By 8:45 p.m. Thursday, the flow of the Boise River was maintaining its abnormally high flow, hitting 8,470 cubic feet per second at the Glenwood Bridge.
Thursday afternoon, Ada County officials said in a media briefing that if the river would have stayed at the 8,100 cfs, problems would be limited to “nuisance flooding.”
The unpredictability of weather and flood flows means Ada County residents in low-lying areas along the Boise River should be prepared, officials said. By Thursday evening, the river proved to be more than just a nuisance.
“We don’t know exactly where the banks will overflow, so the message today is to be prepared,” Ada County Sheriff’s Capt. Dana Borquist said, recommending residents have a plan for how to handle it if access to their homes is compromised.
“If you’ve ever contemplated buying flood insurance, this is the year to do it,” county Emergency Management Director Doug Hardman said, adding that such insurance has a 30-day waiting period. He urged people to get resources and information from the county’s flooding website.
With driving rain and even a little snow hitting Boise Thursday morning, county officials gathered to discuss precautions and potential problems.
The primary area of concern right now is the Sunroc gravel pits near Eagle Island, where high flows are causing sinkholes, pooling water and bank erosion at the pits, Ada County Engineer Angie Gilman said. No flooding emergency currently exists, she says, but if the bank gives way, that would change.
“That would be more than nuisance flooding,” she said.
If that happens, she said, officials should be able to warn area residents between 12 and 24 hours before it happens. County, state and federal agencies are carefully monitoring the situation, she said.
In the meantime, curious residents are asked to stay out of the area near the gravel pits unless they live there.
Homes in the area are not currently considered at risk, Gilman said, “but it’s the river, and we don’t know what the river will do.”
River levels are expected to stay in the current range, which is manageable, for at least another six weeks, she said, but continued heavy rain or warm temperatures to increase snowmelt in mountain areas could change that.
Hardman echoed that theme, noting, “there’s probably no more difficult hazard that we know of than flooding, because there’s too many unknowns”
Residents concerned about flooding can pick up sandbags on the west side of the parking lot at Expo Idaho, Hardman said, describing sandbags as “marginally effective” if used correctly.
“We’ve got another two and a half months to get this water through the Valley,” he said.