CalTrans Erosion Control Toolbox

Wildfire destroys hundreds of thousands of acres of California forest and chaparral each year. Often times these fires occur on steep and remote lands where access is difficult. Occasionally wildfires enter the rural or urban interface zones, often with devastating consequences for homeowners living in the path of the flames.

One of the impacts of a changing climate is that California’s (and the West’s) fire season is starting earlier and lasting longer. Less rainfall in winter means brush dries out earlier. Trees are under stress and dying in some areas. Higher temperatures and seasonal winds can quickly whip a small fire into a catastrophic event. Fires are larger now: seven out of the 10 largest wildfires in California history have occurred in the 21st Century, according to CalFire statistics. In February, 2015, a rare winter wildfire in high-elevation Mono County destroyed 40 homes and prompted Gov. Brown to declare a state of emergency. In fall 2017, in response to several large wildfires, the Governor issued states of emergency for Sonoma, Napa, Yuba, Ventura, Santa Barbara, and Los Angeles Counties. These fires include the largest in California history, the Thomas wildfire in Ventura and Santa Barbara Counties.

Wildfires eliminate the soil’s protective vegetative layer, exposing it to wind and rain. Heavy rainfall on burned lands washes sediments into creeks and rivers, and often onto roads and neighborhoods. Particularly hot or slow-moving fires volatilize the organic matter on the top layers of the soil. When the soil cools a waxy layer forms that repels water. If the hydrophobic layer forms under a few inches of burnt, mineralized soil, then there is potential for dangerous mudslides, such as the one that destroyed 13 homes in Camarillo, CA in December, 2014.

Compost improves the physical, chemical and biological properties of soil. Compost amendments and mulch help protect fire-damaged lands by protecting the soil from the erosive impact of heavy rain. The organic matter in compost helps increase water infiltration and soil water holding capacity, giving seeds more time to germinate. The vital nutrients in compost are tightly bound in organic complexes while  synthetic fertilizers contain highly soluble nutrients that rapidly leach into soil and water; that means they will not easily wash away in the first rainstorm and will be there to boost young plant growth. When soil can re-grow its protective vegetative layer quickly, the result is less erosion, cleaner waterways and less time and money to dig out critical infrastructure.

Types of compost products, what they do, and how they can be applied

There are several different types of compost products, that can be applied in several ways:

  • Compost blankets are typically applied using blowers or by hand, in a 1- to 2-inch layer. Blankets may or may not be vegetated. Vegetated blankets are usually seeded.
  • Compost can be incorporated with a tiller into the subsoil, and then seeded. This is an established practice in erosion control.
  • Filter berms and socks are permeable barriers made of compost packed inside mesh tubing that filter sediments.

Whether the compost is incorporated or applied as a protective layer, soils treated with compost are richer in slow-release nutrients than bare soil, and will see improved water infiltration and retention, creating an environment where plants can thrive. Allowing plants to develop a healthy, extensive, and deep root structure further improves soil structure to minimize or even prevent land erosion. Compost can also bind and adsorb contaminants already in soil, including heavy metals, fuels, and polyaromatic hydrocarbons, making it an ideal treatment for soil remediation and for the filtration of runoff from contaminated land.

Compost blankets and amendments control erosion by:

  • Intercepting and absorbing falling rain, reducing runoff and associated sediment losses.
  • Providing an environment where seeds can germinate and grow to hold soils in place.
  • Improving soil structure.
  • Increasing water infiltration into heavy soils.

Filter berms and socks control erosion by:

  • Slowing the movement of water so that sediments can settle out.
  • Filtering water to remove pollutants.
  • Acting as barriers against the development of erosion rills and gullies.

The benefits discussed above accrue to applications of finished, mature compost and are not associated with applications of uncomposted green materials. Help ensure product quality by purchasing your compost from a facility that follows CalRecycle regulations for pathogen reduction and metals testing and is permitted by or registered with Local Enforcement Agency.

The benefits discussed above accrue to applications of finished, mature compost and are not associated with applications of uncomposted green materials. Help ensure product quality by purchasing your compost from a facility permitted by or registered with Local Enforcement Agency that follows CalRecycle regulations for pathogen reduction and metals testing.

CalRecycle sponsored research into the impacts of compost application on nutrient runoff from fire scarred lands. This research was completed in 2011. Read the report.

When wildfires destroy neighborhoods, CalRecycle often leads the clean-up efforts. More information about CalRecycle’s Wildfire Preparedness and Response efforts.

CalTrans Erosion Control Toolbox | Links