Hydrologic Assessment and Simulations of Groundwater Conditions in Arivaca Basin, Pima County, Arizona.

Abstract

Meeting the water needs of humans while protecting riparian habitat and wildlife is a significant challenge for land use and water resources planning in Southern Arizona. Arivaca Creek is one of the few remaining perennial streams and wetland ecosystems in Pima County and supports one of the largest hydro-meso-riparian corridors. Arivaca is also a rural community with a growing population. A hydrological assessment was conducted and a groundwater flow model was created to better understand the dynamics of the Arivaca groundwater basin. A groundwater flow model had not been created for this basin prior to this investigation. A conceptual model was developed using ArcView Geographic Information System (GIS) software and Groundwater Modeling System (GMS) software to aid in model input and model calibration. GMS was used to convert the GIS-based conceptual information into the input files needed to run the numerical finite-difference groundwater flow model MODFLOW. A new evapotranspiration MODFLOW module (RIP-ET) was used to represent riparian evapotranspiration in the model. A steady-state model was developed for the years prior to 1975 in order to calibrate model inputs and produce initial hydraulic head conditions for the transient analysis. A transient analysis is performed over the period 1975 to 2002 during which stresses to the system are changing over time. Model results are consistent with observed data, indicating the model's utility as a management tool to assess possible land use scenarios and their impacts on riparian habitat along Arivaca Creek and the water resources of the Arivaca groundwater basin.