River Street Bridge and Mill Tunnel
Plainfield, Connecticut

Historic features documented in connection with Connecticut Department of Transportation Project No. 108-160.

Click on images to see them larger.

River Street in the Moosup section of Plainfield, Connecticut has two interesting historic engineering features: one is a highly visible local landmark, but the other is totally hidden beneath the roadway. The visible one is an 1886 wrought-iron truss bridge built by the town of Plainfield following the disastrous flood of that year. The other feature is a tunnel linking the factory buildings on either side of the road. Although it was built in 1957, it made use of archways and stone walls that were built a hundred years earlier as part of the waterpower channels for the woolen mill that previously occupied the site.

Whenever the Conecticut Department of Transportation undertakes highway improvement projects or assists the towns in their projects, it first seeks to minimize any effects on historic and archaeological resources. In this case, the Town of Plainfield needed to replace the 100+ year old one-lane bridge with a structure that meets modern transportation standards. In order to make a record of these historic features before they were obscured or obliterated by the upgraded roadway and bridge, a professional historian and archaeologist were hired to write detailed descriptions and statements of their significance. This web site summarizes their findings.

The Bridge

Click to view larger image The River Street bridge is a wrought-iron through truss 105 feet in length and is an example of the patented lenticular design manufactured by the Berlin Iron Bridge Company, Connecticut's only large-scale manufacturer of bridges in the 19th century. So-called because its profile suggested the shape of a convex lens, the lenticular was one of several unique truss designs popular in that period. In addition to being structurally sound and offering some savings in the amount of material used, the patented design gave the agents of the Berlin Iron Bridge Company something distinctive that they could point to when trying to convince local highway officials of their product's superiority.

Click to view larger image Like most bridges its age, the River Street Bridge has its components connected not with rivets and gusset plates but with large pins. Engineers at that time thought that pinned connections did a better job of transmitting stresses. Later, riveted connections came into favor because they were more rigid, simpler to construct, and easier to maintain. Like its companion bridge upstream at Glen Falls, the River Street Bridge typifies 19th-century truss engineering in its distinctive patented design, wrought-iron material (steel was just becoming commercially available for large structural components), and pinned connections.

Click to view larger image The River Street Bridge was built following the destruction of its wooden predecessor by the disastrous flood of February 13, 1886, one of the worst this part of the state had ever seen. Two days of constant rain, totaling some 8", swelled the rivers of eastern Connecticut and western Rhode Island (where the Moosup River has its source) and created a powerful surge of water and ice that broke through mill dams and carried off bridges, including nearly every bridge in Plainfield. According to one eyewitness, "Moosup is in bad shape on account of the freshet. The bridges are most all gone, and the roads in that section, many of them, are useless." There were no trains, mails, or telegraph service for several days. Although the Cranska mill dam just above this site appeared to weaken, it remained intact; however, the mill race just below was heavily damaged.

Click to view larger image The Town of Plainfield, faced with replacing all of its major bridges at once, voted to raise $20,000 through the sale of bonds, a large sum for that time. The River Street Bridge was one of three large bridges that were replaced with iron trusses purchased from the Berlin Iron Bridge Company. The Town spent $1,758.00 on the bridge, which probably did not include the cost of the stone abutments built by local masons. This crossing was important because it was one of only two highway bridges across the river in Moosup, and the only one at the north end of the village. Mill workers on the east side of the river, where the Cranska mill had some of its worker tenements, would have had difficulty getting to work, nor could supplies be as easily brought to the mill.

The Tunnel

Click to view larger image The tunnel passes under River Street approximately 38 feet west of the bridge and links buildings of the Griswold Rubber Company on either side of the street. It is 146 feet long, 21.5 feet wide, and 7 feet high. The roof of the tunnel is formed from steel I-beams, some of which are encased in concrete. The side walls reflect at least three construction episodes: the oldest are stone rubble walls 18-24 inches thick, inside of which is another layer of larger stone rubble masonry 36-39 inches thick. Portions of the latter were replaced by concrete walls in 1957. Prior to the current state construction project, the tunnel was mainly used for storing and transferring bagged material. The Griswold Rubber Company restored these functions after the rebuilding of the western bridge approach.

Click to view larger image Although it assumed its current configuration around 1957, when the Griswold Rubber Company moved to the site, portions of the tunnel are actually much older. The brick factory complex currently occupied by the rubber company was originally a water-powered textile mill, and the tunnel side walls were the mill's stone-lined headrace, an open channel that conveyed water from the mill dam just upstream to the mill, where the water powered water-wheels or turbines to drive the machinery.

Click to view larger image Joseph S. Gladding built the first mill on this site around 1832 for the manufacture of cotton cloth, and portions may survive as part of the large 3-story factory building south of the tunnel. In 1880 the Gladding mill was purchased by Floyd Cranska, who operated it until his death in 1920, producing high-quality cotton yarn that other firms used for making cloth. Cranska doubled the size of the mill in the 1880s and expanded it further in the period 1907-1916. At the time of his death, the mill was one of the largest employers in Moosup, with 160 people operating 22,000 spindles. A family company continued the business for decades thereafter.

Click to view larger image The mill's headrace sustained heavy damage in the Flood of 1886, and it seems likely that the heavier stonework that forms the inner walls was added at the time the damage was repaired. The headrace remained open, except for a bridge that carried River Street over it (probably represented by the older, concrete-encased beams) until 1957, when the Griswold Rubber Company filled much of it in, roofing over the remainder to provide a connection to link its operations on opposite sides of the street.

Click to view larger image The current River Street improvement project exposed the tunnel walls to daylight for the first time in 40 years. New concrete walls were built to support a new bridging structure. Part of the original stonework from the headrace remains in place, buried beneath the fill that was added before the roadway was reconstructed.

See what the area looked like a hundred years ago

Site Plan

Sources of additional information


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This Web presentation is based upon documentation studies of the River Street tunnel by Michael S. Raber, Raber Associates, and the River Street bridge by Bruce Clouette, Public Archaeology Survey Team, Inc. The documentation was funded by the Connecticut Department of Transportation and reviewed by the Connecticut Historical Commission. A copy of both will be permanently archived as part of the Connecticut Historic Preservation Collection at the Dodd Research Center, University of Connecticut.