From The Pueblo Chieftain (Chris Woodka):
More than 28,000 acres of Arkansas Valley farm ground — roughly a tenth of all irrigated land — is being covered by group plans that guard against increased consumptive use from surface irrigation improvements.
The state pushed consumptive use rules for irrigation through Division 2 Water Court in 2010. The rules are meant to protect Colorado in its 1949 Arkansas River Compact with Kansas.
Rule 10 allows groups to file plans in order to save on legal, engineering and administrative costs.
The Lower Arkansas Valley Water Conservancy District is administering two Rule 10 plans this year.
One covers farms on the Fort Lyon, which represents 18,000 acres. About 12,000 of those acres are under sprinklers, while the remainder are flood irrigated.
The second plan covers 10,000 acres not on the Fort Lyon Canal, with two-thirds of that under sprinklers and 105 acres using drip irrigation.
“About two-thirds of the farm are in the Fort Lyon plan. The goal is eventually to have them in their own group plan that would be self-sustaining,” said the district’s engineer Jack Goble during a presentation at Wednesday’s board meeting.
This year’s Lower Ark plans cover 235 improvements on 92 farms that should require almost 1,900 acre-feet of replacement water. The amount owed is determined by a mathematical model devised by the Colorado Division of Water Resources that determines how much water would have been used before and after improvements.
“It’s a guess of what we’ll owe,” Goble said. “The model is almost like a parallel universe.”
The more water used in irrigation increases the amount owed to replace depletions in the river.
“The more water that comes through the ditch, the more is owed,” Goble said.
Goble walked the board through the complicated model, which takes irrigation flows, precipitation, seepage and runoff into account.
The Lower Ark district is in the second year of a study on pond leakage, which so far is showing that more water is escaping than accounted for in the state’s model. Data from the study in some cases has been applied to specific ponds.
More Ark Valley Consumptive Use Rules coverage here and here.