Boise flood forecast 4/19/2017
U.S. Army Corps of Engineers Lt. Col. Damon A. Delarosa acknowledged Wednesday that federal dam managers were taking a chance by not raising flows on the Boise River above where they are now.
“We have made a very calculated decision to this point,” Delarosa said. “We absolutely could have released enough water to match up with the record runoffs, but the result would have been absolutely flooding Boise.”
Delarosa is commander of the Corps’ Walla Walla District, which has responsibility for Idaho. He joined Gov. Butch Otter at a briefing with federal, state and local officials on the state of flooding statewide and especially the Boise River. Otter said local officials and the Corps, which has the final authority, are on “the same page.”
“We’re all working on this together,” he said.
The facts remain stark. At least 2 million acre-feet of water remains in the Boise River watershed in the form of snow, and that’s expected to melt and flow into the three Boise River reservoirs by July 1.
The reservoirs today have just 300,000 acre-feet of storage space left. The river is flowing at 8,500 cubic feet per second as measured at Glenwood Bridge, causing minor flooding of the Boise Greenbelt, parks and farm fields downstream.
Delarosa repeated the Corps’ plan to keep flows below 10,000 cfs at Glenwood for another month — and possibly beyond. Cool conditions are expected to continue for the next two weeks, said Jay Breidenbach, National Weather Service warning coordination meteorologist in Boise, which is keeping the rate of mountain snowmelt low.
But all it would take is for temperatures to rise into the 90s for several days, or for heavy rains to reach into higher elevations, to melt the snowpack and quickly fill the three reservoirs.
Regular rain has kept farmers out of their fields and limited most demand for irrigation water, which would have taken up to another 1,500 cfs of flows out of the river.
The reservoirs received record inflows during February and March. That’s put federal water officials 640,000 cubic feet behind where they should be in terms of space in the reservoirs, said Idaho Department of Water Resources Director Gary Spackman.
Otter said he’s concerned that some in the public are complacent about the dangers posed by high waters.
“There are areas not taking this potential disaster serious,” Otter said.
But Otter; Delarosa; the mayors of Boise, Eagle and Garden City; and Ada and Canyon commissioners stood before cameras to urge people to be prepared, exercise caution and buy flood insurance.
That would raise the river above many bridges, including Eagle Road and U.S. 95 in Canyon County. It also could place some subdivisions on Eagle Island and downstream underwater, though houses are likely to mostly be above the water line.
“I think we need to deal with it day to day,” Otter said. “I think we’re making the right guesses.”