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Runoff as resource instead of problem

Deborah K. Rich, SF Gate, Special to The SF Chronicle
Saturday, December 6, 2008

"The first year we were here, the water would just sheet down from the property higher up the slope, and this area would be mud. I couldn't even walk out here; it was just slosh and goop," she said.

Her home is near Occidental in Sonoma County, which can receive 60 inches of rain a year. "My husband and I were wondering what we were going to do, and how we were going to figure this out."

Davison met a teacher at her sons' school whose husband, Erik Ohlsen, had recently launched Permaculture Artisans, a landscape design and installation business.

Permaculture - the word plays on "permanent culture" and "permanent agriculture" - strives for sustainability by incorporating ecological cycles and principles into land altered for human use. Ohlsen took his first permaculture class in 1999 from Brock Dolman, who directs the Water Institute at the Occidental Arts & Ecology Center.

Interaction with water in the landscape has become fundamental to Ohlsen's permaculture design practice.

"I was inspired by the concepts of water harvesting, ecological watershed management practices and erosion control and everything to do with water in Brock's course," Ohlsen said. The storm water that turned the property into muck could instead provide a foundation for the garden Davison wanted.

"The Davisons were clear that they wanted an ecological landscape that provided food for their family," Ohlsen said. "Water harvesting wasn't something they had foreknowledge of, but the way we design ecological gardens, water harvesting is always the first piece designed into the system."

Swales and berms
Ohlsen used a small excavator to build a series of parallel swales (a shallow ditch) and berms (a raised area adjacent to the swale) on contour (meaning that they lie across slope, their elevation remaining constant). He dug the first swale along the upper property line and the last where the property levels off.

Each swale is roughly 5 feet wide; its adjoining berm is 2 1/2 feet tall and 6 feet wide. A smaller berm lies across the end of each swale to prevent water from running out the end of the swale.

The swales and berms harvest rainwater by pooling and slowing the water on its downhill course, giving it time and space to soak into the soil. Rock-lined spillways connect the swales and allow water to flow from one to the next if the water pools in the swale more than 8 inches.

In the Davisons' loamy soil, all the rainwater will generally soak into the swale where it is caught, and water will spill from one swale to the next only during a very heavy rain. "We design for catastrophe," Ohlsen said of the oversize catchment systems. Encouraging Davison and her boys to work along with him, Ohlsen planted the berms with an eye toward both feeding the family and creating a self-sustaining ecosystem.

"We chose plants that provide multiple functions - for example, leguminous plants which can provide edible pods while, at the same time, fixing nitrogen in the soil and attracting beneficial insects and hummingbirds, which can then manage pests," Ohlsen said.

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