Reference Documents - MCU23 0070

3.5.3    DETENTION TANK

Table 7 presents the detention tank parameters modelled. Refer to Appendix C for the stage vs area
relationship. Re-analysis will be required if the stage-area relationship is significantly altered.

                                         Table 7 – Detention Tank Details
                                Parameter                                     Value
                 Detention Tank Dimensions (m)                4.5m² surface area x 3m deep (min)
                 Available Volume (m³)                                         13.5
                 Available Depth (m)                                         3.0 (min)
                 Detention Tank IL (m AHD)                                    30.26
                 Orifice Outlet                                    75mm dia at IL 30.26m AHD
                 Weir Outlet                                   1200mm weir at RL 33.11m AHD


3.5.4    POST-DEVELOPMENT PEAK DISCHARGE

The XP-STORM was run for 63% AEP to 1% AEP storms with 15 to 180-minute standard durations.
Table 8 presents the peak flow results.

                             Table 8 – Pre & Post-Development Peak Flows (XP-STORM)
                                                        Peak Flow Results (m³/s)
                     63% AEP       39% AEP       20% AEP           10% AEP      5% AEP          2% AEP        1% AEP
    Post-Dev.          0.012         0.014           0.016          0.018        0.021           0.022         0.025
     Pre-Dev.          0.012         0.017           0.021          0.027        0.032           0.034         0.038
     Variance            0          -0.003           -0.005        -0.009       -0.011          -0.012         -0.013

The results show peak flow rates are not increased. Moreover, the 1% AEP flow is limited to 25L/s
(0.025m³/s).

3.5.5    DETENTION TANK RESULTS

Table 9 presents the detention tank performance. As can be seen, the 1% AEP volume is within the
nominated minimum tank volume.

                                         Table 9 – Detention Tank Results
                     63% AEP       39% AEP       20% AEP           10% AEP      5% AEP          2% AEP        1% AEP
   Tank Inflow
                       0.017         0.022           0.026          0.030        0.034           0.035         0.037
     (m³/s)
  Tank Outflow
                       0.011         0.013           0.015          0.017        0.019           0.021         0.023
     (m³/s)
    Detention
                        4.1           5.5             7.0            8.7         10.3            11.4           12.9
  Volume (m³)
    Depth of
                       0.90          1.22            1.56           1.93         2.29            2.53           2.85
    Water (m)




SITE BASED STORMWATER MANAGEMENT PLAN – Revision B                                    36 & 38 DUKE STREET, SUNSHINE BEACH
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