H&H is serving as lead designer for the replacement of the Blyman Canal Bridge. The existing bridge, built in 1906, crosses the Blynman Canal at a 36°skew and a moveable span length of 57 feet between pinion bearings. The 46-foot wide bridge has a 33-foot roadway and two 6-foot sidewalks. Marine traffic requires the bridge to open 7,000 times per year and as many as 60 openings per day during fishing season. The bridge is the second busiest moveable span along the Atlantic coast.
MassDOT’s goal is to replace the 110-year old deteriorated bridge. The team completed numerous bridge-type studies. Fixed bridge options that would significantly change Western Avenue’s grade were found infeasible primarily due to enormous right-of-way costs with the proximity of abutting residential, business, and park properties. New options include vertical lift and various bascule types to replace the bridge in the same location. The selected options will minimize future maintenance by minimizing components exposed to seawater.
The design of the new bridge will complement the existing aesthetics of the area. Currently, the 100-year flood elevation is near the bridge roadway level. Since the proposed roadway profile will not vary much from the existing one, measures will be taken to protect the machinery and counterweight pits from potential floods. The new bridge’s abutments will be moved back, in line with existing canal walls making longer the span across the canal.
To match the existing approach roadway width, the bridge roadway will be widened from 33 to 40 feet. During construction, traffic will be maintained along Western Avenue by building a temporary bypass bridge south of the existing bridge. The temporary bridge will be a moveable span to maintain canal navigation during construction. A portion of temporary approach roadways and a temporary bridge will be located on park land to the south of the existing bridge.