post-fire

by Guy McCarthy

MODJESKA CANYON, Nov. 8 -- The good news for anyone residing in or below burned watersheds in Southern California is the coming winter is forecast to be much like the last -- dry and drier.
The bad news is that could mean more wind-driven fires before the year is out.
Either way, it is impossible to rule out unexpected, intense rain storms that could trigger damaging post-fire erosion in communities in and adjacent to nearly 800 square miles scorched by the region's latest round of wildfires.
So from Malibu to the San Bernardino mountains and the canyons of Orange and San Diego counties, residents and authorities were hard at work this week preparing for the next potential disaster.
In the close-knit town of Modjeska Canyon on Wednesday, Colleen Wahelan stood outside her hillside home and said she hopes erosion control efforts get started in her neighborhood immediately.
"I think they need to plant smart to re-stabilize the hillsides," Wahelan said. "They need to get the right resources in here as soon as possible. I hope they'll evaluate specifically which homes are at risk."
One look at the fire-ravaged slopes up and down Modjeska underscored her worry. Blackened, ash-coated ridges and steeps loomed above, inter-mixed with stands of chaparral that had not burned. At the east end of town, many homes appeared to be creek-side and just above the floodplain in normal circumstances.
"I've been here for 12 years, but being at the bottom of the hill for the mudslides, and all this ash on the hillsides is a concern," Wahelan said.

'VOLATILE FIRE/EROSION'

The aftermath of the Santiago Fire in Modjeska Canyon illustrates an Army Corps of Engineers description of the recurring fire-flood cycle in Southern California. The Corps has for decades helped design a number of flood control facilities in the region.
"The occurrence of wildfire plays a significant role in the augmentation of erosion rates from Southern California watersheds," states an Army Corps document, "Debris Method," which was updated in February 2000. "Highly flammable chaparral species, steep slopes, loose sediments, hydrophobic soil conditions created by the intense heat generated by wildfire, and the aggravating influence of dry offshore 'Santa Ana' winds provide Southern California with one of the most volatile fire/erosion complexes in the world."
Emergency erosion control work continued Wednesday up and down canyons that had burned in the nearly-contained Santiago Fire. County inmate crews labored, lining stretches of Santiago Canyon Road and other roadways with hay bales held in place by steel rebar. Bigrig and flatbed truck drivers hauled load after load of more baled hay into Modjeska and other canyon communities in need of protection.
Meanwhile, scientists including biologists, geologists and hydrologists did what they could to assess fire damage, in their roles with various Burned Area Emergency Response teams. BAER teams in five counties hope to have reports ready within 10 days of full containment on the respective fires they're working.
Specific information about exactly how many homes are at risk of potential post-fire flood damage in Southern California may not be available for days or weeks. But some BAER teams had compiled preliminary reports by Thursday afternoon, including several in Los Angeles County.

'GRAVITY IS NOT YOUR FRIEND'

Near Castaic and Santa Clarita in north Los Angeles County, where the Buckweed, Magic and Ranch fires burned close to 100,000 acres, there are an estimated 160 homes, two apartment buildings and a strip mall considered threatened by debris flows or mudslides, said L.A. County Forester John Todd. The numbers came from a U.S. Forest Service BAER report, Todd said.
In Malibu, one house is considered at risk from post-fire erosion from above.
"I believe that this is due to the fact that many of the areas that burned in Malibu were away from structures," Todd said. "In addition, many threatened Malibu structures are positioned on ridge lines or viewpoints where debris flows are less of a threat.
"On the other hand, many of the homes that were adjacent to burned areas in Santa Clarita are at the toe or base of the slope," Todd said. "And in debris flow situations gravity is not your friend."
Here is the preliminary list of at-risk structures compiled by BAER teams in Los Angeles County and released Thursday afternoon:

Buckweed, Magic, other Santa Clarita Fires
- 160 Homes
- 10 Outbuildings/barns
- 1 Business
- 1 Strip Mall (including several businesses)
- 2 Apartment buildings
- 2 Mobile Home Parks
- 1 Probation Camp
Canyon Fire, Malibu
-1 House

There are at least 100 personnel assigned to BAER teams in Southern California, according to U.S. Forest Service officials. Preliminary reports from teams and other officials working in San Bernardino, Orange, San Diego and Ventura counties could be available in the next few days.
In the meantime, the outlook for a dry winter may be encouraging for anyone threatened by potential erosion from burned areas. But the remainder of the Santa Ana wind season combined with anticipated low precipitation leaves open the possibility of more fires this fall and winter, said Bill Patzert, a climatologist with NASA's Jet Propulsion Lab in Pasadena.
Whether it rains or not, "we ain't done with further consequences," Patzert said.

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http://www.spl.usace.army.mil/resreg/htdocs/DebrisMethod.pdf