Yucaipa: a remarkable debris flow video from the San Bernardino Mountains

On Tuesday a remarkable video was posted to Twitter showing a series of debris flows at Yucaipa in the San Bernadino Mountains of California:-

This amazing video captured by San Bernardino county public works – watch all the processes of a #debrisflow of the El Dorado scar September 12, 2022 – heavy rain rates on scar at 8000 feet in 1 hour pic.twitter.com/ZApuQZ5FuP

— Alex Tardy Skiwxman (@SanDiegoWCMwx) October 25, 2022

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The video is also on Youtube.  This series of debris flows, which occurred over the period of a single hour, were generated from the scar of the 2020 El Dorado fire by intense precipitation.  The events occurred on 12 September 2022 when the remnants of Tropical Storm Kay triggered heavy rainfall – up to 60 mm was recorded.  The debris flows affected two communities, Forest Falls and Yucaiba.  The Los Angeles Times has reported that a women was killed in Forest Falls.  The same article has some dramatic images of the aftermath:-

The aftermath of the 12 September 2022 debris flows in Yucaipa and Forest Falls, California. Image by Gina Ferazzi / Los Angeles Times.

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The video shows the complex behaviour of debris flows, with multiple pulses or surges of debris travelling down the channel, which is typical for such events.  In the early part of the video, the surges have quite a high density, but note that it appears that there was no rainfall at the site of the camera at the time:-

One of the debris flow pulses in Yucaipa, California. Still from a video posted to Youtube.

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Later in the video there is heavy rainfall at the camera site.  The debris flow had become less dense and was behaving more as a debris flood:-

A later stage of the debris flows at Yucaipa, California. Still from a video posted to Youtube.

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Note however that some evidence of pulses of debris is still seen.

The Los Angeles Times article highlights the challenges faced by communities affected by such events.  This is a quote from Brenda Ebrahim, a resident of Yucaipa whose property has been badly affected by such events:

“We’ve been begging for help for years since they told us this was going to happen,” Ebrahim said. “I’ve been through it, I know how it works. It’s not sustainable. This is California’s new reality.”

Of course we are now moving towards the winter period, when high intensity rainfall events often occur.

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Acknowledgement

Thanks to Steve Beattie, who spotted this and highlighted it to me via Twitter.