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Wet, Warm Weather Forces Northwest Dam Operators To Flush Water Downriver
Posted on Friday, January 21, 2011 (PST)

Water discharge from Dworshak Dam near Orofino, Idaho, has been temporarily increased to make room in the reservoir for flood risk management purposes, US. Army Corps of Engineers operations officials announced.

 

Discharge flow was increased Thursday from approximately 10,500, which is powerhouse capacity, to 14,000 cubic feet per second by sending more than 3 cfs through the spillway and will be maintained until further notice.

 

“The rainfall and associated runoff over the past week or so brought the reservoir water level up to 1,536 feet in elevation,” said Stephen Hall, Walla Walla District senior water manager. “We have to maintain space in the reservoir to manage flood risk through the spring season – that means we need to get the water elevation back down to 1,526 feet to keep on track for having room for the seasonal snowmelt inflows a couple of months from now.”

 

Hall said it would likely take a couple of weeks of increased flows to reach that target elevation.

 

Corps officials advise boaters and other persons using waterways both in Dworshak Reservoir and below the dam on the Clearwater River to be alert to changes in water elevation and volume of flow during this time period.

 

The wet, warm weather has also forced Avista Utilities to adjust its hydro operations for the Spokane River Hydroelectric Project in response to rising Coeur d’Alene and St. Joe River flows and Coeur d’Alene Lake levels. More specifically, the planned drawdown at Lake Spokane, the reservoir created by Long Lake Dam, has been cancelled.

 

Avista’s Spokane River Project includes Post Falls Dam, which affects the level of Lake Coeur d’Alene, as well the Spokane River and the downstream Upper Falls, Monroe Street, Nine Mile and Long Lake dams. Coeur d’Alene Lake was roughly two feet above its summer full-pool elevation of 2,128’ on Wednesday and river flows in downtown Spokane reached 21,000 cfs.

 

In an effort to maintain the level of Coeur d’Alene Lake and to prevent flooding, Avista has opened all spill gates at Post Falls Dam. At the same time operators are working to keep Lake Spokane slightly below full pool to help prevent flood conditions near the confluence of Little Spokane River and Lake Spokane. As flows decrease Avista will probably bring the Lake Spokane elevations up near summer full-pool levels.

 

Depending on weather conditions and subsequent levels along the river and in Lake Coeur d’Alene, Avista will reassess whether to draw down Lake Spokane as previously planned.

Property owners and lake-users are reminded to make necessary preparations, including removing boats from the water, and removing or securing docks and boathouses to accommodate changing water conditions.

 

Water levels are subject to change quickly due to a variety of factors, including weather. Lake and river users should always be alert to signs of such changes and exercise the highest level of personal caution and safety when using the waterway.

 

Updated reservoir level information is available by calling Avista's recorded Lake Information Line at (509) 495-8043. Current lake and river levels can be seen online at http://www.avistautilities.com/inside/resources/Pages/waterflow.aspx.

 

The Corps' Seattle District has wrapped up flood fight operations in the Yakima, Snohomish, Skagit and Chehalis river basins in Washington and at Libby Dam in northwest Montana, but levee patrollers remain on duty in areas of concern.

 

A Yakima River basin flood team completed work in support of Yakima County to shore up an area of erosion on the Rock Creek Levee on the Naches River, and a team in Ellensburg raised a portion of Riverbottom Road along the Yakima River at the Jensen Levee at the request of Kittitas County. The Corps also provided technical support for work on a levee in Mount Vernon on the Skagit River downstream of Interstate 5 in support of Diking District 17.

 

In reservoir operations, the Corps has held Howard Hanson Dam outflows around 7,000 cfs, while inflows peaked above 20,000 cfs. The Corps is operating the dam to keep flows at Auburn about 10,500 cfs, below the 12,000 cfs level of concern for levees from Auburn downstream. The Corps held water behind the dam that pushed the reservoir level to a peak of 1,155 feet above sea level, above an elevation (1,147 feet) that triggers increased on-site monitoring to ensure dam safety, and the dam performed well, according to engineers.

 

Teams are out in the White and Green river basins monitoring conditions in the basin and communicating what they see back to the Seattle District's reservoir control center and emergency operations center. Flows are above or near levels--6,000 cubic feet per second along the White River and 9,000 cfs along the Green River -- that trigger the Corps to monitor levees 24 hours a day.

 

There is a risk of flooding for property owners along the non-leveed middle Green basin, the rural portion of the river upstream from Auburn to Howard Hanson Dam. Flows above 9,000 cubic feet per second as measured at the Auburn gage triggered a flood warning from the National Weather Service due to flooding concerns in the Middle Green River. These flows do not present flooding concerns for the more highly populated areas downstream, including Auburn, Kent, Tukwila or Renton.

 

The Corps keeps the reservoirs empty at Mud Mountain Dam along the White River and Howard Hanson Dam along the Green River until storage is required for flood risk management, and both had empty reservoirs on Jan. 14. Mud Mountain Dam water storage reduced peak inflows of 25,000 cfs to outflows of 6,300 cfs.

 

Current flow information for any of the river basins in western Washington may be found here: http://www.nwd-wc.usace.army.mil/nws/hh/index-j.html

 

The Seattle Seattle District has seen high inflows to Lake Pend Oreille in north Idaho that are now causing operators of Albeni Falls Dam to spill water in an effort to maintain a steady lake elevation.

 

On Tuesday average releases from Albeni Falls Dam increased to 29,000 cfs, up from 21,000 cfs. Current releases are 41,000 cfs. Releases could continue to increase this week in an effort to keep the lake elevation as close to 2,056 feet above sea level as possible.

 

Inflows to Lake Pend Oreille have gone above 41,000 cfs, up from 17,000 the previous week. Water managers will continue to monitor the inflows and make adjustments as necessary, but higher outflows (above 30,000 cfs) are expected to be necessary through the weekend.

 

For real time flow information, visit ://www.nwd-wc.usace.army.mil/nws/hh/basins/

 

The Corps operates Albeni Falls Dam as a multiple-purpose project, providing flood risk management, power generation, navigation and recreation.

 

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The Columbia Basin Bulletin, Bend, Oregon. For information or comments call 541-312-8860.
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