MEAN HIGH WATERFlooding in Charleston

Mean High Water (MHW) is a project documenting the impacts of sea level rise & flooding in and beyond the South Carolina Lowcountry. The title is in reference to the MHW tidal datum defined and maintained by the NOAA Center for Operational Oceanographic Products and Service.
The tides of Charleston Harbor and the Atlantic Ocean are increasingly encroaching into the natural and built environment of Charleston and the Lowcountry. The rate of increase in the number of coastal flood events is alarming. Approximately 53.3% of all coastal floods observed in Charleston Harbor from 1921 through 2022 have occurred since 2010. An average of 18.8 coastal floods occurred per year in the 1990s. In the 2010s, the annual average was 42.4 coastal floods2, an increase of over 200%.

MHW was started in 2020 by photographer and engineer Jared Bramblett. This is intended to be an evolving and collaborative documentation of the impacts of flooding. If you are interested in participating, please reach out.
Jared Bramblett

All thoughts and opinions presented on this site are solely those of the author and are not necessarily those of any other organization.

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© 2024 Jared Bramblett
Tidal Flood Records & Statistics
Charleston Harbor, Cooper River Entrance1

Coastal Floods (>7-ft MLLW)2
  1. 89 (2019)
  2. 75 (2023)
  3. 70 (2022)
  4. 68 (2020)
  5. 58 (2015)

Major Coastal Floods (>8-ft MLLW)2
  1. 7 (2020)
  2. 6 (2023, 2015)
  3. 4 (2021, 2019)
  4. 3 (2022, 2018)
  5. 2 (2009, 1947)

Peak Tide Crests (ft, MLLW)3
  1. 12.52-ft 09/22/1989 (Hugo)
  2. 10.23-ft 08/11/1940
  3. 09.92-ft 09/11/2017 (Irma)
  4. 09.86-ft 12/17/2023 (Nor’easter)
  5. 09.29-ft 10/08/2016 (Matthew)

Statistics current as of 08/31/2023

Sea Level Rise Trend (1901-2022)1

Sea level trend of 1.13-ft per 100 years (1901-2022)

1 Tidal Benchmark Station - Charleston, Cooper River Entrance, SC - Station ID: 8665530

2 NWS Coastal Flood Event Database

3 Advanced Hydrologic Predictions Service, Charleston, SC
Elevations on Mean Lower Low Water
There is a lot of confusion when it comes to land elevations, tide elevations, potential storm surge elevations, and potential storm tide elevations. I’ve been brainstorming the creation of this map through ongoing discussions with Dr. Merrie Koester, who is developing a curriculum to teach flood awareness as part of her effort with Kids Teaching Flood Resilience.

Most topographic maps and FEMA flood maps for the area reference the North American Vertical Datum of 1988 (NAVD88). NAVD88 references all elevations across Canada, Mexico, and the United States to mean sea level at Father Point/Rimouski, Quebec. Essentially, any elevation that reference NAVD88 is the same height about mean sea level at Father Point/Rimouski, Quebec, whether its located in Alaska, Texas, or South Carolina. This map, which is very much a work-in-progress, depicts the elevations of the Charleston Peninsula on the Mean Lower Low Water (MLLW) Datum for the Charleston, Cooper River Entrance Tidal Benchmark (Station 8665530) at the Customs House. MLLW datums vary along the coast due to variations in sea surface topology (e.g. the tides vary along the coast), so they are unique to their locations. Locally, we often refer to tides based on their height above the MLLW datum. The National Weather Service (NWS) defines tidal flooding for Charleston based on this datum, with flood stage beginning at 7.0-feet MLLW, moderate flood stage exceeding 7.50-feet MLLW, and major flood stage exceeding 8.0-feet MLLW.