Rainfall might help extinguish the last, lingering hot spots of the massive Thomas Fire, but the greater concern now is the risk precipitation will unleash torrents of water, mud and debris in the burn zone and down slope from it.
"Now that the foundation of the affected land has been compromised, nearby communities will have an elevated risk of flash flooding and debris flows when the rains come," said Jeff Pratt, Director of the Ventura County Public Works Agency.
He urged residents to register with the county for emergency alerts, and to consider buying flood insurance.
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In the city of Ventura, a Public works crew this week cleared burned vegetation and other debris from the Sanjon Barranca, one of the natural ravines through which runoff flows from the Ventura Hills, and into a large drain underground drain pipe that leads to the ocean.
The concern is that if the pipe becomes clogged, runoff could flood into neighborig areas, according to Sergio Vargas, Deputy Director in the Watershed Protection District.
Decisions on what additional steps will be taken await the results of assessments. County Geologist James O'Tousa is working with state and federal teams.
But from what O'Tousa has already seen, he believes the likelihood of debris flows is 90 percent or greater.
"Every canyon in this burn zone is at risk," O'Tousa said.
The city of Ventura alone has a dozen significant barrancas.
Pratt warned that no matter how much clearance is done, at a certain level of rain, there may be too much erosion to contain.
At that point, "All we can do is help you get out of the way," said Pratt. "Nobody's stopping a flood."
Concern extends beyond the city of Ventura, with the burn zone rangng to the east above Santa Paula and Fillmore, to the north surrounding the Ojai Valley, and upcoast into Santa Barbara County. Slopes burned near the small coastal community of La Conchita, where a 2005 mudflow overran homes and killed 10 persons.
County residents can register for emergency bulletins by going to the Ventura County Recovers website.
Much of the flood control system beneath the city of Ventura was built a century ago, Pratt said, warning that if there is clogging within pipes, flooding could come from below ground considerable distance from the denuded hillsides and barrancas, and for that reason is recommending homeowners look into flood insurance that includes protection from debris flows related to fire.
Because there is a 30 day waiting period, residents left vulnerable by the fire should not delay, Pratt said.
In some locations, it may be possible to shield property with sandbags, wattles, or other protective measures. Jan Denharder, who lives in the foothills on the west side of Sanjon Barranca, said every winter he installs runoff barriers, and will do so again.
But as thousands did earlier this month in the face of fire, in the face of rain, residents must be prepared to evacuate.
"In the same manner they prepared for fire, they should prepare for floods," said Vargas.
That the Thomas fire came so late in the year--after the rainy season typically begins--means preparation time could be short. Ironically, the unseasonally warm, dry weather--with fierce Santa Ana wind---that enabled the Thomas Fire, is continuing to hold off the arrival of rain. But authorities warn the risk will persist until the rain does return.
"Everybody has to help themselves," said Pratt.