Modeling Groundwater Storage in the Tucson Active Management Area

Abstract

Water management in the Tucson AMA is unique and challenging due to its climate and growing population. To maintain a stable aquifer, CAP water and local recharge must equal or exceed recovered groundwater pumping. However, management rules allow users to withdraw recharged water to be pumped anywhere in the AMA. The Tucson AMA consists of six areas known as WAZ’s: Marana, Oro Valley, Tucson, Avra Valley, Southeast Tucson, and Sahuarita/Green Valley. Each area presents its own unique water needs and challenges. These challenges are based on historic and projected growth as well as limited water infrastructure and their capacity. The water use and infrastructure systems results in an uneven distribution of water across the system. CAP water delivered to the Tucson AMA is delivered in the north and west, while severe over-pumping is occurring in the south. The LSCR Basin Study was undertaken to better understand current and future conditions and provide adaptations to ease the long-term water supply system. The uncertainty in future conditions requires the study to assess different scenarios in a predictive model. A System Dynamics model can represent the Tucson AMA using a mass balance of inflows and outflows within and between each WAZ in the AMA. The AMA groundwater system model will provide estimates of the changes in groundwater volume year to year in the six WAZ’s. Data collection has been supported through a collaboration with the Bureau of Reclamation’s Lower Santa Cruz River (LSCR) Basin Study. The model will be able to evaluate a variety of scenarios based on various factors including population and climate. The modeling objective is to assist the LSCR Basin Study in their decision-making process to achieve sustainable yield throughout the Tucson AMA. The model will also improve the public’s understanding of the water issues in the region by providing a simple user interface to analyze the alternative future scenarios.