While all eyes turn to the Jersey Shore during high-profile storms like last week’s Tropical Storm Elsa, the real trouble when it comes to flooding lies in the regular tide cycle. And it’s only getting worse.
Each year since 2015, the National Oceanic and Atmospheric Administration has released a nuisance flooding report and annual outlook that synthesizes data from 97 tide gauges spread along the U.S. East, Gulf and West coasts. And each year, the frequency of high tide flooding, which begins at 1.75 feet above normal high tide levels, has increased at most locations.
In the report’s timeframe — May 2020 through April 2021 — the U.S. coastline experienced an average of four days of nuisance (high tide) flooding, which can occur not just during storm or rain events, but also on sunny days, when tidal swings are larger, or when persistent onshore winds push water into the bays, tributaries or lagoons and hold it there.
Because of 2020’s extremely active hurricane season, the Southeast and Gulf coastlines saw the highest frequency of nuisance flooding, with 17 days. Though lower than the 2019 rate, the Northeast’s 30 tide-gauge locations still saw 6.4 days of high tide flooding last year.
The U.S. coastal average of four events may not seem like much, but it is a frequency that’s doubled in the past two decades. For example, at two of NOAA’s tide gauges in New Jersey — Sandy Hook and Atlantic City — the average number of flood days in 2000 was five; last year, it was 11. By 2030, according to the report, the minimum number of flood days in Sandy Hook will be 25, and 20 in Atlantic City, if mitigation efforts aren’t improved.
Standing water on the streets
For next year, May through April 2022, NOAA is predicting between six and 11 days of flooding in the Northeast, the highest rate in the country. By 2030, the report says, the national frequency will be about two to three times greater than it is today, if flood infrastructure is not made more robust. By 2050, the American coast can expect 25-75 days of nuisance flooding a year, with some places seeing nearly 180 days — half the year — of standing water on their streets.
“The increased frequency of these minor flooding events is the most tangible consequence of sea level rise,” said William Sweet, the report’s lead author, in a recent call with journalists. “That’s significant — the kind of infrastructure and development that are at or below these elevations are increasingly at risk.”
In addition to the standard sea-level rise projections, a recent NASA study, in which Sweet took part, predicts that by the 2030s a shift in the lunar cycle will further accelerate high tide flooding.
For communities up and down the Jersey Shore, nuisance flooding has suddenly become a priority in capital planning budgets.
Decades of heavily federally subsidized beach building on New Jersey’s barrier islands have left their oceanfronts wider and sturdier than they’ve ever been, since mass development began in the 1950s. But the laser focus on only one side of the islands has neglected their bay sides. Today, these areas are the first to flood and the last to drain.
Peril on the back bays
Like an airplane wing, New Jersey’s barrier islands are naturally built up on their ocean sides, sloping to their lowest elevations on the bay sides. In their inattention to back-bay flood risk, towns have developed — and continue to develop — right up to the water’s edge, separating multimillion-dollar properties from bays and lagoons by nothing more than thin, low-slung bulkheads.
In New Jersey, bulkhead construction and upkeep are the responsibility of property owners, not municipal, county or state authorities. The result is a back-bay bulkhead network of “an infinite array of materials, heights, degree of integrity, and water tightness,” said Stewart Farrell, director and founder of Stockton University’s Coastal Research Center. “And that’s a major problem.”
Since the 1980s, Farrell and his team have advised Shore towns on beach replenishment efforts, but lately, they’ve been asked to shift their focus to the back bays. In 2017, the center began conducting its own nuisance flooding study in the South Jersey Shore towns of Beach Haven, Long Beach Township, Brigantine, Avalon, and Stone Harbor.
Unlike NOAA’s, the center’s study is granular. Using cigar-sized sensors called “Hobos,” which are zip-tied to the underside of storm drain grates, Farrell’s team has collected millions of data points on where water is creeping in first and staying the longest in these towns. Over a 9-month period in Stone Harbor, for example, a single sensor recorded 143 flooding “events.”
Farrell emphasized, however, that the center’s study is very different from NOAA’s. While Sweet’s NOAA team analyzes only tide gauges, Farrell’s team examines how and where water accumulates on streets. Most importantly, he said, the center’s threshold for a flooding event is much lower. The Hobos react to pressure, so even an inch of water — not much more than a full storm drain with puddling around it — can trigger an event.
Taken together, the average water depth of an event in the five towns where the center conducted its study was around a foot. The highest events reached 3 feet. Several other factors, from road elevation to drainage capacity influenced the amount of standing water, Farrell said.
‘Where the situation becomes untenable’
“These kinds of events don’t matter much now, except for the fact that if you don’t pay any attention to them and sea-level rise hits the expected three-to-four feet by 2100, a normal high tide is going to be at the level of the worst of these nuisance flooding events — twice a day,” he said. “This is where the situation becomes untenable for these coastal communities.”
Since Superstorm Sandy, new construction along the Shore has been required to be elevated above Federal Emergency Management Agency standards, and towns up and down the coast are installing pumping stations and more robust drainage systems to expel floodwaters at faster rates. The price tags run into the tens of millions of dollars. Farrell pointed to Stone Harbor, which just received a $12 million FEMA grant to build a “very substantial” pumping station near its downtown. Elsewhere in the small but wealthy enclave, another expensive stormwater mitigation project is in the works.
“The problem has gotten worse since 1950 and it’s going to get worse in the next 50 years,” Farrell said of the entire New Jersey coastline. “Sea level rises, plus the storm surges — you can only elevate the houses so far. So, do we bring in a couple 100 million cubic yards of fill and raise the whole barrier island up — all the roads, all the infrastructure, all the properties, everything? Do we dike them like Holland, with 10-foot walls all the way around and just hope it’s not breached by the next big storm?”
While the predictions are dire for New Jersey’s coastal communities, Sweet said the intent of the NOAA report is to continue to spark resilience, not retreat.
“The idea is to give people guidance, not to scare them,” he said. “To just let them know how things are changing, so that decisions can be made with the best data at hand, so that they can adapt and change and maintain their footprint at the coast, because it’s important for us to be at the coast.”