Sensitivity Analysis Methods and Results for Tucson Water's Central Wellfield Groundwater Flow Model, Tucson Basin, Southeastern Arizona

Abstract

A sensitivity analysis was performed for Tucson Water's Central Wellfield (CWF) flow model to determine response to changes in aquifer and stress parameters and to evaluate various comparative methods. Changes were made to hydraulic conductivity, storage coefficients, anisotropy factors, recharge rates, évapotranspiration rates and depths, layer thicknesses, and groundwater pumping. Water table elevation maps and cross sections, head residual maps, head crossplots, hydrographs, and residual statistics were used to compare heads from each sensitivity run with the calibrated steady state and transient state models. Water budgets were also compared. The CWF model is most sensitive to recharge rate changes, storativity decrease, layer thickness, and an increase in the row-to-column anisotropy factor, but is relatively robust to changes in other parameters. No single comparative method should serve as the sole basis for determining model sensitivity to parameter changes.