Groundwater Tracing in the Barton Springs Edwards Aquifer

By

HAUWERT, NICO M., and JOHNS, DAVID A.

City of Austin, Austin, TX,

SANSOM, JAMES W.

Consultant, Austin, TX,

ALEY, THOMAS J.

Consultant, Protem, MO

Groundwater tracing in the Barton Springs Edwards Aquifer is providing new insight on groundwater flow directions and travel rates from major contributing watersheds.

Results demonstrate that the western portion of the Recharge Zone in Barton and Williamson Creeks contributes flow to Cold Springs and other springs on the Colorado River. Remaining portions of the Recharge Zone within these watersheds generally support the Main outlet of Barton Springs and Upper Barton Springs. Groundwater recharging in the Slaughter, Bear, Little Bear, and Onion watersheds flows east towards a potentiometric trough that parallels the east side of the Recharge Zone then travels northeast to Barton Springs. The three major preferential groundwater-flow paths appear strongly influenced by geological fault trends.

Groundwater flow rates vary with proximity and connection to major preferential groundwater-flow paths and groundwater-flow conditions. Under moderate and high groundwater-flow conditions at Barton Springs, groundwater generally travels about four to seven miles per day along the major groundwater-flow paths, but only about one mile per day from the western side of the Recharge Zone to the eastern side. During low flow conditions at Barton Springs, groundwater moves at rates of about one mile per day to 0.6 miles per day across the aquifer.

Rapid travel rates suggest that Barton Springs is closer hydraulically to more distant watersheds than previously believed. Results provide information to improve wellhead protection, anticipate the fate of hazardous material spills, assist in developing monitoring strategies, prioritize purchases of water quality/quantity protection lands, and evaluate sites for recharge enhancement.