Seepage issue causes work delay at Soo Locks area crib dam project

Published May 20, 2011
The U.S. Army Corps of Engineers, Detroit District announces an interruption of work and the possibility of modifying the repairs for the Soo Locks Crib Dam project.

Ryba Marine, from Cheboygan, Mich., was recently awarded a more than $4 million contract to complete a project that will rehabilitate the 60-year old timber crib dam structure adjacent to one of the hydroelectric power generation plants located on Corps property at Sault Ste. Marie, Mich.

The contractor was scheduled to remove the upper 12 feet of the existing crib dam structure due to deteriorated timber and replace it with reinforced concrete, stone fill and a steel sheet pile face to provide a more durable and water tight structure.

While the contractor was working in the area, Corps of Engineers staff noticed an increased rate of seepage through the structure above what was observed prior to construction. Because of this increased seepage the Corps has stopped all work on the project to evaluate erosion rates, find possible sources of the seepage, and develop solutions for controlling or eliminating the increased seepage. Although there are important engineering and construction concerns to be evaluated
and modified as appropriate by dam safety and engineering experts, there is no imminent threat of dam failure, impact to the general public, or change in lock operations. The Corps of Engineers is working to resolve these issues and is monitoring the condition of the dam 24 hours a day.

Throughout the construction project there were anticipated hydroelectric power plant shutdowns scheduled during off-peak hours. While seeking the cause of the increased seepage and developing solutions, the Corps may have to shut down the power plant intermittently during unscheduled times. The Corps will minimize those times whenever possible.

The Corps will continue to monitor conditions and report any changes to the condition of the dam structure repair project. A timber crib dam is composed of interlocking wood planks creating rectangular compartments that are filled with dense material, such as stone, forming an embankment of compacted free-draining material with an impervious zone. The impervious zone is usually found on the upstream face of the dam and can be made of masonry, concrete, plastic membrane, steel sheet piles, timber or other material. The impervious zone of the crib dam under repair consists of
interlocking wood sheets located on the face of the dam which were also coated with a tar based elastic cement material.

Once additional details are available or changes in conditions occur information will be distributed on our website at and by Lynn Duerod, public affairs officer, at 313-226-4680.

Photos of the crib dam at the Soo Locks are available on our Flickr site at Media wishing high-resolution photos should contact the Public Affairs Officer.
Lynn Duerod

Release no. 052011-01