Types of Flooding

Most of the flooding that occurs in the Charleston Region can be categorized as Coastal Flood, Flash Flood, and the general term Flood according to the National Oceanic and Atmospheric Administration (NOAA).

Coastal Flood: Flooding of coastal areas are due to the vertical rise above normal water level caused by strong, persistent onshore wind, high astronomical tide, and/or low atmospheric pressure, resulting in damage, erosion, flooding, fatalities, or injuries. Coastal areas are defined as those portions of coastal land zones (coastal county/parish) adjacent to the waters and bays of the oceans. Farther inland, the Storm Data preparer must determine when and where to encode a flood event as Flash Flood or Flood. 

Flash Flood: A rapid and extreme flow of high water into a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level, beginning within six hours of the causative event (e.g., intense rainfall, dam failure, ice jam-related), on a widespread or localized basis. Ongoing flooding can intensify to flash flooding in cases where intense rainfall results in a rapid surge of rising flood waters. Flash floods typically recede quickly and do not exist for two or three consecutive days.

FEMA Flood Insurance Rate Maps (FIRMs)

FEMA’s interactive Map Service Center can be used to view the currently effective Flood Insurance Rate Map (FIRM), Flood Insurance Study (FIS), and any Letters of Map Change (LOMC). Sources of flood hazards in Charleston include: the Stono, Ashley, Cooper, and Wando Rivers; Wappoo, Orangegrove, James Island, and Church Creek (riverine flooding); small (drainage of <100sq. acres) mapped and unmapped tidal creeks; and the Atlantic Ocean. Information on historic and past flooding events in the area is detailed in the Flood Insurance Study (FIS).

FIRM Changes

Use the SCDNR Flood Risk Map Progress Site to learn about the flood map updates in South Carolina. For additional information on map changes, see Map Changes and Flood Insurance: What Property Owners Need to Know

How to request a change to the Flood Insurance Rate Map (FIRM):

A property owner may request a change by submitting a Letter of Map Change (LOMC) documentation to FEMA. Note, an Elevation Certificate submitted to FEMA for a LOMC can also be flagged for floodplain management compliance violations (i.e. inadequate flood openings in a garage enclosure). A Community Acknowledgement Letter may be required for Letters of Map Revision.

Reasons to submit a LOMC request may include:

• The property is at a higher elevation than the Base Flood Elevation (BFE) on the FIRM.
• The property has been re-graded or elevated with fill.
• More accurate information than shown on the FIRM is available.

Other Flood Hazard Mapping Tools

City of Charleston GIS Flood Maps & Tools:

• Currently effective and preliminary Flood Insurance Rate Maps (FIRM)
• Closed roads due to flooding
• Tide trends and projected tides ("Tide Eye")

National Hurricane Center Storm Surge Risk Maps

• This national depiction of storm surge flooding vulnerability helps people living in hurricane-prone coastal areas. These maps make it clear that storm surge is not just a beachfront problem, with the risk of storm surge extending many miles inland from the immediate coastline in some areas. 

Flood Prone and Repetitive Loss Areas:

• Charleston Regional Hazard Mitigation Plan | Charleston County Building Inspection Services

City of Charleston Stormwater Management Special Protection Areas:

• Stormwater Design Standards Manual

Risk Factor:

• Flood Factor - First Street Foundation can be used to understand a property's risk and takes into account flood prone areas not mapped by FEMA.

Real-Time Harbor and Stream Gauge Data:

• The National Weather Service provides Weather Alerts, Current Tides, Tide Forecasts, Flood Categories and Historic Crests.
  • NWS Advanced Hydrologic Prediction - Charleston Harbor Tide Gauge
  • NWS Advanced Hydrologic Prediction - Church Creek Gauge 
• The National Oceanographic & Atmospheric Administration provides future Astronomical Tide Predictions. And the Coastal Inundation Dashboard provides real-time and historic coastal flooding information.
  • NOAA Tide Predictions - Charleston, SC Station
    • Datums for Charleston, SC
  • NOAA Tides & Currents - Coastal Inundation Dashboard
• The City of Charleston GIS Division summarizes tide projections, current conditions and king tides.
  • City of Charleston TIDEeye

Real-Time Storm Surge and Flood Inundation Maps:

• National Hurricane Center
• SCDNR Flood Impact
• NOAA National Water Prediction Service (NWPS) and Flood Inundation Mapping (FIM)

South Carolina Office of Resilience (SCOR) Resilience Atlas

• SCOR's Resilience Atlas combines many different GIS datasets into one website. Several of the hazard layers linked here are included.

Sea Level Rise (SLR) Projections:

• The City’s 2019 Flooding & Sea Level Rise Strategy makes a planning recommendation of 2.0-3.0 feet of SLR over the next 50 years.
• Projected SLR values can be determined locally using the US Army Corps of Engineers Calculator [TAKEN OFFLINE] or NOAA's Sea Level Calculator.
• Interactive map visualizations are available from the City of Charleston and the NOAA Office of Coastal Management.
• Climate Central has maps for the Land projected to be below annual flood level in 2050 and for Surging Seas: Risk Finder

Land Subsidence:

• SCOR Resilience Planning- Flood Risk and Vulnerability Assessment
• Virginia Tech: Critical observations of sinking coasts

Coastal Erosion and Shoreline Change Risk:

• SC DHEC Coastal Hazard Vulnerability Assessment
• SC DES Beachfront Jurisdictional Lines

Natural Floodplain Functions:

• Coastal Barrier Resources Act CBRS Mapper - FWS
• National Wetlands Inventory - FWS
• Critical Habitat - FWS

Dams:

• Dam Failure - South Carolina Emergency Management Division (SCEMD)
• USGS Latest Earthquakes