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Business prepare for flooding along Front Street in Georgetown Wednesday, Sept. 26, 2018. Grace Beahm Alford/Staff

As Georgetown faced another day of anticipating a flood, a state agency again lowered the amount of water the city might see. 

Floodwaters traveling slowly down the Waccamaw and Pee Dee rivers finally crested in Conway on Thursday, and residents even further up the Waccamaw began to return home, facing a new set of dangers as the water receded.

U.S. Highway 17 — a vital route connecting Georgetown and Myrtle Beach — was briefly reduced to one lane of traffic after flooding.

But water-filled barriers lining the road had more to do with the chokepoint than the swollen river below. The dams actually trapped water on the road after a rain, which workers then pumped out, said Georgetown County spokeswoman Jackie Broach-Akers. 

Elsewhere, flooding had just begun to affect the Waccamaw Neck area, between Georgetown and Myrtle Beach, with water on Kings River Road in Pawleys Island.

"This has been a slow, frustrating process for everybody, including us," Broach-Akers said. "People are antsy and anxious, and they want to go back home."

The S.C. Department of Natural Resources originally expected 5 to 10 feet of flooding in some areas of Georgetown, but by Thursday afternoon that prediction already had been reduced twice. The most recent projection indicates flooding will not reach past the most vulnerable, lowest-lying areas of the city. 

Forecasting river flooding is a challenging science, and the 11 trillion gallons of water that Hurricane Florence dumped on the Carolinas stumped the existing models and methods of of many scientists, said Rick Neuherz, a hydrologist for the National Weather Service in Wilmington. 

Many models only predict the flow of a flooding river, then that information has to be coupled with knowledge of topography to project how high the water might rise. But because the river system had never seen this much flow before, Neuherz said, there was no existing basis off which to pinpoint the rise.

"A lot of people wish we could say, 'You're going to have 3.2 feet of water in your yard a week from now,' and we just can't do that," Neuherz said. 

Neuherz said the crest wave of a river flood flattens as it moves downstream, so that may have affected the forecast's accuracy, too.

As the wave moves, its water spills into surrounding creeks, known as "local storage." That lowers the height of the crest as water has more room to spread out. It also creates a kind of plateau, with the crest staying around longer as those creeks and streams empty back out into the river.

Water is always looking for a place to spread, Neuherz said, and vast expanses of marsh to the north likely will insulate downtown Georgetown from serious inundation. The Winyah Bay, one of the biggest watersheds on the East Coast, will also help move the floodwaters out to sea quickly. 

"There's a lot of capacity for water down there," Neuherz said.

Georgetown Mayor Brendon Barber said the city was relatively calm Thursday. Around high tide, some water flowed onto Front Street, the city's historic strip.

The low-lying road can easily be covered by water when a hard rain falls during a high enough tide, so many businesses there had already moved merchandise or sandbagged their entrances. 

"People are feeling pretty peaceful right now because things have slowed down," he said. "We haven't gotten any impact yet from (the rivers), so we're still waiting."

Reach Chloe Johnson at 843-735-9985. Follow her on Twitter @_ChloeAJ.