When the picture is looked at in detail, the towpath bridge was of the Horseley Ironworks type and would have been erected when the New Main was constructed. The bridge that is now there would be by the Docks & Inland Waterways Executive.
It was reported in the Birmingham Daily Gazette November 2nd 1953, but does not receive a mention on the Railway Archive Website
The ten trucks had been detached so that the loco could delivers other to a factory and the remaining Ten and Brake Van ran back down the line to Harborne Junction where there were catch points. Four Waggons and Brake Van fell onto canal towpath and bridge
The gazette September 9th 1880 reported a similar accident where 9 waggons and van ran down to the junction with some crashing off the catch point siding into the canal