in the Carrizo Aquifer (Layer 5) and theWilcox Aquifer (Layer 8). Please note that in each case, Wilcox Aquifer drawdown is highest inScenario 9 and lowest in Scenario 12 as a result of differences in pumping. However, the changesin Carrizo Aquifer drawdown are minimal across all scenarios in each of these counties. Thissuggests that, according to this GAM, the Wilcox is relatively isolated from the Carrizo, andpumping in the Wilcox will result in minimal drawdown in the Carrizo Aquifer.

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Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

Figure 3. Bexar County Drawdown in Carrizo and Wilcox

Figure 4. Gonzales County Drawdown in Carrizo and Wilcox

7Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

Figure 5. Guadalupe County Drawdown in Carrizo and Wilcox

Figure 6. Wilson County Drawdown in Carrizo and Wilcox
8Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

3.3

Wilcox Aquifer Water Budget

Increases in pumping will result in three impacts: 1) reduction in storage, 2) increased or inducedinflow, and 3) decreased outflow. A water budget is an accounting of all inflows, outflows andstorage changes in an area, and can be useful to evaluate the impacts of pumping increases.
Water budgets for the Wilcox Aquifer (Layers 6, 7 and 8) for the updated calibration period (2000to 2011) and for Scenario 9 are presented to understand the impacts of increasing Wilcox pumping.
These water budgets are presented in Table 4. The water budget comparison for Scenario 12 ispresented in Table 5.
Please note that Scenario 9 represents an increase in Wilcox Aquifer pumping of about 164,000
AF/yr. In response, storage declines increase about 95,000 AF/yr. Thus, after 59 years of pumping(2012 to 2070), storage declines supply only about 58 percent of the pumping.
Induced inflow and decreased outflow account for the other 42 percent of the pumping. Significant
among these components is the induced inflow from GMA 12 and GMA 15, which, together,
supply over 20 percent of the pumping. Induced flow from rivers and stream supply about 21
percent of the pumping.
From 2000 to 2011, groundwater flowed from the Wilcox upward to the Carrizo at a rate of 1,380
AF/yr. Note that in Scenario 9, the rate increased to 6,437 AF/yr, which suggests that increased
pumping in the Carrizo associated with Scenario 9 is inducing additional flow from the Wilcox tothe Carrizo. As presented in Table 5, Scenario 12 (no Wilcox strategy pumping) has a flow ratefrom the Wilcox to the Carrizo of about 19,000 AF/yr, which appears to be a primary factor in therelatively flat drawdown curves in the Carrizo Aquifer, previously presented in Figures 3 through6.

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Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

Table 4. Groundwater Budgets for the Wilcox Aquifer in GMA 13 – Scenario 9
All Values in AF/yr10

Sparta, Queen City, and Carrizo-Wilcox Aquifers: GAM Predictive Scenarios 9 to 12, Region L Strategies
GMA 13 Technical Memorandum 16-01, Draft 1

Table 5. Groundwater Budgets for the Wilcox Aquifer in GMA 13 – Scenario 13
All Values in AF/yr11

Appendix A
Location Maps of 12 Water Management Strategies
Contained in Region L IPP

A‐1

A‐2

A‐3

A‐4A‐5

A‐6

Appendix B
Tabluar Summaries of Pumping and Drawdown forScenarios 9 to 12

B‐1

B‐2

B‐3

B‐4