The June 4, 2013 crest is the fourth highest recorded level at St. Louis since the Corps of Engineer gage was installed in 1861. A 100-year flood is a flood event that has a 1 percent (1-in-100) chance of occurring in any given year. A 500-year flood has a .2 percent (1-in-500) chance of occurring in any given year. *2013 flood crests are preliminary pending official confirmation.