Stop Planks & Slots
As it winds its way through Merseyside, the land to the West of the Leeds and Liverpool Canal is generally lower than the canal. So, if the canal were to develop a leak, all the water would flow downhill onto that land, much of which is occupied. It’s about 26 miles from Liverpool to Appley Locks. At an average depth of 1.5m and an average width of more than 10m, that’s about 250,000,000 litres of water.:-
Most leaks occur when 18th century culverts collapse, but the canal in this area has also been under cut by both rail and road tunnels, and there is are obvious weak points at the locks, of course. To minimise the flooding, and to protect the canal’s water supply, slots were cut into the banks at the narrow points under bridges when the canal was first cut,. “Stop planks” were stored nearby. If a breech occurred, the stop planks were inserted at the bridges on either side of the leak, so that only the water between the stop plank dams would escape.
In Liverpool and Bootle, most of the bridges span a wider gap than the standard stone arch or swing bridge, so there are few bridges with stop plank slots. During WW2, there was a real possibility of the canal being breached by bombs, so extra stop plank points were put in near; Pennington Road, Litherland Road, and Miller’s bridge.
The stop planks were inserted every night, so when the canal was breeched at Bankhall, flooding at Canada goods yard was minimised and it took just 3 weeks to get the canal repaired and reopened. You can still see the repair in Google Maps “Satelite” view as a bright line on the edge of the canal.