Natural Tracer Study to Constrain Transit Times and Flowpaths of Groundwater from Davidson Canyon to Lower Cienega Creek

 

Nicole C. Weber, Erin Gray, and Jennifer McIntosh

Department of Hydrology and Atmospheric Sciences

The University of Arizona, Tucson, Arizona

Multiple reaches of Cienega Creek and Davidson Canyon Wash, located in the Cienega Creek Watershed, Arizona, have been designated as “Outstanding Arizona Waters.”  These surface waters, riparian areas, and underlying groundwater in alluvial basins are under pressure from threats of increasing groundwater pumping, land use and climate change, and potential mining. Yet, little information is known about the regional hydrogeology, which is important for accessing and protecting the sustainability of natural resources in the area. This study investigates the hydrologic connection between the Santa Rita mountains and lower Cienega Creek, along the  Davidson Canyon subwatershed. Davidson Canyon is an intermittent stream with seasonally sustained baseflows and is a large tributary to Lower Cienega Creek. This research aims to: (1) identify areas of recent recharge; (2) determine the relative age and transit time of groundwater; (3) better constrain the Local Meteoric Water Line; and (4) use hydrochemistry and isotopes to evaluate the flowpaths and mixing of groundwater and interaction with surface waters. To address these aims, groundwater and surface water samples were collected seasonally in 2017-2018 and analyzed for major ion chemistry, stable isotopes (δ18O, δD, δ13C, δ34S) and radioactive isotopes (3H and 14C).