The main problem with upgrading the Wakefield branch was the dimensions of George Leather's cast iron aqueduct over the River Calder at Stanley Ferry. Structural analysis showed that parts of the ironwork were overloaded, and so in 1981 a new concrete aqueduct was cast by John Laing Construction Ltd, on a site a little further upstream. The complete structure was then pushed into position by hydraulic jacks in a six-day operation, after which the navigation was diverted over it, although the old aqueduct was left in place and can still be used.