Reference Document - RAL23/0013.02 - Part 2 (As Published)

Appendix E details the afflux map which compares the existing and proposed case for the 1% (2100) AEP
flood levels. It is noted that based on the current development arrangement there are no increases in flood
levels noted either upstream or downstream as a result of the development site itself.

2.2.5.      Peak Flow
The assessment found the peak discharge at the site boundary are predicted to decrease slightly. This is
shown in Table 2-10 which compares the Existing and Proposed peak discharge at the site boundary. As
such it is considered that non-worsening is achieved, and the development does not impact peak flow rates
in the regional flood event.

Table 2-10: Existing and Proposed Peak discharge at the Site Boundary.
          Peak Flow                   1% (2100) AEP
    Existing – E03 (m3/s)                  304.53

   Proposed – P06 (m3/s)                   303.96

         Change (m3/s)                      -0.57



2.2.6.      Flood Storage
A flood storage assessment has been completed over the site to ensure there is no loss of flood plain
storage has resulted from the development. The assessment includes the adjacent site at 25 Pavilion St, as
a small amount of earthworks to extend into 25 Pavilion St is proposed to augment the capacity of the
detention basin. The assessment found that there was some loss of flood plain storage due to the
development. Therefore, a proposed (with cut) scenario is proposed to achieve the flood storage balance.

For the existing flood storage calculation, the existing peak 1% (2100) AEP flood surface was compared to
the existing model terrain (after construction of 25 Pavilion St). Similarly with the proposed flood storage
calculation, the proposed (no cut) peak 1% (2100) AEP flood surface was compared to the proposed model
terrain. The proposed (with cut) scenario incorporates an area of shallow cut to offset loss of floodplain
storage between the building pad fill at lot 8 and the vegetation covenant. Refer to engineering drawings
(Appendix A) for extent of proposed cut.

Details of the flood plain storage within 33 and 25 Pavilion Street, Pomona, in the existing, proposed and
mitigated cases is summarised below in Table 2-11. A summary of proposed cut and fill areas in relation to
the 1% AEP (Climate change) flood level is shown in Figure 2-3.

Table 2-11: 1% AEP Flood Storage Comparison.
         Scenario                                          Flood Plain Storage (m3)
                              25 Pavilion St          33 Pavilion St          Total    Balance
 Existing                          7899                   10440              18339
 Proposed (no cut)                 7890                   10353              18243        -96
 Proposed (with
                                   7890                   10449              18339         0
 cut)




23-0167SMP01-V3 | Stormwater Management Plan | 33 Pavilion Street, Pomona                            Page 26