Weekend rain made for treacherous driving Monday in the flats at Rio Del Mar.
(Kevin Painchaud / Lookout Santa Cruz)
Coast Life

Sorting through the storm’s aftermath: No debris-flow issues make for a good ‘dry run’ before winter

While the Santa Cruz Mountains saw plenty of rainfall Sunday, it wasn’t at the rate and amount that experts believe will pose debris flow issues in the CZU fire burn scar. And it might have been good preparation for weather events ahead.

Sunday’s rainstorm was anticipated to be one for the record books. It didn’t live up to those expectations in Santa Cruz County, and the aftereffects could actually prove that Santa Cruz Mountains residents are more prepared for winter than expected.

In anticipation of Sunday’s “atmospheric river” that swooped off the Pacific Ocean and over the Bay Area, Santa Cruz County first recommended and then later mandated that the mountain residents most vulnerable to debris flow issues evacuate before the storm arrived.

Only a portion of those warned chose to leave their homes, and as of Monday evening, the county had reported zero issues with debris flow — partly, experts believe, because the amount of water that fell was spread out over a long enough time.

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According to county estimates, 3,300 households were a part of the 24-hour evacuation zone window from 8 a.m. Sunday through 8 a.m. Monday. The county opened a temporary shelter for evacuees at San Lorenzo Valley High School but reported that only three people showed up.

According to the National Weather Service, the top of Ben Lomond received 9.63 inches of rain, second only to Mount Tamalpais in Marin County. Other parts of Santa Cruz County saw well in excess of 6 inches. Downtown Santa Cruz reported 5 inches.

County spokesperson Jason Hoppin told Lookout on Monday that 319 households were considered at “extraordinarily high risk” due to the condition of the soil from the CZU fire, and potential issues with debris flow. Of those 319 homes, roughly a third of homeowners signed safety waivers to say they would remain in place.

“Our goal is to give people information they can use to keep themselves and their families safe,” Hoppin said.

Yet, he noted, Sunday’s storm could be a good dry run and assessment for what could come this winter, specifically in December and January.

County geologist Jeff Nolan said that while Sunday’s storm resulted in less rain than expected, the county has to consider the rain intensity more than the total amount.

“The debris flow hazard that we’re grappling with is fire-related,” he said. “It only has to rain for 15 minutes to cause a really large debris flow after a fire, but it has to rain at a very high intensity.”

The threshold intensity would have to be 0.3 inches of rain in 15 minutes, 0.5 inches in 30 minutes or 0.7 in 60 minutes. Nolan isn’t sure if any area of the county hit those thresholds Sunday.

Of course, there was the added worry of power outages and blackouts for many residents. In the tri-counties — Santa Cruz, San Benito and Monterey — more than 10,000 households were affected, Pacific Gas and Electric spokesperson Mayra Tostado said. The company set up staging areas throughout the county in advance of the storm to address the concerns diligently, with 37 crews working Monday afternoon.

“We’ve seen significant outage activity, mainly in the San Lorenzo Valley,” Tostado said Monday, with 4,289 customers in those three counties still affected.

On top of crews addressing felled trees and downed power lines, Tostado said they also needed to assess fallen vegetation, saturated soil, and access issues, which could lead to longer-term impacts for customers.

The SS Palo Alto and Seacliff State Beach saw some big waves Monday.
(Kevin Painchaud / Lookout Santa Cruz)

“This has been a massive effort — we’re seeing a lot of water runoff and roads that aren’t as stable,” Tostado said, further noting that some crews were hiking into affected areas. “We’re hoping we can restore all customers by tonight, but we’re not sure.”

Dave Reid, director of the Santa Cruz County Office of Response, Recovery and Resilience, said there were no reports or encounters thus far of significant debris flow in the affected areas, but the county is still evaluating the sites as well as private properties.

“In general, this was a very big storm — we are fortunate in avoiding a major event,” he said. “We tried to be prudent and keep everyone safe, and keep people aware of the risk.”