Scientist: Change In Way Sand Moves Along Cape Likely To Impact Barrier Beach. (Cape Cod Chronicle)

Circa 1971, my mom made tuna fish on rye sandwiches for us, and we took a $5 launch from Chatham to North Beach, across the Chatham Harbor.  Wonderful memories. Last time I checked, the spot where we dined is gone, removed by Mother Nature, while Congress fiddles with oleaginous Big Oil lies in their ears an d Big Oil contributions in their campaign coffers.  God help us.

From Cape Cod Chronicle:

Scientist: Change In Way Sand Moves Along Cape Likely To Impact Barrier Beach05 July 2023

By: Tim Wood

 Topics: Erosion

Changes in the way sand flows along the Cape’s outershore will impact Chatham’s barrier beach system, in conjunction with more severe storms and sea level rise caused by climate change, according to Dr. Mark Borelli. SPENCER KENNARD PHOTO

CHATHAM – Changes to the way sand moves along the eastern shore of Cape Cod could shorten the documented 140-year cycle of Chatham’s barrier beach.

Dr. Mark Borrelli, a coastal geologist with the Center for Coastal Studies in Provincetown, has been studying Chatham’s barrier beach system since the 1990s. At a talk at the community center June 28 sponsored by the Chatham Garden Club, he said studies of the outer beach indicate that the location where the movement of sand along the shore divides between north and south has shifted since the 1950s.

Prior to that, it was thought that the so-called “nodal point” where offshore waves move sand north toward Provincetown or south toward Chatham along the outer shore was located in Wellfleet.

“We think that’s changing,” he said. “We think that nodal point is shifting south, which would be a big deal.”

The nodal point now seems to be somewhere around Nauset Marsh, judging by the growth of the Nauset Spit, which began migrating north in about 1952. Beaches and spits migrate in the direction of the off-shore transport of sand, he said.

“As far back as we go, there’s never a spit growing to the north” at that location, until 1952. “And it’s still going north,” he said.

For centuries the sand flowing in Chatham’s direction has fed the barrier beach system (North Beach), which much of the time protects the town’s inner shore from direct ocean waves. Dr. Graham Giese and others have shown that every 140 to 150 years, inlets form in the outer beach, which then gradually washes away south of the dominant inlet. Then the beach begins to grow south again, fed by the sand being transported from the north.

The shift means less sand heading Chatham’s way. Combined with stronger and more frequent storm and sea level rise due to climate change, the change in the nodal point may accelerate that cycle, Borelli said, “which means [the beach will be] more dynamic, more variability, more uncertainty.”

The shift occurred over time as Georges Bank, east of the Cape, was submerged and sea level rose, allowing larger waves to reach the outer shore, Borelli said. In 2008, he noted, Giese repeated a series of 229 transects along the outer beach originally taken in the 1880s and found that the shoreline of Cape Cod had rotated two degrees counterclockwise.

“Over 200 years, two degrees is a lot,” he said.

Less sand flowing toward Chatham’s barrier beach “is not good,” Borelli said. “It’s going to change the way the barrier is evolving.”

Borelli, director of the Center for Coastal Studies Seafloor Mapping Program, and fellow scientists are preparing a paper on the change in the nodal point, and will be releasing a study on the future of the Nauset Inlet area funded by the town of Eastham.

“We think this is an incident of sea level rise and climate change changing a tidal inlet’s behavior,” he said.

The Nauset Inlet area, like Chatham’s barrier beach, remains highly dynamic, he said. For instance, a 2019 storm near Nauset Heights eroded the beach by 300 feet, but within two years most of the beach had returned. That’s the way a beach should respond to erosion, when there are no structures in the way.

Addressing the massive erosion on Morris Island recently, Borelli said the loss of the bluff is related to the opening of the April Fool’s cut in 2017, which allowed water to flow freely between the Atlantic and Nantucket Sound. Because the level of the ocean is higher than the sound, that resulted in a one-way “river” moving water, and sand, from east to west.

“As long as the Fool’s Cut is open, it’s going to continue to erode those areas,” he said.

Asked about the future of the fish pier, where recent work included shoring up infrastructure to be more resilient in the face of sea level rise, Borrelli said much will depend on when North Beach Island migrates west toward the mainland, essentially becoming shoals in the harbor. This will subject the mainland to stronger waves until North Beach begins to grow south again.

“It’s going to be this really interesting battle between the spit getting longer and North Beach island going away,” he said. “The next 20, 30 years, it’s going to be very dynamic, it’s going to be somewhat unpredictable.”

Borrelli received his Ph.D. studying Chatham’s barrier beach, which is so dynamic and interesting that it’s the subject of much research.

“Chatham does not disappoint,” he said. “It confuses and confounds, but it’s a really, really exciting place to work.”