Impact of future ground-water development in Cienega Creek area, Pima, Santa Cruz and Cochise Counties, Arizona

Abstract

A finite element computer program known as PLUMP is used in assessing the impacts of a large-scale ground-water development in the Cienega Basin. It was necessary to develop two separate models of the Basin to avoid tenuous assumptions regarding recharge rates in the mountainous areas surrounding the Basin. The first model comprises the Basin lowlands where previous studies have shown vertical recharge through soils to be negligible. The transmissivity distribution in the lowlands area was calibrated, and rates of lateral recharge from the bordering uplands were computed automatically by the model. The results of the Basin lowlands model were subsequently used in constructing a second model consisting of the entire ground-water basin. The absence of any nonsteady ground-water level data for the Basin precluded calibrating either model for storativity. Pumping impacts are investigated for uniform aquifer storativities of 0.01 and 0.1. Simulations in which storativity is 0.1 forecast minor impacts to most wells in the Basin; however, substantial declines in the baseflow of Cienega Creek are indicated. Much more serious impacts are suggested by pumping simulations which assume a storativity of 0.01. The distinct contrast in predicted impacts points out the need for better definition of aquifer storativity in the Basin.