Assigning Water Levels and Ground Water Depletions in the Ogallala Aquifer

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The purpose of this report is to evaluate the assignment of water levels in monitor wells in order to create ground-water depletion maps of the Panhandle Ground Water Conservation District No. 3 (PGWCD No. 3). Ground-water depletion maps document and quantify the decrease in ground-water resources in the PGWCD No. 3 by monitoring the historical lowstand of water levels in the Ogallala aquifer. They are used to assign water-level declines to eligible properties for Federal tax credit. Because area landowners rely on these maps for such assignments and because the maps are used in documenting ground-water resources, the procedures used in their creation should be accurate, fair, and timely. The PGWCD No. 3 currently uses a floating, 5-yr, back- calculated average to guide water-level assignments used in generating ground-water-depletion maps. This approach, however, may significantly underestimate water-level declines in individual wells and may give nonreproducible results from well to well. During this study, we assessed the limitations of this approach, described the complications of assigning water levels, and evaluated alternative approaches to define water levels used in determining depletions more accurately. Our goal was to develop a defensible approach that more accurately represents water levels in the Ogallala aquifer. This report specifies how water levels should be assigned in monitor wells in order to minimize errors and provide the most hydrologically reasonable, defensible, and accurate water- level declines. A subsequent report will discuss an automated and statistically rigorous method for assigning depletions to individual properties. These reports will allow the PGWCD No. 3 to maximize the quality of the data used in depletion analysis and to minimize the errors and time used in assigning depletions in the district.


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