Introduction/Background

The High Plains aquifer is a nationally important water resource that underlies about 174,000 mi² in parts of eight western states. The aquifer serves as a primary source of drinking water for most residents of the region, and also sustains more than one fourth of the Nation's agricultural production (Dennehy and others, 2002). In 2000, water withdrawals from the High Plains aquifer accounted for 21.2 percent of all groundwater withdrawn in the United States (Hutson and others, 2004). This amount of groundwater production makes the High Plains aquifer by far the most intensively pumped principal aquifer in the US (Maupin and Barber, 2005). The High Plains aquifer has gained national and international attention as a highly stressed groundwater supply primarily due to the well documented aquifer depletions in many parts of the aquifer. The U.S. Geological Survey (USGS) has had an active program to monitor the changes in groundwater levels of the High Plains aquifer (fig. 3, McGuire, 2007) and has documented substantial water-level changes since predevelopment. The continued decline in water-levels, particularly in Kansas and Texas, has caused much concern about the sustainability of the aquifer and the associated agricultural production in this important national resource.

Figure 3. USGS groundwater-
level monitoring network within
High Plains aquifer.

The High Plains aquifer occupies the higher elevations of the Great Plains physiographic province which lies east of the Rocky Mountains. Elevations range from about 8,000 feet along the northwestern boundary of the aquifer in Wyoming to about 1,000 feet along the eastern boundary. The topography is characterized by flat to gently rolling terrain which is a remnant of a vast plain of Tertiary and Quaternary sediments deposited by streams originating in the ancestral Rocky Mountains.

Land use over the High Plains aquifer is characterized by a sparse rural population and a few moderate sized cities and towns dominated by an agricultural economy. Population in 2000 was about 2.3 million people with 77 percent residing in rural areas and smaller towns and cities (McMahon and others, 2007). Rangeland and agricultural land were the dominant land uses/land covers in the High Plains in 2001 with 56 percent of the land being classified as rangeland and 38 percent as agricultural land (McMahon and others, 2007).

These conditions of concentrated agricultural land use, semi-arid and variable climatic conditions (which demands agricultural irrigation), and the hydrogeologic setting combine to produce the documented aquifer water-level declines.