By 2045, Shoreline Changes Bring Good News And Bad

By: Alan Pollock

Topics: Erosion , Dredging

A recent aerial view of Chatham Harbor, looking south. Minister’s Point on the right, and the North Inlet (with its S-curve channel) is on the left. SPENCER KENNARD / CAPECODPHOTOS.COM

CHATHAM The shifting sands off Chatham will cause North Beach Island to fold in toward the mainland by the year 2045, experts predict. That will mean more sand to protect parts of the shoreline from waves and storm surges, but more trouble for boats trying to navigate in and out of Aunt Lydia's Cove.

In a recent public forum, John Ramsey of Applied Coastal Research and Engineering presented the predictions from a wide-ranging $250,000 study of changes along the town's east-facing shoreline, including an evaluation of coastal resilience. Carried out with the Provincetown Center for Coastal Studies, the project used computer models to predict tides, waves and the movements of sediments to provide detailed evaluations of the inlets and tidal channels in Chatham Harbor.

“A lot of sand is in motion right now,” Ramsey said. While the predominant flow along the outer beach is from north to south, “a lot of it is moving toward the west,” he said. “Eventually, a lot of that material is going to end up on the mainland,” he said. The barrier beach evolution is a cycle of between 100 and 150 years, and information shows that in the years roughly between 1870 and 1890, the outer beach devolved into a boomerang-shaped island pointed out to sea, with its back side shielding and eventually touching the mainland. Later, it was this sand that made Aunt Lydia’s Cove an actual cove, with its entrance near the Cow Yard. Computer models predict that North Beach Island will follow a similar pattern, migrating west in the decades ahead.

The left two panes show elevations in 2007 (left) and 2018 (center). A computer model (right) predicts that, in 2045, North (Nauset) beach will migrate south to an area roughly opposite the fish pier, and the remnants of North Beach Island will form a boomerang-shaped island close to the mainland. COURTESY APPLIED COASTAL RESEARCH & ENGINEERING

The left two panes show elevations in 2007 (left) and 2018 (center). A computer model (right) predicts that, in 2045, North (Nauset) beach will migrate south to an area roughly opposite the fish pier, and the remnants of North Beach Island will form a boomerang-shaped island close to the mainland. COURTESY APPLIED COASTAL RESEARCH & ENGINEERING

When that happens, parts of the east-facing shore behind the island will be protected from waves and storm surges from the Atlantic, but there will be much less current flowing through Aunt Lydia’s Cove.

“That’s basically going to become kind of a calmer pond,” Ramsey said.

Currently, almost all of the water entering and leaving Pleasant Bay goes through the North Inlet opposite Minister’s Point, where the channel has taken the shape of an S-curve. In 2007, when the North Inlet was relatively new, there was little current or wave action at the point, but now, “we’re getting very, very strong currents in the flood tide and going out, right against Minister’s Point,” Ramsey said.

By 2045, currents will still be strong in that area, “but nothing like the scour that we see today,” he said.

In the shoreline assessment, researchers divided the east-facing coast into five assessment areas between Minister’s Point and Morris Island. The northernmost area is currently very geologically active, and the partial collapse of a revetment on Minister’s Point is related to strong tidal currents, Ramsey said. Revetments are designed to attenuate waves, not to protect against currents, and the best approach is probably to stabilize the base of the rocks. “Obviously it’s not a cheap thing to do,” he said. It may also be possible to use offshore structures to redirect currents away from the point, but doing so might cause scour elsewhere, Ramsey said.

The second area, which includes the Cow Yard, will see worsening wave action during coastal storms in the next few years, but will eventually get more protection from the northern end of the boomerang-shaped outer beach, Ramsey predicted. It might be possible to hasten that protection by nourishing the tidal flat offshore, creating a 3,000-foot-long, 150-foot-wide berm that runs north from Tern Island. Such a barrier would still be overtopped during coastal storms, and “the cost is very expensive and you’re going to have to maintain it,” he said. It might also be possible to install temporary wooden groins along the beach in this area, then filling the voids with sand to provide a buffer against wave action. The area in question is mostly private property, Ramsey noted. “Obviously, one of the challenges is getting everybody on board,” he said.

Area three runs south from Thayer Lane to Chatham Light, where much of the shoreline is already armored, and additional protections are probably not needed, Ramsey said.

“That area got enough action after the ‘87 breach. Maybe some of the people can breathe a sigh of relief, at least for the next couple decades,” he said.

The fourth zone includes Little Beach and Outermost Harbor, areas that are currently seeing severe erosion.

“[It’s] a very low-lying area. Certainly problematic, from that standpoint,” Ramsey said. As it did last winter, much of the area is completely inundated by a surge from a 100-year storm. The problem is related to the creation of the Fool’s Cut in 2017, which allowed a storm surge from the Atlantic to overtop the small dunes protecting Little Beach and pass into the neighborhood through Outermost Harbor. The change also allows waves to reach the shoreline without much impediment, “adding insult to injury,” he said.

While the southern tail of the boomerang-shaped island may provide the area with some protection by 2045, steps will need to be taken in the next few years to help Little Beach and Outermost Harbor resist coastal storms. Area residents and property owners are considering one plan that would elevate the coastal dune coming from the north to a height of nine feet, where it would meet a new nine-foot raised bulkhead around Outermost Harbor, linking with another raised dune to the south.

Another proposal would raise the bulkhead on the northeast side of Outermost Harbor, connecting it with a new inland dike that passes behind homes in Little Beach, crosses Morris Island Road and meets higher ground just north of the intersection of Morris Island Road and Little Beach Road. Where the road meets the dike, it would need to climb eight feet over the top.

“This is really kind of like a levee system,” Ramsey said. “You are trying to keep floodwaters out, so you need to make sure you’re doing a really good maintenance plan and inspection to make sure this doesn’t have any weak points.” The levee would not protect all properties in the area, but would protect access to Morris Island and Stage Island during times of high water, he said. The structure would essentially create a basin, “and you need to be sure that you can drain water out of that basin,” both from any storm surge and from rainfall, Ramsey noted.

Such a system would be expensive and would be built largely on private land. While it would give protection from some storm surges, it does nothing to help the other problem erosion is causing: sediment is rapidly filling the area off Outermost Harbor. The same sediment from the boomerang island that could protect Little Beach from wave-related erosion will also hinder navigation in the area.

“There’s going to be a lot of sediment coming into the system, and it’s going to be increasingly difficult to maintain that marina,” Ramsey said. “And there’s not a lot, from a realistic standpoint, that can be done in the long term.”

It’s less clear what the year 2045 will hold for the southernmost area in the study, which includes Morris Island. Private property on the island is largely protected by revetments, but the Monomoy National Wildlife Refuge property is not. In the years ahead, the federal government will likely need to decide whether to install one or to relocate some or all of its facility in advance of the eroding cliff. Key to predicting the erosion here is knowing where the southernmost tip of the boomerang connects with the mainland. If it does so far enough to the south, Morris Island will not likely see erosion problems during that time frame, but researchers are not fully confident about this.

“[It’s] a little bit at the edge of our understanding,” Ramsey said.