Post-wildfire erosion

The Cocos Fire one month after the 2014 blaze. The May outbreak of fires occurred during a period of offshore flow throughout Southern California that meteorologist deemed highly unusual for the month of May. Beginning on May 11, the situation turned critical and red flag warnings went were issued across the region. By May 14, with the warnings still in effect, daytime temperatures were hovering around 100° F, with humidity below 10%.

The Cocos Fire Upper Canyon One Month After the 2014 fire. The blaze destroyed more than 40 buildings, including a dozen single-family homes. Property damage from the fire is estimated at more than $5.7 million. Three minor injuries were reported.

The Cosos fire scene in San Diego County one year after treatment with hydromulch and wattles. Previously known as the Twin Oaks Fire, the Cocos Fire was a wildfire that ignited on May 14 in San Marcos, in the hills south of California State University, San Marcos. It quickly spread into western Escondido.

The Cocos Fire Upper Canyon one year later. On May 17, 2014, the Santa Ana winds subsided and temperatures started to drop. On May 18, weather conditions had returned to seasonal norms, with lower temperatures around 80° F and higher humidity.

Griffith Park’s Vermont Canyon one month after the May 2007 fire. The major wildfire burned more than 817 acres, destroying the bird sanctuary, Dante's View, and Captain's Roost, and forcing the evacuation of hundreds of people. The fire came right up to one of the largest playgrounds in Los Angeles, Shane's Inspiration, and the Los Angeles Zoo, and threatened the Griffith Observatory,

The canyon in Griffith Park one year after hydromulch treatment. in 2007 fire consumed almost one-fifth of Griffith Park, the 11th largest municipal park in the nation, in Los Angeles and the Santa Monica Mountains. Landslide mitigation plans for southern canyons, which flow to busy streets and communities, differed from those of the north canyons, which flow to ballparks and golf courses.

Griffith Park’s Vermont Canyon one year after the May 2007 fire. As serious as the fire was, it was not nearly as bad as a blaze in the same park in 1933, when 29 people were killed and 150 were injured. That fire started when more than 3000 men were in the park clearing brush as part of a welfare project.

Natural regeneration of native laurel sumac two months after a fire. The large rounded evergreen shrub or small tree grows 10 to 15 feet tall and is glabrous and aromatic with reddish leaf veins, petioles and stems.

Wire mesh containment riparere built for the passage of vehicles by landslides. The risk of a landslide lasts five years after a wildfire.

Public works departments should identify areas of greatest potential damage, determine the best way to mitigate erosion and debris flows in those areas, and develop a plan for quickly funding and implementing measures that will prevent post-fire landslides. The impacts of erosion include public health and safety, public and private property damage, damage to infrastructure such as storm drains, transportation route damage such as key arterial loss, and damage to receiving waters.

Immediately after a fire, slope hazards increase as vegetative cover decreases. Deciding which erosion prevention practices to deploy depends on many things: the risk/liability, implementation and maintenance costs, environmental impacts, regulatory acceptability, public acceptability, aesthetics, and expected severe or extreme weather. Fortunately, developing pre-fire and post-fire plans is considerably easier in today’s web-enabled world.

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