Purposes of this report are (1) to present water-level
changes in the High Plains aquifer from the time before substantial
development of groundwater for irrigation to 2011 and
from 2009–11, and (2) to publish the raster dataset depicting
water-level changes, predevelopment to 2011. The time period
before substantial development of groundwater for irrigation is
termed “predevelopment” in this report; predevelopment generally
is before about 1950, but in some areas (for example, in the
north-central part of the Texas Panhandle), predevelopment is
the late 1990s, and in other areas (for example, in north-central
Nebraska), groundwater has not yet (2012) been developed substantially
for irrigation. Water levels used in this report generally
were measured in winter or early spring, when irrigation wells
typically were not pumping, and water levels generally had
recovered from pumping during the previous irrigation season.
This report also describes drainable water in storage in
the High Plains aquifer in 2011 and changes in both drainable
water in storage and saturated thickness of the aquifer from
predevelopment to 2011. Drainable water in storage is the
fraction of water in the aquifer that will drain by gravity and
can be withdrawn by wells. The remaining water in the aquifer
is held to the aquifer material by capillary forces and generally
cannot be withdrawn by wells. Drainable water in storage is
termed “water in storage” in this report.
Area-weighted, average water-level changes; change in
water in storage, predevelopment to 2011; and total water in
storage, 2011, were calculated for this report using geospatial
data organized as rasters, including available raster datasets
for saturated thickness, 2009, and specific yield (Gutentag and
others, 1984; Cederstrand and Becker, 1998; McGuire and
others, 2012). The methods used for these calculations were
modified from methods used for previous reports (McGuire,
2009, 2011) in an attempt to improve estimates of water-level
changes and change in water in storage.
