* Emergency messages being sent to residents in harm's way
* Potential flood zone encompasses some 3,500 homes
* 46 people killed by storm (Adds details on river threatening coal ash pond, quotes)
By Harriet McLeod and Gene Cherry
CHARLESTON, S.C./RALEIGH, N.C., Sept 25 (Reuters) - A uthorities urged thousands of people to leave their homes in the Georgetown, South Carolina, area as water dumped by Hurricane Florence surged down rivers, threatening to bring devastating floods and disrupt a toxic coal ash pond.
Water levels were still rising on Tuesday, emergency officials said, long after the hurricane made landfall on the U.S. Atlantic coast on Sept. 14 and killed 46 people in three states. The National Weather Service said flooding from Florence likely would persist in coastal parts of the Carolinas for days.
"If the flood map ... shows you are in an affected area, you need to leave," Georgetown County Sheriff Lane Cribb said on Monday. "Your property can be replaced, but your life can't."
Parts of Georgetown could be submerged in up to 10 feet (3 meters) of floodwaters in the next few days as the Pee Dee and Waccamaw rivers overrun their banks, the National Weather Service said, adding that the deluge threatened to cut off highways and isolate communities.
By Tuesday afternoon, the Waccamaw River, which already was well above flood stage, is expected to inundate a coal ash pond in Conway, South Carolina, that holds more than 200,000 tons of toxic ash, according to Santee Cooper, South Carolina's state-owned electric and water utility.
The Waccamaw is forecasted to crest at 22 feet on Thursday in Conway and at 21.2 feet in Georgetown on Thursday, a representative with the South Carolina Emergency Management Division said on Tuesday.
The Santee Cooper utility removed more than 1 million tons of ash from its two ash ponds at the site in the past few years, the utility said.
The potential flood zone encompasses some 3,500 homes in Georgetown, 37 miles (60 km) south of Myrtle Beach, and the coastal resort community of Pawleys Island where as many as 8,000 people live, Georgetown County spokeswoman Jackie Broach-Akers said.
FLORENCE IMPACT "STILL WITH US"
Authorities were sending warnings to residents in harm's way with recorded telephone messages and home visits. The county opened two emergency shelters on Monday, and hotels outside the flood zone in nearby Myrtle Beach were offering discounts to evacuees. Public schools will be closed until further notice, Broach-Akers said.
State transportation crews were working to erect temporary dams on either side of U.S. Highway 17, the main coastal route through the area, and National Guard engineers were installing a floating bridge at Georgetown in case the highway is washed out at the river.
In North Carolina, Governor Roy Cooper said on Monday that seven rivers in the southeast part of the state were at major flood stages and three others at moderate flood stages.
The storm dumped 30 to 40 inches (75 to 100 cm) of rain on Wilmington, North Carolina, alone after making landfall nearby on Sept. 14. The storm moved northwest before turning back east and becoming a post-tropical cyclone over West Virginia three days later.
Insured losses from Hurricane Florence will range from $2.8 billion to $5 billion, RMS, a risk modeling and analytics firm, said on Monday.
(Reporting by Brendan O'Brien in Milwaukee Editing by Andrew Heavens and Bill Trott)
Our Standards: The Thomson Reuters Trust Principles.