Reference Document - MCU24 0155 (As Published)

DCM BUILDING DESIGN

18 SHEARWATER STREET, PEREGIAN BEACH – STORMWATER MANAGEMENT PLAN
Further to the area of pervious surface on the sites natural ground level, the proposed post
development catchment also includes an area of approximately 75m2 of rooftop garden bed. The C10
value for this area has been calculated as 0.7 to allow for a medium permeability soil for the garden
bed. It is assumed that the garden bed will become saturated faster than the natural sandy soils and
bypass flows to the LPOD faster via the roof water drainage networks and therefore the higher C10
value is justified which will increase the overall C10 value for the post developed site.

Calculated C10 values and fraction impervious Fi are presented in Table 3 below.

Table 3: Post Development Catchment Information

                                      CATCHMENT INFORMATION
                                PERVIOUS        Pervious Garden                                     OVERALL
                                Natural         Bed                            IMPERVIOUS
          Area(m )    2
                                     197                     75                          274.5
          tc                                             6
          Fraction
          impervious,
          fi, %                      36.0                 13.7                           50.2
          1
              I10                                       74.8
          C10                        0.35                    0.7                          0.9           0.71

Calculated catchment discharges for events from AEP 1% (ARI 100year) to AEP 63.21% (ARI 1year)
events are shown in Table 4 below.

Table 4: Post Development Catchment Discharges Q

                ARI               AEP(%)        FY                CY            T
                                                                                    Iy           DISCHARGE
                                                                              (mm/h)             m3/s          L/s
                            1        63.21       0.80                  0.57    125.0             0.0108        10.84
                            2        50.00       0.85                  0.61    139.6             0.0129        12.86
                            5        20.00       0.95                  0.68    187.2             0.0193        19.28
                           10        10.00       1.00                  0.71    219.6             0.0238        23.81
                           20         5.00       1.05                  0.75    251.2             0.0286        28.60
                           50         2.00       1.15                  0.82    294.4             0.0367        36.71
                          100         1.00       1.20                  0.86    327.4             0.0426        42.59




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