A worker uses an excavator to move piles of mud off a home on Middlefield Road in the Berkeley Hills. Credit: Supriya Yelimeli

An excavator rotated back and forth in the Park Hills neighborhood Wednesday morning, picking mounds of mud off a home that was hit by a debris flow in the Berkeley Hills last week.

It was among several residences impacted by the rain-related event near The Spiral at the Berkeley-Kensington border, where 14 residents had to evacuate now red-tagged houses.

With geological technicians still determining if the area is safe, none of the residents can return home. Multiple groups are responding to the flow, including a team formed under the city’s Emergency Operations Center.

One major problem is that the debris flow is still technically “active” due to water movement in the area, Councilmember Susan Wengraf said.

Workers have rerouted the water down to a storm drain under the most-affected property on Middlefield Road, but it still has the potential to make mud in the area unstable.

Alan Kropp, a Berkeley resident and geotechnical engineer, explained that water can exist in “pockets” throughout hillside areas, a little bit above what is technically known as groundwater, but with its own flow routes and movement. A large storm increases the amount of water.

“It’s always possible that you would have water … that landed on the ground, potentially uphill — sometimes even well uphill of an area — keep flowing below the ground. And if you have a slide, it exposes that kind of flow route that it has,” Kropp said.

Compared to a burst pipe, for example, that water will eventually lessen.

“Generally speaking, if it’s natural, you would expect it to be slowing. It may never stop because there may be a lot of water stored in the ground, but if it’s a natural thing, normally it slows down,” Kropp said.

Due to the instability, removing the dirt is a key part of ensuring there isn’t another landslide into properties located lower in the neighborhood, as city spokesperson Matthai Chakko said. Workers began moving the debris this week.

“Once mitigation measures are in place, or the hazard is removed, Building & Safety will confirm with the geotechnical engineering teams involved to determine if the homes are clear for re-entry and re-occupancy,” Chakko said.

Berkeley fire officials said none of the residents required relocation support from the American Red Cross the day the flow happened.

Plastic pipes route water to a storm drain from the area where the debris flow happened. Credit: Supriya Yelimeli

Berkeley Hills landslide risks are documented, but debris flows can be unpredictable

The debris flow happened right after a set of several rainstorms storms struck the Bay Area in the first couple weeks of the year.

Accumulated dirt and materials washed down from Zaytuna College’s upper campus into homes in the area of The Spiral — a geological event that can be hard to predict, according to Kropp.

A spokesperson from the school at 2401 Le Conte Ave. said facilities workers are on site trying to determine how the debris flow happened, and the campus is grateful that no students, staff or faculty were injured or in any danger “at any point.”

No buildings were damaged either. Separate from the recent debris flow site, Zaytuna College and previous property owners have worked to address landslide risks on its hillside campus for decades.

The Alameda County Sheriff’s Office’s emergency response team and Federal Emergency Management Agency were also in the neighborhood Wednesday morning conducting a preliminary assessment.

Insurance doesn’t typically cover mudslide damage, but residents may be eligible for individual financial support from the federal government. Last week, President Joe Biden approved increased funding for California in the aftermath of the storms, flooding, landslides and mudslides statewide.

The debris flow in the North Berkeley Hills was among several rain-related events that impacted the hills. A large landslide struck Alvarado Road in the South Berkeley Hills near Claremont, exposing a historically problematic hillside that owners and the city of Oakland had spent millions to stabilize.

Devastating landslides in Berkeley are also possible in the coming years, city officials have warned.

Kropp said a similar event is unlikely to happen again in the same way because it was caused by a buildup of materials that ultimately washed down into The Spiral. It would have to accumulate over decades to cause a similar problem.

For now, residents are awaiting news that would allow their homes to move from red-tag to yellow-tag status and let them return to their neighborhood.

“Everybody has been very cooperative and they understand the danger involved,” Wengraf said. “I think they’re all anxious to get back into their homes.”

Supriya Yelimeli is a housing and homelessness reporter for Berkeleyside and joined the staff in May 2020 after contributing reporting since 2018 as a freelance writer. Yelimeli grew up in Fremont and...