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, area with a 0.2% (or 1 in 500 chance) annual chance of flooding. This zone is also used to designate base floodplains of lesser hazards, such as areas protected by levees from 100-year flood, or shallow flooding areas with average depths of less than one foot or drainage areas less than 1 square mile.


A 500-year flood is based on the same principle: Experts estimate that in any given year, there’s a 1-in-500 (0.2 percent) chance a flood this bad will strike a particular area.


The 50-year flood zone gives you a 45% chance of being flooded; The 100-year flood zone gives you a 26% chance of being flooded; The 500-year flood zone gives you a 6% chance of being flooded When you look at the 100-year flood zone that way, you have a 1 in 4 chance of experiencing flood damage during your 30-year mortgage.


A one-hundred-year flood is a flood event that has a 1 in 100 chance (1% probability) of being equaled or exceeded in any given year.. The 100-year flood is also referred to as the 1% flood, since its annual exceedance probability is 1%. For coastal or lake flooding, the 100-year flood is generally expressed as a flood elevation or depth, and may include wave effects.


More recently, people talk about larger floods, such as the "500-year flood," as tolerance for risk is reduced and increased protection from flooding is desired. The "500-year flood" corresponds to an AEP of 0.2-percent, which means a flood of that size or greater has a 0.2-percent chance (or 1 in 500 chance) of occurring in a given year.


A 20-year flood would have a one in twenty (or 5%) chance of occurring in a particular year. A 500-year flood has a one in 500 (0.2%) chance of occcurring. Likely the 500 year flood would be more catastrophic than the 100 year flood, which would be more catastrophic than the 20 year flood, etc.


A 500-year flood isn't necessarily something that happens once every five hundred years. Rather, a 500-year flood is an event that has a 1 in 500 chance of occurring in any given year .


ZONE CLASSIFICATIONS PLEASE PRINT A COPY FOR FUTURE REFERENCE. Zone C, Zone X- Areas determined to be outside 500-year floodplain determined to be outside the 1% and 0.2% annual chance floodplains. Zone B, Zone X500 - Areas of 500-year flood; areas of 100-year flood with average depths of less than 1


Moderate flood hazard areas, labeled Zone B or Zone X (shaded) are also shown on the FIRM, and are the areas between the limits of the base flood and the 0.2-percent-annual-chance (or 500-year) flood.


The 500 year flood would likely be more catastrophic than the 100 year flood which would be more catastrophic than a 20 year flood, etc. Underestimating true risk – When your structure is within the 500-year flood zone, there is a 6% chance of being flooded over the life of a 30 year mortgage.