Powow River Bridge

The Powow River Bridge was built in 1891 and is a very rare and unusual bridge. This bridge is a very small swing bridge, where most swing bridges have much longer spans. This has led to the truss having an odd and disproportionate appearance. The bridge is a riveted wrought-iron rim-bearing swing bridge and is one of the earliest examples of moveable bridge technology in Massachusetts.

This river crossing was used since the mid-eighteenth century, and this is at least the fifth bridge to have spanned the river at this location. The first bridge was built in 1752 to help access the shipyards that were already in operation along the riverbank. No information is available about what type of bridge was originally built. The bridge was replaced with a drawbridge in 1794. The bridge was replaced in 1824, but again, there is no information available about this bridge, although it can be assumed that the bridge was timber. In New England at that time, the lifespan of an uncovered bridge was about twenty years, so unsurprisingly the bridge was replaced again in 1843. This bridge had two granite arch spans and a single wooden Howe truss span. Interestingly, it was not a drawbridge.

By the 1890’s, the existing bridge was deemed unsafe. The foundations and piers had cracked, and the roadway was too narrow for the amount of traffic it carried. It was decided that a new bridge would be built but there was a great deal of debating over what type of bridge would be built. The town selectman could not remember why the 1843 bridge was not a drawbridge, although it was likely because there was not a great deal of boat traffic. Boats with deep draughts and wide beams found that the river was marginally navigable, and the amount of silt made dredging impractical. However, the War Department ultimately insisted that the current bridge did not meet their specifications, and that the new bridge would include a moveable span. The current bridge was ultimately designed as a metal swing bridge, and construction started in 1890. After numerous delays, the bridge opened on September 12, 1891.

Truss bridges that swung from a central pivot point have been designed since at least the 1840’s, and by the 1870’s they were the dominant form of moveable bridge. The design of the truss reflects the engineering problems associated with operating a swing bridge. When the bridge was closed, the abutments support the bridge ends. In this condition, the upper chord is in compression and the lower chord is in tension, which is the typical condition of a truss. However, when the bridge is opened, the load transfers to the central pier. This causes the forces to reverse, with the upper chord being in tension and the lower chord being in compression. This was accounted for by placing a hinged member in the center of the bridge. In the closed position, wedges under the bridge at the abutments lift the structure and reduce the stress on the upper member. This creates the distinctive polygonal upper chord and A-shaped central panel on this bridge.

This bridge has a long history of repairs and alterations. The floor and deck were rebuilt in 1911, 1921, 1928, 1935, 1946, 1951, 1970 and 1998. The center pier was repaired in 1914 and 1962, and the fenders were replaced in 1945. New gates and warning lights were installed in 1919. The steep grade of the western approach was reconstructed in 1922, which required the bridge’s westerly abutment to be reconstructed.

The bridge stopped operating and was fixed in the closed position in 1928. This was done when it became apparent that the river would not be maintained as navigable because of problems with silting and low boat traffic. The gears and turning mechanism were removed at some later point, but the drum and rollers remain.

The Massachusetts Department of Public Works announced that the bridge would be replaced in July of 1970, in order to eliminate the dangerously sharp curve on the approach. However, this idea was strongly opposed because the new bridge would remove a section of Alliance Park, not because of a sentimental feeling for the bridge. The plans for the new bridge were quickly abandoned, and the existing bridge was repaired instead.

The bridge was rehabilitated again in 1998, and the historic aspects were severely altered. The flooring system was replaced with steel stringers and the trusses are bolted onto these stringers. The trusses no longer carry any load, and are purely decorative. The original lattice railing remains along the wood-plank sidewalk. However, there is no evidence of the original gates. The railing still has the fence medallions, which were a trademark of the Boston Bridge Works, who constructed the bridge.