C2. Eng Report

                                                     Proposed Service Station – 175 Eumundi Noosa Road, Noosaville
                                                                                  Ref: 20769 C R001 Rev 06 09.02.17
                                                                                                     February 2018


8       STORMWATER QUANTITY ASSESSMENT
         The aim of the stormwater quantity assessment is to ensure that the development shall impose no
         adverse effects on downstream properties or receiving water bodies and that the conveyance of
         flows will be in a safe manner with minimal risk of human endangerment as well as the following
         objectives:

          Address the need for stormwater quantity control measures.

          Ensure there is no increase in peak discharges from the subject site for events up to and including
          the 1% AEP event.

          Ensure proposed quantity control measures detain and convey flows in accordance with QUDM
          (2013) minimum freeboard recommendations.

         This section of the report should be read in conjunction with Appendix F which shows the values
         used to calculate the peak flow rates.

8.1     Proposed Development and Associated Issues
         It is essential that there are no increases in volume and flow rate of stormwater runoff, and that any
         increases are mitigated such that post-developed peak flows do not exceed those for the pre-
         developed case. In this development, the development leads to no increase in impervious area,
         which implies there will be no increase in either discharge volume or flow rate.

8.2     Flow Rate Methodology
8.2.1   Design Storm Events

         Based on recommendations within QUDM 2013, AS/NZ 3500.3 and Council standards (NSC-PSP05)
         the major and minor storm events were selected as follows:

          Minor Event: 10% AEP (10 year ARI)

           Underground drainage infrastructure sized for a 10% AEP event through to point of discharge.

          Major Event: 1% AEP (100 year ARI)

           Overland flow capture system is to capture and pipe all flows up to and including the 1% AEP
            (100 year ARI) event through to the LPD.

           Surface drainage overflows in events up to and including the 1% AEP (100 year ARI) event will
            not present a hazard to people or cause significant damage to property.

           Emergency surcharge point to be located at site frontage to ensure flows discharge to Toral
            Drive in the event of a blockage.

         Pipe and overland flow channel sizing will be performed during detailed design and increased as
         required to ensure a safe depth vs velocity is maintained at all times during the major event.

8.2.2   Rational Method for Peak Flow Rate

         The peak flow rate for the site has been obtained using the Rational Method in accordance with ARR
         and QUDM. Summaries of the hydrology calculations can be seen in Sections 8.4 and 8.5 for the
         pre and post-development scenarios respectively.




BRISBANE / SYDNEY / MELBOURNE / GOLD COAST / SUNSHINE COAST / DARWIN / PERTH                               Page 15