Ladybower Reservoir is a large Y-shaped reservoir, the lowest of three in the Upper Derwent Valley in Derbyshire, England. The dam’s design is unusual in having two totally enclosed bellmouth overflows (locally named the “plugholes”) at the side of the wall.
Were you not tempted to drop down the hole and see where it goes? 
The other person I was with went further down…didn’t fancy loosing my drone lol. Looking forward to going back when the reservoir is full and the drain is in full flow.
I think it’s the first drone video, or photo, to not show the overflows … overflowing … to have been posted on GADC (I may be incorrect).
Interesting. After record rain in May, too.
