EXPLAINER: Tackling threat of mudslides in soaked California
So far the debris has mostly blocked roads and highways and has not harmed communities as in 2018 when mudslides roared through
But more rain is in the forecast, increasing the threat.
Experts say
WHY IS
Almost all of the state has received rainfall totals of 400% to 600% above average since Christmas, with some areas receiving as much as 30 inches of precipitation, causing massive flooding. The severe weather has killed at least 19 people since late December.
Since New Year’s Eve, the
The state's prolonged drought has made matters worse.
“You’d think if the ground is dry it should be able to absorb a lot of water, but when ground becomes too dry, the permeability of the ground actually decreases,” he said. As water runs off the hardened soil, moving downward and picking up energy, it can begin carrying soil and debris away, he said.
Added to that, wildfires have left some hillsides with little to no vegetation to hold the soil in place.
WHAT ARE THE MOST VULNERABLE AREAS?
The most vulnerable areas are hillsides that have burned in the past two to three years with communities below them, said
That includes areas that recently burned in
In 2018, the deadly mudslides in
Lancaster warned that the threat of landslides will linger long after the rains have subsided as the water seeps 50 to 100 feet into the soil, dislodging things.
“They can occur weeks later, if not months,” he said.
WHAT CAN BE DONE TO PROTECT COMMUNITIES?
Lancaster said
The state is also working on a system to better pinpoint how much rain might trigger a landslide.
WHAT IS THE MOST EFFECTIVE DEFENSE AGAINST MUDSLIDES?
One of the best ways to manage landslides is with debris basins – pits carved out of the landscape to catch material flowing downhill.
But basins, which can require a lot of land, can also disrupt the natural ecosystem and lead to beaches needing to be replenished by collecting sediment that flows out of the canyons, according to experts.
And they are costly, said Douglas Jerolmack, a professor of environmental science and mechanical engineering at the
Some might also not be big enough to deal with future slides worsened by climate change, Jerolmack said.
After the 2018 mudslides hit
The tragedy galvanized the community, which raised millions to address the problem, said
The organization hired an engineering company to map the canyons and installed debris nets. He said the recent storms put them to the test: One net measuring 25 feet tall filled nearly to capacity.
McElroy said he's still haunted by memories from 2018 but feels better, knowing that the community might be safer now.
“I’m not over it yet. But to wake up, you know, the other day and see no injuries and no fatalities. I just can’t tell you how impressed I am,” he said of the nets.
The best solution for the
But nothing is cheap.
Gurrola said the alternative is more costly. With the recent storms, more than half of California’s 58 counties have been declared disaster areas and repairing the damage may cost more than
“Most importantly these things protect the community and save lives,” he said.
Glass reported from
Floods’ worst ravages will be visited upon California’s poorest
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