At least 11 people are dead after flooding in South Carolina, and tens of thousands of people are without power. Officials warn that the devastation is not over. (Brett Flashnick)

The death toll rose to 11 on Monday after historic floods ravaged South Carolina, closing a 74-mile stretch of Interstate 95 and leaving tens of thousands of people without power or running water.

Although floodwaters receded Monday across the hard-hit central part of the state, officials cautioned that the danger had not passed. Gov. Nikki Haley (R) warned that the flooding could worsen along the coast as swollen rivers make their way to the sea. The Congaree River, which flows past Columbia, the capital, for example, has been at its highest point in nearly 80 years.

“This is not over,” Haley said at a news conference. “South Carolina has gone through a storm of historic proportion.”

A light rain continued to fall Monday, adding to totals that have broken records across the region since the storm began this weekend. On Saturday alone, 11.5 inches of rain fell in Charleston, and an astonishing 24.23 inches fell near Mount Pleasant. Rainfall totals over 16 inches were widespread across 10 counties from Columbia to Charleston.

According to statistics compiled by the National Oceanic and Atmospheric Administration, the torrential weekend downpour has well surpassed a 1,000-year rainfall, making it a once-in-a-millennium storm.

President Obama has declared a major disaster in the state, freeing up resources as officials begin to deal with the aftermath. The damage was poised to worsen here Monday afternoon as a dam broke in Forest Acres, a suburb of Columbia, where officials ordered a mandatory evacuation.

Downstream, police officers ordered people away from a normally bustling shopping center, and the National Guard helped residents evacuate. As he surveyed the downed trees and broken docks nearby, Mark Moore said he couldn’t remember the water flowing so fast. Growing up a few blocks away, he said he used to go biking on the normally dry spillway that had crumbled into a sinkhole and now roared with floodwaters.

“Nothing like this has even come close,” Moore said.

Across the sinkhole, a white pickup truck had been tossed by the floodwaters against a pair of pine trees, where search crews had found it and marked it with several large orange X’s. The truck belonged to Ty Neil, a shaken 45-year-old IT technician, who had taken a wrong turn on his way home from church Sunday morning.

Ty Neil, who declined to give his last name for fear of attracting the attention of TV reporters, said the water washed his truck downstream and trapped him for four hours. As the water rose around him, he said he called his wife and his parents. He apologized for past transgressions, offered his final wishes and said goodbye for what he thought would be the last time. At one point, he said, the water reached as high as his chin.

But then a man in a red kayak spotted the truck and alerted rescuers, who pulled Ty Neil to safety, even as 911 operators worked to clear a backlog of calls.

“There were so many times I thought, ‘This is it,’ ” said his wife, Kerry, whose frantic tweets about her husband’s plight also helped raise the alarm.

Emergency crews reported making at least 175 such rescues by midday Monday. Of the 11 people killed in ­weather-related incidents, seven drowned after trying to drive through floodwaters and four others died in traffic accidents, officials said.

The flooding paralyzed much of Columbia, as schools canceled classes, traffic was snarled by the closure of major arteries and officials enforced overnight curfews.

Across the state, about 40,000 people were left without access to clean water, most of them in Columbia and its suburbs, where pipes have broken, Haley said. About 26,000 people were without electricity.

Residents whose taps still ran were told to boil their water, and officials handed out bottles of water for those whose water was cut off. In downtown Columbia, sirens whirred steadily as fire trucks ferried water to hospitals to keep them open.

Still to be determined is the toll the floods have taken on the state’s roads and bridges, many of which were closed as a precaution or washed out over the weekend. They will be inspected in the coming months, as engineers look for damage and internal weakening, said Christy Hall, the state’s acting transportation secretary.

The cost of the days of flooding is another looming question. County officials have begun assessing the damage, and the state Department of Insurance expects to have an estimate of the damage to cars and homes later this week, said spokeswoman Ann Roberson.

“This is going to be a long process,” Haley said.

Moore is a freelance writer. Jeff Halverson in Washington contributed to this report.