On this day in 1864 The Great Sheffield Flood: The largest man-made disaster ever to befall England kills over 250 people in Sheffield.
On the night of 11 March 1864, assisted by a strong south-western gale, the newly built dam, known as the Dale Dyke Dam, at Low Bradfield on the River Loxley, collapsed while it was being filled for the first time. An estimated 3 million cubic metres (700 million imperial gallons) of water swept down the Loxley Valley, through Loxley village and on to Malin Bridge and Hillsborough, where the River Loxley joins the River Don. The flood continued south down the Don into Sheffield centre, around the eastward bend of the Don at Lady’s Bridge, then to Attercliffe, past the sites of what would later become Don Valley Stadium, Sheffield Arena and Meadowhall Centre and on to Rotherham. A wall of water moved swiftly down the valley, destroying everything in its course. The centre of the town, situated on the hill to the south, escaped damage, although the densely populated district of the Wicker, around the new railway viaduct (constructed by the Manchester and Sheffield Railway), was completely destroyed.
The company’s consultant engineer, John Towlerton Leather, was one of a family of worthy Yorkshire engineers who were involved in such work. His uncle, George Leather, had been responsible for reservoirs around Leeds and Bradford, and one of these was the scene of a dramatic collapse in 1852, when 81 people died. John Leather and resident engineer John Gunson were working closely together during the construction of the dam. Leather designed the dam and oversaw its construction whereas Gunson directed and supervised the construction of the dam. Gunson was on site the night of the collapse and stated that there was a concerning cracks in the outer slope of the embankment. Gunson convinced himself that the crack was not harmful but still took precautions by opening up the valves on the middle of the embankment to allow more water through. Unfortunately these precautions failed to prevent the crack from worsening.