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

Open-file Report - 591

by: Geoffrey C. Rawling and Alex J. Rinehart

Executive Summary:

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 east-central 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.”

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