Quote from Monsterball >>

((In the interests of increasing the pace of play, let's say the same marching order as earlier, but with Clara moving to the front and using her Light-spell empowered flashlight.))

 Clara leads the way climbing up the western escarpment. As she steps onto the level ledge between the two escarpments, it breaks underneath her weight and rubble starts to fall backward down the incline, threatening to take Clara with it. Make a DEX saving throw (with advantage if anyone tries to catch her).

Clara leads the way, clambering up the steep, western slope. Despite her dancer's feet, she occasionally loses her footing on the loose rubble scattered across the ground and practically needs to crawl on hands and knees at times. She steps out onto the ledge between the escarpments, and gasps as the ground suddenly gives way.

"Whoaaa! Watch out!" She calls out in a hushed voice, trying to skitter forward onto the other side without tumbling down the slope. 

Dexterity save: 18. Second roll if advantage: 14.

"Well it seems unlikely they dragged our pals that direction, perhaps we stick to the northern direction?" Herron holds his staff out cautiously to keep those behind him from continuing forward.

Clara manages to keep her feet and avoid hurting herself. Herron suggests backtracking and returning to the northern passage. As you all return to the passageway, you suddenly hear a rushing sound, and suddenly the stream, which had only been about two feet deep, surges to four or five feet deep as a huge torrent of water comes rushing down the passage from the north. 

Everyone make a DC 10 Dexterity saving throw to avoid being swept away by the water. If you fail that, make a DC 15 Strength save to try and hold on to something. If you fail both saves, you are swept back to the cavern entrance and take 4 bludgeoning damage!