1. Sustainable Yield Groundwater in Arid and Semi-Arid Lands in Texas
Presented at
Geological Society of America
South-Central Section by
Ronald T. Green, F. Paul Bertetti,
S. Beth Fratesi, and Nathaniel J. Toll
Southwest Research Institute®
March 13, 2017

2. Sustainable Groundwater
Groundwater sustainability is the development and use of groundwater resources to meet current and future beneficial uses without causing unacceptable environmental or socioeconomic consequences.
(USGS Circular 1186)

3. Common Perception
There are those that believe that Texas does not have a water shortage problem, rather Texas has a water transmission problem.
Further, this perspective believes that local water shortages can be met if water resources are governed by free market forces.

4. Texas Projected Water Usage 2010-2060
(Texas Water Development Board Website, 2010)

5. Basic Facts
1/4-1/3 of Texas is arid and semi-arid (< 20 inches/year)
Urban (municipal) and rural (irrigation) interests compete for finite resources
Recharge and available water are dependent on precipitation and are highly variable
Future threats to water availability from
(i) drought (short-term trends)
(ii) climate change (long-term trends)

6. Managing Water Resources in the Edwards Plateau
Mostly carbonate aquifer with limited storage
Watersheds act independently
Mostly arid and semi-arid

7. Discharge measured at river gauging stations is used to estimate recharge

8. Recharge rate is calculated as baseflow component of river discharge
Storm flow
Baseflow
Storm Surge
Storm flow
Baseflow

9. Distributed Recharge Rates Calculated from Stream Discharge Measurement

10. Recharge rates in study area corrected for actual groundwater catchment areas10

11. Recharge is Minimal when Precipitation is Less than 20 inch/year
Distributed
Recharge
Focused
Blue data – Texas Hill Country

12. Recharge is Minimal when Precipitation is Less than 20 inch/year Additional Supporting Data
R = 0.15 (P – 16.5)
Blue data – Texas Hill Country
Red data – Pretoria South Africa

13. Average Precipitation

14. Distributed Recharge Calculated from Average Precipitation
R = 0.15 (P – 16.5)
No Distributed Recharge
Distributed
Recharge

15. Short-Term Variability in Annual Precipitation Del Rio (inch/year) (1920 to 2000)
Long-term Average
10%
20%
30%
40% occurrence
30% occurrence
20% occurrence

16. Short-Term Recharge as a Function of Precipitation (acre-feet/year)
Crockett
Edwards
Kimble
Menard
Real
Schleicher
Sutton
Val Verde
Recharge under average conditions
56,140
144,160
95,076
61,268
81,200
57,684
75,556
90,496
Predicted recharge at
90% precipitation
13,474
101,760
69,055
43,248
63,840
34,610
48,821
38,784
80% precipitation
59,360
43,034
25,228
46,480
11,537
22,086
70% precipitation
1,837
2,127
300
5,193
40%
30%
20%

17. Watershed Independence is of Critical Importance if Water Resource Management Assumes a Regional Aquifer (i.e., Edwards-Trinity) is a Single Reservoir

18. Each Watershed Has a Separate Water Budget
Colorado
River-Concho
Lower Pecos
River
Colorado
River-Llano
Rio Grande Amistad
Devils
River
Nueces
River
Rio Grande Falcon
Preliminary - Subject to Revision
Edwards-Trinity Aquifer Water Budget
Preliminary - Subject to Revision

19. Effect of Long-Term Drought or Climate Change on Recharge in West Texas

20. Average Year Precipitation threshold below which17
Precipitation threshold below which
distributed recharge is negligible
Area that experiences
distributed recharge
Area that
experiences negligible 17

21. Dry Year (30% decrease) Precipitation threshold17
Precipitation threshold
below which distributed
recharge is negligible migrates
east during periods of drought
30% decrease in precipitation
occurs 20% of the time 17

22. Texas Can be Sub-Divided by Area into Three Categories of Recharge
Area that rarely
experiences
distributed recharge
Area that almost always
experiences
distributed recharge
Area that may or may
not experience
distributed recharge

23. Intermediate Zone Does Not Provide Sustainable Sources for Water Supply

24. Area that almost always
Climate Change that Causes Less Precipitation Will Shift these Zones to the East
Area that may or may
not experience
distributed recharge
Area that rarely
experiences
distributed recharge
Area that almost always
experiences
distributed recharge

25. Locations Targeted for Groundwater Export

26. Managing Water Resources in the Edwards Plateau
Mostly arid and semi-arid
Mostly carbonate aquifer with limited storage
Watersheds act independently

27. Unless significant quantities of water can be stored during times of plenty, carbonate aquifers in arid and semi-arid environments cannot provide sustainable sources of excess water

28. Continental Variability in Precipitation and Recharge

29. Approximate
Threshold of
distributed
recharge

30. Sustainable Yield Groundwater in Arid and Semi-Arid Lands in Texas
Summary
Recharge is limited, uncertain, and varies from year to year
Recharge becomes negligible when precipitation decreases below a threshold of in/yr
Arid and semi-arid regions are vulnerable to limited recharge during short-term periods of drought
Long-term climate change could exacerbate water shortage by increasing magnitude of variability and reducing precipitation/recharge
Water-resource planning needs to account for these potential threats

31. Contact Information
Ronald T. Green, Ph.D., P.G.
Institute Scientist
Earth Science Section
Space Science Division
Southwest Research Institute
6220 Culebra
San Antonio, Texas 78238
(office)
(fax)
(cell)