It’s easy to assume that with sophisticated computer simulations, wireless monitoring, and engineered materials, we’ve conquered water management, but a look into our past might just dampen this hubris. When it comes to erosion control, everything old (really is) new again.
Live stakes were used as early as the first century; the Renaissance guru Leonardo da Vinci also recommended planting willows along river banks, and for the next several centuries, willow, mulberry, and poplar were commonly used in many regions to stabilize and secure soil.
In the pre-geotextile era, German innovators contrived the braided fascine Sinkstück, or “sink piece.” This lattice-like assembly of bark-filled “sausages” was stacked in layers, each one with the pieces perpendicular to the last, then laced together. This assemblage, which could be several yards in diameter, was eventually placed on a riverbank, loaded with stones and gravel, and voila—a hard and soft armoring combination set in place, long before our most recent innovations.
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Water Flows Through It
At Indianapolis-based Hoosier Aquatic Management, many of these same concepts, married to 21st century science and materials, achieve the same purposes they did centuries ago: controlling water, preventing erosion, and mitigating environmental damage.
“After providing services for years with Living Logs, we decided to create another entity and separate the manufacturing from the field management—hence the new name for what this division does,” says company president Matthew Kerkhof. “We manage water using the systems we pioneered for erosion control: Living Logs, Living Soil Tubes, and Breathable Coir Walls.”
Kerkhof notes that coir fiber is a superb growing medium that promotes soil retention as it hold seeds in place, protecting them and promoting germination. Walls of living logs allow water to flow freely through but capture soil particles and give young roots protection from potentially damaging water velocity while they grow.
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“We rarely if ever have to use heavy machinery, and instead just use a cart to carry out these installations. By using native vegetation, which supports robust growth along with less maintenance, you not only benefit from the instant soil protection but long-term aesthetics, and you create a region that can attract wildlife.”
As a result of people now finding the company online, Hoosier Aquatic Management is “getting a lot of calls from engineers, municipalities, and property owners from other regions beyond our local Midwest region.” Still, he says, whether the project is local or hundreds of miles away, “We do all the work ourselves; that way it’s installed correctly, and we have direct oversight on solving the customer’s specific problem.
“For example, a guy called from Massachusetts who found us online and asked if we could make coir logs with native plants, as he needed to comply with their Department of Environmental Protection for the seawall project he was doing.”
The customer explained that years earlier, a load of riprap was placed at the site, but the local water board and the Massachusetts DEP was less than thrilled with this solution. After finding Kerkhof’s firm online, and making application to the regulatory entity who granted use approval, he was able to amend the seawall using Hoosier’s living solutions.
“In this case, the customer got the species material he needed from a local nursery, then shipped it to us. We fabricated the living logs to meet his requirements and then drove out there and, in one day, installed everything.”
The company buys the raw materials for the logs. “We sew it ourselves into the shapes, using a nonwoven geotextile that resembles felt, with grommets attached to it. These grommets are held in place by a strong webbing, like seat belt material, and this creates the ability to securely tie the tubes together. Then, once in place, the tubes allow native species to root into the material and create a strong, resistant, and sustainable root system to withstand the shear stress of high-velocity water,” he explains.
The first tubes were 18 inches in diameter and 15 feet long, “but these were so unwieldy once they were filled with soil, we now make them in five-foot sections instead. Now, two guys can easily pick these up. I can load my pickup with my soil tubes, drive to my site, and quickly get the job done with no heavy machinery involved.”
In one recent project at a small ephemeral stream with massive erosion, the client had heard about the company from the local conservation district. The project involved a 90-foot shoreline that had water coming around a bend and eating a chunk of soil out on the other side. “So we rebuilt the left side, moving four tons of soil every day by hand and building a terrace of the soil tubes. You can backfill the slopes and use live stakes like dogwood or willow. We have a form that we use to fill the tubes by hand and then install them right there onsite.”
The tubes are installed with a foundation row and built up like bricks. “Then we layer in native plants by working from the bottom up with different species.”
The bottom course generally includes water-loving species like swamp milkweed, blue flag iris, and various sedges and rushes. “As you creep up the course, you transition to dry plants like black-eyed Susan and other wildflowers,” he says. “We strive to buy local and use all the right stuff, and we have a permit to do seed collecting ourselves so we can source our own when needed.”
On some projects, the soil tubes are used in combination with other measures such as gabions.
Credit: CONTECH ENGINEERED SOLUTIONS
Harsha Lake dam
Fixing That Dam Problem
Just 30 miles southeast of Cincinnati, the William H. Harsha Lake Dam is a popular destination on any given day, but especially when the fish are biting. The 2,160-acre lake is the leading attraction at East Fork State Park in Batavia, OH, one of Ohio’s largest state parks.
The dam has a side collection channel. “These drainage channels support collection of runoff from the earthen dam face and convey the flow to a drop inlet near the toe of the dam,” explains Dan Priest, general manager with Contech Engineered Solutions. However, on a routine inspection by the US Army Corps of Engineers Louisville District—the agency that has oversight of dams in the southern Ohio region—inspectors discovered a potential disaster in the making.
“They saw that there was significant erosion, and as a consequence, deterioration beneath the existing cast-in-place concrete groin,” says Priest. If this deterioration had been allowed to continue, the worst-case scenario could have been a breach of the earthen dam and a spillover into the Little Miami River floodplain.
Priest says it was essential to immediately replace the channel. This effort would require removing the old concrete and installing a new, hard-armored product to meet two requirements: first, it needed to be low maintenance, and second, it needed the ability to articulate to accommodate any settling that might occur without compromising the overall integrity of the system.
The project went out for bid, and Contech was chosen as the materials provider. ”We worked with the designers at the Louisville ACE to determine that ArmorFlex Class 50-T would provide them the best solution based on their hydraulics, site restraints, and long-term performance requirements.” ArmorFlex is an articulating concrete block system that uses blocks of uniform size, shape, and weight with tested hydraulic performance thresholds to prevent erosion beneath the forces of flowing water. The tapered blocks allow the water to flow over them with minimal impact due to their sloped top surfaces. This allows them to provide protection in areas of extreme water flows.
The critical design criteria for the product chosen, says Priest, includes its ability “to resist a water velocity of 21 feet per second and 14 pounds per square foot of applied shear stress” that was produced within the channel. These attributes, along with maintaining a factor of safety greater than 1.5, were essential for the channel support system.
To manufacture the open-celled blocks, Contech worked with Kentucky-based Lee Brick and Block—one of their 22 US manufacturing partners—to provide the required 6,400 square feet of block for the Harsha Lake Dam project.
The final configuration was more than 600 feet long. The 10.6-foot-long mats were composed of blocks cabled into a matrix 7.8 feet wide. Each mat has loops along the short end, which are then terminated into the ground to ensure the water is forced on top of the mat throughout the U-shaped channel. The mats have a configuration that Priest describes as a staggered matrix; each row is offset by a half-block unit at each end. To accommodate this configuration, Contech manufactures a larger block-and-a-half unit. This ensures that every unit meets the same hydraulic requirements. “Trying to hold up a wall while the water is pushing at it has no margin for error, and even the smallest piece must support the critical shear stress at no less a capacity than the largest piece of the matrix.”
The ArmorFlex installation solved the erosion problems of the channel around the dam. With rainfalls the following spring above normal levels, the system was tested and performed as designed, helping to quietly protect the beautiful Little Miami River floodplain.
Fabricating blocks for the articulated concrete mattresses
Making Turtles Happy
Complex problems might suggest the need for complex solutions, but often they simply require complex thinking to devise what is, ultimately, a very simple solution. Although it took 10 years of start-and-stop efforts, one beach erosion repair reflects the outcome of that approach with breathtaking results.
According to Brevard County engineer Mike McGarry, the Florida coast municipality, at a mere 13 feet above sea level, “is just a little bit higher than Miami-Dade—which is only about 10 feet above sea level,” and as on all East Coast shorelines, residents are concerned about sustaining the beaches. In the face of an unrelenting spate of hurricanes and tropical storms, officials and business depend on the tourism and revenue stream derived from beaches. When beaches are damaged, the local economy feels the direct effect.
Located on a barrier island just a few miles south of Cape Canaveral, accessible by bridge, Brevard County’s expansive Satellite Beach was suffering from critical erosion. “Roads and buildings were at risk, a long-term effect that really began with terrific damage by Hurricane Fay in 2008 almost 10 years ago,” says McGarry. The beach provides protection for the town of Satellite Beach and its 8 miles of developed shoreline.
“We had to come up with a plan that involved putting in more sand to combat the erosion, but after that look at environmental mitigation that would benefit the near-shore habitat.”
He notes that a popular activity in the area is snorkeling and exploring the reefs. Those reefs are crucial links in the food chain supporting sea turtles.
“Typically, to build reefs, our old way of doing it was to simply throw some rocks down. But in this case, the agencies who have oversight for the project required a lower profile. And the challenge of putting in sand for the beach erosion without impacting the reef is another consideration.”
The effort in this case involved input and oversight from multiple stakeholders and regulatory offices. There was much discussion with diverse state and federal agencies to determine the mitigation most effective for the species involved. The Florida Department of Environmental Protection, and the Florida Fish and Wildlife Conservation Commission, as well as the US Fish and Wildlife Service and the National Marine Fisheries Service, were involved.
“They were clear that it [the reef] had to be low-lying and close to the bottom. One of our staff who was familiar with concrete mats came up with an idea that a combination of materials could be used to replicate the original reefs,” says McGarry.
While the beach renourishment was successfully underway, the reef effort eventually would take 10 years to complete with various incarnations of design and experimental techniques. Ultimately, the solution was a novel adaption of articulated concrete mattresses from Ontario-based International Erosion Control Systems (IECS).
Charlie Chase, president of US sales for IECS, explains the connection between the company, the municipality, and what would come to be known as “the largest underwater installed ACM” offering a “revitalized underwater neighborhood for sea turtles and other marine life.”
Working through a network of contacts, including Chase’s local IECS Florida distributor, Larry Larson at R.H. Moore & Associates; Brevard County; and local engineering firm Olsen and Associates, Chase began a conversation about how IECS’s articulated concrete mattresses—with some design modifications—could potentially create a new reef off Satellite Beach.
“The concept was to manufacture an ACM that would have a top surface of native Florida stone, called coquina stone, embedded in the concrete. This would replicate the real thing and would serve the purpose in attracting the sea life that typically adheres to reef surfaces and then acts as a food source for other marine life,” explains Chase.
“Once I learned about this unique need from my distributor, it was really an intriguing challenge, and I was definitely interested,” he recalls. “We started designing different methods to embed the coquina stone into the top surface of the blocks.
“Now, keep in mind, IECS has a precast plant where many specialty products were manufactured, so it was very easy to try several methods and sizes. Once I came up with what we thought was our best option, I presented it to the county,” he says. “They liked the concept, and then we had to start making some prototypes, but since we don’t have access to coquina stone in Ontario I decided to take the prototype forms, drive them down to Florida, and just cast them in place right there.”
With a load of forms in the back of his pickup truck, Chase made the 2,000-mile trip and coordinated with McGarry, who was able to locate some coquina stone for the experiment.
“We actually mixed the concrete by hand and made individual blocks. Then, once the concrete was placed and the forms removed, we strung the blocks together by hand, making very small articulated mats.”
Chase recalls that the mats were placed in the water about 1,000 feet from the last wave break, and growth started occurring within 30 days of placement, proving the concept a success. But this was back in 2006, and with the struggling economy and market recession in 2008, he says, “I thought the project would never happen.”
However, in September 2016, Brevard County and the Jacksonville District of the US Army Corps of Engineers put the project out for bid. “I put together a bid for the project, and Shoreline Foundation Inc. was the successful contractor who then purchased the mats from IECS.”
The process of making the mats to meet the multiple regulatory and environmental demands would pose manufacturing challenges.
“There were two options of how we could manufacture these. The first was making individual blocks like I did with the 2006 prototypes and stringing those together, creating an 8-foot by 16-foot mat. The other option was to create a mold that size, and cast that in place as a complete, full-size mat, which IECS feels is a much stronger unit.”
Nonetheless, it involved a huge undertaking that was, once again, solved through ingenuity and collaboration. The start date was in 2017.
“Making these mats is a very labor-intensive process and must adhere to the Corps specifications. We used a 5,000-psi concrete, which is a very stiff mix to work with, purchased from a local ready-mix supplier.” Chase explains that each mat had to be reinforced with stainless steel rebar placed and secured by hand. Then, after placing the concrete in the molds and vibrating the mix, which was relatively easy, the next step was more difficult.
“Before the concrete was set up, we had to not only hand-place, but, with equal spacing, apply the coquina stone, keeping it all in the specified range and height. It was slow going at first, but with the guidance of lead hands Fred Johns and Joe Hooks it soon became like an assembly line and went very smoothly.”
The next step was to place “seeding” between and outside the perimeter of the concrete blocks while they were still in the mold and while the concrete was still workable. “This is a smaller stone that is sprinkled on top of the concrete and then softly hand-troweled into that top surface, creating an exposed aggregate appearance,” explains Chase.
Once these tedious processes were complete, the molds were covered with burlap and a light mist of water was applied to control the dehydration of the curing concrete.
“The next morning, the demolding crew comes in early and removes the top portion of the mold and reassembles that mold onto another base, and the procedure starts all over again. All the mats are kept in this curing area with automatic water sprinklers on them, allowing them to cure properly for four days,” he says.
It is not a project to be rushed; Chase says the reefs will take two years to complete and install, and due to rough seas during the winter months, the project closes down until it can start up again “hopefully in March or April, but it’s all up to Mother Nature,” he says.
McGarry could not be more pleased with the project, explaining how the mitigation ratio the Corps of Engineers required was actually reduced because of the success of the initial small-scale tests Chase performed.
“Agencies require you build mitigation at a certain ratio under the assumption that similar mitigations did not perform as well as hoped; it’s a bit like raising the bar of expectations. The first Corps mitigation ratio was 3:1 (mitigation acreage:impact acreage). However, after Brevard County developed a specific mitigation plan and did the small-scale onsite tests, the agency reduced it to 1.6:1, almost half of what it was.”
He reports that the reefs are installed 1,000 feet out from shore, just outside the biggest wave break. “We were very happy to see that within a month, a marine monitor tasked with looking for sea turtles saw one, and the reef had barely been in the water. This was great news, as species that are food for the turtle will thrive on the reef, attracting the turtles as well as other fish like sea bass, snapper, and others. They will all use this reef, and it is going to perform a great environmental service for us.”
What a Load of Old Bricks
In Oakville, ON, located outside Toronto, Art Mercer, landfill supervisor for the regional municipality of Halton, relates how a delivery of bricks turned into a landfill erosion solution.
“A local brick manufacturer called me with a unique dilemma. He said he had this huge load of off-spec bricks that couldn’t be used for building, and he was stuck with them and would have to dispose of a very large quantity, and did I have any use for them.”
Mercer said that stone and brick is typically disposed of in the landfill, but in this case, he saw an opportunity to put the bricks to work instead.
“We took all these bricks, lined our channels at the slopes of our landfill with black plastic, and literally just dumped the bricks on them. What this did was create an instant channel for our landfill that is perfect in slowing down the flow of water off the slopes and controlling erosion.”
Mercer says the brick has virtually eliminated erosion in the ditches and saved the landfill money besides.
“Usually we would need to purchase quarried stone to do this job, but not only did we not spend a cent on this from our own pocket by repuposing all this brick; we’re keeping it out of the landfill.”