Design and Engineering
The foundation stone for Island Bridge, or Sarah Bridge as it was known then, was laid in June 1791. Designed and constructed by Alexander Stevens, a Scottish engineer, the work was also supervised by Edward Cope and the project managed by John Blaquiere. In February, Cope reported as regards the completion of work that “Stevens spared no expense to complete the whole of the work properly”, He also makes mention of a “Dam-Head” which would suggest that the abutment foundations were constructed inside some type of cofferdam, probably similar to Semple’s (1753).
Island Bridge spans the Liffey between Conyngham Road to the north and the South Circular Road. It is an attractive single span elliptical arched bridge composed of evenly coursed granite ashlar. The masonry of the abutments is smoothly rusticated while that of the spandrel walls is unrusticated smooth ashlar. The masonry of the archrings comprises a series of large wedge shaped vermiculated voussoirs alternating with voussoirs which are half vermiculated and half-smooth.
The parapet comprises four large granite dadoes and fourteen sections of ornamental wrought iron railings. It is described by Ted Ruddock, author of Arch Bridges and their Builders 1735-1835, as “a single arch of bastard elliptical shape and 31.2m span, which was built in 1791-1792. It bears no resemblance to Stevens’ earlier bridges except those of competent design and construction. It is of generous width, almost 12m and fenced with an iron handrail which was probably erected when first built”. The crown is 9m above low water. The flag footpaths retain the original arch profile though the road has been lowered somewhat to give a less pronounced arch.