Our Aquifer Optimization Program Reports
The Edwards Aquifer Authority has undertaken the Edwards Aquifer Optimization Program (EAOP), a comprehensive program for the study and management of the Edwards Aquifer. A series of interrelated studies known as the Optimization Technical Studies (OTS) were created to support the EAOP. The OTS were created to better understand the needs of protected species that depend on springflow from the aquifer, to increase the understanding of Edwards Aquifer flowpaths, and to evaluate opportunities for increasing recharge to the aquifer. The OTS are divided into three areas of research:
- Biological assessment
- Flowpath/modeling studies
- Recharge enhancement
As OTS projects are completed, the project report is reviewed with the board of directors and placed on the Authority’s website. Each completed report may be viewed in portable document format (PDF) by clicking on the report title below. A brief description of the report purpose accompanies each report title. The completed reports include:
BIOLOGICAL ASSESSMENTS:
Aquatic Ecosystem Monitoring
Authority contractors perform aquatic ecosystem monitoring for the Comal and San Marcos springs systems. The monitoring is performed in two modes, comprehensive monitoring and critical period monitoring. Comprehensive monitoring is performed on a regular basis to characterize the health of the aquatic ecosystem and protected species. Critical period monitoring is performed to assess the response of the aquatic ecosystems during or after extreme low or extreme high flow events. All Authority monitoring reports from 2000 to 2005 are presented below.
2006 Aquatic Ecosystem Monitoring at Comal Springs
The purpose of this report is to document the results of all aquatic ecosystem monitoring conducted in 2006 at Comal Springs located in New Braunfels , Texas. The monitoring and report preparation was performed by BIO-WEST, Inc. Pflugerville , Texas.
2006 Aquatic Ecosystem Monitoring at San Marcos Springs
The purpose of this report is to document the results of all aquatic ecosystem monitoring conducted in 2006 at San Marcos Springs located in San Marcos , Texas. The monitoring and report preparation was performed by BIO-WEST, Inc. Pflugerville , Texas.
Click here to view previous years reports.
Other Completed Biologic Assessment Projects
Variable Flow Study - Seven Years of Monitoring and Applied Research
This report presents a summary of the monitoring and research efforts that have occurred in the Comal and San Marcos Ecosystems since 2000. The report provides background on the monitoring components and the evolution of the overall monitoring program along with results or trends that have been documented during the seven years of observations and research. The report also highlights special research projects or case studies that have been conducted to address issues that were not readily apparent and are important for the protection of the species or habitats. Finally, the report provides recommendations of activities or programs to gather missing information regarding the thresholds of the species and habits and management implications of existing activities that merit further discussion.
Assessment of Factors Influencing Texas Wild-Rice (Zizania texana) Sexual and Asexual Reproduction
The purpose of this study was to identify factors that influence sexual and asexual reproduction of Texas Wild-rice (Zizania texana). Data collected during the study were used to examine the characteristics of pollen viability and dispersal, stigma viability, ability to self-pollinate, seed production and quality, minimum distances for successful pollination within and among stands, and asexual output. New information regarding pollination success and seed production for Texas Wild-rice was documented. The study was completed in June 2004 by the U.S. Fish and Wildlife - San Marcos National Fish Hatchery and Technology Center and the Lady Bird Johnson Wildflower Center.
Assessment of Instream flow and Habitat Requirements for Cagle’s Map Turtle
The purpose of this study was to investigate the instream flow requirements and basic habitat characteristics of the Cagle’s Map Turtle in the Guadalupe River system. The study area was from the upper Guadalupe River (near Ingram) to the lower Guadalupe River (near Tivoli ). The turtle’s population appears to be steady (declining in one area), based on comparisons of population data from this study with that of other studies. The Cagle’s Map Turtle appears to be impacted by physical obstructions in the river more than by varying flow regimes. The study was completed in April 2002 by West Texas A&M University, Canyon, Texas.
Flowpath/modeling studies
Evaluation of the Option to Designate a Separate San Marcos Pool for Critical Period Management
This report presents the findings of the Edwards Aquifer Authority’s investigation into the hydrogeology and hydrodynamics of water discharging from San Marcos Springs in Hays County, Texas. The purpose of the report is to determine whether there is sufficient technical justification for distinct aquifer management rules for the designation of a San Marcos Pool in the San Marcos area regarding critical period management. Historical records indicate that Comal Springs and San Marcos Springs respond differently to rainfall, which could indicate that these springs represent separate hydrologic subbasins or pools within the San Antonio Segment of the Balcones Fault Zone Edwards Aquifer. The report concludes that water for both San Marcos Springs and Comal Springs is derived from the western portion of the aquifer. Groundwater flows through the Artesian fault block and either discharges from Comal Springs or bypasses Comal Springs and discharges at San Marcos Springs. At higher discharge rates, San Marcos Springs is also recharged by water infiltrating from Cibolo Creek, the Guadalupe River, Dry Comal Creek, Sink Creek, and other streams, especially when a groundwater mound forms under Onion Creek. Despite the large volume of water that these streams carry at times, they contribute relatively small amounts to San Marcos springflow. The report concludes that there is not sufficient technical justification at this time to create a separate San Marcos “Pool” and recommends that an index well be established in the San Marcos area for triggering critical period levels. The report was prepared by Authority staff in February 2008.
Robust Representation of Dry Cells in MODFLOW
When MODFLOW calculates a water level that is below the base elevation of a computational cell, that cell is declared to be dry and removed (temporarily or permanently) from the calculation, causing the model to produce unreliable results. This problem with the MODFLOW system is well-known and long-standing. The dry-cell issue was a significant obstacle to modeling water management scenarios with the Edwards Aquifer model because cells in the recharge zone often went dry. This report describes a new variant of MODFLOW, denoted MODFLOW-NR, that incorporates a recently developed robust computational scheme for representing dry cells. The new representation of dry cells combines an upstream-weighting algorithm for intercell conductances with a new solver package. This report summarizes the capabilities, technical basis, data input requirements, software validation/verification tests, and example simulations for the MODFLOW-NR software. The study was completed in May 2007by Southwest research Institute, San Antonio, Texas.
Evaluation of the Aquifer and Springflow Impacts Associated with the
Cibolo Creek Transfer Rules
The purpose of this study was to use available data and the
Authority’s MODFLOW groundwater model to assess the impact to
aquifer water levels and springflow from the transfer of water
rights from Bexar County and the western counties to Comal and Hays
Counties. Water right transfers from Bexar County and west into
Comal and Hays Counties are referred to as “Cibolo transfers”
because Cibolo Creek is the geographic feature between the two
areas. The study was completed on April 13, 2006 by LBG-Guyton
Associates, Austin, Texas.
Tracer Test Work Plan, Kinney and Uvalde Counties
This Work Plan was prepared by Authority staff and defines the scope of work
and the methodology that will be followed during tracer testing in Kinney
and Uvalde counties.
Evaluation of the Edwards Aquifer in Kinney and Uvalde Counties,
Texas
The purpose of this study was to (1) develop an updated
conceptual model of the groundwater systems in Uvalde County that
incorporates existing and recently collected data on hydrology,
geochemistry, and structural geology, and (2) clearly define the
hydrogeologic relationship between the Uvalde pool and the San
Antonio pool of the Edwards Aquifer. The area of investigation
consisted of Kinney and Uvalde counties and included the groundwater
divide in Kinney County to the west and the Knippa Gap to the east.
It includes all the of the principal aquifers in Uvalde and Kinney
counties. The study was completed in June 2006 by Southwest
Research Institute, San Antonio, Texas. Note: Attachment A
data are available from the Authority upon request
Estimation of Hydraulic Parameters for the Edwards Aquifer Management
Model
The purpose of this study was to statistically model hydraulic conductivity measurements and create an input dataset for a computer model of the Edwards Aquifer (MODFLOW model) that is currently under development. The study was completed in May 2002 by Southwest Research Institute, San Antonio, Texas.
North Medina County Flowpath – Electromagnetic Survey in the Vicinity of Seco Creek Sinkhole
The purpose of this study was to obtain an airborne electromagnetic survey of northern Medina County in the vicinity of the Seco Creek Sinkhole. The data indicated that the survey is effective to a depth of approximately 100 meters below grade and that the data shows more detailed geologic structure than previously prepared geologic maps. Geologic structure and their effects on groundwater flow can be interpreted from the data. The study was completed in July 2003 by the United States Geological Survey, Denver, Colorado.
Water-Budget Analysis of Medina and Diversion Lakes and the Medina/Diversion Lake System, with Estimated Recharge to Edwards Aquifer, San Antonio, Texas
The purpose of this study was to estimate groundwater outflow (recharge) from the Medina Lake/Diversion Lake system through the calculation of water budgets over a wide range of lake stages. Results of the study indicate that average monthly losses from the Medina Lake/Diversion Lake system are about 56 percent of the monthly recharge computed by previously used USGS methods. The study was completed in December 2004 by the United States Geological Survey, San Antonio, Texas.
Analysis of Structural Controls on the Edwards/Trinity Aquifers – Camp Bullis Quadrangle
The purpose of this study was to generate a three-dimensional computer model and predictions of localized fault related deformation in the Edwards Aquifer and the Trinity Aquifer in the study area. The study also provided an analysis of the potential for hydraulic communication across the interface between the two aquifers, taking into account fault-related deformation and juxtaposition of the aquifers across key faults. The study was completed in December 2003 by Southwest Research Institute, San Antonio, Texas.
Recharge Methodology Pilot Study of the Blanco and Nueces Basins
The purpose of this study was to evaluate a new method for computing recharge to the Edwards Aquifer. The computer program Hydrologic Simulation Program – Fortran (HSPF) was evaluated using input datasets for the Blanco and Nueces River basins. The HSPF methodology was determined to be a significant improvement over historically utilized methods and will be applied to all basins that recharge the aquifer. The pilot study was completed in June 2002 by HDR Engineering, Inc., Austin , Texas.
HSPF Recharge Models for the San Antonio Segment of the Balcones Fault Zone of the Edwards Aquifer.
The purpose of this study was to develop a new method for estimating recharge to the Edwards Aquifer. The computer program Hydrologic Simulation Program – Fortran (HSPF) was used to develop a comprehensive recharge estimation model for the region. A previously completed pilot study project modeled portions of two of the nine basins applicable to the Edwards Aquifer. The pilot study indicated HSPF as a viable tool for recharge estimation and led to the initiation of this project. This project developed recharge models for all nine basins relevant to the Edwards Aquifer, by modeling the upstream (drainage) area, as well as the recharge zone of the aquifer. The project was completed in March 2005 by LBG Guyton Associates, Inc., Austin, Texas.
Statistical Analysis of Hydrologic Data
The purpose of this study was to evaluate Edwards Aquifer–related hydrologic data from the October 1998 storm event. Surface water and groundwater levels were statistically analyzed to evaluate responses of the aquifer to the major recharge event. The study was completed in November 2001 by Argonne National Laboratory, Argonne, Illinois.
Fracture/Conduit Study (Refining the Conceptual Model for Flow in the Edwards Aquifer – Characterizing the Role of Fractures and Conduits in the Balcones Fault Zone Segment)
The purpose of this study was to evaluate the influence of fractures and conduits on groundwater flowpaths in the recharge and artesian zones of the Edwards Aquifer. Hydrologic and geologic data were evaluated for evidence of karst aquifer flow regimes and specific areas are delineated for focused data collection in the future. The study was completed in January 2004 by the University of Texas – Bureau of Economic Geology, Austin, Texas.
Geophysical Survey to Determine the Depth and Lateral Extent of the Leona Aquifer and Evaluation of Discharge Through the Leona River Floodplain, South of Uvalde, Texas
The purpose of this study was to evaluate the depth and lateral extent of the Leona Formation. This data was combined with previously determined Leona Aquifer parameters to estimate the amount of water that may be flowing from the Edwards Aquifer in the area of Leona Springs. This information will improve the overall understanding of the Edwards Aquifer hydrologic budgets. The project report concludes that there may be as much as 100,000 acre feet of water leaving the Edwards Aquifer in the vicinity of Leona Springs.
Structural Controls on the Edwards Aquifer/Trinity Aquifer Interface in the Helotes Quadrangle, Texas
The purpose of this study was to generate a three-dimensional geologic model of the Edwards Aquifer and Trinity Aquifer in the area of the Helotes Quadrangle and to assess the potential for hydraulic communication across the interface between the two aquifers. the study was completed in February 2005 by Southwest research Institute, San Antonio, texas.
Conduits and Turbulent Flow in the Edwards Aquifer
The purpose of this study was to address the existence of aquifer-scale conduit networks in the Edwards Aquifer and how they could be incorporated in the model of the aquifer constructed by the U.S.G.S. The study was completed in April 2004 by Stephen Worthington of Worthington Groundwater, Toronto, Ontario, Canada.
Recharge Enhancement Studies
Evaluation of Augmentation Methodologies in Support of In-Situ Refugia at Comal and San Marcos Springs, Texas
The study was performed to investigate the feasibility of augmenting flow at Comal and San Marcos springs. Augmenting springflow was evaluated for the purpose of maintaining critical habitat for threatened and endangered species for a very limited period of time during drought conditions. The document addresses three areas:
- The hydrogeology and hydrology of Comal and San Marcos springs.
- The location of the highest quality habitat in the spring complexes.
- The use of additional waters to supplement the natural flows at the springs.
The study was completed in June 2004 by a team led by LBG-Guyton Associates.
Analysis of Recharge and Recirculation – Phase 1
The concept of recharge and recirculation (R&R) for the Edwards Aquifer embodies the integrated use of groundwater, surface water, and storage units to optimize the availability of water for pumpers during drought periods and to accommodate water needs for endangered species in Comal and San Marcos springs. The purpose of this Phase 1 report is to outline work performed by Todd Engineers to evaluate various documents related to the concept of R&R and to document Todd Engineers review of a MODFLOW groundwater model of the Edwards Aquifer for use in simulating R&R scenarios. The report also discusses two preliminary R&R scenarios simulated with the model. Subsequent phases of the project will use the model to simulate numerous R&R scenarios to evaluate possible benefits for aquifer water levels and springflows.
Analysis of Recharge and Recirculation - Phase 2
The Recharge and Recirculation (R&R) Phase 2 Report focuses on Edwards Aquifer responses to recharge as simulated by the Aquifer MODFLOW model. Using the model, aquifer water levels and springflows were evaluated by simulating recharge events at eight different locations across the project area. Numerous combinations of recharge timing, volume, and location were modeled. No specific source of recharge water was considered during Phase 2 analysis. The report contains numerous graphics to demonstrate the relative benefits of the scenarios modeled.
