A coastal engineering firm recommends the town of Tisbury build coastal dunes along the Vineyard Haven waterfront, raise the level of Beach and Lagoon Pond roads, and add culverts to control the flow of water during storms in an effort to ease flooding at Five Corners and the surrounding area.
The study and report looking at the next 30 to 50 years was compiled by Applied Coastal Research and Engineering, and paid for through a $130,000 grant from Massachusetts Coastal Zone Management, with a $44,000 town contribution. The area studied reached from the breakwater in Vineyard Haven Harbor to Eastville Beach. Engineers used historic data, lidar, offshore telemetry, and wave data from a NOAA buoy in Nantucket Sound to do the analysis. The report was released and summarized during a public meeting Tuesday night via Zoom.
John Ramsey, a principal engineer on the project, gave a detailed analysis of the issues faced by the Vineyard Haven waterfront — essentially a low-lying area that can expect flooding, even though the wave action of the Atlantic Ocean during a nor’easter never reaches the Vineyard Haven shore.
“The waves are not tremendously large when they come into the harbor, but they are large enough with the raised water levels to create problems with the moored boats out there, and can move them onto the shoreline and, because of the low-lying area, obviously, can push them up onto the roadways during those severe conditions,” Ramsey said.
Sea level rise and flooding is the greatest vulnerability in the low-lying downtown area, Ramsey said. Storm damage, infrastructure, and erosion are also vulnerabilities, he said.
While sea level has been rising at a steady rate over the past 100 years — the Vineyard Haven shoreline has lost about a foot since buildings were built along the coast — acceleration is a concern in planning what to do in the future, Ramsey said.
Warmer temperatures caused by global warming are expanding the volume of water in the ocean, and ice melt from Greenland and Antarctica is contributing to the volume of sea level rise, he said. In the next 30 to 50 years, the study projects a half a foot to 1.82 feet of sea level rise, depending on various modeling tools.
“The highest curve really is assuming that we are continuing to produce greenhouse gases at an accelerated rate, as it has over the last several decades,” Ramsey said. It also adds in the contribution of ice sheets.
The engineering firm is not recommending an extension to the breakwater in the harbor, or a jetty, because it would not have “enough bang for the buck” in easing the flooding, Ramsey said.
With climate change causing more frequent and more powerful storms and sea level rise, the waterfront area can expect continued “nuisance flooding” unless mitigation steps are taken to direct water away from Five Corners.
Ramsey noted that work about to begin on a Beach Road shared-use path complicates matters, but said his agency would be reaching out to the Massachusetts Department of Transportation (MassDOT) in the next phase to see what might be worked out. As for the culverts, those would require a commitment by the town to put up the gates to block water when a storm is in the forecast.
All of the discussion about mitigation was conceptual in nature, and no exact price was given for the work. He did say that the actual construction of dunes would cost about $6,000, but permitting could be costly and time-consuming. The dunes would also require maintenance, though once they’re built, dredge materials from the harbor could be used to renourish them, Ramsey said.
Grants are available, but Ramsey noted that most come with a local contribution of at least 25 percent.
At one point he displayed an 1887 map that showed protecting the harbor has been on the minds of Islanders for centuries. The map showed a curved “massive jetty” that would have spanned East Chop to West Chop. Ramsey estimated it would cost hundreds of millions in today’s dollars.
The audience for the Zoom presentation included town leaders and residents asking questions about the costs, and whether there is any way to truly protect Five Corners without elevating it.
In answer to a question from Bill Bruno about Five Corners, Ramsey said the strategy of what’s been recommended is to build dunes and create barriers that will move water away from Five Corners. Elevating the intersection, especially with how close buildings are to the roadway, is problematic, he said.
“We know this is a low-lying area; there are always going to be challenges for flooding, but we’re trying to improve things to a level that is beneficial to the town,” Ramsey said. “Just so your town is not as severely impacted when we do have a nor’easter, so you can move through and get around most of the infrastructure, and get to the hospital and the areas you need to get to.”
