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| |} | | |} |
| Before you begin you will need to know the following;<br> | | Before you begin you will need to know the following;<br> |
− | * Catchment area (i.e. contributing drainage area), A<sub>c (m<sup>2) | + | * Catchment area (i.e. contributing drainage area), A<sub>c</sub> (m<sup>2) |
− | * Catchment impervious area, A<sub>i (m<sup>2) | + | * Catchment impervious area, A<sub>i</sub> (m<sup>2) |
| * Catchment runoff coefficient, C | | * Catchment runoff coefficient, C |
| * Design storm intensity, i (mm/h) | | * Design storm intensity, i (mm/h) |
| * Design storm duration, D (h) | | * Design storm duration, D (h) |
− | * Infiltration target for design storm event, I<sub>d (mm) | + | * Infiltration target for design storm event, I<sub>d</sub> (mm) |
| * Drainage time target to fully drain the active storage, t (h), based on long-term average inter-event period for the location or local criteria | | * Drainage time target to fully drain the active storage, t (h), based on long-term average inter-event period for the location or local criteria |
− | * Field infiltration rate of the underlying native soil f<sub>f (mm/h), median of field measurements or based on interpolation from median grain-size distribution results | + | * Field infiltration rate of the underlying native soil f<sub>f</sub> (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 divided by a safety factor (z) | | * Design infiltration rate of the underlying native soil f' (mm/h), median field measured value divided by a safety factor (z) |
− | * Safety factor, z (dimensionless value between 2 and 3) chosen by designer | + | * Safety factor, z (dimensionless value between 2 and 3) chosen by designer based on consideration of risk of failure 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) |
| * Elevation of the seasonally high water table or bedrock surface (metres above sea level, masl), below the practice location | | * Elevation of the seasonally high water table or bedrock surface (metres above sea level, masl), below the practice location |