Mining Water for Irrigation

The Ogallala Aquifer is one of the world’s most remarkable geological structures. It supplies irrigation water to large areas of the Great Plains, and the experience here can be an example of other groundwater irrigation areas.

The Ogallala is enormous with over three billion acre-feet of water below 174,000 square miles in eight states – Nebraska, Colorado, Kansas, Oklahoma, Texas, New Mexico, South Dakota and Wyoming. Three billion acre-feet equals around 977,553,000,000,000 gallons of water. That’s a huge amount of water trapped in saturated gravel beds that start 50 to 300 feet below the surface of the land and are 150 to 300 feet thick. The water in the Ogallala Aquifer actually travels slowly through the gravel layers, moving two to three feet a day, generally to the southeast until it runs into other bedrock layers.

In places, like the Sandhills of Nebraska, the Ogallala almost reaches the surface of the land, directly feeding the root systems of grasses in what are known as sub-irrigated meadows. Here the sand is porous and what little rain there is can move quickly into the aquifer. In other places, this natural “recharge” of the groundwater happens slowly, if at all.

So most of the water in the Ogallala is ancient, injected into the gravel layers by massive flows of water from Rocky Mountain glaciers up to 25,000 years ago. About 10,000 years ago the flows into the Ogallala stopped, possibly because the Pecos and Rio Grande River systems developed and carried off the glacial water. Geologists refer to the Ogallala’s water as “fossil water.”

At least since 1950, farmers and – to a much lesser extent – city dwellers on the Great Plains have been mining this fossil water, extracting it from the Earth in much the same way we mine minerals or gold. We have been drawing out much more water than can ever be replaced.

It’s estimated that since 1950, farmers have installed deep irrigation wells and pulled up one billion acre-feet of water from the Ogallala. Some of that is used by the plants, stored in their seeds and then hauled off when the farmer harvests the crop and ships it around the world. Some of that water is transpired by the plant, or evaporates off the land and winds up as rain thousands of miles away. Some may run off the land, even though it’s not supposed to. Some may percolate down through the soil and rock layers to reach the aquifer again.

But recharge rates in the Ogallala region are typically measured in inches a year, while the dropping water table surrounding an irrigation well is measured in feet.

In parts of Texas, the water table in the Ogallala has dropped more than 230 feet. Some farmers in Texas have had to let their expensive irrigation pumps sit idle for years at a time. In parts of Nebraska, Natural Resource Districts have begun requiring irrigators to put meters on their wells, and keep track of how much water they’re using. Some districts have come close to banning drilling of any new irrigation wells.

There are only a few regions of the Ogallala where water tables have risen. The largest rise was in Nebraska and totaled 84 feet.
In most places, the water table has dropped. On average, over the entire 111.6 million acre range of the aquifer, the drop has been 14 feet. That’s significant because, even though this is one of the most highly irrigated farming areas in the world, irrigated acres overlay only 14 percent of the area of the aquifer.

Mark Kaliff (left) is one of those farmers in central Nebraska who has begun metering his wells and monitoring how much water is actually in the soil before turning the irrigation on. The extended family farm operation he’s a part of has over 100 center pivot systems. “Irrigation in Nebraska is very important, very critical to this area,” Mark asserts. “We do need to monitor the amount that we use and try to use it most efficiently.”

Todd Sneller (right) says that farmers, at least in Nebraska, understand that they are mining a finite resource. “We, historically, have mined water,” Todd says. “Water truly is valuable… Water stewardship has been something that, in Nebraska, we’ve done a good job of in the past. There’s a requirement to do a good job now.”

Dave Vetter (left) put monitors on his irrigation wells in 1976, started testing soil a few years later and installed the newest evapotranspiration gauges recently. “We’ve been trying to find ways to conserve and reduce water consumption,” Dave says. “We’ve put 60 acres of subsurface drip [irrigation] in which reduces the water usage even more.”

There seems to be a general acknowledgment that farmers are mining the underground aquifers, and individual farmers are experimenting with innovative ways to manage their water use and still produce a profit.

Written by Bill Ganzel, the Ganzel Group. First published in 2009. A partial bibliography of sources is here.