Weyerhaeuser Project Will Utilize Innovative Wall | News

Ulteig Senior Engineer and Client Service Manager Roger Clay presents to members of the Morrison County Historical Society Board of Directors, the Morrison County Soil and Water Conservation District and Minnesota DNR, Thursday, at the Charles A. Weyerhaeuser Museum. Listening are, counter-clockwise from top, Historical Society Director Worcester, board members Gary Poser, Pat Quinn and Cathy Adamek, SWCD members Alan Ringwelski and Mike Becker and DNR Hydrologist Mark Anderson.

A plan is essentially in place for the Morrison County Historical Society’s (MCHS) riverbank stabilization project at the Charles A. Weyerhaeuser Memorial Museum.

Thursday, Jan. 26, Ulteig Senior Engineer and Client Service Manager Roger Clay presented the latest plan to a handful of MCHS Board members, as well as representatives from the Morrison County Soil and Water Conservation District (SWCD) and Minnesota Department of Natural Resources (DNR) Hydrologist Mark Anderson. By the time the lengthy meeting adjourned, nary a stone was left unturned regarding the specifics of the project.

Those present felt it was a good plan.

“I have to say, the end result is going to be a lot better than the wall,” said MCHS Board member Cathy Adamek, referring to an early option that included a block retaining wall.

“I don’t know about you folks, but I like what I see here,” added MCHS Director Mike Worcester.

In May, MCHS received $140,000 from Morrison County and $70,000 from the city of Little Falls in American Recovery Plan Act (ARPA) funding to pay for the design and development phase. At that time, the estimated construction cost to stabilize the bank was $597,000.

The project is necessary because two major rain events — one in 2015 and another in 2020 — have caused severe erosion on the riverbank. Currently, the museum is about 20 feet from the edge of a straight drop, and further erosion could cause the museum to fall into the river.

Since the group last met in December 2022, Clay said he and his colleagues had done extensive research on different types of vegetative walls. After going through options with various manufacturers, he felt the project would be a good fit for a mechanical stabilized earth (MSE) wall.

The vegetative wall would provide a natural look while also being strong enough to prevent future erosion on the bank of the Mississippi River.

“They were showing it; it was, like, kind of in the foothills of a mountain type of thing,” Clay said. “They were showing this water shooting down this channel at about 25 feet per second. Afterwards, you couldn’t even tell.”

The estimated cost for construction, presented by Clay, was $618,310. That would not include paying contractors to complete the extensive project. MCHS is exploring several avenues for funding, including a request in the state bonding bill and various grants for which it might be eligible.

The MSE wall would be 120 feet long adjacent to the Weyerhaeuser Museum itself and 15 additional feet to both the north and south.

The wall would be built on a 1:1 slope — one foot vertical for every one foot horizontal — near the water line. On the outside, it will consist of environmentally friendly bags that are filled with a mixture of 60% sand and 40% mulch. The sand provides drainage for moisture, while the mulch will give nutrients to the vegetation planted on top of it.

“These bags, which, they’re kind of a fabric but they’re not,” Clay said. “They’re warrantied for 75 years. They think they’ll last longer. They’ve only been around about 20 years.”

Behind the bags will be layers of soil, reinforced with geogrid. The wall will tie into the natural slope of the bank on the south end, as well as to the grading work done on the north end of the property, alongside the parking lot.

About halfway up the bank, the slope will change to 1.5:1, with a transition area in between.

“Where the MSE wall is, we’ll put in, like, willow branches and live stakes,” Clay said.

In terms of the work, Clay said crews will have to dig out the slope, “right up to real close to the building.” They will likely dig all the way down starting on the south end and work their way back to the access point to the north.

The soil that is excavated will be able to be used for fill and in other areas of the project.

The MSE wall will have a riprap (rock) foundation, which provides more slope stability.

“You’ll never see that after it’s built,” Clay said. “That’s going to be hidden from sight.”

He said he envisioned construction would begin with the wall and, once that is complete, continue north to the area adjacent to the parking lot. That will mainly be a clearing and grubbing project, as the slope can be graded out in that area.

Clay said a survey conducted during summer 2022 identified all of the trees in the area — all of which will have to be removed — that are eight inches around or bigger. The timber can, however, be used in other parts of the project, such as for mulch and for logs needed for seven jetties that will be placed along the waterline. In the end, that will help MCHS save some money on materials.

Clay estimated there are about 16 trees in the 12- to 14-inch range that can be used.

“I know the question that we’re going to get here is, ‘Why couldn’t you save any of the trees?’” Worcester said. “We’ll get that question; I guarantee it. What’s the answer we give them?”

“The answer is, you can’t do the slope stabilization properly unless you take them out,” Clay answered.

Due to there being a steep slope and no longer having any trees present, a guardrail will have to be constructed along the parking lot, as well.

The seed that will be used for the vegetation throughout the project are mixes native to central Minnesota provided by SWCD Technician Mike Becker. Separate mixes will account for the wetter conditions on the lower half of the slope and the drier area on the upper half.

At the water level, the jetties will help protect the bank from the river’s current. They will be placed about 50 feet apart, with a “medium riprap” surrounding them.

“Most of it will be underwater,” Clay said. “There will be a couple of feet of riprap at the ends that will be above water, so that’s all you would really see in terms of riprap.”

A foot-high berm will also be constructed at the top of the slope to prevent drainage from flowing down the bank. The water will run off of the edges, but there will be a pipe installed along the outer edge that will carry the drainage down to the river.

“You’ll have a lot of velocity coming down that,” Becker said. “With it being so steep, it will flow down that pipe pretty quick.”

On the back slope of the MSE wall, Clay said, there will be about a one-foot drainage area. That will consist of a course, clean sand that will control moisture in the soil of the wall.

There will also be little drains coming out from that layer, which will be 4- to 6-inch pipes that will let the water from any rain events get back to the river without the risk of erosion.

Worcester asked if buoys will have to be placed in the water to warn boaters about the jetties in front of the museum. Clay said that was a question for the Army Corp. of Engineers. Anderson added that Worcester should contact Morrison County Water Safety to see if they require any kind of signage.

“My casual observation out here is that most boats don’t get that close to the shore here because of the depth,” Worcester said. “They like to stay a little further out. We just don’t want somebody to come roaring along either in a boat or in a jet ski.”

Clay added that another area where costs could possibly be saved is by using trees that have already slid into the river. If one of those piles can be used in lieu of a jetty, that could be a possibility.

Worcester said there are plenty of areas where that might be the case.

In terms of sediment control, Clay said there will be a floating silt curtain made from moving water. That will trap any sediment that might escape while they’re constructing the riprap.

Speaking from experience on a different project, SWCD Lead Technician Alan Ringwelski suggested to Clay and MCHS that it makes sure the contractors chosen for the project are able to do all of the work themselves.

“There will be a qualification,” Clay said. “It won’t just be a low bid. It will be the lowest qualified bid.”

He added anyone who bids on the project will have to provide references showing they’ve completed projects “of similar magnitude.”

“Otherwise we’ll all be planting seed,” Ringwelski said.

Clay said, for this type of wall, there is also a class that Ulteig and MCHS could have the contractors take. That would give them certification from the manufacturer, Flex, to ensure they know how to do it correctly.

Ringwelski said that was probably a good idea as there probably aren’t many local contractors who have completed such a project.

“This is a pretty specialized project,” Worcester said. “I can’t imagine there’s a lot of contractors that, this is just what they do, right?”

Clay said the geogrid portion isn’t much different from other types of walls. The vegetative face portion is what makes it different. For that, he said they would likely need to subcontract with a landscaper.

“That’s why a project like this is beneficial to our area,” said MCHS Board President Camille Warzecha. “There are smaller businesses that can get involved and make some money on it.”

Addressing the reps from SWCD and the DNR present, Worcester asked if a proposal like this would be “more receptive to receiving funding,” as opposed to a traditional retaining wall.

Clay noted that the project is likely eligible for Leadership in Energy and Environmental Design (LEED) certification. He did not know for sure, but felt that could be beneficial while pursuing funding. He said the fact the materials are environmentally friendly alone should garner 21 points toward LEED certification.

“I think it’s as natural as you can get for the condition on the site,” Ringwelski said.

“That’s why a project like this is beneficial to our area. There are smaller businesses that can get involved and make some money on it.” - Camille Warzecha, MCHS Board President

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