For Southern California counties the periodic, yet unpredictable, arrival of the El Niño climate pattern equates to winter and spring rainfall totals that are significantly higher than historical averages for that region.
This year’s rainfall — coupled with numerous post-fire erosion areas — is capable of causing mudslides and debris flows that can wash out sections of roadway and clog and break underground drainage pipes.
During January and February of this year, several sections of highway within Los Angeles, Riverside and Orange counties all experienced closures and significant damage due to mudslides, which prompted a number of emergency repair projects.
State Route 2
Along the Angeles Crest Highway, SR-2, heavy rains and the lack of vegetation on slopes — due to the Station Fire last September — caused several mudslides that resulted in road washouts and mountain slope erosion during mid-January.
A Caltrans damage assessment team determined that the most significant road washouts ranged between 50 to 110 ft. (15.2 to 33.5 m) along the highway and about 200 ft. (61 m) below the highway at some locations.
The roadway washouts were caused by mud and rock that was carried onto and over the roadway, the result of clogged inlets and down drains.
“In the past we typically have it [mudslides and washouts] much higher up where the snow is,” said Darrell Mackenzie, resident engineer of Caltrans District 7. “This was much lower.”
Baltazar Construction is the general contractor responsible for the roadway clean up and restoration, a contract valued at $7.5 million. Burns Pacific was awarded a nearly $7 million contract to install retaining walls along slopes were mudslides occurred. Other contractors who have contributed to the clean up and repair project include Pave Tech and Alcorn Fence.
“The challenge during construction is making the roadway passable for construction and emergency equipment,” said Caesar Resler, senior transportation engineer of District 7.
During repair work Super 10 dump trucks, 938 Cat loaders, excavators, bobcats and backhoes have been used onsite.
The stretch of SR-2 affected by the mudslides should be reopened to the public by late March with all repair worked finished by late July. However, future rainfall could alter that schedule.
“It is very likely that mudslide and debris flows could persist in the Station Fire burn area,” said Dan Freeman, deputy district director of maintenance of District 7.
State Route 74
On Feb. 6, a heavy storm caused damage along a shoulder and an embankment of the SR-74 Ortega Highway, causing the highway to close between San Juan Capistrano and Lake Elsinore in Orange County.
A $400,000 emergency project contract was quickly awarded to R.B. Holt Construction, who used a quarter ton of rock to support the road and restore the embankment. In one day, the contractor had built back 10 ft. (3 m) of shoulder, meaning the highway could be reopened to traffic, according to Tracey Lavelle, public information officer of Caltrans District 12.
This area of SR-74 had previously suffered damage from a Jan. 18 storm that caused mud and debris flows, resulting in four washouts.
As of Feb. 22, at least 75 percent of the washouts had been repaired, with Caltrans officials expecting the repair work to be fully completed by Feb. 28.
An emergency drainage project is expected to start along the same portion of SR-74. The project will include the placement of reinforced concrete pipe drainage at four locations, as a broken water main was one of the reasons behind the four washouts previously mentioned.
The drainage project contract is estimated to be around $500,000 and has yet to be awarded.
To the Northeast, another portion of SR-74 — between Hemet and Mountain Center in Riverside County — also experienced a roadway washout caused by rainfall, mud and debris that clogged a drainage system.
The clogged drainage system caused a more than 40-ft. section of SR-74 to be washed out on Feb. 8.
According to Fathi Manasrah, resident engineer of Caltrans District 8, a $1 million emergency contract was quickly awarded to Skanska, who worked around the clock for several days and repaired the washed out section of roadway in four days. In order to restore the highway, Skanska first had to install a 24-in. (61 cm) concrete drainage pipe under the damaged section
During repair work construction equipment including excavators and dozers were utilized, with no specialty equipment onsite. The damaged stretch of SR-74 was reopened on Feb. 14, however, drainage system improvements, which could be affected by future storms, were ongoing.
State Route 57 Connectors
As of Feb. 18, Caltrans District 7 closed two freeway connectors due to a landslide that sent mud, rock and debris onto roadways in the city of San Dimas. The westbound San Bernardino Freeway, I-10, connector to northbound Orange State Route 57, and the northbound State Route 71 connector to northbound SR-57 remain closed until further notice.
Since the landslide, crews have worked to stabilize the hillside by removing loose gravel and grading the slope according to Caltrans. During the weekend of Feb. 20 and 21, an estimated 11,000 cu. yds (8,410 cu m) . of loose dirt and rock were hauled away, and 80,000 sq. ft. of plastic was placed to prevent further damage by forecasted rain.
Currently, work crews continue to haul excess soil material and place concrete median barriers (K-rail), which will remain in place until repairs are complete.
Autobahn Construction Inc. is the general contractor responsible for the repairs.
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