Group was sucked into the weir within 20 secondspublished at 12:42 British Summer Time 23 April
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."