Made of wood fiber and specially-formulated tackifiers and applied with hydroseeding equipment, a bonded fiber matrix can be used on most slopes, including near-vertical surfaces. It can be sprayed with seed, mulch and fertilizer or immediately after hydroseeding. The product matrix dries to form a continuous protective cover to protect bare slopes from erosion until newly-seeded vegetation can provide permanent control. In fact, it reduces evaporation and creates a micro-environment that helps promote plant growth. Grass and other plants are able to grow up through the voids in the wood fiber matrix. Once the product cures, this system remains in intimate contact with the soil and contours to minimize exposure to flowing water and the potential for rill erosion.

How It Works

"A bonded fiber matrix gives Landscape Contractors another tool for temporarily controlling wind and rain erosion on bare slopes until vegetation can establish and develop root systems to control erosion permanently," says erosion control consultant Mike Harding, Great Circle International, San Diego, Calif. He helped develop the first bonded fiber matrix in the early 1990s. "These systems tend to degrade at about the same rate that plants establish as soil microbial activity increases and starts breaking the matrix down. So you don't generally lose much net effectiveness in controlling erosion."

This slope from Bonita Canyon in Irvine, California was treated with grass seed and EcoAegis Bonded Fiber Matrix in October 1997. As this July 2000 photo shows (middle right), the only treatment required after the massive rains in 97/98 was installation of groundcover plants. At the bottom of the slope (bottom right) new work is being done during road development.

That cross-linker is the key to the product's performance. Without it, the matrix would lose its cohesion and erosion-controlling qualities when re-wetted by rain or sheet flows of stormwater runoff. Harding likens it to house paint. "Wet paint washes off easily," he explains. "However, once it dries, it won't wash away."

Bonded Fiber Matrix

Scott Johannes, general manager of Sanders Hydroseeding, Inc., Santa Ana, Calif., was involved with work to protect construction sites at Bonita Canyon, a residential subdivision being developed in Newport Beach, from the El Nino storms. He saw how the effectiveness of two erosion control methods varied. In October, 1997, before the El Nino rains began, his crews applied two different erosion control products to about 10 acres of bare, easily-eroded sandy soils on slopes as steep as 2:1.

After receiving 210% the normal seasonal rainfall during the winter of 1997/98, soil loss and rilling on this untreated slope (above and below) were extreme, as was the cleanup required. The severe rains caused underrilling with this blanket, resulting in significant soil loss and accumulation at the bottom of the slope.

Some slopes not likely to be developed for a year or two were covered with erosion control blankets. Areas scheduled for final grading and seeding by following within the next 6 to 12 months, were treated with a gypsum-based cementitious binder to stabilize the soils. It was applied with hydroseeding equipment at the rate of 4,000 lb. per acre . As early as December, the pounding El Nino rains had created rills as deep as 18 in. underneath the blankets. On untreated areas, runoff had slashed 3- to 4-ft. deep cuts into the slopes.

His crew re-treated about 1.5 acres of the bonded fiber matrix slopes and about five acres of the gypsum areas. "By April, the bonded fiber matrix had continued to control erosion well and the annual grasses were becoming established," Johannes says. "There was still quite a bit of erosion in the gypsum areas." No regrading was necessary on the bonded fiber matrix slopes. However, the gypsum-treated slopes required extensive and costly regrading and reseeding to repair them. Other than removing eroded silt, no work was done to repair the blanket-treated areas.

At Serenata, in Irvine, California, the slopes treated with the bonded fiber matrix showed no erosion after the rains, but the untreated flat areas and roadways required significant labor to control run off and rework to bring the areas back to building standards. The Bonded Fiber Matrix "controlled erosion well," according to Scott Johannes.

Gary Weems' experience with bonded fiber matrix products dates back to 1993. His company, Hydro-Plant, Inc., San Marcos, Calif., sprayed it on steep slopes at Laguna Beach, one of several southern California communities ravaged by wildfires that year. That marked the first commercial use of the material, where it successfully controlled erosion at this and other burned over areas when winter rains began a few months later.

Weems has since used fiber matrix products to successfully control erosion on a number of projects. They include one at Serenata, a residential development, in Carlsbad, Calif., during the El Nino winter of 1997-98. There, he used EcoAegis to protect about two acres in November, 1997. The > 2:1 slopes varied from about 100 to 150 ft. in length. "The soils are very erosive and turn to sugar when they get wet," he says.

He applied the product at the rate of 3,500 to 4,000 lb. per acre along with 50 lb. per acre of Plantago insilarus seed. "The combination of the two materials was the key," Weems says. "In addition to the soil protection provided by the bonded fiber matrix, the root structure of the plantago helped hold the soil for about three months until it died out."

He observed the treated areas and untreated areas throughout the winter. "The bonded fiber matrix treatment was a picture-perfect job and worked out extremely well," he reports. "In the untreated sections, even the nearly flat areas eroded as deep as 1 ft. and had to be regraded. However, at the bottom of the treated slopes there was virtually no eroded sediment." Unlike the untreated areas, the bonded fiber matrix treatment required no regrading or other work before landscaping was done.

A large industrial site at Moorpark, Calif., provides another example where EcoAegis bonded fiber matrix protected slopes from the heavy El Nino rains of 1997-98. Grading and excavation work left about 10 acres of exposed cut slopes around the perimeter of the 50-acre SDI site.

Composed of clay and sandy loam soils, the slopes were as steep as 2:1. In November, 1997, before the rains began, erosion control contractor Nature-Grow, Newhall, Calif., sprayed 3,500 lb. per acre of the material plus native grass and broadleaf seed on the slopes.

The slopes survived the winter of severe rain storms with very little erosion, and required no further work to produce a pleasing, natural appearance.

The Tool of Choice in Many Cases

A bonded fiber matrix absorbs the erosive impact of rain drops and foot traffic to hold soil, seed and fertilizer firmly in place. It bonds to most slope surfaces and can be applied by helicopter. Depending on topography and application technique, it dries to a thickness of about 1/8 to 1/4 in. The product can set up to protect a new seeding even when applied at near-freezing temperatures. Once dry, it forms a water-insoluble, porous protective cover to secure soil and seed while improving establishment of vegetation.

This type of product eliminates the labor involved with installing erosion control mats and there is no tenting or rilling that can occur when mats are installed improperly. As more and more landscape contractors are learning, a bonded fiber matrix product can be a cost-effective tool to get the job done, when other alternatives would come up short. LCM