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Shiawassee National Wildlife Refuge

Saginaw County, Michigan

Erosion Control

Technical Description:

• 15,740 sf ArmorFlex ® Class 50 Mats

The 9,870 acre Shiawassee National Wildlife Refuge in Saginaw County, Michigan is managed by the United States Fish and Wildlife Service (USFWS) and located in the central portion of the lower peninsula of Michigan. It was established in 1953 to provide habitat for migratory waterfowl. Known locally as the Shiawassee Flats, the refuge lies in the Saginaw Bay watershed, historically one of the largest and most productive wetland ecosystems in Michigan. 

Over 265 species of birds have been documented on the refuge, including raptors, shore and wading birds and more than 100 songbird species. Shiawassee Refuge is designated as a United States Important Bird Area (IBA) for its global significance to migratory waterfowl. It is also one of six focus areas designated by the Great Lakes/St. Lawrence Basin Joint Venture of the North American Waterfowl Management Plan. During peak populations in late October, up to 25,000 Canada geese and 40,000 ducks are present. A great diversity of other wildlife associated with freshwater marshes and floodplain forests are also found here.

A solution was needed to preserve the road in the area and provide overtopping protection for when the Shiawassee River breaches the roadway. USFWS turned to Contech Engineered Solutions for help. After researching options, it was decided that 15,740 sf of ArmorFlex® Class 50 Mats was the best solution to protect the roadway from being washed out. The flexible, interlocking matrix of cellular concrete blocks are often used for hard armor erosion control and provide ease-of-handling and rapid installation. 

In mid-May 2020, the following spring after the ArmorFlex mats were installed, Midland experienced a 500-year flood when two dams burst, draining a 2,000-acre lake in about an hour. More than 50,600 cubic feet of water was discharged every second from the Sanford and Wixom Lakes. Due to the nature of the floodplain system in which the game area lies, all of the water from Sandford and Wixom lakes flowed to the Shiawassee Flats and onto Saginaw Bay. As a result, the area experienced severe and prolonged flooding, along with some significant infrastructure damage. Overall, the ArmorFlex was a great solution for the site, and USFWS was pleased with the outcome.

"During the major dam failure flood event, the ArmorFlex extension performed exactly as I hoped it would," concluded David Peters with USFWS. "Without it, at least the southern most mats in the as-built spillway would have been fully undermined and numerous tons of aggregate would have eroded. Post flood repairs on the spillway were unnecessary for the first time in years."       

Technical Description:

• 15,740 sf ArmorFlex ® Class 50 Mats

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