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Precipitation, Snowmelt Has River Operators Working To Control Water Flow Through Mainstem Dams
Posted on Friday, March 17, 2017 (PST)

The National Weather Service issued a river flood warning yesterday, March 16, saying the Columbia River could crest at 16.1 feet at Vancouver, Washington, one-tenth of a foot over flood stage of 16 feet, and that the river will fluctuate between 15.8 feet and 16.1 feet into the weekend.

 

That has river operators scrambling to control water flow through Columbia and Snake river basin dams.

 

All four lower Snake River dams are currently experiencing involuntary spill as are the lower Columbia River dams.

 

Flow through Bonneville Dam on March 11 was 307 kcfs with 79 kcfs of spill. On March 15 it was 370 kcfs March 15 with 221 kcfs of spill.

 

Flow at McNary Dam was 298 kcfs with about 84 kcfs spill on March 11. That dropped to 295 kcfs on March 15, but spill was higher at 92 kcfs.

 

Flow at Ice Harbor Dam, the lowest of four lower Snake River dams, was 166 kcfs, with 108 kcfs of spill March 11. That rose just slightly to 168 kcfs March 15, with 110 kcfs spill.

 

Flow at Lower Granite Dam, the upper of the lower Snake River dams, was 151 kcfs, with 75 kcfs of spill March 11. That rose to 163 kcfs March 15, with 75 kcfs spill.

 

Flow information at the dams is from the Fish Passage Center: http://www.fpc.org/river/flowspill/FlowSpill.asp

 

Of the dams on the lower Columbia River, the John Day Dam is the only one authorized for flood control management, according to Tom Conning, U.S. Army Corps of Engineers Portland District spokesperson. The others are run of river dams.

 

“Lake Umatilla (above John Day Dam) will be operating in a lower pool range beginning March 16, increasing through the weekend,” he said. “We are operating at a lower pool in accordance with flood control regulations for managing stages at Vancouver below flood levels.”

 

Conning said that Corps reservoir managers monitor reservoir levels, downstream flows, weather forecasts and snow melt predictions to make real-time decisions about how much water to release from each reservoir.

 

At Dworshak Dam, operators had intended to raise the outflow from the dam this week from 22,500 cubic feet per second to 25 kcfs in order to meet an April 15 flood control target in the reservoir. Instead the Corps announced at the March 15 interagency Technical Management Team meeting that it would keep outflow at the dam at the lower level as a way to help curtail flows through lower river dams and reduce the level of flooding in the lower Columbia River.

 

Dworshak operators opted to hold flows even though NOAA’s River Forecast Center is predicting that inflows to the reservoir in the next few days will rise to about 55 kcfs. Inflows were just 12 kcfs earlier this week. That, according to Steve Hall, Water Program Manager for the Corps’ Walla Walla District, will cause a rise of up to 10 feet in the Dworshak Reservoir.

 

See Dworshak inflow predictions at https://www.nwrfc.noaa.gov/river/station/flowplot/flowplot.cgi?lid=DWRI1.

 

Julie Ammon of the Corps said the District has called on all dams to help manage upper basin reservoirs and flows downstream, even if that puts on hold meeting flood control targets.

 

“The flood control target doesn’t change,” she said. “But we’re still not planning (an outflow) higher than 25 kcfs. If we can’t get to flood control, it will be where it is.”

 

Hall said the capacity for passing water at the dam is 5 kcfs through turbines and 40 kcfs through spill, but Ammon said they would never want to “overtop” the dam and that flows at that highest level would damage hatcheries and property downstream.

 

The cause of the higher flows has been the much higher than normal rainfall throughout the Columbia River basin, especially in the Snake River basin, as well as larger snowpacks and some melting of lower elevation snow.

 

For information on precipitation and snowpack in the Columbia basin, see CBB, March 10, 2017, “Dworshak Reservoir Emptied To Prepared For Snow Melt; Snowpack Above Average Throughout Basin,” http://www.cbbulletin.com/438450.aspx

 

“February precipitation in the North Fork Clearwater River basin was 214 percent of normal,” Hall said of the Dworshak situation in a March 9 news release. “We’re anticipating more water inflow at Dworshak in the next 10 days. That’s what is now driving our flood-risk reduction and public safety decisions.”

 

Also in Idaho, the Bureau of Reclamation and the Corps last week continued to increase flows from Lucky Peak Dam because of a combination of lower elevation precipitation and above-normal winter precipitation in the Boise River drainage. Flows at Boise, Idaho reached flood stage of 7.5 kcfs.

 

See CBB, March 10, 2017, “With Lucky Peak Releases, Boise River Expected To Be Above Flood Stage By Weekend,” http://www.cbbulletin.com/438449.aspx

 

Idaho Power said last week that record or near-record snowpack in Snake River drainages above Brownlee Reservoir is prompting the utility to increase flood-control operations at the dam by lowering the reservoir to accommodate higher-than-normal inflows and to make room for the anticipated large runoff over the coming weeks.

 

There is expected flooding throughout the basin. The Corps’ Seattle District said in a news release that it put its Emergency Operations Center into operation March 13, sending teams to the St. Joe and Coeur d’Alene river basins as those rivers continue to rise.

 

“The Corps has sent out teams of emergency responders who are familiar with the local conditions and the specific threats in the area,” said Doug Weber, Emergency Management Branch Chief at the Corps’ Seattle District.

 

The Corps has sent a team to provide technical assistance to the City of St. Maries at their request and has a team enroute to Coeur d’Alene to monitor levees there, the Seattle District said. It has also supplied a pump to Kootenai County and distributed 5,000 sandbags to the City of Ellensburg.

 

Conning said that the Corps’ Portland District is prepared to augment local and state government with flood fight efforts when local resources are exhausted during an emergency.

 

A National Weather Service hydrograph of the Columbia River at Vancouver is at http://water.weather.gov/ahps2/hydrograph.php?gage=vapw1&wfo=pqr.

Moderate flood stage at Vancouver is 20 feet and major flood stage is at 25 feet. The highest crest was June 13, 1948 when the river reached a level of 31 feet. It hit 27.2 feet February 9, 1996.

 

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