The Federal Emergency Management Agency has issued revised coastal flood-risk maps that may require  more homeowners living on Marin shores to purchase flood insurance. The new maps—which providers use to set flood insurance premiums—determine the boundaries of special flood hazard areas, within which any house backed by a mortgage must carry flood insurance.

According to the Marin County Department of Public Works, 53 more parcels in West Marin will fall within the expanded flood-hazard boundaries once the maps take effect roughly a year from now. A 90-day public comment period is underway until May 9.

Studies involved in revising the maps did not take sea-level rise into account, but FEMA has created an advisory council to delve into issues related to sea-level rise and how projections could be incorporated into future map revisions.

“Every five years, we need to assess whether our maps are up to date, and if they’re not, we need to bring them up to date,” said Ed Curtis, a regional engineer with FEMA. “So the expectation is that we’ll periodically do revisions to the maps for things like sea-level rise.”

For residents who already have flood insurance, the revised maps  establish new minimum-height recommendations—called “base flood elevations”—for some homes in Stinson Beach, Marshall and Dillon Beach that could force homeowners to raise the heights of their houses. 

That costly scenario will depend on forthcoming updates to the county’s Local Coastal Program that will use the maps to establish new building height standards for homes in environmentally sensitive areas, such as flood zones. The county plans to release a report on the updates in advance of an April 19 Board of Supervisors hearing.

A common engineering term, “base flood elevation” indicates the lowest height a building can stand and still avoid damage from large 100-year flood events. Marin requires any new construction or additions that incur costs exceeding the original structure’s value by 50 percent to meet or exceed the base flood elevation.

In Marshall, several homes will face new 12-foot base flood elevations brought about by FEMA’s estimates that waves on Tomales Bay could rise to three-foot peaks. 

But homeowners there wonder whether FEMA’s data is out-of-touch with the bay’s historic wave activity.

“We’ve never seen three-foot waves on Tomales Bay,” Lori Kyle, the president of the East Shore Planning Group, told the Light. “So we’re hoping that number is incorrect.” 

Ms. Kyle’s comments came during a meeting held by FEMA representatives last Thursday at the Marconi Conference Center, where the revised maps and the science behind them were explained. A previous meeting was held in Stinson Beach earlier in the week. 

At both meetings, attendees questioned the methods FEMA used to calculate wave heights capable of causing 100-year floods.

Representing the first revision since 1982, the maps incorporate improved data from several federal agencies and new technology to plot hourly wave and tide activities over the last 50 years, with data pulled from over thousands of tide stations spread out across the entire United States coastline. The agency’s goal was to determine the one-percent annual chance  that a major flood could strike any given point along the coast—a percentage that engineers equate to a 100-year flood.

But residents at the Marshall meeting disagreed with FEMA’s conclusion that Tomales Bay’s still-water elevation—or the height of water without waves—could swell to eight-and-a-half-foot tides when influenced by abnormal “surge” components, such as atmospheric pressure and El Niños. 

Some residents reasoned that they had only seen still-water in the bay reach slightly over six feet at its highest, even during El Niño periods. But FEMA representatives defended the larger figure.

“When you start to add all elements up, you can get to eight-and-a-half feet,” said Justin Vandever, a coastal engineer with an independent contracting company, called BakerAECOM, hired to revise the maps. 

One Marshall resident, Fred Kallander, pointed out that the data FEMA used to estimate potential future maximum wave heights was taken from tide stations located offshore near the Point Reyes Lighthouse, where wave actions differ greatly from those within Tomales Bay.

”That’s apples and oranges,” Mr. Kallander said. “You’re not going to have the same type of surge at the lighthouse that you’re going to have in the bay. That’s
ridiculous.”

Mr. Vandever countered that FEMA did have a small dataset collected from four tide monitors placed intermittently in Tomales Bay by the National Oceanic and Atmospheric Administration, which FEMA engineers drew from to estimate a slightly lower still-water elevation number relative to waters around the lighthouse. But he emphasized that any sort of wave activity on top of the unusually high 100-year still-water levels could cause property damage.

“Even a one-foot wave that breaks on a slope, it’s going to run up that slope for a vertical height of two to three feet,” Mr. Vandever said. “So even with small waves, it can add up pretty quickly to give you something on the order of 12 feet, in terms of the [base flood elevation].”

On the other hand, FEMA determined that many homes in Stinson Beach will enjoy decreased base flood elevations and, as a result, lower insurance premiums. According to Edith Lohmann, a national flood insurance specialist, premiums drop by hundreds of dollars each foot a home’s base flood elevation decreases.

Ms. Lohmann said FEMA will grandfather-in existing premiums for homes built before 1982, when the current flood maps went into effect. For homes built after 1982 and re-zoned into flood-hazard areas due to the revisions, owners who have insurance will have the option to keep paying their current premiums or drop down to a more favorable rate if, for instance, a house was built above a new base flood elevation.

“We want to provide people the maximum flexibility as far as their premium goes,” Ms. Lohmann said. “We don’t want to penalize property owners who built in compliance with the information they had at the time.”

But some homeowners with mortgages—especially in Marshall and Dillon Beach—could be saddled with new insurance premiums costing between $2,500 and $5,500, depending on the type of risk zone. According to Ms. Lohmann, these homeowners will have an opportunity to enroll in a special program created by the United States Congress to “ease into the transition for required flood insurance.”

Under the program, homeowners would start with a $475 premium—the same amount for FEMA’s insurance maximum coverage of $250,000 that would apply to homes in low to moderate-risk flood zones. That rate would increase by around 15 percent annually, until the rate levels out at around $1,500.

Ms. Lohmann noted that many homeowners have been seeing premiums rise by thousands of dollars in recent years because of federal legislation passed in 2012 and updated in 2014 that is phasing out flood-insurance subsidies. 

She said any rate changes brought about by the map revisions would remain in perpetuity, unless Congress enacted new legislation for the national flood insurance program.

Ms. Kyle told the Light that the East Shore Planning Group will explore options to produce new surveys and data for Tomales Bay in order to appeal FEMA’s findings. But that effort could cost in tens of thousands of dollars, she said, and take an extensive amount of time.

“For that, we would need community support,” she said. “It’s very early in our inquiry, but we’d have an analysis done as a first step and see where to go from there.”