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Bioretention (all 3 design scenarios): Includes pretreatment sump at inlet and assumes that rehabilitation of filter media bed is performed at 25 years.
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==Design Guidance==
Bioretention is an ideal technology for fitting functional vegetation into urban landscapes and treating runoff collected from nearby impervious surfaces.
Components include: a 'filter bed' with [[filter media]], storage layer of resovoir [[aggregate]], [[planting]] and a finishing surface layer of [[mulch]] and/or [[stone]].
Additional components include an [[underdrain]] to remove excess water and soil additives to enhance [[Nutrients|pollutant removal]]. <br>
Tool defaults based on STEP recommendations:
* Maximum drainage area to surface area ratio of 20:1
* Default depth of 0.75 meters.
* Default mulch depth of 75 millimeters.
* An underdrain (minimum 200 mm perforated pipe) is only needed when native soil infiltration is less than 15 mm/hr or infiltration is precluded.
===Design Notes===
* Designs include [[pretreatment]] through stone diaphragms at [[Curb cuts|curb inlets]]. Pretreatment through settling forebay and vegetated filter strip not included.
* The tool calculates costs for new designs and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal. Mobilization and demobilization costs not included. The tool adds 10% contingency and additional overhead.
* Design and Engineering cost estimates are not calculated by the tool and must be supplied by the user.
* Unit costs are based on 2018 pricing; the tool automatically adds inflation. See the Assumptions sheet in the tool for further details.
* The cost of retrofitting is ~16% higher than the cost of new construction.
** Retrofit costs are included in the 'Costs Summary' section and can be added to the Total Construction Cost for increased accuracy.
<small>'''Note''': Bioretention (all 3 design scenarios): Includes pretreatment sump at inlet and assumes that rehabilitation of filter media bed is performed at 25 years.</small>
==References==