Collaborative Modeling in New Mexico's Upper Gila and San Francisco River Basin

The 2005 Arizona Water Settlements Act (AWSA) has given southwestern New Mexico a unique opportunity to appropriate water from the Upper Gila River basin. This appropriation calls for Arizona irrigators to "trade" their existing use of Gila River water for Central Arizona Project water to realize New Mexico's legal right to develop water originating in its portion of the Upper Gila River watershed. The complexity of the AWSA and various stakeholders interested in the implications of the settlement has led to the development of a collaborative modeling team. As a team member, Sandia National Laboratories is tasked with building an integrated basin scale system-dynamics model that can implement the constraints outlined in the AWSA by projecting water supply and demand scenarios into the future. By building this model, stakeholders will gain insight into the hydrologic complexities inherent in a river basin, and it will allow them to evaluate whether alternate water use scenarios will be allowed under the constraints outlined by the AWSA. The model replicates historic surface and ground water conditions in the basin using available data for supply, including gauges that measure stream flow, ditch flow, and precipitation. Demands are measured through annual hydrographic survey records for agricultural production, industrial water use by mining, municipal and domestic use in both urban and rural communities, and riparian evapotranspiration. Within the system-dynamics framework, volumetric flow of water is the dynamic state variable calculated from one river reach to the next. Stream gauge, climate and consumptive use data are used to calibrate the historic baseline flows. There is a great deal of uncertainty that must be addressed when attempting to model a large basin. Integrating a watershed model to add the contribution of ungauged tributaries is part of this effort. Another challenge is the presence of federally listed endangered avian and aquatic species whose flow regime requirements are not well understood. Population growth within the basin is an issue that must also be addressed as well as demands from large municipalities located outside of the basin. In addition, climate change and variability can alter the type of and timing of precipitation from one year to the next. To address these uncertainties, team members are given a variety of options ranging from setting future climate and flow conditions, the ability to define critical reaches and set minimum flows for riparian health, ranges for population growth rates, and options for moving water from one use to another. The team will then come up with a prioritized set of model "scenarios" that it anticipates for the future. The predictive dynamic responses due to different scenarios can be assessed relative to their baseline values to enhance our understanding of water balances in the region. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.