C1. Engineering Response Memo

 8.0 Provide additional comment on and a
     preliminary design of the stormwater system
     required on the site. The comment and plan
     must include but not be limited to:

     c) Existing stormwater          connections   and   Refer to the amended preliminary engineering
        drainage paths                                   layout plan (20769_DA03) prepared by this office
                                                         for the existing and proposed stormwater
     d) Proposed stormwater connections and              connection points, surveyed levels and drainage
        drainage paths including finished levels         paths.

     e) Comment from a suitably qualified person         I, Michael Van Itallie (CPEng, RPEQ 13469)
        that demonstrates that the subject site has      confirm that the subject site has the legal right to
        the legal rights to discharge into the           discharge into the neighbouring drainage system in
        drainage system in the adjoining property        accordance with the easement deed (attached).

     f)   A design in accordance with QUDM 2017          Finalised stormwater arrangements, including
          and Council’s Planning Scheme Policy 5         construction of the subject site stormwater outlet is
                                                         to be confirmed during detailed design and
     g) Sufficient detail to demonstrate that the        constructed in accordance with Councils Planning
        downstream drainage system has the               Scheme Policy 5 and QUDM standards.
        capacity to cater for the proposed runoff
        from the site.                                   ADG reviewed the capacity of the constructed
                                                         infrastructure and confirms there is capacity for the
                                                         increase of flow from the subject site development.
                                                         The existing 900mm stormwater main located
                                                         within EMT B on RP154227; using a Manning’s ‘n’
                                                         of 0.013, has a capacity of approximately 5000 L/s
                                                         (size and grade of pipe based on survey & Council
                                                         records). The existing upstream catchment has an
                                                         area of approximately 0.2ha (based on Council
                                                         records). Using BOM rainfall data charts assuming
                                                         a fraction imperviousness of 0.68 yields a
                                                         catchment flow rate of 178 L/s. The proposed
                                                         catchment as previously computed resulted in an
                                                         additional 176L/s. Thus, the flow is still within the
                                                         design capacity of the existing infrastructure for
                                                         capacity requirements. It can be assumed that the
                                                         constructed stormwater infrastructure has been
                                                         designed to cater for upstream developments with
                                                         much higher imperviousness.




20769 C L002 09.02.2018 Council RFI Response                                                         Page 2 of 3