PITTSBURGH -- The flash flooding that killed four people and forced others to swim to safety or climb onto car roofs was a freak accident caused by heavy rainfall that overwhelmed the sewer system just as rush-hour traffic clogged low-lying city streets, officials said Saturday.
A mother and her two daughters died in Friday's flood after becoming trapped in their vehicle, which rising water pinned to a tree. Another woman's body was washed into the Allegheny River, where she was found Saturday morning.
Back-to-back storms pounded the city with 3 to 4 inches of rain. The water drained rapidly onto Washington Boulevard, a main street near the Allegheny River on the city's east side, with a force too great for a pair of sewer pipes 9 feet in diameter. The torrent blew off 60-pound manhole covers.
"We had geysers here," said Raymond DeMichiei, deputy director of the city Office of Emergency Management.
"There's only so much any drainage system can handle," said Jim Struzzi, a spokesman for the Pennsylvania Department of Transportation. PennDOT maintains the roadway, but the city is responsible for the pipes underneath, part of aging sewer system.
The area's topography presents near-perfect conditions for flooding. Hills line both sides of the section of Washington Boulevard that flooded and the boulevard itself slopes down as it stretches north toward the Allegheny River. When heavy rains hit, water rushes in from three directions.
The low-lying area was apparently once a creek bed and "the watershed is huge for this," DeMichiei said.
Flooding is not uncommon in the area, he said.