Thursday, November 29, 2018

Permaculture Design for Stormwater Management

READY trainees at the construction site.
Howard EcoWorks is a nonprofit organization in Howard County, MD. Their "READY" program employs and trains young local residents to build Conservation Landscapes that manage stormwater and reduce flooding from roofs, roads, sidewalks, lawns, and other impervious surfaces.

This past summer, I was asked to design and supervise construction of several Permaculture-style landscapes as part of their "Soak-It-Up" campaign. The techniques we employed harvest and filter stormwater for two suburban sites in Ellicott City, an area of numerous hills and converging streams, that has been in the news recently for severe flooding.

A Rain Garden, Log Terraces, Riparian Buffer, and a Hugelkultur were designated for the first site, a semi-wooded, hillside sloping steeply toward a creek, that floods regularly. The Rain Garden collects water at the bottom of a long gradual slope, and allows it to filter through its basin composed of a sand/compost medium.

Located at the top of a slope, a series of stepped Terraces, built perpendicular to run-off flow, intersect the stormwater. READY youth members cut and filled the existing grade to make the steps, and amended the clay soil with compost. Long fallen logs were collected from native trees on site and bundled together to retain the soil in place. (Rot-resistant Black Locust and Cedar are always best, but we used what we could find.) Native water-loving plants - Ferns, Eastern Columbine, Wild bleeding Heart, Elderberry, Inkberry and others - absorb run-off, and are irrigated passively by this low-tech strategy. Although the Terraces have a practical function, the resulting rustic aesthetic suits its wild setting. Once the plants fill in, the effect will be magical.

Swales and Berms
Our second site, a suburban yard, was seriously eroded due to a neighbor's run-off. READY staff constructed two stormwater practices, both located adjacent to the side yard property line to address the issue as far upslope as possible. Swales and Berms, laid out on contours of the slopes with an A-frame level, intercept the water flow. The swales (level trenches) were filled with wood chips, which act as a sponge, holding water and irrigating our sun-loving native plants - Winterberry, Silky Dogwood, Swamp Milkweed, Black-eyed Susan, Blue False Indigo, Eastern Columbine, Blue Flag, Nodding Onion, and Virgin's Bower (a vine).

Fish Scales with an overflow drain
The second, much larger practice was designed as Fish Scales. Again, another series of swales and berms are laid out on contour, but their ends are staggered like masonry, to allow overflow from one swale to exit into the berm below it. Since this location is shaded by canopy trees, the berms were planted with woody shrubs -Witch Hazel, Serviceberry, Sweet Pepper Bush, Inkberry, and Silky Dogwood - to create an understory. The larger the plant the more water it drinks. Our herbaceous layer included Wild Bleeding Heart, Eastern Columbine, and lots of native Ferns. A border of river rock was installed on one side to slow overflow during large rain events.

There are many strategies for managing stormwater issues. The trick to selecting the right technique, or combination of techniques, is to understand the unique characteristics of a site and its water flow.

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