Attachment 4 - Stormwater Management Plan by O2 · MCU13/0251

6.5.          Time of Concentration
The time of concentration has been calculated for the pre and post development scenarios following the
procedures recommended in Section 4 of QUDM.

For the pre development scenario, the time of concentration was calculated using Friend’s Equation for
overland sheet flow. Details of the pre development time of concentration are shown below in Table 9.
The time of concentration for the remaining portion of flow was calculated using an average flow velocity
that was verified with the results of the hydraulic model described in Section 6.9.
Table 9 – Pre Development Time of Concentration

Sheet Flow Length          Sheet Flow             tc          Channel Flow      Velocity      tc      Total tc (min)
       (m)                  Gradient            (mins)         Length (m)        (m/s)      (mins)

         20                  13.4%               7.77              63             0.9        1.17         8.94



For the post development scenario, the time of concentration of 5 minutes was estimated from the
recommended standard inlet times provided in Table 4.06.1 of QUDM, with an additional 0.5min was
added for the pipe flow component.

6.6.          Rainfall Intensities
Intensity Frequency Duration (IFD) data for the site has been derived in accordance with Australian Rainfall
and Runoff (ARR) though the use of the AUS-IFD software. The rainfall intensities generated for the site are
shown below in Table 10.
Table 10 – IFD Data Applied to Hydrologic Assessment

 Duration                   I1          I2                  I5         I10          I20       I50       I100
 (mins)                  (mm/hr)     (mm/hr)             (mm/hr)     (mm/hr)      (mm/hr)   (mm/hr)   (mm/hr)

 10                       100.0         127.0             156.0         173.0       195.0    225.0     248.0

 15                       84.0          107.0             131.0         145.0       165.0    190.0     209.0

 20                       73.0          93.0              115.0         127.0       144.0    167.0     184.0

 25                       66.0          84.0              103.0         114.0       130.0    150.0     165.0

 30                       60.0          76.0              94.0          104.0       118.0    137.0     151.0

 45                       48.2          61.0              76.0          84.0        96.0     111.0     122.0

 60                       41.1          52.0              65.0          72.0        82.0     95.0      105.0

 90                       31.4          40.1              51.0          57.0        65.0     76.0       84.0

 120                      25.8          33.2              42.3          47.7        55.0     64.0       72.0




STORMWATER MANAGEMENT PLAN – PEREGIAN VILLAGE MARKET                                                           Page 14

Scanlon Property Group
R002616