Intense rain storms could cause flooding that affects neighborhoods below the Cave Fire burn area, particularly along San Antonio Creek in the North Turnpike Road area, according to the Burned Area Emergency Response Assessment from Los Padres National Forest.
The BAER report, released last month, outlines hazards from the 3,126-acre wildfire, including the risk of post-fire flooding and debris flows.
Santa Barbara County emergency management officials have already warned the community that major storms will be a concern for areas below the burn area, and created a risk map specifically for the Cave Fire.
That map is available online here and at ReadySBC.org.
The concern is for low-lying areas along San Antonio Creek and Maria Ygnacio Creek, since post-fire runoff will increase within and downstream of the burn area.
Some of the houses along San Antonio Creek between Cathedral Oaks Road (near Tuckers Grove County Park) and Highway 101 are within the flood plain, and at risk of flooding or debris-flow impacts, according to the BAER report.
(BAER stands for Burned Area Emergency Response.)
The pedestrian bridges and pipelines in the area could cause creek channels to flood or divert into surrounding low-lying areas.
Any debris flow in the upper San Antonio Creek basin would likely transition to a debris-laden flood as it flowed downhill to urban areas, the Watershed Emergency Response Team concluded.
“Thus, debris flows extending past Cathedral Oaks Road and into the built environment appears relatively unlikely. However, sediment- and debris-laden flood flows could cause drainage structures to be blocked and flood waters and floating debris to extend beyond the banks of the channel.”
Deputy Public Works Director Tom Fayram said that since the Cave Fire in late November, crews had to empty San Antonio Creek’s debris basin of sediment after each storm, but no debris or rocks have come down.
He said he’s concerned that sediment will stop in the creek channels, fill them, and cause flooding.
(Giana Magnoli / Noozhawk photo)
County officials said major storms will be a concern for several years until vegetation grows back in the burn area.
The BAER assessment said there would be rapid vegetation recovery in areas with low soil burn severity, which was the majority of the Cave Fire area, and a 3-to-5-year period for areas to recover with higher soil burn severity.
The burn area of the 2017 Thomas Fire is in its third year of recovery, and the risk of debris flows is diminished, but not gone.
Caltrans Works on Fire-Related Repairs to Highway 154
Heavy rainfall could cause debris to block the Maria Ygnacio Creek culvert under Highway 154, which is 9 feet wide and 12 feet high in a deep section of the channel, according to the BAER report.
Clogging that culvert could affect the roadway above.
That’s what happened last year when runoff from the Whittier Fire burn area blocked a Highway 154 culvert near Lake Cachuma, causing erosion and a weeks-long closure while Caltrans crews cleaned up the mess and rebuilt the roadway.
Caltrans has contractors to respond with equipment, including cranes and pumps, to unclog culverts if they get blocked by water and debris, Caltrans District 5 spokesman Jim Shivers said.
“If the drainage system is impacted, full closure of the highway will likely be required,” he said.
Caltrans plans to install an overflow culvert at Highway 154 and Maria Ygnacio Creek to prevent roadway flooding, and will have maintenance crews patrol the highway during rain storms, Shivers said.
Since the Cave Fire, Caltrans crews have been repairing fire-damaged guardrails and doing proactive work, such as installing k-rails, to prevent rockfall, landslides and debris flows from affecting the road.
— Noozhawk managing editor Giana Magnoli can be reached at gmagnoli@noozhawk.com. Follow Noozhawk on Twitter: @noozhawk, @NoozhawkNews and @NoozhawkBiz. Connect with Noozhawk on Facebook.
