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| * Design storm duration, D (h) | | * Design storm duration, D (h) |
| * Infiltration volume target for the design storm event, V<sub>i</sub> (m<sup>3</sup>), based on average annual water budgets for the catchment for pre- and post-development scenarios and equal to the infiltration volume deficit (pre-development minus post-development annual infiltration) | | * Infiltration volume target for the design storm event, V<sub>i</sub> (m<sup>3</sup>), based on average annual water budgets for the catchment for pre- and post-development scenarios and equal to the infiltration volume deficit (pre-development minus post-development annual infiltration) |
− | * Drainage time, t (h), time required to fully drain the active water storage components of the practice (i.e surface ponding and active storage reservoir depths), based on local criteria or long term average inter-event period for the location | + | * Drainage time, t (h), time required to fully drain the internal water storage reservoir of the practice, based on local criteria or long term average inter-event period for the location |
| * Field measured infiltration rate of the underlying native soil, f (mm/h), median of field measurements or based on interpolation from median grain-size distribution results | | * Field measured infiltration rate of the underlying native soil, f (mm/h), median of field measurements or based on interpolation from median grain-size distribution results |
| * Design infiltration rate of the underlying native soil, f' (mm/h), median field measured value, f divided by a safety factor, z | | * Design infiltration rate of the underlying native soil, f' (mm/h), median field measured value, f divided by a safety factor, z |
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| * Effective porosity of the storage reservoir fill material, including any void-forming structures (e.g. pipes, chambers, tanks, soil cells, etc.) and surrounding aggregate, n' | | * Effective porosity of the storage reservoir fill material, including any void-forming structures (e.g. pipes, chambers, tanks, soil cells, etc.) and surrounding aggregate, n' |
| * Types of plants to be supported by the filter media bed (i.e. grasses vs. mix of grasses, plants and shrubs vs. trees) | | * Types of plants to be supported by the filter media bed (i.e. grasses vs. mix of grasses, plants and shrubs vs. trees) |
− | * How runoff will be delivered to the practice (i.e. to surface ponding area, or directly to storage reservoir) | + | * How runoff will be delivered to the practice (i.e. to surface ponding area, or directly to internal water storage reservoir) |
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| This spreadsheet tool has been set up to perform all of the bioretention sizing calculations shown below and allows side-by-side comparison of equation outputs for each potential design approach or constraint scenario.<br> | | This spreadsheet tool has been set up to perform all of the bioretention sizing calculations shown below and allows side-by-side comparison of equation outputs for each potential design approach or constraint scenario.<br> |