Gila River Riparian Groundwater Model
SSP&A conducted a comprehensive study of hydrologic conditions in the riparian corridor of the Gila River to support water use and ecosystem decisions under the Arizona Water Settlement Act. This reach of the Gila River is unique in the West in that it remains largely unregulated, and while low flows are typical, flood flows ranging above 10,000 cfs are not uncommon. The river supports both a rich ecosystem and irrigated agriculture. Water uses in the basin are limited by interstate allocation under a Supreme Court decree, although Arizona Water Settlement Act offers some potential for flexibility in water management associated with the Central Arizona Project. SSP&A’s project included design of a riverine well monitoring network, river seepage runs, LiDAR acquisition and development of high-resolution groundwater models incorporating flow-dependent surface water boundary conditions based on companion HEC-RAS model simulations. Two groundwater models were constructed over approximately 12 river miles, with model cells 60 feet on a side. A framework for a regional model was developed to provide opportunity for exploring regional groundwater conditions relevant to water supply evaluations and to evaluate the sustainability of hydrologic conditions in the riparian zone under climate or water use scenarios. These models are among tools available to support Stakeholder analysis of water supply alternatives under the AWSA; and, to support evaluation of the sustainability of groundwater-dependent ecosystems under modified conditions.