Even if you backup your seed phrase offline in many locations, it is possible that kind of flood can lead to permanent loss of your offline seed phrase.
By definition, different back-ups should not be affected by the same issue that endangers one of them, so if you think of making two back-ups you don't bury both of them 1 meter away in your garden or you don't put it in the same safe in a bank! If you know you can get flooded then no way your basement or your garden is a safe place, if you live in an area threatened by wildfires the whole thing changes and you go with fire-resistant materials and bury the thing deep enough that only another MtHelen eruption would be able to affect it.
Simply, don't put all your eggs in one basket!
Also, if you're that concerned and you live in an area that can be flooded, has earthquakes, wildfires, a few tornados, and a tsunami now and then, there is always another choice: You move the hell out of that area since you might lose your life not just your coins!
Titanium or stainless steel or steel or any good metallic storage is also not 100% safe because flood can move the storage from your location you store the backup to a very far place like a place that another person will be the one to see it on maybe the flood can move it to a river a place that people can not get to it.
And if you pack it in a case with all the flooding if anyone really finds it for sure it will check it out before "thinking" of returning it.
Unless you live in Japan.