Ogallala aquifer

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Thickness of the saturation zone of the Ogallala Aquifer (1997)
Changes in the water level of the Ogallala aquifer between 1980 and 1995

The Ogallala , also known as the High Plains, is a major aquifer in the subsurface of the Great Plains in the United States . As one of the world's largest aquifers, it extends over an area of ​​more than 450,000 km² under the eight US states of South Dakota , Nebraska , Wyoming , Colorado , Kansas , Oklahoma , New Mexico and Texas . Its name is derived from the Ogallala formation , which was named in 1899 by Nelson Horatio Darton after its type locality near the small town of Ogallala in Nebraska.

geology

The most important aquifer-conducting layers, the Ogallala Formation, were deposited in the late Miocene and early Pliocene . It is related to the recent uplift of the Rocky Mountains . The increased erosion in the Rocky Mountains led to siliciclastic alluvial deposits in large parts of their eastern foreland. In addition to the Ogallala formation, other sedimentary formations are involved in the Ogallala aquifer, including Quaternary drift sands .

The thickness of the saturation zone of the Ogallala Aquifer ranges from a few centimeters to more than 160 meters (525 feet ), with generally greater thickness in the north of the Great Plains than in the south. The saturation zone is located at a depth of 122 meters (400 feet) in the north and up to 30-60 meters (100-200 feet) in the south. The recent groundwater recharge rate is very low. Much of the water in the aquifer therefore probably comes from at least the last ice age .

The water in the Ogallala aquifer is generally fresh water with 300 to 1000 mg / l of dissolved components, mainly calcium , magnesium and hydrogen carbonate .

Relationship between groundwater abstraction and groundwater formation

False color image of irrigated fields near Garden City, Kansas, taken from the Landsat-7 satellite

Every aquifer is a water reservoir and therefore part of the water cycle . The US Geological Survey (USGS) has carried out several studies on the Ogallala aquifer to investigate the relationship between groundwater recharge and groundwater abstraction and thus also the development of the water table. This should help to secure the water for the future, because today the aquifer forms the basis for almost all agriculture in the Great Plains and its drying up would mean the end of thousands of businesses.

Groundwater recharge

The groundwater recharge rate in the Ogallala aquifer is relatively low. Most of the Great Plains have a semi-arid climate with strong winds, which promotes the evaporation of surface and rainwater. In semi-arid climates a limestone layer ( caliche ) can form due to the high evaporation at shallow depths , which is almost completely impermeable to seeping water. Thus, the climate is a double barrier to the replenishment of the aquifer.

Groundwater abstraction

The area above the Ogallala Aquifer is one of the most productive agricultural regions in the United States. Here are corn , wheat and soybeans grown in very large quantities, which the Great Plains has been nicknamed the "breadbasket of America" introduced. The yields of the many large farms , which are often located in areas with insufficient annual rainfall and in which the surface waters do not have sufficient water all year round, depend very much on the groundwater, which is brought to the surface by pumps to irrigate the plants.

The aquifer was first used for agricultural irrigation in 1911 , but mass use did not begin until the 1930s and experienced a second boost in the 1950s , when the now almost comprehensive supply of electricity, including in rural areas, and the availability of cheaper and more efficient turbine pumps improved Offered funding opportunities for the water. As the rate of groundwater abstraction soon exceeded the rate of recharge, the water table began to drop rapidly. According to current estimates, the ratio of withdrawn to newly formed groundwater is around 25, which means that for every 25 liters of withdrawn groundwater, only one liter is newly formed. In some places, a drop in the groundwater level of up to 1.50 meters per year was measured. In some extreme cases, boreholes for the pumps had to be driven deeper into the earth in order to access water. Some parts of the aquifer are already waterless, i.e. dried out. If this trend continues, excessive water consumption could lead to a breakdown of agriculture in the area in the medium term.

Furthermore, some rivers in the region, such as the Platte River , are partly still below the groundwater table, which also removes water from the aquifer.

Current situation

Measures to reduce water consumption such as crop rotation, more efficient irrigation methods and the reduction of irrigated areas have recently led to a slight decrease in the lowering of the water table. In some areas such as humid eastern and central Nebraska, however, it has risen slightly again. In 2000, groundwater abstraction was 64 billion liters (17 billion gallons ) per day for irrigation of agricultural land and 1.2 billion liters (315 million gallons) per day for drinking water supply to households in the area.

Potential exposure to the Keystone XL pipeline

In Nebraska the Ogallala formation is in part directly from quaternary layered sands, which at the surface an extensive fossil dunes form field, the sand Hills . These are considered to be ecologically sensitive areas. The route of the " Keystone XL " planned to complement the Keystone oil pipeline was originally intended to run through the Sandhills, which was sharply criticized by environmentalists and local residents. On the one hand, serious damage to the Sandhills ecosystem was feared in the event of a break in the pipeline, which is generally controversial in terms of environmental policy, and on the other hand, the contamination of the groundwater in the Ogallala aquifer by toxins contained in petroleum, with serious consequences for people and agriculture in the region. In the Sandhills, the groundwater is very shallow, and due to the permeable sands, this water would be particularly at risk in an accident. As a result of the criticism, the plans were changed and a route was worked out that bypasses the Sandhills.

literature

  • Edwin D. Gutentag, Frederick J. Heimes, Noel C. Krothe, Richard R. Luckey, John B. Weeks: Geohydrology of the High Plains Aquifer in Parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming. US Geological Survey Professional Paper 1400-BUS Geological Survey, Department of the Interior, Washington, DC 1984 ( online ).
  • Manjula V. Guru, James E. Horne: The Ogallala Aquifer. Kerr Center for Sustainable Agriculture, Poteau (OK) 2000 ( online ).

Web links

Individual evidence

  1. ^ Nelson Horatio Darton: Relations of Tertiary Formations in the Western Nebraska Region. The American Geologist. Vol. 23, No. 2, 1899, p. 94 ( archive.org )
  2. ^ Nelson Horatio Darton: Preliminary Report on the Geology and Water Resources of Nebraska West of the One Hundred and Third Meridian. US Geological Survey Professional Paper 17th US Geological Survey, Department of the Interior, Washington, DC 1903 ( online ).
  3. ↑ Thomas S. Ahlbrandt, SG Fryberger, John H. Hanley, J. Platt Bradbury: Geologic and Paleoecologic Studies of the Nebraska Sand Hills. US Geological Survey Professional Paper 1120-AC. US Geological Survey, Department of the Interior, Washington, DC 1980 ( online ).
  4. ^ A b Lisa Song: New Keystone XL Route: Out of the Sandhills, but Still in the Aquifer. InsideClimate News, April 26, 2012.
  5. ↑ Geoff Dembicki: Gulf Disaster Raises Alarms about Alberta to Texas Pipeline. The Tyee, June 21, 2010.
  6. ^ John M. Broder, Governor of Nebraska Backs Route for Pipeline. New York Times, Jan 22, 2013.

Coordinates: 37 ° 0 ′ 0 ″  N , 101 ° 30 ′ 0 ″  W.