Lake Pepin is the widest stretch of the Mississippi River, covering nearly 30,000 acres between Red Wing, Minn., and the Chippewa River delta.
But heavy sediment loads coming from drainage from four major watersheds — the Minnesota River Basin, Cannon River Basin, St. Croix River Basin, and Upper Mississippi River Basin — have threatened to cut access to parts of the lake off from hunters, anglers and other recreational users.
“The head of the lake in particular is experiencing some impairments,” said Rylee Main, executive director of the Lake Pepin Legacy Alliance based in Red Wing, Minn. “If you imagine a full city block raised 32 stories high, that’s about the volume of sediment that settles at the head of Lake Pepin every year.
“There is cloudy water, it’s filling in so there have been a lot of boat groundings, it’s changing the ecosystem, and it creates turbid water so you don’t get the growth of aquatic vegetation that you need to support healthy fish habitat and waterfowl habitat.”
Now a pilot program announced in early January by the U.S. Army Corps of Engineers has the potential to solve some of Lake Pepin’s sediment issues while finding a beneficial use for additional material dredged from downriver in Lower Pool 4.
The U.S. Army Corps of Engineers removes approximately 250,000 cubic yards of dredged river soil annually from Lower Pool 4, the section of the Mississippi River between where the Chippewa River empties into the Mississippi and Lock and Dam 4 near Alma. Unfortunately, according to the Corps, permanent dredged material placement sites previously used in Lower Pool 4 have nearly reached capacity and additional permanent sites are needed to accommodate dredging needs in Lower Pool 4.
In 2017, the Corps proposed a 40-year dredge material management plan for Lower Pool 4 that included buying agricultural land in the Nelson, Alma and Wabasha, Minn., areas for permanent placement of dredged materials. But that plan drew opposition from landowners, residents and local governments, sending the Corps back to the drawing board.
The U.S. Army Corps of Engineers, St. Paul District, will participate in a national Corps of Engineers pilot program to use dredged material to improve habitat in Upper Pool 4, which includes Lake Pepin. The Upper Pool 4 Islands Complex Project is one of 10 projects selected out of 95 proposals submitted throughout the United States. Corps’ engineers plan to develop islands in the Mississippi River at the head of Lake Pepin to restore backwater habitat.
“Building islands in Upper Lake Pepin will be a great success story for the Corps and its partners,” said Tom Novak, project manager with the U.S. Army Corps of Engineers, St. Paul District. “Not only will we improve the environment with this project, we will also create some additional storage capacity for the dredging requirements near Wabasha.”
The Corps will use dredged material removed from Reads Landing Dredged Material Placement Site in Lower Pool 4, located just north of Wabasha, Minn., to construct the islands. The island construction project could use up to 500,000 cubic yards of dredged material that has already been removed from the Mississippi River at the confluence of the Mississippi and Chippewa rivers.
The island construction project will provide up to three years of additional dredged material storage capacity but will not solve the dredged material placement needs near Wabasha since the Corps removes approximately 250,000 cubic yards of dredged material annually from Lower Pool 4.
“The construction of these peninsulas or island extensions will use some of that material from the lower end of the lake as the base, and the material they dredge from the upper end of the lake will be capped almost like topsoil, because it’s really fine material,” Main said. “The material from the Chippewa is more sandy, so it’s more structurally sound to create the base of the island.
“It certainly won’t solve the problem of the material at the lower end of the lake, but it does alleviate it a bit.”
The pilot project will consist of some restoration of currently existing islands where the Corps will raise some low areas to promote floodplain forest diversity and some construction of entirely new islands, according to Novak.
“Right now the maximum acreage is about 100 acres of several islands at Catherine Pass (near Bay City) and Wacouta Bay (Minn.),” Novak said. “I anticipate this number to come down as we continue refining designs/details and cost estimates that will define the tentatively selected plan.”
According to Novak, the project objectives are to improve and protect aquatic habitat by creating depth and habitat diversity in backwaters, increasing acreage of aquatic vegetation through wind and wave reduction, and incorporating structural habitat features such as islands to protect and improve fisheries; improve the quantity and quality of habitat for migratory bird species by creating suitable habitat for birds such as dabbling ducks and neotropical migrants through the enhancement and creation of a wide variety of plant communities; and increase the quantity and quality of floodplain forest habitat by protecting and enhancing existing floodplain forest habitat and creating new floodplain forest habitat in conjunction with island creation.
Several years ago, Main’s Lake Pepin Legacy Alliance with the Wisconsin Department of Natural Resources and Audubon Minnesota began pushing for a habitat-restoration project with the Corps. Having plans for that habitat-restoration project in place, Main said, is what allowed the groups to apply to the pilot program and will now allow the project, which she estimated as costing about $20 million, to expand to include efforts to make the lake more accessible.
Main said Bay City in Pierce County has been most affected by the sedimentation of the lake.
“When the water level is low, they can’t get boats in and out of their harbor at all. They’ve been really cut off from the lake because of this issue,” she said. “The additional funding can go to things like dredging out Bay City’s harbor. That’s really exciting, because obviously we want the ecological benefits, but we also want people to be able to use the lake and enjoy the lake. Being able to connect Bay City’s harbor to the dredging that will happen to give them access to the lake again is going to be really significant for that community.”
Corps engineers said the next step in the island construction project is to compare the costs and benefits of alternatives and put forward a selected plan for agency and public review. Construction could begin as soon as 2020.
For the Lower Pool 4 dredged material management plan, the Corps completed evaluation of alternatives from the public comment period in 2018 and will make substantial changes to the draft report, requiring a new public review period, which is expected to happen later this year.