White Bridge (The Bacule railway bridge)

Cadw's description

Location

Spanning the Afon Tywi to the SW of Carmarthen.

History

Railway bridge over the Towy of 1908-11 replacing an opening timber bridge by I.K. Brunel of 1852-3 for the South Wales Railway, then no longer considered strong enough for the weight of modern rolling stock and locomotives. The replacement was built as a rolling bascule bridge by the Great Western Railway. In 1933 it was said that the bridge was an early design by the noted engineer Ralph Freeman. The contractor was the Cleveland Bridge and Engineering Co of Darlington. The opening mechanism has been derelict for many years.

Exterior

Railway bridge of 5 fixed spans and one roller lift span. Fourteen iron cylinders (weighted with concrete), braced by lattice girders and ornamented with cast-iron moulded capitals, carry the steel superstructure of cross-girders and rail-bearers carried on bearing girders. The parapet of solid panels is surmounted by lattice-work. Three-sided cast-iron pilasters articulate the bays of each span. Abutments and the sub-structure of the lifting mechanism are brick.

The lifting span (westernmost) is a balanced cantilever carried on steel-plate bearing girders supported on 2 sets of cylinders. Lattice girders curve down to the line of the parapet of the main bridge. Steel-plate cross girders and rail bearers, the cross girders alternately projecting to support outriggers of the main girders. The moving span was operated by gearing carried on trestles on cantilevers either side of the bridge: a curved rack is fixed to the outer face of the main girders, driven by pinions themselves driven by wheels. These details survive, though the small power house which housed the electric motor on the S side of the bridge is now derelict.

Reason for designation

Listed grade II* as a rare surviving example of a bascule bridge, an unusual engineering structure with strong architectural character.