Stormwater Management Plan MCU17/0014

BORNHORST + WARD | DOONELLA STREET UNITS



                    Queensland Urban Drainage Design Manual was used to identify the design storm events for this development
                    as:
                            Minor (piped flow)      -       10% AEP (1 in 10 year ARI)
                            Major (overland flow)   -       1.0% AEP (1 in 100 year ARI)

                    Flow rates for the developed site have been evaluated as a total discharge from the site.

         4.1.1      Rainfall Data

                    The IFD data used in the Rational Method calculations was obtained from the Australian Bureau of
                    Meteorology website based on the approximate latitude and longitude of the development site (LAT
                    26°23'33.15"S, LONG 153° 2'16.94"E). This data indicated the 60 minute, 10 year ARI rainfall intensity
                    applicable to the development site is 72mm/hr. This rainfall intensity was used in conjunction with the fraction
                    impervious values to determine the coefficients of runoff for the existing and developed phases of the
                    development in accordance with QUDM.

         4.1.2      Peak Flow Discharge

                    The coefficient of runoff was taken to be 0.76 and 0.86 for the existing and proposed scenarios respectively.
                    This was determined through investigation of the existing and proposed impervious areas.

                    The time of concentration for both cases was determined in accordance with QUDM. The existing time of
                    concentration for the site was calculated as 16.4 minutes based on a standard inlet time of 5 minutes from the
                    roof to ground, and 30m of overland sheet flow with a 6.7% gradient. This existing time of concentration was
                    evaluated from the residential building to the north of the site to the point of discharge situated in the
                    southeast corner of the site.

                    The developed time of concentration was adopted as 12 minutes based on a standard inlet time of 5 minutes
                    and approximately 2 minutes of pipe flow. The pipe flow travel time was determined using Figure 4.8 of QUDM
                    with a travel length and grade of 45m and 1% respectively, running along the eastern boundary of the site
                    towards the point of discharge situated in the southeast corner of the site.

                    The following table is a summary of the peak site stormwater discharges for varying storm events, calculated in
                    accordance with the Rational Method as outlined in the Queensland Urban Drainage Manual, to the southeast
                    corner of lot 32 Doonella Street for existing and developed conditions




 Bornhorst + Ward Pty Ltd
 Level 4, 67 Astor Terrace, Spring Hill, Qld 4000                                                                      Page 4
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