MEAN HIGH WATER


A project documenting
Sea Level Rise & Flooding
in the South Carolina Lowcountry



01 OVERVIEW ︎︎︎
02 LATEST ︎︎︎   
03 ARCHIVE ︎︎︎
04 RESOURCES ︎︎︎

ABOUT
Mean High Water (MHW) is a project documenting the impacts of sea level rise 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 45% of all coastal floods observed in Charleston Harbor from 1953 through 2020 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%.

This project was started by photographer and engineer Jared Bramblett in 2020. It is intended to be an evolving and collaborative documentation of the impacts of rising seas and how communities are adapting to them. If you are interested in participating and submitting to the project, please reach out. All content on this site is copyrighted. If you are interested in using any content, please submit a request.


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CONTACT 
Jared Bramblett
jaredbramblett@gmail.com

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

RECORDS & STATISTICS
Charleston Harbor, Cooper River Entrance1

Coastal Floods (>7-ft MLLW)2
1.
2.
3.
4.
5.
89 (2019)
68 (2020)
58 (2015)
55 (2016)
46 (2017)

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

Peak Tide Crests (MLLW)3
1.
2.
3.
4.
5.
09/22/1989 - 12.52-ft (Hugo)
08/11/1940 - 10.23-ft (Unnamed)
09/11/2017 - 9.92-ft (Irma)
10/08/2016 - 9.29 (Matthew)
01/01/1987 - 8.81-ft 

22 of the 36 (61%) major flood tides on record have occurred since 2015.3

Statistics current as of 5/31/2021

REFERENCES

1Tidal Benchmark Station - Charleston, Cooper River Entrance, SC - Station ID: 8665530
This is the homepage for the Charleston Tidal Benchmark, which serves as the main tide gauge referenced for tide levels in the Charleston region. The tidal datums (e.g. MLLW, MHW, MHHW) for Charleston are presented here. Lunar tide levels predictions can be found here, and the database of historic tide levels can be accessed here.

2NWS Coastal Flood Event Database
This is a database maintained by the National Weather Service Charleston that tracks coastal flooding in Charleston and Savannah. It is referenced often throughout this site,  particularly when discussing the number of coastal floods that have occurred in Charleston Harbor.

3Advanced Hydrologic Prediction Service, Charleston, SC
Forecasts for water levels at the tidal bench mark based on meteorological predictions are presented here.

 Tidal Floods and Moon Wobbles

August 20, 2021 - Jared Bramblett


As of July 31st of this year, there have been 18 tidal floods (tide levels > 7-ft MLLW) in Charleston Harbor, with one reaching the moderate tidal flooding threshold (>7.5-ft MLLW). Over the same period last year, Charleston Harbor experienced 22 tidal floods and one moderate tidal flood. Analyzing the historic tidal flooding data cataloged in the NWS Coastal Flood Event Database, 2021 is tied with 2014 for the 5th most tidal floods observed from January to July. The table below on the left shows the top 10 years with the most tidal floods over January to July. Historically, September through November are the most active months for tidal floods, with approximately 48% of all tidal floods occuring during the three months. The below table on the right shows the percentage of tidal floods that have occured over each month. It will be interesting to see how the frequency of tidal flooding increases over the coming months.


In early July, a NASA report was released that predicted a dramatic increase in the number of tidal floods as we enter the 2030s. The is predicted because of a naturally occuring wobble in the moon’s orbit that occurs every 18 years paired with predicted sea level rise. I’ll post some additional thoughts on the future implications of this, but another interesting note in the article is that we are currently coming out of a phase of the wobble that increased the tides. Perhaps this helps explain the dramatic increase in tidal floods we’ve seen recently (particularly 2019 & 2020), and maybe we'll see the number of yearly tidal floods decrease over the next five to ten years.
© 2021