The U.S. Army Corps of Engineers said current flood flows on the Boise River will continue well into May and are probably enough to prevent a more serious flood later.
But there is a 1 in 10 chance that federal river managers will have to increase flows to 10,000 cfs, Brandon Hobbs, Army Corps Idaho outreach coordinator, said at Thursday’s Idaho Water Supply meeting.
Flows of 10,000 cfs “would result in significant flooding of Eagle Island and other locations,” said Idaho Department of Water Resources Director Gary Spackman. Projections show that the river would start to cover Eagle Road and many of the streets in the subdivisions on and around Eagle Island. Overflowing waters also could cover ParkCenter Boulevard in Southeast Boise. Flows this week are about 8,600 cfs as measured at the Glenwood Street bridge in Boise.
Spackman read a statement, which had been vetted by state and federal officials, that echoed Hobbs’ comments and committed both state and federal officials to work together to coordinate public outreach well in advance of potential threats. He read a separate statement that he said came from Idaho Gov. Butch Otter, insisting that close collaboration, effective communication and timely deployment of resources were critical to minimizing property damage and risk to people.
“We take this responsibility very seriously,” Otter’s statement said. “City, county, state and federal disaster response personnel are working together to reduce the threat while keeping the public informed and prepared for the potential of more serious flooding.”
The Corps and the Bureau of Reclamation together manage the Boise River’s three-reservoir system. The two agencies estimate that there is still 2 million acre-feet of water in the form of snow in the Boise River watershed, said Brian Sauer, a hydraulic engineer with the Bureau.
Patrick Kormos, a research hydrologist with the U.S. Agricultural Research Service, said its models showed 2.7 million acre-feet of water stored as snow in the watershed. He said his was not an estimate of what would come into the reservoirs as runoff.
Even at the highest elevations, he said, the snow is “ready to melt.” Officials are cautiously optimistic, however, that the cooler weather persisting in high elevations will help with a slow snowmelt. Forecasts call for moderate temperatures the next two weeks.
About 8,100 cfs of water was flowing into Boise’s reservoir system Thursday, with about 298,000 acre-feet of storage space remaining.
Spackman said federal river managers are “doing the best they can.” But he warned downstream residents that, inevitably, one of these years the most careful management won’t be able to hold the water back.
“There will be a year when we see that 16,600 cfs in the Boise River,” Spackman said.