A "series of extraordinary events" led to the December drowning of Kate Fleming, a local audiobook narrator who died when a surge of floodwater slammed into her Madison Valley basement, trapping her in a windowless room, said the consultant hired by the city to investigate the factors surrounding Fleming's death.

On Dec. 14, a storm pummeled Seattle, with the rain falling so hard and so fast that the drainage system in Madison Valley was quickly overwhelmed, said John Rogers, a senior project manager for CH2M Hill, a large Denver-based engineering firm whose Bellevue office was paid $250,000 to conduct an independent investigation.

At a Thursday news conference at Bush Middle School, a few blocks from where Fleming died, Rogers and city officials announced the investigation's findings. The report doesn't say who is responsible for the various contributing factors.

The intense storm caused flooding along Madison Street, which runs at least 40 feet above the so-called Mercer Bowl — a low-lying area at the end of East Mercer Street and 30th Avenue East, where Fleming's house is located, said Rogers, who led the investigation.

The overflow from higher parts of Madison Street caused water to pool in the street's lowest spot, near 29th Avenue East. As water coursed down Madison Street, it overflowed curbs, spilled into parking lots and backyards and continued downhill, causing a 60-foot section of a retaining wall on private property along Dewey Place East and East Republican Street to tip over, he said.

When the retaining wall toppled, a surge of water rushed down the hillside, carrying mud and dirt north along Dewey Place East, around a curve in the road and onto Fleming's property. The debris clogged the neighborhood's water drains, and the water continued to rise, even as obstructions in drain pipes along Madison Street reduced the amount of water the system could handle.

"It's quite clear that the clogging of the drains contributed to the water going as high as it did," Rogers said, noting that the water level "didn't get much higher than the ceiling" of Fleming's basement. After the flood, there was mud more than a foot deep in some places, he said.

Rogers said his firm determined that a retention pond that overflowed about four blocks from Fleming's house did not contribute to the flooding in the Mercer Bowl.

Chuck Clarke, director of Seattle Public Utilities, said a windstorm had been predicted for Dec. 14, but forecasters weren't expecting the heavy rains that doused the city in an hour and a half. "It became very clear within the [Mercer] Bowl that the drains couldn't handle all the water coming in from Madison," Clarke said. "We know if the soil hadn't packed over every one of those, a lot more water would've been drained off."

The area's drainage system was built in the early 1970s and was designed to handle only a 25-year storm, Clarke said. The December storm "was probably a 100- or 150-year storm event," which came after a series of November storms set new rainfall records for the city. "Everything was already saturated," Clarke said.

"In an hour and a half, whether we could've prevented something like this is pretty doubtful," he said, referring to the flooding of Fleming's basement. As a short-term fix, Clarke said, pumping crews will be sent to the Mercer Bowl whenever a big storm is forecast. But it will take up to five years and $30 million to $100 million to create a long-term solution.

Fred Podesta, the acting director of the city's Department of Executive Administration, said the report released Thursday "is a jumping-off point for investigating claims" filed by area homeowners. By understanding what led to flooding, Podesta said, his office will be better able to determine the city's responsibility in compensating homeowners.

About 300 claims were filed citywide as a result of the Dec. 14 storm, but Madison Valley is the only neighborhood that suffered such concentrated damage, he said.

So far, the city has settled 22 damage claims with Madison Valley residents and has partially paid an additional 42 claims, Podesta said. Only one claim there has been denied, versus 51 citywide, he said. Fleming's partner, Charlene Strong, has not filed a claim with the city.

More than 50 Madison Valley residents attended a community meeting Thursday evening to hear CH2M Hill's report and ask questions. Several said they were angry at the city for avoiding responsibility for Fleming's death and not providing more information about the claims process.

"We had been led to believe," said private attorney Richard Maloney, "that the city would announce its willingness to pay for diminution of value, mental anguish and loss of use, and we are bitterly disappointed that the city continues to delay payment and to force its citizens to hire lawyers and engage in legal action to obtain fair compensation."

Deputy Mayor Tim Ceis told Maloney and others at the meeting that the city's law office hasn't received any such claims, but will review them on a case-by-case basis.

Times reporter Sanjay Bhatt contributed to this report.

Sara Jean Green: 206-515-5654 or sgreen@seattletimes.com