Rain Gardens and Stormwater Management

Rain gardens, which are also known as bio-retention facilities, are designed for the purpose of treatment for polluted stormwater (EPA Green Infrastructure). Pollutants carried by rainwater runoff accounts for a large portion of all water pollution, so figuring out ways to implement green infrastructure than can help combat this issue is critical.

Rain gardens provide various benefits and incorporate native plants, so there is little maintenance required after a certain period. Rain gardens provide other community and environmental benefits like; they treat the polluted water at the source; up to 80% of sediments, and are cost effective (Alliance for The Bay). We are going to explore the anatomy, and benefits, along with best practices of rain gardens.

Components and Functions

A rain garden is a bowl shaped depression that functions to capture, and absorb rainwater (Native Plant Herald). While this is the main function of these gardens, they also perform secondary processes to clean the water before it empties out into storm drains. They can be broken down into three main components; plants, soil, and the cover (Alliance for The Bay). Selecting the appropriate pants to occupy the garden is a critical first step, and depending on the environment and ecology of the area the correct plant will contribute to biodiversity. The native plant that is chosen should contribute to native wildlife, and should also be aesthetically pleasing. Native plants have better root systems, and can better utilize the soil and nutrients that are available.

There are many factors to consider when selecting the plants, for example; what are the specific conditions of the area? Are there invasive species nearby? How about foot traffic? The best recommendation is to plant a variety of shrubbery to fulfill each specific need that the garden is being created for.

Soil and Cover

The soil and cover are also very important when talking about rain gardens, this is because the soil, cover, and the plants that make up that soil go hand in hand. Soils support the plants in multiple ways including; stabilization, oxygen, and nutrients (Soil: The Foundation of Agriculture). For the purpose of a rain garden, the soil also has to have a high water holding capacity. Loose soils that allow growth and offer filtration are the ideal soil types for rain gardens, and depending on what the rain garden is created for, the soil can be amended.

A good cover, usually gravel or mulch, is a factor to consider when building a rain garden because in a sense it is the defense mechanism of the garden (Alliance for The Bay). It should be able to trap moisture in the soil, and also serve as a reinforcement during storms.

When combined, all these different components make up a well designed rain garden. They are usually “bean” shaped and are made up of a depression, where the soil is placed on the downhill side to allow the runoff to sit and absorb into the soil. The architecture of these gardens are very important because by design they should be able to allow a large flow of runoff, while also having enough space to store the polluted water but not for a long enough period to where mosquitoes can hatch (Blue Thumb).

See Fig 1. for a diagram of a functional rain garden.

Fig 1: Functional Rain Garden, Source: Alliance for the Bay

Benefits and best practices

A well placed rain garden provides multiple benefits for the surrounding community, and contributes to the biodiversity as well. They capture rain, and prevent the sudden release of storm water into the drains, which will eventually end up in the bays and bayous. This overarching benefit of the gardens can be applied to urban areas, neighborhoods, and even individual lawns (Native Plant Herald). One best practice is to choose a variety of plants, mostly native but also some non native plants, for a variety of conditions. Another important thing to do is to choose plants that are scaled to the garden. This not only prevents the overgrowth of the plants, but also enables the aesthetics of the garden to flourish. In addition to capturing the rain, these gardens also improve the water quality of the surrounding area. By limiting the number of pollutants that reach the water sources, along with traditional aquifer systems, the quality of the water is significantly improved.

A rain garden is an ecosystem in itself, and it is also aesthetically pleasing, and a functional way to solve an issue.

In Conclusion…

Rain gardens can be an attractive yet functional way to reduce stormwater runoff and improve water quality. Stormwater runoff can carry fertilizers, pesticides, and even grass clippings from various sources. This runoff can negatively impact the environment by washing pollutants into the riverways and untreated sewage into our rivers. A well designed and appropriately stationed rain garden will function by collecting the runoff from those various sources, directing those pollutants into the garden, and then filtering those pollutants with a mixture of topsoil, sand, and soil plants. The stormwater is cleaner, and is less of a source of water pollution. As an effect of the functionality of rain gardens, their popularity has grown and they can be found in urban cities, homes, and even commercial parking lots. In addition to providing a habitat for native pollinators, rain garden add positive aesthetic aspects to the surrounding area and in my opinion every city should have multiple rain gardens.

References:

Alliance for the Bay: Rain Gardens. Alliance for the Chesapeake Bay. http://www.stormwater.allianceforthebay.org/take-action/installations/rain-gardens. Accessed September 24 2019.

EPA Green Infrastructure: What is Green Infrastructure? Environmental Protection Agency. https://www.epa.gov/green-infrastructure/what-green-infrastructure. Accessed September 24 2019.

The Native Plant Herald. The Beneficial Beauty of Rain Gardens. http://nativeplantherald.prairienursery.com/2013/05/the-beneficial-beauty-of-rain-gardens/. Accessed October 15 2019.

Parikh, S. J. & James, B. R. (2012) Soil: The Foundation of Agriculture. Nature Education Knowledge 3(10):2.

https://www.nature.com/scitable/knowledge/library/soil-the-foundation-of-agriculture-84224268/ Accessed December 15 2019.