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Tight pipes

03/04/2013 @ 11:32am

That drip, squirt, or stream of water coming off of gated pipe may not seem to be much of a loss at the time. But time certainly takes its toll. “While leaks are not losses from the field, they do reduce the amount of water delivered to the set being irrigated,” says Dean Yonts with the University of Nebraska. “And losses of water not being distributed across the field can be significant.”

How significant can these losses be? A study in Nebraska's Tri-Basin Natural Resource District in the early 1990s showed that water losses can exceed 50%. More realistic losses of 20% to 30% are common, however, Yonts says.

At that latter range, you are losing 5 to 6 gallons per minute per 30-foot length of irrigation pipe. That means a quarter-mile run of irrigation being fed by a 1,000-gallon-per-minute pump is actually only delivering 750 gallons per minute.

Leaky pipe also boosts labor cost

Eliminating leaks cuts labor costs “by having to have fewer sets per season,” Yonts says.

He roughly estimates the cost of eliminating leaks would be $1.03 per acre per year by replacing leaky gaskets and gates. This is based on the cost of replacing four gaskets (at $5 per gasket) and 69 gates (90¢ per gate) in 2,640 feet of pipe.

So, if you were to eliminate two irrigation sets at 12 hours per set with a 1,000-gallon-per-minute well that did five irrigations per year at $10 per acre-inch pumped, it would result in an added profit of about $32.10 per acre.

Fixing leaks may also improve water quality, Yonts says.

Severe leaks can add a constant supply of water to one area during irrigation. On silt-loam soils, 1 gallon per minute running down a row will advance only about 100 feet. If that loss were to occur uniformly along the pipeline, it would amount to about 3 acres along the pipe. If 250-gallon-per-minute leaks run for three days, 40 acre-inches per irrigation will be applied to about 3 acres of cropland.

Groundwater contamination

Previous research found this could move an estimated 5 pounds of nitrate with every inch of water that leaches below the root zone. “Continuous leaking has the potential to flush hundreds of pounds of nitrogen into the aquifer,” he says. “Aside from contamination of the aquifer, it would take excess nitrogen to offset the loss – or acceptance – of fewer bushels produced from those 3 acres.”

Eliminating leaks is not, unfortunately, a winter job. Certainly broken gates or gaskets that are cracked from age can be found prior to the irrigation season, Yonts says. And it always pays to inspect these components as you are taking pipe out to the field at the start of the season, he adds.

But don't assume that a preseason inspection will catch all problems, because most leaks go undetected until the pipe comes under pressure during the season. So Yonts recommends that you flag leaky gaskets or mark leaky gates during the season. 

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