Biofilters

[[File:Planter.png|thumb|Bioretention without infiltration] See also Stormwater Planters

Overview

Over subsurface infrastructure, soils prone to subsidence, or pollution hotspots, it may be necessary to prevent all infiltration. These BMPs can also be squeezed into tight urban spaces, adjacent to buildings and within the usual setbacks required for infiltrating facilities.

Materials

Biofilters are often fitted into tight spaces within highly urbanized contexts. In these cases the cell may be constructed of concrete. This can be further waterproofed/have added resiliency from the application of a liquid sealant. Alternatively, a liner may be used.

• Underdrain
• Filter media
• Erosion control
• Mulch
• Planting considerations and Recommended species

Performance

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A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

A bioretention BMP featuring an impermeable liner and underdrain that prevents infiltration of runoff into the underlying native soil; provides sedimentation and filtration of urban runoff as it passes through the mulch layer, engineered filter media and vegetation root zone.

A bioretention cell that features an impermeable liner that collects and treats stormwater through sedimentation and filtration only (i.e., no infiltration).