12. APP G. Stormwater Management Plan

                Detailed catchment plans and assessments are also provided in Appendix B.

                RATIONAL METHOD CALCULATIONS
                In the existing case analysis the time of concentration for the above catchment 3 areas have
                been derived with the use of the Friends Sheet Flow Equation in accordance with the
                Queensland Urban Drainage Manual (QUDM Equation 4.5) and Argue’s Flow travel time in
                pipes and channels (QUDM Section 4.6.7). These equations require parameters including the
                total length of the flow path, slope and surface roughness/channel type.

                In the developed case analysis a combined application of standard inlet time for industrial areas
                has been employed to determine the time of concentration (QUDM Sections 4.6.5 and 4.6.7).

                The Coefficient of Runoff was determined using QUDM Tables 4.05.3a & 4.05.3b.

                The rational method, as prescribed by QUDM Section 4.03 was then used to determine
                discharging flow rates for standard average return intervals (ARI’s) of 1, 2, 5, 10, 20, 50 and 100
                years. Detailed Rational Method calculation results are attached in Appendix E.

                XP-RAFTS
                XP-RAFTS is a computer based program which generates detailed event hydrographs for
                specified storm events. XP-RAFTS was used to determine the critical storm duration for a range
                of standard recurrence interval storm events for all catchments. Detailed catchment parameters
                are used by XP-RAFTS including manning’s values, vectored slope of the site and percentage
                impervious.

                The results of the Rational Method calculations were employed as a basis for calibration and
                verification of the development of hydrologic models for each of the included catchment areas.
                Presented below is a summary of the peak discharge flow rates for all ARI’s calculated using
                XP-RAFTS.

                Table 4.3\4: Peak Discharge Flow Rates – XP-RAFTS
                       Storm Event                        Existing                       Developed        Difference (%)

                            1 in 1                          0.039                          0.161
                                                                                                             +313%

                            1 in 2                          0.054                          0.206             +281%

                            1 in 5                          0.076                          0.239             +214%

                           1 in 10                          0.094                          0.269             +186%

                           1 in 20                          0.117                          0.311             +166%

                           1 in 50                          0.135                          0.342             +153%

                          1 in 100                          0.155                          0.408
                                                                                                             +163%




139 Eumundi Noosa Road & 30 Lionel Donovan Drive, Noosaville Service Station and Retail Site—Stormwater
Management Plans
Hyder Consulting Pty Ltd-ABN 76 104 485 289                                                                                7
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