Work is about to start on a $1.7 million project to protect Sonoma County's water supply in the case of a large earthquake.
Contractors will begin work this month on an effort to shore up the banks of the Russian River around a key part of the water plant in Forestville that supplies much of the water that the Sonoma County Water Agency sends to 600,000 customers in Sonoma and Marin counties.
That plant is built on a sandy soil type that has a nasty tendency to turn into a slick mush under pressure from earthquakes, a process known as "liquefaction," said engineer Steve Koldis of the Water Agency. The resulting sliding can damage buildings and break pipelines.
The project, which should last into the spring, will protect a building that funnels water out of the Russian River and into a series of nearby holding ponds, where it soaks into the ground and recharges wells used to draw out drinking water. In the case of a major earthquake, beyond a 7.0 on the Richter Scale, the building could be damaged so badly by sliding soil that it would be put out of service.
This is the second phase of a multi-year effort to shore up the sprawling system that supplies water to a wide swath of the region. The effort is expected to cost more than $18 million, about half of which will be paid by the Federal Emergency Management Agency and the rest by ratepayers in the cities that rely on the Water Agency.
The first phase replaced parts of a pipeline through Santa Rosa that supplies the city of Sonoma and much of the southern end of the county. The agency was worried that a major quake on the Rodgers Creek Fault could crack that older pipe. A quake on that fault could also cause the soil liquefaction at the Forestville plant, Koldis said.
Later phases of the project will shore up other pipelines where they cross waterways, including Mark West Creek and the Russian River at the Forestville plant. It also will see the installation of a series of cut-off valves throughout the system that will allow engineers to more quickly isolate leaks or earthquake damage.
None of the projects should be as disruptive as the work on the Sonoma pipeline, which wrapped up last year after causing lane closures on Sonoma Avenue, Koldis said.
The new project at the Forestville plant will not affect drinking water service to the public. It may, however, pose a headache for the Water Agency should the current drought persist. The work may require the agency to lower the inflatable rubber dam that backs up water for use at the plant.
Normally that dam is used only in the summer when river flows are low. But coming out of the driest year in county history, the dam remains inflated to maintain water levels at the plant.
If there is no significant rain before spring, Kolids said, engineers will have to figure out how to work around the rubber dam or deflate it temporarily, though Koldis said he is not worried that water supplies would be interrupted by the work.
Once completed, the work will allow the installation of a new screen and fish ladder that will allow spawning salmon and steelhead trout to travel up the river more easily. This will replace the old system, installed around 1975, and a more modern design will nearly guarantee that no fish will be sucked into the water intakes and killed, Koldis said.
It will also allow the public a first-hand view of the fish themselves. The new ladder, a bypass channel around the existing dam, will include an observation room and window so visitors can watch fish swimming upstream to spawn.
The agency hopes to have the new ladder and intake screen in place by the end of the year, though it may drag into 2015 depending on how smoothly construction goes, he said.
[END_CREDIT_0]You can reach Staff Writer Sean Scully at 521-5313 or sean.scully@pressdemocrat.com. On Twitter @BeerCountry.
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