Revetments, armories, groins, jetties, ripraps — the walls of stone built to protect a length of bluff from erosion go by many names, but in whatever guise they pose a growing threat to the Vineyard shoreline, according to several prominent Island environmentalists.

A modern Vineyard revetment constitutes tons of boulders, often freighted to the Island by barge and fitted, puzzle-like into the bluff over geofabric layering to absorb the force of storm impact. Despite the large associated costs, it’s a security that more homeowners are likely to seek in an era of global climate change, says Vineyard conservation society chairman Brendan O’Neill.

“There’s an understanding that we’re looking at increased storm events,” he told the Gazette, “and people will look to protect their property. But armoring the coastline is a very bad idea.”

Mr. O’Neill said several recent and prominent examples have drawn attention to the practice.

A new, 195-foot revetment was approved in West Tisbury, fronting a 1.4 acre Pebble Beach Road property by the town conservation commission late last year, and is currently under construction.

“I got calls from alarmed Makonikey beach walkers saying, ‘There’s equipment on the beach. That can’t be legal.’ There are those thinking that’s not permissible, that’s it’s something from an earlier time, but it is,” said Mr. O’Neill, “and the Edgartown revetment has kind of become a poster child for the practice.”

In Edgartown a revetment refurbishment for a 4,700-square foot property fronting Sengekontacket Pond was approved in March, 2007. The town conservation commission unanimously approved the application from previous owners Peter and Priscilla Bettencourt.

In changes to the property, the house was moved back from the shoreline but because a swimming pool was added in front of the house it increased by 10 per cent the total amount of the property below the shoreline.

Acting on a complaint, representatives of the Massachusetts Environmental Protection Agency came to the Island to investigate the property in November, taking pictures of the revetment.

Agency spokesman Theresa Barao said yesterday that the agency intends to take action on the property.

“At minimum they will need a license,” she said. “The property is in jurisdiction [of the state].”

She said it was too early to say what the agency response would be to a property built without the license.

“At this point the response is being considered internally,” she said.

Mr. O’Neill was part of a group that advocated for the wild and scenic north shore district of critical planning concern (DCPC) which came into force in 2001. The district runs from Aquinnah to West Chop and puts stringent checks on conservation of the coastline passing through four Island towns, outlawing on-water construction.

But revetments, if set back from the shoreline, bypass the ruling.

“The biggest threat at the time was the potential proliferation of private moorings,” said Martha’s Vineyard Commission coastal planner Jo-Ann Taylor.

“It’s just slightly out of the scope of the planning overlay,” said Mr. O’Neill. “It’s frustrating. Particularly in an era of global climate change erosion, it’s a threat to the character of the north shore.”

Mr. O’Neill said that not tackling the politically sensitive revetment issue under the DCPC was a conscious decision.

“We didn’t want to threaten the bill as a whole,” he said, adding, “but they go against the spirit of the law. They change the littoral drift. You have two tides a day depositing sendiment. Any permanent barrier like that changes the drift,” he said. “You’re storing a percentage of the beach in the lee of these structures. I’d like to see towns revisit the DCPC.”

John Best, chairman of the Vineyard Haven conservation commission, said the state act provides enough scope to deny most revetment applications but equally there is significant leeway for discretion.

“With the regulations we have, you could turn down a lot more requests than people do,” he said. “Sometimes it’s a matter of how they feel or who’s making he application.”

Mr. Best said he is generally against revetments.

“Most of the evidence says beach armouring is not good,” he said. “I’m somewhat opposed [to revetments], because they snowball.”

Known as the end effect, a revetment creates pressures on either side of it, resulting in increased erosion for neighboring beaches. This makes the abutter’s application even stronger, said Mr. Best.

“We’ve had cases where people are between two revetments — in these cases, it’s given, because they’ll be beaten up pretty badly,” he said, adding: “but we have approved the buildings of new ones when the house is not specifically threatened by someone else’s revetment.”

The state Wetlands Protection Act, signed into law on August 10, 1978, puts various restrictions on revetments for houses built after that date.

Permits are issued by the town conservation committee; applicants must make the case that a revetment is a necessary protective measure and that it is impractical to move the property back from the shoreline as an alternative.

Mr. McKenna explained the state act leaves much up to the discretion of local boards.

“The state regs are necessarily broad-brush,” he said. “They have to apply to the rocky north shore of Massachusetts, with its robust granite coastal bank, and to the sandy eroding bank we have here.”

Most towns in Massachusetts have a local wetlands protection bylaw adding to aspects of the state act as the towns see fit. Some Barnstable towns use their bylaws to add stringency to the revetment restrictions.

“Local bylaws can be more dynamic [than the state],” said Mr. McKenna.

On Nantucket all revetments are prohibited for private properties. In Oak Bluffs, revetments are outlawed on any property built after 1978.

“Towns have different approaches,” said Ms. Barao. “On Nantucket they only use soft solutions, like beach nourishment, planting grass. They are often preferable.”

Cape and Islands regional coordinator of Massachusetts Coastal Zone Management (CZM) Stephen McKenna said modern riprap is more obtrusive.

“No question that the structures are more permanent,” he said. “And we’re seeing more robust structures for a variety of reasons, but one is that the structures built in the 30s, 40s and 50s had more beach.”

Beachfront with existing revetment, he explained, has received less sediment supply, resulting in rapid erosion. Sand naturally replenished for millennia is no longer produced by the riprap protected bank.

“The diminishing sand in these areas can be because they’ve already been revetted. For millennia, sand has been provided by the banks but they have to be more robust because now there’s less protection in front. It certainly happens very quickly.”

He said that design innovations have made modern revetments more effective.

“[Back then] Joe Contractor would put in whatever was in the truck,” he said, “loose boulders, vertical wooden pilings — now they have rough surfaces to better dissipate energy, and geofabric underneath the rocks as a separator.”

The CZM is an advisory body with no regulatory powers.

“We help local boards understand the science of it as they review applications and offer information to help minimize the impacts of these things,” he said.

One measure Mr. McKenna advises is for a homeowners to build far enough back from the shoreline that the end effect occurs mainly on their property rather than an abutters’.

“It helps but it doesn’t account for all of the impact by any means,” he said. “You’re still starving the property further down of sand.”