[Lonesome in Massachussets]

The water will simply make the tunnels unusable.

A lot depends on percolation and soil mechanics. It could well cause buildings to collapse. The first result will probably be a failure of the electrical system, then the ventilation system. If the water penetrates the floors and saturates the soil under the tunnels, the tunnels may sag and collapse. Continued injection of water may cause the foundations of nearby buildings (built to the strictest Palestinian codes!) to fail and topple, like that apartment building Florida a few years ago. The possibilities are as delightful as they are numerous!

High Quality Chinese Construction

[bert]

The universally accepted term by the Chinese public for such is “Tofu Drang”

Buildings made from tofu fail

That has been extended to all Chinese manufactured goods that are virtually worthless

[caww]

True....Egypt flooded tunnels and buildings fell.....but perhaps it doesn’t matter if that happens in Gaza. It would not be my concern at all.

[oldvirginian]

“A lot depends on percolation and soil mechanics. It could well cause buildings to collapse.”

IDK but isn’t most of that area composed of sandstone, the softest of stone? I know from past reading that at some point water soaked sandstone just starts to crumble.
Flooding the tunnels could make Gaza uninhabitable.