33522 Stormwater report018-01 SWQA issued 180704 · MCU18/0001

                                                                                    CIVIL ENGINEERING PROJECT MANAGEMENT
                                                                                           SEDIMENT AND EROSION CONTROL




The dimensions of the constructed infiltration system using Atlantis Flo-Tank (Matrix Triple Modules) were
also provided in the Aquaintel report. This system comprises of 18 modules connected in 2 rows of 9 modules
formation. The dimension of each cell used is 408mm wide x 685mm long x 1310mm high, this provides a
volume of 0.366m3 per cell.

Using the Atlantis Flo-tank dimensions, the capacity to accommodate the original flows and the increased area
of impervious were calculated using the Design Event Method volume. The results are shown in Table 3.


Table 3 – Required Infiltration Tank Size

          Required Volume                   Existing Tank Properties (18 modules)
                                                                                         Acceptable Capacity
        (Design Event Method)               Surface Area            Volume
         Original
                              6.36m3           4.9m2                6.59m3                          Yes
 (70% impervious fraction)
        Proposed
                              6.94m3           4.9m2                6.59m3                          No
 (90% impervious fraction)



It is demonstrated that the increase in impervious area would increase the runoff volume calculated using the
Design Event Method. This increase in volume is larger than the available capacity of the infiltration system
currently installed.




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