White Plume Mountain Aquarium Hydrodynamics

(Updated 6/29/17)

The aquarium room in the dungeon White Plume Mountain is a very complex encounter that will quickly have DM’s trying to figure out hydrodynamics of water flow and volume. Last night I had the pleasure of co-DM’ing a nearly disastrous attempt on the room in an Adventurer’s League game at Giga-Bites Cafe. The players, through recklessness and bravado, started to try to take on all of the room’s creatures at once. In the end, they managed to withdraw from the room and their actions probably set them up for an easier take on the room later. This experience got me thinking that maybe I could help out with some volume and flow calculations.

  • Water Volume of Area B: 34,000cu ft (34 10’x10’ cubes)
  • Air Volume of Area C: 26,000cu ft (26 10’x10’ cubes)
  • Water Volume of Area D: 18,000cu ft (18 10’x10’ cubes)
  • Air Volume of Area E: 10,000cu ft (10 10’x10’ cubes)

If the glass wall at B is broken, water will flow into area C, fill it and then flow into D and finally overflow and flow into area E, filling it to a depth of 8 feet (if the drains are blocked somehow). This will take about 25 minutes (250 rounds) to complete. If left alone, Area E will drain in about 30 minutes, resulting in very little water actually accumulating in Area E for any length of time.

If the glass wall at C (once filled with water or B and C at the same time) is broken the water will flow into D, overflow and flow into area E, filling area E to a depth of 22½ ft, Filling Area D to a total depth of 12½ ft and 2 ½ ft of water will remain in Area C. This will take about 12 minutes (120 rounds) to complete. If left alone, the extra water will drain in about 2 hours, resulting in water only in Area D.

If the glass wall at B is broken and the party waits for the water to drain out, and then the glass wall at C is broken, C, D and E will fill completely and E will fill to a depth of about 21 feet, D to 11 feet and C to 1 foot. This will take about 15 minutes (150 rounds) to complete. This water will drain from Area E & C in about 90 minutes, leaving 10 feet of water in area D.

If the glass at D (but not at B) is broken, the water will flow into Area E, completely filling it to a depth of 12 ¾ ft and 2 ¾ ft of water will remain in area D. This will take about 12 minutes (120 rounds) to complete. If left alone, this water will drain from area E & D in about an hour.

If the glass at B, C and D are all broken the whole mass of water will drain in about 3 hours.

For simplicity’s sake opening a second hole will halve the drain time.

Trying to climb up through a hole where water if pouring out is extremely difficult, the DC should be at least 25. Trying to act under a flow of water should require a STR check at DC 15 and all actions should be at Disadvantage. However, this will only be the case for the first few minutes of drain time, the flow will get weaker over time and after about half the time, will be slow enough that it will not impede heroes from action. Unless you want it to.

A quick Google search reveals that an ASU biologist says that some Scorpions can survive for up to 2 days under water. In that case, I’d rule that these scorpions can swim. That should freak out the players. However, these are all unintelligent, hungry animals. The Manticores are a little smarter, but the rest of the animals will try to eat each other given the chance.

The Manticores have learned that shooting spikes at the Sea Lions is useless, even if they killed a Sea Lion, the body would just sink to the bottom of the tank and they would not get any food.

But the Scorpions, Crayfish and Sea Lions will all attack each other given the opportunity. The Manticores will also attack anything that they can reach and eat. Nothing will drown in the event that their enclosure fills with or drains of water.

The Manticores can theoretically reach any part of the room with their tail spikes, except that the glass walls prevent them hitting targets not standing in a gap in the glass or on top of a glass wall. (The red line in the diagrams indicates the attack angle on the Manticore’s spike attack.)

In the event that the players break the glass wall at B, the water will flow into C, the Scorpions and Crayfish will co-mingle and kill one another, with the exact results being dependent on the exact situation. In the water, the Crayfish will likely get the better of the Scorpions. The water that flows into E will drain out in about 30 minutes. The Manticores will be well and truly pissed off wet cats.

In the event that the players then break the glass at C, any surviving Crayfish will probably be OK and will stay away from the Sea Lions, meanwhile the Sea Lions and Manticores will fight one another, with the Manticores trying to get out of the water and fleeing up into the dry area at A. They should be able to jump from the top of glass wall to top of glass wall to escape. Its likely that the Sea Lions will kill one and eat it given time. The excess water will drain out in about 90 minutes.

Edit: Upon reflection, the drain times from one level to another have been updated. Since the rate at which water drains is kinda based on the square of the height difference between the top of the water and the bottom of the hole, the water will drain 100 times slower at the end of the drain time than at the beginning, not 4 times. Oops. So I have made the drain times 25 times slower than they were in version one. This ends up having a pretty significant effect given the published drain time of all the water (3 hours), which is probably way too fast but it’s a given in this physics problem.