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              Design Storm Event            Existing Case              Proposed
                                                                   Developed Case
                    1-Year ARI
                                                 17 L/s                   16L/s
                    (63% AEP)
                   10-Year ARI
                                                  29L/s                   29L/s
                    (10% AEP)
                  100-Year ARI
                                                  51L/s                   51L/s
                    (1% AEP)

                        Table 4.1 Rational Method Calculation Peak Flow Rates



Results for the design storms listed in Table 4.1 are comparable between the existing and
developed case. The 10-Year and 100-Year ARI was found to be 29L/s and 51L/s,
respectively, for both existing and proposed development scenarios. This is attributed to the
relatively small site catchment, and high existing fraction impervious value, which the
proposed development marginally reduces.


Peak stormwater flow discharging from the property will be relative to the existing case.
Refer to Appendix C for calculations. In the existing case the entire site drains to Noosa
Drive, whereas the proposed development will pipe the roof, and a small portion of ground
catchment will discharge as sheet flow to Noosa Drive. By reducing the sites fraction
impervious, the development ensures no worsening of flows from the site.