Officials respond to lingering flood questions

<p>Did the Payran flood-control project push the flooding problem upstream? The experts say no.</p><p>And why didn’t the city ask county emergency services to issue automated phone advisories for north Petaluma on Jan. 25, as it did three weeks prior?</p><p>According to Fire Chief Chris Albertson, the calls are only valuable if there’s new information provided that residents and business owners don’t already have.</p><p>That wasn’t the case three weeks ago, when the sustained, heavy rainfall was obvious — but whether that meant flooding was a certainty can’t be predicted, he said.</p><p>“I can tell you it’s raining, I can tell you the creeks are rising, but I can’t tell you where, or if, it’s going to flood,” Albertson said.</p><p>“We use our professional judgment” in deciding whether to issue the calls, he said. “We look at what the issue is before us that we would need to use the system for.”</p><p>The calls are made using a “reverse 911” system operated by the Sonoma County Department of Emergency Services. The time it takes to issue the calls depends on the time of day and the size of the area targeted, Albertson said.</p><p>On Jan. 3, calls went out to some 7,900 homes and businesses near the northern Petaluma River floodplain, advising that heavy rains were expected.</p><p>The calls also told recipients where sandbags could be obtained and advised them to monitor weather reports. They were not sent as a warning of imminent flooding, Albertson said, and only minimal street flooding occurred during that storm.</p><p>On Jan. 25, more than 5 inches of rain fell in the northwest Petaluma watershed, running off into Liberty and Marin creeks, which flow into the Petaluma River north of the Industrial Avenue business park area.</p><p>The city did receive a handful of complaints that its weather event hotline, 781-1283, was not updated frequently during the Jan. 25 storm, Albertson said. Other residents said they tried unsuccessfully to find updated storm information on the city Web site.</p><p>“That’s a valid concern,” Albertson said. The city will work on ways to keep its Web site updated during severe weather, he said.</p><p>Runoff from the Jan. 25 storm swelled the river north of Corona Road and also flooded street intersections. Several businesses between the river and the Petaluma Auto Plaza were flooded, as were a handful of homes in the unincorporated county along Petaluma Boulevard North.</p><p>“It was simply a matter of more rain and runoff than the creeks and the river could handle,” said Mike Ban, the city’s director of water resources and conservation.</p><p>The northwest Petaluma creeks received up to an inch more rain than others flowing into the river, he noted.</p><p>“In a typical storm, the system performs as it should,” Ban said. But when heavy rains overwhelm the creeks, “the water seeks the path of least resistance.”</p><p>Water was reported flowing south from the intersection of Petaluma Boulevard North and Stony Point Road/Industrial Avenue, traveling through streets and parking lots in search of the river channel.</p><p>The Payran flood-control project further south was not the culprit, Ban said.</p><p>Since the 2005 New Year’s Eve flood, some flood victims have blamed a concrete transition weir for flooding, saying it acts as a dam that holds floodwaters in north Petaluma.</p><p>But the weir is designed to keep the Petaluma River at its natural flow rate, as if the Payran project was never built, Ban said.</p><p>Otherwise, the enlarged channel through the Payran area would cause water to pour through there at a faster-than-normal speed, scouring the banks and bringing silt and rushing water into the downtown area, he said.</p><p>The river typically flows at 3,000 cubic feet per second, Ban said. Without the weir, the river could flow at up to 10,000 cfs through Payran, he said.</p><p>“The way the watershed behaves right now is exactly the way it would have performed in that Industrial Avenue area if the Payran flood-control project had never been built,” Ban said.</p><p>Plans are being made to alleviate flooding north of Corona Road. A $509,000 project to excavate the east bank of the river channel along a vacant lot on Industrial Drive is slated to go forward this year.</p><p>The project would create a terrace system, with more room for floodwaters, and restore the wetlands habitat areas upstream of similar work done near the intersection of Industrial Avenue and Corona Road.</p><p>On the western bank of the river, a floodwall north of Corona Road would be extended by 1,500 feet.</p><p>Ban said the city and Sonoma County Water Agency are also proposing that the U.S. Army Corps of Engineers, which built the Payran flood-control project, conduct a study of the northern Petaluma floodplain “to try to better understand the dynamics of the watershed in that area.”</p><p>However, it could be several years before the study is finished, he said. The first step is to secure federal funding from Congress.</p><p>(Contact Corey Young at corey.young@arguscourier.com)</p>