A rain garden is among the dozens of simple storm water best management practices (BMPs) anyone can use. Its simplicity enables anyone with the right gardening tools at home or in the office to make one. On the other hand, its effectiveness in lessening storm water runoff can be attributed to a process called bioretention.
Bioretention gets rid of sediments and other pollutants from storm water by allowing the earth in the garden to filter the water naturally. The rain garden is patterned after the profile of terrestrial forests and meadows, which uses thick vegetation to initiate the process. Rain gardens are common in parking spaces where the oil and grease from vehicles may mix with storm water. They are actually your typical gardens with a few modifications.
Layout and structure
The bioretention area is a depressed section of the rain garden designed like a catch basin to collect storm water more effectively. When the runoff flows into the bioretention area, layers of mulch, soil, and vegetation naturally filters the storm water. The storm water can flow into an underdrain, undergo evapotranspiration, or seep into the ground.
Most rain gardens for stormwater BMP come with what is known as a sand bed. When runoff flows to the bioretention area, the sand bed slows the flow of the runoff to allow the latter to be evenly distributed throughout the area. In some cases, clay is added to the organic layer to aid with the absorption of pollutants such as hydrocarbons and heavy metals.
Simplicity and effectiveness
A rain garden uses readily available raw materials which make it affordable even for non-commercial purposes. Instead of using artificial filters and filtration systems, a rain garden for stormwater BMP harnesses the natural filtration properties of organic materials such as clay, mulch, and soil. Its center depression prevents the outer areas from flooding by leading the runoff to the bioretention area. Experts claim that its efficiency has been proven over time.
For more information about BMPs for storm water management, visit the website of the U.S. Environmental Protection Agency at EPA.gov. Simple solutions such as these are widely recognized by authorities and considered acceptable for stormwater certification.
Bioretention: Cleaning Stormwater Using Organic Materials