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Lower Guadalupe River Project
Updated November 2002

The proposed Lower Guadalupe River Project is an effort of the Guadalupe-Blanco River Authority (GBRA), the San Antonio River Authority (SARA), and the San Antonio Water System (SAWS). This project, as initially proposed, would transfer an estimated 94,500 acre-feet of water per year from the mouth of the Guadalupe River to Bexar County via a 120-mile pipeline. There have been subsequent references to larger amounts of water. Since the water from this project would be used primarily for municipal purposes, it must be available as firm yield (available to the municipalities 100% of the time.) In order to provide this guarantee, water would be obtained from several sources including existing surface water rights owned by the GBRA, groundwater from the Gulf Coast aquifer, and the granting of water rights to additional streamflow from the Guadalupe River. The streamflows would be diverted into two 20,000-acre off-channel reservoirs from a location near the Saltwater Barrier, which is just above San Antonio Bay. The water would then be treated and pumped via the pipeline to Bexar County.

There are many years during which there might be plenty of water for this project as well as adequate flows to maintain a healthy bay and estuary system. However, during dry and drought years, further reducing already depleted flows would worsen stressful conditions for fish and wildlife that rely on flows from the river. That could be disastrous for the bay system. It also would worsen conditions for the people who earn their living catching or helping others catch or view that fish and wildlife.

To learn more, click on a topic:

    Environmental Concerns

    Project Specifics and Timeline


    Public Participation

    Contact Information

Environmental Concerns

Bays and Estuaries
There is reason to be concerned about the impacts of reduced freshwater inflows to the San Antonio Bay system. Freshwater inflow is necessary to keep the salinity within a range that will support a healthy estuarine and marine environment and to provide critical nutrients and sediments. Without the freshwater inflow, the bay system would become too saline to serve as a nursery area for the spawning of the numerous commercial and recreational species dependent on it . Similarly, without the nutrients and sediments carried by those inflows, the food chain of the bay would collapse.

The recreational and commercial fishing industries in the bays supported by inflow from the Guadalupe River have an estimated economic value of $575 million dollars a year. Other natural resource-related tourist activities, such as bird watching and particularly viewing the endangered whooping cranes, also add millions to the local economies around the bay. All of those activities depend on fish and wildlife populations that, in turn, depend on a sufficient amount of freshwater making it to the bay at the right time of the year via the Guadalupe River. 1Reduction in inflow to San Antonio Bay could also adversely impact the Mission and Aransas Bays, which are hydrologically connected to San Antonio Bay.

This proposed project could dramatically reduce flows to the bay during dry periods.. In many years, there might be enough flow to allow for project diversions while also maintaining a healthy estuarine system. In dry or drought years, there are no adequate protections in place to maintain a level of flow to the bay which ensures ecological health.

Groundwater Withdrawals
In order to attain the 94,500 acre-feet of water for San Antonio with greater reliability, the project proposes to pump groundwater from the Gulf Coast aquifer to supplement surface water supplies. Landowners and ranchers in the lower Guadalupe region have expressed concern over the proposed "conjunctive use" of groundwater in this project. When withdrawals from aquifers are made in excess of recharge (also referred to as "aquifer mining"), the levels in the aquifer drop, making it more costly and difficult for local landowners and farmers to get the water from their wells. The long-term average amount of groundwater to be withdrawn is 14,196 acre-feet per year, but withdrawals could range from 0 to 41,376 acre-feet per year. In response to the concerns associated with the development of additional groundwater supplies in this aquifer, the GBRA has developed a Groundwater Policy that will be used to guide the development of groundwater resources.

Off-channel Reservoirs
The capturing of river flows to be stored in off-channel reservoirs has an additional set of environmental concerns associated with it. There is potential for localized impacts at the two-20,000 acre off-channel reservoirs sites. Furthermore, reduction of inflow of freshwater to the bay could greatly reduce nutrient inputs to the estuary, limiting the productivity of the system. Also, reduced freshwater inflow, especially in dry times, will drive salinity levels up in the bay, and could possibly weaken species dependent on a less saline environment for reproduction and growth . Compounding the situation, higher salinity levels provide better environments for the growth of certain parasitic organisms that attack traditionally harvested species.

1 TPWD (2000). Citation.

Project Specifics and Timeline

The Project is projected to be online within the next 10 years. The GBRA has already submitted an application to the Texas Commission on Environmental Quality (TCEQ) for new water rights to pump additional stream flow from the Guadalupe River.

Project Specifics
This project includes the following components:
  • Existing , but currently unused, surface water rights held by the GBRA and Union Carbide Corporation (UCC) will provide up to 67,200 acre-feet of water per year.
  • Currently unappropriated streamflow would provide up to 54,500 acre-feet per year. Although 54,500 acre-feet was the amount originally proposed, GBRA recently has applied for a permit to divert up to 289,000 acre-feet of water per year.
  • Two off-channel reservoirs, with a combined capacity of approximately 50,000 acre-feet, will be used to capture flood flows in the Guadalupe River Basin.
  • Groundwater from the Gulf Coast aquifer, in amounts of up to 41,400 acre-feet per year, with an average of approximately 14,000 - acre-feet per year, may be used to supplement project water during times when surface water flows are inadequate to meet project needs.

Initial cost estimates for water from this agreement are approximately $900 per acre-foot. Other options, such as further water conservation efforts in the region, are estimated to only cost between $50 and $200 per acre-foot or water.

Public Participation
Contact us if you would like additional information or for suggestions on how you can become involved in this issue.

For More Information
Contact Laura Brock Marbury at Environmental Defense, 512-478-5161.