2508-47877 SRA - Attachment 5 - Plans and docs referenced in SARA response

                                                                                                           ingeniir




6.    STORMWATER QUANTITY
The development is proposed to incorporate stormwater detention to mitigate the increase in peak discharge
from the site and maintain or improve on the pre-developed stormwater performance.

The Bureau of Meteorology 2016 IFD service has been used for all analysis in this report.

A Rational Method estimation of the stormwater discharge has been used to estimate the pre-developed
runoff performance of the site. In accordance with Noosa Shire Council recommendations, the detention
analysis has been proportioned to match or improve on the pre-developed flows as determined by the
Rational Method. As it is only roof water that is proposed to be collected and detained, a linear methodology
has been employed with storage volumes calculated in accordance with AS3500.3.

Rational method and detention calculations are presented in Appendix 3 | Rational Method & Detention
Calculations.


6.1     Detention Sizing and Details

The required detention volume that was determined to maintain or improve the pre-development discharge
rates to Myall Street was 36,300L. This is proposed to be comprised of two 18,000L All Cast Pre-Cast tanks
with properties as listed in Table 1. The remaining 300L in capacity is comprised of the top section of the
retention tank when over flowing into the detention tanks and upstream pipes to the eaves gutters.

                                         DETENTION TANK PROPERTIES
                           Roof/Impervious Area Connected                        100%
                           Eaves Gutter Size                                 1% AEP
                           Number of Tanks                                        2
                           Storage Capacity                                  36,000L
                           Height                                            2400mm
                           Length / Diameter                                 3500mm
                           Through Connections                        300 dia PVC at base
                                                                   All Cast Pre-Cast (T44 LID
                           Example Product
                                                                            CLASS D
                                            Table 1: Detention tank properties

The outlet configuration of the tanks is proposed to be constructed of outlet orifices drilled into side of the
tank connecting into the immediately downstream pit, the outlets will be located below the tank access
internally, which provides immediate access to either side of the outlet configuration for maintenance. As the
rainwater detention has a preceding retention and re-use component, the inflows will be filtered by leaf traps
prior to entering the system. The proposed detention system outlet details are presented in Table 2.




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