“The bridge is 275 feet long, from abutment to abutment,” he explains. “There are four main piers that are within the creek during heavy flows, and two main piers that are in the creek pretty much 100% of the time.
“Our contract was to do the HEC-RAS modeling analysis. The government’s intent was just to add some riprap to this location for some armament around the piers for some erosion control.” HEC-RAS, for Hydrologic Engineering Center River Analysis System, is a hydraulic modeling program developed by the US Army Corps of Engineers.
“After we did our HEC-RAS modeling, we found that due to the amount of runoff from a 100-year flood-this being a collection point near springs, neighborhoods, and industrial areas-erosion depth reached a depth of 15 feet. So the riprap wouldn’t work with the velocities involved,” Tourville continues. “So we had to hit the drawing boards again. We contacted International Erosion Control Systems [IECS] and their distributors, and some others as well, to try to figure out the best way to get the government what they wanted, because the alternative was to use 5- to 6-foot riprap and going down 15 feet. That would have undermined the footings of the piers.
“We ended up selecting the IECS CC90 mat, leveled the creek bed, and we went up about 60 feet on either side of the bank. We laid the CC90 mat down and anchored it along the upstream and downstream side every 4 feet.” The Cable Concrete articulated concrete block mat is a flexible system of concrete blocks connected with cables.
“From an engineering perspective, the CC90 is one of the heaviest mats on the market. The issue with this creek in particular is the high velocity it reaches, so it has the potential for a lot of uplift. The engineers therefore wanted a lot of weight.”
Tourville notes that existing riprap on the creek banks will be recycled on top of the mats, which will be placed over the top of the pier footings, extending to the top of the stream banks.
He adds, “A lot of permitting needed to be done – a permit from the Corps of Engineers, a FEMA permit, the state and local dewatering and water discharge permits. We had to apply for a no-rise permit from FEMA, to show that we’re not going to change the flows of the creek, by adding material or removing material.”
Stabilizing a Railroad Ravine
The Southeastern Pennsylvania Transportation Authority (SEPTA) operates a passenger railway, and a stretch of track in Gwynedd, PA, had suffered from erosion along very steep hillsides mere feet from the tracks.
“There had been some erosion on the hillside that caused delays, but so far no injuries as a result,” says Deborah Johnson of Geobrugg North America. “The redesigned project was for a mesh drape pinned at the bottom. The interesting thing about this project was the night construction. Because the slopes are along an active track for a passenger railway, they could not interrupt the daytime schedule for commuters.”
John Szturo of infrastructure consulting firm HNTB worked on producing a solution for the railway. “SEPTA had a speed restriction on their trains through this narrow rock cut,” he says. “They wanted to stabilize the rock cut. While they were in there, they wanted to stabilize some slopes where they had been having erosion problems.
“We stabilized the rock slopes, scaled them, and put some Geobrugg product on them. On the soil slopes, we cleared and grubbed those, regraded, and then put down TECCO mesh and planted vegetation over them. We did have to work around the catenary lines, the electric lines that powered the trains through there. In addition, there was an historic 6-inch rainfall around the beginning of the project, which was a pretty big challenge.”
Szturo seemed to have a clear idea from the start what he wanted to use for this project. “I don’t think we really considered anything else,” he says. “We asked the Geobrugg representative to come to the site, and they evaluated it along with us. They suggested some products that they had, and we selected the TECCO mesh.”
Johnson notes that remnants of a large hurricane passed through the region, washing out a portion of the hillside. The TECCO mesh, however, held firm.
Pervious Pavement in Georgia
A private residence in Sandy Springs, GA, needed a new 400-foot driveway, but because of a buffer zone related to an adjacent creek, additional impervious material could not be used. An asphalt driveway, built some 30 to 40 years ago, had been in place but was already gone by the time Nustone Technologies was called in to install the new surface.
Steep hillsides erode along a commuter rail line.
A representative of Nustone examined a variety of options and settled on the Gravelpav2 system, from Invisible Structures. It’s a ring and grid structure, with rock fill material placed within the rings, that allows 100% water passage. It also has a geotextile fabric that is injection-molded to the underside.
“I had some experience with it, perhaps 12 to 15 years ago, with a previous contractor that I worked for,” notes the Nustone representative. “I like the way this Gravelpave system works. You can cover a large amount of area. There are some other systems out there that use individual pavers that are 18 inches by 18 inches, and it’s the same basic principle, but you don’t get the coverage as you do with Gravelpave. One other system that I looked at didn’t have a geofabric attached to it already.”
The geofabric that attaches to the underside of the Gravelpave2 structure helps to keep out silt and prevents the growth of weeds through the honeycomb ring material.
The Nustone contractor explains the makeup of the system: “We’ve got a layer of about 4 inches of 89 stone [a coarse material roughly between one-quarter and three-eighths of an inch in size], which is screened, and clear stone over 6 inches of crusher run, and that’s our base system. I’ve also got some French drains running through the driveway as a backup. Then I’ve got the Gravelpave system attached with nails. Then there’s an inch and a half of decorative gravel that goes on to the gravel base surface. You can run fire trucks over it. We’ve driven loaded concrete trucks over it and haven’t had an issue.
“It’s flat, but it looks like a gravel road,” he continues. “I’ve got some natural river rock on top, so it’s a really good-looking stone. There’s some angularity in the stone-it’s always better to have angularity in your stone, because it compacts a lot better than a round stone does.
“The system had to be approved by the city of Sandy Springs. They dictated what we could and could not do around the area. They were perfectly happy, and actually quite glad to see us doing what we did. We also had city erosion control to work with, the city inspectors to work with, and the city engineers were involved. There were a lot of municipal groups that had to be satisfied for us to be able to do anything.”
The installation went quickly and was nearly trouble free. The only difficulty was that “It doesn’t want to bend. This driveway was winding through woods and around a creek, so it’s difficult to get it to bend. We have a lot of cuts. Also, you’ve got to nail it down a lot, otherwise it does tend to want to pop up. But it still looks great.
“You have to maintain it; it’s got to be raked. After a period of driving over it, this will move the rock around a little bit, so you can see some of the honeycombs. But a quick rake, and it looks brand new again.”
Although more than 7,000 square feet of Gravelpave2 was installed, the job was completed in about a day and a half.
Fish, Bears, and Culverts
Just minutes away from Tacoma, WA, and less than an hour from Seattle, quaint Gig Harbor lies at the south end of Puget Sound. It has miles of shoreline, deepwater bays, and scenic islands.
It also had decades-old culverts on Warren Creek that were badly in need of replacement.
“There were two 24-inch culverts that were put in in the 1940s,” says Helmut Schmidt, project manager for Pierce County Surface Water Management in Tacoma. “Of the two culverts, one of them was horribly impaired-it sagged-and the other one was partially blocked also. They were 150 feet long. There was too much culvert. It was a velocity barrier, and a passage barrier for fish.”
Ryan Heathers, project manager for Active Construction Inc., adds, “During times of flooding, what had happened is that a bunch of silt was carried along, and it plugged up one of the culverts altogether. Then it was just down to one remaining culvert that was flowing, and it was causing backup and scouring.”
The culverts were located in a narrow gorge, with a roadway about 38 feet above the stream. The decision was made to replace the aging and damaged culverts with a single, larger passageway. The project began in the fall of 2011, with the roadway shut down to allow for removal of the existing culverts, installation of the new culvert, construction of a new support for the road.
“We had to move about 11,000 yards of material to get down to the ravine and existing grades,” says Heathers. “The new culvert that was put in was 67 feet long and approximately 20 to 25 feet high.
“The culvert itself sat 10 feet below the streambed elevation. We put 10 feet of fill back in the culvert to get to streambed elevation. That was a requirement that was put on by Pierce County Surface Water by the [Washington State] Department of Ecology. I think a lot of it is to prevent scouring, to avoid getting that embedded in the stream. The culvert’s not going to go anywhere.
“The new culvert went in, and at the edges of the new culvert were the MSE [mechanically stabilized earth] wall, wire baskets, and Tensar grid that went vertically from the outside limits of the culvert, vertical to the road. That’s what held the road up.”
A partially blocked culvert on Warren Creek near Gig Harbor
Schmidt adds, “We wanted to go for a softer approach, something that would fit in more with the environment out there. There was a biaxial and a uniaxial material that was supplied by Tensar. They basically make giant pillows, and they’re stacked on each other. There is geogrid underneath. You put the soil on top of that, and then you wrap it around the top, and then you put your next layer on.
“This was a very, very narrow site, a ravine. So access with equipment was an issue. That style of construction was very conducive to that. Also, the culvert was at a skew. Typically, when you do that kind of a culvert, you’d like to go perpendicular to your wall. But we were at a skew, somewhere around 34 degrees. That skew angle also affects how you construct your wall. That was one of the major challenges we had, and Tensar worked with us on that.
“It was very cumbersome to actually work down in there,” he adds. “When the culvert was set, the contractor-Active Construction Inc.-did a fabulous job. They had to attack it with two separate crews, because until they got beyond the top of the culvert, they were filling both ways. They used a telebelt, a large conveyor belt that brings down the material for the backfill.”
Another situation that had to be addressed was the temporary rerouting of the creek during construction. As Heathers describes, “We had to bypass the existing stream the entire time we were working. That included a primary bypass pump and a backup bypass pump. It was hooked up to a cell phone calling system, so if one of them went down, it went to the backup and we’d get phone calls.
“Then we encountered a lot of rainfall during all of September and into October. It was a big hurdle to get through while trying to keep the stream clean, with no turbid water going into the stream, yet we had to work in the stream. We had 40-plus-foot slope walls on each side of us, and it’s pouring down rain. So it presented a lot of issues, trying to keep everything clean.”
The stream bypass worked well, but during those heavy rains, there was a heightened level of concern.
“If it was just regular rain, it would be fine,” Heathers says. “But when we had large amounts of precipitation, the stream would surge. We were under the impression, along with Pierce County Surface Water, that the stream really wouldn’t surge much, that it would just soak into the ground. But in big rainfall events, the volume of water would double or triple. We did come close to breaching and having some discharges into the stream. We didn’t overall, but we came close.”
To protect the slopes of the ravine, a variety of other BMPs were used, including straw mulch, permanent erosion control mats, and wattles to slow down water. In addition, some areas were armored with spalls. Hydroseeding was used to apply seed.
Schmidt notes, “Everything got planted back with native material, all the plant species on the slopes, everything from devil’s club to snowberry, which are some of the native species we have out here.
“It looks fantastic now,” he continues. “It’s growing back in, the wildlife are using it. We put up a wildlife camera on the upstream end of it, and we’re seeing deer and raccoon using that passageway.”
“There is a lot of wildlife that runs along that area,” Heathers adds. “When we first got out there, we saw bear tracks in the stream. We thought it was a fluke, but they were known to be in the area. At one point in the job, mid-morning, a couple of our guys turned around and there was a bear crossing the road. There were a lot of times we were out in the forest about 5 o’clock in the morning, walking around in the dark down there in the creek, and there would be a bear close by.
“That’s one of the features of that large-diameter culvert. It allows for wildlife crossing at the stream rather than at the road level, 38 feet higher. So that’s a major benefit to traffic using that road, not having to share the road with wildlife.”
“What was really interesting about this site is that it has a road that bisects the property that is owned by one property owner,” Schmidt comments. “They own basically the bulk of the watershed. It’s an estuary system with a good upland habitat area that hasn’t been reconnected in more than 40 years. So this is reconnecting a lot of habitat that is still pristine. That’s hard to find now.”
Containing Buffalo Creek
The Village of Palatine, IL, is located in the northwest suburbs of Chicago. It lies in a wooded marshland with a number of streams within several separate watersheds, including the Buffalo Creek watershed on the town’s northeast side.
According to Danielle Walter of Crane Materials International (CMI), erosion problems had been occurring on a stretch of Buffalo Creek, a tributary of the Des Plaines River that runs between an apartment complex and individual homes.
“That creek doesn’t typically have water in it, or perhaps 6 inches of water,” she says, “but when the snow melts and there’s snow runoff, or if there’s heavy rain, it starts to fill up quite quickly and swell beyond its banks.
“They were having some issues with private property, such as the residential homes, and there is also a parking lot for the apartment complex on the other side. The water was eating into that private land. So the town needed to do something to protect the townspeople and their land.”
The Village of Palatine, with a history of independent and active citizens (who recently considered secession from Cook County because of high sales tax rates) became very involved in the issue.
“They had the residents vote on what product would be installed, what product they felt worked best for them,” says Walter.
One consideration was the very restricted site with tight property easements. “This project had very little space, because property was on both sides-very little space to install, and very little space to store the materials,” Walter explains.
After ample consideration, the town opted to use the SheerScape retaining wall system from CMI.
“The project is on a canal, which is very unusual for retaining walls,” Walter continues. “Typically, retaining walls can’t be exposed to water, because of scour. Because of the way our system works, with sheet piling, you can embed the toe of that sheet without using a foundation or footer, and you can embed it as far as the engineer feels he needs to go.”
In this case, the SheerScape panels were installed several feet below the existing grade to ensure that running water wouldn’t scour and undermine the structure.
Stephen Manning of CMI adds, “What’s typically done with retaining walls is a segmental block retaining wall, so instead of a block face, here you have a sheet pile face. Vinyl sheet piling has been used for many, many years, typically in marine applications.
“The sheet that we specifically used for our retaining wall has a flat face, so as you go along, it’s a flat wall. You don’t see corrugations like you would typically for a marine application. So it has a lot better aesthetics. It is quite unique. You drive it in the same, and you connect geogrid to the back of it, and it’s a typical MSE-type retaining wall.”
Walter explains that one of the requirements of the project was that the contractor fully finish each section before closing the site for the day. This meant rather than excavating the entire length of the wall and installing the sheets, crews had to work in small sections at a time.
The contractor used a Komatsu 228 excavator to initially excavate the soil behind the wall, and then replace the soil after installation of the geogrid layers. A mini-excavator was used to dig a trench for the wall panels.
The SheerScape sheets come in 24-inch widths and can be combined to achieve any length desired. For this Buffalo Creek project, both a standard wall and a tiered wall segment was used, for a more interesting appearance.
Michael Heer, SheerScape retaining wall manager, commented about the section of the wall that sits in the creek itself. “It’s embedded into the ground, a couple feet in the ground, at the water line,” he says. “The sheet pile has a 50-year warranty. The government’s done studies on it, and there are certain engineering parameters that say it has a 100-year design life, but the warranty is a 50-year warranty.”
Walter notes that the village was concerned about the ease of cleaning the wall surface. That was one of the reasons the residents selected SheerScape, with its textured PVC surface.
“They can pressure-wash it,” says Manning. “With any construction, you might get some soil that gets built up on it, and before they leave the job, they’ll pressure-wash it. The town wanted to know if that’s going to take away any of the textured surface, and that’s not an issue.”
Addressing the limited work room available, Manning adds, “Space was a concern, so they wanted to go with a grid system behind the wall. We do have other sheet piles that work in water applications, but the city chose this one for the aesthetics and for the fact that they needed to use a grid system behind the wall, not a typical anchored wall.”
For fill material behind the wall, onsite soil was used, as well as clean gravel placed directly behind the sheet piles.
Another element that aided in the project was the limited weight of the SheerScape. “Being a lightweight material really benefited the contractor,” says Heer. “They didn’t have to have big, heavy equipment carrying big rock pavers, that type of thing. The lightweight nature of the material surely helped the installation go smoothly. The project actually went a lot quicker than the contractor and the village expected. They were pretty impressed with the speed of installation.”
It’s unclear whether the “green” nature of this retaining wall played a part in its selection for the project, but Manning notes that the material used in manufacturing SheerScape is 90% recycled and 100% recyclable.
“In certain situations, that can result in additional funding for projects like this,” Walter says. She also notes that both the village manager and councilman came out to the site and were especially pleased with the appearance of the project, as well as its success in reducing flooding risk.
Although she frequently works with Department of Fish and Wildlife staff on various erosion control projects, Walter notes that for the Buffalo Creek work, it was not necessary. Even though a portion of the retaining wall sits in the stream, “The wall is not constructed of steel, so it doesn’t corrode, and it doesn’t have any chemicals that will wash off over time,” she says.
Author’s Bio: Steve Goldberg writes on issues related to erosion control and the environment.