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and David Purkey of the Stockholm Environment Institute in creating the framework and logic of the Rio Grande/Bravo model is greatly appreciated. The Rio Grande/Bravo basin is located in North America between two riparian nations, the United States (U.S.) and Mexico. This river is currently considered a water scarce area with less then 500 m3 per person per year of water available. Throughout the decades there has been a lot of population growth in the basin, with population expected to double over the next three decades. The Physical Assessment Project promotes regional cooperation between the U.S. and Mexico to work towards more effectively managing the Rio Grande/Bravo’s resources. This report falls under Task 3 of the project by documenting and testing the basin-wide model constructed Using WEAP software. The documentation of the model addresses all of the inputs for demands and supplies for the river. The model is also set up to include operating polices of the different countries and how they each allocate water to their demands. The supplies in the model include tributary inflows, as well as reservoir and groundwater storage. This report is the first of many testing phases. The two items that were evaluated here, by comparing them against historical records, were the reservoir storage volumes and the streamflow for six International Boundary Water Commission (IBWC) gages. This testing demonstrated that the model has the right logic and flow pattern, however adjustments need to be made to the reservoir releases in order to fully represent the existing system.- i