Tidal change averages 5.2 feet in the Lowcountry, but can rise to more than 6 feet.
Tides are semi-diurnal: High and low tides tend to occur twice per day.
The change can vary widely in height and timing due to factors such as moon phases, winds, storms, water temperatures or sea level fluctuations. For example: Tides tend to be higher in September and October, when sea level rises. A passing tropical cyclone pushes tides up in front of it but can drop them in its wake.
Maximum tidal current, or a "run," is a surge in the stream speed as resistance to the tidal change is overcome. In the Lowcountry, that tends to occur mid-tide, or about 2 to 2Ĺ hours into an outgoing tide. But the strength and timing also can vary.
Upper river tide levels in an estuary depend greatly on rainfall and runoff.
Tides in the Lowcountry are tricky and deceptively strong. The inlets are treacherous. Just ask anybody who has tried to swim or work a boat through a strong tidal "run."
With thousands more beachgoers, anglers and boaters out on the waters in the summer - not all of them experienced - the chances increase that someone will misjudge or simply be ignorant of the dangers. This raises the possibility a person in jeopardy could drown or get stranded and need to be rescued.
Paddlers get stuck in the mud in the back creeks. Sailboaters and motor-boaters hit bottom where they hadn't the day before. Swimmers who loiter on sandbars find themselves trying to make it back to the beach against forceful currents.
Among recent incidents: In May, two kayakers were rescued after stranding in Compahee Sound near Awendaw. A few weeks ago, three swimmers had to be rescued from a sandbar in Breach Inlet between Isle of Palms and Sullivan's Island.
Swift-flowing inlets are chronic trouble spots, and Breach is notorious for drownings and other crises spurred by its powerful currents. In its most publicized incident, two North Charleston teens launched there in 2005 to fish from a small boat with only one paddle for propulsion. They were swept out to sea and lost for six days until a fishing boat happened across them in the ocean off Cape Fear more than 100 miles north.
Tidal runs, or "maximum tidal currents," are peak periods in the tide change when its stream surges. They are particularly dangerous on ebbing, or outgoing tides, when river flow works with them.
Tides themselves can vary widely and unpredictably for any number of reasons. And they affect water levels farther inland than a lot of people realize. In the drought years around 2000, when inland water levels dropped precipitously, National Audubon staff at the Beidler Forest sanctuary could watch the water in Four Holes Swamp rise and fall slightly to the tidal change at the coast - some 50 miles down the river.
Tideline Tours operator Anton Dumars once spent a New Year's Eve night fetching a friend's boat caught in ebbing tide in a creek behind Morris Island.
"Years back," he said. The friend, out with his family, was forced to leave the boat at anchor late in the afternoon in bitter cold. A passing boater took them to the east end of Folly Beach. They walked four miles back to their house and called Dumars.
"That evening, four of us left the boat landing around 10:30 p.m. in my old Simmons Sea Skiff on a rescue mission. We reached his boat, now floating, at high tide just at midnight," he said. "One of my favorite New Years parties."
Nature Adventure tour operator Kathie Livingston has seen the normally six-hours-at-a-time tide reverse in two hours on Wambaw Creek near McClellanville, because of dam releases upstream in the Santee River that Wambaw feeds.
She's heard the tales of kayakers and canoeists who find the shallow stream in upper Wadboo Creek abruptly rush out from underneath them - near Moncks Corner more than 20 miles inland. The paddlers had to drag boats or slog their way out of the bottoms.
"Everything is tidally influenced around here," she said. "Wadboo is beautiful, but it's an 'ephemeral' stream.' You don't run it in the summer unless you've had rain."
She remembers years ago getting caught in the powerful outgoing tide between Capers and Dewees Island, as a storm blew up from the mainland. The swells were so strong they kicked her out her kayak a few times as she fought them, she said. If she hadn't been a training instructor, she doubts she would have made it.
"It's coastal Carolina. We're a large flood plain here. The biggest thing you have to watch for is (how much) runoff we've had. Thank God for our swamps taking off some of that runoff," Livingston said.
Reach Bo Petersen at 937-5744, @bopete on twitter or Bo Petersen Reporting on Facebook.
People walk along a dangerous Breach Inlet sandbar last week during low tide at the Isle of Palms.×
Children fill up their buckets with sand on Sullivanís Island beach last week during low tide.×
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