Water Retention and Diversion

Last week while mulching, I had to stop and admire some of the water diversion and reuse tactics we’re employing here at Wellfield. This of course, led me to think about what more I could be doing at home, and what I notice is being done in our respective communities to tackle everything from spring rains to floodplains. While most businesses and municipalities have to factor in regulations and cost/benefit analysis, private property owners get to have a little more leeway. So, I thought I’d discuss a few methods of water diversion and absorption you’re likely to see out and about.

Detention basins are larger, gulley-like trenches dug to hold stormwater runoff to slow the flow into larger bodies of water and help trap some sediment. They’re usually planted with native water-tolerant plants. This helps control erosion and flooding. Detention basins are typically found near roadsides and larger construction/development sites and are most often man-made. Because water passes through the basins so quickly, it is inefficient to rely on detention basins for pollutant filtering.

A swale, however, is designed to be up to that task! A swale is a shallower, meandering channel designed to divert and absorb water and keep it available to plants in the areas surrounding the swale. Swales typically have more gently sloped banks than detention basins, relying on the natural curvature and slope of the land, but are still filled with native vegetation. Large swales which are expected to frequently hold water benefit from tree plantings, which help to avoid a swampy mess. Large swales can typically be found on roadsides, ditches, farm fields, and parking lots. There are also “dry” swales, which contain mostly grass and are commonly used as buffer strips in areas with minimal flooding or runoff. Wellfield has a smaller swale garden within the Children’s Garden. Located between the porous pavement and the vegetable garden, Wellfield’s swale is planted with native sedges Cardinal flower, Monkey flower, Blue Vervain, and Joe-Pye Weed. Along the edges are a tulip tree and some non-native yews, hostas, and herniaria ground cover. The swale is filled with river rock to help with water absorption, and the edges are gently sloping. Swales can be appropriate for homeowners with larger yards, pond areas, or drainage ditches. Common swale plants can be divided into two categories: upland and wet basin. Wet basin plants should include water tolerant sedges, rushes, iris, and reeds. Native plants are best suited for this purpose. Upland plants can be a combination of native and ornamental. They must be able to tolerate periods of wetness in between dry conditions. Commonly used upland plants are: dogwood, viburnum, and mesic prairie plants (common rain garden plants). 

As far as homeowners are concerned, we’re more familiar with the idea of rain gardens, planted as a 6-9” deep basin to store and filter rainwater back into the soil, where it can rejoin the groundwater table. Wellfield’s rain garden is located on the northside of our Garden Restroom building. A rain chain hanging from the gutters guides runoff from the roof into the graded slope, which is planted with a variety of moisture tolerant plants, both native and ornamental. An extra layer of rock and shallow drainage tile helps with drainage in the deepest area. Wellfield’s rain garden contains Joe-Pye weed, Golden Alexanders, Blue Lobelia and Cardinal Flower, various sedges, Blue Vervain, Swamp Milkweed, Monkey Flower, Witch Hazel, Spiderwort, Ironweed, and ornamental Lespedeza, Black Gum and Ninebark. The shallower edges contain hostas and black-eyed susans. Other common rain garden plants include: Iris, Purple Coneflower, Prairie Dropseed, Mountain Mint, Switchgrass, Rudbeckia fulgida and R. triloba, Brown Fox Sedge (Carex vulpinoidea), Blazing Star (Liatris spicata), and Ohio Goldenrod (Solidago ohioensis). 

Our rain chains on our Garden Restroom building are fun to watch, but they also help slow down the flow of water, while diverting it into our garden beds, which are planted with a variety of moisture-tolerant plants.
This swale in our Children’s Garden helps divert water, but also adds visual interest to the space.
Rain barrels on the south side of our Garden Restroom building capture runoff to help water our plants.

On the south side of the restrooms, you’ll notice gutter runoff being directed towards two rain barrels. These are connected to black drip irrigation tubing that flows to the landscape plants on the south side garden bed.  Back at the Horticulture Maintenance Bay, runoff flows from the building to a large plastic cistern that is used to water plants in our shade area or to rinse vegetables before we take them to the food pantry. In the winter, we’ll take the rain chains down and divert the melting snow away from the cistern and the rain barrels with flexible downspouts to avoid freezing and damaging the plastic. There are many creative ways to use rain barrels and drainage strips in the home landscape, too. A quick Google search can provide me with hours of entertainment! Happy planning!

More information on stormwater runoff management and water gardens:

Detention Basin fact sheet.pmd 

Plants for swales – Minnesota Stormwater Manual 

Green Infrastructure: Rain Gardens | thewatershed.org

What Is A Rain Garden, Exactly? (3 Types of Rain Gardens + 2 Myths + 6 Benefits)

Rain Barrels & Cisterns

Mary Wojcik, Lead Horticulturist

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