Under Our Feet: The Edwards and Trinity Aquifers

Learn about the unique and vital aquifers under your feet and how you can protect them!

Scroll through or click on each heading above to learn more about what's under our feet in Central Texas -- the Edwards and Trinity Aquifers!

Learn about where the aquifers are, what the groundwater cycle is like, what makes the Edwards Aquifer so unique, and how to protect the two aquifers. Then, get your feet wet in aquifer protection by "adopting" a Texas Blind Salamander and taking the aquifer protection pledge!

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Our Aquifers

The Edwards and Trinity Systems

Are you located in the Recharge or Contributing Zone of the Edwards Aquifer or within the Trinity Aquifer system?

Type your address into the search button (magnifying glass in the upper left) on the map below to find out! Then scroll down to see what each zone of the aquifer means.

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Edwards Aquifer Zones and Trinity Aquifer Map

The Karst Limestone Aquifer Groundwater Cycle

Both the Edwards and Trinity aquifers are karst limestone aquifers. The Edwards is more porous (full of holes) than the Trinity and recharges much more quickly, but both aquifers follow the same groundwater cycle!

Formation

Karst aquifers form in areas where bedrock is composed of limestone. When water interacts with the limestone, it forms carbonic acid. As carbonic acid seeps into the ground and dissolves the soluble bedrock, a network of sinkholes, caves, fractures, and caverns form. This porous network forms the aquifer system.

Recharge

The porous nature of karst limestone formations allows water to move quickly and freely from the surface into the network below ground, recharging the aquifer. Karst limestone aquifers recharge much faster than other types of aquifers, like sand aquifers, such as the Ogallala Aquifer. Recharge between different types of karst aquifers varies. The Edwards is much more porous than the Trinity, meaning it recharges more quickly after runoff events.

Risks

The same ability of karst aquifers to recharge more quickly and freely than other types of aquifers also places them at greater risk of contamination. Pollutants, waste, bacteria, and other contaminants can easily infiltrate into our aquifers during recharge and can rapidly travel long distances within the aquifer system. Human actions on the surface of karst landscapes can easily pollute water supplies below the surface.

The Edwards and Trinity Aquifer Levels

Aquifer and spring flow levels signify the health of the aquifer and help cities and water providers determine drought stages. Knowing the aquifer conditions and stages can keep you informed and help you understand the actions of your local governments!

Find out the daily Edwards Aquifer levels and spring flow levels, collected by the Edwards Aquifer Authority, in the chart to the right (or in the chart above, if viewing on a cellphone).

Click  on this  link to see data from the Trinity Aquifer, collected by the Cow Creek Groundwater Conservation District in Kendall County. The levels can be found in the "Drought Conditions" chart on the right side of the website's homepage.


The Hidden Heart of Texas

The Edwards Aquifer is the lifeblood of dozens of communities - and millions of people - in Central and South Central Texas. So too for over 60 species of plants and animals that live in the Edwards Aquifer Ecosystem and nowhere else on the planet.

The Greater Edwards Aquifer Alliance

The Hidden Heart of Texas - the Edwards Aquifer ecosystem - is the essential life source for many of Central and South Texas' cold springs, clear streams, world-class caves, stunning vistas, unique plants and animals, big cities, small communities, and treasured parks and natural spaces. The Edwards Aquifer and its watersheds, including the Trinity Aquifer, provide drinking water to more than 2.5 million people.

What are some defining characteristics of the Edwards and Trinity aquifers and the land, springs, and streams that they sustain?

Karst Limestone

Little Filtration

Caves and Crevices

Little Streamside Vegetation

Fluctuating Flows

High Water Quality

Responsive Spring Flows


Protecting Texas Treasures

The Edwards and Trinity aquifers are extremely important to Texans. They are the main water supply for Central Texas and the Hill Country. These aquifers supply water to millions of people, support local ecosystems and many endangered species, are integral to agricultural and industrial activities, recharge the seven largest springs in Texas, and are the source waters for many of the iconic Hill Country rivers and streams.

Hill Country rivers travel to the Texas Gulf Coast, where they contribute fresh water to maintain the balance of salt and fresh water in the bays and estuaries. Wildlife, including the protected whooping cranes, and the gulf coast seafood industry rely on the in-stream flows that originate in the Texas Hill Country from the underlying aquifers.

Human activities directly, and often negatively, impact the quality of these aquifers, which means we must think differently about how we treat our land and water resources in the region, especially in the recharge zones!

What's happening in the Recharge Zone and the Edwards and Trinity aquifer region?

Development in the Recharge Zone and upstream...in the Contributing Zone of new subdivisions, shopping centers, office buildings, highways, golf courses, sewer lines, wastewater treatment plants, and rock quarries all create increased risk of contamination of the aquifer.

Greater Edwards Aquifer Alliance

Development in the Edwards Aquifer Recharge Zone

Search a location or zoom in on the first map to see development in the Edwards Aquifer Recharge Zone. What do you notice? Do you think adequate protection of the recharge zone is occurring?

On the second map, see where population growth is occurring. What are the risks to the aquifer that could come with this increasing population growth? Keep scrolling to learn why development and population growth can impact water quality.

Edwards Aquifer Recharge Zone and Development Map

Texas County Population Growth with Edwards Aquifer Recharge Zone

How has the Edwards and Trinity region changed over time?

Urban development creates numerous sources of water pollution. Construction transforms farm, ranch, forest, and pasture land into large areas of disturbed soil. Development transforms pervious land into impervious cover, which means any surface that water cannot pass through, such as roofs, parking lots, and roads. Rainfall that hits impervious cover rather than healthy pervious soil washes oil, grease, bacteria, and other contaminants into creeks, streams, and other recharge features.

Interacting with the map below, what do you notice? What are some trends that have occurred over the past roughly 30 years?

Use the slider on the map below to see the changes in development and impervious cover between 1992 and 2019. The legend shows which colors correspond to different types of land cover. For example, red indicates impervious surface. This means developed, or built-up, land. Pink is less intensively developed urban areas, and darker red is more intensively developed.

Land Use Map showing the  changes in development intensity  between 1992 (left) and 2019 (right).

How to protect the Edwards and Trinity aquifer region

For the aquifer to be protected, the land above it needs to be protected too. Scroll through the images below and click on the resources that follow to learn more about how to protect the aquifer and the land it relies on!


Take the Pledge

Despite the aquifer's immense value to human, animal, and plant life in Central Texas, urban development now threatens the basic integrity of the Edwards Aquifer Ecosystem. Hill Country watersheds that feed the aquifer are increasingly targeted for residential, commercial, and industrial development, often without the necessary regulations to protect water quality and water quantity. Increased development is not only polluting the aquifer and its springs, it is also creating demand for water that exceeds what the aquifer has the capacity to provide. Human needs and agricultural production; the needs of endangered and threatened species; and Hill Country and coastal economies and ecosystems are at risk from contamination and over-pumping of the Edwards and Trinity aquifers.

Now that you have a greater understanding of the Hidden Heart of Texas, it's time to put your knowledge into action! There are countless ways in which you can protect these Texas Treasures, including what you've learned above, but we've highlighted a few more of them in the Under Our Feet Aquifer Protection Pledge.

Scroll to learn more and then use the button that follows to take the Under Our Feet Aquifer Protection Pledge and commit to doing your part to protect the Hidden Heart of Texas!


Adopt-A-Salamander

The Texas Blind Salamander is an endangered species that lives deep within the Edwards Aquifer, and these not-so-furry-friends need your help to keep their home clean and safe. By participating in GEAA's Adopt-A-Salamander program, you are supporting projects and programs that are designed to protect and preserve the Edwards Aquifer.

With your help, we can ensure that these tiny critters have a home for years to come!

When you adopt a salamander with GEAA, you will receive our Certificate of Adoption!

Not interested in adopting a salamander but still want to support projects and programs dedicated to protecting our Texas Treasures? Not a problem! Click on the button below to learn how to contribute to this cause.


The Aquifer in the News

Headline

News Source

Link

'Like walking on the moon': Conservation deal helps uncover rare Hill Country cave

The San Antonio Express-News

Exactly where does rain need to fall in South Texas to fill up the Edwards Aquifer?

The San Antonio Express-News

Report: New law puts Edwards, Trinity aquifers at greater risk

San Antonio Report


Additional Resources


Thanks to the following for their contributions to this site:

Primary Content and Maps

Rachel Hanes

Additional Content

Olivia Walshak, Annalisa Peace

Infographics

Olivia Walshak

Review

Annalisa Peace, Nathan Glavy

Website Connection

Kellie Fichter

Support

National Wildlife Federation, Wells Fargo

Land Use Map showing the  changes in development intensity  between 1992 (left) and 2019 (right).