Runoff As Resource Instead of Problem

San Francisco Chronicle Article by Deborah K. Rich (12/6/08)

Laura Davison’s garden at her home near Occidental which landscaper Erik Ohlsen designed to control water and provide a natural working garden to provide food

When Laura Davison decided to spend some of her inheritance on landscaping the weedy slope next to her house, she knew she wanted a garden that would nourish both the land and her family. She also knew she had a problem.

“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.

“We incorporated fruits, nuts and vegetables with plants grown specifically to build soil: your leguminous nitrogen fixers, your mineral-accumulating herbaceous plants, and your deep-rooting tuber plants which build biomass in the soil.

“When you choose plants that can provide the various functions necessary to meet our human needs and the ecological needs of the garden, you create a very harmonic dynamic community that can provide permanent food production and ecological regeneration.”

A chicken coop and run built at the far end of the slope anchors the garden, providing manure as well as food.

Erosion control

Any gardener who has wrestled with watering and fertilizing, or simply with maneuvering around a sloping yard, will find swales useful.

Swales capture rainwater and help prevent flooding and erosion – of increasing importance as global warming brings more rainfall and higher temperatures, which dry out the soil. (Although the young shrubs and trees planted on the berms were drip-irrigated during the summer, Ohlsen expected their roots to soon reach the water that the swales are banking in the soil. Annual vegetables grown on the berms will probably always need summer irrigation.)

Each year, a different swale becomes the compost spot for garden trimmings that will be tossed into adjoining berms in the spring.

In the other swales, Ohlsen planted clover. The blooms attract bees, beneficial wasps and flies, butterflies and hummingbirds, while the roots host nitrogen-fixing bacteria that increase soil fertility. These swales also serve as level garden paths and provide easy access to the plantings on the berms.

“There is an incredible beauty expressed in shaping the land to harvest water,” Ohlsen said. “People respond to the beauty, perhaps because we are made of water and naturally attracted to patterns that mimic water.

“And when you design a system like this around water’s energy and flow, as people walk through they also flow like water and are periodically caught and held in the garden, in a sense, just like we’re catching and holding the water.”

He hopes his ideas won’t appear “like something alternative but rather just beautiful and smart.”

“What I’ve learned over the last several years is that we can create landscapes that meet our desire to surround our homes in beauty, and that, at the same time, harvest water; build soil; provide beneficial habitat for birds, insects and microorganisms; produce food; and create a base for food security.”