Group was sucked into the weir within 20 secondspublished at 12:42 British Summer Time
Mrs Justice Stacey says the group "fell down the face of the weir" in no more than 20 seconds.
They were sucked into the hydraulic jump - or spin - a recirculating flow similar to a washing machine.
The judge adds: "The ankle leashes attached to the boards of those stuck in the hydraulic spin, which are totally unsuitable for fast-flowing water, made it even harder for them to get free."