Do you know how close each one of those people were to drowning? What they're standing on a wier which is basically a small dam, but waterfalls and normal dams also cause an effect called hydraulic pump. Because of fluid motion, if anything or anyone were to fall in there, the water causes an infinite "vortex" horizontally, effectively keeping them not quite at the bottom of the water but rather swirling around in a hellish sideways whirlpool. It's so bad that you can't even swim sideways out of it. As a matter of fact, canoists and kayakers call weirs "drowning machines" because of how dangerous they are. God smiled on each and every one of those people and their families on that moment because if any of them had slipped, they would have all had an awfully traumatic death.
What they did was so dangerous that if I was stuck in there and people tried to form a human chain, I'd tell them to just kill me. Water is like electricity. Respect its power and don't even think about fucking around with it.
Regarding what I would do to/for the dog, I'd preferably have a rope and harness for someone to go, but in lieu of that I'd just shoot it. Not even the vilest torturers deserve the terror of drowning in that storm, and I'm not risking anyone else's life to that fate.
I can't disagree with your scientific assessment of the perils. Water in volume is a truely terrifying thing. But... this is what sets us apart, is that we would risk life and limb to ensure the safety for others, strangers and even other species.
Regarding what I would do to/for the dog, I'd preferably have a rope and harness for someone to go, but in lieu of that I'd just shoot it. Not even the vilest torturers deserve the terror of drowning in that storm, and I'm not risking anyone else's life to that fate.