With a storm lingering again over Los Angeles County, experts warn that even its modest rainfall could elevate the risk for mudslides, debris flows and flooding because the ground is already waterlogged from the monster storms earlier this month.
“In normal winters where we haven’t had as much rain, this type of rainfall doesn’t cause that much [of an] issue because the ground can still absorb water,” said National Weather Service forecaster Ryan Kittell. But once the ground becomes completely saturated, he said, flooding can occur “really easily” and the earth can start to move, either with mud or rock slides.
Most populated areas of L.A. County have received 1 to 3 inches of rain since Monday morning, while foothill and mountain regions have gotten between 3 and 6 inches, according to the weather service. As of 9 a.m. Tuesday, 1.25 inches had fallen in downtown Los Angeles, 3.31 inches in Bel-Air and 6.07 inches in Topanga Canyon.
Downtown L.A. has received 16.87 inches of rain since the water year began on Oct. 1 and 11.64 inches just during February. That’s almost 2 inches more the area’s average for a full year, and 7 inches more than it typically gets by this point in the water year.
“This is one of the wetter Februarys on record,” Kittell said. “It’s been an incredibly wet month.”
A flood watch is in effect for all of L.A. County except the Antelope Valley through 10 a.m. Wednesday, according to the weather service. Rivers, streams and low-lying areas could see flooding. Freeways and areas with poor drainage could also become inundated with water. There’s an increased risk for mudslides in vulnerable areas.
There was a brief lull in the rain Tuesday morning, but the showers are expected to pick back up and then intensify Tuesday night and Wednesday morning according to Kittell.
On top of the current totals, the L.A. area could get an additional 1 to 2 inches of rain, with up to 4 inches or more in the foothills and mountains. There’s also a “very small but nonzero chance” of severe weather, including strong local winds, small accumulation of hail or even a brief tornado, according to Kittell.
The storm is forecast to taper off Wednesday night. It’s expected to be dry at least until the weekend, when there’s a chance for another storm Saturday night, becoming more likely Sunday and Monday.
Next week’s storm could bring an additional half an inch of rain to the area.
The weather service has received reports of mud and debris flows and flooding in the Santa Monica Mountains and the Pacific Palisades area. Most of the reports have been in Santa Barbara County, where the rainfall totals have been higher.
“Usually when we start to get rainfall totals for the season above 10 inches, the areas that are really vulnerable to mudslides and landslides become especially vulnerable to those type of issues,” Kittell said.
Residents of Rancho Palos Verdes, where a slow-moving landslide complex has been shifting for decades, are bracing for the aftermath of this week’s storm. Although only about 1 inch of rain has fallen in the area, record-setting rainfall over the past several months has saturated the ground, causing the landslide area to shift more rapidly, according to City Manager Ara Mihranian.
“In some areas, [the land] is moving up to 10 feet a year,” he said. “That’s significant movement, and we’re seeing the damage that’s being sustained throughout the community. We have approximately 400 homes that are threatened by this landslide.”
Two homes have already been red tagged, and other residents have reported sinkholes, cracks in their walls and doorways that have split. The pavement on Palos Verdes Drive South, a major roadway through the community, is buckling.
The Rancho Palos Verdes City Council on Tuesday is set to consider asking Gov. Gavin Newsom to declare a state of emergency in the city, an effort that could help them fast-track a $33-million landslide remediation project to stabilize the area.
In past storms, landslide damage has occurred sometimes months after the wet weather subsides.
The early February storms drenched much of the state in historic rainfall, knocking out power for hundreds of thousands of people, flooding neighborhoods and triggering mudslides. Several people in Northern California were killed in the onslaught.
Those storms hit certain neighborhoods particularly hard. Nearly 14 inches fell on Bel-Air over five days. So much rain in such a short period of time can be catastrophic for densely constructed hillside neighborhoods.
For the most recent storm, Los Angeles County authorities issued an evacuation warning for Santa Maria Road north of Topanga Canyon Boulevard through 9 a.m. Wednesday because of possible mud and debris flows.
A large sinkhole has also closed down the Skirball-Mulholland northbound 405 Freeway offramp indefinitely while crews make repairs, according to the California Department of Transportation.
Portions of the 101 Freeway from Seaward Avenue to California Street in Ventura are closed on account of flooding, according to Caltrans.
Highway 1 is closed from 6 p.m. to 7 a.m. in both directions from Sycamore Canyon Road to Las Posas Road in Ventura County because of erosion on the southbound shoulder.
Highway 150 is closed in both directions between Stonegate Road and Topa Lane because of slides and storm-related damage.
This story originally appeared on LA Times
