Changes

==Design Assumptions==

==Design Assumptions==

Bioretention is an ideal technology for fitting functional vegetation into urban landscapes and treating runoff collected from nearby impervious surfaces.

Infiltration trenches are an ideal technology for installing below any type of landscape with requirements to infiltrate excess stormwater whilst conveying excess. Components include: layers of coarse [[aggregate]] (to bed the pipe, store and redistribute water), [[underdrain|perforated pipe or udnerdrains]] and [[geotextile]]. <br>

Components include: a 'filter bed' with [[filter media]], storage layer of [[reservoir 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>

Design and operation and maintenance program assumptions used to generate cost estimates are based on tool default values and the following STEP recommendations:

Design and operation and maintenance program assumptions used to generate cost estimates are based on tool default values and the following STEP recommendations:

* Native soil infiltration rates for Full, Partial and No Infiltration Design scenarios were assumed to be 20 mm/h, 10 mm/h and 2 mm/h, respectively, and a safety factor of 2.5 was applied to calculate the design infiltration rate.  

* Native soil infiltration rates for Full, Partial and No Infiltration Design scenarios were assumed to be 20 mm/h, 10 mm/h and 2 mm/h, respectively, and a safety factor of 2.5 was applied to calculate the design infiltration rate.  

* Operation and maintenance (O&M) cost estimates assume annual inspections, removal of trash and debris twice a year, removal of sediment from pretreatment structures annually, and removal of weeds twice a year (where applicable). Verification inspections are included every 5 years to confirm adequate maintenance, and every 15 years to confirm adequate drainage performance through in-situ surface infiltration rate testing (where applicable)

* Operation and maintenance (O&M) cost estimates assume annual inspections, removal of trash and debris twice a year, removal of sediment from pretreatment structures annually, and removal of weeds twice a year (where applicable). Verification inspections are included every 5 years to confirm adequate maintenance, and every 15 years to confirm adequate drainage performance through in-situ surface infiltration rate testing (where applicable)

*Maximum impervious drainage area to permeable surface area (I:P area) ratio of 20:1.

* Designed with an impervious drainage area to treatment facility area ratio of between 5:1 and a maximum of 20:1.

* Length to width ratio of bioretention area is 10:1.

* Length to width ratio of infiltration trench area recommended from facilities receiving road or parking lot runoff is 10:1.

* Default filter media depth of 1.0 metres to accommodate trees in planting plan.

* Default mulch depth of 75 millimetres.

* An underdrain (200 mm diameter perforated pipe) is included in Partial Infiltration and No Infiltration design configurations only.

* Default filter media depth of 1.0 metres to accommodate trees in planting plan.

* Default maximum depth of 3 - 4 metres, as there are cost implications with using trench boxes to retain the side walls.

* An underdrain (300 mm diameter perforated pipe) is included in Partial Infiltration & Full Infiltration design configurations.

===Notes===

===Notes===

* Designs include [[pretreatment]] through stone diaphragms at [[Curb cuts|curb inlets]] and two inlet structure sumps (Rain Guardian bunkers).

* Designs include [[pretreatment]] through hydrodynamic separator ([[Oil and Grit Separator]]).  

* Operation and maintenance cost estimates assume rehabilitation of the filter media bed surface is required after 25 years of operation.

* Operation and maintenance cost estimates assume rehabilitation of the filter media bed surface is required after 25 years of operation.

* The tool calculates costs for new (greenfield) development contexts and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal.  

* The tool calculates costs for new (greenfield) development contexts and includes costs for contractor overhead and profit, material, delivery, labour, equipment (rental, operating and operator costs), hauling and disposal.