RECHARGE FEASIBILITY OF TUCSON STORMWATER INFRASTRUCTURE

Abstract

Growing water scarcity in semi-arid regions has renewed interest in green infrastructure (GI) as a complementary strategy for both flood mitigation and groundwater sustainability. This study evaluates the recharge potential of the Rita Ranch Detention Basin in Tucson, Arizona, a 60-acre regional facility that receives runoff from a 4.5-square-mile residential watershed. Using HYDRUS-1D, we developed a conceptual unsaturated-zone model constrained by site-specific soil hydraulic parameters, atmospheric boundary conditions, evapotranspiration estimates, and root water uptake dynamics. Soil properties were derived from field sampling and Rosetta generated van Genuchten parameters, while daily meteorological inputs (2011-2023) were converted to ponded depths using a precipitation-to-ponding function informed by PCRFCD data and Curve Number methods. Three scenarios were simulated to explore the influence of vegetation and soil characteristics on infiltration: (1) current conditions with velvet mesquite, (2) replacement of mesquite with desert grass, and (3) removal of vegetation with a sand surface layer. Results show that under existing vegetation, only 2.33 m (9.9%) of 23.59 m of ponded input contributes to deep percolation, with the majority lost to transpiration. Recharge increases markedly when deep-rooted vegetation is removed: scenario two yields 19.67 m (83.5% recharge), and scenario three produces 23.05 m (97.7% recharge). These findings indicate that vegetation structure dominates recharge efficiency in the basin.