Mountain-front recharge from the Santa Rita Mountains to the Tucson Basin

Abstract

This study analyzes mountain-front recharge from the Santa Rita mountains. Trilinear diagrams, finger-print diagrams, and scattergrams suggest that two types of water recharge the regional aquifer by effluent seepage as Madera Canyon Stream flows onto Madera Canyon fan. One type of water is dominated by calcium and bicarbonate ions, and the other type is dominated by calcium and sulfate ions. Deuterium and oxygen-18 data support these interpretations and indicate that recharge occurs over a broad range of elevations. Furthermore, the isotopic data indicate that the deuterium and oxygen-18 gradients are -3.5 0/00 and -0.4 0/00, respectively, per 1000 foot increase. Evidence is lacking for the presence of deeply circulating waters. Calculations based on a flow-net analysis and a water balance approximate annual mountain-front recharge to be between 200 and 400 ac-ft/yr/mi of mountain-front recharge. Recharge studies from the nearby Santa Catalina mountains estimate recharge to be between 25 and 50 ac-ft/yr/mi of mountain front and present evidence for minor amounts of deep circulation through the mountain block into the basin. The Santa Rita Mountains, significantly, have a more permeable alluvial fan which favors recharge.