For more than a century, for good or ill, New Jersey has led the nation in coastal development. Many of the barrier islands along its coast have long been lined by rock jetties, concrete sea walls or other protective armor. Most of its coastal communities have beaches only because engineers periodically replenish them with sand pumped from offshore.
Now much of that sand is gone. Though reports are still preliminary, coastal researchers say that when Hurricane Sandy came ashore, it washed enormous quantities of sand off beaches and into the streets — or even all the way across barrier islands into the bays behind them.
But even as these towns clamor for sand, scientists are warning that rising seas will make maintaining artificial beaches prohibitively expensive or simply impossible. Even some advocates of artificial beach nourishment now urge new approaches to the issue, especially in New Jersey.
The practice has long been controversial.
Opponents of beach nourishment argue that undeveloped beaches deal well with storms. Their sands shift; barrier islands may even migrate toward the mainland. But the beach itself survives, because buildings and roads do not pin it down.
By contrast, replenishment projects often wash away far sooner than expected. The critics say the best answer to coastal storms is to move people and buildings away from the water, a tactic some call strategic retreat.
Supporters of these projects counter that beaches are infrastructure — just like roads, bridges and sewer systems — that must be maintained. They say beaches attract tourists and summer residents, conferring immense economic benefits that more than outweigh the costs of the projects. Also, they argue, these beaches absorb storm energy, sparing buildings inland.
New Jersey has embraced this approach with gusto. Stewart C. Farrell, a professor of marine geology at Stockton College of New Jersey, said that since 1985 80 million cubic yards of sand had been applied on 54 of the state's 97 miles of developed coastline: a truckload of sand for every foot of beach.
Dr. Farrell and his colleagues have calculated that the work cost more than $800 million — before adjusting for inflation.
Typically, the federal government pays 65 percent of the cost; the state and towns share the rest.
By now in New Jersey, most beaches "are engineered dikes," said Thomas Herrington, a professor of ocean engineering at the Stevens Institute of Technology in Hoboken, who has been working with the state to assess its coastal protection. About half of its coastal communities have projects still under way, so their beaches are already approved — at least in theory — for topping up with sand as needed.
But even if there is money for that work, engineers must find the sand. Around the nation, that is getting more and more difficult. The problem is particularly acute in New Jersey.
"We know from geological surveys — and New Jersey is a prime example — that offshore sand, high-quality sand, is a highly finite resource," said S. Jeffress Williams, a coastal scientist with the United States Geological Survey and the University of Hawaii.
Underwater ridges of sand lie offshore, but engineers must go farther and farther (and spend more and more) to find them, Mr. Williams said, adding that eventually "it is not going to be there."
And while it is theoretically possible to replenish a beach with material mined inland, that approach would create other problems, said Robert Young, a coastal geologist who directs the program for the study of developed shorelines at Western Carolina University.
"Trucks full of sand weigh a lot," he added. "There is a tremendous toll on highway infrastructure." And excavating inland sand "would create holes that would be miles in diameter."
Howard Marlowe, a prominent advocate of replenishment projects, agrees that the nation needs "a better way of managing short supplies of sediment."
Mr. Marlowe is president of Marlowe & Company, a lobbying concern that represents many Atlantic and Pacific coastal communities. He said in an interview that sand supplies should be managed "holistically" — and on a regional basis, not town by town, as is now largely the case.
Managers should look at inlets, ports and the Intracoastal Waterway, as well as offshore sand sources, Mr. Marlowe said, adding, "You have to have an interstate approach."
That is particularly true in New Jersey, he said, because towns in New York and Delaware also often find themselves on the hunt for sand. Elsewhere in the country, towns feud over who is entitled to offshore sand. Towns in Florida have gone to court over the issue.
Avalon, N.J., about 20 miles north of Cape May, looks to Townsends Inlet north of town for its sand, according to Harry deButts, who retired in 2008 as the town's director of public works and now works part time on its emergency management efforts. He said Avalon shares that sand with Sea Isle City, the town across the inlet.
Mr. deButts said the Army Corps of Engineers dredged about 450,000 cubic yards of sediment from the inlet in 2003, and applied "a couple hundred thousand cubic yards" more about five years later. The town is scheduled to receive more sand in December, to repair damage from Hurricane Irene last year.
He said "the beaches did their job" during Hurricane Sandy, saving buildings in Avalon from flood damage. The town had built a dune more than 20 feet high, adopting what he called "an education program" to explain the advantages of second-floor living rooms to residents whose views were blocked.
That can be a hard sell. In Harvey Cedars, on Long Beach Island, homeowners have sued for compensation over loss of ocean views because of a proposed project. The case is before the New Jersey Supreme Court.
Where artificial beaches failed to protect their communities, it was probably because "this storm just exceeded the design conditions," said Dr. Herrington, of the Stevens Institute, who has been working with the state to assess coastal protection. Typically, he said, projects in New Jersey are engineered to withstand the kind of storm that on average occurs only once every 75 years.
But as the climate warms, sea levels are rising and bad storms may come more frequently. And New Jersey is particularly vulnerable because of tectonic forces and changes in ocean currents.
When the glaciers retreated about 15,000 years ago, land in the region bounced up; now it is sinking again. Meanwhile, ocean circulation patterns are changing in ways that push water up against the mid-Atlantic coast.
"We cannot sustain the shoreline in the future as we have in the past," said Mr. Williams, of the Geological Survey. "Particularly from a beach nourishment standpoint."
—Written by Cornelia Dean for The New York Times