City and other crews on Wednesday are filling in a sinkhole that opened Tuesday on the northbound lane of Poplar Street just north of 13th Street.

"We had a crack or a hole in one of the storm water lines that runs down Poplar Street," said Peter Meyers, the city's assistant public works director.

"It washed out a void, or basically an open space beside the line, and apparently last night it gave way," Meyers said.

The cause of the pipe's failure isn't known, he said.

Nor is it known when it started, Meyers said. "But certainly it must have been growing for some time, and of course with the dirt missing that eventually caused the street to collapse."

It started as a hole about two yards in diameter, with dirt washed away from under the pavement that remained.

But the entire section of road had to be excavated to access the damaged pipe, which was mostly concrete with some corrugated steel pipe, Meyers said.

The project eventually was about 35 feet long, 10 feet wide and about eight feet deep, he said. "They already have a new pipe inserted into that location. It's a 27-inch PVC pipe."

For the rest of Wednesday, crews were filling in the hole with sand and eventually will pave it, Meyers said.

"If it all goes well, we should have it all done today, though perhaps not by five p.m.," he said.

See the sinkhole when first discovered on Tuesday: