Did you do civil? I did mechanical and barely just heard of LRFD and probalistic design. Not very common in mechanical, maybe in aerospace.
These are all probabilistic in nature, you do not generally seek to build something to be flood proof. You instead design it to survive perhaps a 1 in 100 year flood, or perhaps 1 in 1000 if it's important.
There is a trade-off being constantly made, between the price of a project and the (estimated - of course) chance of it still being standing in a year.