16-001014-01A (Swmp)

3.2.8     INTERNAL DRAINAGE STRATEGY

An internal stormwater drainage strategy is required to ensure that runoff is managed effectively through the site during
minor and major storm events. The following is proposed:

       Management of Internal Site Runoff -The proposed site stormwater network and road system is proposed to
        convey the major and minor storm events through the site. Typically, road drainage is designed to convey the
        minor storm only as per Council’s requirements. However, drainage has been upsized due to the limited
        overland flow or road capacity. This will decrease the frequency of runoff conveyed over the road, which
        promotes safety. As a minimum the minor drainage design capacity will be the 10% AEP storm event with road
        network or overland flowpaths to convey 1% AEP storm event.

       Management of External Catchment Runoff - As indicated in Drawing No. B14158.W-SK101 provided in
        Appendix G, stormwater drainage through the site will be upsized to convey major storm runoff from the
        external catchments (Sub-Catchment C1 and C2) through the site.

       Drainage Easements – Drainage easements are indicated on Drawing No. B14158.W-SK110 & SK111 provided
        in Appendix G.

       Discharge to Existing Swale on Site – Manning’s calculations were undertaken to compare peak flows and
        velocities through the existing swale located along the boundary of Lot 4 on RP215922. Results indicate that
        flood levels are less in the swale under existing conditions due to the proposed peak flow mitigation measures
        (i.e. detention basins). Refer to Appendix E for details. Furthermore scour protection has been designed based
        on QUDM (2013) at pipe outlets discharging to the swale to prevent scour and erosion. Refer to the SMCMP
        Report (No. 16-001014-02A dated September 2016).

       Basin Scour Protection – Rock scour protection has been designed at each basins inflows and outflows. Energy
        dissipater calculations for each basin are provided in Appendix E. To protect from vegetation damage velocity
        checks within each basin have also been undertaken with details provided in Appendix E.




16-001014-01 | STORMWATER MANAGEMENT PLAN (SWMP)                 COOROY RETIREMENT COMMUNITY, TRADING POST
| PALM LAKE RESORTS                                                                          ROAD, COOROY               | 14