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Tailwater return systems are gaining in popularity on farms

This article appeared in Ag Alert on February 25, 2004

By Eric McMullin, Special to Ag Alert

Tailwater return systems are making a comeback

It's long been known that the systems can improve irrigation efficiency, conserve water and lead to a better growing environment for crops. But with new water regulations coming, it's an often-overlooked benefit-water quality-that has caught people's interest.

"A tailwater return system can keep contaminants from going downstream," explains Larry Schwankl, statewide irrigation specialist at Land, Air, and Water Resources at the University of California, Davis.

Those contaminants can be synthetic-fertilizers and pesticides-or they can be natural-salts and sediment. Either way, it's expected that the new regulations are going to be much more strict about the quality of the water leaving California farms.

"I don't think the new regulations will require a tailwater return system," says Schwankl. "I think they will talk more about specific water quality standards, then let the growers decide how to meet those standards. But to meet those standards, a tailwater return system is an obvious option."

The systems cost anywhere from $3,000 to $15,000 and are little more than a pit to catch runoff water, a pump to return that water to the head of the field, and the PVC pipes required to get it there.

There are several hundred such systems around the state, built largely in the 1970s and 1980s with federal grant money. That number is expected to at least double in the next 10 years, and again federal grant money is available.

"We have cost-sharing money available under EQIP, the Environmental Quality Incentive Program," reports Dan Johnson, state water management engineer with the U.S. Department of Agriculture's Natural Resources Conservation Service.

Local boards determine the amount of money available and the type of projects covered, says Johnson, "but, generally, water management projects are approved across the board and usually at a 50/50 cost-share level."

Johnson agrees that tailwater return systems will be a popular option.

"It sure seems like it," he says. "We're preparing ourselves for that, getting our manuals up to date and getting ready to sit down with growers."

The latest NRCS manual was written in 1979. The latest UC guidelines came three years later and Schwankl is working to update those with Terry Prichard, UC irrigation specialist in San Joaquin County, and Mick Canevari, UC field crops farm advisor in San Joaquin County.

The three are surveying the state's growers as to the number of tailwater return systems currently in place and how they're used. That survey should be completed this spring.

The trio also is writing new guidelines to assist growers in planning and building their tailwater return systems. Those guidelines should be completed in six to eight months.

Canevari's involvement illustrates the win-win situation that tailwater return systems can be.

Alfalfa is a major crop in California, and four years ago the state Department of Pesticide Regulation detected small mounts of an alfalfa herbicide in two wells in the Tracy area.

"There was the potential for groundwater contamination, so we had to locate the source quickly," reports Canevari. "What we found was that the herbicide residues were not moving through the soil profile, but had run off of fields. That was a relief because it's much easier to capture runoff water than it is to prevent a chemical from moving through the soil.

"Our studies looked at tailwater return systems already being used," says Canevari. "I would expect most of the alfalfa growers in the area to consider this option if they don't already have one."

The systems aren't that difficult to install, says Keith Robertson, who farms 2,000 acres of walnuts, tomatoes, alfalfa, lima beans and cantaloupes outside of Tracy.

"We have close to two dozen of these. Either we put them in or they were on land we've bought or are leasing," says Robertson. "The biggest expense is the pump and piping."

The pumps are 10-15 horsepower, and the piping is eight to 12 inches in diameter. A float in the pit controls the pump.

Generally, the pits have a capacity of one-fourth to one-half the volume of a single irrigation. Water is not allowed to sit in the pits for long, so they don't need to be lined. Water is brought halfway up the field or to the head, or is pumped to a neighboring field.

Robertson says the systems have a life of "25 to 30 years, easy," and the only maintenance required is that the pits need to be dug out every two to four years to keep them from filling with silt.

The benefits of a tailwater return system are varied and widespread.

Irrigation efficiency is improved because flows can be increased with no concern of lost water. Water is conserved, both by catching it at the end and by reducing deep percolation. Drainage problems are reduced. There are cost savings due to better irrigation efficiency and no lost water, and more efficient use of fertilizer due to better irrigation uniformity and the return of dissolved fertilizers to fields. Better use of water leads to better weed control, better plant growth, and a more uniform germination. It also promotes lower energy use.

Still, the benefits would not justify the cost of putting in a tailwater return system, says Robertson.

"There's not enough there to pay back these systems on their own," he says. "But with cost-share money available and the new water regulations, there's more than enough to justify a tailwater return system.

"We must be responsible for drainage that returns to our rivers," declares Robertson, "but this also includes city storm and sewer drains, and industrial sites and roads."

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