Flow rate at Wilf's in Staveley

 I took these pictures from the balcony of the wonderful Wilf's cafe in Staveley. My ancestors come from round here and there are lots of people with my name here. Wilf's used to be a wood turning mill. My ancestors worked in bobbin mills like this. The weir is to hold up and redirect the water to power the mill. I noticed how much faster the water emerged from the duct. Then I remembered volume flow rate. Water flows by volume, and the volume per second = cross-sectional area x speed. This should be the same for the river above and the duct through (not quite true because there was water redirected to the mill). The pipe has a smaller cross-section so a higher speed. The depth seemed the same in bot. The river was about 10 metres wide and the pipe 50cm wide so the speed would be 20x faster.

I also noted that the wheel to close the hole was much bigger than the ratchet. Equal work done at each end means smaller force on the bigger wheel,