The potential for springflow augmentation at Comal and San Marcos Springs, central Texas

The Edwards aquifer, a regionally-extensive carbonate aquifer in Central Texas, is the sole source of water for nearly two million people, including the City of San Antonio. Pumpage from this aquifer is jeopardizing springflow from Comal Springs (in New Braunfels, Texas) and San Marcos Springs (in San Marcos, Texas), two of the largest springs in the state. These springs provide a habitat for a number of endangered species, and are an integral part of the local economies and the overall distribution of water in Central Texas. For these reasons it is important that flow from these springs be maintained, either through aquifer management plans that limit the withdrawal and usage of water from the aquifer, or through physical augmentation of the springs. In this thesis, the feasibility of maintaining springflow by augmenting discharge from the springs is investigated. Five potential methods of springflow augmentation (enhanced recharge, subsurface flow barriers, direct addition of water to the spring lakes, injection wells, and infiltration galleries) are presented and described. Based on present knowledge of the springs, the effectiveness of each method is evaluated, and the uncertainties associated with each are discussed. Computer models of the aquifer in the vicinity of the springs are constructed and used to model the effects of two of the augmentation methods (injection wells and infiltration galleries) on aquifer levels and spring discharges. The model results are used to estimate the efficiency of each of these methods and to develop general trends related to how the aquifer responds to the introduction of water through wells and infiltration galleries. Based on model results and the hydrogeology of each spring, an assessment of the each of the augmentation methods is presented, and recommendations are made as to the appropriateness of the various technologies at each spring.