Water Level Maps of the Edwards and Middle Trinity Aquifers, Central Texas

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BSEACD Fact Sheet 0314 Water Level Maps of the Edwards and Middle Trinity Aquifers, Central Texas

March 2014 Brian B. Hunt and Robin H. Gary eek Cr B rton ar Ba to n Austin C re Abstract ek W 45 ill iam 0 son The District periodically creates water level, or potentiometric surface, Cr eek maps during dierent hydrologic conditions to better understand regional groundwater storage and ow. Four water level Sla ugh ter (potentiometric) maps are provided in this fact sheet. The available data C r 0 e e cover water level conditions in the Barton Springs segment of the 5 k Edwards Aquifer during the drought of record, recent extreme drought 6 0 5 0 0 (2009), and recent high ow conditions (2002) and low-ow conditions 7 0 in the Middle Trinity Aquifer. L i Manchacacha ca ion Creek tt n le B O e ar 0 Hays 5 Creek 5 5 7 0 Water Level Maps A water level map (also called a potentiometric map) is an imaginary water Buda

0 level surface dened by water level elevations in wells (Figure 1). The maps 0 6 represent the general direction of groundwater ow for a given area at a particular time because ow always occurs from higher to lower (potentiometric) elevations. Water level maps provide critical information Mountain City about the hydrologic relationships of recharge and discharge within an aquifer. lanco Ri B v e r In karst landscapes, like central Texas, water level maps are commonly used Kyle to better understand groundwater ow; however, they should not be used to solely characterize groundwater ow direction or velocity in a karst 01.5 3 6 Miles aquifer. Water level maps should be combined with hydrogeologic mapping, dye trace studies, and other information for a more complete understanding of ow within a karst system (Kresic, 2007). Edwards Recharge Zone Trinity Outcrop Edwards Confined Zone Water Level To construct a water level map one must measure the depth to water in a well from the land surface. This is usually done with an electronic tape Figure 2: Water level map showing estimated groundwater elevations called an eline. The depth to water is then subtracted from the land surface during the drought of record, in the 1950s. Relatively few data points were elevation to obtain the elevation of the water level in the well. These data available, so the water level contours are a very coarse estimation of are then plotted on a map and either contoured by hand or by computer groundwater conditions at that time. The Recharge Zone is the area where the Edwards Group rock units crop out and water enters (recharges) the programs (Figure 2). aquifer. The Con!ned Zone is the area where the aquifer units are below Water level elevation con!ning units and transition from uncon!ned to con!ned hydrologic conditions. Water Elevation (potentiometric) in water well contours fa ce 718 ft 800 652 ft Ground Sur 588 ft 450 ft 765 ft 700 700 800 Flow 600 523 ft 800 500

600 700 Water T Water able Table 500 600 Elevation (ft-msl) Elevation Aquifer 500

Figure 1: Schematic diagram of an aquifer showing a water level contour map and the wells used to draw the contours. Fig. 3A: High Flow Conditions - Feb. 2002

D Edwards Aquifer Water Levels

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WX [

YZ Like all aquifers, water levels in the Edwards Aquifer vary according ]

\ to the amount of water stored in the aquifer, which is dependent

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! upon the climatic conditions. In addition, the location (unconned

( ) * + , - . / ' or conned zones) within the aquifer can also inuence the water

levels and how much they may vary over time. Water levels do not

show long-term declines in storage, but generally recover from

low conditions quickly (Smith et al., 2001), typical of many karst

¡ systems. Barton Springs and some wells respond very quickly to recharge events reecting their inuence by conduit (fast)

permeability (Lindgren et al., 2004; Worthington, 2003). Most

h c i j k c j c

c i j k c j c

h water wells show a combined inuence of matrix (slow) and

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b c _ d

c _ d

b conduit ow.

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GH I J K L M N O P QR

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e f g c

f g c e High Flow Conditions

In February of 2002, Barton Springs discharge was ~100 cubic feet

þ ÿ ¡ ¢ £ ¤ ¥ ¦ § ý per second (cfs) reecting high-ow conditions. Throughout the

District, water levels in 172 wells were measured within a month.

h l f i m c n i o n m _

l f i m c n i o n m _ h These water level measurements were contoured to make a potentiometric map. Contours represent 10-foot intervals and the

100-foot intervals are labeled (Figure 3A).

0 1 2 3 4 5 6 7 8 9 :

^ _ ` a

^ _ ` a ¨ © Potentiometric troughs along known preferential ow paths are

pronounced as broad features that extend from Buda to Barton

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n ` a d h Springs. The troughs in the Barton Springs aquifer appear to occur along the east side of the recharge zone (unconned) boundary. Signicant mounding due to recharge along Onion Creek, and due

to Antioch Cave, is evident in the potentiometric surface during

t u v w x u y z { | } w x ~ { t u v w x u y { u x | x high-ow conditions. Depressions in the potentiometric surface are evident around areas that have high levels of pumping, such as

Fig. 3B: Drought Conditions - Mar. 2009 the City of Kyle.

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Drought Conditions

³ ´ µ ¶ · ¶ In March of 2009, Barton Springs discharge varied between 16-26

cfs, reecting drought conditions. The District had been in Stage III

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Critical Drought since early December 2008. Throughout the

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¤ District water levels in 274 wells were measured within about a § ¨

month. Contours represent 10-foot intervals and the 100-foot ¨ ©

intervals are labeled (Figure 3B).

The aquifer shows signicant declines (contours shift to the south)

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from wet (Figure 3A) to drought conditions (Figure 3B). Troughs in

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ë the potentiometric surface are very pronounced with steep

Î Ï Ð Ñ Ò Ó Ô Õ Ö × ØÙ Í gradients. Multiple troughs begin to develop as seen in the 500-ft

contour. In addition, troughs develop along known preferential

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ï ð ì î ow paths (conduits) documented by dye tracing, such as the one

originating at Antioch Cave. Signicant troughs in the

þ ÿ ¡ ¢ £ ¤ ¥ ¦ § ý potentiometric surface appear to develop in the conned portion

of the Barton Springs aquifer.

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Figure 3. Potentiometric contour maps of the Barton Springs segment

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ç è é ê ËÌ Ê of the Edwards Aquifer. The map on the top was constructed with 172 well and spring measurements during a relatively wet period, February

2002 (modi!ed from Hunt et al., 2007). The map on the bottom was

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÷ é ê í

ñ constructed with 274 wells and springs during a relatively dry period,

March 2009.

BSEACD Fact Sheet 0314 Barton Springs/Edwards Aquifer Conservation District www.bseacd.org (512) 282-8441 Middle Trinity Aquifer Water Levels

The Trinity Aquifer is the primary groundwater source for a variety Nine GCDs and several other organizations collaborated to collect of needs throughout the Texas Hill Country. The Trinity Aquifer is 232 water-level measurements from the Middle Trinity Aquifer composed of Cretaceous-age limestones and sandstones that are during the Spring of 2009. Spring 2009 was a period of extreme to divided into the Upper, Middle, and Lower Trinity Aquifers. In the exceptional drought according to the U.S. Drought Monitor, and District the Edwards Aquifer overlies the Trinity Aquifer, and these water level measurements reect a drought condition because of faulting, can also be adjacent to the Trinity Aquifer. potentiometric map; contours represent 100-foot intervals (Figure Groundwater quality of the Trinity Aquifer is generally poorer than 4). the Edwards Aquifer containing higher total dissolved solids (TDS) and undesirable constituents such as sulfates. Due to low yields and The Spring 2009 potentiometric map suggests that ow within the poorer water quality the Trinity has not historically been targeted Middle Trinity is generally from northwest to southeast. This is for production except along the western part of the District, where predominantly down-dip of the geologic units from outcrop into the Edwards Aquifer is thin. Where the Edwards is thin, the subsurface. A prominent potentiometric ridge exists along the water-supply wells commonly penetrate the lower Edwards units Blanco-Kendall County line and separates a more west to east ow and are completed in units that comprise the Upper and Middle system within Blanco, Hays, and Travis Counties. A portion of the Trinity Aquifers. ow appears to deviate to the northeast along the Balcones Fault Zone as it approaches Travis County. The Lower Glen Rose is The Middle Trinity Aquifer is composed of (from stratigraphically exposed along the Colorado River west of the Balcones Fault Zone lowest to highest) the Cow Creek, Hensel, and the Lower Glen Rose and could be the discharge point for the Middle Trinity in that area. Formations. It is the primary aquifer in the Trinity Aquifer system for Other features noted in the map include predominantly converging water-supply needs in the Hill Country. Nine Groundwater ow centered along the Guadalupe River west of Canyon Lake. Conservation Districts (GCDs) within the Texas Hill Country are tasked with managing groundwater resources in that area. Increasing water-supply demands have raised concerns about the availability of groundwater in the Texas Hill Country.

Lakeway Fig. 4: Drought Conditions - Mar. 2009

Lost Creek TRAVIS k Johnson City Cree Fredericksburg n to GILLESPIE ar Hye B 0 700 Hye 0 1 Stonewall 5 BLANCO Dripping Springs

0 Driftwood 6

B lanco River 0 1 k 600 0 Blanco n Cre e 50 Onio 1 HAYS Buda

Woodcreek 0 Woodcreek 7 Wimberley Kyle lup Fischer KERR 0 ada e R Kendalia 0 Comfort Gu iv 4 er 1 Center Point KENDALL

0 Spring Branch 0 Spring Branch 0 9 San Marcos Canyon Lake 0 San Marcos 1 8 1 0 0 Bergheim 0 0 Boerne 0 0 0 Boerne COMAL 0 3 2 0 1 1 1 BANDERA GUADALUPE BEXAR Bulverde

03 6 12 Miles Trinity Outcrop Edwards Recharge Edwards Confined

Figure 4: Potentiometric contour map of the Middle Trinity Aquifer of the Texas Hill Country during relatively dry period of March 2009 (modied from Hunt and Smith, 2010).

BSEACD Fact Sheet 0314 Barton Springs/Edwards Aquifer Conservation District www.bseacd.org (512) 282-8441 Conclusions

Water level maps can create a snapshot of aquifer conditions for a given area at a particular moment in time. Both the Edwards and Trinity Aquifers have dynamic water levels that are substantially inuenced by drought, wet weather patterns, and geology. In some areas, wells can uctuate more than 100 ft between the high and low ow conditions in the Barton Springs aquifer. Inuences of discrete recharge and discrete discharge (pumping) are evident on potentiometric surfaces. Troughs and ridges in the potentiometric surfaces correspond to preferential ow paths (conduits), or potential barriers to ow, respectively. Selected References

Broun, A.S., D.A. Wierman, A.H. Backus, B.B. Hunt, 2007, Geological Analysis of the Trinity Group Aquifers in Western Hays County, Texas, with Focus on Implications to Groundwater Availability. in Reimers Ranch and Westcave Preserve: Landscapes, Water, and Lower Cretaceous Stratigraphy of the Pedernales Watershed, Western Travis County, Texas. Trip Coordinators B. Hunt, C. Woodru, and E. Collins. Austin Geological Society Guidebook #28, 130 p. + appendix.

Hovorka, S., R. Mace, and E. Collins, 1998, Permeability Structure of the Edwards Aquifer, South Texas—Implications for Aquifer Management: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 250, 55 p.

Hunt, B.B., B.A. Smith, 2010, Spring 2009 Potentiometric Map of the Middle Trinity Aquifer in Groundwater Management Area 9, Central Texas: Barton Springs Edwards Aquifer Conservation District Report of Investigations 2010-0501, 26 p.

Hunt, B.B., B.A. Smith, and J. Beery, 2007, Synoptic Potentiometric Maps, 1956 to 2006, Barton Springs segment of the Edwards Aquifer, Central Texas, published by the BSEACD, Figure 5: Picture of sta measuring the depth to 65 p. +CD. December 2007. water in a well with an eline.

Hunt, B.B., B.A. Smith, J. Beery, D. Johns, N. Hauwert, 2006, Summary of 2005 Groundwater Dye Tracing, Barton Springs Segment of the Edwards Aquifer, Hays and Travis Counties, Data Availability Central Texas, Barton Springs/Edwards Aquifer Conservation District, BSEACD Report of Investigations, 2006-0530, p. 19. This fact sheet, the maps, as well as the data that was used to construct them, are available in Lindgren, R., A. Dutton, S. Hovorka, S. Worthington, and S. Painter, 2004, Conceptualization and Simulation of the Edwards Aquifer, San Antonio region, Texas. U. S. Geological Survey digital format. To access the data online, visit the Scientic Investigation Report 2004-5277. District's Scientic Publications page:

Kresic, N., 2007, Hydrogeology and Groundwater Modeling, second edition. CRC Press, www.bseacd.org/publications/reports/#WaterLevelsRpt Boca Raton Florida, 807 p.

Smith, B., B. Morris, B. Hunt, S. Helmcamp, D. Johns, N. Hauwert, 2001, Water Quality and Flow Loss Study of the Barton Springs Segment of the Edwards Aquifer: EPA-funded 319h Acknowledgments grant report by the Barton Springs/Edwards Aquifer Conservation District and City of Austin, submitted to the Texas Commission on Environmental Quality (formerly TNRCC), Regional synoptic water level maps require August 2001. 85 p. + Figures, + Appendix collaboration, cooperation, and input from multiple agencies, well owners, and scientists. Taylor, C., and W. Alley, 2001, Ground-Water level Monitoring and the Importance of The maps and data presented in this factsheet are Long-Term Water level Data. U.S. Geological Survey Circular 1217, Denver Colorado, 68 pp. the result of many hours of data collection and analysis. The District would like to thank all (TWDB) Texas Water Development Board, 2002, Water for Texas- 2002, Volumes I – III, agencies, well owners, and scientists that Document No. GP-7-1, January 2002, 156 p. +attachment. contributed to this body of work. Worthington, S., 2003, Conduits and turbulent ow in the Edwards aquifer: Worthington Groundwater, contract report to Edwards Aquifer Authority, San Antonio, Texas, December 20, 2003, 42 p. Suggested Citation

Wierman, D.A., A.S. Broun, and B.B. Hunt (Eds), 2010, Hydrogeologic Atlas of the Hill Hunt, B. and R. Gary, 2014, Water Level Maps of the Country Trinity Aquifer, Blanco, Hays, and Travis Counties, Central Texas: Preparted by the Edwards and Middle Trinity Aquifers, Central Hays-Trinity , Barton/Springs Edwards Aquifer, and Blanco Pedernales Groundwater Texas, Barton Springs Edwards Aquifer Conservation Districts, July 2010, 17 plates+DVD. Conservation District, BSEACD Fact Sheet 0314, 4 p. + geodatabase. BSEACD Fact Sheet 0314 Barton Springs/Edwards Aquifer Conservation District 1124 Regal Row, Austin, Texas 78748 www.bseacd.org (512) 282-8441 [email protected]