Second - the physics involved. Golismorga lies 10000' below sea level ( 3 km, or roughly 2 miles), with the water kept back only by the cerulean curtain...... While I am not a physics guy, Finn, one of my players just looked at me and said "no way", because the water pressure at that depth is quite enough to crumble titanium-hulled russian submarines and anything human built besides a very few dedicated craft. If the Cerulean Curtain failed - there would be an instant massive increase in athmospheric pressure inside the chamber, followed by high speed (Finn calculated something around 80 + mph walls of onrushing water - basically solid walls at enormous speed - don't ask me for the math and formulas, I simply trust his engineering degrees ) jets of water ramming down the access tunnels. Crushing everything in their way, digging new tunnels and cracking open seams, gorges and ventilation shafts...... sheer and utter destruction.
Playing through Lightless Depths now and perusing the board for ideas when I came across this statement.
I realize few people are going to read this reply more than eight years later, but while I trust Finn's calculations he made some inherent assumptions about how the water was going to get in.
If the water entry points are two miles below sea level, then yes the water rushing through those tunnels would be very high speed and tremendous pressure. But most of the entry points shown on page 35 are considerably higher elevation than that, and thus those tunnels won't see as much water pressure and speed. Those which have the highest water pressure are below Golismorga and will be pushing against gravity and be flooding the city from below...they won't be obstructing the PCs who have to ascend the tunnels to get out.