Was deficient drainage or extreme storm to blame?

For the second time in a year, Seattle homeowners pumped out their basements and threw away their soaked belongings — and some blamed the city's drainage system.

Last December and this month, the city had the same response: These storms are extreme events.

As Mayor Greg Nickels put it Monday, the city's drains "simply were not built to handle this kind of rainfall."

In a city that already gets a lot of rain, is it time to start thinking about expanding the drainage system?

City officials say no. They called Monday's storm, and last year's December storm, torrential downpours for which it would be impractical to build a new system.

"There's just no way, and you couldn't afford to design systems to deal with that," said Deputy Mayor Tim Ceis.

The drainage system in the city is designed to handle a 25-year storm, and Monday's rainfall hit a historic high in some neighborhoods.

But City Councilmember Richard Conlin, chairman of the council's utilities committee, said the drainage system does need more capacity.

Ceis said Seattle Public Utilities has done "really well" with maintenance, cleaning streets and clearing catch basins, and the utility has no backlog of repairs.

The utility spends $5 million a year replacing sewer lines, and the city is building drainage systems such as swales in South Lake Union and High Point.

Whether climate change is leading to more intense storms, however, is worth asking, Ceis said, and the city plans to talk to scientists about that.

"If the answer is yes, then we do have a responsibility to look at adaptation strategy," Ceis said.

Monday, utility crews dealt with water mains breaking, ponds and creeks overflowing, and sewers backing up. In a few cases, rising water forced evacuations.

Throughout Monday, the department fielded more than 1,400 calls.

After the Dec. 14-15 storm in 2006, the city received more than 350 claims from residents blaming the city for flood damage. Seattle Public Utilities has since paid out $3.2 million, settled 123 claims and denied 124. Most of the money went to residents in Madison Valley, where a retention pond overflowed into people's homes.

The utility has since worked to keep drains clear in the area. Although some yards flooded Monday, utility officials say the pond performed fairly well.

Parts of North Seattle however, faced severe flooding. Along lower Thornton Creek, one contributing factor was the city's failure to clear debris that blocked a stream culvert, said resident Gary Peltz, whose home on a small hillside took on 7 inches of water.

The culvert is an opening, lined in concrete, that lets the creek flow beneath Northeast 95th Street, near Sand Point Way Northeast. Fifteen feet of water accumulated behind the blocked opening, Peltz said, with the creek at his nearby house rising at least 6 feet above normal winter levels.

"Why didn't they keep this clear? That's the question of the day," said Peltz, whose house has not flooded before.

Around noon Monday, he said, he explained the culvert problem to an SPU crew chief working at a nearby retention pond. The crew scooped away a downed log, filled a dump truck with debris and unclogged the culvert.

Almost immediately, the standing water receded, said Dan Montano, a homeowner upstream whose basement was flooded.

If the crew chief hadn't acted, "it would have been a way-worse disaster," said Peltz, who plans to file a claim against the city.

SPU spokesman Andy Ryan said the culvert was checked before the rainy season and would have been checked periodically through the fall.

He said it is very likely the clog materialized during the storm, not as a result of a maintenance lapse.

As to whether crews should have checked out that spot Monday morning, Ryan called that "an ultimate example of armchair quarterbacking. There are hundreds of possible critical areas that backed up. How would you know to check that one out? You know where we had crews standing by? Madison Valley."

Councilmember Conlin suggested that Seattle's drainage system may not be adequate for the changing climate. "Here's the problem," he said. "Our drainage system is sized for the typical Seattle rain."

"What that means is that it's used to rain coming and falling, and being conveyed away, and yes, we get some storms, but they're not as long or intense as what we're experiencing now."

The utilities department hosted a workshop in October with utility experts from the Netherlands and the United Kingdom to talk about how they are dealing with changing weather patterns.

"Most people are not saying we need to build huge pipes and storage vaults," said Paul Fleming, a utility manager for a climate-change initiative. He says the future could include a mix of public outreach, more detailed weather forecasts and low-impact development such as green roofs.

Sharon Pian Chan: 206-464-2958 or schan@seattletimes.com. Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com.