The anatomy of a flood

Most flooding was caused by a 'wave' that moved south from San Francisquito Creek

As San Francisquito Creek overflowed its banks in the wee hours of Tuesday morning, residents to the south had little inkling that a wave of water from the creek was coming toward their homes, creating a 2-mile path of water, mud and debris, ending in a pond near Oregon Expressway and U.S. Highway 101.

"(Flooding) was primarily caused by San Francisquito Creek spilling out of its banks and then the water running overland through Crescent Park, past University, Hamilton, Channing, over Embarcadero, running in a southeastern direction and (winding) up by Greer Park. It flooded through a whole bunch of homes along the way," said Palo Alto Public Works Director Glenn Roberts.

At four points near bridges that cross the creek--Byron, Seneca and Chaucer streets, and University Avenue at Woodland, the water became constricted, overflowing the creek banks and heading in a southeasterly direction. Farther to the southeast, at a bridge over East Bayshore Road and at the back of the Baylands Athletic Center, the creek also overtopped its banks.

On the other side of the creek in Menlo Park, the water overflowed the creek banks in three spots: Woodland Avenue at Laurel Avenue, the Chaucer Street bridge, and Oak Court and Emma Lane, two small streets off Woodland Avenue, which runs along the creek.

East Palo Alto was also heavily damaged, as the creek overflowed its banks at the University Avenue bridge, swamping Whiskey Gulch and East O'Keefe Street, and the strip of Woodland Avenue between the bridge and West Bayshore Road. A bit farther south, creek water overtopped the bank at East Bayshore Road, flooding The Gardens area of East Palo Alto.

"The lay of the land is such that the land slopes away from the creek," said Palo Alto Senior Engineer Joe Teresi. "As it got closer to 101, it slowed down at the lowest point (near the intersection of Oregon Expressway, 101 and Greer Road), where it ponded. From there, it was kind of stuck, and had to empty out by flowing into the storm drains, (which flow) into Matadero Creek."

The water left layers of mud and debris in its wake, eroding many creekside back yards. Wednesday, a relatively rain-free day, rows of sandbags prepared for the next storm lined driveways and doorways of homes along Palo Alto Avenue, which faces the creek, as well as homes along University Avenue.

"The storm drains flow to creeks. When the creeks are full, there's no place for the water to go," Roberts said, so the water pooled onto streets, turning them into virtual lakes and rivers.

A pump station near Greer Park that takes water from low storm drains and pumps it up to Matadero Creek was overwhelmed by the amount of water. "It took a real long time (to pump) the water into the creek," Teresi said.

It will be several weeks before officials know the scale of this week's flood--whether it was a legendary "100-year" flood, or a 50-year event. But, many say it's at least the worst since 1955.

The three concrete-lined creeks, Adobe, Barron and Matadero, didn't flood, he said, partly due to the interim plan developed by the city and the Santa Clara Valley Water District. This year, the water district discovered a design error in the Louis Road bridge over Matadero Creek. Under certain conditions, that means Matadero Creek would not be able to hold the capacity of water it should because the water would be stopped by the bridge. That didn't happen Monday.

Water district officials stayed through the night monitoring a diverter at Barron and Matadero creeks in Barron Park. "The good news about that is it worked. The operating plan worked like it was supposed to. The water district staff was very responsive."

"The creeks that are more urban, like Barron, Matadero and Adobe, didn't flood," Roberts said. "What flooded was San Francisquito, which has the tremendous area in the mountains. I think there must have been a tremendous amount in the (watershed)."

Several major underpasses flooded, including both Oregon Expressway and Embarcadero Road under Alma Street, University Avenue under the railroad tracks, and El Camino Real under University Avenue.

Oregon is operated by Santa Clara County, and apparently pumps failed there. At University, the city's system was operational, Roberts said, but it couldn't handle the amount of water. El Camino Real is operated by the state Department of Transportation.

With storms forecast throughout the week, city officials will remain on alert. "We have to watch everything. It can vary by the nature of the storm," Roberts said.

--Elizabeth Lorenz

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