Southwest Texas Water Resources, L.P. (“STWR”) proposes the Southwest Texas Water Project, a hydrologically sound plan to better manage the Edwards Aquifer.  Without the project, there will be a continuation of the existing trend where unrestricted permits for Edwards groundwater in the Uvalde Pool will be leased or sold for pumping in the San Antonio Pool.  This trend will continue the concentration of pumping in the San Antonio Pool, placing additional stress on flows at Comal Springs and San Marcos Springs and increasing the frequency of Critical Management Periods in the San Antonio Pool.  The Southwest Texas Water Project will protect springflows and reduce the frequency of Critical Management Periods in the San Antonio Pool, without any significant risk of reducing the water supplies necessary to meet the demand for Edwards groundwater in Uvalde County.

The hydrologic impact of the Southwest Texas Water Project is driven by two factors.  First, the Knippa Gap restricts the flow of water from the Uvalde Pool into the San Antonio Pool, creating higher well levels and less variability in well elevations west of the Knippa Gap (in the Uvalde Pool) than east of the Knippa Gap (in the San Antonio Pool).  When examined within the context of the Critical Period Management triggers of regulation by the Edwards Aquifer Authority (“EAA”), pumping in the Uvalde Pool enjoys a distinct supply reliability advantage over pumping in the San Antonio Pool.  Second, the hydrologic impact of the Southwest Texas Water Project depends on the relative impact of pumping in the Uvalde Pool versus the San Antonio Pool.

STWR’s Phase I due diligence examined two types of evidence: (1) analysis of the historic record of publicly available data on springflows and well elevations with the location of pumping and recharge, and (2) EAA groundwater model applying the EAA’s Critical Period Management triggers with assumptions used by EAA staff in the current SB 3 Recovery Implementation Process examining the impact of pumping the maximum allowable permits in the Edwards Aquifer.  The findings are summarized below.

• • Analysis of the historic record concludes that pumping in the San Antonio Pool has a different impact on total springflows in the Edwards Aquifer than pumping in the Uvalde Pool:
  • • the long-term impact of a sustained increase in pumping in the San Antonio Pool reduces total springflows in the Edwards Aquifer by approximately 60% of the sustained increase in pumping.
  • • the long-term impact of a sustained increase in pumping in the Uvalde Pool has no significant impact on total springflows in the Edwards Aquifer. 
• • Under the EAA Groundwater Model assessment, pumping of all permits in the Edwards Aquifer will reduce springflows.  Flows at Comal Springs are estimated to fall by 55 cfs (18% of the historic average) and flows at San Marcos Springs are estimated to fall by 10 cfs (5.6% of the historic average).  From an environmental perspective, the Southwest Texas Water Project increases flows at Comal Springs by 8 cfs but does not reduce the adverse impact of pumping all Edwards permits on flows at San Marcos Springs.  The 8 cfs improvement in springflow at Comal Springs equals approximately 15% of the impact of increasing pumping in the Edwards Aquifer to the fully permitted amounts.
• • By avoiding further concentration of pumping in the San Antonio Pool, the Southwest Texas Water Project will increase the elevation of Well J-17 in the San Antonio Pool.  The magnitude of the estimated impact depends on the evidence reviewed: 14 foot increase in the lowest recorded elevation during the year based on analysis of historical data, a couple of foot increase in average elevation in a year based on analysis of the EAA groundwater model.
• • The Southwest Texas Water Project will increase pumping in the Uvalde Pool.  The estimated reduction in the lowest recorded elevation during a year of Well J-27 in the Uvalde Pool depends on the evidence reviewed: less than 5 foot decline based on analysis of historical data, or less than 10 foot decline in average elevation during a year based on the EAA groundwater model.

The EAA Groundwater assessment finds that the Southwest Texas Water Project significantly reduces the risk of Critical Management Periods in the San Antonio Pool with little risk of triggering Critical Management Periods in the Uvalde Pool.  The San Antonio Pool will face no restrictions 41% of the time with the Southwest Texas Water Project, but will face no restrictions only 36% of the time without the project.  For the Uvalde Pool, it will face a Critical Management Period only 2% of the time with cutbacks of 5% with the Southwest Texas Water Project.

From the perspective of reliability of water supply, the Southwest Texas Water Project reduces the risk of significant cutbacks in allowed pumping in the San Antonio Pool, ranging from 20% to 35%.  The increased pumping in the Uvalde Pool poses a 2% risk of cutbacks on the order of 5% within the Uvalde Pool.

The scenarios used in the groundwater model provide a conservative assessment of the impact of the Southwest Texas Water Project on water supplies from the Uvalde Pool.  The analysis assumes that all permits in Uvalde are pumped.  In fact, agricultural use has been on a declining trend and substantially below the 115,712 acre feet of total permits for irrigation use in the Uvalde Pool.  Since 1999, irrigation use in Uvalde has averaged only 43% of permitted amounts, with a peak use in the dry year of 2006 at 70% and a low use of 20% in the wet year 2007.  Therefore, even during the infrequent periods of a Stage II Critical Management Period in the Uvalde Pool when pumping is restricted to 95% of permitted amounts, available supplies will exceed actual irrigation use including circumstances such as the peak use of irrigation water in 2006 when rainfall was very low.  The situation is similar for commercial, industrial and municipal users in Uvalde County.  Since 2000, reported commercial, industrial and municipal water use has declined significantly and has consistently fluctuated below the amount of water available under existing permits for these uses, averaging 80% of permitted amounts.

For more information and discussion, please see Hydrologic Impact of the Southwest Texas Water Project.