how much groundwater is OK to take?

A few weeks ago I turned in the final draft of a book I wrote on groundwater sustainability to the publisher. Editors will now have their way with it and, hopefully, it will come out by the end of the year. It was a neat, but challenging, experience, something that the pandemic allowed me to pursue with all the extra time I had from not commuting between north-central Austin and San Marcos. Amazingly, the editors let me write the book I wanted to write with all of my mild goofiness and references to Joy Division and the Talking Heads.

In the book, I tell the full story of the development of sustainable management of groundwater, the misplaced angst of scientists and engineers over safe/sustainable yield, and definitions of concepts and terms. Ultimately, to truly define groundwater sustainability, someone has to define the unacceptable environmental, economic, and social consequences (or, more positively, the acceptable outcomes). But in a case like Texas, where most local regulating bodies do not manage groundwater sustainably nor even consider sustainable levels of pumping, how should sustainability be defined to introduce it into policy discussions?

I, and other scientists, have proposed that, in these cases, we should report the maximum sustainable production amount. This is not an endorsement of this level of production and consequences but rather a number on the sustainable pumping spectrum that is devoid of the yuckiness of human interaction. In other words, it doesn’t require a policy decision. I also hide behind the argument that the number is simply a suggestion of what sustainable pumping could be and that if a regulating body decided they wanted to pursue it, they could then have the stakeholder meetings and discussions to fully explore unacceptable consequences. More appropriately, some have run a range of model simulations encompassing a range of consequences so folks can see how much can be pumped with what impacts. However, multiple numbers can be confusing.

The maximum sustainable production amount causes some folks consternation, and for good reason. If you value springs and the ecosystems and water that springs provide, the maximum sustainable production amount may result in a number of springs going dry. After all, sustainable production is generally met by capturing natural discharge, and springs are a part of that natural discharge portfolio. Furthermore, the presentation of the first number can result in anchoring where the receiver perceives the number as a reference point (or the point) to compare all others. In this case, perhaps a different point should be used that splits the (water) baby.

I’ve been thinking about this question while reading Braiding Sweetgrass: Indigenous Wisdom, Scientific Knowledge, and the Teachings of Plants by Robin Wall Kimmerer. Kimmerer has a Ph.D. in ecology but is also part of the Potawatomi Nation and steeped in the tradition of her tribe’s ways and how they interact with the landscape (I recommend listening to the book because she reads it with the singsongy, whispered wisdom of the woods). The book explores the symbiotic relationship between nature and people and laments how modern society neglects its place in the environment. Along those lines, with respect to harvesting plants from the wild, Kimmerer shares the Potawatomi’s adage that you never take more than 50 percent from nature.

Fifty percent. Maybe example groundwater sustainability runs should plan to not use more than 50 percent of the natural discharge. That also got me to thinking that groundwater production from the San Antonio Segment of the Edwards Aquifer here in Texas is about 50 percent. Indeed, using my calibrated eyeball, that appears to be true:

image from Edwards Aquifer Authority.

That’s not to say that this level of production has not had its consequences: San Antonio and San Pedro springs have not been reliable for over a hundred years since production started in the late 1800s. But, setting those two springs aside, most folks seem OK with this 50 percent reduction (although many had their hand forced via the Endangered Species Act). For example, San Antonio was initially not happy with pumping restrictions.

As Texas considers groundwater sustainability, perhaps the reference number is one that preserves at least 50 percent of natural discharge. It could go higher or it could go lower with a formal process to define groundwater sustainability for a particular aquifer.

4 thoughts on “how much groundwater is OK to take?

  1. Robert, please explain how you determine what amount of water is “natural discharge”. In Teaxas, we have a pretty limited data base of historic “natural discharge”. Is the explanation in the book?


    1. That’s the rub, isn’t it? My preference is through numerical groundwater flow modeling constrained by available data, which includes spring and baseflow measurements, hydraulic properties, etc. This is easier in some places than others, and in some places the natural discharge is relatively untouched by production. I qualified how much to pump with “not more than” because in some cases (such as the confined zone of the northern Trinity Aquifer), one can sustainably pump with large water-level declines and impact natural discharge in the outcrop less than 5 percent.


  2. How much ‘ groundwater extraction is ok’ is a big issue in Arizona. When asked, what I advise is to follow the water-law approach of Colorado. I used to work in water law/rights in Denver (1981 – years ago, things may have changed since then!). To get a drilling permit you first had to propose the rate of extraction, and then calculate the extent of the drawdown cone after 100 years. You were allowed that volume of water for 100 years after well completion. However! If, when mapped, your cone intersected or overlapped a pre-existing well, their volume of water (or the percentage your cone would have taken) is subtracted from your allowable total volume. And your allowable pumping rate reduced.

    This protected the existing wells. Over time, however, it will exhaust the Aquifer. The community, however, felt a part of the process.

    Good luck with that book! I was offered a book contract back in the early 90’s, by the ASCE, to write a book on remediation. That was the early days! But my employer would not allow me to take the time (my own time!!) and insisted I name the VP as a co-author. That same VP was pissed that I wrote for the ASCE, telling me that if I was a team player I would have named him as the author. Too many times I was expected to be a ghost writer.

    I would love to buy your book! Let me know!!

    Kristine Uhlman

    Sent from my iPhone



    1. Thanks for the comment and example! In my mind, the ideal method is through a stakeholder process where the decisonmakers hear all of the concerns and hopes and desires of affected parties before settling on a number and the resulting impacts.

      The book, “Groundwater Sustainability: Conception, Development, and Implementation,” should be out later this year through Palgrave-Macmillan. Sorry your book fell through. People can really be doofballs. You should write one now!


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