Oh dammit all, I always was a b++lsh+++......and people can tell you know...
As a side note, in 1978 a maintenance team was dredging the bottom of the canal to remove rubbish. Later that day, they were told that a large whirlpool had formed and the canal was quickly losing water. It turned out, one of the first things removed from the canal was a large plug that had been installed to allow the canal to drain in an emergency.[12]
http://en.wikipedia.org/wiki/Chesterfield_Canal
last sentence in Restoration
I remember when it happened. I hadnt realised it was 1978