© 2022 International Association for Hydro-Environment Engineering and Research.A water availability modelling system implemented in the state of Texas in the United States consists of the generalized Water Rights Analysis Package, which can be applied to river/reservoir systems throughout the world, and datasets for all the river basins of Texas. A monthly version of the modelling system has contributed greatly to improving water allocation and statewide and regional water planning. A recently developed daily version adds capabilities for simulating flood control operations and environmental flow requirements. The simulation study reported here employed the daily modelling system to explore the interactions between the multiple-purposes served by a 12-reservoir system owned by the U.S. Army Corps of Engineers and Brazos River Authority. Interactions between this reservoir system and numerous other water users and reservoirs in the Brazos River Basin are also reflected in the model. The investigation focuses on relationships between water supply, hydropower, flood control, and environmental flow needs.