Idaho is facing a possible flooding disaster from melting mountain snowpacks, Gov. C.L. “Butch” Otter said April 19, flanked by about a dozen federal, state and local officials to alert residents to the danger.
“There are areas that are not taking this potential disaster seriously,” the governor declared at the news conference in Boise.
Experts and elected leaders described the snowpacks of more than double the average in some areas.
Most of the concern is in highly populated southwest Idaho along the Boise River due to a giant snowpack and dwindling space in three reservoirs near the state’s capital city.
Two dams operated by the U.S. Bureau of Reclamation for irrigation and a third downstream called Lucky Peak Dam and operated by the U.S. Army Corps of Engineers for flood control have about 300,000 acre feet of space available. An acre foot is the amount of water it takes to cover an acre with a foot of water.
Officials said based on historic data and formulas intended to prevent flooding, the three-reservoir system should have 640,000 acre feet of space available.
Currently, there is about 1.85 million acre feet of water in the 2,680-square-mile watershed above the reservoirs — about six times more water than space to hold it.
Officials have been releasing large volumes of water from Lucky Peak, causing some minor flooding downstream, but the reservoirs over the past two weeks have lost space as more water has been entering. Officials say peak runoff won’t occur until May.
Lt. Col. Damon Delarosa of the Army Corps of Engineers said the plan is to continue to release large amounts of water from Lucky Peak over a longer duration into the summer to avoid more severe flooding. That means controlling river flows at Glenwood Bridge just downstream of Boise, likely into June.
“We have made a very calculated decision at this point,” DeLarosa said.
If the weather turns warm, he said, the Boise River flow could increase at the bridge. Chances of that happening are about 10 percent, experts say.
Additional areas of concern, officials said, include the Payette River in west-central Idaho, the Big Wood and Little Wood rivers in central Idaho, and the Upper Snake River and Bear River basins in eastern Idaho.
Jay Breidenbach of the National Weather Service said the forecast for the next week is for continued cool and mild weather.
Gary Spackman, director of the Idaho Department of Water Resources, said part of the problem is that low-lying agricultural areas are already soaked from an unusual amount of snow at lower elevations this winter, meaning farmers don’t need to run irrigation systems.
“We really don’t have a demand for water, and as a result a lot of it has to stay in the river,” Spackman said.
Officials warned residents to stay away from closed areas of the river. Tom Dale, a commissioner in rural Canyon County downstream, said a bull that got too close to the Boise River in his county was swept away.