Snowpack ratchets up flood risk

SANDPOINT — Landowners around Lake Pend Oreille who experienced flooding in 2011 are probably in for similar headaches this year, according to the U.S. Army Corps of Engineers.

“We’re well above average precipitation this year,” said Logan Osgood-Zimmerman, an engineer at the corps’ Water Management Section in Seattle. “In Bonner County, it’s 110- to 150-percent of average.

“In particular, our big concern this year is the snowpack, which is primarily in the upper Pend Oreille River basin and that’s 130- to 300-percent of average.”

The snowpack in the basin Sunday was 157-percent of average. Snowpack in the basin on the same day in 2011 was 154-percent of average, according to the National Weather Service in Spokane.

The lake’s flood stage is 2,063.5 feet above sea level. The lake crested at 2,064.29 feet in 2011, making the eighth-highest historic crest.

When the lake reaches 2,064 feet, it has been known to cause minor flooding of driveways and lowlands in the Pack and Clark Fork river valleys. It also leaves most dock ramps around the lake underwater and floods part of the parking lot behind the Old Power House and the sidewalk behind the Edgewater Resort in Sandpoint. That level can also cause minor flooding at the Trestle Creek recreation area and parts of Scenic Bay at Bayview.

Flooding of lakeside homes and docks can be expected if the lake reaches 2,065.5 feet, according to the weather service.

The average spring inflow to the lake between April and July is 12 million acre feet.

“This year, we’re expecting between 16-19 million acre feet, so that’s 4-7 million acre feet more than we would normally see,” said Scott Lawrence, a spokesman for the corps’ Seattle District.

The corps manages the top 11 feet of the lake, which provides approximately 1 million acre feet of storage.

“We have a 60-percent chance of exceeding flood stage on the lake and we have a 25-percent chance of exceeding what happened in 2011,” Lawrence said. “If you had problems in 2011, there’s a pretty good chance you’re going to have problems this year.”

Inflows into the lake usually peak in May. But due to colder temperatures this spring, peak inflows may not be reached until early June, said Osgood-Zimmerman.

The timing could prove important because landowners considering obtaining flood insurance through FEMA have to do so at least 30 days prior to a flood event.

“It’s a little early to tell how it’s going to come off,” Osgood-Zimmerman said of the snowpack.

The ideal scenario is a longer warm-up with no precipitation, which would allow for higher flows over a longer period of time, said Kevin Shaffer, chief of the corps’ water management section.

Given the prodigious amount of snowpack in the basin, the corps is doing its best to make room.

“What we can do is make as much space as possible before we reach those high-flow conditions. That will provide as big a buffer on that inflow as we possibly can,” Shaffer said.

Keith Kinnaird can be reached by email at kkinnaird@bonnercountydailybee.com and follow him on Twitter @KeithDailyBee.