Evolving Tools and Analyses for Managing Depletion Impacts in the Lower Rio Grande Basin, New Mexico and Texas

The Lower Rio Grande Basin, spanning areas within New Mexico, Texas and Mexico, is a stream-connected deep alluvial aquifer, traversed by the Rio Grande, a transboundary river with flow obligations specified by international treaty; and, interstate allocation implemented by the operation of the Rio Grande (irrigation) Project.  Groundwater pumping for municipal, agricultural and other uses causes depletion to aquifer storage; and, associated impacts to surface water flows and to groundwater quality.  As the majority of the aquifer lies within New Mexico, and because of interstate and international surface water delivery issues, agencies of the State of New Mexico have undertaken significant technical studies to understand the depletion impacts of pumping and to inform the groundwater management process. 

 With most wells located such that groundwater withdrawals will result in lagged stream depletion, quantifying the magnitude and timing of impacts to the river and associated drains is of paramount importance.  The potential for pumping-induced gradients to cause migration of high-salinity groundwater or to increase concentrations of salts in shallow groundwater zones is an additional and serious concern.  To address these questions and to support the development of groundwater management schemes for controlling or mitigating adverse depletion impacts, the State of New Mexico has developed a multi-layer groundwater model incorporating detailed surface water features and representing key recharge and discharge processes in the basin.  The model and supporting analyses are being used to identify triggers for groundwater management of stream depletion impacts; and, to assess flux patterns and the potential for movement of salts in the aquifer as a result of existing and potential future groundwater withdrawals.