RFI -Civil Technical Memorandum

RECOR RESPONSE:

A 12d Model drainage analysis was conducted for the entire site. The 1% AEP (Q100) and 10% AEP
(Q10) hydraulic grade lines (HGLs) are presented in the stormwater long section plans for reference.

The following flow results were derived from the 12d Model outputs:

          Flow Event                        Discharge (m³/s)             Climate Change Incl. (m³/s)
         Q10 (10% AEP)                           0.022                             0.026
          Q1 (1% AEP)                            0.031                             0.037


The climate change adjusted events are then compared to that of the existing development scenarios
flows:

           Flow Event                    Existing Scenario(m³/s)         Climate Change Incl. (12D)
                                                                                  (m³/s)
         Q10 (10% AEP)                            0.040                            0.026
          Q1 (1% AEP)                             0.062                            0.037


In both the major and minor events it can be seen that there is a significant reduction in the overall
flows from the development. We therefore confirm that Acceptable Outcome 2.4 of the water quality
and drainage code has been achieved.

The model also confirms that there is sufficient capacity in the external pit to take all flows from the
development.

Issue – Subsurface Disposal of Stormwater

SCCE’s Stormwater Management Report (24083, Rev. 00) dated 8 November 2024 and Basement
Stormwater Layout Plan (C0402, Rev. B) dated 22 November 2024 proposes an ‘overflow pipe’ from
the proposed OSD tank in the basement to discharge over a landscaped rubble pit. Section 6.5 of
Tectonic’s Proposed Unit Development report (24265-001-Rev0) dated 30 September 2024 states
that “subsurface disposal of stormwater must not be undertaken”.

Information Required

Provide an amended Stormwater Management Report and Basement Stormwater Layout Plan that
does not direct stormwater to a rubble pit. Alternatively, provide written confirmation from a suitable



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