Quick Answer
Biological filters are not essential in rain gardens for pollutants, but they can be beneficial in removing excess nutrients and excess particulate matter. A well-designed rain garden can effectively filter pollutants through natural processes such as sedimentation and plant uptake. However, in areas with high levels of pollutants, additional treatment measures may be necessary.
The Role of Rain Gardens in Water Filtration
Rain gardens can be an effective means of filtering pollutants from stormwater runoff through natural processes such as sedimentation, infiltration, and plant uptake. These processes can remove up to 90% of sediment, 75% of nutrients, and 50% of bacteria and viruses from stormwater runoff. The design of a rain garden is critical in ensuring its effectiveness as a filter; features such as a shallow depression, a mix of vegetation with varying growth habits, and a permeable surface can all contribute to its filtering capacity.
Design Considerations for Effective Pollutant Removal
When designing a rain garden to remove pollutants, it’s essential to consider factors such as the size of the garden, the type of vegetation used, and the design of the inlet and outlet structures. A general rule of thumb is to use a minimum of 10-20 square feet of garden area for every 100 square feet of impervious surface being drained. Additionally, plants with deep roots, such as native grasses and sedges, can be effective at removing nutrients and excess particulate matter. The use of a sedimentation pond or a constructed wetland can also enhance the garden’s filtering capacity.
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