MCU21.0117 OPW21.0199-Att 5 Stormwater · MCU21/0117

            3. STORMWATER QUANTITY
                    3. 1. D I S C H A R G E T O P E A R L S T R E E T

            As the existing site and upstream catchments currently drain overland into private property
            to the north and east, and the proposal seeks to discharge the run-off to a new legal point
            of discharge in Pearl Street, a comparison of the pre-development discharges to post-
            development discharges at the point of discharge is not appropriate. To demonstrate the
            impact to the receiving environment (system), an assessment of the existing street drainage
            capacity in Pearl Street has been undertaken. This demonstrates that the receiving system
            (the street table drain system) has the capacity to carry the 1% AEP storm event from its
            contributing catchment (including the development site) to the sag point of Pearl Street to
            drain to the trunk stormwater drainage line.

            Based on contours of the locality, surface run-off generally drains to the northeast towards
            the existing drainage channel in the environmental park to the north. The existing
            contributing catchment is predominately comprised of residential properties, road and
            verge strips. The area currently draining to the street drainage system (where the new
            proposed legal point of discharge is located) is shown below in Figure 3.1 – Existing Street
            Drainage Catchments.




                                          Figure 3.1 – Existing Street Drainage Catchments.

            The peak storm event for the 1% AEP was modelled using the Autodesk Storm and Sanitary
            Analysis module, with the catchment hydrology configured in accordance with the Bureau
            of Meteorology’s IFD curves for the locality, and a minimum time of concentration of 5
            minutes for each catchment. All catchments for the proposed development and the internal
            drainage network and storage areas have been modelled, along with the upstream and
            downstream catchments within Pearl Street (estimated based on contour maps and site
            inspections), and the street drainage characteristics to determine a maximum discharge
            from the development. The catchment details for the proposed development site (Figure
            2.6 – Proposed Catchments Plan.) are shown below in Table 3.1-Development Catchment
            Areas.



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