The paper Exploring Groundwater Recoverability in Texas: Maximum Economically Recoverable Storage by Justin C. Thompson, Charles W. Kreitler, and Michael H. Young is in the current issue (Volume 3, Issue 12) of the Texas Water Journal. As the teaser says, 'This study addresses the question: What are the economic and physical limits to recoverability?'
I recommend it.
I have reproduced the abstract, introduction, conclusion and Figures 1-3 here to whet your appetite. Download the full paper by clicking here.
Abstract
The 2017 Texas state water plan projects total supply deficits of 4.8 and 8.9 million acre-feet under drought-of-record conditions by the year 2020 and 2070, respectively, driven by a growing population concurrent with declining available water supplies. Reductions in groundwater supply account for 95% of anticipated declines in total water supply. Meanwhile, restrictive groundwater management plans may be creating a regulation-induced shortage of groundwater in Texas, given the significant groundwater storage volumes that are unutilized under many management plans. However, these estimates do not account for many of the physical and none of the economic constraints to groundwater recoverability. We report an analysis of groundwater extraction feasibility and simulate maximum economically recoverable storage for conditions representative of the central section of the Carrizo-Wilcox Aquifer under economic constraints associated with agricultural uses. Two key limitations are applied to simulate recoverability: (1) the value of water pumped relative to pumping costs and (2) the capacity of the aquifer and well to meet demand. Our results indicate that these constraints may limit certain uses to as little as 1% of current groundwater availability estimates. We suggest that Texas groundwater managers, stakeholders, and policymakers assessing groundwater availability need an alternate approach for estimating recoverability.
Introduction
Is Texas running out of groundwater, blessed with abundance, or somewhere in the middle? This question, historically shrouded in scientific uncertainty and political controversy, represents a complex nexus of hydrogeology, economics, and policy with many relevant and potentially conflicting considerations. Hydrogeologic conditions and management objectives vary significantly across the state, and as a consequence there is no universal yield solution.Nonetheless, one key element common to all human groundwater demand is recoverability, defined as the relative ease or difficulty of extraction. Recoverability is constrained by aquifer characteristics, well design, and economics. While recoverability data is crucial to groundwater planning and management, particularly with respect to availability assessments, Texas’ best estimates of recoverable groundwater volumes reflect only the volume in storage and take no account of well design or economic constraints. This study therefore addresses the question: What are the economic and physical limits to recoverability? By establishing these limits, we can better estimate potentially available groundwater for given uses and infrastructure.
Conclusion
We conclude that Texas groundwater managers, stakeholders, and policymakers assessing groundwater availability need an alternate approach for estimating recoverability. The current metrics employed by the state for estimating groundwater storage and recoverability, total storage and TERS, are highly limited in scope and function. Irrespective of the name, TERS values do not scientifically account for many of the physical and none of the economic constraints upon groundwater recoverability, as noted by the TWDB (Bradley 2016).The system of equations described above, which constitute the MERS model, represents one method for estimating the limits of groundwater recoverability that accounts for some of the physical and economic constraints upon yields. These constraints can be significant and may limit recoverability to as little as 1% of local storage (or 1.1% and 3.2% of comparable TERS estimates) in deep and confined settings. This suggests that the majority of water stored in the Carrizo-Wilcox Aquifer (45% of major aquifer storage in Texas) may not be economically recoverable for some agricultural uses. Conversely, recoverability of water stored in shallow and unconfined settings may be limited only by the capacity of the well and aquifer to meet demanded pumping rates.
Future studies expanding on these methods may refine drawdown estimates by replacing specific capacity estimates with drawdown solutions that account for partial well penetrationthough the analyses would become more complex. These or similar methods could also be integrated with the TWDB groundwater availability model and groundwater database data to estimate local recoverability for any use and aquifer.
Ultimately, what is recoverable for a microchip manufacturer may not be the same as what is recoverable for a farmer, and what is recoverable for an alfalfa farmer may not be the same as what is recoverable for a tomato farmer. Moreover, the limits to what is economically recoverable for any user are not economically efficient and pumping costs increase for all users in all cases where depth-to-water increases. Nonetheless, quantifying planned and potential changes to groundwater recoverability using scientific methods with known assumptions, conditions, and infrastructure provides important information for Texas policymakers and stakeholders looking to the future.
Enjoy!
"There are lies, there are damn lies, and there are hydrologist reports." - Texas legislative hearing, 2 February 2016 (thanks to Robert Mace)
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