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Zone AO

The purpose of this page is to define Zone AO, a commonly used term in floodplain management.


Areas subject to inundation by 1-percent-annual-chance shallow flooding (usually sheet flow on sloping terrain) where average depths are between one and three feet. Average flood depths derived from detailed hydraulic analyses are shown in this zone. Mandatory flood insurance purchase requirements and floodplain management standards apply.

Some Zone AO have been designated in areas with high flood velocities such as alluvial fans and washes. Communities are encouraged to adopt more restrictive rquirements for these areas.

NFIP Requirement


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Last Updated: 
05/23/2019 - 08:47