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.

"One of the world's great karstic aquifer systems, the Edwards aquifer system supplies water for more than 2 million people and for agricultural, municipal, industrial, and recreational uses. This volume reviews the current state of knowledge, current and emerging challenges to wise use of the aquifer system, and some technologies that must be adopted to address these challenges"--

The Edwards Aquifer in south-central Texas is the primary source of water for one of the fastest growing cities in the United States, San Antonio, and it also supplies irrigation water to thousands of farmers and livestock operators. It is also the source water for several springs and rivers, including the two largest freshwater springs in Texas that form the San Marcos and Comal Rivers. The unique habitat afforded by these spring-fed rivers has led to the development of species that are found in no other locations on Earth. Due to the potential for variations in spring flow caused by both human and natural causes, these species are continuously at risk and have been recognized as endangered under the federal Endangered Species Act (ESA). In an effort to manage the river systems and the aquifer that controls them, the Edwards Aquifer Authority (EAA) and stakeholders have developed a Habitat Conservation Plan (HCP). The HCP seeks to effectively manage the river-aquifer system to ensure the viability of the ESA-listed species in the face of drought, population growth, and other threats to the aquifer. This report is the third and final product of a three-phase study to provide advice to the EAA on various aspects of the HCP that will ultimately lead to improved management of the Edwards Aquifer. This final report focuses on the biological goals and objectives found in the HCP for each of the listed species.

Groundwater is an indispensable resource in many parts of the world, where it supports domestic water supply, irrigated agriculture and industry. Its increased, and often intensive, use during the last half century has created problems and raised concerns regarding the potential depletion of local aquifers, water quality degradation and various geo