RFI - Stormwater management (flood report)

      2.1.3. Developed Scenario

      The Developed Scenario has been modelled in WBNM by adjusting the site’s fractions
      impervious values and catchment delineation to represent the proposed development. The
      impervious fraction for the developed portion of the SUB1 has increased from 11% to 50%
      (values consistent with ‘Urban Residential – low density (Including roads)’ catchments in
      QUDM (2017)). The developed catchment delineation is shown in Figure 2-2. SUB1 represents
      the development with flows being routed through the proposed detention basin. SUB2 enters
      the site from the south and will be routed around the building envelope of Lot 10. The
      catchment parameters are summarised in Table 2-4.




      Figure 2-2: Developed Catchment Delineation

      Similar to the existing scenario, the existing drainage capacity of Pavilion Street is
      approximately equivalent to the 10% AEP storm event, with flow greater than this
      overtopping the verge and entering the site. To account for this, the peak flow for SUB1-Ex
      was determined for the 10%, 5%, 2% and 1% AEP. The portion of flow greater than the 10%
      AEP was converted into a ratio, which was then applied to the catchment area as detailed
      below in Table 2-4. This ensured that flows from SUB1-Ex greater than the 10% AEP were routed
      through the site.
      Table 2-4: Summary of Developed Catchment Parameters

       Sub-catchment                          Area (ha)                     Imperviousness (%)
       SUB1                                      2.018                             50
       SUB2                                      1.317                              5




21-0166SMP01-V1 | Stormwater Management Plan | 25 Pavilion Street, Pomona                             |8