Realgâr, being a Paladin, would probably be best served behind the ranger so he can protect the rest of group behind him.

"I should probably be second in line. I can take a hit or two no problem. You lot with no armor that use spells or ranged attackin' should be behind me."

Summary: OK, so I believe this is where we are at this point:

Following the stream passage, bridge 20 feet above us connecting two tunnels…

Heard a noise, and Randaler made a Perception check (21) to determine what is was…

Marching order

• Randaler (point/scout)
• Realgar (Tank)
• Chad (wand at the ready with Fire Bolt)
• Haize (Malcom in the Middle)
• Mary & Kres (guarding our backs)

Did I miss anyone or any important details?

Chad

”What is with the delay Randaler? Let’s make haste before we get ambushed. I don’t have a good feeling about this.....”

As the group is conversing and planning their actions, there is a low rumbling, that then turns into a mighty roar. A huge torrent of water rushes down the passageway ahead of the group, sweeping into them at an incredible speed.

Here is how the scenario goes down:

• Those near the front (Randaler, Realgar, and Chad) are going to get caught in the flooding wave regardless. They can make a DC 15 Strength Saving Throw to grab hold of the walls or rocky outcrops to not be swept away. Randaler has Advantage, as he got just enough time from his Perception check to work out what was going on.
• Those near the back (Haize, Mary, and Kres) can either do the above, or if they wish attempt to leap out of the way into the rocky incline to the west they just walked past. If they do so, I would like a DC 10 Dexterity Saving Throw to attempt to escape the torrent by getting into the side passage in time.
• If you have any imaginative methods to rescue yourself or others, feel free to suggest them!

Kres will see the water and attempt to jump and fly up and out of the way of the water.

Dex Save 20

Dex save adv 20

Kres, using your wings, you fly upward towards the ceiling. Since it is an easier way for you to escape, I'll allow advantage on that saving throw.

Chad

Strength: 4

21 Randaler: Strength Save with Advantage 

Haize will levitate over the rushing water till it passes by.

"Well, that's unfortunate good luck everyone I shall pray for you."

Just to make sure, Dexterity saving throw: 18

Randaler senses the oncoming rush of water, and leaps to the side, grabbing onto a rocky outcrop and holding fast as the water rushes past him, soaking him below the waist.

Looking back over his shoulder he sees Kres fly into the air just before the wall of water would have engulfed him. It looks like Chad takes the full brunt of the torrent, but the light is too dim to see clearly. He cannot see the fate of his other companions further back...

Realgâr sees the water plowing its way forward and yells, "Dwarves never bathe!" attempting to hold on to a rock at least, despite getting a very intense wash.

Strength ST 9

(Gargled with water) "He..p!"

Randaler calls out over the rush of water. “Is everyone alright?”

"I think it got some people it was hard to tell."  Kres shouts back from above.

Mary attempts to leap out of the way.

Dexterity[: 23

As she dodges the water gracefully, (can mary attempt to throw a rope at the people being washed away?)

Realgâr attempts to take a javelin in both hands then outstretches his arms forward to form a T shape with the javelin perpendicular to his body, facing it against the flow of water. His goal is to attempt to get the javelin wedged inbetween some rocks as he gets pushed downstream so he has something to grab onto.

 Athletics to hold on?: 7

The torrent of water gushes down into the tunnel.

Chad attempts to hold his ground against the water, however he is swept away. He takes 1 bludgeoning damage as he is whisked away to the entrance of the cave again, falling prone.
Haize, thanks to the forewarning of the others, manages to deftly dash over the trickle of the stream before the rest comes gushing down and is in the western side passage, the rocky ground feeling a little uneasy beneath the feet.
Kres leaps into the air, his wings holding him aloft out of the way of the overflowing river.
Mary follows Haize into the side passage, managing to keep her footing and avoiding the flow of the stream.
Randaler, seeing the waves ahead, manages to grab onto a rocky outcrop and hold on as the water bashes against him, he manages to keep his ground.
Realgâr is swept up into the stream as he attempts to use his javelin to hold on. He jams it into some rocks, but his grip slips as he is also washed to the entrance of the cave, taking 2 bludgeoning damage and falling prone.

If Chad, Randaler, or Realgâr were holding any lit torches, they have now gone out as they are drenched.

Kres will look around and land back down when the water stops, he light a torch and see who of his companions is still around. "Is everyone okay?"

"I'm fine anyone have a spare torch?"

Haize will check his supplies to see if anything is damaged.

Chad

I get up from the ground and adjust my hair and mustache. I draw my quarterstaff and rush back into the cave, "someone is going to pay for this!" 

Haize checks over his equipment and everything seems to be there and still usable.

Kres lights a torch while aloft. As he does, he then notes ahead of him, on the bridge that was overhead of the people in front, a lone goblin walks over to inspect the aftermath. It notes the aarakocra in the air and screeches, rushing back the way it came (east).