From The Pueblo Chieftain (Chris Woodka):
Understanding irrigation in the Lower Arkansas Valley
Consumptive use refers to the amount of water a crop uses to grow, either through uptake into the plant and transpiration, or through evaporation. Usually it is measured in inches, but presumptive factors have been incorporated into the hydrologic-institutional model under the U.S. Supreme Court Kansas v. Colorado case.
Return flow is excess water applied to fields that runs off as tailwater or infiltrates soil. Water also can seep out of earthen ditches as it makes its way to the fields.
Water-short ditches, such as the Fort Lyon Canal or Holbrook Ditch, typically have more ground available to irrigate than water supplies will cover. Other ditches, such as the Catlin or High Line canals, have plentiful water except in very dry years.
Sprinklers, drip irrigation and ditch lining allow water to be applied more efficiently to fields. In the process, more water could be consumed as more acreage is planted on water-short ditches or used more often on ditches with adequate water. Return flows could be reduced as a result.
State engineer rules were adopted in Division 2 water court in 2009 to prevent shortages of return flows on the Arkansas River, to downstream users in both Colorado and Kansas…
This year, the Lower Arkansas Valley Water Conservancy District established a group plan for farmers who use ponds to feed sprinklers to comply using formulas under Rule 10 of the surface irrigation rules. The plan also covers other types of improvements such as ditch lining and drip irrigation, but sprinklers account for nearly all of the impact so far. The Lower Ark district will use water from other sources, such as a five-year lease agreement with the Pueblo Board of Water Works, to provide augmentation water to make up depletions from increased consumptive use.
While the group plan requires a retainer fee and payment for augmentation water if the formula shows depletion, the payment is far less than farmers otherwise would spend on engineering at each site to show losses. So far, 88 farms with 104 improvements covering 19,767 acres are enrolled in the Lower Ark’s Rule 10 plan, said Heath Kuntz, the district’s engineering consultant. “We’re anticipating a lot of growth over the next few years,” Jay Winner, general manager of the Lower Ark district, told the compact administration.
From the state’s point of view, the program has been the backbone for enforcing the new rules. About 75 farms were signed up at the beginning of the program in April, and the others have signed on at the end of the irrigation season as the state assessed impacts, said Bill Tyner, assistant engineer for Water Division 2. “The Rule 10 plan has turned out to be the most successful part of the rules,” Tyner said, thanking the Lower Ark district and the Colorado Water Conservation Board for the seed money which launched the group plan.