County water agency working on flood fix for Petaluma watershed

The Sonoma County Water Agency is embarking on phase 2 of a project aimed to control flooding and recharge groundwater supplies in the upper Petaluma River area, thanks to an extra $101,915 allotment approved by the Sonoma County Board of Supervisors late last month.

The funds will pay for models and a feasibility study to pinpoint areas most affected by heavy rainfall, and identify where flood abatement infrastructure would be most useful.

For almost a decade, the Water Agency has been actively seeking opportunities to improve flood control across the county’s three main watersheds: Laguna-Mark West, Petaluma River and Sonoma Creek. With the go-ahead to complete modeling work, the Petaluma River project is furthest along of the three, said Susan Haydon, project manager for the water agency.

The city already has an existing surface water model, used to construct Petaluma’s recent flood-control improvements, but the model only covered the city limits.

The modeling paid for by the county will go beyond that.

“So we’re expanding that model to … go into the upper watershed in the rural area and start looking at the dynamics of the water there,” Haydon said.

The surveying, to be completed by Woodard & Curran, Inc., a San Francisco-based engineering firm, will look largely at what can be done to improve the area around Lichau and Willowbrook creeks, and how stormwater flow can be collected to recharge groundwater in those areas.

“(The modeling) tells us when we have storms at certain durations in certain locations this is how it falls on the ground, this is how it moves through the watershed, this is how fast certain quantities of water move,” Haydon said. “If we understand the dynamics of the water and its movement on the landscape, then we can better predict where it floods at peak times and we could begin to look at opportunities in the upper watershed to collect that water.”

Despite record rains this winter, flooding in the southern portion of the county was modest compared with previous years, mostly thanks to the 2016 completion of a $43 million flood abatement project, started after two particularly destructive floods in the 1980s, said Petaluma City Councilwoman Teresa Barrett. She also attributed the lack of significant flooding to work done by the Water Agency to maintain and clear creeks that feed into the Petaluma River, and is eager to see what fixes come out of the proposed work.

“The more we know, the better we are,” she said.

Sonoma County Supervisor David Rabbitt, whose district covers the swath of land the flood control project would affect, applauded the work of the city to mitigate flooding, and the Water Agency’s continued stream maintenance, but noted that more work could be done.

“We always have to be diligent,” he said. “And we always have to look for long-term solutions.”

You can reach Staff Writer Christi Warren at 707-521-5205 or christi.warren@pressdemocrat.com.