Interstate Island Restoration and Stabilization

Challenge

Interstate Island is a small island in Lake Superior that sits directly on the Minnesota and Wisconsin border, running through the Duluth-Superior harbor. The rare common tern bird nests on this island – one of only two tern colonies remaining on Lake Superior – but has become threatened by habitat loss in recent years.

One of these threats is the fact that the island is disappearing into the St. Louis River estuary (the largest U.S. tributary to Lake Superior) due to fluctuating water levels caused by erratic weather patterns. The local gull population has also become a threat due to the island’s diminishing size and its predation of the rare common tern. In fact, in recent years, 13,000 gull nests have been found on the island compared to just 200 tern nests.

In response, multiple agency stakeholders and wildlife experts including the Wisconsin Department of Natural Resources (DNR), Minnesota DNR, U.S. Fish and Wildlife Service and Minnesota Land Trust put into motion a stabilization and restoration plan for Interstate Island and the tern population. The objective was to expand the footprint of the island in order to create resiliency to changing water levels and storm events, and to provide suitable shorebird habitat for terns and other endangered birds, such as piping plovers.

These efforts sought to and ultimately accomplished protecting the rare common tern’s critical nesting habitat for the next 40-50 years. The St. Louis River estuary is a critical source of fish, wildlife and nutrients for Lake Superior. As such, the restoration reaches far beyond protecting the local tern population and supports surrounding restoration projects, all of which have collectively become vital to protecting and nurturing the ecosystem.

Solution

SEH was selected to lead various engineering and natural resources responsibilities, including developing the restoration and stabilization plan design while also accounting for challenges such as multiple state jurisdictions; planning for difficult construction access to an island; trade-offs between stability, cost and habitat needs; and an accelerated timeline (the direct result of fast-rising waters).

The SEH team leaned heavily on its civil engineering, water resources engineering and natural resources expertise to come up with the most strategic, sound and efficient plan for both stabilization and restoration. The design plan was accepted and embraced by stakeholders, with construction completed between 2020-2021 using strategic timing to avoid disturbing the birds during nesting.

In the nesting season after spring 2020 work, local terns had nearly 100% success fledging chicks ("bringing up" a young bird until its wing feathers are developed enough for flight) from the nests in the colony.

Construction took place in two phases to protect the island habitat, inhabitants and Lake Superior waters:

Phase 1 – Raise tern nesting colony elevation.
This phase raised the nesting colony near the center of the island so that it’s at a safe elevation for the terns. The project team used an elaborate system of wires and erected fencing to keep gulls out of the nesting colony. This phase also involved filling various flooded areas on the island itself.

Phase 2 – Raise island elevation/expand size.
In 2019, Interstate Island sat at 2.5 acres due to immense flooding and rising waters that began in 2014. The project added 5.5 acres in island size and raised the island’s bank elevation by approximately 10 ft. (600-610 ft.). The project team accomplished this by strategically adding sand and gravel materials, some of which were taken directly from dredged sand in the nearby harbor.