Federal scientists say risk of mudslides from Station fire extremely high

The U.S. Geological Survey today issued a grim forecast for foothill communities hit by the Station fire, saying huge mudslides and debris flows are highly likely during the winter rainy season.

Scientists have been spending the last few weeks studying terrain destroyed by the largest fire in Los Angeles County history to determine which areas have the greatest risk of mudslides.

They identified Pacoima Canyon, Big Tujunga Canyon, the Arroyo Seco, the West Fork of the San Gabriel River and Devils Canyon as being 80% likely to experience flows of up to 100,000 cubic yards of debris, enough cover a football field with mud and rock to about 60 feet deep.

“Some of the areas burned by the Station fire show the highest likelihood for big debris flows that I’ve ever seen,” said Susan Cannon, a USGS research geologist and one of the authors of the emergency assessment. Cannon has been studying debris flows after fires for 11 years.

“We don’t have the science to model where it will travel, but there’s a really good chance of a big debris flow happening within that drainage system," she added.

USGS geologists used computer models to estimate the likelihood of debris flow in 678 drainage basins in the burned area, as well as how voluminous the material might be and where it might go.

They based their projections on the steepness of the slope, the extent and severity of the fire, soil characteristics and possible rainfall. The assessment posed two scenarios -- a three-hour, high-intensity thunderstorm, and a 12-hour gentle rainstorm -- and found high probabilities that each would cause large debris flows in neighborhoods that front the San Gabriel Mountains.

If drainage basins in the mountains fill up, Cannon said, debris flows could stream into neighborhoods in 12 urban areas.

Triggered by rainfall, debris flows can travel faster than a grown person can run, and the rushing water, soil, and rocks can destroy bridges, roads and buildings, and seriously injure or kill people in the way. The Station fire burned through a 250-square-mile expanse in August and September.

The goal of the assessment, officials said, is to help guide state and local planners as they work to protect lives and homes when rains come to the burn area. Cannon, the geologist, said the situation in the San Gabriel Mountains is reminiscent of conditions in the San Bernardino Mountains in 2003, when on Christmas Day a flash flood hit a campsite near a burn area, killing 14 members of a church group.

--Tony Barboza

Photo: A home sits high above Vogel Flats, surrounded by charred hillsides now at risk of winter mudslides that threaten homes that survived the Station fire along Stonyvale Road below. Credit: Robert Gauthier / Los Angeles Times

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Comments

[Jim]

Millions of able-bodied people are unemployed. Why not create another WPA and send workers in to build retaining walls, diversions, and plant trees? For that matter, why not hire the unemployed to plant trees across the U.S., repair bridges, teach vocational skills, create art?

[kooo]

I'm with you Jim, but a recent Federal court denied more road building into the Angeles National Forest. Obama should seriously consider doing another WPA program that directly "bails out" middle America by creating "green" jobs funded by taxpayer money. It's a win-win for the environment as well as for the unemployed in California.

[Joe McVeigh]

Twenty years ago writer John McPhee extensively chronicled the danger of these mudslides in his article "Los Angeles Against the Mountains," first published in the New Yorker and later included in McPhee's book The Control of Nature, published by the Noonday Press/Farrar, Straus and Giroux. Anyone who thinks this information is new or unexpected should read McPhee's excellent accounts of massive mudslides in the San Gabriels in 1978 (and earlier in 1969, 1938, and 1934.) McPhee also writes about the causes of the mudslides and the fruitless attempts to stop them with debris basins. Meanwhile, developers and oblivious homebuyers continue to build and purchase homes that are directly in the path of millions of cubic feet of earth.

What will county and city officials do to warn residents of these dangers? Will people listen, or will there be more deaths as a result of unwillingness to hear bad news and move?

[Jon Hainer]

My wife Deb Halberstadt and Nancy Rigg did a fifteen-minute video called Danger: Debris Flow that is still available on the LA County website. It covered a debris flow above Sierra Madre that killed a father and his son. The video also explains the phenomenon and shows it in action.

Btw, I too recommend John McPhee.

Jon Hainer

[Jon Hainer]

I found the link for the Danger: Debris Flow video. It is on the DPW website. Here is the link:

http://dpwprod2.co.la.ca.us/prg/pressroom/video.aspx?vfile=6

Don't miss it. Great shots, great explanation of the phenomenon, and a compendium of information that the public really needs now. Don't miss it.

Jon Hainer

[moi]

If the State of California owns one or more of the water-dropping planes and/or helicopters (I'm not sure if we do) I've been wondering if they might not be re-purposed.
I mean, would it be effective to drop water now on some of the hillsides with the worst slide threats? Would that be of any effect, to help foliage take root before the rainy season?
And if so, would it be cost-effective to do so (weighed against potential mudslide losses)?
If it were indeed effective, perhaps the State of California could make money by charging private landowners to drop water upon their land, as requested?
I realize I'm out of my league, not knowing much about the water-dropping equipment.
I'm just using my imagination, and wondering...

[danette]

I live across from the burn area but Im not goin to move. We were here for the last mudslide of 78 after the big fire of 75. I believe that mudslide was helped by scientists seeding the clouds to help the drought back then.

The mudslide broke open the streets destroying underground pipes for utilities, no electricity, no water, gas escaping. It was very scary. However the mud passes us on the mountain wrecking havoc but ends up at the bottom so no one is completely safe.

In the 1934 flood it was assumed some were washed to sea, never confirmed but confirmed deaths were at the bottom in the evacuation centers were the mud ended up taking lives. Studying where the mud will go is a good idea.

[joe]

Well since it hasn't rained in LA since about 2006 I'm not too worried about mud slides.

Those huge fire breaks/ roads they cut in to the front range sure make for a good work out though (running up them that is). Those things will be flowing like rivers if it does rain hard, and I live right at the bottom of Mt. Wilson.

Still not too worried...I think I saw about three rain drops all of last year in LA

[thealaskan]

the upside: usgs thinkers share this info.-- the downside you live there. so does your realtor need to disclose it? I mean why should one be required to disclose the obvious to someone from ohio?

[Daniel Borders-Ashe]

Jim and kooo -- I agree with you both. But the question is: where will the money come from? In order to support any such program money from both the State of California and the federal government would be used.

I'm afraid this is once again an example of something that seems to be more or less distinctly American: we love our governmental services (especially in California) but we hate taxes.

Raise taxes for God's sake! Then we'd be able to afford this and a lot more (and California wouldn't be in budget hell).

[La Crescenta Observer]

Although I'm in the flood path (more or less), I agree with Joe - history says we're living in the middle of Nature's highway, and it's only a matter of time before one of Her "big rigs" comes a-truckin' on through.

I used to be a news photographer, and saw firsthand a huge mudslide in north San Bernardino/Highland that buried a swath of neighborhoods. Miraculously, no one was killed. However, within a few years building new developments in that area began again.

As long as developers stand to gain from building in unsafe areas, people remain uninformed about the risks, and government officials do not proactively warn them (this is *exactly* the kind of scenario that libertarian free-market bullshit won't address - that there is no profit motive or self-interest in warning others, but we should do it, no?), the tragic cycle will continue:
• underwater cities (New Orleans)
• fire cities (most of Southern California)
• earthquake cities (er...what I just said)

not to mention this type of thing internationally.

[Danny]

Check out historical photos from the Massive 1934 La Crescenta debris flow here - http://www.cvhistory.org/thennow/thennow.htm

This flood occurred two months after a similar fire in the foothills. Hopefully people will understand the magnitude of whats geologically possible this winter.