Beautiful series you've captured Richard
Good question Phil.
Looking at this other photo from a different angle, it's technically a weir.
View attachment 873396
It was taken on my 50th birthday back in 2003 when we met up with my son, who was at Uni in Sheffield and my parents from Cheshire.
I've got a feeling we might have walked from Monsal Head along the river to Cressbrook and Millers Dale, but I can't pinpoint that weir on any of my maps. I'm sure you'll be able to work out where it is sometime.
I don't recognise the first waterfall Brian. Do you remember where that was?