Lifetime projections for the High Plains Aquifer in east-central New Mexico

Abstract

Several thousand water-level measurements spanning over 50 years, from over a thousand wells, were used to create aquifer lifetime projections for the High Plains aquifer in eastcentral New Mexico. Lifetime projections were made based on past water-level decline rates calculated over ten- and twenty-year intervals. Projected lifetimes were calculated for two scenarios. One scenario is the time until total dewatering of the full saturated thickness of the aquifer, and the other scenario is the time until a 30-ft saturated thickness threshold is reached, which is the minimum necessary to sustain high-capacity irrigation wells. Agricultural water use has largely determined water-level decline rates in the past. Assuming future decline rates match those of the past ten to twenty years, the two scenarios may be viewed as the usable aquifer lifetime for domestic and low-intensity municipal and industrial uses, and the usable lifetime for large-scale irrigated agriculture.The resulting maps show the projected lifetime graphically, along with progressively enlarging areas of zero saturation. Several measures of the robustness of the method indicate that projected areas of declining water-levels and decreasing aquifer life are more reliable than projected areas of increases in these quantities. There is high confidence in the results in the region surrounding Clovis and Portales. Comparisons of projected lifetimes from past time periods to present conditions show reasonable agreement. The discrepancies between projections derived from the past and current conditions are largely due to differences between actual decline rates and those projected into the future from any given time period in the past. The spatial pattern of projected lifetimes matches very well with lifetime projections made across the state line in the Texas Panhandle. The effects of groundwater pumping and water-level declines in eastcentral New Mexico are similar to those observed in the High Plains aquifer across northwest Texas and western Kansas. Much of the region already has insufficient saturated thickness for the operation of large-capacity irrigation wells. Even when considering the lifetime of the entire thickness of the aquifer, projected lifetimes across much of the study area are a few tens of years or less. If agricultural water use decreases once the 30-ft threshold is reached, then the usable lifetime for domestic and low-intensity municipal and industrial uses presented here may be considered a "worst-case scenario."