Gradient Self-Potential Logging in the Rio Grande to Identify Gaining and Losing Reaches across the Mesilla Valley

The Rio Grande/Río Bravo del Norte (hereinafter referred to as the “Rio Grande”) is primary source of recharge Mesilla Basin/Conejos-Médanos aquifer system in Valley New Mexico and Texas. Basin U.S. part water supply several communities along United States–Mexico border near Valley. Identifying gaining losing reaches Grande therefore critical for managing quality quantity surface groundwater resources available stakeholders downstream. A gradient self-potential (SP) logging survey was completed across between 26 June 2 July 2020, identify where surface-water gains losses were occurring by interpreting an estimate streaming-potential component electrostatic field river, measured during bankfull flow. survey, Transboundary Aquifer Assessment Program, began at Leasburg Dam northern terminus ended ~72 kilometers (km) downstream Canutillo, Electric potential data indicated a net condition ~32 km Diversion Mexico, with one ~200-m long reach showing isolated saline-groundwater condition. Downstream from Dam, electric-potential neutral-to-mild 12 that transitioned mild-to-moderate ~22 dam, before transitioning back remaining 18 reach. interpreted are substantiated potentiometric mapping hydrostratigraphic units 2010 2011, corroborated temperature conductivity relative median streamflow losses, quantified measurements made annually 16 seepage-measurement stations 1988 1998 2004 2013. Valley, electric data, compare well 72-km