Measure the Water Before the Walls Dry

Caroline Virenius lives in Sea Bright, on the New Jersey shore, where this weekend's nor'easter pushed water into town on round after round of high tide. "It's getting wet again and again," she told reporters.

That sentence is the most useful flood data a coastal county will collect this week. Almost nothing in the official system is built to record it.

The weekend nor'easter was serious without being historic. A New York City housing worker was killed by a falling tree in Brooklyn. More than 150,000 customers lost power at the peak, mostly on Long Island and the Jersey Shore. Fox Weather reported water in Atlantic City running more than three feet above normal high tide, the highest reading there since Superstorm Sandy. Governors Hochul and Sherrill declared emergencies. In North Carolina, Highway 12 closed between the Basnight Bridge and Rodanthe.

Most of the damage people will remember came from two things the federal flood map handles badly: water that comes back tide after tide, and ground that simply leaves.

The map is an insurance instrument, and too many councils read it as the county's risk map.

A FEMA flood insurance rate map shows one scenario, the storm with a 1% chance of happening in a given year. Massachusetts' own guidance says not to use those maps alone and warns that erosion and rising seas can change conditions after a map is drawn. The map does not show the street that floods six times a year at moderate tide. It was never meant to. It is an insurance instrument, and too many councils read it as the county's risk map.

Erosion falls through an even wider gap. On the Outer Banks, 32 homes have been lost since record-keeping began, and the National Park Service at Cape Hatteras tracks 100 threatened structures in Rodanthe and Buxton, according to Inman. The standard federal flood policy does not cover damage from gradual erosion. And last year FEMA quietly took down the online viewer New England towns used to project coastal erosion out to 2100.

So the most current picture of where the water actually went is not in Washington. It is in the heads and phones of the public works crews, code inspectors and firefighters who drove those streets Saturday night.

The U.S. Geological Survey calls high-water marks "perishable" evidence, and they are. Mud lines on garage doors, debris wrack along fences and stains on drywall fade fast, and the homeowners you would want to ask are the ones scrubbing them off. Those marks are what feed inundation maps, flood-frequency estimates and hazard assessments.

Send people out this week. Photograph each mark with a location and a timestamp. Log every address that took water and note whether it took water last time too. Over two or three storms, that becomes a repeat-flooding layer no federal agency will draw for you. It tells you which road to raise, which outfall needs a check valve and which block goes first in a buyout application.

There will be more chances to collect it. NOAA warned in May that El Niño would steer more storm surge toward the Atlantic coast this season, and forecasters expect it to bring more nor'easters this fall. A county that starts logging now will see a pattern by spring. One that waits will be holding the same FEMA panel it had on Friday.