Flooding can happen anywhere. My previous house backed up to a canal and a summer of 2016 a monsoon rain event dropped 2" of water in 30 minutes in a two square mile radius around my neighborhood. The house was in a flood plain, I had flood insurance, and I knew the risks. However, until it happens to you, do you really ever know the risk?
Due to the soil conditions, we typically don't have basements here in Arizona. However, the residence portion of my property had 8" of water around it only because I had wall around the property. The garage had as much as 18" of water against it, but luckily the door metered the water and it kept the flooding inside the house to an inch or less. My train building in the back yard had 4-6 inches of water in it due to the finish floor being lower. A previous flood event that only affected the train room 6 years prior with about 1/2 of water put me in the habit of placing everything at grade level in plastic crates. Not thinking I got lazy over time and some items ended up on the floor again.
When it was all said and done, the damage to my trains was minimal. Mainly damaged boxes that I had to dispose of while the cars dried out. The tool box that had all the collets for my Uni-mat lathe was not so lucky. I didn't get to it right away and within 24 hours they completely rusted and I had to throw all of them away. Most of the crates had train magazines in them and a few were cracked on the bottom. They filled to the flood line with water and as luck would have it, they were all my 1940's Model Railroader magazines. I have a digital subscription now, so no big loss in the end.
When I moved out of that house, most of my trains went into storage. The most valuable stayed in my new house. When I cleaned out the storage unit last month to downsize my collection, I discovered wind driven rain came through the rear doors and damaged some boxes for trains I had in crates and some shipping boxes I was saving. Again no major loss.
Moral of my tale? Don't think it can't happen to you. While some of my trains will be going into a new shed on my property, every precaution will be taken to preserve the items I put in that shed. If an item is special in any way, it stays in the house. I also will think twice before purchasing property in a flood plain, or if I do verify that the finish floor of any space is well above the 100 year flood plain elevation.