A large concern in civil design loads is rain, wind and earthquakes.
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.
