The Ogallala aquifer, the largest unit of the hydrologically connected High Plains aquifer system, is one of the world’s largest fresh groundwater resources. It underlies 175,000 square miles/112 million acres in eight states. The High Plains Aquifer system slowly formed as hundreds of feet of silt, clay, and gravel eroded from the Rocky Mountains and other sources were laid down by braided streams during the Miocene and Pliocene (23 to 2.6 million years ago) and Pleistocene (1.8 million years ago to 11,700 years ago) epochs. The water in the High Plains Aquifer system is relatively old, accumulating over thousands of years primarily through infiltration of precipitation.
This region, mostly characterized as semi-arid grassland and steppe, was labeled the “Great American Desert” on early maps (1820-1850). Early American explorers including Major Steven Long and General Zebulon Pike considered the High Plains region to be both unfit for farming and a natural barrier protecting civilization to the east from the nomadic horse people of the Plains.
Technological advances in the early to mid-20th century led to an explosion of irrigated acres, from 2.1 million irrigated acres in 1949 to more than 15 million acres only half a century later. Today, it’s hard to overstate the importance of water pumped from the High Plains aquifer as a principal driver of the region’s largely agricultural-based economy and way of life. Current annual withdrawals from the aquifer are estimated to be on the order of 19 million acre-feet. Water pumped from the High Plains Aquifer system supports nearly 30% of the U.S. irrigated crop production as well as significant proportion of cattle, dairy and hog production.
At the beginning of the 20th Century, the High Plains Aquifer system contained roughly 3.3 billion acre-feet of water. Precipitation, the main source of the aquifer system’s recharge, is limited, averaging 18-20 inches per year over the aquifer, while potential evapotranspiration (water leaving soil through evaporation + use by plants) exceeds 40 inches.
The Ogallala aquifer is heavily relied upon by communities in portions of eight U.S. states. Most of the water pumped from the Ogallala aquifer is used for agriculture, by far the chief driver of the region’s economy. Decades of pumping from the Ogallala aquifer have steadily and significantly lowered the groundwater table at rates greater than natural recharge from precipitation have led to significant water level declines, particularly in parts of the central and southern High Plains.
Approximately 9% of the total original aquifer volume is estimated to have been withdrawn since the start of wide-scale pumping after WWII. Based on current depletion rates, it is estimated that more than a third of the Southern High Plains will be unable to support irrigation within the next 30 years. Portions of the aquifer also are affected by water quality issues related to agriculture, including nitrogen loading.
Local and state-level policies have generally treated the Ogallala as an essentially finite resource which can be mined for “beneficial use,” with that use bounded by the expectation that some percentage of water volume (40%, 50%…) relative to pre-development of the aquifer resource must remain over defined periods of time (i.e ~50 or 100 years into the future).
Timeline of Ogallala aquifer development
Today, widespread recognition of the aquifer’s water quantity and quality declines is generating significant concern about the near- and long-term economic security and longevity of communities in the region.
Click here to access USGS’s June 2017 report on the Ogallala aquifer and changes in groundwater levels from pre-development to 2015 and 2013 – 15
The challenges facing the Ogallala Aquifer region today are relatively well defined. For example, we know how much groundwater is in the aquifer, and how much and how fast it has declined since irrigation started with sufficient accuracy to identify key depletion hotspots and anticipate future rates of decline.
How we will respond as a region to these challenges? What management shifts can support productive, profitable farming while slowing declines or even stabilizing groundwater levels?
Addressing the Ogallala region’s serious challenges requires:
- involvement of a wide variety of knowledgable stakeholders working together towards encouraging shifts in field and irrigation management,
- investment (local, regional and Federal) in research, effective regional education and communications, and other initiatives with potential to extend the usable life of this vital resource.
Next: Ogallala Water Coordinated Agriculture Project | Scope