Timely Topic: Central canals are recharging the High Plains Aquifer
by Betty Sayers
We occasionally hear about people who change the course of history. We call them change makers, leaders, visionaries. By thinking large and pushing the frontier of science and technology, a group of business leaders and farmers in central Nebraska changed a semi-arid region into a lush garden growing food for America, food for export to world markets, and generating 239 million kilowatt-hours of electricity per year from hydro-power.
Instead of being overcome by years of a national drought and depression, they designed and built a system that regulates the flow of a great river.The North Platte River water flows into Lake McConaughy and directly or indirectly irrigates more than 530,000 acres in Nebraska and produces power.
A commodity is thought to be sustainable when its use can be maintained over time. An aquifer that increases or maintains equilibrium is said to be sustainable. Mike Drain, hydrologist with Central defines sustainable irrigation as “forever continuing with irrigation without exhausting the water supply upon which it is dependent.”
“The tremendous pressure for water use impacts stream flow, lakes, river, and wetlands in rural Nebraska, and we make sure our operations are moving toward sustainability,” adds Steinke, engineer with Central . “We don’t want to be found wishing we had done something different 25 years ago.”
Science of Recharge
Recharge is water that soaks through the soil and replenishes the aquifer, and it may include extra water brought to an area that drains back into the aquifer, or, as in the Central project, supplements the ground water by collecting like a mound on top of the aquifer.
The Central project started in 1935 although irrigation deliveries did not begin in earnest until 1942. Changes in science and technology are constantly progressing, and over the 79 years of progress, Central engineers noted the impact of surface water irrigation on ground water levels. Water stored in the aquifer increased under acres irrigated by the Central project.
“References of increases in the mound of water forming above the High Plains aquifer were noted,” Drain said, “But in the late ‘30s and early ‘40s, basic knowledge of impact of ground water levels wasn’t well known nor appreciated, and the technology wasn’t available to measure the increases in underground water levels. By the 1980s, we acquired the technology to measure incidental groundwater storage, and we knew the mound was growing.”
Data from EA Engineering, Science and Technology, Inc. study released in January 2014 show that the water table beneath Central’s service area has risen since pre-development by 10 feet to more than 50 feet. Similar data from counties just outside Central’s service area show just the opposite — declines in the ground water table of five to more than 30 feet in the last 50 years. Central’s system of canals and diversions significantly increased the mound.
The mound is sensitive to rainfall and ground water pumping. Scientists determined that the growth of the mound has slowed or halted and, in places, is declining as groundwater use increases and diversions of water into the area have diminished.
Central’s role in the management of surface water is significant. “Recharge is a long-term positive story and is the root of sustainable irrigation,” Drain says. “The canals were designed and constructed to transport water to fields, and today we know that recharge, an incidental outcome of the system, may be its biggest benefit.”
Farmers irrigating with ground water primarily drawn from the mound with little or no use of surface water reduce the water stored in the mound, and during drought years, the water in the mound may drop by 5 to 20 feet.
The incidental surface water diversions are a factor in recharging the mound, and thereby, the aquifer. What is often referred to as “losses” from the surface water system are, in fact, recharge to the groundwater supplies in and adjacent to the canal system.
Central’s project is not just an irrigation system. It is a multi-purpose, multi-benefit system that provides irrigation, hydroelectric generation, recreational opportunities, groundwater recharge, fish and wildlife habitat, and cooling water for coal- and gas-fired power plants.
The following are questions for Nebraskans to consider in the management of water in and above the High Plains Aquifer:
How can we sustain our current level of water for future generations?
What amount of change can occur in a system before sustainability of the system is no longer guaranteed?
Should recharge move from being an incidental benefit to one that is actively managed and compensated?
More on this timely topic at www.Nebraskaruralliving.com