SEATTLE – The St. Maries, Idaho, levee system is bustling with activity recently as U.S. Army Corps of Engineers’ officials return to complete repairs along the St. Joe River’s left bank.
The $2.6 million federally-funded project was split into two phases, pre- and post-flood season, to address seepage and erosion damages from previous flood events. The first phase, completed in November 2012, included immediate repairs and risk reduction measures ahead of flood season.
Workers are now prepositioning equipment and materials with plans to initiate the second construction phase after Memorial Day weekend.
Phase two repairs focus on removing a levee segment near the 17th Street pump station, replacing two old wood stave drainage pipes and reconstructing the levee. One drainage pipe diverts a town creek underground and out to the St. Joe River, while a second is used to pump out excess water from an adjacent wetland.
Video inspections conducted during phase one confirmed the wood stave pipes were damaged, but blockages prevented a complete and thorough examination. While inspections were inconclusive because of blockages, replacing the pipes was always planned as part of the phase two work, according to Brian Nelson, the Corps’ project manager.
In addition, the Corps is constructing a 1,500 foot seepage berm to reinforce the levee’s backside. “The seepage berm is essentially rocky material emplaced to weigh down and apply pressure on the landward side of the levee,” Nelson said. “It ensures structural integrity is maintained while allowing some water, but not levee material, to seep through.”
In order to complete levee repairs and install the seepage berm, a stretch of road had to be removed and Corps planners worked with a local firm to design its replacement.
“We designed the seepage berm and levee repairs, but we worked closely with the City of St. Maries engineering firm, Welch Comer, to design a road which met our requirements and the city’s needs,” Nelson said. When reconstructed, a new asphalt road segment will be built on top of the seepage berm.
Expected to be complete by early September, the second construction phase will cost about $1.75 million of the $2.6 million in total project cost.
The Corps coordinated with a number of agencies during the planning, design and construction phases, including: The City of St. Maries; the Environmental Protection Agency; the Coeur d’Alene Tribe; U.S Fish and Wildlife Service; and Benewah County. Collaboration and contributions to the design were provided by the City of St. Maries design engineering firm, Welch Comer.
Once levee repairs are complete, flood protection which had been reduced to a 5-year level will be restored to a 100-year level, meaning a one-percent annual chance of exceedance.