SUPERSEDED NEGOTIATED - OPW25 0042 - REFERENCE DOCUMENT (As Published)

        2. OVERLAND FLOW ASSESSMENT
        The objective of this assessment is to investigate the impacts the proposed development has on peak flows discharging from the Site to the
        receiving drainage path (and lawful point of discharge) to determine if no nuisance of flow conditions is achieved.


        2.1          Local Hydrology Model
        The objective of the hydrologic assessment is to investigate the potential impact the development may have at the site outlet (southwest
        boundary where flow path exists the site) and identify if any further mitigation measures are required.

        Hydrologic modelling of the catchment has been carried out using WBNM software developed jointly by the University of Wollongong, Rienco
        Consulting and Balance R&D. The 2019 version has been used for this investigation with ARR2019 hydrology being used.

        Modelling has been carried out for the 1%, 10% AEP storm events and 1%, 10% AEP Climate Change (2100) for a range of durations. The
        following scenarios have been investigated:

        (1)    Developed Scenario – Represents the proposed development, associated earthworks and proposed drainage network.


             2.1.1    Catchments
        The flow path that influences the Site includes properties on northern side of Serenity Close to the properties on western side of Serenity
        Close and entire Serenity Close. Details of the catchments can be found in ALTA Engineering Catchment Layout Drawings (ref. A6769-23-
        SMP07, dated 20/01/2025). The Developed (Post-development) catchment and impervious percentages detailed below in Table 2.1. Fraction
        impervious values have been based on the ALTA’s drawings.

        A catchment plan is provided in Figure 2.1.

        TABLE 2.1: EXISTING AND DEVELOPED CATCHMENT PARAMETERS

                                                                                        Developed
                  Sub-Catchment
                                                              Area (ha)                                     Fraction Impervious (%)

         Lot 12                                                  0.96                                                  80

         Lot 4                                                   0.25                                                  80

         Lot 5                                                   0.28                                                  80

         4A                                                      0.08                                                  80

         4B                                                      0.08                                                  80

         Road                                                    0.61                                                  80

         CA_4                                                    0.21                                                  20

         CA_5                                                    0.19                                                  20

         6                                                       0.1                                                   20

         7                                                       0.15                                                  80

         8                                                       0.13                                                  80

         TOTAL                                                   3.04                                                   -



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                   23806878                                                                                                                      4
Version: 0, Version Date: 01/01/1900