Jax: You follow down the tunnel, and see some flickering light and smell a fire with some meat cooking. You hear several animated goblins chattering from where you see the tunnel open up into a cavern.
Everyone else:
Just as the first of you cross under the bridge, you hear a shout in goblin, and the thunderous roar of another flood.
Brother Lantern, Lupin:
You are in back and still close enough to that rubble filled side passage to jump for it with a DC 10 Dex Saving throw. If you succeed, you avoid the flood. If you fail, you must withstand the flood.
Everyone else can't avoid the flood this time. Make a strength saving throw, DC 15 or be washed out of the cave mouth, taking 1d6 bludgeoning damage, and being knocked prone.