Table 9: Adopted Hydrologic Model Calibration Loss Parameters

Table 9: Adopted Hydrologic Model Calibration Loss Parameters

Area Rainfall Loss

Adopted Value October 2018 November 2018 Effective Impervious Area1 Initial Loss (mm) Continuing Loss (mm/hr) 0 0 1 0

Remaining Area Initial Loss (mm)

0 Continuing Loss (mm/hr) 1.8 23.1 1.8

1 According to ARR2016 (Reference 2), the Effective Impervious Area (EIA) represents the portion of a catchment that has an impervious response. The DRAINS manual outlines that the EIA is approximately 60% of the total impervious area in a catchment.

6.6 Other Hydrologic Model Inputs

DRAINS utilises the following additional data to derive flow hydrographs for input in the hydraulic model:

• Catchment Area (ha); • Flow path length (m); • Catchment slope (%); and • Manning’s ‘n’ based on surface type.

The catchment area, in hectares, was automatically calculated using the delineated catchment in GIS.

To calculate a flow path length for each sub-catchment, a relationship was derived based on 20 measured flow path lengths for sub-catchments of various sizes within the study area. This relationship was applied to each sub-catchment.

The sub-catchment slope was calculated using the maximum and minimum elevation within each sub-catchment and the calculated sub-catchment flow path length.

The following Manning’s ‘n’ values were applied for each surface type:

• Paved areas – 0.015; • Grassed areas - 0.03; and • Supplementary areas – 0.03.