AN INTEGRATED APPROACH TO WATERSHED AND WATER QUALITY MANAGEMENT IN THE LOWER COLORADO RIVER BASIN, TX

The Lower Colorado River Authority (LCRA) provides water services to all or a portion of 33 counties within the state of Texas, including the metropolitan area of Austin, TX. The agency is also charged with protecting water quality in the lower Colorado River basin. The Austin metropolitan area is currently undergoing rapid population growth with concomitant changes to the local land use and watershed characteristics. These changes prompted LCRA to enact a nonpoint source ordinance in watershed areas upstream of Austin. This ordinance supplements a discharge ban enacted by the state regulatory agency, the Texas Commission on Environmental Quality. To better understand the effectiveness of these regulations and to forecast future water quality conditions throughout the entire system, LCRA has designed a master plan for developing modeling and analysis tools to be used as part of a watershed management program.This program, called the Colorado River Environmental Models program (CREMS) will consist of an integrated tool-kit of models, databases, and graphical user interfaces to assist with a broad range of management decisions. The objective of the CREMS program is to develop and apply these tools to more effectively and efficiently manage existing resources and proactively safeguard the system from environmental degradation. This presentation covers the first two phases of the CREMS program: 1) the design of the CREMS master plan, and 2) the development of the first tool, the Phase 1 Lake Travis watershed and reservoir model.The CREMS master plan was developed to provide a blueprint for implementing the future components of the CREMS system. It includes the following key features:input from all of LCRA business units to identify needs and establish priorities;inventory of existing data;inventory of existing analysis methods and models;identification of potential modeling tools; anddevelopment of work packages for each priority area of the system.Based on input from each LCRA business unit and other stakeholders, the master plan identified five priority areas for incorporation into CREMS:two reservoirs upstream of Austin: Lakes LBJ and Travis;the watersheds areas and stream segments associated with these reservoirs; andMatagorda Bay.Following completion of the master plan, the first phase of the program was initiated. This phase consisted of a relatively simple linked watershed-water quality model of Lake Travis. Lake Travis is a large (approximately 60 mi. long), run-of-the-river reservoir on the Colorado River that is highly prized for its water quality and clarity. The primary goal of this component of the master plan was to provide a quantitative link between nutrient loadings and eutrophication in the lake. The model is built on 18 years of water quality data and is fully accessible through an HTML-based interface to allow for multiple end-users. Using this tool, a variety of scenarios were evaluated, including:various future land use patterns;changes to the existing nonpoint source ordinance; andchanges to the existing point source discharge ban.These efforts have improved our understanding of eutrophication in this system and have focused our efforts to collect additional data and build a more comprehensive model in the future. This effort will also contribute to a similar model of Lake LBJ and its watershed, further enhancing the capabilities of the CREMS toolbox and the ability of LCRA to manage their water resources.