Groundwater in Unconfined New Mexican Aquifers

Unconfined aquifers form a major source of freshwater in the Rio Grande and neighboring basins, and in the Ogallala aquifer of the Southern High Plains. It is, however, unknown how much water has been withdrawn during the historical record. In this study, we provide a systematic analysis of water level changes and basin-wide groundwater storage changes for the alluvial aquifers of Rio Grande basins and neighboring basins, and in the Southern High Plains of New Mexico from the 1950s to the 2010s. We review USGS, NMOSE, county-level and NMBGMR well and water level data to exclude pumping-effected measurments. For each basin studied, we estimate a correlation length of water level measurements and derive a specific yield from the literature. We then interpolate the water level measurements and find the differences through time between the interpolations. We exclude regions outside the correlation length of both well networks used for the two interpolations, and regions in bedrock or historical unsaturation and find the differences in water levels and storage on decadal time-steps. Not all of the reviewed basins had adequate well and measurement coverage to be used. Overall, groundwater storage in unconfined aquifers is declining in populated regions, especially in areas isolated from perennial rivers. Areas without intensive irrigated agriculture or major population centers have shown smaller decreases or remained roughly static. Observable recharge appears to only come from mountain fronts or from major rivers. The Southern High Plains have a dwindling water supply. Basins with the Rio Grande and large populations show loss of connection with river recharge through time.