Slow it, Save it, Sink it

Slow it, Save it, Sink it

Daniel McGlynn

EstApr2013Cover172 Download: Estuary News, April 2013 PDF

In the city landscape, rainwater pools quickly and then travels in torrents and sheets down roofs, sidewalks, parking lots, and roadways, all-the-while gathering volume and wicking pollution from encounters with countless sources of contamination. The water is going somewhere. Often it’s urban creeks on the way to the Bay. The hardened hydrology of the city means creeks are getting hammered.

That’s why the City of Oakland is advocating that citizens help to create a decentralized stormwater management system by retaining rainwater in barrels, and then releasing it slowly to mimic the function of the natural water cycle.  “The goal, really, is percolation,” says Kat Sawyer, who works for the Watershed Project, the lead contractor for the City of Oakland’s Rain Barrel Program.  “Slowing the water down allows it to get into the soil and not overwhelm the creeks.”

The Oakland Rain Barrel Program is in its final months of a three-year grant awarded to Oakland by the American Recovery and Reinvestment Act and the California State Water Board. A little over 1,000 households obtained rain barrels through the grant, or the equivalent of 350,000 gallons of water storage citywide, Sawyer says.

Equipping homes with rain barrels fits into larger stormwater mitigation efforts called low intensity development (LID). “For the last 100 years the goal of engineers was to make straight channels to pave and pipe water,” says Scott Stoller, an engineer who works for the firm ESA PWA. “Recently we’ve been realizing that maybe that wasn’t the best thing to do.”

Instead, the new mantra for stormwater managers is slow it, save it, sink it. Stoller and his colleagues, who partnered with the Watershed Project on the rain barrel program, are using software modeling tools to try to determine the effectiveness of rainwater catchment on a watershed. “We are trying the take the peak off the hydrograph, which really helps creeks respond to runoff,” Stoller says.

Rain barrels are just one strategy to slow stormwater. Other methods advocated by LID practitioners are building rain gardens, amending soils so that they are more retentive, and creating water-slowing structures like berms and swales to aid with short-term water storage. Stoller recommends calculating a home’s impervious surfaces, like the area of a roof and driveway and dedicating between four and ten percent of that number to bio-retention activities.

Another major partner in the Oakland Rain Barrel Program is the DIG Cooperative, an eco-design and build firm active in getting the rain barrels installed. DIG works with homeowners to come up with a stormwater storage system to fit their individual needs. DIG members are also providing support for rain barrel installations at the institutional-scale. They recently installed barrels and rain gardens at the Chabot Space and Science Center and Skyline High School.

With the rain barrel subsidies ending at the close of the federal grant funding, the active partners are hoping that there is enough traction to sustain a citywide interest in backyard stormwater management. “All of this is easily replicated,” Sawyer says, “This whole thing is like a big pilot project. Who knows where it will go from here.”

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