Survey conducted of exposed cables

At Town Beach
Thu, 12/13/2018 - 6:45pm

A geophysical survey of the ocean floor at Block Island’s Town Beach is being conducted to determine a solution to prevent two of the Block Island Wind Farm’s transmission system cables from remaining exposed. The results will be analyzed by National Grid and Ørsted U.S. Offshore Wind, and released to the public in the near future. Ørsted purchased Deepwater Wind, which owned the Wind Farm.

“We are working to collect more information on the subsurface conditions in the area of the cables to help us develop plans in the low sediment coverage areas,” said Ted Kresse, Director of Strategic Communications for National Grid. “National Grid and Ørsted will analyze the survey results. All of the information will be shared with the appropriate state agencies and the town as our work progresses.”

The geophysical surveys were conducted on National Grid’s sea2shore cable and Ørsted’s cable via a remotely operated underwater vehicle from the shore out to about 2,500 feet into the water.

A press release issued by Ørsted stated that the “geophysical survey is part of ongoing efforts to characterize this dynamic near-shore environment.” 

“The survey team is using an ROV with special equipment onboard to map soft and hard materials beneath the seafloor,” said Kresse. “The areas around both cables were surveyed.” The surveys began on Dec. 8 and will be completed on Dec. 17.

There has been an issue of improper burial depth with National Grid’s sea2shore cable since it was installed in June of 2016. The subsea cables are heavily armored and were intended to be buried four to six feet beneath the seabed when installed, but after Grid’s technicians encountered hard seabed off Town Beach they were unable to meet the burial depth requirement in that locale.

After performing some analysis, the companies learned that shifting sands atop hard bedrock are the reason for the cables becoming exposed. National Grid’s sea2shore cable links Block Island to the mainland, while Ørsted’s export cable connects the wind farm to the island and its power grid.

Attempting to address the issue, shortly after installation in June of 2016 National Grid installed a protective plastic sleeve around a portion of its sea2shore cable. In June of 2018, National Grid designated a no anchor zone using a field of buoys beginning about 200 feet offshore where the sea2shore cable was exposed. In August, Ørsted’s cable became exposed. Both cables were covered with sediment as a temporary solution.

New Shoreham town officials have insisted that National Grid and Ørsted implement a long-term solution to mitigate cable exposure at the beach. At a Town Council meeting in June, Town Manager Ed Roberge said that, “The cable needs to be relocated. They did not get their designed depth and they need to.” He believes the companies need to provide a long-term solution.

“We are committed to providing a long-term solution to the low sediment coverage, and we are working with Ørsted, state agencies, and the town to identify the best path forward,” said Kresse.