In December 2017, the Thomas Fire ignited in Southern California and quickly expanded to become-at the time-the largest wildfire in modern California history. The fire caused more than $2.2 billion in damages. More than 8,500 firefighters worked to control the blaze, but when all was said and done, the fire burned more than 281,893 acres; destroyed or damaged more than 1,300 structures; and forced 104,600 people to evacuate. For the thousands of people who have been affected by the devastating wildfires in California, controlling erosion is about much more than reestablishing vegetation; it is about preventing further devastation and helping reestablish their communities. 

This rebuilding included Montecito, Calif., a small town along the coast in Santa Barbara County that is home to many Hollywood elite. As the fire spread in mid-December, firefighters prioritized protecting the homes in the area, but unusually strong Santa Ana winds and dry brush accelerated the burn. The fire quickly swept across the landscape, torching the area and leaving nothing but debris in its wake. By early January, the fire moved on from Montecito, but the damage of barren slopes and gnarled trees lingered.

Unfortunately for the community, the destruction was far from over as California’s rainy season was about to move in. Homeowners along the hillside scrambled to find an erosion control solution that would offer protection until sustainable vegetation could form. 

Developing a Plan

A construction company based in Santa Barbara was in the middle of a remodel for a home at the top of 1H:1V and 2H:1V slopes in Montecito. Prior to the fire, the construction company hired a crew to install a straw-coconut 70/30 erosion control blanket in an attempt to stabilize the slopes above the construction site. Once the fire moved in, the blankets burned, leaving the slope once again susceptible to erosion. With strong storms in the forecast, the construction company reached out to Acacia Environmental to survey the site and provide options for protecting the land.

James Colbert, the estimator and project manager with Acacia Environmental, knew they were under a time crunch to find and apply a solution that would stabilize the slopes before the storm. Colbert and his team started with a site survey. Along the 400-ft curving driveway, the terrain was barren with several large rocks jutting out and debris scattered on the site.

“Anything that we could do wouldn’t take care of the rocks,” Colbert said. “The least we could do is try to get some glue up on there and some seed in the dirt around the area just to discourage movement of the soil.”

Colbert’s team suggested a hydraulically applied erosion control product (HECP) for the fire reclamation site because of its ease of application and erosion control effectiveness. In most cases, applying a rolled erosion control product on roughed and debris-laden slopes can be ineffective, whereas HECPs can be applied on extremely rough terrain. The HECP is mixed with seed to ensure good seed-to-soil contact upon application and reduce installation time. The HECP also protects the seed and soil from rainfall impact and greatly enhances seed germination. For this project, Colbert’s team chose Flexterra High Performance-Flexible Growth Medium (HP-FGM), a hydraulically applied medium specifically designed for erosion control on steep slopes. 

“When we see slopes that are crazy 1H:1V like that, we usually think of some heavy-duty fiber matrix products” Colbert said.

Flexterra HP-FGM is composed of long-strand, thermally refined wood fibers; crimped, interlocking fibers; micro-pore granules; naturally derived biopolymers and water absorbents. It forms an intimate bond with the soil surface to create a continuous, porous, absorbent and erosion-resistant medium that allows for rapid germination and accelerates plant growth. Flexterra HP-FGM has a functional longevity of up to 18 months. Most importantly for this specific project, Flexterra HP-FGM requires no cure time to become effective, an advantage when rain is in the forecast. 

Repairing the Slope

Colbert’s team of three workers began the application Jan. 6. Using a 3,000-gal hydroseeder, the workers added a native seed mix supplied by S&S Seeds to the hydraulic slurry. The team applied the slurry at 4,000 lb per acre on the 2-acre project site. On all of the 1H:1V slopes going up the driveway, Flexterra HP-FGM was applied from the tower on top of the hydroseeder. At the top of the hill near where the home was being built, space became more limited. There, the team applied Flexterra HP-FGM to the remaining areas using the hose on the hydroseeder. Colbert said that was another advantage of hydroseeding to complete the work. Hose work allowed the team to easily maneuver around the foundation of the house without disturbing the project site. With this setup, he said his team was able to easily spray the rocky slopes from several angles to ensure the product had complete coverage on the site. 

“The 1H:1V slopes had a lot of half-burnt shrubs and trees, so there was a lot of bumpy ground to cover,” Colbert said. “Hydroseeding saved us time in comparison to using a blanket because labor-wise it wouldn’t be easy to install any kind of netting product on those kinds of slopes. You’d have to do some crazy rope operation that would take a lot of labor. I don’t think you’d even bother at that point. And even on the 2H:1V slopes, it would take twice as long to do netting with a bigger crew.”

When it Rains

On Jan. 8, Acacia Environmental returned to complete the Flexterra HP-FGM application. That same day, a storm began brewing over Southern California, bringing a deluge of rain. Due to the barren slopes in the area, the storm prompted mandatory evacuations in Los Angeles, Santa Barbara and Ventura counties on account of an inevitable mudslide. On Jan. 9, the storm intensified and dropped 4 in. of rain over Southern California in the next two-day period. 

Montecito was one of the hardest hit areas, receiving up to 0.54 in. of rainfall in as little as five minutes. That torrential rain on the scorched slopes resulted in rapid erosion, mud flow and debris flow of soil in streams. In all, as of press time, 21 people died, two people are still reported as missing, 129 homes were destroyed, and 307 homes were damaged.

Colbert said his team applied the medium at just the right time. When workers with the construction company returned to the site, they said it was spared compared to the rest of the community. They attributed that success to the hydroseeding strategy and application that Acacia Environmental completed just days earlier. The application spared the house from further damage and limited the amount of soil movement to areas subjected to concentrated water flow.

“The customer said they’re very thankful that we were able to get there when we did,” Colbert said. “That site wouldn’t look the same without that application.”

Following the storms, Colbert reassessed the site. The team reinforced areas of concentrated flow with waddles and touch-up applications of Flexterra HP-FGM in preparation of more rainfall over the next several months. 

More than a year later, the site has not experienced any further erosion control issues. The construction on the home now is complete and the landscape is revegetated. The homeowner was able to continue with the remodel and eventually reestablish their life in Montecito.

Original article written by Matt Welch and Adam Dibble for Storm Water Solutions. View the online version.