Local officials may be at least halfway to solving a major erosion of the steep, fragile bluffs along the Minnesota River in southeastern Eden Prairie.
Included in the $2.6 billion infrastructure bill passed by the Minnesota Legislature on Monday, May 22, is $2.75 million to the Lower Minnesota River Watershed District (LMRWD). The funding will help the watershed district correct a 60-foot-high, 700-foot-long gouge in the bluffs and stabilize the banks where the river makes a sharp bend below Riverview Road, east of Flying Cloud Landfill.
But, since that’s only 50% of the estimated overall cost of the remedy, put at $5.5 million, the watershed district is now tasked with raising most of the remainder, either with a one-time tax levy or through the sale of bonds repaid over time.
Linda Loomis, administrator for the watershed district, said that because additional study and permits are also required, riverbank stabilization work is unlikely to begin before 2024.
Studies documenting the problem since at least 2008 point to a number of factors that have led to the severe erosion. In addition to the steep turn of the river in that location, they include the sandy bluff soils, groundwater seeps, higher river levels, a lack of vegetation on the bluff, and housing development near the top. It’s estimated that the riverbank is eroding at a rate of about 3 feet per year.
“This is an area that’s been on our radar for a number of years,” said Loomis.
Studies have considered the potential threat to houses near the top of the bluff, but engineers “don’t feel any of the homes are in danger,” she said. If there were a catastrophic failure, the angle of repose wouldn’t go as far back on the bluffs as the houses, said Loomis.
“That’s all theoretical,” she added.
Closer to the riverbank, erosion has taken out Riverview Road, a segment long closed to traffic but used as a trail until part of it eroded and fell into the river.
A study in 2010 and an update in 2021 have examined the problem in detail and proposed several solutions, but the best approach still needs to be identified, Loomis said. The recent preferred alternative for which legislative funding was sought involves stabilizing the toe of the slope using large rocks, starting below the river’s ordinary high water mark. Vegetation further up the slope, in order to reinforce the soils, may also be part of the remedy.
The district described the course of action to legislators as follows: “Armor the bluff toe and flatten the slope as needed to protect the slope from the Minnesota River.”
A city stormwater pond on the north bank of the river in that area is said to exacerbate the erosion problem and is expected to be decommissioned, said Patrick Sejkora, water resources engineer for the City of Eden Prairie. The Minnesota Pollution Control Agency has authorized the change, and area stormwater will be handled in other ways, Sejkora said.
Removing the pond will allow the watershed district to stabilize a longer stretch of the riverbank.
Although the Lower Minnesota River Watershed District is about 80 square miles in size along the Minnesota River between Carver and the river’s confluence with the Mississippi River near historic Fort Snelling, Loomis said that ultimately the entire Minnesota River basin to western Minnesota contributes to the river’s frequent high waters and erosion of riverbanks.
“We felt the state had a role to play in this,” she said about solving the Eden Prairie erosion problem. A funding request was carried to the Legislature a year ago, but the 2022 legislative session ended without a bonding bill. The request was resubmitted this year and approved.
The erosion has washed tons of sediment into the river, a big concern for the watershed district because the agency is required to work in concert with the Army Corps of Engineers to maintain navigation on the river – commercial navigation to the grain terminals in Savage so barges can reach that area, and recreational navigation west of Savage. So, there’s continual dredging, and it’s the watershed district’s obligation to dispose of the material that’s dredged, said Loomis.
“This is a pretty large project for us,” Loomis said about the $5.5 million riverbank-stabilization endeavor. The watershed district has a $1.8 million annual budget with an annual tax levy of about $875,000, she added.
The city, in its own capital improvement program, has set aside at least $400,000 for the project, the city’s Sejkora said.
In addition to raising funds, the watershed district still needs to complete additional studies, said Loomis, including an archeological study and a review of potentially threatened or endangered species. State and local permits will also be needed.
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