The Changing Face of Streambank Stabilization

Nov. 1, 2004

They call it a river, but Randall Shuey knows better. The Merrimack, as it winds its way through portions of Manchester, NH, might as well be a lake. When it hits Intervale Country Club, a more-than-100-year-old facility, a dam that controls it turns the Merrimack River into what is essentially a very long, narrow lake, one stretching more than 4 miles in length.

The Merrimack, of course, adds some luster to Intervale. It attracts crowds of boaters, water skiers, and jet ski enthusiasts, a bunch of people who like to zip up and down the river as fast as possible. The problem is, this attention has also resulted in erosion-lots of it.

Shuey, senior soil and wetlands scientist with Gove Environmental Services Inc. in Stratham, NH, faced the challenge back in 2002 of stabilizing the Merrimack’s bank and halting its erosion. This was no easy task. The country club has been losing shore frontage on its property ever since 1903, the year the US Army Corps of Engineers built Intervale. By 2002, the water line had crept just inches from old and valuable trees lining its banks. Members worried that they’d lose the trees.

The club hired Shuey and his firm to develop some way to stop this erosion, and they wanted the firm’s engineers to do so by using “green” methods that were not only beneficial to the surrounding environment but would be aesthetically pleasing to the club’s golfers and guests.

As a special challenge, the Merrimack here provides a winter nesting site for federally protected bald eagles. This meant that Gove engineers couldn’t do any work between November 15 and April 15, the eagles’ nesting period.

Despite these challenges, Shuey and Gove’s team finished the first phase of the project, stabilizing 1,000 feet of streambank, in late 2002, and they did it in a way that pleased club officials. Gove used a variety of methods, turning to everything from vegetated gabions and rock baskets to thousands of newly planted shrubs and willow stakes. The company even developed a new set of standards for club maintenance officials to use when mowing and landscaping around the banks.

The club’s request that Gove use such aesthetically pleasing methods-as opposed to simply turning to riprap-came as no surprise to Shuey. Such requests have become commonplace, he says. “People are really interested in these green methods of stabilization. We’re pretty proud of this project-proud that we were able to use these different methods and work together with everyone to come up with a plan everyone liked. It’s been great now to watch all the vegetation over the last year or so really take off. It looks great right now.”

Shuey, of course, is far from the only engineer out there who is exploring new options in the battle against streambank erosion. Landowners, businesses, and municipalities are all asking that engineers turn to more “natural” solutions to solve the problems of erosion along their neighboring rivers, streams, and lakes. The good news is that manufacturers are listening, and are constantly developing new options for engineers and contractors.

“The push behind this is really coming from the people who live along these banks. They are making sure that their municipalities know that they want more natural-looking erosion solutions,” says Randy Wilkins of Houston, TX-based Modular Gabion Systems. “People are looking for something that will revegetate. There is almost an entire industry right now centered around more natural looking environments.”

Wilkins knows the situation firsthand. In Houston alone, an entire army of volunteer-minded residents has formed a coalition dedicated in large part to preventing engineers from creating any more concrete-lined ditches in their neighborhoods. Members of this Buffalo Bayou Partnership are typical of the growing numbers of residents who prefer so-called soft-armor techniques to hard-armor erosion solutions.

To be sure, there are many times when hard-armor solutions are the only acceptable choice in an erosion control project. But when there are options for softer solutions, engineers more often than not are choosing such products as turf reinforcement mats and gabions that can support vegetation. Members of the erosion control community expect the pressure to turn to such options to increase as more residents and municipalities become better educated about soft techniques.

“The local populace has certainly been interested in more natural options,” notes Matt Showan of Williamsport, MD-based Maccaferri Gabions Inc. “But we are also seeing now in certain states that the state governance, the legislature, is saying that we need to have bioengineering as a solution. New Jersey, for instance, has recently said that if an erosion protection project totals an area more than 100 feet long it has to incorporate some sort of bioengineering technique.”

Shoring Up the Third River

As the municipal engineers for the Town of Nutley in New Jersey, officials with Cranford, NJ- based Pennoni Associates Inc. have tackled countless streambank stabilization projects over the years. But when in the summer of 2004, when Pennoni Associates took on a new job for the Nutley Department of Parks and Public Recreation, the firm was asked to work for the first time with “green” gabions that would support vegetation. The reason? The parks department wanted an erosion control solution that was not only effective but also aesthetically pleasing.

“This was all new to us,” says Stuart Levitch, senior engineer with Pennoni, the municipal engineer for the township of Nutley. “We’d never used such a product, so we were curious about how well it would work.”

Pennoni, along with general contractor NAVKA Construction of Newark, spent two months stabilizing the streambank along roughly 1,400 linear feet of the Third River as it wound through Kingsland Park in Nutley. The construction turned out to be fairly simple, and wrapped up by the end of June.

When Pennoni first approached the project, the company planned on shoring up the river’s banks with standard gabions. But the State of New Jersey now requires that contractors and engineers turn to more natural methods when working on such a large project. Levitch approached Maccaferri Gabions for an alternative.

Levitch eventually settled on the company’s Green Gabions, baskets that are first lined with a biodegradable coir blanket and then filled with a stone mix. They not only help halt erosion along streambanks but also sustain vegetation, giving an erosion control project the more-desired natural look.

At the Third River, construction workers first installed a standard gabion to provide a base. They then installed two rows of Maccaferri’s Green Gabions on top of this base. “They went in without a problem,” Levitch said. “In fact, they went in quite easily.” Levitch suspects that this is not the last time he will work with Green Gabions or other more natural-looking forms of soft armor.

“Based on the way the State of New Jersey is going, yes, I’d say more projects will include these products,” Levitch said. “But that’s not a problem. The product works well. We had absolutely no problems with them.”

Writing the Book on Alternatives

John McCullah, president of Salix Applied Earthcare in Redding, CA, is well aware of the many environmentally sensitive ways in which engineers can protect streambanks. And he should be. He pretty much wrote the book on the subject.

Salix recently completed a three-year research project commissioned by the National Cooperative Highways Research Program, a division of the National Academy of Sciences. As part of the $350,000 project, Salix studied all the environmentally sensitive methods of stabilizing streambanks that the company could find and eventually compiled information on 44 different methods. The National Cooperative Highways Research Program will distribute this information, which is now in the final review phase, to highway departments across the country.

The result of the research is E-SenSS, which stands for Environmentally Sensitive Streambank Stabilization. E-SenSS is a book and CD created by Salix and filled with highly detailed information on the many alternatives highway engineers now have when it comes to halting erosion along rivers, streams, channels, and lakes. McCullah says that the highways research program is dedicated to passing out from 4,000 to 5,000 copies of the book and CD. Officials with the program then want Salix to continue marketing additional copies of E-SenSS across the country.

The manual and CD are no light reads. The CD contains, after all, 44 technique guidelines, 19 special topic documents, and a total of 56 technique-typical drawings in both AutoCAD and MicroStation format.

“The basis of this entire project was a problem statement written several years ago by various departments of transportation across the country. The highway engineers said that they didn’t have the tools to protect streambanks in any way that would be environmentally sensitive,” McCullah says. “They were going with riprap and concrete in all situations, even ones in which more environmentally sensitive techniques would have been effective.”

While conducting its research, Salix found a number of stabilization alternatives that were woefully underused. As an example, McCullah points to what are known as redirective methods. As the name suggests, redirective techniques bump high-velocity sections of rivers away from banks. This is a method that most engineers rarely consider. This isn’t surprising; most stabilization techniques focus on ways of restricting a river’s high-velocity areas, not redirecting them.

But redirective techniques, McCullah explains, come with several benefits, the main one being that they are less intrusive on the surrounding environment. Contractors can more easily vegetate a river’s surrounding banks when they turn to redirective methods.

The rock vein method is one of the main forms of redirection, McCullah says. It’s also deceptively simple. Engineers create a small rock arm that juts out into a stream or river. This simple technique effectively guides a high-velocity flow away from eroding banks.

McCullah also notes that bendway weirs are another effective alternative in the same vein. These are entire fields of rock jetties that stick into rivers at precise angles. Many of these have already been built in Kansas, California, and Indiana, McCullah says, and they have proven especially effective in forcing high-velocity flows away from banks. One particular success story took place at Buckeye Creek in California.

The creek, which abuts the Dunnigan Burn Dump, a closed disposal site, suffered extreme erosion as a result of winter storms. Burn ash and solid waste seeped into about 500 feet of the creek and floated downstream during periods of high water. To solve this problem, McCullah, along with hydraulic engineer David Derrick and soil bioengineering contractor Doug Hanford, designed a solution that called for the installation of 13 weirs and more than 2,300 feet of longitudinal peaked-stone toe protection along the exposed bank.    

The E-SenSS CD not only holds information on such alternatives but also contains information that engineers can use to turn traditional riprap into a more natural-looking solution. For instance, they can use willow and cottonwood pull plantings to make riprap more aesthetically pleasing.

“Hopefully this product will provide highway engineers some of the tools they need,” McCullah says. “They certainly realize that they do have a need for it. Environmental permitting and regulations can be large obstacles to many engineering projects. By getting these alternatives out there, we have an opportunity for some real win-win situations. I know I’m excited by this. I’ve been teaching some of this information for several years. I hope that the engineering community embraces it.”

Spreading the Word

McCullah needn’t worry about Sherri Dunlap. She has long embraced bioengineering when it comes to stabilizing streambanks. Dunlap is manager of applied technology and new products for the Harris County Flood Control District in Texas. The district is responsible for protecting about 3,000 miles of channels, which means officials have lots of room to experiment with a whole host of engineered products.

Dunlap can quickly reel off the types of erosion control techniques her district uses: gabions, gabion baskets, mattresses, side inlets-the works. The district also turns in some cases to articulated concrete blocks. Dunalp is a fan of these: the blocks function as well as concrete, but the district can easily grow vegetation over them to effectively make them disappear from the public view.

But the main tool Dunlap and her peers turn to is vegetation. The district relies on some sort of vegetation, mostly grass, to stabilize the banks along its many channels. The reasons are simple: vegetation is beneficial for the surrounding environment and it is far more visually appealing than is riprap or concrete.

“The goal for us is to get all of our projects back to some sort of vegetated state,” Dunlap says. “People do not want to look at something that looks like an engineered erosion control project. We want something that is doing its job, but in the background, where no one notices it.”

Much of the soil in Harris County is highly erodible, and erosion control is a major focus of the flood control district. To meet this challenge, the district still turns at times to traditional riprap, but when it is used, workers always bury it beneath the ground. In other cases, the district relies on cellular confinement systems.

Dunlap is also exploring more unusual methods of erosion control. For example, the district is experimenting with using compost as one means of building up streambanks. “A third of the county has truly dispersive soils,” Dunlap says. “They are extremely susceptible to erosion. It can be difficult to find what works well for that kind of soil. So we are always experimenting with new methods.”

This is a big change from the way the county approached flood control when Dunlap first arrived. “When I came to flood control 10 years ago, we didn’t know a thing about growing grass,” Dunlap says. “If you are depending on vegetation to be your primary means of erosion control and you don’t do it well, you have a problem. Fortunately, we’ve gotten a lot better at working with vegetation.”

The Alternatives Keep Coming

There are a lot of people like Dunlap out there, engineers who want more alternatives for stabilizing streambanks. According to industry pros, they won’t have to wait long. Al Florez, vice president with Houston’s GeoProducts LLC, says his firm is well aware of this demand.

“We quite often get phone calls from engineers who are looking for options,” Florez says. “Part of it is due to them trying to get an alternative that is aesthetically a lot nicer. A community doesn’t want to see riprap in a stream running behind expensive homes. Community members are looking for something that can be filled with soil and vegetation and still handle the velocity of the water.”

GeoProducts manufactures a three-dimensional cellular confinement system that is receptive to vegetation. Florez says engineers across the country are interested in the product because of its aesthetic benefits. “When we talk to engineers they are very pleasantly surprised that there is something else out there that has been proven to work,” Florez says.

There are times, of course, when engineers must turn to more heavy-duty products, especially when they are dealing with highly dispersive soils. Such soils require more than a surface treatment of vegetation. This is where companies such as Modular Gabion Systems come in. Its gabion basket units are strong, providing solid support to dispersive soils. But they also allow for revegetation after a project is completed.

“We are called in to do the heavy hitting,” says Wilkins from Modular Gabion. “But the good news is that we can provide this structural support but still offer something that can be aesthetically pleasing.”

Many manufacturers are offering engineers a combination approach-both soft- and hard-armor techniques. Maccaferri, for instance, is well known for its gabions, a hard-armor erosion control solution. But the company also offers logs and natural blankets to be used in conjunction with its gabions.

“We have made it a corporate policy to try and alter and introduce new products that embrace bioengineering,” says Showan. “We view it as being a combination of the benefits of traditional products and natural materials and live plants. It provides an overall system. The total is more than the sum of its parts.”

A Mixed Bag

Things looked grave for Intervale Country Club back in 2000, the year in which Gove Environmental Services first began designing solutions to the erosion problem the club faced. The banks along the Merrimack River, in fact, were eroding so quickly, the river threatened some of the club’s fairways.

“There were some 30- to 40-inch-diameter pine trees that you used to, according to some golfers, be able to drive a car around on the river side. When we got to the site, the top of the riverbank was at those trees,” says Randall Shuey.

Gove identified several reasons for the erosion. One of the biggest was that the river attracted scores of boaters and water skiers. As they zipped across the water, their motorboats and Jet Skis helped accelerate the erosion process. Of course, once Gove identified the problem, its engineers had to meet the more challenging task of developing an environmentally sensitive way to solve it.

When studying the club’s history, Gove discovered that in 1997, engineers had completed a previous bank stabilization project at the site. At that time, workers cut down trees alongside the river’s bank, graded the slope, and applied riprap to its bottom half and erosion control blankets to its top half. That, though, didn’t stop the erosion, and in 2000 Gove took up the challenge, designing a plan that would incorporate a mix of stabilization methods to halt the erosion of 1,000 feet of riverbank.

To do this, Gove engineers studied the river during several seasons.  Shuey and his engineers wanted to see how the river acted during the spring flooding season, how much ice came through it during the early spring, and how much recreational use it attracted in the summer.

Once the company created a plan to attack the erosion, it had to alter these plans so as not to impact the bald eagle habitat along the river. “I think that resulted in a better design, though,” Shuey says.

Rather than cutting back a number of slopes along the river, Gove engineers instead set out to save as many trees as possible, especially some impressive pine varieties. By the time planners finished their alterations, Gove managed to save nearly 90% of the trees. The company even hired an arborist to clean up the trees after construction ended in 2002.

Gove’s basic plan was to protect the toe of the riverbank with hard armoring. Engineers then planned to grade the slope back slightly, depending on how much room they had, and grade out the river’s slope. The company planted vegetation over the hard armor, which, in this case, happened to be vegetated gabions. Working during the less-than-ideal summer construction period, the company’s workers planted non-dormant growing plants, something they had to do to avoid working in the winter season when the bald eagles would be nesting. The plan also called for the planting of thousands of live willow stakes. In all, Gove added about 4,000 shrubs and about the same number of willow stakes to the streambank.

The company also created a new management plan for the country club to follow. The plan states that landscapers should no longer mow to the very edge of the riverbank. It also states that they should no longer throw brush or debris over the side of the bank.

“This project was a real balancing act,” Shuey says. “We had to balance saving trees with stabilizing slopes. We had to consider how to protect the bald eagle habitat. Fortunately, everyone worked together, and everyone is pleased with the results.”

About the Author

Dan Rafter

Dan Rafter is a technical writer and frequent contributor.