Rain Garden

Rain garden is a small to medium scale garden that allows stormwater runoff from impervious urban areas to be absorbed into the groundwater system. This system can be incorporated to reduce the risk of flooding, water pollution, erosion or diminished groundwatwer. However, the main purpose of this garden is to act as water filters and improving the water quality in nearby areas. Research shows that if this system applied in larger scale can cut down pollution in streams or creeks by up to 30% 1.

The stormwater in raingarden is being absorbed faster than the one in retention basin or wet swale, therefore leaving no chance for mosquitos to breed. The other difference between rain garden and bioswale is rain garden generally smaller in scale, handling stormwater from one or two building roofs. While bioswale can act as an alternative for urban drainage system. Bioswale also tend to lead to a destination, while a rain garden does not.

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Rain Garden section ©Rodica Parto

Native plants are recommended for the rain garden because of their innate ability to withstand local’s climate and providing habitat for local wildlife, such as bird or insects. In general, there are 3 zones for planting. The more it gets to the center, the wetter the area and vice versa. Therefore, the choosing of plant type also should take this zoning situation into consideration. Plant with deep fibruous root also very good for cleaning and water filtration.

The permeability of the soil has to be checked before the rain garden is installed. If it is not permeable enough, the existing soil has to be removed and replaced, then underdrain system is installed. The soil mixture generally should contain 60% sand, 20% compost and 20% topsoil.

 

Reference:

1. Sandy Coyman; Keota Silaphone. “Rain Gardens in Maryland’s Coastal Plain”. p. 2. Retrieved 11 October 2011.

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