Ogallala Aquifer

By Marlena Bludzien

How much water does it take to grow the food we eat daily? Most of the food we grow and irrigate in the U.S. comes from the western part of the country called High Plains. Under this area lays the largest single water source in the United States, called the High Plains Aquifer or Ogallala Aquifer. It is incredibly vital to the High Plains land. This aquifer alone supplies a very large 81% of the water used in the area. This land accounts for 27% of our Nation’s IrrigatedLand. It is a very important area for growing wheat, cotton, and corn: the basics of our daily diet.

An aquifer is a region of subsurface rock that is saturated with groundwater. An unconfined aquifer such as the Ogallala aquifer is an area of groundwater composed of permeable surface soil layer. Below the soil lies an unsaturated zone, an area where the water table has not risen to. Perhaps the most crucial part of the aquifer is the aquiclude. This element is impermeable to water and usually consist of clay rock. It traps groundwater above it creating what we know as aquifer. The primary source for the aquifer recharge is precipitation but because of the Ogallala Aquifer location in the Western U.S,, it receives little precipitation throughout the year. The water table is the natural level at which the groundwater is present. The water table can rise and fall depending on how much water is recharged to the aquifer.

The aquifer lies under parts of South Dakota, Wyoming, Nebraska, Colorado, Kansas, New Mexico, Oklahoma and Texas. The Ogallala Aquifer covers approximately 174,000 square miles. It’s massive. If the groundwater was spread over the entire 50 states it would be foot and a half deep. Nebraska is home to some of Ogallala Aquifer’s deepest water. On average the aquifer is 200 feet in depth. In parts of west-central Nebraska, the aquifer reaches as far down as 1,000 feet. However, further south in Texas, the Ogallala is most shallow ranging in depth here from 0 to 50 feet. Because of the stress placed on this resource, it is in danger of drying up.

The Ogallala Aquifer supplies agriculture industries, mining, livestock and domestic use. About ninety four percent of its total groundwater usage is for irrigation. Nebraska, Texas, and Kansas withdraw the greatest amount of water for irrigation. Nebraska uses about 46%, Texas uses 36% and Kansas 14%. With this being said, the Ogallala is facing serious problems. The root of these problems is that its depletion rate is much higher than its recharge rate. From 1940 to 1980 the aquifer’s water table declined approximately an average of 10 feet. This means that overall 329.5 cubic miles of water were removed from the aquifer over a 40-year period. An average of 21.59 millimeters of water per year are recharged back into the aquifer but this number is vastly outweighed by the amount of water being drawn out of it. An astounding 76.5 millimeters per year! In fact, the recent data shows that the aquifer’s water table has been dropping at a net rate of 56.86 millimeters per year in recent years.

As mentioned before, irrigation is the primary use of the aquifer. In the year 2000 seventeen billion gallons a day of the aquifer’s water were pumped from the ground to be used for agricultural purposes. On top of this, water from the Ogallala supplied 1.9 million people that same year with their domestic water supply. To put this in perspective, 315 million gallons per day were pumped for human use. It is important to see the magnitude of water needed for successful irrigation in this region. The bit of recharge that the Ogallala receives is due to precipitation. Overall the lack of recharge in the area further enhances the aquifer’s problem with depletion. The land has low permeability, many areas consist of thick unsaturated zones which makes it even longer for the surface water to penetrate and recharge the groundwater. The rate of evaporation is also very high due to high temperatures in the region making it even harder for the water to collect.

If the Ogallala Aquifer was to be completely drained, it would take 60,000 years for it to return to its original levels. Given the current rates of use, the aquifer can only be sustained for 15 to 250 more years depending on the area. Texas and New Mexico are facing the greatest risk of depleting their share of the Ogallala.

The depletion of the Ogallala Aquifer presents problems not only for humans but for the biodiversity in the plains region. Ogallala is also at risk of contamination due to expand in agriculture industry in the western states, and increasing amount of nutrient-rich water running off into the aquifer. There is also a threat of oil pollution from the major pipelines such as TransCanada’s Keystone XL. Any leaks or spills out of this pipeline would be disastrous to the agricultural industry in water supply in the western states.

Farmers, scientists and residents of the area are starting to see the need for a change. The Ogallala Aquifer initiative of 2011 is designed to reduce water depletion rates, keep the water quality high and bring forth more conservation and alternative methods of irrigation. For this to be accomplished different practices are being implemented. Irrigated lands are being converted to dry land. Permanent vegetation that does not require irrigation is being planted. Flood irrigation systems that are less efficient are being replaced by center pivot and subsurface drip irrigation in order to use less water. There is still hope to save this precious resource but the forces must be joined in order to conserve Ogallala’s water.