Soft Healing at the Arb
Innovative projects combat erosion
by Steve Gilzow
Last November, several U-M students met to study methods for preventing riverbanks from collapsing. They cut red osier dogwood from one bank of the Huron River into short sections called "live stakes" and pounded them into a bank upstream. This spring, the stakes will sprout roots and leaves, anchoring the soil and strengthening the bank.
This was the latest in a series of group projects to repair and restore areas in Nichols Arboretum and Matthaei Botanical Gardens. Since 2001, volunteers on these efforts have included convicts, Ford Motor Company engineers, and ordinary folks who love the Arb. Each project was a collaboration between Bob Grese, the Arb's director, and Don Gray, an emeritus U-M professor of civil and environmental engineering.
Grese looks younger than his fifty-three years. One of eleven children of a Lutheran minister, he is gracious and self-effacing. He's good at bringing people of varied backgrounds together for a common goal.
Ten years ago, Gray, now seventy-one, began making the annual trip to his Lake Michigan cottage by bicycle. Tall, with a neatly trimmed beard, Gray was president of the Friends of the Arboretum when Grese became director in 1999.
School Girls' Glen
Their first project was saving School Girls' Glen, a steep ravine that begins near the Washington Heights entrance to the Arb and runs 1,150 yards down to the Huron. For years, storm-water from Forest Hill Cemetery had been badly eroding the glen.
"I became aware of the erosion problems back in the mid- to early 1990s," says Grese. "Liz Elling, who was an employee here at the Arboretum, was working on her master's degree at the School of Natural Resources. She did a poster, showing the amount of water running off the cemetery into School Girl's Glen. Here was this neglected, wonderful place in the Arboretum that was badly eroding."
Don Gray remembers it this way: "Twenty acres of cemetery land draining down the roadway. After a good rain, you had to hike your trouser legs
up in order to cross the stream to enter the Arb."
Another master's student, Zayn Gregory, found that School Girls' Glen was losing the equivalent of 480 cubic yards of earth per year. Each day, a pick-up truck's worth of soil, about 1.3 cubic yards, was sliding into the river, always at the same point. Over time, the dirt was plainly visible in the landscape and the river.
Gray and Grese wanted to use "bioengineering" or "soft engineering" to control the erosion-techniques such as live staking that mimic nature-to slow down the storm-water and keep the soils from being flushed into the river. Gray literally wrote the textbooks on these methods.
But initially they had to overcome in-house resistance. "At first, the university engineers were extremely skeptical," says Grese. "There was one engineer in particular who thought we should just let a large pipe carry all the water directly into the river and discharge it there. We were sort of forced into a challenge."
The "large pipe" solution might have ended the erosion, but it would have been ugly and might have created new problems as high-velocity, warmed storm-water shot into the Huron. Grese persuaded the decision-makers to let him try some of the low-impact methods found in Gray's textbooks.
The first step was removing non-native invasive plants. Unlike native plants such as dogwood or willow, invasives do a poor job of anchoring the soils. Rocks and boulders needed to be relocated by hand to maximize their reinforcement of the slope.
A group of Engineering students going through orientation were recruited to do the necessary hard physical labor. "The idea was for the students to have a chance to really be engaged, develop some group dynamics, kind of like a ropes course only doing useful work," says Grese.
Gray recalls, "The engineering students thought this was going to be strictly a classroom exercise. We did spend some time talking about runoff and erosion control techniques. But then we put them all to work." Gray laughs about how resistant they were initially. "But the funny thing is, I later ran into one of these students at the Produce Station. He had very fond memories of carrying rocks around. It struck a chord with him, that he was able to do cerebral work and manual labor combined."
The next step was "vegetated mechanically stabilized earth repair fill"-or "soil wraps." A team of volunteers filled large cavities in the ravine's slope by packing them with sandy loam wrapped in fabric. Like a tortilla pinned with toothpicks, the soil wraps were kept in place with live stakes. Instead of using fabrics manufactured commercially for just this application, Grese had the volunteers use old carpeting to lower the costs. "We found that we could get old carpet remnants from dormitory rooms. One of our employees was working at the grounds department. He was able to secure as many carpet remnants as we wanted to wrap the soil."
Another phase of the work in School Girls' Glen was the building of a "gabion dam"-a structure of large galvanized wire baskets filled with rocks- in the main channel of the ravine to slow the velocity of flowing water. Ford Motor Company provided ten volunteers to build it, including materials-handling engineers-white-collar workers who spend their office hours devising efficient ways to avoid handling the same material twice. One of them, Tony Webb, recalls: "I remember seeing the large wire baskets at the bottom of this gully-many twice the size of a human coffin-that we were supposedly going to fill with rocks about the size of footballs. I couldn't imagine how our work team was going to move that much rock down the hill into the glen in just eight hours."
At first, the engineers formed kind of a bucket brigade, handing rocks down a human chain to the bottom. Then, they spied a large flexible drainage pipe that would be used in a later project. They began experimenting with rolling rocks through the pipe. They learned to flex the pipe so the rocks landed closer to the baskets. They cheered as they began scoring direct hits.
Grese didn't need to wait long to learn if the gabion dam would make a difference. "Two days after we put the dam in, we had a huge rainstorm that nearly filled the whole back of the dam with soil in one rain event. It showed the dam worked. All that soil was kept out of the river. I was able to send the Ford team pictures of how well it worked and they were really excited."
The soil wraps and gabion dam helped slow the water rushing down the lower reaches of School Girls' Glen, but there was still that stream at the top near the cemetery that you had to ford on rainy days to reach the James D. Reader Jr. Urban Environmental Education Center.
Formerly the Burnham House, the Reader Center is one of the U-M's oldest buildings, dating back to 1837, when the newly formed university moved to Ann Arbor from Detroit. The building was moved to the Arb from Wall Street in February 1998.
In 2003, volunteers built a Gateway Garden in front of the Reader Center, right up to the chain-link fence that separates it from Forest Hill Cemetery. The garden slowed the storm-water flow dramatically. "The water was brought down in a series of pools, stepped waterfalls," says Gray. "It used to be a real eyesore. We've taken a liability and converted it into an asset. The first thing you see when you enter the Arboretum now is this gorgeous Gateway Garden. The plants look like they've always been there."
School Girl's Glen presented the worst erosion problems, spread over the greatest distance, but other places in the Arb and at Matthaei Botanical Gardens also needed help. In 2005 and 2006, the River Landing project changed a key area in the Arb's trail system. Located just upstream of a railroad bridge, at the point where a heart-shaped arrangement of boulders creates a distinctive, well-known riffle in the river, the River Landing site had long been popular - and neglected.
"Sometime in the 1970s," says Grese, "the river shoreline was badly eroding. What was thought to be the solution was to take busted concrete from old sidewalks and dump it down there, cover it over with soil, and plant grass on it. So that's what had happened. A lot of soil had washed off it and rebar was sticking up in points, so we were looking for ways to repair that. At first we didn't have a good sense of what it would cost. We were looking at various approaches that could maybe keep the concrete in place. So Don and I ran an experiment on half of it, using live staking between the joints in the concrete to see if we could rebuild soil on top of the concrete slabs."
Though that experiment yielded some success, it felt like a halfway measure. Grese decided to pursue outside funding. He found out about a group called the Southeast Michigan Resource Conservation and Development Council that had a grant from the Michigan Department of Environmental Quality to do demonstration projects on stabilizing badly eroded stream banks. "We convinced them that this was a highly visible section of the river shoreline that could help educate people about restoring stream banks," Grese says. "One of the keys to them financing this project was that it could serve as training for road commission people who might use some of the same techniques on other projects."
The scale of the project was beyond what volunteers and a modest budget could accomplish. Eventually, the list of project participants would grow to include many government and private organizations, local businesses, and university staff. In 2005, the old concrete was removed and massive granite steps were installed to hold the bank. Native species were planted, using a combination of bioengineering methods. In 2006, the area immediately downstream of the new steps was cleaned out and a canoe landing was landscaped. Once again, one of the Arb's biggest eyesores became one of its greatest assets.
Further upstream, near the parking lot below University Hospital, bank erosion posed an even worse problem. Nichols Drive, the road leading from that lot, runs close to the river, interrupting a steep bank of glacial moraine that rises at a forty-degree angle to a height of eight-five feet.. At a wicked curve in the Huron, the roadway was in danger of being undercut from below and washed out from above. By 2007, the outer edges of the road were collapsing into the river.
This part of the Arb actually belongs to the City of Ann Arbor, so Grese helped put together a partnership with the city and other agencies.
"A combination of waterlogged soils and the river eating into the shoreline was causing the road to collapse," he explains. "It's the emergency entrance into the Arb and access to a main sewer line. The City couldn't risk not being able to get to that sewer line if it were to fail, and the University couldn't risk not being able to get someone out of the Arb in an emergency. That's the only one of our roads that a fire truck can access."
Design and construction supervision for this project was done by Marty Boote and his firm, Environmental Consulting Technology. Don Gray lent some expertise as an advisor. A key element in the design was three "river vanes" that were placed into the water using heavy equipment. These are long, tapered piles of large crushed limestone curving out from the bank into the river. Their shape and proportions bring to mind the horn on a rhinoceros. The three rock vanes are widely spaced; one at the beginning, one at the midpoint, and one at the end of the river's curve. They point upstream into the water at about a thirty-degree angle to the bank.
Their effect on the water is counter-intuitive. Looking at them, you'd think they would split the flow and send a sheared volume of water into the bank with even more force than before. In fact, they deflect the water's flow back into the river's main channel. The water behind each vane is very slow-moving-almost quiescent-as it laps against the bank.
When plans for the Nichols Drive remediation were shared with interested parties, staff from the Gallup Park canoe livery expressed concerns. Cheryl Saam, the livery's director, says, "Initially we were concerned that paddlers would get stuck behind the vanes and this would cause boats to turn over as they swung sideways to the current. The Arb and the design contractors then changed the original proposal of the vanes from protruding one-third of the way across the river to much less distance from the riverbank. It was a pleasure working with the Arb staff-they listened to our concerns, and the resulting smaller vanes have worked out well for the paddlers."
During a weekend in mid-September, 2008, the Ann Arbor area was hit with near-record rainfall. Don Gray was eager to see how the vanes were working in high water. Though the vanes were completely submerged, subtle patterns on the water's surface made it clear they were still deflecting the rain-swollen power of the water away from the bank.
A downsized version of those vanes also saved a collapsing bank of Fleming Creek in the Botanical Gardens. ThereFleming, a small tributary of the Huron, was undermining the bank of a footpath. In the summer of 2006, crushed limestone rocks were brought to the site in a tractor driven by project manager Sarah Weiss, a Matthaei employee. With a blond ponytail flowing out the back of her baseball cap, she emanates the enthusiasm and lean energy of a long-distance runner.
Weiss worked closely with Don Gray planning the project. "I worked with Don over the course of many months, getting approval from the Department of Environmental Quality and the DNR. Then we had to wait for frost laws to lift so we could get our materials in. There was all this buildup, and me chomping at the bit. We got the supplies, trucked it out there, got absolutely ready. There had been months of preparation-and then to build both vanes in two days was just mind-boggling. We anticipated having more staff on one of the days but we were short-handed-so Don was one of the heavy lifters. Which is really amazing."
Something else amazing is that Fleming Creek is considered a "navigable waterway" by the DEQ. In this case, it is not canoeists who need to be accommodated. According to Weiss, the vanes needed to be constructed in such a way that "even if the creek is low and only has a few inches in it, it has to stay clear enough for a duck to float by-or the fish."
Weiss is grateful for the guidance she received from Gray: "It was numerous meetings with me, really coaching me through all the research he had done related to stream-bank erosion and the different techniques that are suitable given all the variables. So I felt really lucky that as a part of my job I got to have this kind of personalized 'course.' I'm a better professional for having worked with him and learning what I did about 'green' or 'soft' engineering."
The "volunteers" for this project were members of the Community Work Program-individuals who, convicted of crimes, chose to do some heavy lifting rather than spend time in jail. Under the guidance of Sheriff's Deputy Brian Wild, they spent a day building the rock vanes by hand, one heavy boulder at a time. It was just one of many weekly projects the Community Work Program does at Matthaei.
"In a way, it's a crapshoot," says Wild. "We never know what we're gong to be doing until we get here. It could be weeding, cleaning flower pots, or moving rocks into a creek. But when a project is done, you really know you've done something. It's not like picking up trash off the road, where it's back two days later."
For their part, these individuals who have strayed outside the law-like the Ford engineers, the loyal cadre of longtime Arb volunteers, and those slightly surprised orientation students-take away unique memories of their time helping out on Grese's and Gray's projects. One tattooed young man proudly shows a photo of a Massasauga rattlesnake-not terribly uncommon at Botanical Gardens-he took on his cell phone. An older man looks forward to bringing his children out to Matthaei "when I have time." He wants to show them something special. He laughs. "Purple love grass. Can you believe it, this place has purple love grass!"
A shorter version of this article, "Saving Nichols Drive," was first posted in the News channel on January 9, 2009.
[Originally published in February, 2009.]