Bioswale is an alternative system for storm sewer that use vegetation to filter the stormwater. The chosen local plants must be the one which use nutrients very efficiently and able to withstand the heavy amount of water or drought. It has similar purpose to raingarden, but bioswale are designed to manage the runoff from a larger impervious zone, such as parking lot or roadway. They often using engineered soils, such as the one who slow down, and retain the water, and also can absorb phosphorus and nitrogen in high amount. This linear system also normally deeper than rain garden, as well as larger in length and width.


Bioswale section ©Conrad Gartz

The application of bioswale varies depending on the soil type, groundwater table, size of the area serviced, and dimensions and the slope of the swale system. It is not suitable for flat areas or steep slope. It should be used to serve areas with less than 10 acres and slopes no greater than 5%. The total surface area of the swale should be at least one percent of the area which receiving the stormwater. Vegetated swales should not be installed where the groundwater table is high, almost reaches the bottom of the swale 1.


Bioswale is classified into dry and wet swale. The wet swale absorbs more pollution rather than dry swale through the incorporation of wetland plants. However, the problems such as maintenance, landscape preferences and mosquite breeding can be solved by the application of dry swale. Wet swale is more suited for the flat terrain or area with high water table.


Large scale bioswale application for the city. Source: US Department of Agriculture

1. University of Florida. Florida Field Guide to Low Impact Development: Bioswales / Vegetated Swales. 2008. Available from:

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