Fighting the threat of landslides in soggy California

SAN DIEGO – Relentless storms from a series of atmospheric rivers saturated the steep mountains and bald hillsides damaged by wildfires along much of California’s long coast, triggering hundreds of landslides this month.

So far, the debris has mostly blocked roads and highways and has not damaged populated areas in 2018 when landslides swept through Montecitokilling 23 people and destroying 130 houses.

But more rain is forecast, increasing the threat.

Experts say California has learned important lessons from the Montecito tragedy and has more tools to pinpoint hot spots, as well as more basins and nets to catch falling debris before it hits homes. Recent storms are putting those efforts to the test as climate change creates more severe weather.


California has relatively young mountains in terms of geology, meaning much of its steep terrain is still in motion and covered in loose rock and soil that can easily peel off, especially if the ground is wet, geologists said.

Almost the entire state has seen between 400% and 600% more rainfall since Christmas, with some areas receiving up to 30 inches of rain, leading to widespread flooding. Since the end of December, at least 19 people have died as a result of bad weather.

Since New Year’s Eve, the California Department of Conservation landslide mapping team documented more than 300 landslides.

Prolonged drought in the state has worsened the situation.

Dan Sugar, an associate professor of geophysical sciences at the University of Calgary, said the drought could have an unintended effect when combined with the incredible rainfall seen in California in recent days.

“You would think that when the ground is dry, it can absorb a lot of water, but when the ground gets too dry, the permeability of the ground actually decreases,” he said. As water drains from hardened soil, moving downward and gaining energy, it can begin to carry away soil and debris, he said.

In addition to this, wildfires have left some hillsides with little to no vegetation that holds the soil in place.


The most vulnerable areas are the hillsides that have burned in the past two to three years and the communities below them, said Jeremy Lancaster, who leads the California Department of Conservation’s geological and landslide mapping team.

That includes areas that recently burned in Napa, Maripaso and Monterey counties, he said.

In 2018, the deadly landslides in Montecito came about a month after one of the largest wildfires in California history swept through the same area, burning 280,000 hectares.

Montecito is sandwiched between the Santa Ynez Mountains and the Pacific coast. On the fifth anniversary of this tragedy, on January 9, the entire community was ordered to evacuate as rains lashed the area and debris blocked roads.

Lancaster warned that the threat of landslides will remain long after the rains subside as water seeps 50 to 100 feet into the soil, shifting things.

“They could happen in weeks, if not months,” he said.


Lancaster said California has dramatically increased its efforts to identify hot spots since the Montecito landslides. His department is constantly updating its map to keep local communities informed and able to make decisions, including community-wide evacuations.

The state is also working on a system to better determine how much rain could trigger a landslide.

Maarten Giertsema, who studies natural hazards and terrain analysis at the University of Northern British Columbia, said agencies use a variety of tools to assess the likelihood of landslides in a given area, including terrain maps and lidar — pulsed light from lasers to penetrate foliage to see. the earth They can then monitor for early warnings, such as changes over time in aerial photographs, satellite images, or data from GPS monitoring stations, inclinometers and other on-site instruments.


One of the best ways to deal with landslides is with debris basins – pits cut into the landscape to catch material that flows down.

But the pools, which can require a lot of land, can also disrupt the natural ecosystem and lead to the need to replenish beaches by collecting sediment that flows out of canyons, experts say.

And they’re expensive, said Douglas Gerolmak, a professor of environmental science and engineering at the University of Pennsylvania. And if the old debris is not removed, it can be covered by new landslides or mudslides.

Some also may not be large enough to handle future falls that will be exacerbated by climate change, Jeralmak said.

After the 2018 landslides that hit Montecito, the Los Angeles Times reported that the debris basins above the community were inadequate and had not been cleaned.

The tragedy galvanized a community that raised millions to address the problem, said Patrick McElroy, a retired Santa Barbara fire chief who founded the nonprofit The Project for Resilient Communities.

The organization hired an engineering company to map the canyons and set up debris nets. Recent storms have put them to the test, he said, with one 25-foot net filled almost to capacity.

McElroy said he’s still haunted by memories from 2018, but he feels better knowing the community can be safer now.

“I’m not done yet. But to wake up, you know, the other day and not see either the wounded or the dead. I just can’t tell you how impressed I am,” he said of the networks.

According to Larry Gurola, a geologic engineer employed by the organization, the best solution for the Montecito and Santa Barbara area is to have nets and trash basins.

But nothing is cheap. Santa Barbara County spent $20 million on the new pool beyond 2018, while McElroy’s organization spent about $2 million to install the nets, which includes liability insurance and other fees. They have a five-year network permit that will be removed if not renewed.

Gurola said the alternative is more expensive. Due to the recent storms, more than half of California’s 58 counties have been declared disaster areas, and damage repair could cost more than $1 billion.

“Most importantly, these things protect the community and save lives,” he said.


Glass reports from Minneapolis.

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