Hydromulching is a common approach to post-fire erosion control. Water, wood fiber mulch, and often a tackifier are combined in a slurry and applied to minimize soil movement. If seeds (and possibly fertilizer) are added to the mix, it is referred to as hydroseeding.

Finn Corp. explains that hydroseeding is most commonly used for erosion control, to retain moisture, and to protect against damage from wind and rain. The elements that make up the hydroseeding slurry bind with the ground surface, allowing it to gradually revegetate and provide natural erosion control.

This hydroseeding or hydromulching mixture is typically applied via a hydroseeding machine. The Finn line of HydroSeeders, for example, runs the gamut from a small T-30, with a 335-gallon-capacity tank, up to the T-400, which can hold up to 3,600 gallons of slurry. Bowie Industries also produces hydroseeding units, and a number of other manufacturers offer similar equipment.

The Gap Fire
Late in the afternoon on July 1, 2008, a group of five teenagers started a fire in the hills above Goleta, CA, in Santa Barbara County. They claimed that they thought the fire had been extinguished before they left the area.

Unfortunately, it continued to smolder as the youngsters left. The fire eventually spread to more than 9,400 acres, and took nearly a month before it was brought under control. Hundreds of residents left their homes and four outbuildings were destroyed, but no homes were lost nor were any major injuries reported.

Forty-eight percent of the burned acreage in what came to be known as the Gap Fire was on National Forest property, and as a result, the Forest Service assembled a Burned Area Emergency Response (BAER) team to study the likely aftermath of the fire and to suggest treatment solutions.

This Gap BAER team determined that 76% of the burned area sustained “moderate or high burn severity” and concluded “Because the Gap Fire removed nearly all of the vegetative cover over the majority of the burned area, especially on steep slopes, there is high to very high potential for increased water runoff leading to flooding and debris flows. Runoff and sediment yield is expected to increase substantially during the first three years after the fire. Native vegetation will resprout, but it will take about five years for an effective vegetative cover to be reestablished.”

The report noted that property “at risk within or below the Gap Fire burned area includes homes and businesses, power lines, water pipelines, a water treatment plant, reservoirs, roads, bridges, orchards, the Santa Barbara Airport, railroad tracks, and Highway 101.”

Due to the very steep slopes and lack of access roads on Forest Service property, the Gap BAER team decided that aerial hydromulching offered the best opportunity to replace lost vegetative cover. The Forest Service specified an all-organic hydromulch mix of paper and wood fiber, water, and guar as a tackifier. Green dye was added to the hydromulch to help pilots easily identify which areas had already been treated. This mixture was selected for its safety and for its ability to bind to the soil while allowing native plants to sprout.

Neither seeds nor fertilizer were used. As the Forest Service stated, “Research has shown that reseeding chaparral areas is usually counter-productive because the native vegetation will resprout faster and more effectively-and hold the soil in place better-if it doesn’t have to compete with introduced seeds. We are not using fertilizer, because it could contribute to an excess of nutrients in the water.”

Western States Reclamation was selected to handle the hydromulching, working with Aero Tech, Erickson Air Crane, and Wildlands Inc. Colby Reid, of Western States Reclamation, explains that crews treated 1,531 acres for the Forest Service and then another 1,000 acres for the Santa Barbara County Flood Control agency.

“It was all aerial hydromulching,” says Reid, “and it took just a little over a month to complete all the acreage. We had two operations going on at the same time. We had a fixed-wing operation with AT-802 Air Tractors flying out of the Santa Barbara airport, and then we had a Skycrane helicopter flying from the other side of the mountain off a private ranch over there. The airplane holds right at 800 gallons of slurry, and the Skycrane holds 1,800 to 2,000 gallons at that elevation.”

The projects were completed with no major problems, and not much retreatment was necessary. “We would touch up light spots,” Reid says, “but basically, it’s a one-pass application. They overlapped each other, each pass did. Of course, there’s a little touchup of some light spots and a little drift.”

The Forest Service closed the hydromulch-treated area to the public during the hydromulching operation and for the subsequent 12 months, to prevent disruption to the regrowth. The area has slowly begun to revegetate, and Forest Service time-lapse photos of one limited area particularly show growth beginning in February and March of 2009.

Big Spring and Trigo Fires
New Mexico’s Cibola National Forest, near the border with Mexico, is home to stands of ponderosa pine, mixed conifer, gambel oak, and pinyon-juniper. Early in the morning of April 15, 2008, a small fire, reported at approximately 10 acres in size, was observed in the extremely steep and rugged Trigo Canyon portion of the forest. Crews were immediately dispatched to the scene, but high winds hampered fire-control efforts, and by evening the fire had spread to cover 100 acres.

Five days later, the burn had grown to 1,350 acres, and by the time it was essentially contained, a month after its start, the wind-driven fire had scorched more than 13,000 acres of forest land. Then, on June 23, 2008, about five miles away, lightning sparked the Big Spring fire. This event reached nearly 5,500 acres before being contained nine days later. Hundreds of residents had been forced to evacuate their homes.

“These were extremely hot-burning fires. They just basically disintegrated everything up there,” says John Larson, owner of Apex Curb and Turf in Washington state.

The US Forest Service selected Larson’s firm to help stabilize the area. It was challenging work.

“For the Trigo fire, we started on June 26, and we finished the project on July 2. We were dealing with all those big rains and it just gets crazy down there,” he says. “It rained and flooded it out. We couldn’t even get to the site at times in any kind of vehicle.”

Fifteen hundred acres needed to be treated with straw mulch, at a rate of 2,000 pounds per acre. Larson enlisted the help of Leading Edge Aviation of Clarkston, WA, to handle the aerial mulching operation. “We were lifting off through trees,” Larson says. “It was pretty crazy.”

By that time, the Big Spring fire had occurred, and Larson’s firm was called in again to treat 1,210 acres in this area, again for the Forest Service. This project began on August 3 and was completed August 8, after nearly 50 flight hours from Armstrong Helicopters, based in Colorado. But work went on nearly around the clock.

“On that job we had to use a Cat with a trailer to get the material into the site,” says Larson. “We had people working 18 to 20 hours a day, and we had stuff staging almost 24 hours a day to make this happen in the time frame required by the Forest Service.” Crews used a 205 A++ helicopter that was capable of carrying about 1.5 tons of mulch at a time, and Larson estimates that around 1,800 drops were accomplished for both projects together.

He explains why the Forest Service had specified a quick turnaround time for the projects. “The only thing that was really difficult was the weather. We would get torrential downpours, downpours that turn a dirt road into a river. It’s dangerous-at one point we were driving in our vehicles through 2 feet of water just to get back out of the job sites. We weren’t even sure if we could get back to our material. That’s why there was a tight window on this and why we acted as we did.”

For these projects, no seeding was done, but Larson also frequently performs aerial hydroseeding. “We supply the seed a lot, but it just really depends on the contract. We’ve found that super-hot fires will germinate the seeds-they’ll get stuff going. We’ve found that a lot of the vegetation reseeds itself.”

Asked when hydroseeding is most beneficial, Larson says, “When you get into anything that is 2H:1V or over, I think the hydroseeding is very beneficial. If you have loose soils that are very erodable, hydroseeding is helpful. In our experience, we have found that when the ground starts getting really steep, the Forest Service will hydroseed over the straw, because it just doesn’t hold otherwise.”

Larson has been in the business for 16 years and is called on for both post-fire and other erosion control work. “It’s a very competitive environment, and we’re really busy,” he says. “Right now, we have close to 60 state and federal contracts that are in the process of starting or are ongoing. We have jobs going in Washington, Idaho, and Montana. We’ve done a lot of work in California-revegetation down there-but we cover jobs wherever we can get them. There are half a dozen groups that pursue this type of work, and we’re one of them.”

Larson’s company also has been building and distributing its own line of hydroseeding and hydromulching machines worldwide since 1996. “We pretty much target large reclamation contractors. Our machines are the largest and highest production machines that are available in the world, but they’re also the most expensive!” he notes.

Southern California Freeway Complex Fire
October and November of 2008 brought a multitude of wildfires to southern California, with the worst occurring on November 15, 2008. That morning brought the first reports of a vegetation fire at the westbound 91 Freeway and Green River, which was called the Freeway Fire. With humidity under 10% and winds in excess of 60 miles per hour, the fire spread quickly to the west.

Less than two hours later, another major fire was spotted in the area of the Olinda Alpha Landfill, near Carbon Canyon, and was referred to as the Landfill Fire. By the following morning, the two fires had merged, and the Orange County Fire Authority gave them the combined name of the Freeway Complex Fire, providing a single base of operations to combat the blaze. Until the fire was controlled, some 40,000 residents would be evacuated from their homes.

Four days later, the Freeway Complex Fire was declared contained, but not before consuming more than 30,000 acres of land, destroying or damaging more than 380 homes and commercial structures, destroying or damaging countless vehicles, and damaging sensitive ecological areas in Chino Hills State Park and the Santa Ana riparian area.

Shortly thereafter, Leo Brendis, owner of HydroSprout in Escondido, CA, was called in to treat the most critical areas. “We had approximately 125 acres of burned area adjacent to the freeways and to a vital route called Carbon Canyon that allowed people access from the outlying areas to get into Anaheim or to the city area,” he explains.

He was asked to work on three separate locations: Carbon Canyon, the Orange (57) Freeway, and State Route 91. “They were triaged as far as levels of priority, and the Carbon Canyon was the number-one priority,” Brendis says. “It was just a two-lane highway, but it had a lot of use. It had a lot of steep terrain and trees. It wasn’t one of your newer highways, since it was going through these mountainous areas, so that burn put some significant stress and strain on the highway. There were downed power lines and burnt trees that had the potential for falling.”

He also notes, “Carbon Canyon has only a 3-foot or 4-foot shoulder, and then you go into a 1:1 slope that goes for 300 feet. So the propensity for boulders to come tumbling down once we got a minor rain and some soil displacement was a concern. There would be all the silt and sediment coming down, dead trees that would fall eventually because the wind would blow, and trees burned out at the base so that they have no structural integrity. Then you have a 300-foot tree coming down-that was why that area was the number-one priority.”

Because the road through Carbon Canyon is critical, Brendis was faced with tight deadlines. “We had a very short window,” he says. “We had maybe two weeks worth of work with normal 8-hour days, but it got compressed down, working from sunup to sundown, because we had to get the road opened as quickly as possible. We had a two-lane highway where we had multiple agencies working on top of each other. We had Southern California Gas & Electric in there, Southern California Edison, and the phone company, AT&T. There were residents that had been burned out, there were erosion control people, and there were municipalities in there trying to clear the roads. Everyone was on top of each other, so it was kind of difficult. There were police, and there were residents trying to get back in to those closed areas, so it was just one thing after another.

“We actually got everything done in four days,” he continues. “That included tree trimmers coming in, trimming back and cutting and removing all the dead trees. Carbon Canyon is over a mile long. All the downed culverts had to be cleaned out, fiber rolls had to be installed, silt fences had to be installed, and then we had to come through and spray everything. It was a lot of work.”

To stabilize the fragile soil in the steeper areas, Brendis combined 3,000 pounds of wood-fiber mulch with 10 gallons of EarthGuard Fiber Matrix per acre. He was able to cut back a bit in the less-steep areas while still achieving adequate control. “What we’re doing is we’re adjusting the additive into the wood-fiber mulch to meet the demand or the need. So we might use only 8 gallons an acre or 5 gallons an acre on some flatter areas where it’s not a steep 2:1 terrain.” To apply the EarthGuard, he used his fleet of 3,000-gallon Bowie hydroseeding machines.

Brendis says that he chose EarthGuard because “there’s some confidence involved. We’ve got the wood-fiber mulch; it’s the same as in any product out there, but with a BFM [bonded fiber matrix], if you try to put it down at a 2,000-pound rate, you’re really not doing any good. It’s not designed to work that way. EarthGuard is a polymer-stabilized fiber matrix.”

The primary effort involved stabilization rather than reseeding. “The school of thought is that Mother Nature has a really good way of returning itself back the way she was,” says Brendis. “These fires burned so hot and did so much damage to the soil-it actually crystallized the soil-that they were concerned that it wasn’t going to return itself. We did a lot of stabilization, but there were also some seeds that we put in. We added native grasses to help with the germination when the rains do come back.”

While work was ongoing, portions of the freeways had to be closed, and Brendis notes that it wasn’t just area residents who were inconvenienced. “There are always traffic-control issues, trying to close a lane on a freeway that’s heavily used. Our 91 freeway is one of the most congested freeways in southern California, morning and afternoon. When you remove a lane and then you have to drive two or three miles to get your water, get back on the freeway, stay in the traffic, get off the freeway, do your work, get back on the freeway, go through two miles of traffic-it takes a lot of time. We had up to four or five hydroseeding machines at one time, and we even used a water truck to supplement, because there just aren’t hydrants everywhere. We had to try to do the best we could with what we had.”

There also proved to be unexpected shortages of some necessary items. “We had a shortage of Dumpsters because of all the people that got burned out of their homes, so companies that provide Dumpsters were out of them. The Porta Potties-they were out of them, too. You had people bringing Porta Potties from San Diego and Orange County. The resources are not there that you’re used to. You make a phone call and usually you can get something right away, but here they told us, “˜No, we’re about two weeks out,’ or “˜We don’t have any-we just don’t have any.’ So that was a challenge, too.”

As difficult as the task was, it could have been even more so. “The initial assessment was much greater than what we ended up actually doing,” Brendis says. “In the beginning it was 2,500 to 3,000 acres that they felt they needed to address. I think they might still have to eventually, but the state just doesn’t have the money, and we’ve been fortunate enough not to see the kind of rainfall that would cause more problems. If we get another El Niño winter coming off those fires, those areas will drop off again and be exposed.”

Malibu Glass Fire
“It went right through the Malibu Glass facility. The fire was so hot it melted glass. It looked like candle wax on the ground-it was melted glass and aluminum from the framework on the building.”

This is how Phil Davis of North American Green describes the devastating wildfire that struck Malibu, CA, in the fall of 2007. “They lost everything they had,” he continues. “Malibu Glass, a private business, had a total, 100% property loss in a matter of minutes. The fire swept down on their facility and they lost all their buildings, their fleet of trucks, pretty much their whole business operation, all in a matter of minutes.”

Nothing could be saved, but the company decided to rebuild. In order to do so, however, the slopes on its land needed to be stabilized before the winter rains arrived. “They were interested in stabilizing some very steep slopes, 1.5:1 slopes, that surrounded the property. The property was somewhat of a horseshoe or bowl-shaped configuration. It was about an acre-and-a-half to two acres in size. They just wanted to do some very quick erosion control.”

The slopes in question measured about 80 feet from the top of the slope to the bottom. Malibu Glass contacted North American Green for help in stabilizing them. After surveying the site, Davis recommended that they consider the use of the new hydraulic erosion control product, HydraCX2 Extreme Slope Matrix, which is made from a proprietary blend of straw, reclaimed cotton plant material, tackifiers, and polymers.

Davis explains why he selected the CX2 mulch. “There was somewhat irregular terrain. It was not necessarily conducive to the application of blankets. In addition, the CX2 product requires less water than most of the materials that are out there. Water conservation is a big concern in California, and we have a low water-to-mulch ratio. It makes for a faster installation and more coverage per truckload.”

He adds, “We see very rapid vegetation establishment with this product. And we have passed extensive EPA toxicity testing with our product. It’s very environmentally appropriate for sensitive areas. The material contains absolutely no synthetic fiber.”

A local company, Acacia Erosion Control, was selected as the installer. With the assistance of an erosion control specialist from Aqua-Flo Supply, crews applied the hydromulch with a 3,000-gallon Bowie hydroseeding machine. “Logistically, there was fairly good access,” Davis notes. “They were able to drive their truck into what had been the parking area. Just by moving the truck around, they were able to access and shoot from the cannon to reach most of the slopes. But it is pretty much always required to shoot from two directions so you don’t have shadowing or bare areas. They did go up to the top of the slope and shoot with the hose to ensure that they had the backside of any protrusions. Approximately 90% of the work was accomplished with the cannon, using a truck-mounted nozzle. The remaining 10% was by hose at the very top of the slope.”

Malibu Glass elected not to add seed to the hydromulch, Davis says. “Their thought was that it would just increase the potential amount of fuel in the event of another fire. So the mulch was sprayed without any seed. We’re seeing more of a tendency, especially in California, to go without seed. Basically, they’re looking at armoring, with the expectation that whatever native vegetation is there will either regenerate or seed will blow in.”

At this site, the hydromulch was installed in one day, right after Thanksgiving. The following January, the area received record rainfall: more than 12 inches. “It was an incredibly wet winter, but there was virtually no soil movement at all. There was no erosion that occurred,” says Davis. “The previous vegetation, which still had deep roots, came back, and I think the mulch helped stimulate that vegetation establishment. It turned out pretty well.”

About the Author

Steve Goldberg

Steve Goldberg writes on issues related to erosion control and the environment.