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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