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Halfway River Bridge

From DARwiki

Halfway River Bridge/Hantsport Aboiteau

Mile 37.17 on the Halifax Subdivision

DAR work crews repair the Hantsport Aboiteau, August 1971, photographed by Bill Linley.

Located just east of Hantsport, the bridge crossed the Halfway River (so named because in early times it marked the halfway point between Grand Pre and Windsor) where it meets the larger Avon River.[1] The Halfway River is small, but it has a deep tidal estuary surrounded by wide tidal marshes where it is crossed by the DAR. This crossing required regular upgrades and repair throughout the history of the DAR.

The river was first bridged by the DAR in 1869 with a 1,800 foot trestle and a covered wooden truss bridge.[2] By 1873, an engineer's report indicated that the trestle was 640 feet long (32 trestle spans, each each 20 feet long) and the bridge was a 150-foot long wooden truss bridge. The report by engineer Alexander MacNab noted that the main span was weak and needed a pier in the middle and that many of the pile trestles were gradually being replaced by trestle bents.[3] The wooden bridge was replaced by a causeway with an aboiteau in 1879.[4] The aboiteau was rebuilt in 1914-1915.[5]

By 1969, most of the trestle approach had been filled and converted to an embankment leaving a 40-foot-long pile trestle over a spillway on the east side of a causeway crossing the Halfway River over an aboiteau with three 60-inch corrugated metal pipes.[6] The roadbed and aboiteau was washed out by heavy flood waters on August 16, 1971 [7] but the line and aboiteau was was quickly repaired by DAR crews who installed new culvert pipes.[8]

The railway ceased to be used in 2011. The causeway slowly began to erode and the aboiteau gates ceased functioning. Erosion increased dramatically in September 2017 and a large washout occurred in the causeway, leaving the rails hanging in mid-air and exposing the pile trestle work of older versions of the bridge.[9] The Windsor and Hantsport Railway put up barricades and removed the hanging rails on February 7, 2018,[10] but the washout grew leading to extensive tidal flooding of the formerly protected Halfway River Valley which raised fears about erosion and flooding of roads and power lines. The flooding has led to a dispute between the Province of Nova Scotia and the Windsor and Hantsport Railway over who owns the aboiteau and who bears the responsibility for the washout.[11] After the site the site was documented by arachaeologists, the province rebuilt the aboiteau in the fall of 2019 and is suing the Windsor and Hantsport Railway for the cost.[12]

Gallery

2017 Washout

2019 Archaeology

Description of the aboiteau site by Laura de Boer, archaeologist at Davis MacIntyre & Associates:

The structure of the existing aboiteau appears to feature two broad stone-filled wood boxes (wooden gabions) on either side of the aboiteau entrance on the west or upstream side, followed by three additional roughly square stone-filled boxes on either side of the aboiteau just downstream, and also including some brush on the north side. Nearly a dozen steel rails were also recovered from this area, some of which were marked “DOMINION”, “MACKIE”, and “D I & S Co”, indicating they were made in Sydney, Cape Breton. At least four of the rails were also deliberately bent at either end, pointing to their reuse as some element of structure or erosion control for the aboiteau. One of these rails was covered in grey "fat clay," which had preserved traces of sawdust against the steel.

The middle of the aboiteau, being formerly in the middle of the embankment, appears to have needed no ballast to either side to hold it in place. Some additional wooden boxes of stone visible nearer to the eastern mouth of the aboiteau suggest that the structure may have been originally symmetrical, being reinforced and held in place on either end with heavy wooden-planked boxes of stone. The sluice itself is a heavy wooden culvert with two internal partitions, creating three passages for the water, decked on top with two layers of thick wooden planks. Some of the side timbers feature roman numerals presumably designed to guide the proper placement of the pre-constructed aboiteau during installation. Precise measurements were not taken and the original position and nature of the flap for the sluice gate is no longer clear (at least without risking exploration in close proximity to the fast-moving tides).

The vertical wooden piles on either side of the aboiteau structure are almost certainly the original 1869 wooden trestle bases for the rail bridge. It was necessary to cut or break the trestles off during the course of the archaeological monitoring, as attempts to pull them free of the grey clay proved impossible even when applying 40 metric tonnes of pulling force using the on-site crane, both directly and with a vibrator unit. Elements of the rock-filled wooden boxes also had to be dug out, as pulling them out resulted in the boards breaking and the bottom ends being held in place by the suction of the fat clay.

References