Stormwater plan paying off, city says

Despite widespread flooding and sewage overflows, the city of Seattle's investment in greater stormwater capacity and larger detention ponds appeared to be succeeding, city officials said.

One of the most chronically flood-prone areas — Madison Valley, where more than 30 homes flooded in a December 2006 storm — appeared to escape major damage following millions of dollars in detention-pond improvements completed over the past two years.

And in the Meadowbrook neighborhood near Lake City, where more than 100 homes flooded in December 2007, storm waters this weekend closed 35th Avenue Northeast near Nathan Hale High School and overflowing sewage closed a city park. Still, that damage was much less extensive than in the past, said Renee Barton, president of Meadowbrook Community Council.

"In aerial shots of the neighborhood in the 2007 storm, we looked a lot like Chehalis [which suffered catastrophic flooding the same year]. Seattle Public Utilities [SPU] has made a lot of improvements," she said. Still, a major expansion of capacity of the Thornton Creek stormwater-drainage system isn't in the city budget until 2012, she said.

During the storm, the utility received more than 700 calls about flooding and sent crews to 332 locations, said Andy Ryan, SPU spokesman.

"Our map of where our people were deployed, it's a Christmas tree. Basically, the whole city was lit up," he said.

Most of Seattle received 3 to 4 inches of rain Saturday and Sunday, according to data taken from 22 rain gauges across the city monitored by SPU. West Seattle received 4 inches of rain. Green Lake and South Park got more than 3 inches, or about the amount of rain expected in a 100-year-storm event, according to James Rufo-Hill, meteorologist for SPU.

Seattle and King County officials worry that global warming may cause more frequent and more severe storms, straining the stormwater and sewage infrastructure more quickly than it can be expanded.

Ryan said the system was "generally designed for what we used to call a 25-year storm. But those storms appear to be coming more frequently."

In Madison Valley, the city spent more than $3 million to enlarge a detention pond at 30th Avenue East and East John Street, the site of some of the city's worst flooding over the past three decades. In previous rainstorms, floodwaters overtopped the pond.

By the end of 2011, SPU expects to spend $27 million more to add six blocks of stormwater pipes and a huge stormwater-storage tank at Washington Park.

While it's costly, the city has paid out millions in claims for flooding over the past decade — more than $6 million for damage as a result of the December 2006 rainstorm, according to city figures, and at least $1.4 million after a 2004 storm.

Mayor Mike McGinn toured North Seattle on Sunday with Ray Hoffman, director of SPU.

McGinn said ongoing investments are improving the city's capacity for stormwater, but a little more rain over the weekend likely would have caused more flooding.

He said several detention facilities in the North End were at or near capacity by the time the storm subsided.

"We've spent millions to prevent flooding, but there's more to be done as far as how we handle big storms," McGinn said Monday.

Lynn Thompson: 206-464-8305 or lthompson@seattletimes.com