COLUMBIA — The northbound lanes of Interstate 95 remained closed Monday near the North Carolina border due to widespread flooding that continues to shut down roads across northeastern South Carolina.

Flooding and fallen trees caused hundreds of closures across the Pee Dee, with the majority in Chesterfield, Dillon, Horry, and Marlboro counties.

Roads with all lanes blocked included U.S. 501 north of Conway, which closed Sunday due to flooding. Traffic headed to Myrtle Beach along that major artery was diverted to S.C 22, known as the Conway Bypass.     

Other roads were partially blocked.

In downtown Georgetown, one lane of U.S. 17 was closed for a quarter-mile. In another small section, only the center lane was open. 

The northbound lanes of U.S. 501 in Conway by Lake Busbee closed while the Department of Transportation builds a 1.5-mile temporary barrier intended to keep floodwaters off the highway.

That work should be finished Wednesday, said DOT spokesman Pete Poore.  

The Waccamaw River, which flows under the highway there, could reach historic levels as the up to 2 feet of rain that Hurricane Florence dumped across the border in North Carolina continues to move south, combining with the 1 to 2 feet of rain that fell in the Pee Dee region, said Leonard Vaughan, a hydrologist with the National Weather Service.

By 4 p.m. Monday, the water was already at 15 feet — 4 feet above the riverbank, or flood stage, at that crossing. It could surpass the previous record of 17.9 feet, set after Hurricane Matthew in 2016, by at least an additional foot of water when the river crests sometime next week, Vaughan said. 

"It's going to take well into October" for water levels along the watershed to return to normal as the rainfall slowly makes its way to Winyah Bay near Georgetown, he said.   

The DOT designated U.S. 378 to U.S. 501 as the main artery to the Grand Strand once other major routes wash out. But that requires also building a one-mile barrier along U.S. 378 where Lynches River flows under it in Florence County. Work there should be completed by Monday night, according to the DOT. 

"We've got to keep that open," Gov. Henry McMaster said Monday while watching DOT traffic cameras from the State Emergency Operations Center outside Columbia. "People need to get in and get out." 

Flash flooding from the heavy rainfall inundated towns such as Cheraw, in Chesterfield County, beginning Sunday. Flooding shut down dozens of roads in that county alone.

McMaster surveyed the damage by helicopter Monday afternoon, stopping in Chesterfield to pick up state Rep. Richie Yow, R-Chesterfield, to assess the flooding in Cheraw. McMaster will also assess the work at U.S. 501 by air, as well as efforts nearby to prevent toxic coal ash from Santee Cooper's closed utility plant from flowing into the flooded Waccamaw, said the governor's spokesman, Brian Symmes. 

The 233 road closures as of 4 p.m. Monday included 37 bridges, according to the DOT.   

Floodwaters blocked some highways in multiple locations, including along S.C. 9, a main route from Chesterfield to North Myrtle Beach.

U.S. 52 is blocked in both Chesterfield and Darlington counties, near Society Hill. The Great Pee Dee River flows south from North Carolina through Cheraw and Society Hill.  

The Great Pee Dee is expected to rise another foot in Cheraw before cresting Tuesday afternoon at nearly 50 feet, which would be 20 feet above the flood stage, according to the National Weather Service. 

In Horry County, flooding closed U.S. 701 in two spots, including a 1.5-mile section between Loris and Conway and a tenth of a mile by Brown Swamp closer to Conway. Carolina Bays Parkway, or S.C. 31, is closed for 1.5 miles due to a washout of two bridges. Flooding has closed a nearly 4-mile section of the highway elsewhere.

Large swaths of Dillon County are also under water.  

Flooding closed two sections of U.S. 301, both over a mile, in Dillon County.  

I-95 is closed from exit 181 to exit 190 in Dillon County near the border. Large segments of the interstate are also closed in North Carolina. 

The DOT is advising traffic from Georgia to either use Interstate 85 northbound through South Carolina, or take I-95 to Interstate 26 to Interstate 77 into North Carolina. From the city of Florence, traffic can take Interstate 20 to I-77.

As of noon Monday, there were still 13,800 power outages in South Carolina, about a quarter of those in Dillon. That's down from a peak of about 180,000 outages, said Derrec Becker, spokesman for the state's Emergency Management Division. 

Follow Seanna Adcox on Twitter at @seannaadcox_pc.

Assistant Columbia bureau chief

Adcox returned to The Post and Courier in October 2017 after 12 years covering the Statehouse for The Associated Press. She previously covered education for The P&C. She has also worked for The AP in Albany, N.Y., and for The Herald in Rock Hill.