Drought Proof your Garden with Earthworks

By Joshua Burman Thayer | August 20, 2015
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Drought

In some areas of the Bay Area drought can be extensive. Long periods routinely pass without a single drop of rain. Here in California, up to six months or more can pass without a rain storm. When the rain finally does arrive, it can bring a torrent of water. It is these stormy moments that define the function of our landscapes. Earthworks are strategically designed ways of shaping the earth to slow the flow of storm water. They are human scale and are not compacted but rather planted. The water spreads out and slowly soaks into the soil. As this process takes anywhere from several hours to several days, it prolongs the time the soil is moist after a rain storm. This gives all of the crops and fruit trees just down hill from the earthworks swale more time to sip the water. They are now able to utilize more of the rainfall, which is better for plants and for the soil, as the plants soak up more of each and every storm. Rather than running downhill, moister is retained where you want it, in the garden, reducing both water waste as well as erosion.

Rain sheets down driveways, on-ramps and downslopes, eventually to the sea. As it gains momentum, it picks up particles of topsoil and erodes the landscape along the way. Always finding the most efficient route downhill, water will take the path of least resistance; that is if we don't direct it. By doing this important work now in the dry season, you will be ahead of the game and ready to harness liquid abundance when it does finally arrive.

“Slow it, Spread it, Sink It”

By creating on-contour (or ditch) earthworks, called “swales” we can create repositories, which can fill in storms and slowly soak into our hill slopes at a rate that fruit trees can drink. Once the rain has entered into a swale, its velocity is slowed and spreads to fill the on contour trench, which is roughly two feet deep. As the swale fills to capacity, the water can overflow into a connector pipe that runs downhill to the next swale system. In this way, the water works slowly downhill in broad arcs much in the way a marble maze slowly leads the marble through a wooden series of slow slides. At each level, runoff is slowed down enough to begin to percolate the soil, thus rehydrating dry land. At 20° slope or less, these swale systems will work effectively.

Swales and Net and Pan Systems

On steep hills of more than 20° slope, another earthworks approach will be better suited. “net-and-pan," earthworks systems funnel rain and direct it to each fruit tree basin. Upslope from each hillside fruit tree, a pair of diagonal one foot by one foot french drains direct rain water into the fruit tree basin. Now, the area of reception is widened from the width of the young tree roots to perhaps 10 feet. This creates more water harvest to upslope crops. By staggering these net-and-pan systems downslope, all parts of the hill can become catchments and directed into these basins, thus reducing chances of runoff and erosion.

Swales and net-and-pan are two earthworks systems that are simple, human scale strategies to drought-proof our lands. By catching the water where it will be consumed by crops, we can reduce the cost of transporting water long distances from large dams and utilize what does fall in our areas. These systems will increase our capacity to irrigate and cultivate in up-slope areas and make our homes more “in-the-flow” with mother nature by guiding water intentionally through the land. Start now to drought proof your home and create edible abundance!

Article from Edible Silicon Valley at http://ediblesiliconvalley.ediblecommunities.com/food-thought/drought-proof-your-garden-earthworks
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