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| * 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 the infiltration volume deficit (pre-development minus post-development 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 the infiltration volume deficit (pre-development minus post-development infiltration) |
| * Drainage time t (h), time required to fully drain the active storage components of the practice (i.e surface ponding and infiltration water storage 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 active storage components of the practice (i.e surface ponding and infiltration water storage depths), based on local criteria or long term average inter-event period for the location |
| * Field measured infiltration rate of the underlying native soil f<sub>f</sub> (mm/h), median of 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 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 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 |
| * Safety factor, z (dimensionless value between 2 and 3) chosen by designer based on consideration of risk factors | | * Safety factor, z (dimensionless value between 2 and 3) chosen by designer based on consideration of risk factors |
| * Proposed surface grade elevation at the practice location (metres above sea level, masl) | | * Proposed surface grade elevation at the practice location (metres above sea level, masl) |