Kansas Geological Survey, Public Information Circular (PIC) 18
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Rex C. Buchanan, Robert W. Buddemeier, and B. Brownie Wilson
Kansas Geological Survey
The High Plains aquifer, which includes the well-known Ogallala aquifer, is the most important water source for much of western and central Kansas (fig. 1), supplying 70% of the water used by Kansans each day. Water from the High Plains aquifer supports the region's cities, industry, and much of its agriculture.
However, large-volume pumping from this aquifer has led to steadily declining water levels in the western portion of the region, and the area faces several critical water-related issues. This Public Information Circular describes the High Plains aquifer, the effect of decades of large-volume pumping, and some responses to water issues in central and western Kansas.
Aquifers are underground deposits containing permeable rock or sediments (silts, sands, and gravels) from which water can be pumped in usable quantities. The High Plains aquifer is a regional aquifer system composed of several smaller units that are geologically similar and hydrologically connected--that is, water can move from one aquifer to the other. The High Plains aquifer system lies beneath parts of eight states in the Great Plains, including about 30,500 square miles of western and central Kansas (fig. 1).
Figure 1--Saturated extent of High Plains aquifer in Kansas.
Aquifer characteristics are determined in large part by geology. The High Plains aquifer is composed mainly of silt, sand, gravel, and clay--rock debris that washed off the face of the Rocky Mountains and other more local sources over the past several million years. The aquifer varies greatly from place to place: thick in some places, thin in others; permeable (able to transmit water easily) in some places, less so in others. Where the deposits are thick and permeable, water is easily removed and the aquifer can support large volumes of pumping for long periods. In most areas, this water is of good quality.
The most important component of the High Plains aquifer is the Ogallala aquifer, generally the western half of the High Plains aquifer in Kansas. In some locations (such as Lake Scott State Park in Scott County), the Ogallala Formation crops out at the surface, forming a naturally cemented rock layer called mortarbeds. In the subsurface, the Ogallala largely consists of silt and clay beds that are interlayered with sand and gravel that is mostly unconsolidated, or not naturally cemented together.
The south-central extension of the High Plains aquifer is composed of younger sediments that are similar to the Ogallala. These younger sediments, deposited during the Pleistocene Epoch, or Ice Ages, include the "Equus beds" aquifer (in McPherson, Reno, Harvey, and Sedgwick counties) and the "Great Bend Prairie aquifer" (in Stafford, Edwards, Pratt, Kiowa, and other counties). Also lying above the Ogallala Formation are other Pleistocene deposits and other younger deposits in the valleys of modern streams. Where these stream deposits (known as alluvium) are connected to the Ogallala or Pleistocene aquifers, the alluvial aquifers are considered part of the High Plains aquifer (fig. 2).
Figure 2--Schematic (A) and map (B) showing aquifers that make up the High Plains aquifer.
Beneath the High Plains aquifer is much older, consolidated bedrock, usually limestone, sandstone, or shale (fig. 3). In some places this bedrock holds enough water to be called an aquifer, and it may be connected to the overlying aquifer. Layers of permeable sandstone in the Dakota Formation, for example, are connected to the High Plains aquifer in parts of southwestern or south-central Kansas. Some layers of the underlying bedrock contain saltwater; where these are directly connected to the High Plains aquifer, they pose a threat to water quality.
Figure 3--Generalized cross section showing the High Plains aquifer and underlying bedrock. The Ogallala Formation, Pleistocene deposits, and alluvium combine to form the High Plains aquifer.
Usable water in the High Plains aquifer is in the pore spaces between particles of sand and gravel. This water (called ground water) accumulated slowly--in some of the deeper parts of the aquifer, over tens of thousands of years. In the subsurface, water in the aquifer generally moves slowly from west to east, usually at the rate of tens of feet per year.
Recharge is the natural movement of water into an aquifer, usually from precipitation. Natural recharge to the High Plains aquifer from precipitation is low, in part because much of the rain falls during the growing season, when plant roots intercept the soil moisture. In western Kansas, where precipitation is scant and the water table is relatively deep (several hundred feet) in many places, recharge occurs infrequently and the long-term average is less than an inch per year. In central Kansas, where the aquifer is closer to the land surface, where soils are sandier, and precipitation amounts greater, recharge can be significant, as much as 4 to 6 inches per year.
Water volumes and use are measured in various ways. One measure is an acre-foot, or the amount of water necessary to cover an acre of ground (a parcel about the size of a football field) with a foot of water. An acre-foot equals 325,851 gallons of water. In the year 2000, about 21 million acre-feet of ground water was removed from the High Plains aquifer eight-state region (McGuire, 2009). In Kansas, the High Plains aquifer yielded 4.4 million acre-feet, of which 2.4 million acre-feet came from the Ogallala aquifer in 2007. Estimated average annual natural recharge to the Ogallala in Kansas is 0.72 million acre-feet.
Another measure of ground water is saturated thickness--the thickness of the sands, gravels, and other materials that are saturated with water. Saturated thickness is commonly measured in feet, but "feet of saturated thickness" is not the same as feet of actual water. Only about 10 to 25% of the aquifer volume is pore space that can yield extractable water. Therefore, in an aquifer with 17% pore space, removing 1 acre-foot of water causes the water table to drop by about 6 feet. In Kansas, saturated thickness in the High Plains aquifer is generally greatest in the southwestern part of the state (see fig. 4). There, saturated thicknesses of 300 feet and greater were common before the onset of large-scale irrigation, a time that is often called "pre-development."
Figure 4--Predevelopment saturated thickness for the High Plains aquifer in Kansas.
Ground water can also be measured in terms of its availability: how much water can be removed by a well over short periods. Large volumes of water can be pumped rapidly (1,000 gallons or more per minute) from the High Plains aquifer in many locations. This contrasts with much of the rest of the state, where wells generally produce smaller amounts (less than 100 gallons per minute). By way of comparison, a good household well produces 5 to 10 gallons per minute, although many household wells produce less.
Large-scale irrigation began in western Kansas in the late 1800's, with the use of ditches to divert water from the Arkansas River. As technology improved, ground water became the major irrigation source because surface water (lakes, rivers, and streams) is relatively scarce in western Kansas. With the advent of large-capacity pumps that were capable of drawing several hundred gallons of water per minute, people began to develop that ground water. Using a technique called flood irrigation, water was pumped through long pipes or ditches along the edges of a field, then out onto rows of crops (fig. 5A).
Figure 5--Aerial photos of (A) flood and (B) center-pivot irrigation (photos courtesy of Tom Schmiedeler, Washburn University).
In the 1950's and 1960's, technological developments led to a dramatic increase in large-scale pumping. In particular, center-pivot irrigation systems--large sprinklers that roll across the land on wheels--allowed people to irrigate uneven terrain, thus opening up large new areas for irrigation (fig. 5B). These irrigation methods led to the cultivation of crops, such as corn, that could not previously be grown reliably in the area. That grain production led, in turn, to large feedlots and packing plants and a boom in the economy of much of western Kansas, all largely dependent on ground water. One study in 2001 estimated that the economic impact of irrigation in southwestern Kansas alone amounts to more than $188 million annually (Gilson et al., 2001).
For many years, people believed that the High Plains aquifer contained an inexhaustible amount of water. However, large-volume pumping (mostly for irrigation) eventually led to substantial declines in the water table, and people realized that the amount of water in the aquifer was finite and could be exhausted. Much of the Ogallala portion of the High Plains aquifer has declined since predevelopment, with some areas having declines of more than 60% (fig. 6).
Figure 6--Percent change in saturated thickness for the High Plains aquifer in Kansas, predevelopment to 2007-09.
Nonetheless, in much of the aquifer, considerable amounts of water remain. For example, declines of 100 feet or more may have occurred in parts of southwestern Kansas, but that represents less than half of the original saturated thickness, and 100 to 200 feet (or more) of saturated thickness may remain. On the other hand, in parts of west-central Kansas--such as Greeley, Wichita, Scott, and northern Finney counties--the original saturated thickness was much less, often less than 100 feet. In these places, where early flood-irrigation systems were prevalent, less than 50 feet of saturated thickness remains.
Perhaps the most common and important question about the High Plains aquifer is: How much longer can it support large-scale pumping? It's a simple question with a complicated answer. First, the aquifer will probably be able to support small, domestic wells far into the future. With proper planning, most cities and towns should be able to provide for their water needs. Second, the future of agricultural use of the aquifer depends on a variety of factors, including the price of irrigated crops, the price and availability of energy (the deeper the water table, the more energy it takes to pump water), climate, and how the water is managed. Third, it is important to remember that the aquifer is not one consistent, homogeneous unit. Rather, it varies considerably from place to place. In places, the aquifer consists of less than 50 feet of saturated thickness and receives little recharge. In other places, the aquifer is far thicker or receives considerably more recharge.
With those qualifications in mind, researchers at the Kansas Geological Survey have made projections about the aquifer, based on past trends in water-level declines. Obviously, the actual future use of water will be affected by commodity prices, energy prices, climate, and management policies. Relatively little data are available for some parts of the aquifer, and projections are not practical in those areas. Assuming saturated thickness sufficient to support pumping of at least 400 gallons per minute, researchers concluded that parts of the aquifer are effectively exhausted in Greeley, Wichita, and Scott counties (fig. 7). Other parts of the aquifer, in areas such as southwestern Thomas County, are projected to have a lifespan of less than 25 years, based on past decline trends. However, the biggest share of the aquifer in southwest Kansas would not be depleted for 50 to 200 years. It is important to remember that these projections are based solely on past water-level trends, and future changes could alter the actual depletion rate.
Figure 7--Estimated usable lifetime (1998-2008) trend for the High Plains aquifer in Kansas.
By Kansas law, water is a public resource that is dedicated to the use of the people of the state. Individuals, companies, municipalities, and other entities can obtain permission to use water for beneficial purposes by obtaining a water right, either new or existing. In general, all beneficial uses of water, except most domestic use, require a water right. Kansas water law is based on the doctrine of prior appropriation. That is, when there is insufficient water to meet all water rights, the date of the water right determines who has the right to use the water. This doctrine is commonly expressed as "First in time, first in right."
Responsibility for managing water use in Kansas is spread over several agencies. The Division of Water Resources of the Kansas Department of Agriculture is responsible for administering water rights, and thus is primarily responsible for regulation related to the quantity of water used. Water issues also are subject to local control and management. Five groundwater management districts have been created in Kansas to provide local management of the resource within the framework of the State's water laws. Together, they cover nearly all of the state underlain by the High Plains aquifer (fig. 8). Groundwater management districts, through staff and an elected board, develop and implement policies and rules and regulations to manage and protect the quality of water, undertake educational activities, and work with State and Federal water-related agencies to regulate and manage the High Plains aquifer.
Figure 8--Groundwater management district boundaries in Kansas.
A variety of other agencies deal with other aspects of water in the state. The Kansas Geological Survey, for example, a research and service division of the University of Kansas, undertakes a variety of water-related activities, but has no regulatory responsibility. The Kansas Department of Health and Environment monitors water-quality issues. The Kansas Water Office, working with the Kansas Water Authority, is responsible for water planning. That planning is according to drainage basins, or areas that are drained by a common stream, such as the Cimarron River or Neosho River. Each of those basins is represented by a volunteer basin-advisory committee. The Kansas Department of Wildlife and Parks, Kansas State University's Extension program, the Kansas Biological Survey, the U.S. Geological Survey, and other State and Federal agencies have various responsibilities for water.
Individuals, governmental agencies, and private organizations are all attempting to address issues related to the High Plains aquifer. In addition, several new institutions have recently been proposed to deal with issues concerning the aquifer on a regional basis. Irrigators have implemented a number of techniques that have improved the efficiency with which they use water--using low-pressure application methods on center-pivot systems, for example, instead of spraying water high into the air.
Among the more far-reaching proposals for extending the life of the aquifer is the idea of sustainable development. This is the concept of limiting the amount of water taken from the aquifer to no more than the amount of recharge, and perhaps less, depending on the impact on water quality and minimum streamflows. This level of use is the target of the safe-yield management policies currently in effect in the Big Bend and Equus Beds Groundwater Management Districts in the eastern part of the High Plains aquifer. Adoption of a similar policy in other areas of the High Plains aquifer would require a substantial decrease in the amount of water currently used. This would have an impact on the type and amount of crops grown in western Kansas and, in turn, on a variety of economic activities. Because many of the water rights in the High Plains aquifer were established long ago and thus have priority, the implementation of sustainable-development approaches to water resources has serious legal implications. Other methods for dealing with the High Plains aquifer are being proposed, discussed, and implemented. All are aimed at extending the life of this crucial resource.
[The authors thank Dave Young, formerly of the Kansas Geological Survey, and Bob Sawin, Kansas Geological Survey, for their help in the preparation of this curdular.]
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Gilson, Preston, Aistrup, Joseph, Heinrichs, John, and Zollinger, Brett, 2001, The value of Ogallala aquifer water in southwest Kansas: Docking Institute of Public Affairs, Fort Hays State University, 82 p.
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Kromm, David, and White, Stephen, 1992, Groundwater exploitation in the High Plains: Lawrence, Kansas, University Press of Kansas, 240 p.
McGuire, V. L., 2009, Water-level changes in the High Plains aquifer, predevelopment to 2007, 2005-06, and 2006-07: U.S. Geological Survey, Scientific Investigation Report 2009-5019, 18 p.
Opie, John, 1993, Ogallala--Water for a dry land: Lincoln, Nebraska, University of Nebraska Press, 412 p.
Schloss, Jeffrey, Buddemeier, Robert, and Wilson, Blake, eds., 2000, An atlas of the High Plains aquifer: Kansas Geological Survey, Educational Series 14, 92 p.
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Kansas Geological Survey--http://www.kgs.ku.edu/
Kansas Department of Agriculture, Division of Water Resources--http://www.ksda.gov/dwr/
Kansas Water Office--http://www.kwo.org/
U.S. Geological Survey's Water Resources Division Office, Lawrence--http://ks.water.usgs.gov/
Kansas Geological Survey, Public Outreach
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Web version December 2009