Flood zone letters as Charleston County publishes them

Charleston County Building Inspection Services publishes these definitions verbatim (checked 2026-09-04): Zone A — 'No base flood elevations determined.' Zone AE — 'Base flood elevations determined.' Zone AH — 'Flood depths of 1 to 3 feet (usually areas of ponding); base flood elevations determined.' Zone AO — 'Flood depths of 1 to 3 feet (usually sheet flow on sloping terrain); average depths determined.' Zone A99 — 'To be protected from 100-year flood by Federal flood protection system under construction; no base flood elevations determined.' Zone V — 'Coastal flood with velocity hazard (wave action); no base flood elevations determined.' Zone VE — 'Coastal flood with velocity hazard (wave action); base flood elevations determined.' Shaded Zone X — 'Areas of 500-year flood; areas of 100-year flood with average depths of less than 1 foot or with drainage areas less than 1 square mile; and areas protected by levees from 100-year flood.' Zone X — 'Areas determined to be outside 500-year flood plain.' Zone D — 'Areas in which flood hazards are undetermined, but possible.' Coastal A Zone is NOT a separate FIRM zone letter: it is the portion of an AE zone between the VE line and the LiMWA, where the Town of Mount Pleasant defines it (Town Code s.152.04) as 'an area subject to inundation by at least the 1-percent-annual-chance flood event as determined by detailed methods, and where wave action is expected with wave heights between 1.5 and 3.0 feet.'