Originally published in The Weekly Packet, March 1, 2018
MDOT outlines plans for Benjamin River Bridge
Jim Wentworth, a senior project manager with Kleinfelder, an engineering firm which designed the replacement for the Benjamin River bridge between Brooklin and Sedgwick, points out features of the design during a recent meeting in Brooklin.
by Rich Hewitt
Engineers working with the Maine Department of Transportation have designed a longer and higher bridge to span the Benjamin River between Brooklin and Sedgwick, but they still have some work to do to address local concerns about the project.
The project team presented the draft design for the $1.5 million planned bridge replacement last week to a handful of residents from the two towns. According to Jim Wentworth, an engineer with Kleinfelder, the Augusta-based firm that developed the design, a key factor in the bridge design was one that was raised at the last public meeting on the project: sea level rise.
“Sea level rise is a big factor in what will happen out there,” he said.
The existing bridge was built in 1935 and rebuilt in 1965. It is rated as a Level 4 bridge which means it is in poor condition, according to Emily Walton from Kleinfelder’s staff. Problems include scouring—erosion around the pilings and bridge abutments—and spalling—deterioration of both the concrete and the steel reinforcements on the bridge. Although the bridge will hold any traffic that is currently traveling over it, Wentworth said it is near the end of its useful life.
The new design, Wentworth said, takes into consideration the projected rise of between two and four feet in the next century due to the changing climate and also protects the new structure from the scouring effects of the tidal river. The draft design calls for a bridge that is two feet higher above the water than the current bridge. The existing bridge is about 6.7 feet above low water, and the river already rises almost to the roadway, Wentworth said. The new design raises the bridge to 8.7 feet above low water.
“The design allows for some sea level rise,” Wentworth said. “It provides for some head room.”
Raising the bridge, however, has some other design impacts. In order to accommodate the new height, the bridge needs to be longer, 62 feet instead of the existing 27.5 feet, and, in order to support the new length, Wentworth said, the bridge supports need to be thicker as well. In all, that will raise the grade of the bridge about four feet higher than it is now.
The design also widens the area under the bridge in a V-shaped pattern with a 62-foot opening at bridge level that narrows down to about the current 27-foot opening at the bottom. The change will not have a significant effect on the velocity of the water passing under the bridge, Wentworth said, but it will provide space for additional rip-rap to ease the scouring effect of the river.
He acknowledged that there still might be some flooding along the bridge, depending on the level of sea rise. But he stressed that the design team had to balance not only the demands of the bridge itself, but also the cost and the impact on the properties on both sides of the river.
Residents raised concerns about the design, mainly having to do with high water coming over the road. Lori DePretoro from Sedgwick said that, from her reading, new FEMA flood maps indicate the potential of high water at 12.7 feet, over the proposed level of the new bridge.
And Peter Neill, also of Sedgwick, argued that the “Achilles heel” of the design is on the Brooklin side of the bridge where, despite raising the road level elsewhere, one section of road will remain at its current level. Rising water, Neill said, will flow to that low spot and regularly flood the roadway.
“They’re spending 1.5 million and it’s still going to flood,” he said.
Wentworth agreed that there likely will be some flooding in that area, but stressed that the department was trying to keep all of the work on the project within the MDOT right-of-way. Any work in that area on the Brooklin side of the bridge would expand the project onto the Preble property located at the end of the bridge.
Residents questioned whether the state could acquire that property so that impacts from the project would not be a problem, and suggested that the owners might be willing to work with the department. Joel Kittredge, the MDOT project manager for the project, said they had not discussed property acquisition with anyone, noting that there are specific rules and regulations about how and when those kinds of talks can take place.
Wentworth added that the property would be an expensive one to acquire, and added that, based on local comments, there is likely oil contamination on the site.
“I wouldn’t want to take that property,” he said.
Although Wentworth said they had looked at several options to deal with traffic during construction, they plan to close the bridge for about 12 weeks during construction. There are two detour options for the site: one, on state roads, involves a 20-mile detour up through Blue Hill; the other, on local roads, would be a five-mile trip across the Hales Hill road. Both options have issues.
The longer detour on state roads follows Rout 175 up to Blue Hill, crossing the Falls Bridge, the site of another proposed MDOT bridge project, which already has been posted for heavy loads. The route across the Hales Hill Road involves crossing a small bridge, which was never built to carry the kinds of loads the detour would generate.
Selectmen from both towns have raised concerns about the impact of the detour options on local traffic and the effect that increased traffic will have on local roads. They met briefly with the engineers after last week’s meeting to discuss those concerns and how the department will address them.
“The Falls Bridge is posted and there’s only one way in and out for large trucks,” said Sedgwick Selectman Colby Pert. “That bridge was not built to handle truck traffic.”
They pressed the department to have an engineer examine the bridge in order to determine its condition before the project begins.
Both Kittredge and Wentworth said they would review the comments from the meeting and, before sending it out to bid, will review the design with the local concerns in mind. Kittredge said he would funnel any new information through Brooklin Selectman Deborah Brewster.
If all goes as planned, the department will advertise for bids this fall and begin construction about this time next year. The project should be done before Memorial Day, Wentworth said.