Environmental Stewardship Celebrates a Water Achievement in the Central Texas

“Improved” Groundwater Availability Model includes groundwater-surface water interaction between the Colorado River and the Central Carrizo-Wilcox Aquifer


GAM predicted impacts of planned Simsboro pumping. Click here for more information

UPDATE 9/10/2018

Recently we accomplished an important milestone in our efforts to protect the surface waters of the Colorado River and the groundwater aquifers of the Central Carrizo-Wilcox Aquifer Group.  INTERA’s work to improve the groundwater availability model for Groundwater Management Area 12 (GMA-12) has now been completed and the model is undergoing final reviews before being adopted for use.    The GMA-12 Groundwater Availability Model (GAM) now has a surface water-groundwater interaction (SW-GW) package that enables the model to more accurately represent the current interactions between the Colorado River and the Carrizo-Wilcox Aquifer Group — in particular the Simsboro Aquifer — and quantitatively predict future impacts of planned pumping on the river and its tributaries.  Importantly, the “improved” model is able able to provide quantitative estimates of the current impact of pumping on surface waters on both a regional and local level, making it suitable for evaluating specific situations within Bastrop and surrounding counties.   In addition to improving the  SW-GW capabilities of the model, important improvements were made in the way faults in the region are represented and data was updated to include additional empirical studies that have been completed.  Environmental Stewardship has retained a groundwater hydrologist to compare the results from the new model with earlier reports prepared using the old model.

With the “Improved” GAM, we are now seeking support to install a surface water-groundwater monitoring network in Bastrop County to provide empirical data on groundwater and surface water conditions and flow directly into the new model.   Over the next ten years we anticipate that scientific studies that will result from this monitoring and use of the improved GAM will provide vital information for guiding public policies regarding how these Central Texas resources are managed and used.

This is an important achievement for four reasons:

1) The GAM improvements will provide a platform for quantifying the relationship between the Colorado River and the Carrizo-Wilcox aquifer group (which included the Simsboro) on a localized basis.

2) An initial monitoring plan is now being developed that, when implemented, will enable an better understanding of the relationship between the Colorado River and aquifers as required in groundwater permitting and development of desired future conditions.

3) It furthers a dialogue between the entities responsible for managing the river and groundwater resources in the basin and those who advocate for the protection of these resources.

4) The GMA-12 Improved GAM will be available in time to be used in the current round of review of the currently adopted desired future conditions (DFS).

Click her for more information on the technical aspects.


After eight years of advocating for action on groundwater-surface water interaction  issues in Central Texas, we have accomplished a major step forward in our efforts to protect the Colorado River and its tributaries from over-pumping of groundwater.   Work that has now been completed on the contract between the Texas Water Development Board (TWDB) and INTERA  will play a vital step in helping planners understand and manage this important ecological and hydrological relationship.  With this information, planners will be able to establishing a science link between groundwater and surface water that can inform policy and management decisions.

Conservation Districts (GCDs) in Groundwater gma_12Management Area 12 (GMA-12), recognizing weaknesses in the capability of the groundwater model used to guide their management decisions, raised over $100,000 to make improvements in the model’s ability to predict regional groundwater-surface water interactions that result form groundwater pumping. Both the Lower Colorado River Authority (LCRA) and the Brazos River Authority (BRA) provided $20,000 each in additional funding for the project.

Environmental Stewardship, working through the Colorado-Lavaca Bay and Basin Area Stakeholder Committee (CL-BBASC), was able to raise an additional $60,000 to enhance the model still further and develop a monitoring plan (See bulletin for details). These improvements, when combined with other improvements funded by the TWDB, will provide a Groundwater Availability Model (GAM) for the Central Carrizo-Wilcox and associated aquifers that will enable better modeling of the relationship between the Colorado River and the aquifers that provide groundwater base-flow to the river as it flows through Bastrop and Fayette counties. INTERA won the contract to make the necessary improvements to the GMA-12 GAM and the completed GAM is expected to be available in April, 2018 (See final report below).   In addition, the CL-BBASC requested SB3 funding in 2017 for initial data gathering to implement groundwater-surface water interaction field work resulting from the GAM improvements study (see below).

UPDATE (11/22/17)

On July, 21, 2016, the Texas Water Development Board (TWDB) authorized the Executive Director to negotiate and execute eight contracts in a total amount not to exceed $745,000 for environmental flow studies in the Brazos, Colorado and Lavaca, and Nueces basins.  These improvements to the GMA-12 Groundwater Availability Model are now near completion, however, we are awaiting release of the final report on the CL-BBASC portion of the report that was due September 1, 2017.

The GMA-12 Groundwater Availability Model (GAM) Improvements project was one of the studies included for contracting. This authorization completed authorization for 27 projects totally $2 million in funding for environmental flow studies across the state. Once completed, this project will provide a robust groundwater-surface water interaction model for predicting and managing the Simsboro and other aquifers in GMA-12. See below for background and more details.

INTERA’s RFQ Proposal. 

ES Review of Draft Report

INTERA’s DRAFT Final Report

INTEA’s Final Report to the Colorado-Lavaca Basin and Bay Stakeholder Committee

INTERA’s Final Report, Volume 1

INTERA’s Final Report, Volume 2

CL-BBASC Request for SB3 Funding for Field Studies: 

Initial Data Gathering To Implement Groundwater-Surface Water
Interaction Field Work From GAM Improvements Study