Research question: Water flooding into a subterranean chamber

[Flannery]

So I have a situation in my current urban fantasy WIP novel where a group has a house on Lake Michigan. Beneath their house, the have a secret setup, including a library, conference rooms, operational rooms, etc. In said underground library, the back wall extends out into Lake Michigan--and I'm well aware that this is likely highly implausible, but it's magic! *wiggles fingers*--and a thick wall of glass provides an underwater view of the lake itself. (I have a whole section in my book that talks about water being an excellent carrier of magical energy, so water plays a pretty significant role throughout.)

A big scene toward the end of my second act has my protagonist and his little crew stuck in this underground library with no way out. Creatures are beating at the library door, about to bust through. So, they decide that the only way out is through the lake. Magic, magic, boom, tension-filled scene with the bad monsters coming at them just as the thick glass is shattered--you get the picture. Water floods into the library. (They're protected because, well, magic! *wiggles fingers*)

Now to the science part: What would happen to the house above? Would the lake water flood into the house, up the stairs, and out through the first floor? Would it be gushing out of the front and back doors of the house? Or would the water top off at the level of lake? I'm fine with magic explaining away some of the stuff above, but this part, I feel, needs to nod toward actual physics.

Thanks!

ETA: And mods, if this would be better suited in the Writing discussion forum, feel free to move me there. I wasn't sure if I should post it here or there.

 

[Jo Zebedee]

I can't help with the house part but it did occur to me that having the magic protect them so easily (which, of course, it might not be in the book) rather robbed some of the tension.

 

[Brian G Turner]

would the water top off at the level of lake

I would think so - though with some dramatic splashing about before it settles.

I do like the idea of escaping through the lake, though - sounds like a dramatic scene.

 

[Flannery]

I can't help with the house part but it did occur to me that having the magic protect them so easily (which, of course, it might not be in the book) rather robbed some of the tension.

Yeah, I've tried to mitigate that somewhat in the actual writing. The magic part isn't as easy as I described it here. I definitely want to make it a tense and dramatic scene and not one where magic, well, magically solves all their problems.

I would think so - though with some dramatic splashing about before it settles.

I wrote the scene with the water spouting out the doors but then settling to the level of the lake. I think I'll be okay. I just had a moment as I was skimming through it a little bit ago where I envisioned some Amazon reviewer flogging me for being a physics loser. lol! (Even as it's a story about spell casters and dark gods of myth and legend. lol!) I'm also considering having the house collapse in on itself due to underground supports failing from the force of the water.

 

[HareBrain]

It would settle at the level of the lake, but how much higher it surged beforehand would depend on the force of it coming through the breach. I think it would have to be a big breach for it to get up the stairs and out of the doors. Probably big enough to fill the basement almost instantly.

 

[Mad Alice]

The lake water would take the path of least resistance unless there were some kind of vacuum or other pressure build up involved. Because they burst through the glass there is an explosive force directed outwards upon the lake water. The water of the lake would move in as the glass disintegrated. Think of a thin plastic water bottle suddenly pierced. The water comes out in blurts, then plumes, then is awash. The air would move as well, bubbling up rapidly. Again taking the path of least resistance. If there was a stairwell, it would flood. But each door and wall presents a resistant path the water would divide around. If, say there were a stairwell jutting out into the room, with a wall on each side of the base of the stairs for a good distance, then like pressing your thumb upon a garden hose, more force would be expressed through more water travelling faster through the narrowed conduit.
So conceivably there could be water frothing up the stairwell until the lake manages to get through any restrictive barriers in the basement of the house. Say there were a door at the top of the stairs. This door would again act as a barrier and the water would build up behind it until the door was opened.

 

[Vertigo]

The water would not rise above the level of the lake except, as @Brian G Turner and @HareBrain say, there might be a brief surge. This of course assumes that the ground floor (first floor for Americans) of the house is at or above the water level of the lake. For plausibility you need to think carefully about that one. If you want the water to completely fill the basement then the house needs to literally be built at the same level as the lake; a probably very unwise way to build a house close to a lake (unless magic is involved here as well).