The projects detailed in this article are examples of revegetating landscapes that are subject to significant soil erosion using carefully selected seed and, in many cases, soil amendments. The oldest “natural” type of best management practice (BMP) on Earth is becoming an increasingly highly engineered solution to problems created by, or affecting, human activity. Erosion control contractors and materials suppliers can’t afford not to refine methods and materials as budgets and environmental regulations continually tighten.
It was initially believed that SR 330 would take up to two years to repair. Caltrans officials acted quickly by releasing three contracts. Contracts for work on the two lower sections were awarded to Skanska USA Civil West California District Inc., and the contract for the upper section was awarded to SEMA Construction Inc. The initial cleanup work was performed by Skanska to provide clear access for construction crews, Caltrans, emergency services, and the US Forest Service (USFS).
Pacific Restoration Group Inc. (PRG) was contacted by Skanska and SEMA and asked if PRG would join the team as one of the subcontractors to provide habitat restoration and erosion control. PRG works primarily in southern California, specializing in public works projects, according to John Richards, president. About 70% of the company’s sales come from highway, landscaping, and revegetation projects, and 30% are strictly erosion control-mainly hydroseeding, Richards says. The SR 330 work would be a typical project for PRG, at least in the sense that it was publicly financed. The Federal Emergency Management Agency paid 75% of the cost of the repairs, with the state, local counties, and local communities covering the remainder of the total cost.
The combined projects grew to a $1.78 million emergency reconstruction of a 13-mile stretch of SR 330-which had failed in multiple slopes at three major road areas due to heavy runoff from the storms-at elevations of 1,900 to 5,550 feet. The drainage system in the area had been overwhelmed because the existing culverts and pipes were aging and of insufficient size, according to Richards. Skanska and SEMA bid the three emergency contracts to Caltrans with the stipulation of mobilizing within days. PRG’s first call in February 2001 came from the prime contractor, SEMA, on a Friday-a day after the bid was submitted. PRG was to meet with Jeremy Wiest, SEMA’s project manager; Azzan Saad, Caltrans vice president; and USFS staff the following Monday to begin work.
Two weeks later, PRG got a call from Skanska requesting erosion control services as early as April after an 11-foot-diameter drain culvert and 80 feet of fill were completed. Initially, PRG was to provide just hydroseeding but increased its services to include installing coir fiber rolls, streambed hand-seeding, planting locally collected cuttings, installing erosion control coir blankets, temporary application of Profile Products’ Flexterra HP-FGM (High Performance-Flexible Growth Medium) hydraulic mulch, and subsequent hydroseeding.
On the SEMA project, PRG provided much more than erosion control work from February to November 2011 on multiple slopes covering a 7.9-mile stretch of the road. Construction work included temporary BMPs for the stockpiled soil that was removed from the road, excavating the eroded slope several hundred feet down, grading, installing soil-filled gabions, and seeding. SEMA also had PRG assist with the installation of additional culverts and riprap dissipaters at inlet pipes to slow potential runoff and promote native habitat.
Richards recalls that many of the slopes were eroded down to 1:1 and, in some locations, nearly vertical. He also recalls that PRG often had to transport its equipment 200 to 300 feet down slopes to regrade them. “Even when they were done, a lot of the finished slopes-we tried not to exceed 2:1, but some of them were 1:1,” Richards says. “So gabions, fiber rolls, and subsequent seeding were a challenge.”
On the Skanska projects, PRG provided installation of coir fiber rolls on slopes and coir blanket along the City Creek streambed, planting of native cuttings, and application of temporary Flexterra. The permanent seeding and Flexterra cover were applied in the fall on all three projects.
Strict Material Selection Criteria
The USFS provided Caltrans with specific Notice To Proceed letters for each contract section. The soil used for backfill had to be native. The USFS set strict guidelines for types of erosion control material limited to coir (coconut fiber) or wood excelsior with organic netting. The seed species had to be from same geographical area to avoid introduction of plant material that could have degraded the genetic integrity of the native species. Additionally, no products could be used that could potentially migrate into the City Creek watershed and impact mountain yellow-legged frog habitat. Additionally, the permanent seeding could not occur until October 1.
The erosion control work included the installation of coir fiber rolls and other erosion control BMP solutions. PRG seeded slopes and applied Flexterra HP-FGM to the slopes upon completion of the projects in May and June to protect the slopes and slow runoff. PRG and Caltrans presented this product to the USFS as an alternative to the blankets required in the Notice To Proceed. “Caltrans’ staff was an important key to approving the Flexterra,” Richards notes. Through the efforts of Profile Products’ Doug Graham and S&S Seeds’ Bruce Berlin, PRG obtained critical information on the use of Flexterra near waterways. PRG initially proposed a spray-on product because of the rough, uneven grade, and access limitations for temporary application at a minimum.
Flexterra is a biodegradable material consisting of recycled and “thermally refined” wood fibers, crimped interlocking manmade biodegradable fibers, micropore granules, natural cross-linked biopolymers, and water absorbents that provides flexible slope protection. The material requires no cure time and is designed to establish turf very quickly. The gabions, grading, revegetation planting, fiber roll installation, and temporary Flexterra work was completed-preliminarily-by the end of June 2011, six months ahead of initial estimates.
Richards says the type of seed used was subject to strict selection criteria on the project. Within days of meeting with Caltrans and the USFS, a tentative species list was provided to PRG. PRG immediately contacted S&S Seeds, which was under an existing contract to collect seed for another Caltrans project in the Big Bear Basin at the Route 18/38 Dam. As with the emergency projects, project-specific requirements were enforced for a special seed collection initiated in 2009. Unfortunately, the elevations and watershed were different for the emergency projects.
S&S Seeds provided a potential seed mix based on Caltrans’ list. Biologists for both Caltrans and the USFS-the latter of which has jurisdiction over some of the land-agreed on the seed species that would be planted on a total of 10 acres. Richards recalls that seed had to be taken from an acceptable geographic region surrounding the project and from roughly the same elevation. The final seed mixes were developed for slopes above a 4,000-foot elevation and below a 4,000-foot elevation. Two other mixes were developed for the Caltrans property above the USFS 4,000-foot-elevation area and along the City Creek streambed.
“In the USFS areas, they had us broadcast seed only and rake to the top one-quarter to one-half inch,” Richards says. “In Caltrans property areas, we hydroseeded with the Flexterra using the Caltrans standard two-application method. Timing is critical to erosion-stabilizing vegetation and the project’s ultimate success, and the USFS knows this from experience. As part of the requirement, no seeding could be performed until after October 1. This created a significant effort to protect the already prepared-and expensive-slopes. Thus Caltrans had us apply 3,500 to 4,000 pounds of Flexterra per acre over approximately 8 acres of the slopes for temporary erosion control.
“On that job, we applied well over 10 acres of Flexterra for erosion protection, and then we came back in October to seed 8 acres” to adhere to the USFS requirement of no seeding prior to October 1, Richards continues. “The USFS and Caltrans agreed to have all of the previous Flexterra hand-raked off, fiber rolls with any collected sediment cleaned, hand-seeding, and a cover application of Flexterra reapplied. S&S Seeds provided a recommended bagging of seed species based on their type, weight, and size. Since we were hand-seeding, it was critical to get an even disbursement of seed on each slope.” PRG premeasured each slope to ensure that the correct seed amount was applied.
Logistically, the project was particularly difficult for the first two months because the road was completely closed, Richards says. Crews had to get to the job site from an alternate road, Route 18, and descend in elevation to the job site. “What would ordinarily be a 30-mile drive turned into a 60-mile drive one way just due to the access to the site,” he says. “So that they could get the slope of the lower section rebuilt, they opened up the road to just construction traffic and emergency services. Although much work still needed to be completed after the culvert and slope repair and the road replacement, Caltrans opened Route 330 to local traffic at the end of May. Once they did that, we had time limits. We had two crews working 12-hour shifts seven days week for several weeks straight. And, of course, it snowed, so that shut us down from one activity for a couple of days and added other work, like snow plowing-so these were very challenging projects, that’s for sure.”
The Skanska projects were located down the road over a 4-mile section ranging in elevation from 1,900 to 3,600 feet. A large slope that had been badly eroded by a creek-turned-raging-river due to the heavy rains was repaired with 80 feet of fill on a slope that was steeper than 2:1. PRG was not actually contracted for any construction work but, rather, revegetation of the slope with Flexterra and native seed collected below the 4,000-foot elevation. The seed mix consisted of quick-emerging native grasses, annual wildflowers, and shrubs.
The Skanska projects were difficult in their own unique ways, Richards notes. “It was pretty much the same constraints at a lower elevation, so we would get hit with snow there, but I would say the slopes were much higher. It made for a steeper working environment for our crews. There was a combination of rock-filled gabions and slopes-much different from the SEMA upper-elevation slopes that were shorter and had adjacent tree canopy.
“With respect to erosion control, all three contracts were treated similarly in methods and materials, so the only thing that was different was the fact that it was a lower elevation, so we used a different seed mix,” Richards continues. “Basically, the 330 job had four different areas, and each area had a unique seed mix just for that slope. When we were working with the Forest Service and Caltrans’ biologist, Jason Bills, they went back and looked at their historical surveys. Some of the seed mixes that grew up there were pretty good, but they said that some were located 3 miles away-they’re not on the slopes, so we don’t want to them in this area. So that was unique. On the lower project, Skanska did all of their own grading and they took care of all of the civil work. We did the seeding with the Flexterra-3,500 to 4,000 pounds per acre.”
Richards thinks the Flexterra was a good fit for these projects. “It holds the soil almost as well as erosion blankets, but it works well with culverts in harsher environments where you can you can have slopes,” he says. “With erosion blankets, you have to really strip slopes, because if you have any gaps, you get erosion. Where the Flexterra works nicely is if you do have rocks or undulations, it adheres right to the soil.” He adds that the system adhered to the requirements of the USFS, which avoids the use of netting products that could potentially break down and trap the yellow-legged frog.
PRG’s seed provider, S&S Seeds, worked with Caltrans and the USFS to develop special mixes that were acceptable to both agencies. It took several weeks to obtain approvals on the seed mixes. Seed was collected from the areas near the job sites, and then it was cleaned and prepared for use in October. The USFS rejected the use of fertilizers as well as compost.
Richards reports that the improvements, including the erosion control work and revegetation, are faring well. “The thing about the Flexterra-it does hold up for an extended time to protect the soil,” he notes. “The seeds, most of them, are coming up pretty well. On both projects, the Flexterra held up exceptionally well. They have harsh, steep slopes, so it’s going to be a few years before it fills in completely.”
Developing suitable seed mixes constituted a big challenge on these projects, Richards says. It involved several coordination meetings with Caltrans and the USFS to develop the mixes. Actual seed availability was another matter entirely. “We can come up with a mix we want, but if the seed is not available, it doesn’t matter,” he says. “It was good working with S&S, to have them on board. They have an extensive seed inventory, but you never know when these types of projects might come up-you could never plan for them. And the Forest Service has strict guidelines; in California, at least, they want seeds that come from a similar elevation and within the same watershed area.
“Since the seed is permanent and hard to remove if selected improperly, that’s the biggest challenge-finding and developing a seed mix that is acceptable and will work in the area. You only have seed viability for so long. These weren’t giant jobs; it’s just that there were a lot of constraints that made them unique.”
Landscaping Makeover: Utility Edition
Significant soil erosion is obviously not an ideal situation at an electric utility, considering the critical infrastructure contained on a site. Rectifying significant erosion at a substation in Union City, GA, was the challenge that Georgia Transmission Corp., a firm that constructs and maintains high-voltage power lines and substations for electric cooperatives in Georgia, recently faced. Permanent revegetation turned out to be a key erosion control tactic used on the 46-acre site to prevent future erosion.
The facility was constructed in 1969, and by fall 2011 was approaching the end of its useful life. Georgia Transmission undertook a process of getting the site back to a consistent elevation and permanently stabilizing the soils. Over the years, the site had experienced some drainage problems, thanks to the presence of a variety of soil types from sandy soils to Georgia red clay, and to hilly terrain. Rick Lipcsei, civil project manager for Georgia Transmission, noted that the company had to repair eroded banks by working a little deeper in the soil profile than it usually does, due to the extent of the erosion. Additionally, corrugated metal pipe used in the storm drain system had begun to deteriorate, and Georgia Transmission did major repair work on the whole substation pad area, filling the subgrade with 18,500 tons of graded aggregate base and 4,000 tons of No. 89 stone.
“We ended up scraping back a lot of the gravel and removing a lot of the soil that was in there for all those years,” Lipcsei recalls. “We used that material to build some roads and a retention pond and get it down to the pad and use that for structural fill.” Lipcsei adds that some of the site had grass cover, but getting new grass to grow in the site’s soils appeared to be an iffy proposition.
Lipcsei and Georgia Transmission consulted with Pennington Seed Co., which worked to develop a proprietary, fast-growing, low-maintenance seed mix tailored to the site. “It would be a permanent mix with very low maintenance,” Lipcsei says. “A lot would depend on what fell out of the sky.”
Besides developing a seed mix, Pennington also recommended using a combination of stabilization materials, including Profile Products’ Flexterra HP-FGM and GreenArmor System. A total of 7.2 acres was seeded in the retention pond, roads, and erosion areas outside the fence.
The GreenArmor System combines Flexterra with Enkamat turf reinforcement mat (TRM) and provides a permanent, open matrix. This combination bonds the soil and seeds together, protecting against elevated levels of hydraulic lift and shear forces while accelerating turf establishment and long-term root reinforcement. One location where the GreenArmor System was particularly needed to maintain the slope was a vegetative swale measuring 350 feet long and 20 feet wide with a vertical drop of 12 feet. The flows going through the swale will come through at moderately high velocity, Lipcsei notes.
He adds that the Flexterra was sprayed directly onto the Enkamat and the Slopemaster seed mix was then planted. “As the seed germinates, the roots grab right onto that Enkamat, and it provides you with enough strength to carry the shear stresses from the flow,” he says.
The Slopemaster seed mix that Pennington Seed provided contains proprietary seed varieties and Durana white clover for permanent vegetation. The Durana found in each mix forms a thick, water-penetrable mat that holds highly erodable soils in place and generates up to 150 pounds of nitrogen per acre annually. The mix is designed to provide permanent and sustainable vegetative erosion solutions for slopes in areas such as construction sites, retention ponds, pipelines, powerline rights of way, and roadsides. The mix is engineered for erosion control in areas where soil conditions and fertility are poor and rapid establishment is necessary with little or no follow-up maintenance. The provider custom-blends a product of durable and adaptable legumes and grasses for the various climatic regions of the country.
At Union City, Pennington Seed provided a Winter Slopemaster Mix containing rye grain, Durana clover, Greystone fescue, Mohawk Bermuda, and Pensacola Bahia. The mix, like all Slopemaster mixes, was inoculated with MYCO Advantage and Germax seed coating, which are engineered for increased germination and long-term sustainability. Pennington chose this mix formulation because the site is in the southern Piedmont region, and the long-term vegetation is usually warm-season perennial varieties. This mix contained cool-season temporary and permanent varieties as well as warm-season perennial varieties for long-term coverage. “It’s more of a cool-season grass,” Lipcsei says of the mix. “The soil temperature is a little bit cooler and if you get it established in the fall, it generally it makes it through the next hot summer.”
Lipcsei describes Flexterra as something like a “spray-applied blanket. It cures very rapidly in one or two hours in case you get a high-intensity rainstorm. We were looking at something that would get us through one to two growing seasons. Here in Georgia, we’ve dealt with everything from severe droughts to thunderstorms and high-intensity rainfall.”
A 14-14-14 fertilizer from Howard Johnson Enterprises containing Nitroform was also used after seeding to provide uniform growth and sustained feed. Lipcsei says Georgia Transmission uses soil amendments based on comprehensive research. “Before we start these projects, we get soil samples done and we send them to the extension service at the University of Georgia. The extension gives us the fertilizer and nutrient mix that we need to use. That’s why we got the 14-14-14 for this project.” The entire project was expected to be completed in the second quarter of 2012.
Working around high-voltage equipment presented some challenges, Lipcsei notes. “The biggest constraint was that this is an energized substation area. We have voltages from 115,000 all the way up to 500,000 volts coming in and out of that station, so we had some obstructions in terms of actually removing the soil from inside the pad. The station was in service the whole time, so we had to be very careful about that. We had a lot of obstructions when we were doing our erosion control. We had a lot of transmission towers and guy wires throughout the site-that proved to be a little challenging.”
Aside from the pad and revegetation work, the stormwater pipe rehabilitation work presented another challenge, he says. “The stormwater system had deteriorated and we couldn’t do a normal cut-and-cover operation. To repair the pipes, we actually used a cured-in-place system with a liner inside the stormwater pipes.” Georgia Transmission replaced nearly 6,000 feet of 18- to 48-inch-diameter pipe that way.
Lipcsei advocates the customization of a seed mix to a given site to ensure a successful revegetation project. “The biggest thing is to learn exactly the characteristics of your slope by doing an analysis early on so you can determine your nutrient and fertilizer design as well as your seed mix, what you have to work with,” he concludes.
