Thursday, January 1, 2015

Depleting the Ogallala

The High Plains aquifer commonly known as the Ogallala aquifer (because the Ogallala formation makes up about three quarters of the aquifer) became news and burst into public awareness due to the protests associated with the Keystone XL Pipeline. Concern for the porous soils of the Sandhills and fears of a possible oil leak into the Ogallala aquifer is one of the reasons the route through Nebraska was changed. The High Plains aquifer underlies about 175,000 square miles in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming which make up one of the primary agricultural regions in the United States. There is a much bigger threat to the Ogallala; the aquifer is being depleted because the groundwater within it is predominately non-renewable. This groundwater aquifer is the primary source of water for the High Plains. This was open range land until the groundwater from the aquifer was used to turn the range land into irrigated crops. However, according to John Opie in “Ogallala: Water for a Dry Land” this is essentially fossil water that was generated 10,000-25,000 years ago by the melting of the glaciers of the Rockies.

The High Plains aquifer is the most intensively used aquifer in the United States and 97% of the water is used for irrigation. Groundwater withdrawals from the High Plains aquifer represent about 20% of all groundwater withdrawals within the United States and have turned the dry range land in the center of the country into the breadbasket of the world. There are only about 2.5 million people living on the 175,000 square miles of land covering the High Plains aquifer.

The High Plains aquifer is being depleted by irrigation. The grains we grow for consumption, ethanol and export are slowly depleting our water reserves. Farmers and ranchers began extensive use of groundwater for irrigation in the 1930s and 1940s. Estimated irrigated acreage was 2.1 million acres in 1949, 13.7 million acres in 1980, and 15.5 million acres in 2005 (U.S. Department of Agriculture).

About every 5 years, groundwater withdrawals for irrigation and other uses are compiled from water-use data and reported by the U.S. Geological Survey (USGS) and State agencies. Groundwater withdrawals from the High Plains aquifer for irrigation increased from 4 to 19 million acre-feet from 1949 to 1974; fell slightly and then reached 21 million acre-feet in 2000 and an estimated 19 million acre-feet in 2005 (USGS).

According to a recent report from the U.S. Geological Survey (USGS), total water stored within the aquifer was about 2.92 billion acre-feet in 2013 a decline of about 8% (or 266,7 million acre-feet) since irrigation began. Water stored within the aquifer fell 36 million acre-feet from 2011–13. The water depletion was uneven, the decline in Texas alone was 13,2 million acre-feet, while over the same period there was no change in water storage in South Dakota and Wyoming. According to Virginia McGuire the lead author of the report and a water scientist with the USGS, “The measurements made from 2011 to 2013 represent a large decline. This amount of aquifer depletion over a 2-year period is substantial and likely related to increased groundwater pumping.” This level of groundwater use is also unsustainable. We need to rethink our agricultural policies and environmental regulations in terms of sustainable water.

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