Abstract: Springflow Augmentation Possibilities at Comal and San Marcos Springs, Edwards Aquifer

Matthew M. Uliana, John M. Sharp Jr.

Three federally-listed endangered species at Comal and San Marcos Springs of central Texas are dependent upon springflows which issue from the Edwards aquifer. Historic drought conditions will lower discharge rates beneath the levels specified by federal regulations. Projected withdrawals upon the Edwards aquifer will exacerbate periods of low discharge from the springs. One option which has been proposed for Edwards aquifer management is the augmentation of springflows by one of several methods: injection wells, infiltration galleries, direct addition of water to the lake/river systems, or enhanced recharge of the Edwards aquifer. Each method is considered based upon the local hydrogeological characteristics of the two spring/river systems, and each has distinct advantag s and limitations. Mathematical modeling of the injection wells and infiltration galleries calculates the efficiency of these two processes. The former depends upon proximity to the spring orifices and the subsurface permeability structure. The latter depends upon the vertical permeability of the regional dense member of a lower permeability layer, such as the Regional Dense Member. Water-quality considerations for the fauna are not yet documented, but the Edwards aquifer is a definitely compatible source. The habitat requirements for the endangered species are only generally known so that direct discharge from spring orifices might be a requirement. Augmentation is not at panacea, but it is feasible from hydrogeological and technical standpoints and can be considered as part of a water esources management system.

AAPG Search and Discovery Article #90950©1996 AAPG GCAGS 46th Annual Meeting, San Antonio, Texas