DEVELOPMENT OF A REVISED CRITICAL PERIOD MANAGEMENT PLAN FOR THE EDWARDS AQUIFER TO PROTECT ENDANGERED SPECIES

The Edwards Aquifer is recognized as a vital water resource for a multitude of agricultural, environmental, industrial, municipal, and recreational uses. Several springs, specifically Comal and San Marcos springs, provide habitat for several species protected under the Endangered Species Act. Following a lawsuit and recognizing the specter of federal control of the aquifer, the Texas Legislature created the Edwards Aquifer Authority to regulate pumping in the aquifer and to ensure that, by December 31, 2012, endangered species dependent on springflow are protected to the extent required by federal law. In 2007, the Texas Legislature formalized a recovery implementation program that included the creation of an Edwards Aquifer Area Expert Science Subcommittee. The legislature charged this subcommittee with analyzing species requirements in relation to spring discharge rates and aquifer levels and developing withdrawal reduction levels and stages for critical period management associated with species requirements. In addressing these charges, the legislature directed the subcommittee to consider all “reasonably available science” and to base its conclusions “solely on the best science available.” The 15-member subcommittee is composed of biologists and hydrologists. The biologists developed flow regimes protective of the species for long-term average flow, minimum 6-month average flow, and minimum 1-month average flow (225, 75, and 30 cubic feet per second, respectively, for Comal Springs and 140, 75, and 60 cubic feet per second, respectively, for San Marcos Springs). Using a numerical groundwater flow model, the hydrologists investigated various critical period management scenarios resulting in a single-stage critical period with an 85 percent cut in permitted pumping achieves the minimum flow criteria during a simulated repeat of the drought of record. The results of this study do not address the effects of additional aquifer management or other actions that might be included in the development of a habitat conservation plan; therefore, these results can be considered as the beginning of a conversation among scientists, stakeholders, and various agencies on the ultimate management of the Edwards Aquifer to protect the endangered species that rely on springflow from that aquifer for survival.