BOISE—Irrigation shortages are expected throughout Southern and Central Idaho following a dry and warm April, according to a Natural Resources Conservation Service report published May 6.
NRCS water supply specialist Ron Abramovich said the Owyhee Basin in Western Idaho and low-elevation mountains in Eastern Idaho, including the Portneuf, Willow and Blackfoot basins, received about 90 percent of normal April precipitation. Precipitation ranged from 40 to 75 percent of normal for the month in the rest of the state, Abramovich said.
Abramovich said Idaho snowpack levels peaked on March 1, a month earlier than normal, and current snowpack levels are more appropriate for early June.
He said March and April temperatures were high enough to gradually melt much of the state’s mid-elevation snowpack and even some high-elevation snowpack, causing moisture to gradually seep into the ground rather than pouring into streams and filling reservoirs, as occurs when warm May weather “ripens” the snowpack.
Lyle Swank, watermaster for the Upper Snake reservoir system, which is at 83 percent of capacity, said many of his users have experienced record early season demand.
“Everything is early,” Swank said. “The ground dried out early. The farmers planted early in some cases. The runoff is early. Demand is early.”
Swank said many irrigation companies are still optimistic about making it through the full season, but the supply outlook has gotten much tighter than it was just a couple of months ago.
The report shows streams throughout Southern Idaho have already reached peak flows and dropped to summer base-flow levels. Drainages in the Wood and Lost basins are near record-low levels, ranging from 1 to 35 percent of normal streamflow forecasts for May through July. Streamflow forecasts for the three-month period range from 10 to 20 percent of average in the Owyhee, Salmon Falls, Bruneau and Oakley basins.
NRCS predicts agricultural shortages in the Big Wood, Little Wood, Big Lost, Little Lost, Oakley, Salmon Falls and Owyhee basins, as well as the Upper Snake River.
The Payette reservoir system is 90 percent full and the Boise reservoir system is 88 percent full. Abramovich said Boise River irrigators are operating in “conservation” mode, having reduced deliveries from the usual 4 acre-feet to 1.6 acre-feet. He said irrigators who draw from Magic Reservoir near Shoshone ran out of water in July last year, and this season’s supply should be shorter. Irrigators who draw from Owyhee Reservoir, which has peaked at 21 percent full, should also run out of water earlier than last year, Abramovich said.
Salmon Falls Reservoir reached its peak storage on April 19 and is 18 percent full. Oakley Reservoir is 30 percent full.
Alan Hansten, manager of Northside Canal Co. in Jerome, said he’s already cut back his deliveries to 90 percent of normal.
“I think we’ll probably be able to make it into September,” Hansten said. “Beyond that is a crap shoot now.”
In Southeast Idaho, Aberdeen-Springfield Canal Co. General Manager Steve Howser is optimistic he’ll maintain deliveries for a full season, though his natural flows could run out as much as six weeks earlier than normal. Howser said early demand is up significantly.
On May 5, he diverted 30 percent more water than normal for the date to meet grower demands. Howser aims to reduce operational water spills by up to 40 percent to help stretch his supply.
Source: www.capitalpress.com