The NWS issued a flash flood watch for the area that lasts until 11 a.m. Friday.
County officials reported the dam's "imminent failure" at around 9:30 p.m.
EMERGENCY evacuations have been ordered in a city of 80,000 people over fears a dam is about to burst.
The National Weather Service said up to six inches (15 centimeters) of rain fell within hours, filling College Lake near Lynchburg beyond capacity. City officials posted pictures Thursday of rescuers using a raft to take families from a flood-threatened apartment complex as well as the partial collapse of one road into an adjacent creek. The city said it would open a gate in the spillway on Saturday to drain some of the water from the reservoir before fix work could begin on the dam and roadway.
Authorities near Lynchburg in the usa state of Virginia sought to evacuate more than 100 people after weather forecasters warned that heavy rainfall could cause a dam to fail and flood the city.More news: Man taunts bison, narrowly misses charge in Yellowstone National Park
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However, even if it's deemed okay for residents to return to their homes, it was expected that certain roads would continue to be closed, due to flooding damage.
Firemen waded through flood waters on Thursday in Lynchburg.
Parts of that area saw three to five inches of rain in a three hour span.
Given the condition of the dam and the state of the lake, Perrow says, the most likely "fix" isn't actually a repair - he says the city is likely to tear the dam down completely and replace it with a bridge.
The City of Lynchburg has created an interactive map to see if you're in a potential flooding area should the College Lake Dam fail.
The lake is the largest urban lake in Lynchburg.