Water Availability Modeling for Regional Water Planning in Texas

Abstract

In 1997, the Texas Legislature passed Senate Bill 1 (SB1) and created a grassroots regional water planning process in which local representatives develop strategies to address the demand for water based on a 50-year projection. Planning is controlled at the regional level and overseen and funded by the state. The Texas Water Development Board (TWDB) oversees development of the regional plans and develops a State Water Plan based on them. The state of Texas consists of 16 water planning regions that include the following 11 interest groups: water districts, river authorities, municipalities, industry, environment, public, small business, counties, water utilities, electric generating utilities, and agriculture. Texas has completed three rounds of regional water planning under SB1. As part of the SB1 regional water planning effort, Water Availability Models (WAMs) are applied to determine the quantity and reliability of currently available surface water supplies. The difference between currently available supplies and the projected water demand results in either a net surplus or a shortage for water users. Water management strategies are developed to meet projected water supply shortages. The impacts of potential water management strategies involving surface water supplies are also analyzed using the WAMs. Utilizing WAMs provides a consistent approach to determining water supply availability in the state's 16 water planning regions. WAMs are run using the Water Rights Analysis Package (WRAP) computer software program that was developed and is currently maintained by Dr. Ralph Wurbs at Texas A&M University. The WRAP program was designed for the analysis of water availability under the Texas water right system, in which the available water is allocated based on the seniority of the water right. Consultants developed the WAMs for 23 river basins in Texas, and the Texas Commission on Environmental Quality (TCEQ) maintains the WAMs and associated data. The WAMs are modified for regional water planning to include sedimentation conditions, actual operational rules, and physical limitations such as minimum water elevations. Water planning in Texas considers such issues as rapid growth in population and demands, future development of surface water resources, the need for water for the environment, limited groundwater resources in some areas, and permitting challenges. The regional planning process provides a vehicle for local input and resolution of complex, and often conflicting, water supply issues. This paper presents three examples of how WAMs have been applied to evaluate water supplies in conflicting situations.