RFI - stormwater report

3 Stormwater Quantity
The objective of this component of the study is to investigate the potential impact that
the proposed development will have on peak flows discharging downstream of the site.
Where any increases of peak flows are found, potential mitigation options will be
investigated in the form of a detention system.
Hydrologic modelling of the catchment has been carried out using WBNM software
(Boyd et al, 2019), developed jointly by the University of Wollongong, Rienco Consulting
and Balance R&D. The September 2019 version has been used for this investigation,
which utilizes ARR2019 hydrology.
Modelling has been carried out for the 1, 2, 5, 10, 20, 50 and 100 year ARI storm events
in both the local (site) and regional catchments. The following scenarios have been
investigated:
        1.    Existing Scenario
        2.    Developed Scenario
        3.    Mitigation Analysis
3.1.1 Site Existing Scenario
Sub-catchment fraction impervious values have been calculated based on aerial imagery
data and consistent to with existing rural residential land-use. The existing scenario sub-
catchment areas and fraction impervious values for each sub-catchment are tabulated
below in Table 3-1. The existing catchment plan is shown below in Figure 3-1.
Table 3-1: WBNM Sub-Catchment Fraction Impervious Values – Site Existing Scenario
                                                                  Existing Scenario
     WBNM Sub-Catchment                 Area (ha)
                                                                   Impervious (%)
              A01                         1.256                           5
             TOTAL                        1.256                           -




                                                  Catchment
                                                     A01




Figure 3-1: Existing WBNM Site Catchment Plan

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