High temperatures could melt snowpack, bring disaster
By DAVE WILKINS
The threat of significant flooding in the Pacific Northwest is on the rise.
Idaho Gov. Butch Otter on May 27 announced a statewide declaration of emergency due to flooding conditions and the potential for record runoff in many areas of the state.
Rivers were at or slightly above flood stage at several locations around the Northwest on May 27.
So far the damage has been minor, but officials with the Idaho Bureau of Homeland Security said they're concerned that things could get worse. The high river flows threaten to erode the soil around some levees and bridge abutments, they said.
Jefferson and Bingham counties were the only counties listed under the emergency declaration. State officials said other counties would be added if conditions warrant.
The Pacific Northwest has escaped severe flooding this spring, unlike the South and Midwest.
Whether the region can continue to avoid major flooding along the Columbia-Snake River and tributaries will depend largely on the weather over the next several weeks, officials said.
The best case scenario would be for continued cool temperatures with no rain, which would allow the mountain snowpack to melt off fairly slowly, said Art Hill, a civil engineer with the U.S. Bureau of Reclamation's Snake River Area Office in Burley, Idaho.
"The worst case scenario would be very, very hot temperatures and a lot of rain," Hill said.
Heavy snowpack and high runoff projections have put federal water managers at the bureau and U.S. Army Corps of Engineers in a bind this year.
They need to release enough water from reservoirs in the upper part of the system to make room for what could be near record inflows, without creating major flooding downstream.
The Northwest is expected to see the highest river flows in 14 years, according to water managers.
The Columbia River at Vancouver was right at flood stage at 16 feet on May 26, causing minor flooding to some beaches and low-lying campgrounds.
"The impacts are minor at this stage," said Scott Clemans, a spokesman for the U.S. Army Corps of Engineers district office in Portland.
The situation could change if the region experiences a sudden warming trend, he said.
The Columbia River was expected to move slightly above flood stage, which is 16.5 to 17 feet, by early June, according to the Northwest River Forecast Center.
Some flooding could occur to undiked pasture and farmland in low-lying areas if the Columbia gets above 18 feet at Vancouver, according to the center.
Farmers haven't been using as much irrigation water as they typically would this time of year because of the cool, wet weather.
Demand is just now starting to pick up, said Brian Olmstead, general manager for the Twin Falls Canal Co. in south central Idaho.
"It's picking up some. Quite a few people are watering hay and grain," Olmstead said May 25. "We're nowhere near full demand, but probably more than half now."
Tepid demand for irrigation water, coupled with high Snake River flows, have prompted water managers to release water from Milner Dam, the main diversion point for irrigation projects in south-central Idaho.
The releases have dramatically increased the flow at Shoshone Falls, creating a spectacle for tourists.
On May 25 the falls were flowing at a rate of 20,000 cubic feet per second. A flow of just 1 cfs would be enough to cover a football field 2 foot deep in 24 hours.
For more information about river flows across the Northwest visit www.nwrfc.noaa.gov .