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→Design Variations
===Design Variations===
===Design Variations===
The figures below illustrate three design variations for a parking lot bioretention cell that differ according to whether or not drainage via infiltration into underlying native soils is to be promoted (i.e., lined or unlined) and their outlet configuration (i.e., with or without an underdrain and location of the perforated pipe in the cross-section). Partial infiltration design, that includes an underdrain and internal water storage reservoir is recommended where native soil infiltration rate is less than 15 mm/hr and is the most common. Full infiltration design does not include an underdrain and is suitable on highly permeable soils (>15 mm/hr infiltration rate) and residential rain gardens. No infiltration or "filtration only" designs feature an impermeable liner and underdrain and are suitable on all soil types. All the figures are image map drawings from the following pages to compare side-by-side the differences between varying configurations.
The figures below illustrate three design variations for a parking lot bioretention cell that differ according to whether or not drainage via infiltration into underlying native soils is to be promoted (i.e., lined or unlined) and their outlet configuration (i.e., with or without an underdrain and location of the perforated pipe in the cross-section). Full infiltration design does not include an underdrain and is suitable on highly permeable soils (>15 mm/hr infiltration rate) and residential rain gardens. Partial infiltration design, that includes an underdrain and internal water storage reservoir is recommended where native soil infiltration rate is less than 15 mm/hr and is the most common. No infiltration or "filtration only" designs feature an impermeable liner and underdrain and are suitable on all soil types. All the figures are image map drawings from the following pages to compare side-by-side the differences between varying configurations.
rect 1392 2865 1439 3193 [[Liner|Impermeable Liner]]
rect 1392 2865 1439 3193 [[Liner|Impermeable Liner]]
</imagemap>
</imagemap>
===Sizing and Modelling===
===Sizing and Modelling===
Bioretention facilities should be sized to accommodate runoff from approximately 5 to 20 times the footprint area of the facility. i.e. they should have an I/P ratio of 5 to 20.
Bioretention facilities should be sized to accommodate runoff from approximately 5 to 20 times the footprint area of the facility. i.e. they should have an I/P ratio of 5 to 20.