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When a major rainstorm rolls through a community, it has the potential to wash away gardens and lawn debris. In addition, it may carry pollutants directly into our stormwater systems, and eventually into our rivers and lakes.
For this reason, stormwater management remains a top priority for communities as more scrutiny by environmental agencies has been placed on them to control runoff of stormwater pollutants. In fact, many watershed districts and watershed management organizations have created stricter permit requirements for property owners and developers to address the volume of stormwater runoff from their proposed project/property sites.
Instead of building a drainage system that can often be invasive and expensive for property owners and managers, stormwater specialists are educating municipalities, organizations, and the general public about the use of rain gardens as a cost-effective, low-technology alternative to stormwater management. Rain gardens — resembling perennial gardens — consisting of wet-tolerant plants, serve as a natural infiltration or as an on-site collection system for stormwater runoff. The garden absorbs and filters rain that would otherwise run off property and down a stormwater drain.
"Stormwater runoff usually comes from an impervious surface that rain cannot soak into, such as building roofs, lawns, and parking lots, which drains to a stormwater collection system. Rain water should be treated as a resource, not a waste product," SEH Municipal Engineer Chris Cavett, PE, said. "A rain garden can filter out those pollutants absorbed by the flowers' roots and soil, allowing only clean water to enter our streams and become that resource nature intended it to be."
Rain garden popularity has steadily increased due to the environmental benefits and improvement to water quality, but also for aesthetic appeal. Rain gardens offer landscaping features of flowers, grasses, trees, and shrubs, making them more attractive than traditional stormwater management practices.
"In most cases, any environmentally conscious community interested in combining stormwater run-off treatment with neighborhood beautification would be a good candidate for creating a rain garden system," SEH Environmental Designer Veronica Anderson said. "Rain gardens are increasingly becoming an accepted landscape aesthetic in communities due in part to an increased awareness of their functionality in treating storm water runoff and our ability to create rain gardens that are similar in appearance to a conventional flower garden."
Rain gardens, whether used as a sole tactic or as part of an integrated stormwater management system, provide an abundance of benefits and if effectively managed will:
"We need to remember that rain gardens are stormwater management systems designed primarily for water quality treatment purposes," Water Resources Leader Ron Leaf, PE, said. "Owners that place a rain garden on their properties make them a part of a solution to stormwater pollution. Gaining an aesthetically pleasing landscape is an added bonus."
Traditional gardens work as well as rain gardens. Traditional gardens cannot serve as rain gardens as they don't contain the proper filtering and absorption system required to handle large amounts of water. Also, a major storm can wash away a traditional garden. Unless stormwater runoff is directed into a garden, it is not considered a rain garden.
Rain gardens only work on sandy soil. While sandy soils make great locations for rain gardens, in reality, there are many variations on types of rain gardens and specific design features that allow many different settings to be suitable for rain gardens.
Rain gardens require no maintenance. All things need care at some level. If designed properly, including plant selection based on native plants that need minimal care once established, the rain garden with minimal effort can become sustainable, provided there is a method of monitoring and controlling sediment levels in place. Infiltration systems plugging or failing over time are due to lack of maintenance and/or proper provisions to protect the system during construction and prior to final stabilization.
Upfront Site Work Not Necessary
When embarking on residential or commercial development projects, a contractor may be unenthusiastic about staying off a future rain garden area. While most contractors may take the extra steps, they will have to make more of an effort to move around the rain garden to reduce the compaction of the natural soils, which is a critical consideration. Bypassing the rain garden site will generally save effort and costs in both short and long-term maintenance by reducing the heavier sediment loads associated with construction from entering the system. Some type of pre-treatment to the soil is also recommended to help filter the larger sediments from entering the rain garden.
SEH used a variety of native plants for the rain garden planted at the Washington County South Service Center in the Ravine Regional Park in Cottage Grove, Minn. The rain garden provides the park with an integrated stormwater management system and a visually appealing landscape that compliments the natural park site.
Chris Cavett, PE
Ron Leaf, PE