A Swale Idea!

Strategies for growing food
in an episodic drought environment

By Joshua Burman Thayer

Gardener's Notebook, April 2020: I recently finished work on a large hillside landscaping project in Danville, California. Designing this orchard and herb garden "food forest" (and others I've done recently for East Bay homeowners) gave me a chance to apply some strategies from permaculture theory that I wrote about in 2015 for the Mother Earth News, specifically, how to install water-saving earthworks in drought-prone environments.

As we know and experience year after year in the American West, our climate is subject to episodic drought. The long dry seasons define the look of our landscape. They affect what grows here and also how we live.

Here in the Bay Area, we are accustomed to living through six months with no significant precipitation. When the winter rainy season finally does arrive, the rain can fall in torrents. By designing our properties to catch rainwater via a series of small earthworks, we keep that valuable moisture around longer to be utilized by our cultivated plants.

 

 

Swales on a Slope

Unless we actively redirect it, water will always take the path of least resistance, finding the most efficient downhill route into streams and rivers that eventually reach the sea. While it’s easy to observe the way rainwater sheets down a hillside on our hardscape surfaces, what we often don’t see is what happens as it runs down open sloping hillsides, often eroding the ground as it picks up particles of topsoil and perhaps even causes large portions of ground to collapse.

By creating on-contour two-foot-deep earthworks called “swales,” we can reduce the load of silt going into creeks and also gain the value of that moisture for our landscaping. Storm water detained in a swale will soak slowly into the surrounding slope at a rate our landscape plants can better utilize.

 

 

As rain enters a swale aligned along the horizontal contour of the slope, its velocity is slowed, and it spreads to fill the trench. When the swale fills to capacity, the overflow can be directed into a connector pipe, which runs downhill to the next swale in a well-designed system. In this way, the water flows slowly downhill in broad arcs, retained at each level to percolate into the soil.

 

 

 

Net and Pan

On a slope of 20 degrees or less, a swale system will work very effectively. If the hillside is steeper than 20 degrees, an earthworks approach called “net and pan” is better suited, especially when you are trying to plant and maintain an orchard. A net-and-pan system funnels rain into basins around your fruit trees. Upslope from each tree, two diagonal 1-foot by 1-foot French drains direct the rainwater into the basins. Imagine a shape like a medallion with the fruit tree as the medal. The medallion can widen catchment area for each tree to perhaps 10 feet. This allows you to retain more water on higher levels of the property. By staggering these net and pan systems down the slope, all parts of the hillside can become catchments, thus reducing all the runoff—and potential for erosion—and retaining the water where you need it.

 

 

Swale and net and pan earthworks systems are simple, human scale strategies for drought-prone lands. By catching water where crops can use it, we reduce the cost of transporting water long distances and make best use of precipitation that falls on our sites. By guiding water intentionally through the land, these systems increase our capacity to cultivate upslope areas and they put our properties more “in-the-flow” with mother nature.

The two-part video tour below of the just-completed project in Danville shows how these earthworks systems work to support a food forest. Scroll below the videos for my site plan as well as lists of the plants that are included in the food forest.