I was very interested to see the innovative dual waterway aqueduct constructed to take the Kennet & Avon Canal across the A350 (NCE 20 November).
But as to innovative construction, can I draw your attention to the Bullbridge aqueduct of the Cromford Canal across Stephenson's North Midland Railway in 1839?
Not only was the aqueduct channel constructed first, in cast iron, it was actually floated to the site before being sunk into position and the railway excavated underneath.
Williams* describes it thus: 'Across the path of the future railway lay the Amber River and the Cromford Canal, so near together but at such different levels that the line must pass over one by an embankment and bridge, and almost at the same moment under the other;
and yet the works must be, if possible, so constructed to avoid stopping the navigation for more than a few hours.
'As the line where it passes under the canal was itself on an embankment, the foundations of the piers which were to carry the aqueduct overhead had necessarily to be laid at a considerable depth, and then raised to a sufficient height to support an iron trough which was to carry the water.
'This trough was made the exact shape of the bottom of the canal, was fitted together closely, was then floated to its destination, and was finally sunk on its resting place without disturbing the navigation, or being thenceforth itself disturbed.
'At this point, known as Bull Bridge, we have, therefore, a remarkable series of works.
'At the bottom is a river, and over it there are in succession a bridge, a railway and an aqueduct; on the top ships are sailing, and underneath trains are running.'
Regrettably this aqueduct and the adjacent one over the A610 road were demolished in 1968 to permit road widening, although the river arch and an accommodation arch through the same canal embankment survive.
Times have again changed, and the charity set up to promote restoration of the canal is now seeking innovative methods for a new aqueduct across the railway and main road.
John Boucher Boucher. sons@btinternet. com *Frederick Williams, The Midland Railway, its rise and progress, Strahan & Co, c.1876