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

Table 2-3: Comparison of WBNM and Rational Method Peak Flows – SUB3

     Event AEP           63.20%         50%       20%         10%     5%         2%          1%       1%CC
      Rational             0.15         0.18      0.28        0.34    0.41       0.52       0.60       0.72
   Existing (m3/s)         0.13         0.16      0.30        0.38    0.47       0.58       0.68       0.88
     Change (%)            -13%         -10%       7%         11%     14%        11%        13%        22%


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 (adjoining approval) and SUB3 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 and SUB3 represents the development with
flows being routed through the existing detention basin (which has been increased in volume). The
catchment parameters are summarised in Table 2-5.




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 and Table 2-5. This ensured that flows from SUB1-Ex greater than the 10%
AEP were routed through the site.




23-0167SMP01-V3 | Stormwater Management Plan | 33 Pavilion Street, Pomona                              Page 21