Island-Building Technique In St. Paul Engineer District Is New To Inland Rivers

The St. Paul Engineer District is using a new technique for building up habitat islands on the Upper Mississippi River. The McGregor Lake Habitat Rehabilitation and Enhancement Project is being built near Prairie du Chien, Wis., and Marquette, Iowa, using a method that’s never been done before on the Upper Miss.

It’s called thin layer placement and is a technique that has historically only been used on coastal waterways. Thin layer placement places sand in thin, uniform layers over eroding islands.

“It’s a newer concept that we’re trying to incorporate in UMRR [Upper Mississippi River Restoration Program] to target a much larger area on a less intrusive scale to help raise some of these island areas into a more suitable habitat for tree species to grow in a less impactful way than what island building has been in the past,” said John Henderson, project manager. “Thin layer placement raises the forest levels to a point where it’s more suitable and gets the islands out of the inundation period where the trees would see harm.”

“This is another tool in the toolbox,” Henderson said. “We can use this in areas that are more sensitive to erosion and work around some of the limitations we have on these projects.”

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One of the highlights of the McGregor restoration project is that the sand base material is coming directly out of the main channel of the river, Henderson said. Normally, the material would have to be hauled upland to a placement site.

“Here at McGregor, we’ve beneficially used almost 500,000 cubic yards of clean river sand, which is about half of our district’s annual dredging capacity,” he said. “This is a testament to how we can beneficially put together two of the Corps’ missions–maintaining the 9-foot navigation channel and habitat restoration.”

Enhance Backwater Fisheries

Henderson added that the project will use 200,000 cubic yards of backwater dredging material, which will help enhance backwater fisheries and improve ice fishing and other recreational opportunities.

The UMRR is a federally funded partnership with both state and federal partners between a multitude of Upper Mississippi River agencies spanning from St. Paul, Minn., to the  southern tip of Illinois.

The program targets the Upper Mississippi River wildlife refuge and other areas across the Upper Mississippi River to rebuild, restore, study and implement better practices and rehabilitate some of the islands that have seen change based on climate change, flooding and invasive species.