LATE RFI - SCG 33114 (SWM) Rev A

6.1.1     Existing Catchments
The existing site consists of a single lot with a dwelling, with landscaped ground areas. The existing
surface generally falls to the west towards the rear boundary. Roof runoff from existing dwellings
appears to discharge directly to ground level.
The total impervious area has been estimated using the detailed site survey and was found approximately
5% Impervious Area (Fi = 0.05) which equates to approximately 105m2.
The existing site catchment is as follows.
    -    Area – 0.203 Ha
    -    Tc – 12 mins
    -    Fraction Impervious (Fi) – 0.05
Peak flow rates for the median design storm for the existing site are given in Table 6.3
                                  Table 6.3 – Existing Site Peak Flow Rates

        Storm         Q1         Q2              Q5          Q10     Q20     Q50    Q100
        Event       (1EY)     (0.5EY)         (0.2EY)    (10%AEP) (5%AEP) (2%AEP) (1%AEP)
                     (L/s)      (L/s)           (L/s)       (L/s)   (L/s)   (L/s)   (L/s)
 Existing             24         33              45           56              69     83         95
 Peak Flow
 Rate




6.1.2     Proposed Site


The development consists of the construction of 10 residential townhouses along with a shared access
driveway and ground level landscaping/ courtyards. The total pervious area for the site was calculated
to be approximately 680m2 which equates to a fraction impervious of 0.67.
The Developed site catchment is as follows.
    -    Area – 0.203 Ha
    -    Tc – 6 mins
    -    Fraction Impervious (Fi) – 0.67
Peak flow rates for the median design storms for the developed site are given in Table 6.4
                                 Table 6.4 – Developed Site Peak Flow Rates

        Storm         Q1         Q2              Q5          Q10     Q20     Q50    Q100
        Event       (1EY)     (0.5EY)         (0.2EY)    (10%AEP) (5%AEP) (2%AEP) (1%AEP)
                     (L/s)      (L/s)           (L/s)       (L/s)   (L/s)   (L/s)   (L/s)
 Developed
 Peak Flow
 Rate                 40         50              62           69              83    102         118




SCG Consulting Engineers                     Page 12                               SCG Ref: 33114(SWMP)