This report on the High Plains aquifer addresses issues arising from the legislative mandate to the Kansas Water Authority under SB287. It is based on an updated and expanded version of the High Plains Aquifer Atlas; phrases in boldface type are derived from the titles of individual sections and appendices. The report focuses primarily on the western Kansas groundwater-related conditions and trends. However, groundwater and surface water resources are inseparable, even where one is the dominant water supply. Following a general Introduction to the report and the subject, a section on Surface Water in Kansas and its Interactions With Groundwater places the High Plains aquifer in perspective ¾ both in terms of statewide water resources, and in relation to its interactions with surface water. Above the High Plains aquifer, stream channels and river valleys are locations of both preferential recharge and of groundwater discharge to the surface. This means that both the potential for and the effects of groundwater use vary across the land surface in ways that are not directly accounted for in most present water laws and management practices. A particularly troublesome effect is the shifting and reduction of stream baseflow as aquifer water levels are reduced.

Understanding groundwater requires some familiarity with the terms and concepts of geohydrology. A report section describing the Aquifers of the High Plains Region explains the geography and interactions of western groundwater resources, and technical appendices on Aquifer Types and Terminology, Saturated Thickness, and Groundwater Storage and Flow provide background on the concepts and nomenclature. A major tool being used in modern resource studies, including this report, is GIS ¾ Geographic Information Systems applications. Some of the approaches by which geologic and hydrologic data are generalized and transformed for mapping, modeling, and visualization are presented in the technical appendix on Bedrock/Mapping Methods.

The High Plains aquifer in Kansas is often regarded as a single feature ¾ a major resource that is the primary source of water for people, agriculture, and industry in a large area of the state where precipitation and surface water resources are in short supply. This view is not inaccurate, but it is seriously incomplete. The groundwater resource is far from uniform ¾ different regions have a wide range of characteristics. Before the intervention of man, the amount of water in the aquifer varied from place to place; groundwater pumping has modified and in some cases intensified the patterns of distribution. These patterns, and their change with water use, are shown in the sections on Saturated Thickness (Predevelopment, Current, and Change) and Water Storage (Predevelopment and Change). Technical appendices provide background information on the concepts of Saturated Thickness and the processes of Groundwater Storage and Flow. The systematic differences in groundwater distribution influence Availability and Accessibility, and interact with variations in the amount and nature of water use, water quality, recharge and sustainability (discussed below), groundwater-surface water interactions, and a variety of other factors. Understanding how the aquifer system varies across time and space is a key factor in analyzing, preparing for, and responding to socioeconomic issues such as resource depletion, the transition to dryland farming, competition for water resources, and so on.

In broad outline, the Ogallala aquifer portion of the High Plains (Groundwater Management Districts 1, 3 and 4) is located in an area where the Estimated Annual Groundwater Recharge is low and variable, and therefore difficult to measure or predict. However, there is no doubt that the Current Maximum Authorized Use of groundwater is significantly in excess of the average recharge. Evidence of this is seen in the change in saturated thickness and water in storage (discussed above), in the findings presented in the appendix on the History of Decline, and especially in the maps of Estimated Usable Lifetime of the aquifer ¾ based on present water amounts and historic pumping rates. Water Usage in these areas is strongly climate-dependent (as is recharge), and is dominated by Irrigation Systems.  Even though the Percentage of Authorized Quantity Used is typically less than 100%, the Changes in Use Necessary for Sustainability are generally at or above the 75% level. However, even in this overall region, major differences exist. Some high-use, high-decline areas have large reserves of groundwater remaining, which means that the measures needed to forestall resource exhaustion are not yet urgent. Other areas are at or very close to effective groundwater depletion (see discussion in the technical appendix on Drawdown and Pumping), and relatively prompt action will be needed to insure that a sustainable reserve of water is kept as a public trust to support essential basic needs, such as domestic and community water supplies. Within both of these classes, different sub-areas have significant local differences in recharge and discharge of surface water, as well as in water quality concerns and present or potential demand or conflicting needs.

In the eastern High Plains, Groundwater Management Districts 2 and 5 operate under safe yield policies, and issues are different from the western regions. Because of higher populations, higher municipal uses, shallow water tables, and natural and artificial contamination, water quality is an issue that is at least as important as water quantity. Both quantity and quality, however, are influenced by groundwater extraction, and the spatial variations in quality and use point to differential classification of aquifer regions in ways similar to the depletion and sustainability issues in western Kansas.

The hydrogeologic characteristics of the aquifer provide a natural basis for classifying aquifer subunits in terms of their potential for use. An example of one possible approach to classification is presented in the section on Groundwater Availability and Accessibility Provinces. However, water use is influenced not only by physical availability, but also by water quality. Both natural geochemistry and human influences have shaped the Groundwater Quality Provinces of the High Plains aquifer. In order to preserve the greatest possible social and economic benefits of the groundwater resource and to minimize the negative effects of competition for a diminishing resource, the natural aquifer subunits must be evaluated in the light of the trends and changes in the resource over the past three to four decades of intensive groundwater development. This combined approach provides a basis for identifying and prioritizing aquifer regions where specific management activities are most needed in order to preserve a sustainable reserve of water to support the basic social structure of the region.

Approaches to identification of aquifer subunits and the urgency of their conditions have been developed, and can be compelling; a good example is provided by the Estimated Usable Lifetime projections, which show a consistent picture of the regions most likely to exhaust the groundwater resources. However, variations in detail depend on the exact depletion trend adopted, and the appendices on the History of Decline and Drawdown and Pumping illustrate some of the issues involved in determining the appropriate time and space scales (i.e., size of the subunit considered and the timing of measurements). The technical concepts and tools are available to support the development and implementation of improved resource conservation and management approaches; the most urgent need is policy consensus on the relative priorities of the potentially competing socially beneficial uses of High Plains groundwater.

Similar issues arise in consideration of surface water resources; In-Stream Water Resources and Minimum Desirable Streamflows are relevant to groundwater-surface water interaction in the High Plains region, as well as to the eastern areas of the state that are more dependent on surface water resources.  In central and eastern Kansas, Potential Groundwater Supplies are more limited and poorly characterized, but are drawing increased attention as concerns about reliable water supplies grow.

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