Breaking: Melinda's Take on New Flood Map
Residents grilled county officials about the latest hazard designations for their embattled community on Thursday night, as the rollout of the new Federal Management Agency Recovery map for Montecito began.
The map represents a major expansion of the flood plain in Montecito and the Carpinteria Valley, based on the changed landscape in the wake of the disaster.
The flood plain, marked in yellow lines as “high hazard areas,” now appears roughly to cover half of Montecito and two-thirds of the Carpinteria Valley.
Although it is interim and advisory in nature, the new map is designed to help homeowners decide whether, where and how to rebuild in order to withstand or avoid future flooding from a 100-year storm – an extreme weather event.
“This FEMA map shows the minimum elevation that the county will allow for a rebuild,” county Supervisor Das Williams, who represents Montecito and the Carpinteria Valley, told a packed audience at the County Administration Building on Thursday evening.
“It does not mean it is the advisable level to rebuild. It does not mean it is the safe level to rebuild. It isn’t gospel. Each individual should be looking to have the most resilient plan to rebuild that they can do.”
Where to find it. The recovery map is interactive; it can be viewed on the Ready Santa Barbara County website here.
The map was created within five months of the catastrophic debris flow of Jan. 9 – a record turnaround for FEMA.
A more comprehensive map that will update the Flood Insurance Rate Map of 2012 for both communities will not be completed by FEMA for another four or five years. The county Board of Supervisors is expected to adopt the interim recovery map next Tuesday in Santa Maria.
A second community meeting to discuss the map is scheduled for July 11 with FEMA officials present, sponsored by the Montecito Association.
Twenty-three people died and 470 structures were destroyed or damaged in the torrent of mud and boulders that surged down the burned mountainside above Montecito on Jan. 9.
The who’s in-who’s-out conflict. At Thursday’s meeting, several residents asked county officials why FEMA hadn’t mapped the risk of debris flows, rather than floods.
They wondered why some properties that were undamaged on Jan. 9 wound up in high hazard reason the recovery map, while others that were totally destroyed did not.
Mike Davenport, whose own property was untouched but is now in a high hazard area, said the county should limit those areas to properties that were damaged or inundated by mud and debris on Jan. 9.
“Models are wrong, they’re always wrong,” he said.
“It seems to me there are no boots on the ground in this model,” Davenport added. “You’re conveying a very serious message, saying it’s a high hazard area. It’s going to impact property values and property taxes and private insurance. I would really encourage you to go back and look at the neighborhoods that didn’t have any damage.”
Jon Frye, the county Flood Control engineering manager, said the new map was a flood map, not a debris flow map.
“It’s virtually impossible to predict where debris flows are going to go,” he said.
The new high hazard areas, or flood plains, are not based on clearwater flows as in previous FEMA maps for the area, Frye added.
The recovery map, he said, takes into account the debris-laden runoff that typically flows down burned mountain slopes and clogs bridges during heavy rains. The Thomas Fire was not even fully out when an extreme rainfall sent a torrent of mud and boulders coursing downstream.
Until the vegetation on the burned slopes grows back – a process that may take up to five years – the communities are still at risk, officials said.
Some properties that were untouched on Jan. 9 may still be susceptible to flooding in heavy rains, Frye said, noting that water spreads out farther than mud. Some homes that were destroyed in the debris flow may have been buried in five or six feet of mud, he said; at their new ground elevation, they may not flood in a 100-year storm.
“We think that this model represents a much truer picture of the threat and the risk,” he told residents. “I invite anybody to describe a flood event that we’ve had that doesn’t bring down debris. We call them debris-laden floods. They’re not debris flows, but channels fill in, bridges plug, culverts plug. That’s what really happens in real flood events.”
Underlying scientific assumptions. The FEMA recovery map is based on aerial LIDAR data – remote sensing imagery that was collected by air shortly after Jan. 9, using light from a laser to survey the ground.
For mapping purposes, FEMA assumed that 15 inches of rain in 24 hours in the mountains or eight inches of rain in 24 hours on the coast of Montecito and Carpinteria would trigger a 100-year storm – that is, an event with a one-percent chance of occurring in any given year.
That’s a worst-case scenario; even the powerful floods of January and March 1995, were not 100-year events, Frye said.
On the map, the limits, or perimeter, of the high hazard areas is drawn with yellow lines; it encompasses all the land that likely would be inundated below a burned watershed in a 100-year storm. “Depth grids” along the creeks are shaded from light blue to dark blue, denoting floodwaters six inches to more than 10 feet deep.
How maps will affect rebuilding. The county floodplain ordinance will require the first floor of new homes in the blue-shaded areas to be at least two feet above the advisory flood elevations; these are shown in hundreds of tiny boxes on the map.
Many but not all of these elevations are higher than those on the 2012 FIRM map. In making decisions about rebuilding, officials said, homeowners should compare the two and use the higher elevation.
Property that is within the mapped high hazard area but not shaded in blue is subject to shallow flows of less than six inches during a 100-year-storm.
But property owners in those locations “can’t take that as carte blanche to do whatever they want,” Frye said in an interview. If, for example, they were to excavate down to pre-debris flow levels, they might find themselves back in the flood plain, he said.
The recovery map can be modified to correct mistakes, Matt Pontes, assistant county executive officer, told the crowd on Thursday.
For example, Marshall Miller said his swimming pool appeared on the map as a blue dot, showing that it was susceptible to flooding. If only a flood would fill up the pool, he said, to audience laughter.
Another resident asked whether the map would be updated to reflect the fact that tens of thousands of truckloads of mud and debris have been cleared from creeks, roads, debris basins and private property since Jan. 9. Pontes said it would take months and months to get better LIDAR data, but the county was working on it.
“It’s a super-important part of the puzzle,” he said.
Map navigation and evacuations. Finally, several residents said they could not locate the map legend on the recovery map: It can be found by clicking on the horizontal bars in the upper right-hand corner.
To compare the old flood plain with the new, click on the stacked papers in the upper right-hand corner and check “National Flood Hazard Layer” at the bottom of the list. Then uncheck “Depth Grids” and “Water Surface Elevation Contours” to viewthe old and new high hazard areas.
The recovery map is not an evacuation map, county officials said, and it will not be used to set new insurance rates. The 2012 FIRM map is still in effect for the disaster area. And when FEMA updates that map, it will not be based on a burned watershed, Frye said.
Melinda Burns is an environmental reporter based in Santa Barbara.