Stormwater Management Plan

                              STORMWATER MANAGEMENT PLAN
Client: Hass Holdings ATF The Quasar Trust                                           Location: Taylor Court, Cooroy

                                      Table 6 – Initial and Continuing Losses

                                          Pervious Catchments                   Impervious Catchments

                                      Initial Loss       Cont. Loss        Initial Loss           Cont. Loss
                Event                    (mm)             (mm/hr)               (mm)               (mm/hr)
               AEP 1%                     0                 2.5                  0                    0
          AEP 10% and 39%                12.5               2.5                  0                    0

6.3.5 Pervious and Impervious Areas

The proposed development site and external catchment in its existing state has a total area of
0.924 ha and is completely pervious.

The proposed development and external catchment has a total area of 0.924 ha and a proposed
impervious area of 0.63 ha for the developed case, equating to 62%. This will increase total
contributing catchment’s percentage impervious from 0% to 62%.

All pervious and impervious areas for the existing and developed scenarios are detailed in Table 7.

                           Table 7 – Existing and Developed Catchment Areas and Slopes
                 Catchment             Area          Pervious         Impervious          Slope
                                        (ha)             (ha)            (ha)               (%)
                 Existing
                 Site                   0.92             0.92             0                  5
                 Developed
                 Site                   0.92             0.29            0.63                5

The stormwater quantity catchment boundaries are shown in Appendix D.

6.3.6 Manning’s Values

Manning’s values varied due to the differing catchment characteristics / land uses and were
applied independently to the catchment. The values were generally adopted as follows:

     Pervious Area, n = 0.032; and
     Impervious Area, n = 0.018.

6.3.7 Catchment Slope

The Equal Area method was used to determine the catchment slope, which is summarised in
Table 7. The catchment slope in the developed case is unchanged from the existing case scenario.

6.3.8 Storm Durations

Standard storm durations of 15, 20, 25, 30, 45 60 and 90 minutes were modelled to estimate the
peak discharge.

6.4 Calibration

6.4.1 Rational Method

Rational Method calculations were undertaken for the site for calibration of the existing case XP-
RAFTS model – Table 8.

Covey Associates Pty Ltd                             8                                             Project No: 161968
Consulting Engineers                                                                                  100415 Rpt Iss A