The Brief

The impacts of the historic rainfall that Southern California saw in the last few days was felt most in the region’s canyons and hillside areas. Mud and rock slides hit the Hollywood Hills and resulted in evacuations in Studio City, Tarzana and Beverly Crest.

Videos on social media appear to show mud flowing through the streets of Laurel Canyon along with debris.

Rick Seireeni, a board member of the Laurel Canyon Association and resident of Laurel Canyon since 1978, said storm clouds come in from the ocean to the area.

“They come in, and then the first obstacle they hit, the first wall they hit, is the Santa Monica Mountains and the clouds get pushed up over the mountains, they release all their moisture,” he said. “So particularly on the east side of the canyon, we get a lot of water coming down as a result of just clouds colliding with the mountains.”

Seireeni, who has documented Laurel Canyon’s history, said in photographs he has observed of the area from the early 1900s, “Laurel Canyon Boulevard in the canyon area was a stream and it was paved over at the turn of the century.”

The road has washed out in Studio City and an underground pipe is exposed in an archival photograph.

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Courtesy Los Angeles Public Library Photo Collection

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This means that when it rains “there would be no place for this water to go other than on top of those streets” at the bottom of the canyon.

Pictures from the early 1900s show Laurel Canyon buried under a deluge of mud, with houses sliding and vehicular traffic coming to a standstill. Over a 100 years later, the area continues to be a hotbed when a storm occurs, albeit with some improvements.

Archival photograph of the Laurel Canyon underpass, flooded from rain.

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Courtesy of Los Angeles Public Library Photo Collection

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Seireeni recalled a storm that happened a few years after he moved to the neighborhood. "Garbage cans were being sent down the street,” Seireeni said. “There were cars that were being floated actually right out into Laurel Canyon Boulevard. There were quite a few slides in the area.”

Archival photograph of storm damage at Laurel Canyon Boulevard, Jan. 18, 1952.

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Courtesy of University of Southern California Libraries. Los Angeles Examiner Photographs Collection

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University of Southern California

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“In the intervening years we've had rainstorms, we've had wind storms, combinations, trees go down, power would frequently go out, there would be flooding on certain streets,” he said. “But this year with this historic storm, there are problems here and there, but it's not as bad as it used to be.”

And he says that’s because Los Angeles has done work to keep the sewer lines clear of debris as well as work on the power lines to prevent them from snapping during heavy winds.

“I think that that's helped contribute toward less damage this time than potentially in the past,” he said.

Currently, Seireeni said there is relatively less damage at the top of the canyon but as you go down, water is funneled through the streets and gathers at the bottom and there is “erosion on the sides of the street where the dirt’s exposed.”

Other reasons why canyons bear the brunt of rainfall

Amy Rechenmacher, professor of civil and environmental engineering practice at the University of Southern California, says rain can exploit weakness on hillsides: from trash laying around and being diverted to a place it wouldn’t have otherwise gone or wildfire burn scars. “So, when you have a hill,” Rechenmacher says, “gravity wants to pull that hill down, and anything that can help pull the hill down, Mother Nature will take the help.”

Josh West, an earth sciences and environmental sciences professor at USC, says building homes in canyons create pathways for water to flow down faster.

“The built infrastructure exacerbates flooding because we create all these impervious surfaces, all the road surfaces, paved yards, and so on that don't let water filter into the ground as it would do on a natural soil,” he said.

What does this mean for the future?

The climate crisis, Rechenmacher said, is going to bring extremely wet and extremely dry weather so it's up to governments to invest in resilient infrastructure for existing developments in the hillsides.

“As humans have decided to develop the mountains, We thought we could conquer and control nature, but anybody will tell you, Mother Nature always wins,” she said. “I think the outlook is to stop right now further development on hillsides.”