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Corps to hold public meeting to gain input on Fort Peck Spillway test

Published April 2, 2012

Omaha, Neb. – The U.S. Army Corps of Engineers, Omaha District, will hold an informational meeting on April 16 at 1 p.m. to gain public and Tribal input on a proposed spillway test at Fort Peck Dam. The meeting will follow the Spring Public Meeting being held by the Water Management Division at the Fort Peck Interpretive Center.

The purpose of the test will help engineers to determine whether a subdrain system that relieves potential pressure beneath the spillway is functioning properly.

The test will consist of spillway releases of 3,000 cubic feet per second (cfs) up to 30,000 cfs at periodic intervals over a four-day timeframe. Hydraulic modeling shows the river stage rising directly downstream of the dam up to 4.7 feet with the highest test releases of 30,000 cfs. That rise in river stage would quickly dissipate the further downstream the water travels with the river gage near Wolf Point, Montana, at River Mile 1700.5 rising 1.7 feet. At River Mile 1619.7 near Culbertson, Montana, the stage would rise 1.1 feet.

At the 20,000 cfs, test release level those corresponding rises in river stages would be 3.1 feet directly downstream of the dam; 1.1 feet at Wolf Point and 0.8 feet at Culbertson.

During the test, releases from the Fort Peck Power Plants will be minimized to lessen the downstream impact.

The Corps anticipates that the flow test will be conducted between May and September 2012. The public and Tribes are invited to provide input on when the flow test should be performed in order to minimize negative impacts on agricultural production and other activities along the river.

The public and Tribes will be given specific notice that the test will commence a minimum of 30 days prior to the actual event.

During the original construction of the Fort Peck Spillway, waterstops were placed within the joints between the concrete slabs that line the spillway chute. These waterstops consist of metal strips that form an impermeable barrier to prevent infiltration of water and subsequent development of high uplift pressures during spillway operation. As a precautionary measure, the original construction also included an extensive subdrain system beneath the concrete slabs to relieve potential pressures that could develop due to the release of water through the spillway.

Engineers are in the process of performing assessments on the spillway features, which include detailed sampling and inspection programs. Instrumentation will be installed beneath the slabs to allow engineers to monitor pressure within various portions of the subdrain system as test releases are made through the spillway. It will be necessary to vary the magnitude of releases to assess the subdrain’s efficiency. That information will help determine whether corrective measures are needed to ensure adequate performance of the subdrain system during future spillway use.

In response to the flood of 2011, the District Engineer for the Omaha District identified a need for a special execution cell or team to engage in time-sensitive rehabilitation of flood controls structures - including dams and levees - in the Missouri River Basin. Drawing on funding provided by the Disaster Relief Appropriations Act signed Dec. 23, 2011, by President Barack Obama, the Omaha District Systems Restoration Team was established to focus the vast skills and abilities of the district to execute an estimated $280 million in repairs on 18 levee repair projects and $234 million on some 100 projects at the mainstem dams and related flood control structures along the Missouri River.

At Fort Peck, the estimated cost of projects is $41.7 million.

For regular updates on the repair efforts to flood control structures in the Missouri River Basin, visit the Omaha District’s Flood 2011 Repairs Systems Restoration Team web page.

Kevin Wingert

Release no. 20120402-001