Kansas Geological Survey, Open-file Report 2007-32
by
Geoffrey Bohling and Brownie Wilson
KGS Open File Report 2007-32
Dec. 2007
The High Plains aquifer is the primary source of water for the High Plains region of western and south-central Kansas. Some water is also withdrawn from bedrock units, primarily Cretaceous strata, in this region. The Kansas Geological Survey (KGS) and the Kansas Department of Agriculture's Division of Water Resources (DWR) measure water levels in aquifers of the High Plains on an annual basis in a network of over 1300 wells, in order to assist in the management of this vital resource. This report presents statistical and geostatistical analyses for the High Plains region in Kansas based on data from the 2007 water-level measurements and water-level changes for the one-year and five-year periods preceding the 2007 measurements. In contrast to previous years, when the majority of water level measurements were obtained in a short time frame (a few weeks) in January, the 2007 measurement campaign extended into April 2007, due to heavy snowfall throughout much of western Kansas. However, it should be noted that wide-scale pumping had not yet started.
Section 3 of this report examines temporal variations in the water level measurements over the time frame of the 2007 measurements (Dec. 2006-April 2007), showing that it is difficult to discern systematic temporal trends over this time period. Therefore, these measurements are treated as a single snapshot of the water table, nominally referred to as the "January 2007" measurements, following the practice of earlier water level reports.
Throughout this report we refer to water-level declines, with a positive decline meaning an increase in depth to water from the land surface (or decrease in water-table elevation) and a negative decline meaning a decrease in depth to water from the land surface (increase in water-table elevation). Water levels are measured in the winter so that the water table (or potentiometric surface) will have had a chance to recover from the more transient and localized effects of pumping for irrigation. The measurements are presumed to represent a new "static" water level, with the difference from the previous year's measurements representing the net loss or gain of saturated thickness over the preceding year. The difference in depth to water between the January 2007 and January 2006 measurements represents the water level decline for 2006.
The overall average water-level decline in the High Plains region over the 2006 calendar year was 1.28 feet. This represents a return to declines like those for the early 2000's (ranging from 0.92 feet for 2001 to 1.98 feet for 2002) after two years of relatively small average declines (0.14 feet for 2004 and 0.57 feet for 2005). Below-average precipitation during the 2006 growing season (April to September) is a likely cause. Precipitation levels, particularly in the western portions of the High Plains region, influence the amount of ground-water pumping, which in turn, affects water levels.
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Kansas Geological Survey, Geohydrology
Placed online May 6, 2008
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