Water quality as well as quantity can be important in determining water-supply reliability. Saline ground water emissions in the upper watersheds of the Brazos and other major river basins in Texas and neighboring states contribute large salt loads to the rivers. Water management and use is severely constrained by the natural salt pollution. A modeling and analysis approach, using a generalized river/reservoir-system simulation model called RESSALT, was applied in an evaluation of the water-supply capabilities of a system of 12 reservoirs in the Brazos River Basin. The general evaluation methodology is also applicable to other river basins where salinity is of concern. Simulations with the RESSALT model combine a specified water-use scenario and associated system operating rules with sequences of adjusted historical monthly stream flows, evaporation rates, and salt loads for a simulation period of many years. Alternative water-use scenarios represent water use during a specified past year, projected future use, and hypothetical yields. Relationships between water demands, allowable salt concentrations, and reliabilities are developed for alternative modeling assumptions and management strategies including multiple-reservoir release policies and impoundment of runoff from primary salt-source areas.
