BIOSWALES AND RAIN GARDENS
The fundamental basis for encouraging use of native plant species are for improved soil erosion control in waterways, and the slowing of storm water run off. Many homeowners have a problem with seasonal, storm water accumulating on their property. Again, the solution lies with the installation of native plants in bioswales or a rain gardens. The difference between the two are: A bioswale is generally sloped to facilitate the movement of water, and a rain garden holds the water to be infiltrated into the local soil. Both are great for the environment and also promote and provide wildlife habitats.
Bioswales (also known as infiltration swales, biofilters, or grassed swales) are vegetated open canals purposely designed to reduce and treat storm water runoff. Like open ditches, they convey storm water from one source to a discharge point, but unlike ditches, they deliberately promote slowing, cleansing, and infiltration of the water along the way.
There are some design variations of the bioswale, including grassed channels, wet swales and dry swales. Grassed channels are primarily grass, and are the easiest to install, but it lacks in the slowing of storm water and removal of pollutants. A wet swale involves standing water at times, and is not usually wanted by homeowners. The dry swales are the most beautiful and functional of the three. These generally include many different types of plants, and the best method for the slowing and pollutant removal in storm water. Because they are made to move higher volumes of water, they may include an underlying rock reservoir, and / or a perforated drain-tile.
One of the biggest benefits of a bioswale is its pollution filtering properties. Above ground plant parts (stems, leaves, and stolons), retard flow and thereby support particulates and their associated pollutants to settle. The pollutants are then leeched into the soil where they may become immobilized and/or decomposed by beneficial bacteria. A well-constructed bioswale installed along a roadway could reduce the amount of carbon-based pollutants like motor oil in the environment. Among the many benefits of vegetative swales, they also provide stabilization and prevent erosion, cost less to install than traditional curbs, and again, are much nicer to look at compared to concrete and asphalt.
Rain Gardens are landscape features designed to treat storm water runoff from hard surface areas such as roofs, roads and parking lots. They consist of depressed garden areas, where runoff can pool and infiltrate into the native soils below. Storm water enters the rain garden via an inlet pipe, such as the downspout of a residence. Small storm events can usually be temporarily stored until they infiltrate into the ground. Most rain gardens are designed to pond no more than 2-3 inches above the soil bed. Where native sub-soils have low infiltration rates, rain gardens often have a drain rock reservoir and perforated drain system to take excess water to another point. The constructed soils of the rain garden, and the overlying mulch layer, are designed to replicate many of the pollutant removal mechanisms that operate in wetland ecosystems. Though rain gardens do remove pollutants from runoff water much like a bioswale, if the pollutants are of a higher concentration, a bioswale may be a wiser choice.
There are many native plants adapted to having “their feet wet”. Some wildflower, fern, grass, and sedge options for the Lake County area are:
- Aster puniceus, Purple-stemmed aster
- Caltha palustris, Marsh marigold
- Eupatorium maculatum, Joe-pye weed
- Eupatorium perfoliatum, Boneset
- Geum rivale, Bog avens
- Helianthus grosseratus, Big-toothed sunflower
- Liatris pycnostachya, Prairie blazing star
- Lobelia spicata, Pale-spiked lobelia
- Mimulus ringens, Monkey flower
- Solidago spp., including S. gigantea, S. ohioensis, and S. riddellii, Goldenrods
- Verbena hasta, Blue vervain
- Vernonia gigantea, ssp. gigantea, Tall ironweed
- Thelypteris palustris, Marsh fern
- Calamagrostis canadensis, Canada bluejoint
- Carex comosa, Bottlebrush sedge
- Carex muskingumensis, Palm sedge
Population growth of Lake County will cause stress on the native environment unless residents are informed of mitigation efforts and encouraged to use native plants in their landscape. By using native plants, a community can reduce water use, pesticide/herbicide use, and maintenance cost/time. The extended root systems of natives help stop erosion and promotes soil health. Native plants restore the surroundings, and encourage native insects and animals to inhabit the area.
Here’s a great link to the Wisconsin Extension Natural Resources Departments “Guide to Bioswales and Rain Gardens”, one of the best I’ve scoped out. It has ‘recipes’ for rain gardens that supply all the names of plants that do well in different types of soils and light requirements.
© Ilex Farrell – Midwestern Plant Girl