The Sonoma County Water Agency will start construction next month on a complex, costly project on the Russian River that's designed to permit migrating fish to travel more safely and efficiently past the seasonal Mirabel Dam in Forestville.
The $12 million project was initiated under a federal mandate to replace a deficient screen system meant to prevent fish from getting hung up in submerged pumps that draw water from the river for filtration and consumer delivery.
But the project has been expanded to include a new, improved fish passageway, as well as a subsurface viewing gallery with expansive windows into the river for more than 3,000 students and other visitors who tour the site each year.
"It's an opportunity that comes along fleetingly to construct a facility like this, to maximize its benefit and allow public education, which we think is just a critical component of the community understanding our water supply," said David Manning, environmental resources coordinator for the water agency. "This is a facility that will be on the river for many generations to come."
Construction of the large, more integrated facility about a half-mile south of historic Wohler Bridge, enables the Water Agency to make a variety of improvements that will more naturally guide fish into a state-of-the-art passageway during upstream and downstream travels.
The change is intended to benefit numerous species, especially endangered coho salmon, as well as Chinook salmon and steelhead trout, both of which are listed as threatened under the federal Endangered Species Act.
The work is expected to last through two construction seasons, with completion expected in late 2015, agency spokeswoman Ann DuBay said.
Staging and construction will begin over the next few weeks, though crews have been at work since January drilling more than 300 columns deep into the earth and filling them with compacted rock to stabilize the ground in event of an earthquake, Manning said.
The new facility will replace an outdated system — the existing fish ladder was installed in 1976 — that is set into the western river bank. It serves a pumping network that draws water from the river, pipes it underground into nearby ponds and filters it through deep gravel beds before sucking it back out and delivering the water to 600,000 consumers in Sonoma and northern Marin counties.
An inflatable, rubber dam stretches about 200 feet across the river during dry, low-flow months to hold back the flow and raise the water level so more can be pumped and filtered for consumption.