It turns out that last month’s storm was a blessing in disguise.
The rain along the Gaviota Coast was light, with the short periods of cloud burst focused more along the coastline than the charred inner mountain slopes.
The potential debris flows turned out to be nonevents. There were a few feet of ash-black flows in Arroyo Hondo and Arroyo Quemada canyons — enough to set nerves on edge but do almost no damage.
At Refugio Canyon near Circle-Bar-B Ranch, there was barely a trickle meandering down the creek, a godsend to those at the ranch.
In all, a very good rain.
There was an inch-plus, enough to wet down the ash, compacting it a bit, perhaps enough to provide a solid enough surface for roots to begin anchoring things in place.
That’s if there is enough time before the next rain and enough sunshine for the roots to set and the chaparral burls to sprout.
BAER Report Due Soon
On Friday, Los Padres National Forest was scheduled to provide critical data that may help understand how the 17,000-plus-acre Alisal Fire — much of it burned to mineral soil — will impact these canyons.
The Burned Area Response Team (BAER), mandated after such large fires, is charged with conducting a rapid assessment of the effects of the fire on vegetation, soils and watershed function.
That usually occurs within seven days after the fire’s containment, and is used to develop a plan designed to stabilize the fire-affected landscape and mitigate post-fire hazards.
The BAER Team includes specialists from a number of fields, including hydrologists, geologists, biologists, archeologists, and soil and wildlife specialists. Each produces a report and those, in turn, are assimilated into a final document known as a 2500-A.
“Primarily, this is a tool we use to document our findings in order for us to request funds to implement what we are recommending be done,” team leader Yonni Schwartz said.
Critical to Recommendations
As part of the review process, the BAER Team is required to produce three products that will be used to assess the fire impacts: a soil burn-severity map, debris flow modeling maps, and hydrology modeling data used to evaluate possible outcomes.
While those are usually made available to the public together, it turns out the burn-severity map was made public well before that — on Oct. 23.
“When the rain came, just as we were beginning our assignment — literally two days into it — it was critical we get that out immediately in order to get the agencies prepared for when it hit,” Schwartz said.
As it turns out, the burn-severity map was extremely valuable for those preparations, but it also created some confusion.
Given that only 1% of the burn area, less than 260 acres, was classified as severely burned and more than 60% had been classified as low or very low, some wondered whether there was anything to worry about.
“Most people don’t really understand the concept of burn severity,” Schwartz said. “The critical value isn’t how much vegetation has burned, but its impacts on the physical and chemical structure of the soil.
“Specifically, in regards to debris flow hydrology modeling, the moderate and the high are actually equal. So, it’s really a big misunderstanding to look at the low and moderate burn severity areas with little high and think that it’s not too bad, or they don’t have the potential for debris flows and flooding.”
Soil Structure Plays Crucial Role
In both moderate and severely burned areas, impacts to the soil are critical to understanding the potential for debris flows to develop.
Impacts include a breakdown in soil structure, reduced ability of the soil to retain moisture, and the potential for the development of water repellency, all of which increase the potential for erosion.
According to a number of scientific journals, impacts also may include changes or loss of microbial species, reduction or loss of invertebrates, burning of organic soil materials and loss of critical plant roots.
Devastation to Surface Organics
Even more critical to burn severity are the organics. The most impactful issue isn’t what burned above ground, but the organic layers immediately below that help form the soil structure.
Those include the surface leaf litter, and beneath that, the layers of decaying vegetation that are critical to a slow release of minerals and other nutrients needed for plant growth.
Normally, it is a slow process that takes years. A wildfire like the Alisal Fire has the potential to rapidly accelerate the process, suddenly releasing nutrients such as nitrogen, sulfur and phosphorous.
Much of that vaporized, and what doesn’t vaporize is often lost when carried downhill during storm activity.
“In terms of burn severity,” Schwartz said, “these types of impacts not only provide us with an understanding of how large the potential is for a major debris flow event this winter, but how long it may take for the soil and vegetation to recover.
“These things can take a few years to bring us back to pre-fire conditions, and perhaps longer in the more severely burned areas.”
Who Should Worry?
Pointing to the burn severity map, Schwartz said there are three things that should be looked at more carefully.
One of those is topography; a second, the fire history; and third, where the most severely burned areas are located.
In looking over the map to identify areas with similar characteristics, clearly the most critical area for potential debris flows are Arroyo Quemada and Arroyo Hondo canyons and the areas surrounding Circle-Bar-B Ranch.
Post Fire & Debris Flow Mitigations
Another misconception about the BAER process is that it is designed to look at the entire area and develop recommendations for mitigations.
“While BAER identifies critical values at risk associated with life, and life and safety, or property, which includes roads and trails, and campgrounds, and resources like wildlife, biology and cultural resources,” Schwartz said, recommendations for specific mitigations are made only for federal lands.
“While we recognize there are critical values downstream of federal land, and we do identify these critical values in those areas,” Schwartz said, “the BAER report will not come with specific recommendations.”
WERT to the Rescue?
When it comes to a more detailed look at the values at risk on the nonfederal lands, that is being done by the state’s Watershed Emergency Response Team (WERT).
Assembled in a similar fashion to the BAER process, the team’s focus is on similar values at risk as BAER, with a much higher emphasis on life, safety and property.
According to Schwartz, the WERT process is much more detailed, with the team assessing risks on a house-by-house basis. That is a critical task given that 11,954 acres of the Alisal Fire’s 17,845 total (67%) occurred on private lands.
Currently, the WERT Team is conducting field evaluations in the Gaviota area, with scheduled visits to Arroyo Hondo, Arroyo Quemado and Tajiguas at the end of the week and other areas within the next few days.
The WERT report could be made available to the public as early as next week. Recommendations for the mitigations on private lands within the burn area are expected to cost millions of dollars.
A Note of Caution
Though the recent rain turned out to be a positive event when measured against what might have occurred, Schwartz cautioned against reading too much into that.
“When you look at the debris flow map, for example,” Schwartz said, “you’ll see that most of the upper parts of a number of the watersheds have the perfect ingredients for devastating debris flow similar to what happened in El Capitan Canyon (after the 2016 Sherpa Fire).
“You have steep slopes, you have channels that are loaded with fine sediments and large sediments, and hillsides filled with rocks and boulders on all sides. Then you add the soil burn severity, which is in the moderate to high range.
“And now the only ingredient that is missing is a short-duration, high-intensity rainstorm that will mobilize all of this.”
Immediate Responses
Meanwhile, at the Arroyo Hondo Preserve, the word is caution. Public access to the ranch is closed until further notice. Conditions are being monitored closely for the safety of the staff, and efforts are underway to evaluate burned area vegetation near trails and erosion-prone areas.
“The Land Trust (for Santa Barbara County) looks forward to welcoming the community back to the preserve when it is safe to do so,” said Meredith Hendricks, the organization’s executive director.
While that may not occur until the winter rainy season is over, Hendricks looks forward to a time when a range of programs might be offered so that everyone can all learn together about fire ecology and the regeneration of what she termed “this spectacular place.”
Baron Ranch is also closed to the public while conditions are being monitored, and early indications are that public access may not be reopened until late spring.
— Ray Ford is a Noozhawk outdoors writer.