Temporary Structures Could Ease Need For Dredging At Stage Harbor Entrance

By: Alan Pollock

Topics: Erosion , Waterways , Dredging

Currents flowing through the Fools Cut (bottom right) carry sand toward narrow Crescent Beach and the Stage Harbor entrance channel (top center). SPENCER KENNARD PHOTO

CHATHAM — A detailed study commissioned by the town is recommending the installation of temporary structures likely made of sheet steel in the waters off Crescent Beach as part of a strategy to reduce the need for expensive annual dredging to keep Stage Harbor open.

“Our Stage Harbor entrance channel has sort of been under attack, if you will, from the Atlantic Ocean,” Coastal Resources Director Ted Keon told the select board last week. The inlet in the barrier beach known as the Fools Cut – so called because it formed in 2017 on April Fools’ Day – has caused sand to flow from east to west, choking the harbor entrance and threatening the viability of the harbor. Dredges have visited the area, sometimes several times a year, to keep the waterway navigable.

“Those that have been watching our dredging and nourishment have seen a lot of work. Those who’ve been watching the finances have seen a lot of money, all in support of trying to maintain that channel,” Keon said. In the quest for options “beyond simply dredging ad infinitum,” the town applied for and received a Coastal Resiliency Grant from the state’s Coastal Zone Management office, which funded the study by Mashpee-based Applied Coastal Research and Engineering.

Principal researcher John Ramsey of Applied Coastal said his group and the Center for Coastal Studies in Provincetown have been watching the changes in Chatham’s barrier beaches for years, and when the Fools Cut formed, “we knew there were going to be some rapid changes. And sure enough, we’ve all seen what’s happened,” he said. The sand coming through the inlet, combined with sand scoured away from Crescent Beach, moves generally toward the Stage Harbor entrance.

“That beach is actually eroding extremely rapidly,” Ramsey said of Crescent Beach. Created as a dike built by the Army Corps of Engineers in 1964 as part of an effort to relocate the natural harbor entrance farther to the west, Crescent Beach is now only about 125 feet wide at its narrowest part, and is losing nearly 20 feet of sand each year.

Based on research by the Center for Coastal Studies, Ramsey predicted that the Fools Cut will remain open for another 10 to 15 years before it closes as part of the cycle of barrier beach regeneration. Well before that happens, likely in five or six years, Crescent Beach will be breached, Ramsey said. Major storms could accelerate that process, he added.

The study considered a variety of options, including one that would angle the existing harbor entrance channel to the southwest – which would provide little relief from shoaling – to digging a new harbor entrance through a point on Harding’s Beach further to the west, near the elbow of Oyster River.

“Obviously, that comes with a whole slew of problems,” including possibly causing new erosion to properties along the river, Ramsey said. After brief discussions with regulators, “that basically is a non-starter,” he said.

The study then considered a range of temporary structures designed to control the flow of currents and the sand they carry. “These types of structures would just be made of vertical piles that could be pulled once the problem goes away over the next 15 or 20 years,” Ramsey said. The best two designs were L-shaped configurations, with groins extending southward from Crescent Beach, and a line of separate “vanes” angling to the southeast to trap sand.

The preferred location for the structure would extend to a point just outside the jurisdictional boundary of the Monomoy National Wildlife Refuge, where such structures would not likely be permitted. Computer models predict that the structure would reduce sediment flow toward the harbor by around 60 percent.

“We’re looking at a great reduction in the amount of transport that’s heading towards Stage Harbor,” Ramsey said. “There’s no silver bullet that’s going to solve everything, but this is something we’re looking to take to the next level,” he said.

For that purpose, the town applied for and received a second Coastal Resiliency Grant to give the proposed alternative a closer look, focused on what impacts it might have on adjacent shellfish beds, and what concerns might be raised by the U.S. Fish and Wildlife Service and the Army Corps of Engineers.

Given the strong currents, “how the heck do you keep them anchored?” select board member Jeffrey Dykens asked. “It’s wild through there.” Ramsey said the second phase of the study would consider specific materials, but the structures would probably be built from sheets similar to steel bulkheads, driven into the sand and supported by piles. While they would be substantial, they could be readily removed when no longer needed, he said.

Board member Shareen Davis, whose family has worked at Stage Harbor for many generations, said she recognizes the need for action.

“I’ve seen the dramatic changes in the last year. The back side of Crescent Beach is just sheared straight down,” she said. Erosion there has unearthed old brick foundations and a large rock, and has contributed to the annual, expensive dredging at the harbor entrance.

Davis said there is a strong need for the town’s water-related committees to weigh in on the proposal throughout its development, providing feedback from the professional mariners who make up their membership. She said there should also be some consideration about whether the structures might have impacts on the revetments that protect properties on Morris Island, “because for every action there’s a reaction,” she said.