Warm temperatures have triggered spring
flooding in parts of the Columbia Basin, particularly in watersheds below
mountains with heavy snowpack.
The U.S. Army Corps of Engineers issued press
releases this week related to flooding hot spots including Montana’s Clark Fork
River Basin, Idaho’s Pend Oreille River below Albeni Falls Dam, and on the
Okanogan River in Washington.
The Northwest River Forecast Center in
Portland reports that 22 rivers are reaching their banks, 15 are at flood
stage, and four are at major flood stage. Those include the Clark Fork River
above Missoula and at St. Regis, Mont.; the Okanogan River near Tonasket,
Wash., the Chehalis River in Washington; and the Pend Oreille River exceeding
flood stage below Albeni Falls in coming days.
Warm temperatures combined with above-average
snowpack have created a situation where Pend Oreille River flows downstream of
Albeni Falls Dam are likely to exceed flood stage this week.
The U.S. Army Corps of Engineers is releasing
the full capacity of Albeni Falls Dam between now and when Lake Pend Oreille
reaches the peak elevation for the year.
The normal maximum elevation for Lake Pend Oreille during the summer is
between 2,062 and 2,062.5 feet above sea level. The lake could rise higher than
normal summer elevation.
“Corps modeling using National Weather Service
River Forecast Center hydrologic forecasts suggest we could see peak Lake Pend
Oreille elevations ranging between 2,062.5 and 2,066 feet sometime between May
19-29, and outflows exceeding 100,000 cubic feet per second by May 11,” said
Logan Osgood-Zimmerman, Upper Columbia Senior Water Manager for the Army Corps
Lake Pend Oreille was lowered to the bottom of
the one foot band at 2,051 feet above sea level before spring inflows began to
rise. Albeni Falls Dam transitioned to free-flow April 29 and will remain on
free-flow until further notice.
Albeni Falls Dam outflows are now completely
controlled by the natural constriction between Lake Pend Oreille and the dam;
outflows will vary gradually as the lake level varies. This free flow operation
will allow Albeni Falls Dam to release the maximum flow possible, based on the
natural constriction. The operation will reduce the eventual peak lake level,
to the extent possible. It will also conserve space in Lake Pend Oreille,
reducing the likelihood of releasing even higher flows downstream during the
peak of the snowmelt event. Inflow to Lake Pend Oreille has been on a continued
upward trend, as the warming spring weather increases snowmelt.
Meanwhile, flooding is well underway on the
Clark Fork River, and some of its major tributaries, including the Blackfoot
A Corps of Engineers team is assisting the
City of Plains and Sanders County, Montana, with implementing emergency
protective measures to reduce the risk of scour on the 1948 levee at Plains.
Work is estimated to conclude May 14. The team is providing technical
assistance in Missoula at the request of Missoula County, Montana, with some of
those efforts directed at the upper Blackfoot Basin near Lincoln, Mont.
The Corps’ Seattle District initially provided
25,000 sandbags to Missoula, with an additional 75,000 sandbags delivered later
About 20,000 sandbags were sent to Okanogan
County, 5,000 to Tonasket, Wash., and about 15,000 sent to the Colville
Flood fight teams are coordinating with the
States of Washington, Idaho and Montana. Agency representatives will continue
to coordinate with the counties and cities along the rivers, and the Colville
The Northwest River Forecast Center shows
rivers currently at or exceeding flood stage within the next few days to
The Bitterroot River near Darby, Victor and
Missoula, Mont.; the Blackfoot River near Bonner; the Chehalis River near Grand
Mound, Wash.; the Clark Fork River above Missoula and downriver at St. Regis, Drummond
and Plains; the Flathead River at Columbia Falls; the Methow River and the
Similkameen River near Nighthawk in Okanogan County, Wash.; the Stehekin River
in Chelan County, Wash.; the Moyie River in Idaho; the Okanogan near Tonasket;
the Pend Oreille River below Albeni Falls Dam and on Lake Pend Oreille near
Hope, Idaho; the St. Joe River at St. Maries, Idaho; the Swan River near
Bigfork, Mont.; and the Yaak River near Troy, Mont.
Private citizens seeking sandbags should
contact their local government offices. The National Weather Service issues
flood watches and warnings and should be consulted for that information.