CWCB: Study for the Lower Ark shows that the average unlined farm pond leaks as much as 20%

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From The Pueblo Chieftain (Chris Woodka):

Most ponds used by farmers to feed sprinkler systems are losing more than 20 percent of the water stored in them because of leakage.

A preliminary written report was released this week detailing the findings of the study, being conducted by Agritech Consulting and Valley Ag Consulting for the Lower Arkansas Valley Water Conservancy District. The study is being conducted in hopes of altering a state formula that assumes only 3 percent loss. At a meeting earlier this month, the district reported that farmers in the study already are able to claim greater leakage, but officials held out little hope the assumptions of the state formula could be changed. The study found 13 of the 22 ponds in the study had leakage rates higher than 20 percent. Measurements were taken as water flowed into ponds and as it ran through sprinklers. Overall, seepage cost farmers 300 acre-feet of the 1,340 acre-feet that flowed into ponds. The state’s formula would have given them credit for just 40 acre-feet.

Gerald Knudsen of Agritech, who analyzed the results of the study, said drought may have been a factor in the data from the first year of the study. The study will continue next year that will help researchers evaluate the relationship between seepage and physical or environmental conditions. “This further review may be significant since the data collected to date represents drought conditions when there is a longer period of time between runs and more frequent use of the ponds may reduce the seepage rates,” the report stated.

The study is being funded by the Colorado Water Conservation Board.

The state uses pond leakage as one factor in its formula to evaluate consumptive use of surface irrigation improvements under 2010 rules designed to head off future disputes with Kansas. The Lower Ark district offers a group plan that helps farmers repay water the state says is owed to the river.

More coverage from Chris Woodka writing for The Pueblo Chieftain:

A study of leakage in ponds that feed field irrigation systems already is saving some farmers thousands of dollars in water cost.

But a state formula that assumes only 3 percent of the water leaks won’t be changed until the study results are final — and maybe not even then. The formula is used under Rule 10 of the state engineer’s 2010 consumptive use rules to prevent expansion of water rights under surface irrigation rules. The state pushed for the rules to avoid further challenges by Kansas of Arkansas River Compact violations.

Farmers have to pay for replacement water, so if they can show they are losing more than presumed, they spend less.

The Lower Arkansas Valley Water Conservancy District is funding the study by Gerry Knudsen of Agritech and Brian Lauritsen of Valley Ag Consulting to determine how much water leaks out of the ponds.

Seepage varies from 3-5 percent in some ponds to 44 percent at others, depending on how dry the ponds are when they first fill and the type of soil. A total of 26 ponds are in the study, located mostly on the Fort Lyon Canal, where most of the sprinklers are.

The ponds had 1,340 acre-feet of inflow, and lost 300 acre-feet, or 22 percent.

The results from individual ponds already are being used by the Colorado Division of Water Resources to calculate losses on specific farms, but have not altered the presumptive model.

The study, funded by a $60,000 grant from the Colorado Water Conservation Board that was obtained by the Lower Ark district, won’t be complete until 2014. Even then, it might not change the state’s outlook on pond leakage.

“My view is that the ponds will have to be measured forever,” said Jay Winner, manager of the Lower Ark district. “The ponds which have instrumentation will get the credit.”

Knudsen agreed, saying it’s similar to how GPS systems were incorporated into cultivation several years ago because the initial technology soon became essential rather than optional.

Lauritsen added that better meters are needed and must be properly calibrated to get the best results.

More Arkansas Valley consumptive use rules coverage here and here.

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