The
Ogallala Aquifer, also known as the
High Plains Aquifer, is a vast yet shallow underground
water tableThe water table is the level at which the groundwater pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the groundwater in a given vicinity. It usually coincides approximately with the 'phreatic surface', but can be many feet above it...
aquiferAn aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
located beneath the
Great PlainsThe Great Plains are the broad expanse of prairie and steppe which lie west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...
in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
. One of the world's largest aquifers, it covers an area of approximately 174,000 mi² (450,000 km²) in portions of the eight
statesA U.S. state is any one of 50 federated states of the United States of America that share sovereignty with the federal government . Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile...
of
South DakotaSouth Dakota is a state located in the Midwestern region of the United States of America. It is named after the Lakota and Dakota Sioux American Indian tribes. South Dakota was carved out of the southern half of the Dakota Territory and admitted to the Union on November 2, 1889...
,
NebraskaNebraska is a state located on the Great Plains of the Midwestern United States. The state's capital is Lincoln and its largest city is Omaha....
,
WyomingWyoming is a state in the Western United States. The majority of the state is dominated by the mountain ranges and rangelands of the Rocky Mountain West, while the easternmost section of the state includes part of a high elevation prairie region known as the High Plains. While the tenth largest...
,
ColoradoColorado is a U.S. state located in the Rocky Mountain region of the United States of America. It may also be considered to be part of the Western and Southwestern regions of the United States. Colorado entered statehood in 1876 and was nicknamed the “Centennial State”...
,
KansasKansas is a state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa tribe, who inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south wind," although this was...
,
OklahomaOklahoma is a state located in the South Central region of the United States of America. With an estimated 3,617,316 residents in 2007 and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...
,
New MexicoNew Mexico is a state located in the southwestern region of the United States. Inhabited by Native American populations for many centuries, it has also been part of the Imperial Spanish viceroyalty of New Spain, part of Mexico, and a U.S. territory. Among U.S...
, and
TexasTexas is the second-largest U.S. state in both area and population, and the largest state in the contiguous United States.The name had wide usage among native Americans, meaning "friends" or "allies"...
. It was named in 1898 by
N.H. DartonNelson Horatio Darton was a geologist who worked for the United States Geological Survey. He was born in Brooklyn, New York, and started working in his uncle's drug business at the age of 13, also becoming a practicing chemist. His interest in geology started as a sideline, and he was hired by...
from its
type localityIn some natural sciences, type locality — or type locale — is the typical or representative location and is typically the first example of a newly discovered or described object. Often it is namesake for the term....
near the town of
Ogallala, NebraskaOgallala is a city in Keith County, Nebraska, United States. The population was 4,930 at the 2000 census. It is the county seat of Keith County. In the days of the Nebraska Territory, the city was a stop on the Pony Express and later along the transcontinental railroad...
. About 27 percent of the irrigated land in the United States overlies this aquifer system, which yields about 30 percent of the nation's ground water used for irrigation. In addition, the aquifer system provides drinking water to 82 percent of the people who live within the aquifer boundary.
General characteristics
The deposition of the aquifer material dates back 2 to 6 million years to late
MioceneThe Miocene is a geological epoch of the Neogene period and extends from about 23.03 to 5.33 million years before the present . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the...
to early
PlioceneThe Pliocene epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present....
age when the southern
Rocky MountainsThe Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in Canada, to New Mexico, in the United States. The range's highest peak is Mount Elbert in Colorado at above sea level...
were still tectonically active. From the uplands to the west, rivers and streams cut channels in a generally west to east or southeast direction.
ErosionErosion is a gravity driven process that moves solids in the natural environment or their source and deposits them elsewhere...
of the Rockies provided alluvial and aeolian sediment that filled the ancient channels and eventually covered the entire area of the present-day aquifer, forming the water-bearing Ogallala Formation. The depth of the formation varies with the shape of the pre-Ogallala surface, being deepest where it fills ancient valleys and channels. The Ogallala Formation consists mostly of coarse sedimentary rocks in its lower sections, which grade upward into finer-grained lithologies.
The water-permeated thickness of the Ogallala Formation ranges from a few feet to more than 1000 feet (300 m) and is generally greater in the northern plains. The depth of the water below the surface of the land ranges from almost 400 feet (122 m) in parts of the north to between 100 to 200 feet (30 to 61 m) throughout much of the south. Present-day recharge of the aquifer with fresh water occurs at a slow rate; this implies that much of the water in its
porePorosity is a measure of the void spaces in a material, and is a fraction of the volume of voids over the total volume, between 0–1, or as a percentage between 0–100%...
spaces is paleowater, dating back to the last
ice ageThe general term "ice age" or, more precisely, "glacial age" denotes a geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual...
.
Aquifer water balance
An aquifer is a groundwater storage reservoir in the
water cycleThe water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above and below the surface of the Earth. Since the water cycle is truly a "cycle," there is no beginning or end. Water can change states among liquid, vapor, and ice at various places in the water...
. While groundwater is a renewable source, reserves replenish relatively slowly. The USGS has performed several studies of the aquifer, to determine what is coming in (groundwater recharge from the surface), what is leaving (pumping and baseflow to streams) and what the net changes in storage are (rise, fall or no change — see figure above). Simply put, water in, minus the water out, is equal to the change in water stored in the aquifer. This type of
mass-balanceThe law of conservation of mass/matter, also known as principle of mass/matter conservation is that the mass of a closed system will remain constant over time, regardless of the processes acting inside the system. A similar statement is that mass cannot be created/destroyed, although it may be...
"accounting" is how hydrologic budgets are performed, and is a crucial first step in sustainable management of any natural resource.
Withdrawals from the Ogallala Aquifer for irrigation amounted to 26 cubic km (21 million acre feet) in 2000, which is slightly greater than the historical discharge rate of the
Colorado RiverThe Colorado River , or the Red River, is a river in the southwestern United States and northwestern Mexico, approximately long, draining a part of the arid regions on the western slope of the Rocky Mountains...
. As of 2005, the total depletion since pre-development amounted to 253 million acre-feet (312 cubic km). Some estimates say it will dry up in as little as 25 years. Many farmers in the
Texas High PlainsThe High Plains are a subregion of the Great Plains in the central United States, generally encompassing the western part of the Great Plains before the region reaches the Rocky Mountains. The High Plains are located in eastern Colorado, western Kansas, western Nebraska, central and eastern...
, which rely particularly on the underground source, are now turning away from irrigated agriculture as they become aware of the hazards of overpumping.
Groundwater recharge
The rate at which recharge water enters the aquifer is limited by several factors. Much of the plains region is
semi-aridIn physical geography, a steppe is a biome region characterised by grassland plain without trees . The prairie can be considered a steppe. It may be semi-desert, or covered with grass or shrubs or both, depending on the season and latitude...
with steady winds that hasten evaporation of surface water and precipitation. In many locations, the aquifer is overlain, in the
vadose zoneThe vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the phreatic zone or zone of saturation . It extends from the top of the ground surface to the water table...
, with a shallow layer of
calicheCaliche is a sedimentary rock, a hardened deposit of calcium carbonate. This calcium carbonate cements together other materials, including gravel, sand, clay, and silt. It is found in aridisol and mollisol soil orders...
that is practically
impermeableHydraulic conductivity, symbolically represented as , is a property of vascular plants, soil or rock, that describes the ease with which water can move through pore spaces or fractures. It depends on the intrinsic permeability of the material and on the degree of saturation...
; this limits the amount of water able to recharge the aquifer from the land surface. However, the soil of the playa lakes is different and not lined with caliche, making these some of the few areas where the aquifer can recharge. The destruction of playas by farmers and development then decreases the available recharge area. The prevalence of the caliche is partly due to the ready evaporation of soil moisture and the semi-arid climate; the aridity increases the amount of evaporation which increases the amount of caliche in the soil. Both mechanisms reinforce the difficulty recharge has in reaching the water table.
Groundwater discharge
The regions overlying the Ogallala aquifer are some of the most productive regions for ranching
livestockLivestock are one or more domesticated animals raised in an agricultural setting to produce commodities such as food or fiber, or labor...
, and growing
cornMaize , is a herbaceous plant domesticated in Mesoamerica and subsequently spread throughout the American continents...
,
wheatWheat is a worldwide cultivated grass from the Fertile Crescent region of the Near East. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
and soybeans in the United States (often called the "breadbasket of America"). The success of large-scale farming in areas which do not have adequate
precipitationIn meteorology, precipitation is any product of the condensation of atmospheric water vapor that is deposited on the Earth's surface. The main forms of precipitation include rain, snow, ice pellets, and graupel...
and do not always have perennial
surface waterSurface water is water collecting on the ground or in a stream, river, lake, wetland, or ocean; it is related to water collecting as groundwater or atmospheric water....
for diversion depends heavily on pumping groundwater for irrigation.
Early settlers of the semi-arid High Plains were plagued by crop failures due to cycles of drought, culminating in the disastrous
Dust BowlThe Dust Bowl or the Dirty Thirties was a period of severe dust storms causing major ecological and agricultural damage to American and Canadian prairie lands from 1930 to 1936 . The phenomenon was caused by severe drought coupled with decades of extensive farming without crop rotation, fallow...
of the 1930s. The aquifer was first tapped for
irrigationIrrigation is an artificial application of water to the soil. It is usually used to assist in growing crops in dry areas and during periods of inadequate rainfall...
in 1911. Large scale use for irrigation began in the 1930s and continued through the 1950s, due to the availability of electric power to rural farming communities and the development of cheap and efficient electric turbine
pumpA pump is a device used to move fluids, such as gases, liquids or slurries. A pump displaces a volume by physical or mechanical action. One common misconception about pumps is the thought that they create pressure. Pumps alone do not create pressure; they only displace fluid, causing a flow. ...
s. It was only after
World War IIWorld War II, or the Second World War , was a global military conflict which involved a majority of the world's nations, including all great powers, organized into two opposing military alliances: the Allies and the Axis...
that affordable technology became available to substantially extract water. This transformed the High Plains into one of the most agriculturally productive regions in the world. During the early years, this source of water was thought to be inexhaustible, and its hydrology a mystery. However, because the rate of extraction exceeds the rate of recharge, water level elevations are decreasing. At some places the water table was measured to drop more than five feet (1.5 m) per year at the time of maximum extraction. In extreme cases, the deepening of
wellA water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a vertical turbine pump, a handpump or a mechanical pump...
s was required to reach the steadily falling water table; and it has even been drained (dewatered) in some places such as Northern Texas. Utilizing treated recycled sources of water in agriculture is one approach at safeguarding the future of the aquifer. Another method to reducing the amount of water use is changing to a crop that requires less water, such as
sunflowerSunflowers are annual plants native to the Americas, that possess a large inflorescence .-Description :...
s.
Several of the rivers in the region, such as the
PlatteThe Platte River is a river in the Western United States, approximately long. It is a tributary of the Missouri River, which in turn is a tributary of the Mississippi River. The Platte is one of the most significant river systems in the watershed of the Missouri, draining a large portion of the...
, are below the water level of the aquifer and therefore the rivers actually receive groundwater flow (baseflow) rather than supply recharge to the aquifer.
Change in groundwater storage
The USGS estimated that total water storage was about 2,925 million acre feet (3,608 km³) in 2005. This is a decline of about 253 million acre feet (312 km³) (or 9%) since substantial ground-water irrigation development began, in the 1950s.
Water conservation practices (
terracingIn agriculture, a terrace is a leveled section of a hill cultivated area, designed as a method of soil conservation to slow or prevent the rapid surface runoff of irrigation water. Often such land is formed into multiple terraces, giving a stepped appearance...
and crop rotation), more efficient irrigation methods (
center pivotCenter-pivot irrigation , also called circle irrigation, is a method of crop irrigation in which equipment rotates around a pivot...
and drip), and simply reduced area under irrigation have helped to slow depletion of the aquifer, but levels are generally still dropping. See the figure above for an illustration of the places where large drops in water level have been observed (i.e., the brown areas in southwest
KansasKansas is a state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa tribe, who inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south wind," although this was...
, and in or near the
Texas panhandleThe Texas Panhandle is a region of the U.S. state of Texas consisting of the northernmost 26 counties in the state. The panhandle is a rectangular area bordered by the state of New Mexico to the west and the state of Oklahoma to the north and east...
). In the more humid areas water levels have actually risen since 1980 (i.e., eastern and central
NebraskaNebraska is a state located on the Great Plains of the Midwestern United States. The state's capital is Lincoln and its largest city is Omaha....
and south of
LubbockLubbock is an American city in the state of Texas. Located in the northwestern part of the state, a region known historically as the Llano Estacado, it is the county seat of Lubbock County, and the home of Texas Tech University. According to the 2000 U.S. Census, the city population was 199,564,...
).
Other mentions of Ogallala aquifer
The importance of this aquifer has been recognized recently in many works, ranging from increased attention from journalism to a mention in a plot for world domination in the
Amazing Spider-ManSpider-Man is a fictional Marvel Comics superhero. The character was created by writer and editor Stan Lee and artist and co-plotter Steve Ditko. He first appeared in Amazing Fantasy #15...
comic book made by Marvel Comics. It also figures prominently in the novel
That Old Ace in the Hole by E. Annie Proulx, and as part of the historical background of the plot of the Canadian television mini-series
H2OH2O is a Canadian political drama two-part miniseries that first aired on the CBC Television October 31, 2004 starring Paul Gross and Leslie Hope with Belinda Stronach making a cameo appearance in the film. Written by Paul Gross and John Krizanc and directed by Charles Binamé, it was...
.
In the 1980s,
Texas PanhandleThe Texas Panhandle is a region of the U.S. state of Texas consisting of the northernmost 26 counties in the state. The panhandle is a rectangular area bordered by the state of New Mexico to the west and the state of Oklahoma to the north and east...
organic foods
farmerA farmer is a person who raises living organisms for food or raw materials.- Definition :The term farmer usually applies to a person who grows field crops, and/or manages orchards or vineyards, or raises livestock or poultry such as chicken and cows...
and spokesman
Frank FordJesse Frank Ford, known as Frank Ford , is a retired Texas farmer and health-foods advocate who in 1960 founded Arrowhead Mills, the largest natural foods wholesaler in the United States. The company is based in Hereford, the seat of Deaf Smith County west of Amarillo in the Texas Panhandle...
successfully prevented the location of a nuclear waste repository in his native
Deaf Smith CountyDeaf Smith County is a county located in the U.S. state of Texas. As of the 2000 census, the population was 18,561. Its county seat is Hereford.The Hereford Micropolitan Statistical Area includes all of Deaf Smith County.-History:...
on the grounds that the material could poison the Ogallala Aquifer. The repository was instead located in
Yucca MountainThe Yucca Mountain Repository was the United States Department of Energy proposed deep geological repository storage facility for spent nuclear reactor fuel and other radioactive waste. Although the proposal has been highly contested by environmentalists and residents near the area, it was approved...
in
NevadaNevada is a state located in the western region of the United States. The capital is Carson City and the largest city is Las Vegas. The state's nickname is Silver State, due to the large number of silver deposits that were discovered and mined there...
.
Additionally, while not having a prominent role throughout James Michener's novel
Texas, it carries great importance in the final chapter entitled "Power and Change."
External links