Santa Rosa set to showcase rainwater capture at new City Hall garden

It has been an exceptional year for rainfall in Sonoma County, and Santa Rosa is getting ready to catch some of it.

The centerpiece of City Hall's new water-efficiency demonstration garden - a gleaming silver rainwater harvesting tank - was lowered into place Wednesday morning, a milestone in a project to showcase the benefits of rainwater capture and inspire people to build their own such systems.

Assuming this year's wet winter pattern continues, the 2,200-gallon corrugated steel tank will soon begin collecting runoff from a 1,600-square-foot section of City Hall roof.

That water will be used to irrigate the new water-efficient landscaping being planted on the north side of City Hall, an area of neglected lawn that has been replaced with a cascade of river rocks, mulch and native plants including California aster and dwarf coyote brush.

The cistern system has some fancy technology behind it, such as a weather-sensitive irrigation controller and a pump feeding city water into the system when needed. But at its core, the gravity-fed system is little different from the do-it-yourself rain barrels that reroute runoff from downspouts.

“You can do this in your yard. You can do this at your commercial facility. You can do this anywhere,” said Deb Lane, a water resources analyst for the city. “Everything we're showing here are best practices that can be implemented elsewhere. That's what's cool about this.”

The $1 million project, most of which is funded by a state grant, is actually far more than a water catchment system. It involves a large underground area that captures and retains the runoff from the City Hall parking lot. Crews are also sculpting swales to slow down the roof runoff that exceeds the cistern's capacity.

Instead of going straight into the storm drain to the nearby Santa Rosa Creek, which flows beneath City Hall, the swales are meant to hold back the rainwater to give it time to seep into the ground, cleaning it naturally and helping recharge aquifers, Lane said.

“When you slow water down, it doesn't hit the creeks as fast,” Lane said.

For smaller storms, the water may never even reach the creek. It will take about 2 inches of rain to fill the silver cistern, built by American Tank Co. in Windsor. Excess runoff will pour out an overflow near the top of the tank and splash into a swale.

From there the water will follow the largest swale along a meandering, gently sloping course lined with plants, rocks and some chunks of granite from the downtown courthouse that was demolished in 1966.

Over the course of 250 feet, the water will have the chance to both soak into the soil and or be absorbed by the plants around it.

Over a typical year, the tank will fill up and drain at least five times, saving 11,000 gallons of water, according to city estimates. Because of budget constraints, the system was not sized to be large enough to get the garden through long dry stretches on captured rainwater alone. City water will be used to irrigate the area during most summer months, Lane said.

Though conceived of and funded during a period of intense drought, the fact that the project is coming online during a decidedly different weather pattern doesn't make the project any less satisfying or important, Lane said.

Santa Rosa has recorded 52 inches of rain since Oct. 1, which is 203 percent of average for this time of year.

“I'm excited to have this showcase, this cutting- edge project that is going to draw people to see it and to learn about it and to replicate and even improve on it,” she said.

A ribbon cutting is planned for late spring.

You can reach Staff Writer Kevin McCallum at 707-521-5207 or kevin.mccallum@pressdemocrat.com.