Continuing studies are being made in west-central Kansas to provide up-to-date information that will aid in the management of groundwater for irrigation. This report, prepared by the U.S> Geological Survey in cooperation with the Western Kansas Groundwater Management District No. 1,  presents the results of the seventh in a series of studies that uses a statistical technique, called kriging, to produce hydrologic maps.

The kriging technique interpolates water-level altitudes at the center of each 1-square-mile section in the study area on the basis of water-level measurements from 164 observation wells.  For this study, measurements made at each site during the winter months of 1985, 1986, and 1987 were averaged. These interpolated altitudes (1859 in all), along with bedrock-surface and base-year water-level altitudes were used to prepare a hydrologic map that illustrates percentage change in saturated thickness.

Saturated thickness, as used in this report, is the thickness of the High Plains Aquifer between the groundwater surface, as indicated by water-level altitudes, and the bedrock surface. Because irrigation development in west-central Kansas was minimal prior to 1950, the saturated thickness during 1950 represented a nearly static condition in the aquifer. Thus, the decrease in saturated thickness of the aquifer since 1950 is related to the effects of irrigation withdrawals on the volume of water in storage.