The California Department of Transportation (Caltrans) took preventive steps this week ahead of a storm that brought heavy rain across the Southern California region.
With significant downpours opening up the possibility for debris flows, flooding and downed trees, Caltrans worked to keep freeways and highways in Los Angeles and Ventura Counties open and safe for travel, particularly in recent burn areas along State Route 33, State Route 150, State Route 27 and Interstate 210 (Foothill Freeway).
On an approximately four-mile stretch of State Route 27 (Topanga Canyon Boulevard) from Pacific Coast Highway (State Route 1) to Grand View Drive near the town of Topanga, crews cleared debris from drains and culverts using a truck-powered vacuum.
We also had maintenance crews continuously monitor the drains, culverts and highway conditions in areas like State Route 27 that have been prone to mudslides and flooding in the past following wildfires.
With preventive work in place, including the installation of concrete barriers (commonly known as "K-rail") with fencing, debris flow barriers and clearing drainage pipe below the roadway, Caltrans was able to limit debris from going onto the roadway, and preventing the closure of State Route 27 for the third time this month.
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| Culvert built below debris flow barrier helps direct runoff during storms away from roadway. |
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| What debris flow barrier looked like following March 15 storm and mudslide. |
Back in July 2017, a 50-acre wildfire left a trail of scorched slopes along Topanga Canyon, leaving the area susceptible to slides and flood risks during any rain event that could follow.
Storms on March 2 and March 15 caused multiple slides on State Route 27, a key route used by residents and commuters from the San Fernando Valley to access the beach, the cities of Malibu and Santa Monica and the west side of Los Angeles.
Even in areas where vegetation and trees did not burn up in the fire, the soil and roots were loosed. As a result, heavy amounts of rain over a short period of time cause the soil to become saturated, which can lead to slides and debris flows.
MANAGING FLOOD PRONE AREAS OF FREEWAYS AND HIGHWAYS
In areas prone to flooding like Interstate 5 at Sheldon Street in the Sun Valley area of Los Angeles County, Interstate 110 (Harbor Freeway) in downtown Los Angeles and the South Bay area of Los Angeles, we ensured pump houses were operational and in working order, as well as positioning portable pumps in strategic areas.
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| Flooding on southbound Interstate 5 near Sheldon Street exit Jan. 9 following severe winter storms. |
Maintenance crews also stocked up on cold mix asphalt and base materials to repair washouts, and prepared "flooded" signs mounted on barricades that could be placed in affected areas.
WHAT CAUSES SLIDES/DEBRIS FLOWS
According to the
California Office of Emergency Services (Cal OES), burning vegetation releases gas during a fire. The gas gets into the soil, causing roots to weaken. Once the gas cools, it solidifies, forming a wax-life layer that makes the surface resistant to water.
As rain starts to accumulate, the precipitation weakens the top soil above the wax-like layer, causing the soil to break loose and slide down slopes, taking rocks, mud and trees with it. The now saturated soil can last for years, causing water to run off like pavement.
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| Graphic courtesy: National Weather Service |
It is this flood risk that makes it important to clear sediment and debris from drains, basins and culverts, and use erosion control measures like plastic sheeting, sandbags and concrete barriers to help prevent loose dirt and rocks from falling onto highways.
On Interstate 210 near La Tuna Canyon Road, crews placed hyrdroseeding on slopes that burned in the La Tuna Canyon fire, cleared mud from a large culvert, and regraded hillsides to stabilize slopes.
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Culvert cleared of debris and hillside fitted with mixture of mulch and seeds off
Interstate 210 (Foothill Freeway) |
IMMINENT CLOSURES DUE TO WEATHER
Ultimately, the most significant storm event of the rainy season makes flooding, mudslides and debris flows inevitable in mountain areas with steep, rugged terrain, especially when scarred by recent fires.
Multiple slides March 21 on State Route 33 north of Ojai and in the Los Padres National Forest forced the closure of this rural mountain route from Fairview Road to Lockwood Valley Road.
Crews are working to clear the roadway as quickly and safely as possible, but the route, which is in the Thomas Fire burn area, remains closed to traffic for an unknown period of time. However, residents with identification will be allowed through.
In the San Gabriel Mountains, Angeles Crest Highway is closed until further notice from Islip Saddle/State Route 39 to five miles west of Big Pines near the Los Angeles/San Bernardino County line due rock slides.
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| Portion of State Route 2 (Angeles Crest Highway) closed March 22 due to rock slides. |
The Mountain High Ski Resort remains open, and drivers are advised to use Interstate 15 and State Route 138 as alternates.
In the event of slides, flooding or adverse weather conditions, drivers should plan ahead, use alternate routes, and follow instructions from emergency officials.
We will continue to keep an eye on roadways that have the potential to flood or fill with mud and debris.
Be sure to follow us on Twitter for updates
@CaltransDist7, or on Caltrans
QuickMap, which is also available as a free app on Google Play or the App Store.
