King tides in Charleston: why the street floods on a sunny day

Spring tides: the moon's twice-a-month push

Tides are the ocean responding to the pull of the moon and sun. Twice a month, at new moon and full moon, the two line up and pull together, and the tidal range gets noticeably bigger — higher highs, lower lows. Those are spring tides. The name has nothing to do with the season; it's the old sense of water "springing forth." A few times a year, a spring tide lands while the moon is also at its closest point to Earth, and the high tides get bigger still — those outsized spring tides are what coastal communities call king tides. None of this needs a storm. It's gravity, on a calendar.

Why Charleston feels it more every year

A king tide only floods what sits low enough to reach — and Charleston keeps getting easier to reach. The NOAA tide gauge in Charleston Harbor has been recording for over a century, and the water now runs roughly a foot higher than it did a hundred years ago. That foot is the difference between a high tide that stops at the seawall and one that keeps going. The National Weather Service counted 89 coastal flood events at Charleston in 2019 — a record at the time, and a number that would have been unthinkable a generation earlier. Flooding that used to be a hurricane story is now a calendar story.

• NOAA's minor-flooding threshold at the Charleston Harbor gauge is 7.6 feet above the tidal datum; big king tides can clear it with clear skies.
• The highest tide crests on record at the gauge run above 8.5 feet — one recent king tide tied for the fourth-highest crest ever measured there, matching the storm surge of Hurricane David in 1979.
• Add an onshore breeze or a heavy rain landing at high tide, and low-lying streets flood well below those record numbers.

What tide flooding does to a house

Tide water is not rainwater. It's salt water that's crossed roads, yards, and storm drains on the way in — corrosive to fasteners, wiring, and appliances, and contaminated enough that soaked porous materials usually need removal rather than drying. The most common damage pattern we see isn't dramatic: a few inches in a garage, a flooded crawlspace nobody notices for a week, water wicking up through a ground-floor slab. The crawlspace version is the quiet one — salt water sits under the house, evaporates slowly into the framing, and shows up months later as musty rooms and mold.

If tide water gets in

• Don't wade through it barefoot — it's been through the storm-drain system and carries whatever the street carried.
• Photograph everything before cleanup, including the waterline outside and in.
• Know your policies: rising tide water is flood damage, which is excluded from standard homeowners policies and covered only by separate flood insurance (NFIP or private).
• Get salt-flooded spaces professionally extracted, rinsed, and dried — salt residue keeps pulling moisture from the air long after the water's gone.
• Check the crawlspace after any king tide that ponded near the house, even if the living space stayed dry.

You can see these coming

King tides are predictable months out — NOAA publishes the tide calendar for the Charleston Harbor gauge, and the City of Charleston maintains a king-tide page and flood-map tools that show which streets go under at which gauge heights. If your block or your crawlspace has flooded on a past king tide, the calendar tells you when to move vehicles, roll up garage contents, and check vents and seals — before the water arrives, not after.

Why we're named after this

Spring tides are the Lowcountry's oldest rhythm — the twice-monthly surge that shaped the marsh, and lately the reason your street floods on a sunny day. We took the name because that's the water problem this company is built around: local, predictable, and worth taking seriously before it's inside your walls.