tidal flood

Tidal flooding in downtown Charleston closed streets and turned intersections into ponds on Friday, Nov. 23, 2018, such as this one at Wentworth and Barre streets. Tony Bartelme/Staff

Blame it on the wind.

Gusts out of the Northeast approached tropical storm strength by Friday morning before starting to wane.

Those winds, exacerbated by the full moon, pushed up the high tide that caused widespread flooding across the low-lying waterfronts and streets. On top of that came the rain on Friday — all of it spun down our way by one of the first real blasts of cold weather rolling across the Northeast states and out to sea.

The winds began to ease Friday, and it all goes away on Saturday, leaving South Carolina a few degrees warmer than the chilly Thanksgiving holiday. Less than an inch of rain is expected.

Tides peaked at higher than 8 feet Friday morning but were forecast to reach little more than 7 feet Friday night at about 8 p.m. The Saturday morning high tide is expected to peak at 7.6 feet just before 9 a.m., according to the National Weather Service, Charleston.

The tidal level called king tide, or astronomical high tide, is 6.6 feet or more, at least a foot above the usual tidal range. The higher the tide reaches, the more flooding and damage it does. Tides at 8 feet can undermine properties as well as exacerbate erosion.

At high tide Friday morning, the Ashley River breached Lockwood Boulevard and flowed into streets near the southwestern edge of Charleston’s peninsula. With floodwaters knee-deep in spots, barricades were stationed at Lockwood Boulevard and Wentworth Street, forcing a parade of cars to detour.

At Wentworth and Barre streets, saltwater stranded a police cruiser. Trash and recycling bins floated into intersections. Two of four lanes on Calhoun Street in front of Roper Hospital were covered.

The high tide also tested the city’s new check valves — valves hidden in the city’s stormwater tunnels that close at high tide and are supposed to prevent water from flowing into surrounding streets.

In some areas of downtown, the check valves did the job, especially at Ashley Avenue and Bennett Street, a low spot with a history of severe flooding. That stretch was dry. But in other areas where the Ashley River overtopped Lockwood, the check valves were rendered useless.

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Reach Bo Petersen Reporter at Facebook, @bopete on Twitter or 1-843-937-5744.

Science and environment reporter. Author of Washing Our Hands in the Clouds.

Tony Bartelme is senior projects reporter for The Post and Courier. He has earned national honors from the Nieman, Scripps, Loeb and National Press foundations and is a three-time finalist for the Pulitzer Prize. Reach him at 843-937-5554 and @tbartelme