RIVER SYSTEMS INSTITUTE TEXAS STATE UNIVERSITY‐SAN MARCOS INTEGRATED ASSESSEMENT OF THE PEDERNALES WATERSHED Year 1 Final Report August, 2008 CONTACT INFORMATION Emily R. Armitano Assistant Director River Systems Institute 601 University Drive San Marcos TX, 78666 512‐245‐4476 Table of Contents Introduction ............................................................................................................. 3 Pedernales Watershed Assessment ......................................................................... 4 Introduction ........................................................................................................................ 5 Executive Summary ............................................................................................................. 8 Geology ............................................................................................................................. 11 Soils ................................................................................................................................... 18 Land Cover ........................................................................................................................ 33 Precipitation ...................................................................................................................... 41 Surface Flow ...................................................................................................................... 52 References ........................................................................................................................ 62 Appendices ........................................................................................................................ 65 Spatial and Temporal Patterns in the Pedernales River Drainage ......................... 65 Methods ............................................................................................................................ 66 Results ............................................................................................................................... 67 Liturature Cited ................................................................................................................. 70 Tables and Figures ............................................................................................................ 71 Water Quality Anaylisis of the Pedernales River .................................................... 82 Methods ............................................................................................................................ 85 Results ............................................................................................................................... 86 Liturature Cited ................................................................................................................. 94 Hydraulic Geometry of the Pedernales River ......................................................... 96 2 Introduction The purpose of the Integrated Assessment of the Pedernales Watershed project is to provide current watershed data for the development of a conservation plan for the Pedernales river basin, from its headwaters in Kimble County to its confluence with the Colorado River. A secondary purpose is to make a contribution to the development of data sets needed to inform the Texas Instream Flows Program framework for the Pedernales River that will rigorously evaluate future water management projects. Texas State University researchers implemented a multi‐disciplinary approach to address key data gaps, evaluate impacts of land management, and develop strategies for integrated watershed management. The four research areas and lead investigators include: 1. Integrated Assessment of the Pedernales Watershed – Dr. Vicente Lopes 2. Spatial and Temporal Patterns in the Pedernales River Drainage Fish Assemblage – Dr. Tim Bonner 3. Water Chemistry and Water Quality in the Pedernales River Watershed – Dr. Alan Groeger 4. Hydraulic Geometry of the Pedernales River – Dr. Joanna Curran Due to the relatively rainy summer in 2007, researchers requested an extension through the 2008 summer to gather data during a dry season and have a more robust study. In addition, several students used this project as part of their masters’ work. The final report presented here provides an overview on work completed during the first year of study and findings in each of these research areas as required in the Pedernales River Project Agreement with The Nature Conservancy. 3 PEDERNALES RIVER WATERSHED ANALYSIS Vicente L. Lopes and Leonard L. Oliver Department of Biology Texas State University San Marcos, Texas 2008 4 INTRODUCTION Traditional water resource management has focused on establishing water quality targets and the use of dams and diversions to maintain a target level of supply to meet the demands of agriculture, industry and municipalities. However, while this method establishes a minimum standard of integrity for the aquatic ecosystem, it ignores the health of the linked riverine‐ terrestrial ecosystem as a whole. There is increasing evidence that the success of managing a target variable, such as water, for sustained production has often resulted in inflexible management practices, producing less resilient systems that are increasingly dependent on human manipulation for regulation (Holling 2004; Berkes and Folke 2000). The alteration of in‐stream flow regimes as a result of dams and diversions has been identified as one of the leading causes of the degradation of aquatic habitats (Pringle et al. 2000). In addition, ecosystem functions and services provided by freshwater systems have also been compromised (Postel and Carpenter 1997; Vorosmarty et al. 2005). There has been increased interest in determining and maintaining the flow regime necessary to ensure sustainable aquatic ecosystems and to maintain the desired level of ecosystem services provided by river systems (Richter et al. 2003; Mallard et al. 2005). Maintaining adequate water supplies, however, has been a serious issue for decades. Moreover, global climate change, population growth and increasing urban development are likely to amplify the problems facing water resources management in the near future. In 1997, recognizing the need for more integrated management of water systems in Texas, the state legislature passed Senate Bill 1, creating 16 Regional Water Planning Groups. This bill requires each Regional Planning Group and the Texas Water Development Board (TWDB) to provide new water management plans every 5 years. In 2001, the 77th Texas Legislature amended state water law further to enhance regionally‐ based water management in the state and to encourage conjunctive planning for surface and groundwater usage. In addition, the new legislation included provisions for protecting environmental needs, including in‐stream flows, freshwater inflows to bays and estuaries, and fish and wildlife habitats. Combining science and policy into an effective water management program, however, is a challenge that requires detailed knowledge of both the historical and current social, political, and economic systems in which management decisions are imbedded. Integrated Water Resources Management (IWRM) has gained recognition in recent years as an approach that recognizes the complex and integrated nature of social‐ecological systems. IWRM is based on a perspective that explicitly includes humans and social systems within ecosystems, as linked social‐ecological systems. IWRM can be defined as “a process which promotes the coordinated development and management of water, land and related resources, in order to [maximize] the resultant economic and social welfare in an equitable manner 5 without compromising the sustainability of vital ecosystems” (GWP 2000). This approach holds promise for managing river systems such as the Pedernales River Watershed, which are experiencing multiple conflicting demands on limited resources and where conflicts can only be expected to increase in the future. The Pedernales River is one of Texas’ most pristine and beautiful rivers ‐ vast stretches of the river are lined by privately owned ranches and remain largely free of development, making the watershed a top priority conservation area. However, the projected level of population growth in Texas and the associated increase in water demand, particularly for the municipal needs of growing urban centers, creates a conflict with the ecological and legislative imperative to ensure environmental flows in the Pedernales River Watershed. A further complication arises from the multiple and still relatively poorly understood linkages between surface water flows and cross‐cutting subsurface aquifers in the region. The implementation of an integrated approach to water planning and management in the Pedernales River Watershed will require an integration of both human and ecosystem needs. This means recognizing that although in‐stream flow programs are based upon a scientific foundation, they must be implemented in a legal, social, political, and economic context. This context is furthermore constrained by its historical trajectory, or how it has evolved throughout its history. The purpose of this study is to investigate the Pedernales River Watershed’s current structure and function to enable evaluation of the likely effects of future land and water use change on water quality and quantity. We envision that planners and communities will use the information gained from this study