Video: Colorado's St. Vrain River roars over banks

© 2013 Keith A. Alderman

DENVER — In this video, Frederick, Colo., resident Keith Alderman captured the surge of the St. Vrain River in northern Colorado on Friday, as the usually placid creek rose significantly from its normal levels after heavy and lingering rain.

“The St. Vrain River is typically only a foot or two deep,” said Alderman, who shot the footage from I-25 and Colorado Highway 119. “After the record rainfall over the last three days along the Front Range, the St. Vrain is way out of its banks and up to the bottom of the Interstate 25 bridges — which are probably 15 feet above the water normally.”

The area is under a flood advisory. The town of Firestone, where Alderman shot the video, sits on the state’s plains, about 20 miles from the start of the Rocky Mountains.

“I've lived in Colorado for 27 years and have never seen anything like it,” Alderman told Yahoo News.

As bad as the river is there, it’s worse farther west. The St. Vrain flows through Lyons, a 1,500-person mountain hamlet about an hour northwest of Denver and 30 minutes north of Boulder. Floodwaters at times have impeded search and rescue teams' efforts to reach the town.

Emergency flood sirens blared in Lyons overnight, according to the Denver Post, and some residents have been stranded on higher ground. The National Weather Service says it’s unable to measure the height of the area’s waters, noting starkly on its website: Gauge readings "unreliable due to flood.”

Up to 15 inches of rain, according to the National Weather Service, has fallen this week in areas along Colorado’s Front Range, which is the eastern edge of the Rocky Mountains.

Four people have died. At least 20 more are missing in Boulder County.