Wet soil, holes may cause Columbia storm pipe collapse

When it’s not falling from the sky, it keeps moving on the ground. Rain water in downtown Columbia moves from drains and inlets on the street, through underground pipes and into the Flat Branch Creek.

It’s that middle step that Columbia city leaders have been worried about. City Manager Mike Matthes said some pipes in Columbia are close to a century old.

Storm water engineer Steve Hunt said downtown Columbia has a combination of stone and corrugated metal pipes leading to the Flat Branch Creek. The metal ones have a structural life of 40 years, and many metal pipes in town have reached or passed that age.

“As water continues to flow through that, it will erode the bottom, like a ditch, under the pipe and eventually, the pipe will collapse,” Hunt said. “It’ll either cause a sinkhole or cause a road to cave in.”

For something that drastic to happen, he said weight on the aging pipe and water running through it cause the most damage. Wet soil resting on top of the pipes could cause a collapse, but only if the soil was thoroughly saturated. Hunt said if a smaller metal pipe that led into a larger one collapsed, the spilled water could cause weigh the soil down enough to collapse the larger pipe. Hunt added the metal pipoes are designed to bear large weight.

“They’re designed to be buried very deep,” hunt said. “They’re designed when they’re put in to have a lot of weight on them, there’s no real limit on how deep you can bury them.”

The city has 45 projects related to storm water improvements identified for the next 10 years. Nearly $7 million of those projects will go towards downtown improvements.