Swmp Rfi

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)                                          0.047*                     50
     Ex1 (2% AEP)                                          0.095*                     50
     Ex1 (1% AEP)                                          0.138*                     50
    Ex2 (<10% AEP)                                           0.0*                      -
     Ex2 (5% AEP)                                          0.455*                     50
     Ex2 (2% AEP)                                          0.979*                     50
     Ex2 (1% AEP)                                          1.388*                     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 10mm and 2.4mm/hr has been applied (refer to Rational Method Check). 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 – SUB3

      Event AEP             63.20%          50%        20%            10%     5%       2%       1%     1%CC
    Existing (m3/s)           0.13          0.16       0.30           0.38   0.47     0.58     0.68     0.88



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 Table 2-3. A time of concentration of 20.6 minutes was determined for SUB3
rational method. It can be seen there is values are generally within ten percent difference across events
assessed, indicating that the WBNM model flows are suitable for use. Refer to Appendix B for a summary of
rational method parameters used.

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%




23-0167SMP01-V2 | Stormwater Management Plan | 33 Pavilion Street, Pomona                              Page 14