Geophysical signatures of Barton Springs (Parthenia, Zenobia and Eliza) of the Edwards Aquifer, Austin, Texas

Mustafa Saribudak
Alf Hawkins
Nico M. Hauwert

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Barton Springs is a major discharge site for the Barton Springs Segment of the Edwards Aquifer and is located in Zilker Park in Austin, Texas. Barton Springs actually consists of four springs: (1) The Main Barton Springs discharges into the Barton Springs pool from the Barton Springs Fault and several outlets along a fault and from a cave, several fissures, and gravel-filled solution cavities on the floor of the pool west of the fault. The thin-bedded unit on the southwest side of the fault is the regional dense member, and the lower Georgetown Formation of the Edwards Group is exposed on the northeast side of the fault. The offset of the fault is between 40 and 70 ft (12–21 m). (2) Old Mill Springs is located in the sunken gardens southeast of the Barton Springs Pool and is primarily fed by relatively mineralized groundwater from the Saline-Line Flow Route. (3) Eliza Springs is also located along the Barton Springs Fault north of Barton Springs pool. (4) The Upper Barton Springs is located upstream of the Barton Springs pool on the south bank. Surface geophysical surveys [resistivity imaging and natural potential (NP)] were performed over the first three springs (Main Barton, Old Mill and Eliza Springs). Conductivity (EM) surveys were conducted in some areas to distinguish utility lines. The purpose of the surveys was to: (1) locate the precise location of submerged conduits carrying flow to Main Barton Springs on the north and south banks of the Barton Springs pool; (2) characterize the hydraulic relation between the Main Barton, Old Mill and Eliza Springs; (3) determine the potential location of caves and active flow paths beneath the three springs; and (4) characterize the geophysical signatures of the fault crossing the Barton Springs pool. The geophysical surveys revealed three general types of anomalies. Resistivity results from the south of the Barton Springs swimming pool indicate presence of a thick, laterally extensive high conductivity layer above the pool elevation. This high conductivity layer is in