CHATHAM — Like a sticky cupboard on a humid day, the new Mitchell River drawbridge sometimes jams when it closes. Open for just over a year, the bridge cost taxpayers about $14 million, and town officials sometimes have to park a truck on top of the span to force it to lower fully.
“Clearly that's not something we want to have to do every time,” Natural Resources Director Robert Duncanson said.
Though the town has been operating the bridge since a ribbon cutting last June, it remains the property of MassDOT and its general contractor until town officials formally accept ownership, something that was expected to happen in October. But that may not happen until the glitches are worked out, Duncanson said.
“We've had issues with misalignment with one of the barrier gates” on the east end of the bridge, he said, and the span itself experiences some expansion horizontally and laterally, most likely during humid weather.
“That's caused some binding, primarily when it's being closed,” Duncanson said. As a result, two large pins that join the closed span to the stationary bridge deck like deadbolts on a door sometimes don't line up with their sockets. Currently, when harbormaster staff close the bridge, they park their pickup truck on the movable span once it is lowered to help the alignment.
It's not entirely clear that the problem is related to humidity, though it seems to happen only during hot, sticky weather. But it's also possible that the problem is only noticeable in the summer, when bridge openings are more frequent. MassDOT and the contractor are aware of the problem.
“The state has been down, and they had the engineers down as well last week looking over all the issues,” Duncanson said. Crews made interim repairs, “but the problem is continuing, so they're taking a closer look at it.”
So far, the glitches haven't prevented officials from opening the bridge as needed, Duncanson said. Because the bridge is permitted by the U.S. Coast Guard, the town is under obligation to ensure that it works when needed, he said. Until a permanent fix is applied, town officials are trying to operate the bridge “in a way that doesn't result in any significant long-term damage,” Duncanson said. Still, the town shouldn't have to “baby” the new bridge, “because that's not a long-term solution,” he said.
Chatham's drawbridge is unique, and was the product of a lengthy back-and-forth between highway officials, engineers and preservationists. After years of debate, the final design adopted by the state was a modern concrete-and-steel substructure with a wooden superstructure reminiscent of the former wooden drawbridge, which was believed to be the last remaining wooden drawbridge of its kind in the nation. That bridge was taken out of service because it was structurally unsound, didn't open fully and was extremely difficult to operate. The hybrid design of the new bridge is likely behind some of the glitches, Duncanson said.
“Some of the issues that we're dealing with are related to the fact that it's a wooden superstructure,” he said.
But Duncanson said he's confident the problem can be solved, since engineers were breaking new ground with this kind of design. “It may just take a little bit of tweaking,” he said.
If engineers can't devise a permanent fix, the town has some recourse.
“Basically, if push came to shove, we would just not accept the bridge,” he said. Town officials have already put the state and the contractor on notice that they won't assume ownership in October, as planned, if the problems aren't solved.
“Why would we take it over if the bridge still has issues?” Duncanson said. “Those issues would just become the town's issues.”