- The Texas water availability modeling (WAM) system consists of the water rights analysis package (WRAP) river/reservoir system simulation model, which is generalized for application any place in the world, and WRAP input data sets for all of the river basins of Texas. The WRAP/WAM system combines historical natural river basin hydrology with specified scenarios of water resources development, management, and use. Multiple-year sequences of monthly river flows for natural and alternative conditions of development are simulated. The paper compares flow-frequency statistics for nine major Texas rivers under natural and current conditions. The WRAP modeling system was recently expanded to provide flexible additional capabilities to develop stream flows representing various other user-specified conditions. An investigation of the Brazos River Basin demonstrates the new methodologies for adjusting river flows to reflect specified water management scenarios of interest. 2011 ASCE.