Updated SWMP

Table 2-1: Summary of Existing Catchment Parameters

   Sub-catchment              Downstream              Area (ha)                   Imperviousness (%)
                               Catchment
           Ex2                     SUB3                  1.960                           50
           Ex1                     SUB1                  0.287                           50
          SUB3                     SUB4                  2.085                           21
          SUB1                     SUB2                  2.079                           11
          SUB2                     SUB4                  1.354                            5
          SUB4                     SINK                  0.511                            5


    Ex1 (<10% AEP)                                        0.0*                            -
     Ex1 (5% AEP)                                       0.049*                           50
     Ex1 (2% AEP)                                       0.093*                           50
     Ex1 (1% AEP)                                       0.116*                           50
   Ex1 (1% AEP CC)                                      0.152*                           50
    Ex2 (<10% AEP)                                        0.0*                            -
     Ex2 (5% AEP)                                       0.300*                           50
     Ex2 (2% AEP)                                       0.618*                           50
     Ex2 (1% AEP)                                       0.782*                           50
   Ex2 (1% AEP CC)                                      1.032*                           50
 * area factored based on flow rate for events greater than 10% AEP


The WBNM model has been run for events from 1 to 100-year ARI and for durations of 20 minutes to 3
hours. A WBNM catchment lag factor of 1.6 was applied which is within the recommended range. An initial
and continuing loss of 35mm and 2.4mm/hr in line with ARR2019 datahub values. The resulting peak flows
for the critical duration are provided in Table 2-2 for each event at the outlet reporting locations.

Table 2-2: Existing Catchment Peak Flows

         Event AEP              63.20      50%        20%         10%           5%      2%       1%    1%CC
                                 %
 Existing (m3/s) – SUB3          0.13      0.16       0.30        0.38          0.47    0.58    0.68   0.88
 Existing (m3/s) – SUB4          0.33      0.43       0.72               0.92           1.21    1.55   1.86




2.1.2.      Rational Method Check
Pre-development peak flows have been checked against peak flows determined using the Rational Method
(RM) for SUB3, as shown in




23-0167SMP01-V3 | Stormwater Management Plan | 33 Pavilion Street, Pomona                               Page 19