photo credit: Sonoma Water
Map of the Central Sonoma Watershed Project

Flooding was once persistent throughout Santa Rosa, and in the 1950’s Sonoma Water, with the help of the federal government, set about building the Central Sonoma Watershed Project to mitigate the issue.

This month the County moved forward a major rehabilitation of the project.

If you’ve been to Spring Lake in Santa Rosa, you’ve been to the heart of the 65 year old Central Sonoma Watershed Project - and you might not even know it.

The Santa Rosa Creek Reservoir - a.k.a. Spring Lake - is the largest of four reservoirs scattered throughout the city.

They, along with a number of culverts, bridges, diversions, and 21 miles of channelized creek bed make up the flood control project.

"The end goal of this planning effort is to have a federally approved watershed plan and environmental assessment," Said Sonoma Water's Carlos Diaz.

Diaz said a number of concerns have prompted the rehabilitation efforts.

"The original design life of these facilities was 50 years," Diaz said. "We are now pushing 60 years."

"Also significant development and associated land use changes have occurred since 1958, altering the watershed response and flooding within the watershed," Diaz said. "The facilities were also constructed without an extensive knowledge of prominent faults and seismic risk, and we also now expect future climate to bring with it greater rainfall extremes."

The Matanzas Creek Dam - part of the watershed project - was identified as uniquely vulnerable in 2016 and is undergoing a separate expedited rehab process.

Supervisor Susan Gorin noted the effects recent rains have had on flood control infrastructure in other parts of California; and of the importance of improving the Matanzas Creek Dam.

"We see damage happening all the time with failed levees and failed dams, so we need to build in additional capacity in that location because there are a lot of properties downstream," Gorin said.

Final designs for the Central Sonoma Watershed Project are expected in 2026 and for Matanzas Creek Dam as soon as next year.