Alternative Title

BSEACD Report of Investigations 2007-1201

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Publication Date

January 2004

Abstract

EXECUTIVE SUMMARY The combined effects of drought and substantial pumping can result in a decline in water levels and spring flow in an aquifer. This report evaluates potential impacts on groundwater availability in the Barton Springs segment of the Edwards Aquifer (Barton Springs aquifer) during a recurrence of drought-of-record (1950's) conditions and various rates of pumping. A numerical groundwater model and hydrogeologic data were the primary tools used in this evaluation. The Barton Springs aquifer is an important groundwater resource for municipal, industrial, domestic, recreational, and ecological needs. Approximately 50,000 people depend on water from the Barton Springs aquifer as their sole source of drinking water. Additionally, various spring outlets at Barton Springs are the only known habitats of the endangered Barton Springs salamander. The amount of groundwater available to meet current and future needs is limited, however. A statutory mandate charges the Barton Springs/Edwards Aquifer Conservation District (District) with the responsibility of conserving, protecting, and enhancing groundwater resources of the Barton Springs aquifer. Part of this responsibility is to determine the amount of groundwater available for use in the aquifer, referred to as "sustainable yield" by the District. State law requires water planning for drought conditions and use of groundwater modeling information in conjunction with other studies or data about the aquifer. The purpose of this report is to provide scientific foundation and documentation for policy makers' use so that future water needs are met during times of severe drought. The Barton Springs aquifer is located within parts of Travis and Hays Counties in Central Texas. It lies along the Balcones Fault Zone and is generally bounded to the north by the Colorado River, to the south by the southern groundwater divide near the City of Kyle, to the east by the interface between the fresh- and saline-water zones, and to the west by the Balcones Fault. A numerical model was developed for the Barton Springs aquifer (Scanlon et al., 2001; Appendix A). However, the model was constructed to match water levels and spring flow from a period wetter than that of the 1950's drought. Because the model was calibrated to a relatively wet period, it overestimates spring flow and underpredicts water-level elevations compared with measurements taken during the 1950's drought of record. The model was recalibrated so that simulated and measured spring-flow and water-level data from the 1950's drought matched better. The recalibrated model was then used to predict spring-flow and water-level declines under 1950's drought conditions and various future pumping scenarios. Hydrogeological data, such as saturated-thickness maps, potentiometric-surface maps, and well-construction and yield data, were evaluated alongside the model results so that impacts to water-supply wells under 1950's drought conditions and various rates of pumping could be estimated. Results of the evaluations indicate that water levels and spring flow are significantly impacted by 1950's drought conditions and projected pumping. The model indicates that 10 cubic feet per second (cfs) of pumping, combined with 1950's drought conditions, produces a mean monthly spring flow of about 1 cfs. According to a minimum daily discharge of 9.6 cfs, such as that measured in 1956, spring flow could temporarily cease for periods less than 1 month. At 15 cfs of pumping, spring flow would cease for at least 4 months. Simulations indicate that a given pumping rate applied under 1950's drought conditions would diminish Barton Springs spring flow by an amount equivalent to the pumping rate. As many as 19% of all water-supply wells in the District may be negatively impacted under 1950's drought conditions and a pumping rate of 10 cfs. Negative impacts might include wells going dry, water levels dropping below pumps, or intermittent yield due to low water levels. Finally, under 1950's drought conditions and high rates of pumping, potential for saline water to flow from the saline-water zone into the freshwater aquifer would increase, impacting water-supply wells and endangered species. Information presented herein is based on the best science and information currently available for evaluating sustainable yield of the Barton Springs segment of the Edwards Aquifer. Results of this sustainable-yield evaluation will be considered in District sustainable-yield policies for resource management. Open Access - Permission by Publisher See Extended description for more information.

Keywords

Barton Springs (Austin, Texas, United States), United States, Geology

Description

1 online resource

Subject: topical

Geology

Subject: geographic

United States

Language

English

Type

Text

Genre

Reports, Technical

Format

application/pdf

Identifier

K26-01375

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