Michael Stuhr, the Portland Water Bureau director, said Thursday his agency feels badly that a 30-inch water main burst and flooded Northeast Portland homes in March, but said the rupture was unforeseeable.

About a dozen homeowners whose homes suffered water damage from the catastrophic pipe failure on March 16 have since had damage payment claims denied by insurers and the city. They’ve been stuck with repair bills that, for some, have exceeded $50,000.

Dramatic pipe breaks like the one in question, which at its peak gushered 40,000 gallons a minute into neighborhoods around Northeast 23rd Avenue and Skidmore Street, are exceedingly rare, Stuhr said.

And this one, he said, was impossible to see coming: The circa-1915 cast iron pipe that failed had shown no signs of breakage and had not reached even half its 230-year lifespan, he said.

“Water is a powerful thing and it can be terribly destructive,” Stuhr said during an interview at his downtown office. “This was a big deal,” he added.

In his 15 years at the Water Bureau – as head of maintenance and construction, engineering and, today, its director – there has never been a worse water main failure, Stuhr said. He called it “a 25- or 30-year event.”

Such ruptures are unavoidable as Portland’s vast drinking water infrastructure ages, he said, but the Water Bureau assesses its pipes for likely failures and takes action accordingly.

To illustrate the difficulty monitoring the city’s more than 2,200 miles of water pipes, Stuhr approached his office window and pointed down. There, beneath the street, lie a crisscross of water mains, sewer pipes, gas lines and fiber optic cables, he said.

The obvious challenge, Stuhr said, is “you can't see it.”

Cameras snaked through Portland’s water pipes for inspections don’t help, he said, because the pipes are pressurized and a biofilm forms on pipe walls. “You can’t see squat” he said.

Still, Stuhr repeated a motto three times Thursday: “Portland is a good place to be a pipe.”

The soil is not especially corrosive. The ground does not freeze much in winter. And pipes are buried close to the surface to avoid undue stress from the weight of the soil above.

Portland’s rate of broken water mains – about nine per 100 miles of pipe per year – is less than the national average of 14, Stuhr said. And the vast majority of those are on much smaller lines, not the 30-inch transmission main that ruptured March 16.

Large pipes like the transmission main are buried throughout Portland, and about 25 percent of those pipes, or 42 miles, are cast iron, according to Water Bureau data.

The bureau replaces about seven miles of all kinds of pipe each year, based on its risk assessments and actual main breaks, of which there about 200 in an average year, Stuhr said.

“I think we’re in good shape,” he said.

Yet the question remains of what happened to the pipe in Northeast Portland.

“It’s a common question. People want to say, ‘Why? Why, why, why?’” said Ty Kovatch, the Water Bureau’s head of maintenance and construction.

“It could have been an underlying weakness that worked on itself for a long time,” Kovatch said. “Any choice that we make about why it happened would be pure speculation.”

And the evidence of what caused a burst pipe often washes away with the water it spews, Stuhr said.

For its part, the city’s damage claims office said the rupture was “spontaneous.”

Stuhr said he has a “hard time" with that explanation but accepts it. “I leave that to the risk management department and the city attorney’s office,” he said.

“I don’t care what you do,” Stuhr said, “You’re going to have main breaks.”

-- Gordon R. Friedman

GFriedman@Oregonian.com