Town, Consultant Study Aging Floodgate

CHATHAM – It’s an aging bit of town infrastructure that’s only been used a handful of times, with varying degrees of success. It’s the floodgate under Morris Island Road, and the town has hired a consultant to decide whether it’s worth replacing — and if it is, what specific conditions require its use.

The floodgate was installed by the Army Corps of Engineers as part of the larger project to move the Stage Harbor entrance channel and install the Morris Island causeway. It is a simple system of timber blocks that can be dropped in a frame on the east side of the road, blocking tidal flow between Stage Harbor and the marsh northwest of the Little Beach neighborhood.

“We know that the floodgate is 60-odd years old and is in need of attention,” Harbormaster Stuart Smith told a Dec. 6 public meeting. Last used in the 1990s, the structure is now believed to be inoperable. The town has hired Maura Boswell of the consulting firm Geosyntec to research the issue and provide recommendations.

Smith said the floodgate has been used around twice during his tenure, and was designed to protect from a wind-driven storm surge that enters Stage Harbor when winds are from the west or southwest. It proved useful during Hurricane Bob, but less so during the Halloween storm that followed.

“There was a lot of debate about whether or not it should be deployed in that type of a storm,” Smith recalled. “It really shouldn’t be, in an easterly storm. You want the waters to leave,” he said. When the floodgate is closed ahead of an easterly storm, a storm surge from the ocean can pass through Little Beach and the waters will be retained in the marsh behind the neighborhood, worsening residential flooding, Smith said.

Adding to the problem is the primitive design of the timber floodgate panels.

“They get wet, then they swell, and they’re a misery to get out,” he said. It can also be a challenge for town crews to reach the gate if flooding blocks off the only access from the north.

“It’s obviously to help protect the structures on the upland side from flooding, but we don’t want to cause any adverse impacts,” Boswell said. Even a southwesterly storm that brings heavy rains could pose a challenge if the gate is closed. “You could cause flooding on the back side,” she said.

The study will involve a detailed review of weather and tide data and an analysis of the elevations and bathymetry around the floodgate, along with input from property owners and conservation groups, Boswell said. “That anecdotal evidence can really help with the design,” she said. Together, the data will guide the decision about whether and how to rebuild the floodgate, and when to use it most beneficially.

The challenge, Smith said, is that there’s little information about how well the gate has performed in real life.

“We’ve had a lot of close calls, but not a lot of hurricanes in Chatham that create that environment when we would deploy that gate,” he said.

A number of residents of Little Beach and Morris and Stage Islands attended the public meeting at the community center, and many had questions about flooding from easterly storms like the one in 2018 that inundated Little Beach. This study is focused on the floodgate, Smith said, but “I wouldn’t be at all surprised” if it leads to bigger questions about flooding in the area. Trying to stem flooding from the east side is a much bigger problem, “and it’s far more complicated,” he said.

Is it possible that the study will recommend simply removing the floodgate and not replacing it? Smith said he doesn’t think that’s likely.

“I think the answer is, yes, we do need it, for those infrequent storms that come up and hit us from the southwest, and that storm surge that comes into Stage Harbor,” he said. There are many more houses in the area than there were when the original floodgate was installed, he noted. Any replacement of the structure will likely require extensive review and permitting and will not happen quickly. Even if it is built, a new floodgate probably still won’t get much use.

“Under most storm conditions that Chatham faces, deploying it would probably do more harm than good,” Smith said.