The Rain Garden as a Low Impact Development Tool

Storm water runoff results from an increase in development whether it’s within a city, town, or local community. Urbanization means the addition of impervious surfaces, soil compaction, and vegetation removal, all of which alter the movement of water throughout the environment. An impervious surface describes anything that prevents water infiltrating the ground. Impervious surfaces include sidewalks, streets, parking lots, rooftops, and driveways. Storm water has been identified as one of the leading sources of pollution for all water types in the United States, and as development and urbanization increase, stormwater pollution increases. Urbanization increases the damaging effects of poor run-off control: intensified flooding downstream, destruction of natural creeks and streams, reduced infiltration, decreased groundwater recharge, and increased surfacerunoff /pollution resulting in poor water quality.

Conventional storm water management systems focus on the removal of storm water runoff from a community by disposing of it. Storm water runoff is transported and treated in large, costly end-of-pipe facilities. Traditional approaches to storm water management involve infrastructure such as curbs, gutters, and piping. Storm water is typically incorporated into a combined sewer system or is transported to a treatment facility.

Low Impact Development (LID) practices are new innovative ways to manage storm water. LID practices aim to leave little or no change to an area’s ability to infiltrate, recharge groundwater, or uphold water quality regardless of development. LID practices try to incorporate water runoff within the vicinity using decentralized approaches rather than remove runoff by disposing of it. They prove to be cost-effective when compared to traditional approaches in storm water management. LID designs require less material than what is needed for installing curbs, gutters, and other infrastructure. LID practices, like the rain garden, use natural drainage mechanisms to treat storm water runoff.

Rain gardens are one of the most recognized alternative storm water management practices and are used in residential, commercial, and certain industrial settings. Rain gardens are an interesting choice of storm water management because of their environmental benefits as well as their added aesthetic value. Rain gardens are highly vegetated areas that can serve as a habitat while managing storm water runoff. Rain gardens detain and filter runoff, remove pollutants, and provide infiltration. Infiltration systems are those that encourage water movement downward into underlying soil. As more and more water is infiltrated, there is less storm water runoff and pollutants from overland. Water can be directed to rain gardens through “grass swales,” alternatives to curbs and gutters.

Somerset Community, located in Prince George County, Maryland, has incorporated rain gardens in each lot to control storm water quantity and quality. The installation of rain gardens resulted in a total cost savings of more than $4,000 per lot and the ability to develop six extra lots. The rain gardens range between 300 to 400 square feet, with one or two rain gardens per lot. The rain gardens are located at low points in the lots and water is allowed to pool to a depth of six inches after each storm event. Complete infiltration occurs within 48 hours. The installation of rain gardens combined with the use of grass swales eliminated the need for curbs and gutters, reducing infrastructure cost. Once all of the rain gardens were developed, the total cost savings was calculated to be over $900,000.