Interbasin Groundwater Flow at the Benson Narrows, Arizona

Abstract

This study investigates interbasin groundwater flow at the Benson Narrows, a constricted reach of the San Pedro River marking the boundary between the Upper and Lower San Pedro basins in southeastern Arizona. Historically, underflow through this area was estimated at only 120 acre-feet per year, assuming flow was limited to the floodplain alluvium. Recent hydrogeologic analyses at The Nature Conservancy’s Three Links Farm, located downstream of the Narrows, indicate that more than 3,500 acre-feet of groundwater annually pass through the floodplain alluvium aquifer. Fieldwork included surveying wells, constructing groundwater contour maps, aquifer testing, and soils mapping. Results suggest that most of this water originates as interbasin underflow from the Upper San Pedro Basin via thick alluvial basin-fill deposits flanking the Narrows. Chemical analyses and recharge estimates rule out local sources such as streambed infiltration, irrigation return flow, or mountain-front recharge. These findings have significant implications for water management, as increased pumping in the Upper Basin could reduce flows supporting riparian ecosystems in the Lower Basin. Published in March/April 2005 issue of Southwest Hydrology.

Citation

Haney, J.A. and Lombard, J., 2005. Interbasin groundwater flow at the Benson Narrows, Arizona. Southwest Hydrology, 4(2), pp.8-9.