39 A Tale of Two Aquifers: Deciphering Characteristics of the Edwards and Trinity Aquifers in Central Texas

Friday, 5 April 2013
7:00 PM - 9:30 PM
Underground

FINE-SCALE HYDROLOGIC AND GEOCHEMICAL RESPONSES IN CONTINUOUS DATA PROVIDE CLUES TO UNDERSTANDING EPIKARST STRUCTURE AND HYDROGEOLOGY IN THE EDWARDS PLATEAU, TEXAS, USA

Paper number: 39-7
Program: Theme Sessions
Time: 9:00 PM – 9:20 PM

Authors

Abstract

In Cave Without A Name near Boerne, TX, continuous multi-parameter data logged at 10-15 minute intervals have allowed detection and analysis of hydrologic and geochemical variability that would otherwise be considered ‘noise’, and development of a working model that explains this variability. Recent work specifically focused on explaining the clear relationships between hydrologic and geochemical changes and changes in barometric pressure. These relationships are observed at a variety of sites including speleothem drip sites and an in-cave stream, and the strength of these relationships is also dependent on hydrologic conditions (wet vs. dry).

Our data and results support the notion that the epikarst is a variably saturated system, with high fracture density and, in the case of the Edwards Plateau, substantial matrix porosity and storage. A conceptual model describes barometric pressure changes causing trapped gas pockets to expand and contract, and these changes result in small volumes of water being pumped into and out of storage that is connected to, but peripheral to, the main flow paths. This has implications for rates of epikarst dissolution and evolution and may explain previously unexplained noise in datasets from other cave drip studies.