Leaving the Fire Island breach open — and even allowing it to grow naturally — is the National Park Service’s preferred option for dealing with the superstorm Sandy-caused gap.

The Park Service says the width of the breach shouldn’t expand beyond about 1 1/2 miles due to bracketing layers of clay that serve as natural “geological controls.”

“We believe it wouldn’t go past that because they are so strong,” said agency spokeswoman Elizabeth Rogers.

The agency’s recommended plan, released Friday, calls for closely monitoring the breach, ripped open by Sandy in October 2012 in the Fire Island National Seashore wilderness area at Old Inlet.

Should the opening expand beyond the natural borders, its path would become more unpredictable because no other such barriers exist in the area, according to the Park Service.

In that case, the agency would conduct more analysis, consult with scientists and other agencies, and decide whether to close it.

That would occur only “to prevent loss of life, flooding, and other severe economic and physical damage to the Great South Bay and surrounding areas,” the Park Service said in its draft environmental impact report.

If the breach closed naturally, the Park Service said it would not reopen it.

The agency’s other two options are to take no action — allowing natural processes to take their course; and to close the breach with dredged sand.

The width of the breach ranged from 2,345 feet on the south end, or less than a half-mile, to 1,476 feet on the north, according to the most recent measurements in May.

advertisement | advertise on newsday

Though some South Shore residents say the breach has worsened flooding, scientists say it only lets in a fraction of the water that flows through Great South Bay navigational channels.

The agency’s report cited studies by Stony Brook University research professor Charles Flagg that show that the daily average mean high water in the bay has increased by one inch or less since the breach formed.

In a statement, Brookhaven Town Supervisor Ed Romaine agreed with environmentalists and fishermen who say the breach improves the bay’s water quality, calling it “a wise approach to keep the inlet open.”

But he added: “They must keep an eye on this to make sure it does not widen or create flooding on the South Shore.”

A public hearing on the environmental impact report will be Nov. 7 at 7 p.m. at the Patchogue-Watch Hill Ferry Terminal. The comment period ends Dec. 12.

The new report said the U.S. Army Corps of Engineers overestimated how much flooding and damage the breach might cause because it assumed the breach’s size did not change and, in some research, “used a breach model that was larger than would ever be expected to occur.”

“The models predicted flooding levels that are substantially higher than, or contrary to, observed or empirical data,” the agency said.