Crow Wing County, MN, is located within a recreation area known as the “Region of Thousand Lakes” or “Brainerd Lakes Region.” This central Minnesota county is a popular location for boating in the summer and ice fishing and snowmobiling in the winter. More than 400 lakes in the county draw visitors year round. The fifth largest, Bay Lake, covers more than 2,300 acres and has 19 miles of shoreline. Keeping the county’s roads safe for both visitors and residents is a priority for the Crow Wing County Highway Department. Crow Wing County State Aid Highway 10 (CSAH 10) runs alongside part of Bay Lake’s shoreline. Just a few years ago, the road’s embankment was in danger of failing due to erosion. This erosion was the result of both wave action of the lake and ice heaving in the winter and spring. To stabilize the shoreline of Bay Lake, the Crow Wing County Highway Department worked with Progressive Consulting Engineers and contractors North Pine Aggregate and Anderson Brothers.
The project involved rebuilding 6 miles of the road. The revetment installed along the shoreline of Bay Lake covered about a half mile. Work on the project took about two weeks.
Because people access Bay Lake from docks that lead from CSAH 10, the County Highway Department staff wanted a more manageable slope than what traditional riprap or other hard armor would allow. In September 2009, crews installed just over 3,000 square yards of ArmorFlex Class 40 articulating concrete block (ACB).
ArmorFlex is made by Contech Engineered Solutions of West Chester, OH. The system of flexible interlocking individual cellular concrete blocks comes in various sizes. With a 20% open area, it fosters vegetation growth.
ArmorFlex was chosen for many reasons, including its quick and easy installation and its open-cell configuration, which allows water to move easily between the blocks. It was the only product certified by the Minnesota Department of Transportation as a dry-cast erosion block.
“We did all of the grading work on the road prior to the revetment,” says Rob Hall, assistant county engineer for Crow Wing County’s Highway Department.
Challenges faced during this project included determining how to install the ArmorFlex mats along the curve of the bay, rather than in a straight stretch. To meet that challenge, Hall says, there was “some tweaking as the installing was being done.”
The mats also needed to be installed 5 feet out into the water and in water up to 3 feet deep. North Pine Aggregate excavated a trench at the staked offsets before keying in the fabric and ACB.
Another challenge, Hall says, “was that it was hard to know whether or not the toe was in, under the lake where we couldn’t see.”
“Our main concern was way down the slope where the ice and waves were causing us problems. We made sure the revetment was in [securely] at the bottom, under the water. There were some gaps at the top that we filled in by hand,” says Mark Melby, county engineer for the Crow Wing County Highway Department.
“We put some riprap where the ArmorFlex ended,” says Hall. “That’s where there is less wave action.”
For vegetation, “we planted a roadside type of mixture of native grasses and lawn seed,” says Melby. “We came back in the spring and reseeded, too.”
Melby says the project has turned out well and the residents are pleased. “When we were building, they couldn’t use their docks to access their boats, so the work was done in the fall. That way they had most of their summer season as usual.”
He adds, “Once you get that vegetation [established] you can’t see the revetment, and it’s easy to set the end of a dock on it.”
This project won the 2010 Minnesota Concrete Masonry Association Award in the “Special Concrete Masonry Project” category.
When it comes to stabilizing shorelines and streambanks, Hoosier Aquatic Management of Indianapolis, IN, follows a natural approach. Company owner Matthew Kerkhof and sales manager J. Eric Spangler install their own Living Logs, which they also make available to other companies.
Living Logs are 8-inch coir (coconut fiber) logs. They contain native plant plugs large enough to grow well when the logs are placed within a project.
Hoosier Aquatic Management installs native plants that will thrive within a specific environment, such as uplands, prairies, or wetlands. The company’s projects are noted for becoming gradually invisible, blending into the shorelines and streambanks as native vegetation takes root and grows out.
One of those projects, completed in a week during the summer of 2010, is a 40-foot-long native plant buffer. It’s growing along the shoreline of a detention pond adjacent to the town hall of Fishers, IN, a suburb of Indianapolis. The detention pond measures about 50 feet by 200 feet. The restored shoreline planting circles around it.
“It takes two to three years for prairie plant seeding on bare soil to grow in,” explains Spangler. “There’s a saying that the first year the plants sleep, the second year they creep, and the third year they leap.”
Living Logs, containing water-tolerant native plant plugs, were installed 4 inches below the water line and 4 inches above it. They were secured with stakes and lashing. Seeding of native prairie plants was then done to cover the 40-foot slope that angled upward at about a 4:1 ratio. These plants included brown-eyed Susan, bergamot, and New England aster. Some hydromulching and a liquid erosion blanket were also added.
Spangler says the detention pond was fairly new, but was surrounded by existing vegetation. Getting rid of it so that the project could begin was a challenge.
Four years later the plants have filled in well. “You wouldn’t see the Living Log, but it’s still there, under a network of roots,” says Spangler.
Watering wasn’t needed. And along the pond’s edge, the pond water softens the clay soil so the plants’ roots can penetrate well.
In May 2014, Hoosier Aquatic Management created a smaller erosion control project northeast of Indianapolis in Marion County. Called the Devore Slope, the site is on private residential land that adjoins the Geist Reservoir, a source of drinking water for Indianapolis.
Spangler says that the 60-foot-tall slope “is near vertical-very, very steep.” Like roofing contractors, he and Kerkhof had to “stand on a log to keep from sliding down. It was all hand work, no machines.”
Spangler says that they always “try to do projects without tearing up grass or bringing in machines,” but extra care was needed on this site. Even so, the project was completed in only four days.
Another challenge was removing the limbs, grass clippings, and other types of yardwaste that the homeowner had been tossing down the slope for years. A big rainstorm a year earlier had made a tree slough down the slope. An unexpected bonus was that this yardwaste had turned into usable compost.
The slope faces north, so more shade-tolerant native plants were installed. Upland-type plants were suitable for both the plugs in the Living Logs and seeding on the upper sections, as the slope is adjacent to a wooded area.
The steepness of the 40-foot-wide slope required the installation of six terraces. Each was anchored by a Living Log, then native plant seeds were added.
Spangler says the vegetation both slows velocity of stormwater runoff at the top of the slope and keeps nutrients out of the Geist Reservoir below. Performing these functions allowed the homeowner’s cost of the project to be reimbursed by the Upper White River Watershed Alliance.
Stabilizing a Bluff
Another challenging erosion control project to stabilize a homeowner’s steep bank happened in South Haven, MI. The homeowner’s lot is on a bluff, 100 feet above the shoreline of Lake Michigan. The project covered about 100 linear feet.
“A clay lens runs through the area. The flow of groundwater on top of the clay soil was destroying the bluff, along with a new set of access stairs,” explains Brian Majka, senior restoration ecologist and project manager for CardnoJFNew, the Michigan- and Indiana-based engineering firm chosen for the project.
Erosion was “accelerated by the installation of the stairs down to the lake,” he adds. “That section of the dunes is known for being unstable because of geological formations.”
Installing a groundwater interception system was part of the project. Well points were set back and hooked into pumps that fed excess water into the town’s stormwater system.
The project took two years from initial discussions to completion. Actual construction work took place over several weeks in 2007.
Majka says that the site’s slope was “about .5 to 1, steeper than 1 to 1.”
To protect the homeowner’s property by stabilizing the bluff and preventing future erosion, Majka and his team relied on Presto Geosystems’ Geoweb for the top section of the bluff from the crest downward for 20 feet, the most damaged part, which contains the layer of clay lens. The Geoweb stabilizes the upper layer of soil and is particularly effective on embankments.
“This is a product that’s great for settings like this one. The way that it’s infiltrated, it can handle steeper slopes,” says Majka. “It holds the whole slope in by anchoring it, by giving it more stability.”
The workers “put the top of the Geoweb anchor into a trench and set it back a bit. Since it’s all once piece, the product itself helps pull the land back,” says Majka, noting that his company has used Geoweb before with success.
The lower 80 feet of the bluff were terraced. North American Green’s SC250 erosion control blanket helped maintain stability here.
“The width of the terraces varied from 12 to 18 inches and they ran the length of the slope. They were set back 2 to 3 feet from the edge,” says Majka.
Seeding of native plants included species that were already growing in the area. “We put in more little bluestem and switchgrass,” notes Majka.
No soil additives were used. Because the work was done during midsummer, when the weather was hot and dry, the homeowner watered the plants to help them get well established. Majka says that the hot weather was fine for the project overall because heavy rainstorms would have caused problems and delays.
The most challenging part of the project was the access. “The houses are nestled into the woods and the dunes and are close to each other. Equipment was very difficult to get in and around. A mini-excavator was the biggest piece,” says Majka.
The most surprising part of the bluff stabilization project was “the really pretty cool collaboration from the different companies. We put our heads together to come up with a solution,” notes Majka.
He adds, “There was also the willingness of the landowner. He was very grateful and appreciative, even though it cost more than expected because of so much hand work.”
Majka says the clay lens soil layer runs for 10 or 20 miles in the area. “We’ve seen numerous bluffs that needed stabilization, but nothing as big as what we have done with this job.”
Sarah Bolton Park
Another erosion control project that employed Geoweb from Presto Geosystems was done for the city of Beech Grove, IN. The project’s purpose was to stabilize the banks of Little Buck Creek, which runs through the town’s Sarah Bolton Park.
“Little Buck Creek is a very urbanized stream. It floods very frequently, and when we have a once-in-10-year storm, the creek has a high velocity, approximately 8 feet per second,” explains Jim Blazek, general manager for D2 Land and Water Resources.
D2 Land and Water is a general supplier of erosion control and stormwater products, including products from Presto Geosystems. Blazek’s advice helped determine that the Geoweb would be a good choice to stabilize the banks of Little Buck Creek.
“It is one of those products that, when it’s the right system [for the site], it’s typically the least expensive of the options,” says Blazek. “When we use it on rivers and creeks it allows us flexibility because of utility, road, or property concerns.”
The erosion on the banks of Little Buck Creek was threatening a power pole and also a road that runs through the Sarah Bolton Park. That made Blazek think of using Geoweb first.
“It can go nearly vertical and still have vegetation spreading, with stone infill below or to the ordinary high water mark, then stone blended with soil above,” says Blazek.
He likes Geoweb because “it allows you flexibility to meet your site’s geometry. You can surface apply and vertically stack. They do mix together very well.”
The west bank of Little Buck Creek already had a stacked gabion wall that had grown up with vegetation after it was installed in the late 1990s. Part of it had rusted, so Beech Grove officials did not want to install a product that would rust.
PVC-coated gabion mesh was used to make repairs on the creek’s west bank, along with an earth anchor. The east bank required a completely new installation. The total project was approximately 900 feet long.
Turf reinforcement mats were placed at the top surface of the creek’s banks. Vegetated coir fiber logs went on top of the infilled geocell structure after it was seeded, right at the transition point.
Riparian native vegetation for this region of Indiana was chosen for the seeding mixture.
That included a combination of sedges and grasses, a rye cover crop, and an oats cover crop to hold the soil in place while the plants took root.
Blazek says that the project’s biggest challenge “from a design perspective was to find a vegetated system that would withstand high water and stay out of the drip line of mature trees.”
He adds, “There was a gravity wall by the power line. The rest was slope. We wanted a system that was flexible regarding its geometry, and one that would be well accepted by permitting officials. We could not excavate far into the bank because of the utility pole.”
Until about 30 years ago a dam had existed downstream. It provided the power needed to operate Beech Grove’s wastewater treatment plant. After the dam was removed a lot of development occurred in the area.
Ground around the utility pole had been eroding 6 to 12 inches a year into the bank. The Geoweb’s flexibility allowed it to be placed around the guy wires holding the utility pole in place.
“It would have been very expensive to relocate that power pole. By using the Geoweb, we saved the utility company a lot of money,” says Blazek.
Another concern was working around an existing drain and outlet pipe on one of the creek banks. That had been installed years earlier because Sarah Bolton Park lies within a floodplain. Whatever new erosion control system was installed had to accept these existing structures.
Blazek explains that the Geoweb has eight pockets in a linear row, each 6 inches tall. They range in from 2.62 to 5.5 feet wide. From front to back there can be three, four, five, six, or seven cells connected. “That’s a lot of flexibility, a big gravity structure or a geosynthetic soil mass,” says Blazek.
The Geoweb is put into place on a stretcher frame to hold the cells open as they are filled with soil from a backhoe, loader, or conveyer working at 3 feet or lower. Then the structure is compacted. As soon as the cells are filled, the structure is strong enough to be driven on.
Before the Geoweb was installed, a small coffer dam was put in place. Pumps kept water out of the work area.
“We were already building in a drought year, so that was a benefit,” Blazek says. However, the drought that was an advantage during construction was not an advantage during the time that new vegetation was trying to get established.
“We came back to reseed and water a couple of times. That was in late spring, before the one-year maintenance contract ran out. We put in some overseeding,” says Blazek. “In 2014 we had a cool, wet growing season, so we’re fortunate.”
Fitzgerald and Fitzgerald of Indianapolis served as general contractor for the project. Excavation was done by Meyer Excavating, also of Indianapolis.
Elizabeth Lake Road
Granite Construction holds one of the oldest construction company licenses in the state of California. Granite was involved in many famous projects, including the building of the first roads in Yellowstone National Park and the construction of the iconic American highway Route 66.
A more recent Granite Construction project, performed to control erosion on a slope, took place in Palmdale, CA. It was done to protect the slope on the south side of Elizabeth Lake Road, about 600 feet east of Joshua Ranch Road. Total project area was 18,500 square feet.
Stormwater runoff coming from the roadway and from the box culvert outlet can reach high volume during major storms. The south side already had a natural drainage channel.
“We used a slurry of sand and mortar to cap the bottom,” says Nick Jenkins, project manager for Granite Construction.
As a filter underneath, a 6-inch-thick layer of three-quarter-inch crushed aggregate was put in place. Filter fabric was added and topped with sections of EnviroFlex, which are about 21.5 by 21.5 inches square. EnviroFlex is an ACB system that interlocks vertically. It is made by Soil Retention of Carlsbad, CA.
“The EnviroFlex panels have a lip on two sides, so they lock together,” says Jenkins. “In some sections, we were working under low-voltage power poles. We set the EnviroFlex with a mini-excavator, a 307 Caterpillar excavator. It can pick up four blocks at a time to set.”
The EnviroFlex blocks are stacked two squares by two squares, two wide and two long, four courses high, on a pallet.
“We had to dig deep, 4 to 8 feet down to get to the toe of the slope,” recalls Jenkins.
The slope was about 2 to 1; in some places it was 3 to 1.
“Wherever there’s runoff, a lot of silt will get trapped in the pockets of the EnviroFlex squares. Silt carries seeds with it and fills in voids. Mother Nature does the planting,” he explains.
The Elizabeth Lake Road project was done during July and August 2014. “Because of the drought, the weather was not a factor for the work,” says Jenkins. “We had plenty of water and temporary shade canopies for the worker’s break times.”
He mentions that Soil Retention has crews to install EnviroFlex, but “we have our own labor force, so we bought the product and rented the machines needed.”
The project’s biggest challenge was “getting acclimated with installing EnviroFlex for the first time. EnviroFlex did a really good job of providing a foreman to help troubleshoot. They back up their product,” says Jenkins.