DNR biologist Jim Thompson said Dead Run, a normally tranquil stream near Security Boulevard, went from a foot deep to nearly 10 feet deep in a matter of two hours.
Elsewhere, transportation officials reported road closures on both sides of the city, including Hilton Parkway and Franklintown Road, as well as Erdman Avenue at Pulaski Highway and Harford Road between Gorsuch and Homestead avenues.
MTA spokesman Terry Owens said five bus routes had to be diverted at the peak of the flooding around 2 p.m., but light rail and the Metro subway kept operating.
The potential threat to Port Deposit continued, even as the rain let up.
Exelon officials said Thursday morning they have opened 25 floodgates as runoff surges down the Susquehanna. That could increase to as many as 30 gates by Friday as the river continues to rise, according to company spokesman Bob George. Evacuations would begin at 31 gates.
Exelon said the company could not yet project how many of the dam's 53 gates might have to be opened.
But the water was rising quickly. Between 3:15 and 3:30 p.m. Wednesday, the river rose nearly a foot, according to the U.S. Geological Survey.
"Exelon is keeping us up to date," said Kathy Gray, Port Deposit's town administrator. "We are still not overly concerned. … We have been through this a number of times, and we know when we have to move to the upper floors."
In Ellicott City, Padgett also took the mess in stride.
He was helping to mop out the company's first floor office, where all but about two square feet remained covered with brown sludge. In the basement, the entire floor was covered in several inches of muddy water.
"We have had an earthquake, a hurricane, and now a flood. I'm just glad it's not a cicada year. Then, we would have the end of the world," he joked.
Despite all the muck, he said he wouldn't want to change locations. "Not at all. We're right next to the brewery," he said, referring to Ellicott Mills Brewing Company.
Sun reporters Mary Gail Hare, Timothy B. Wheeler, Steve Kilar and Candus Thomson, and Patuxent Publishing reporters Phil Grout and Kayla Bawroski contributed to this article.
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