Attachment I - Updated Engineering Report & SWMP

       6.2    Stormwater Quantity Management

       The proposed development will see the percentage impervious area
       increase. Un-attenuated this would result in an increase in peak flow
       discharge off the site. As a result, a mixed use detention and reuse tank is
       proposed to capture runoff, detain flows and slowly release captured runoff
       to ensure non-worsening of peak discharges is achieved. Q100 roof podium
       flows will be directly connected to the detention tank.

       Hydraulic modelling of the attenuation tank is provided in Appendix D.
       The model identifies that a 75.4KL (18.4KL detention and 57KL reuse) tank
       will ensure discharged flow rates do not increase with this development.
       Figure 6.2 shows the assumptions that were used in the calculating an
       adequately sized detention tank. Rainfall Intensity Frequency Duration
       Data and Temporal Patterns were taken from the Bureau of Meteorology,
       using latitude and longitude coordinates provided by Google Maps. Once
       all data was imported into excel a rainfall intensity table was created.
       Appendix D includes Bom IFD chart and curves for ARR19 rainfall event of
       varying frequency.




                                      Figure 6.2
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A6035/21/Engineering Report/30-32 Doonella Street, Tewantin                  Page 4 of 9
May 2021    WM/tk
                                    Alta Projects P/L