RFI - Stormwater management (flood report)

             Response to Information Request
      An Information Request was received on 13 September 2021 as part of Reconfiguration of Lot
      Application No: RAL21/0017. Items relate to Flooding, Stormwater Quantity and Quality, with
      response to each item detailed below:
      Issue: Flooding
      The proposal plans show the flood hazard overlay extent. This overlay is intended to be
      indicative of the flood inundation extent, however for an application the actual modelled
      flood levels for the 1%AEP (at year 2100) is required to be obtained from Council and
      accurately mapped against the detailed site topography in order to produce an accurate
      plan of the flooding constraints at the site.
      Information Request:
      4. Provide an accurate plan of the 1% AEP inundation extent at year 2100 for the
         development site and demonstrate that all proposed filling is located outside of this
         inundation extent.


      Response: The corner of Lot 10 is shown to be partially inundation in the 1% (2100) AEP (noting
      it is flood free in smaller events including the 1% AEP). A flood impact assessment was
      completed using NSC “Pomona Flood Model” in order to demonstrate no off-site impacts, no
      loss of floodplain storage and compliance with the Flood Overlay Code. The proposed 3m
      wide open drain along the southern boundary to Lot 10 is able to manage the flood flows
      through this part of the site. Refer to Section 2.2 for this assessment.


      Issue: Flooding
      The preliminary engineering plans indicate that the fill batter associated with the building
      envelope for Lot 10 extends to within the flood inundation extent and would result in a loss of
      floodplain storage and possibly reductions in flood conveyance and off-site impacts.
      Information Request:
      5. Either amend the proposal plans and preliminary earthworks plans to demonstrate no
         filling within the 1%AEP (2100) inundation extent or provide a flood impact assessment
         which demonstrates no loss of floodplain storage and no off-site flood impacts
         associated with the filling.


      Response: The corner of Lot 10 is shown to be partially inundation in the 1% (2100) AEP (noting
      it is flood free in smaller events including the 1% AEP). A flood impact assessment was
      completed using NSC “Pomona Flood Model” in order to demonstrate no off-site impacts, no
      loss of floodplain storage and compliance with the Flood Overlay Code. The proposed 3m
      wide open drain along the southern boundary to Lot 10 is able to manage the flood flows
      through this part of the site. An additional shallow cut area is to be provided in Lot 10 to off-
      set the loss of flood plain storage. Refer to Section 2.2 for this assessment.




21-0166SMP01-V1 | Stormwater Management Plan | 25 Pavilion Street, Pomona                                 |4