Bioretention: Partial infiltration

Partial infiltration bioretention cell draining a parking lot. This design variation includes an underdrain and surface overflow pipes that allow excess water to leave the practice. A monitoring well is included so drainage performance can be evaluated over its operating lifespan. For more details on this variation of a bioretention feature and others, click here for the City of Toronto's Green Streets Technical Guidelines (GSTG)., Note: The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.

Overview

Over soils with slow infiltration rates, it is advantageous to drain a portion of the stored water prior to any upcoming storm. This popular design choice can optimize annual water balance, mitigate peak flow rates and by ensuring water flow through, can reduce the accumulation of sodium and chlorine ions from winter salting.

Partially infiltrating bioretention with underdrain.

Partially infiltrating bioretention with anaerobic/aerobic storage zone.

Materials

• Underdrain
• Biomedia
• Erosion control
• Mulch
• Planting considerations and Recommended species

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References

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

Penetration of water through the ground surface.

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

A perforated pipe used to assist the draining of soils.

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.