BSA Life Structures Blog

In recent years, the use of rain gardens has become a popular way to achieve stormwater quality requirements on a site. It's no longer just an option for residential development or office buildings. We are using rain gardens as stormwater BMP's (Best Management Practices) on our healthcare designs, higher education facilities, and even research facility designs. The environmental benefits appeal to many facility owners. However, our experience in Indiana has shown that once they are constructed, many do not perform as they should.  This is usually due to the clay/silty soils that are prevalent in this area and poor erosion control during construction.

To alleviate this, our Civil Engineers have taken additional effort to detail the design and get involved in the construction phase so that the rain gardens specified are functioning properly when the project has completed. A properly functioning rain garden will not only achieve local stormwater quality requirements (for permitting), but also bring natural beauty to a developed site, save money by reducing sewer sizes and help the environment by reducing stormwater runoff to creeks and streams.

A poorly functioning rain garden is typically caused from having erosion occur on the sides which deposits impervious silt and clay in the bottom of the rain garden. This reduces stormwater infiltration into the soil. When the sides of a rain garden erode before the vegetation is established, the seed that is sowed in the bottom gets covered up. When the bottom has silted in, the rain garden starts to hold water and the seed can not germinate.

The result is a bare, muddy, depression that holds water. The appearance of having a rain garden on the site that looks like a permanent pool of muddy water with no vegetation (or just weeds) is unsightly and cause for concern. Even minor flooding issues can occur if the rain garden is not flood routed or causes water to back up in storm sewers.

To prevent this from happening, we've taken the following steps in handling the design and construction of rain gardens:

1. We are specifying a more intense erosion control measures on the plans. This consists of rain garden bank stabilization of blankets on the slope even if the slope is gradual. The base of the slope near the bottom of the rain garden needs a silt fence or similar measure.
2. The rain garden needs to be properly detailed on the plans. This includes specific cross sections that show the plant medium soil, stone filter, and underdrain if needed as well as side slopes to the rain garden.
3. We often recommend that the contractor consider "cutting" in the rain garden after the area has established vegetation. By doing the earthwork after the area has vegetation, the chances of erosion from the adjacent area is reduced. 
4. Pre-installation meetings on site during construction will also help the contractor understand the goals and pitfalls of installation. It also helps to discuss how inclement weather can affect the construction and erosion control maintenance that will be necessary.

Focusing on these aspects, has allowed us to experience success with the use of rain gardens. When properly designed and built, a rain garden can help the environment and enhance the natural beauty of the land.

Filed Under:
Healing, Learning, Discovery, Sustainable Design Architects